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To study the enhancement effect of carbon nanotubes (CNTs) on the splitting tensile properties of foamed concrete backfill in which cement and fly ash were used as the cementitious materials and natural sand was used as the aggregate, specimens of CNT-modified foamed concrete backfill were prepared. Brazilian splitting tests were used to investigate the splitting tensile strength of the CNT-modified foamed concrete backfill, and the digital speckle correlation method was used to analyze the stress field characteristics and crack expansion law of the specimens during splitting tensile testing. The stress–strain characteristics and energy dissipation laws of the backfill were studied at various static loading rates, and a relationship between the splitting tensile strength, ultimate strain, and loading rate was established. The results showed that at the optimum CNT content of 0.05%, the peak strength and ultimate strain of the modified foamed concrete backfill increased by an average of 67.2% and 21.7%, respectively. Moreover, after modification with CNTs, the foamed concrete backfill was less likely to develop strain concentration areas before reaching peak strength. The triangular stable loadbearing structure formed by the modified foamed concrete backfill after splitting caused the end of the stress–strain curve to exhibit varying degrees of "backlash". For the CNT-modified foamed concrete backfill, the peak strength correlated logarithmically with the loading rate, while the ultimate strain correlated as a power function of the loading rate. At a low loading rate, the CNT-modified foamed concrete backfill dissipated less energy, and the reverse was true for higher rates. [ABSTRACT FROM AUTHOR]

Highlights The tensile failure mechanism of standard composites has been extensively investigated, but is not clear for stitched composites with z‐stitch method. This work systematically explored the tensile performance of the stitched composites with z‐stitch method under different stitch patterns and densities. The tensile strength and Poisson's ratio of stitched composites are reduced especially under high stitch density and 45° and 90° stitch patterns due to the induced defects and suppression effect on the crimp of load‐bearing yarn. Most importantly, the strain at failure moment is meticulously characterized to elucidate the failure strain mechanism by digital image correlation. For the stitched composite with 0° stitch pattern, obvious strain concentration only occurs in high stitch density specimen. In contrast, the strain concentration occurs in any stitch density for stitched composites with 45° and 90° stitch patterns, and is located around the stitch thread, especially becomes small with the increase of stitch density. High stitch density, 45° and 90°patterns reduce strength and Poisson's ratio. Strain concentration occurs at failure moment in high stitch density specimen. Strain concentration is located around stitch thread. [ABSTRACT FROM AUTHOR]

Structural safety performance is intricately tied to the stress level of rebars. The force-magnetic coupling relationship of rebar is a current focal point. Research gaps exist in the influence pattern of the appearance and shape of rebars on the mechanical and magnetic properties. This study conducted axial tensile failure tests on HRB400 ribbed rebars and HPB300 round rebars with different diameters. Variations in mechanical and magnetic indices were monitored and recorded to analyze the force-magnetic coupling effect in rebars. Results reveal that, concerning mechanical properties, increasing rebar diameter led to higher yield and ultimate strains, resulting in increased ultimate deformation. Ribbed rebars with a bumpy cross section differed from the smooth cross section of round rebars, leading to variations in the curves of tensile elongation percentage (l) versus section reduction percentage (r) for different rebar types. Regarding magnetic properties, the self-magnetic flux leakage (SMFL) intensity of ribbed rebar surpassed that of round rebar. SMFL curves in the elastic-plastic articulation stage exhibited contrast wave peaks, with rebar diameter positively correlating with the fluctuation range. Variations in leakage gradient curves indicated a stronger force-magnetic coupling relationship in the elastic and yielding stages and a weaker relationship in the strengthening stage. This research establishes the groundwork for nondestructive testing of rebar stress and enhances understanding of force-magnetic coupling in different rebar types. [ABSTRACT FROM AUTHOR]

Acoustic emission (AE) and particle flow code (PFC3D) are utilized to characterize microcracking nature in mode-I fracture of coal with strong bursting liability. The microcracks are represented by AE moment tensor (MT), which corresponds to displacement discontinuities involving opening/closing and sliding motions. The microcracking source parameters, including shear/tensile type, volume, orientation, motion, and magnitude, are calculated by minimizing the errors between the analytical and measured displacements, with an imposed constraint. Then, the detailed fracture processes, including microcracking source mechanisms and energy dissipation during coal tensile failure, are analyzed using both experimental and numerical approaches. The results show that the time-varying of crack mode angle and decomposed crack volume suggest a mixed-mode mechanisms locally with both normal and tangential displacements for microcracks. However, the orientations of microcracks with bigger magnitude are almost parallel to the direction of the crack propagation path, and their movement directions are mainly along the direction of the maximum principal stress, which is compatible with the expected fracture mechanism of mode-I opening globally. The dissipated energy and crack opening displacement obtained from AE inversion are approximately consistent with results calculated from energy release rate G and opening displacement measured using DIC, respectively. A new AE MT simulation method, based on particle motion, is developed using PFC3D to verify the reliability of the above-mentioned microcracking characterization results. The mechanical properties as well as AE responses (including AE rate, magnitude distribution, spatial location, and MT) from PFC3D numerical simulation are in good agreement with the experimental results, which reinforces the reliability the microcracking characterization results from AE inversion and simulation. Due to the tortuous crack propagation path and the inhomogeneity between grains, the maximum principal stress and resultant displacement coexists both on the normal and tangential of the inclined crack surface. Under the combined action of tensile and shear stress, the normal and tangential motion displacement components along the crack plane are generated, respectively, resulting in mixed-mode microcrack. This research provides a new approach for characterizing the microcracks in loaded rock/coal, which can deepen the understanding of meso-process and mechanism during rock/coal fracture. Highlights: Microcracks are represented by acoustic emission moment tensor subjected to displacement discontinuity. A new method for acoustic emission simulation is developed using particle flow code to verify test results. Time–space–energy evolution process and focal-mechanism of microcracks are analyzed. Meso-mechanism of mixed-mode microcracks during coal tensile failure is explained. [ABSTRACT FROM AUTHOR]

The tensile properties of fiber metal laminates were examined at temperatures ranging from 30 °C to 180 °C in this paper through the integration of numerical simulation techniques, experimental measurements, and digital image correlation techniques. The laminates were initially modeled using finite elements, and the failure behavior of porous basalt-fiber-reinforced aluminum alloy plates was numerically simulated. Consequently, metal fiber laminate stress–strain responses were varied by numerous tensile experiments conducted at varying temperatures. Simultaneously, a scanning electron microscope was used to scan a porous basalt-fiber-reinforced aluminum alloy laminate at different temperatures to determine the tensile mechanical behavior and micro-damage morphology. Lastly, the laminate's dynamic response to the tensile process was observed through digital image correlation technology. The stress distribution was determined to be concentrated around circular openings through analysis. The strain distribution graph exhibited a "band" shape as the number of perforations increased. The findings indicate that fiber metal laminates lose tensile strength as temperatures increase. The ultimate tensile strength of the laminate decreases as the number of perforations increases at the same temperature. Complex damage mechanisms, including matrix debonding, fiber withdrawal, and matrix fracture, can be captured through scanning electron microscopy at varying temperatures. The tensile behavior and damage mechanisms of laminates with hole-containing structures under thermal conditions are examined, and the results can be used to inform the design and utilization of laminate structures. [ABSTRACT FROM AUTHOR]

Highlights This paper focuses on CFRP‐Al bonded joints, experimentally investigating the effects of joint geometries, different types of adhesives, and overlap lengths on the mechanical properties of bonded joints. Digital Image Correlation (DIC) technology was used to monitor the entire tensile processes, and the deformations and fracture processes of the bonded joints were captured. The strain evolution processes of the joints were obtained through analysis, and quantitative analyses of the joint fracture surfaces were conducted. The results indicate that the special geometric shape of the Flat‐Joggle‐Flat (FJF) bonded joint reduce secondary bending effects. Additionally, the joggle section participates in load transfer, significantly enhancing the joint's mechanical performance and altering its failure mode. Joints using ductile adhesives exhibit higher tensile mechanical properties compared to those using brittle adhesives. Compared to the bearing capacity of single‐lap bonded joints with the same overlap length and adhesive, the mechanical performance improvement of FJF bonded joints using ductile adhesives is less pronounced than that of FJF bonded joints using brittle adhesives. Increasing the overlap length enhances the mechanical properties of bonded joints. This study is expected to provide a reference for the engineering application of FJF bonded joints. FJF joints have higher bearing capacities compared to single lap joints. Ductile adhesives can effectively increase the bearing capacities of joints. Increasing the overlap length can improve the bearing capacities of joints. The end and middle of the FJF joints jointly bear the load effect. The failure modes of FJF joints are different from that of single lap joints. [ABSTRACT FROM AUTHOR]

Softening of the heat-affected zone degrades the mechanical properties of high-strength steel-welded joints. This work revealed the key mechanism to suppress the adverse effects of the soft zone on joint performance by analyzing the constraint between different zones. The base metal (BM) can compete with the soft zone for plastic deformation when the soft zone is strongly constrained by the hard zone, which helps to disperse local strain and prevent premature necking. The constraint mode of the soft zone tends to evolve asymmetrically from bilateral to unilateral during the deformation. Reducing the width of the soft zone helps to achieve unilateral constraint, thus shifting the fracture location from the soft zone to the BM. [ABSTRACT FROM AUTHOR]

The existence of cracks is a key factor affecting the strength of concrete. However, traditional numerical methods still have some limitations in the simulation of crack growth in fissured concrete structures. Based on this background, the numerical treatment method of particle failure in smoothed particle hydrodynamics (SPH) is proposed, and the generation method for concrete meso-structures under the smoothed particle hydrodynamics (SPH) framework is developed. The concrete meso-models under different pre-existing micro-fissure inclinations and bridge angles (the inner tip line of the double pre-existing micro-fissure is defined as a bridge, and the angle between the bridge and the horizontal direction is defined as the bridge angle) were established, and numerical simulations of the crack propagation processes of concrete structures under tensile stress were carried out. The main findings were as follows: The concrete meso-structures and the pre-existing micro-fissures all have great impacts on the final failure modes of concrete. The stress–strain curve of the concrete model presents four typical stages. Finally, the crack initiation and propagation mechanisms of fissured concrete are discussed, and the application of smoothed particle hydrodynamics (SPH) in crack simulations of fissured concrete is prospected. [ABSTRACT FROM AUTHOR]

To investigate the failure behavior of composite open-hole plates under tensile loads, a highprecision finite element simulation model is established based on tensile tests of open-hole plates, and a dataset of tensile force-displacement curves is generated in batches. Then, dual long short-term memory (LSTM) neural network models are proposed to predict the force-displacement curve. The first LSTM model is responsible for extracting input features, while the second one directly predicts the force displacement curve. The research results indicate that this model can efficiently and accurately predict the tensile force-displacement curves of open-hole plates. The coefficient of determination R² on the test set reaches as high as 0.975 5, with the prediction error of key features such as the initial stiffness E0 being only 1.85% and the prediction error of the maximum load Fmax being only 2.16%. [ABSTRACT FROM AUTHOR]

Adhesive bonding plays a pivotal role in structural connections, yet the bonding strength is notably affected by the presence of pore defects. However, the invisibility of interior pores severely poses a challenge to understanding their influence on tensile failure behaviors under loading. In this study, we present a pioneering investigation into the real-time micro-failure mechanisms of adhesively bonded structures using in situ X-ray micro-CT. Moreover, the high-precision finite element analysis (FEA) of stress distribution is realized by establishing the real adhesive layer model based on micro-CT slices. The findings unveil that pores induce stress concentration within the adhesive layer during the tensile process, with stress levels significantly contingent upon pore sizes rather than their specific shapes. Consequently, larger pores initiate and propagate cracks along their paths, ultimately culminating in the failure of adhesively bonded structures. These outcomes serve as a significant stride in elucidating how pore defects affect the bonding performance of adhesively bonded structures, offering invaluable insights into their mechanisms. [ABSTRACT FROM AUTHOR]

The induction welding has been recognized as one of potential and high-efficiency joining methods for thermoplastic composite materials. In this study, a numerical simulation model with containing both induction wielding heat transfer and joint tensile failure process for CF/PPS-Al alloy interlocking induction welding was established based on software COMSOL Multiphysics and Abaqus/Explicit. The CF/PPS-Al7075 interlocking welding joints with special designed macro-scale interlocking were tested under tensile loads, and the corresponding single-lap shear strength, energy absorption, and failure mechanisms were investigated by combining the experimental and numerical approaches. Finally, the influence of macro-scale interlocking geometric parameters on joint tensile strength was also discussed. The results indicate that the proposed model can effectively predict the temperature distribution in the welding process and the tensile failure process of the joint. It is also presented that the addition of macro-scale interlocking features can effectively improve the ultimate load (47%) of the CF/PPS-Al alloy induction welded joints. Meanwhile, the number of addition PPS films in the welding zone and the inclination angle have greater contribution on the tensile strength of the welded joints. [ABSTRACT FROM AUTHOR]

We propose a tensile failure criterion for transversely isotropic rocks that distinguishes tensile fracturing mechanisms either through the anisotropic rock matrix or along the weak bedding planes. For failure through rock matrix, we extend the isotropic tensile failure criterion by constructing an augmented normal stress component based on the alternative stress concept. Failure governed by the bedding planes occurs along the bed-parallel direction once the corresponding normal stress component exceeds the strength of the interface. We then discuss the analytical solution of rock strength and failure plane orientation for transversely isotropic rocks in uniaxial tension tests, and investigate possible shapes of the curves describing the variation of these quantities with bedding plane orientation predicted by the proposed criterion. In the end, we validate the proposed failure criterion with experimental data on four different transversely isotropic rocks and elaborate that the proposed criterion can achieve unified reproduction of various types of rock strength and failure plane orientation variation curves with bedding plane orientation. [ABSTRACT FROM AUTHOR]

This paper investigates the effects of defects on tensile failure of additive manufactured AlSi10Mg alloy focusing particularly on the role of large pancake shaped loss of fusion (LOF) defects lying perpendicular to the build direction (BD). Time-lapse in situ synchrotron radiation X-ray micro-computed tomography during straining reveals how, when tested parallel to the BD, the LOF defects extend laterally with straining connecting to other defects and giving rise to low plasticity and an essentially brittle failure mode. When they are aligned edge-on to the straining direction, failure is characterised by a ductile cup-cone failure with significant elongation of the defects axially and extensive necking prior to failure. The soft fish-scale melt pool boundaries were also found to affect the fracture path. These results highlight the anisotropic effect of loss of fusion defects in controlling tensile ductility and the need to minimize their size and aspect ratio. In cases where these cannot be fully eliminated the component should be fabricated such that the BD is not aligned with the dominant in-service loading direction. [ABSTRACT FROM AUTHOR]

[Display omitted] • Carbon/glass 2.5D woven hybrid composites were prepared by RTM process. • Using Micro-CT, a 2.5D woven hybrid composite cell model was developed and progressive damage analysis was performed. • The tensile failure mechanism of the material at different temperatures was revealed through experiments and numerical analysis. The combination of 2.5D woven structure and hybridization is one of the effective ways to achieve the integration of high-load functions in fiber-reinforced resin matrix composites. However, the sensitivity of resin matrix composites to temperature makes the damage and failure process at high temperatures quite complex. This paper presents the influence of temperature on the tensile failure mechanism of carbon/glass 2.5D woven hybrid composites using both experimental and numerical methods. The tensile properties and failure morphology of 2.5D woven hybrid composites were studied at three different temperatures: 25 ℃, 150 ℃, 300 ℃. The internal morphology of the composites was obtained through X-ray computed tomography (Micro-CT) for subsequent meso -scale model reconstruction of 2.5D woven hybrid composites. The results showed the tensile strength and modulus at 300 ℃ were only 64.83 % and 35.35 % of those at 25 ℃. Additionally, the maximum errors in the predicted stiffness and strength were 8.05 % and 8.16 %, respectively, indicating that the established finite element model was relatively accurate. Furthermore, the tensile failure mechanisms differed at various temperatures. At 25 ℃, the damage forms were primarily warp fracture and resin debonding cracking. In contrast, at 300 ℃, the patterns of damage were largely interface debonding and delamination damage. [ABSTRACT FROM AUTHOR]

The failure mechanisms of engineering rock masses primarily involve tensile and shear failure. Differentiating between the acoustic emission (AE) signals generated during the tensile and shear damage processes in rock can provide a scientific basis for the classification of acoustic signals in field rock fracture monitoring. This paper presents a study on acoustic emission monitoring during the direct tensile testing of granite, proposing a method for classifying AE signals based on the damage and failure processes of the samples. Additionally, the classification of tensile and shear AE signals is explored. The main conclusions are as follows. The proportion of low-frequency signals (frequency <200 kHz) and high-frequency signals (frequency >200 kHz) in all AE signals was found to be 81.6 % and 19.4 %, respectively. Based on an integrated classification and statistical method for AE signals in rock tensile failure, which involves steps such as "denoising the raw waveform, time-frequency domain data transformation, fuzzification processing, extraction of dominant frequency and corresponding amplitude, and identification of secondary dominant frequencies," the AE signals were categorized into two types, A and B. Type A signals accounted for an average of 7.6 %, while Type B signals made up 92.4 %. Based on the polarity determination method, the focal mechanisms of AE (Acoustic Emission) events were identified. In tensile events, the average proportion of Type A signals was 8.34 %, while the average proportion of Type B signals was 91.66 %. The Brazilian splitting test also yielded classification results similar to those obtained from direct tensile testing. Thus, it was preliminarily concluded that Type A signals, characterized by the presence of both a primary and secondary frequency, correspond to shear signals, whereas Type B signals, which only exhibit a primary frequency without a secondary frequency, correspond to tensile signals. • A classification method of AE signals in rock failure process was proposed. • The AE signal discrimination method of tensile and shear failure was proposed. • The dominant and secondary frequency characteristics of AE signals were analyzed. • The distribution characteristics of high and low frequency AE signals were analyzed. [ABSTRACT FROM AUTHOR]

The acoustic emission monitoring with artificial neural networks predicts the ultimate strength of glass/epoxy composite laminates using Acoustic Emission Data. The ultimate loads of all the specimens were used to characterise the emission of hits during failure modes. The six layered glass fiber laminates were prepared (in woven mat form) with epoxy as the binding medium by hand lay-up technique. At room temperature, with a pressure of 30 kg/cm2, the laminates were cured. The laminates of standard dimensions as per ASTM D3039 for the tensile test were cut from the lamina. The Acoustic Emission (AE) test was conducted on these specimens under the load of uni-axial tension in the 10 Ton capacity Universal Testing Machine (UTM). In the monitoring process, acoustic emission parameters such as hits, counts, energy, duration, Root Mean Square (RMS) Value and amplitude were recorded. The RMS Values corresponding to the amplitude ranges from tensile test were used to characterise the failure load of all the similar glass-epoxy composite specimens. [ABSTRACT FROM AUTHOR]

A stochastic morphological modelling framework has been established to predict the tensile behaviour of Randomly Oriented Strands made of ultra-thin Carbon Fibre Reinforced Thermoplastic prepreg tapes. The tape properties from their distributions are generated in a Monte Carlo simulation. The Young's modulus of a laminate is accurately predicted using classical laminate theory. Fibre-dominant tensile failure is also accurately predicted in Carbon Fibre Reinforced Thermoplastics Sheet Moulding Compounds using Weibull theory. Material discontinuity is accounted for via the introduction of a stress concentration factor, as a result of tape overlaps. The predicted tensile strength values and scatter were found to increase with increasing tape length, which agrees well with literature data, and thus demonstrates the reliability of the proposed modelling framework. The rapid modelling framework is well-suited for application in structures. [ABSTRACT FROM AUTHOR]

Complex coupled thermo-hydromechanical (THM) loading paths are expected to occur in clay rocks which serve as host formations for geological radioactive waste repositories. Exothermic waste packages heat the rock, causing thermal strains and temperature induced pore pressure build-up. The drifts are designed in such a way as to limit these effects. One has to anticipate failure and fracturing of the material, should pore pressures exceed the tensile resistance of the rock. To characterise the behaviour of the Callovo-Oxfordian claystone (COx) under effective tension and to quantify the tensile failure criterion, a laboratory program is carried out in this work. THM loading paths which correspond to the expected in situ conditions are recreated in the laboratory. To this end, a special triaxial system was developed, which allows the independent control of radial and axial stresses, as well as of pore pressure and temperature of rock specimens. More importantly, the device allows one to maintain axial effective tension on a specimen. Saturated cylindrical claystone specimens were tested in undrained conditions under constrained lateral deformation and under nearly constant axial stress. The specimens were heated until the induced pore pressures created effective tensile stresses and ultimately fractured the material. The failure happened at average axial effective tensile stresses around 3.0 MPa. Fracturing under different lateral total stresses allows one to describe the failure with a Hoek–Brown or Fairhurst's generalized Griffith criterion. Measured axial extension strains are analysed based on a transversely isotropic thermo-poroelastic constitutive model, which is able to satisfactorily reproduce the observed behaviour. Highlights: Thermal pressurization of clay rock in deep radioactive waste repositories can reduce the effective stresses, which can lead to damage or failure. Our novel laboratory triaxial device is able mimic in situ conditions: Constant vertical total stress, zero lateral deformation and thermal pressurization. Pore pressure increase, vertical extension strains and thermal pressurization failure were recorded in a series of tests on Callovo-Oxfordian claystone specimens. The effective tensile strength was reached at values around 3 MPa in tension and temperatures between 53 and 64 °C, creating sub-horizontal fractures. The experimental responses can be well reproduced using a thermo-poroelasticity model. Hoek–Brown and Fairhurst generalized Griffith criteria appear suitable to account for the rock's tensile resistance. [ABSTRACT FROM AUTHOR]

Understanding the fracturing mechanisms of rock on both macro- and micro-scale is important for properly designing rock engineering applications. However, there is still a lack of understanding of why macro and micro-scale fracturing mechanisms differ. In this study, acoustic emission (AE) and digital image correlation (DIC) techniques were employed to track the microcracking processes in granite specimens subjected to indirect (Brazilian) and direct tensile loadings. The moment tensor inversion of the AE waveforms and the DIC strain field data revealed that the ultimate so-called tensile macro-fracture was predominantly composed of shear microcracks in Brazilian tests and tensile microcracks in the direct tension tests. The different contributions of shear and tensile microcracks to the formation of the macro-fracture explain the difference between direct and indirect tensile strengths. Our results showed that the compressive stress in the Brazilian test due to its biaxial stress field and the grain size are the two critical factors affecting the microcracking mechanisms in the tested coarse-grained granite. Characterizing the surface of the generated macro-fractures and the results of a series of complementary tensile tests performed on fine-grained mortar specimens suggested that reducing the compressive stress and grain size decreases the contribution of shear microcracks. The results of this study can be used in rock fracture applications in granitic rocks such as hydraulic fracturing for geothermal energy extraction, where the knowledge of the cracking location and mechanisms is critical for enhancing the reservoir's productivity. Highlights: So-called tensile macro-fractures are composed of both shear and tensile cracks at the microscale. The ratio of shear-to-tensile microcracks depends on the grain size and stress states. Microcracks are predominantly shear in Brazilian and tensile in the direct tensile loading. [ABSTRACT FROM AUTHOR]

In this study, the tensile strength, failure mechanism and ductile behaviour of geogrid-reinforced high-strength self-compacting concrete discs subjected to both the Brazilian tensile strength test and a biaxial compressive test are studied. To determine the combined effects of geogrid layer numbers and inclination angle on the ultimate tensile strength of concrete samples, 21 experiments were conducted with up to three layers of geogrids inclined at angles of 0° to 90°, at increments of 15°. In addition, discrete-element numerical simulations were conducted using two-dimensional particle flow code to examine the failure behaviour of geogrid-reinforced high-strength self-compacting concrete discs. The numerical models were first calibrated by the experimental results and then the failure behaviour of models containing geogrids was investigated. Both experimental and numerical results demonstrate that augmenting the concrete discs with geogrids increases the ductility of specimens, especially after failure. As the number of geogrid layers increased, the tensile strength of specimens also increased, whereas the tensile strength and absorbed energy were the same for specimens with different numbers of geogrid layers and inclination angles of 75° and 90°. The specimen with three horizontal geogrid layers had the highest tensile strength, biaxial compression strength and ductility of all specimens tested. [ABSTRACT FROM AUTHOR]

• A nondestructive monitoring method of failure behaviors of fiber-winding composites is proposed based on infrared thermography. • The abilities of infrared thermography to evaluate the failure process and failure modes are validated in fiber-wound composites. • Infrared thermography has a certain advantage for comparing fiber volume fractions when professional testing devices are lacking. This paper presents a new method for evaluating the failure and processing technology of fiber-winding composites based on infrared thermography. Firstly, infrared thermography was used to monitor the surface temperature evolution during the loading of Naval Ordnance Laboratory (NOL) rings. Secondly, the mechanical and temperature data were recorded simultaneously until the failure of the NOL rings occurred. Thirdly, the mechanical results were compared with the monitoring results obtained from infrared thermography concerning the failure of the NOL rings. Lastly, an evaluation was conducted regarding the capability of infrared thermography to elucidate the failure of the NOL rings. The experiment results demonstrated that infrared thermography can characterize the failure process and failure modes of fiber-winding composites with limited mechanical or optical technology. Besides, this testing technology provides a significant advantage when comparing fiber volume fractions, particularly in situations where professional testing devices are unavailable. This work provides a new reference for the application of infrared thermography within the domain of fiber-winding composites. [ABSTRACT FROM AUTHOR]

• The crack propagation characteristics of coal samples with prefabricated cracks of different sizes were studied. • The size effect of coal tensile fracture and the law of multi-parameter spatial–temporal response are analyzed. • The multi-parameter precursory information of coal samples with different sizes is analyzed. Tensile fractures in deep coal and rock mass can readily trigger dynamic calamities like rock bursts, significantly impacting the safety of coal mining. To enhance our understanding of coal's tensile failure mechanism, Brazilian splitting failure experiments were conducted on coal samples with prefabricated cracks of different sizes. Acoustic emission (AE), electromagnetic radiation (EMR) and digital image correlation (DIC) techniques were used to analyze the instability failure process and precursor characteristics of coal samples. The results showed that, for coal samples of the same thickness, the tensile strength and peak strain gradually decreased with the increase of coal sample size, whereas the elastic modulus increased gradually, highlighting more pronounced brittleness characteristics and revealing a noticeable size effect. The time-varying evolution of AE energy, EMR energy and VE (virtual extensometer) elongation during the tensile failure process of coal samples is closely correlated to the stress evolution trend, exhibiting distinct characteristics at various loading stages. The failure modes of coal samples of varying sizes exhibited a strong correlation with the spatial distribution of AE events, as well as the strain and displacement field measured by DIC. With the coal sample's growing size, the percentage of AE high energy events rose while the total number of AE positioning events fell, the proportion of DIC strain concentration area decreased, displacement zoning characteristics became more obvious, and the critical opening displacement of cracks increased. The variance of AE, EMR and DIC related parameters in coal samples showed significant critical slowing down characteristics. Based on their response timescales, EMR energy was identified as an "Early warning", AE energy as a "Medium warning", and VE elongation as a "Short-imminent warning". A comprehensive analysis of multi-parameter monitoring information proved beneficial in accurately pinpointing precursory response points of coal mine dynamic disasters, thereby enhancing monitoring precision. [ABSTRACT FROM AUTHOR]

Purpose: The influence of the number and arrangement of bolts on the tensile properties of bolted composite laminates was studied in the present study. Design/methodology/approach: Based on the finite element model, the stiffness degradation method is used to simulate the damage evolution process for the failure of bolted composite laminates. Using ABAQUS finite element software combined with material failure criteria, the numerical calculation of the connection strength and failure mode of bolted composite laminates was carried out. Findings: The results of the study show that the tensile strength of the composite laminates connected by three bolts is higher than that of the laminates connected by two bolts. And the arrangement of different bolts has a great influence on the failure strength of bolted laminates. Originality/value: Bolted connection of composite laminates is a common problem in engineering practice. The effect of bolt arrangement and number on the strength of composite laminates is studied in this manuscript. [ABSTRACT FROM AUTHOR]

Tensile strength is a vital mechanical property of rock and the deformation and failure process of rock under tension is of much significance in rock mechanics and engineering. In this study, a micro analysis on rock direct tensile failure was made based on the newly introduced quantitative analysis of acoustic emission (AE) waveforms. Direct tensile tests of common rocks were carried out, accompanied by real-time AE monitoring. The spatial and temporal distributions of AE signals were studied over the whole loading process. Distribution and evolution laws of dominant frequencies of AE waveforms with normalized applied stress were statistically analyzed. The statistical relationship between the energy ratios of AE waveforms distributed in low and high dominant frequency bands (L-type and H-type waveforms) and peak strengths of rock specimens was built. Microstructural observations with SEM were further conducted. Results show that the dispersion degree of rock tensile strength corresponds to the complexity of mineral composition. Initial release moments of L-type waveforms appeared earlier than H-type waveforms. L-type waveforms of the same proportion carry more energy compared to H-type waveforms in rock subjected to tension. There is an overall downward trend for peak strength of rock specimens with the increasing energy ratios of L-type waveforms. The tensile strength of rock obtained by fitting in this study is smaller than that obtained by averaging. There exist micro shear fractures during the macro tensile failure process of rock according to the microstructural observations with SEM. The peak strength corresponding to the case that L-type waveforms (or micro tensile failures) account for 100% can be considered as the "ideal" tensile strength from the microscopic perspective. The determined tensile strength by fitting can be used as a conservative design parameter for rock engineering. Highlights: Statistical relationship between energy ratios of AE waveforms distributed in low and high dominant frequency bands and peak strengths of rocks under tension is built. There exist micro shear fractures during the macro tensile failure process of rock. Peak strength in the case that L-type waveforms (or micro tensile failures) reach 100% can be considered as the "ideal" tensile strength. The determined tensile strength by fitting can be used as a conservative design parameter for rock engineering. [ABSTRACT FROM AUTHOR]

The paper presents a novel family of strain-based beam finite elements (FE) for analysis of tensile failure of a reinforced concrete bar (RC bar), with results of the analysis being independent of the applied FE mesh. The composite bar consists of a continuous longitudinal ductile reinforcing bar(s) surrounded by brittle concrete cover, which are considered separately in the model. Longitudinal slip at the contact between the concrete cover and reinforcing bars is allowed, while their relative displacements perpendicular to the axis of the RC bar are prevented. Cracks in concrete cover occur when tensile stress in concrete exceeds its tensile strength. Propagation of partially connected crack, that is, softening of the material at the crack, is described through constitutive law in form of nonlinear relationship between stresses in concrete at the crack and the width of the crack. Each separate crack is considered discretely as a discontinuity in geometry of the element. In the analysis of cracking of concrete, it is commonly assumed that the discrete crack can occur at the nodes of FE only. However, this assumption leads to dependence of the analysis results on the employed FE mesh. The presented family of FE enables occurrence of the crack anywhere along the FE. In order to achieve this, the discrete crack is excluded from equations of FE and additional boundary conditions are introduced at the discontinuity. This approach ensures that the location of the cracks, their number and their propagation are independent of the applied FE mesh. Advantages of the novel family of FE are thoroughly presented in a parametric study which investigates influence of number of FE as well as influence of degrees of interpolation and integration on the cracking of RC bar under tensile loading. Experimental results of tensile tests on the analysed bar are available in literature. It can be concluded that the results obtained with the minimal possible number of novel FE and sufficiently high degree of numerical integration scheme, applied for solving integrals in equations of FE, are considerably more accurate than the results of previous analyses with model of discrete crack at the nodes of FE only. [ABSTRACT FROM AUTHOR]

Both computed tomography (CT) and notched semicircular bend (NSCB) tests are performed for coals with high and medium bursting proneness to extract the scientific expression of pore-fracture and its influence mechanism on the tensile failure behavior. The acoustic emission (AE) parameters in the sample during loading and failure are monitored, and the influence mechanism of pore-fracture on tensile failure behavior of coal is analyzed. The result illustrates that the spatial distribution feature of the pore-fracture in coals with high and medium bursting proneness is extremely different. The deformation and failure mode of the coals are affected by many factors, loading mode, notch depth and width, mechanical properties of matrix and minal, spatial distribution feature of pore-fracture, etc. The influence of primary pore-fracture in the coal on the extension and penetration of the secondary fracture could be divided into two types: bifurcation and promotion, which would cause different local damage in the sample and affect the final failure mode. The feature of acoustic emission parameters indicates that the deformation and failure process of a sample under loading could be divided into four stages: compaction stage, elastic deformation stage, displacement plastic growth stage, and post peak failure stage, which is the result of comprehensive action of many factors. The evolution process of secondary fracture is accompanied by the dissipation of elastic strain energy and the intensification of internal damage of coal, which reflects the failure process of coal. [ABSTRACT FROM AUTHOR]

A comprehensive finite element analysis at the mesoscopic level has been conducted into the complex topic of size effect coupling dynamic strain-rates. Taking the lightweight aggregate concrete (LWAC) dumbbell-shaped samples as the object of numerical investigation, the influence of strain-rate (with the range of 10−5/s ∼ 100/s) on direct-tensile failure of LWAC (including different lightweight aggregate volume fractions V agg = 40%, 30% and 20%) was discussed. Subsequently, the structure size of LWAC samples was further expanded (width W = 100, 200 and 300 mm) and the dynamic size effect on direct-tensile strength was investigated. Numerical results show that both the direct-tensile strength and its corresponding size effect of LWAC exhibit a strain-rate dependent behaviour. The increasing strain-rate can gradually weaken the size effect of LWAC and direct-tensile strength would be independent to the structure size as the strain-rate reaches the critical strain-rate. The increasing lightweight aggregate volume fraction can reduce direct-tensile strength. Furthermore, a dynamic size effect model establishing the direct link between the strain-rate effect and size effect was proposed, which can quantitatively predict the dynamic direct-tensile strength of LWAC. [ABSTRACT FROM AUTHOR]

• Dynamic tests were conducted on Brazilian disk (BD) specimens at various hydrostatic pressures using a modified triaxial split Hopkinson pressure bar system. • An AE transducer and a strain gauge were attached to the BD specimens to monitor the dynamic fracture process. • Continuous wavelet transform was used for processing the dynamic acoustic emission signals. • The results indicate that hydrostatic pressure has a significant enhancing effect on the dynamic tensile strength by restraining crack initiation. • AE signals within the 50–100 associated with crack initiation while those above 100 kHz are produced by crack propagation following failure. We develop a novel experimental apparatus, integrated into a dynamic testing system, for the real-time monitoring of the failure process of deep rocks. Four groups of Brazilian disc (BD) granite specimens subjected to various hydrostatic confinements (0, 10, 20, 30 MPa) are tested under different loading rates. A strain gauge and an acoustic emission (AE) transducer are attached to each specimen to obtain the real-time failure signals during the impact. The continuous wavelet transform is utilized to analyze the recorded AE signals. It is observed that tensile crack initiation and propagation effectively absorb AE signals produced by stress waves above 50 kHz, which indicates that post-failure AE signals are predominantly generated by the cracks themselves. It is also found that the proportion of AE signals within the 100–150 kHz range increases with the loading rate, suggesting that higher loading rates encourage the emergence of smaller cracks. Moreover, higher hydrostatic stress enhances the dynamic tensile strength of the rock, thereby restraining crack initiation. When the confining stress is applied, the AE signals exceeding 100 kHz are delayed in their occurrence as compare with the failure, contrasting with those within the 50–100 kHz range that appear simultaneously with the failure. This pattern indicates that cracks generate AE signals within the 50–100 kHz range during the tensile failure, while those with frequencies above 100 kHz are produced by tensile crack propagation following the failure. [ABSTRACT FROM AUTHOR]

At the mesoscale, concrete is considered a three-phase composite material comprising stone, mortar, and the interfacial transition zone. Even though mortar is an important component of concrete, its material parameters have not been determined systematically, and they are often modeled by assuming that they are weaker versions of the concrete parameters. Therefore, accurately describing the role of mortar in concrete and the failure mechanism of concrete is difficult. The quasi-static and dynamic direct tensile tests were performed to obtain the stress–strain curves and failure modes of mortar specimens and to establish a formula describing the mortar strain-rate effect. Numerical simulations were then performed using the improved Karagozian and Case concrete models, and the obtained experimental data to clarify the differences in the failure mechanisms of mortar and concrete under dynamic tensile loads. Results showed that concrete had a higher tensile strength but a lower strain-rate effect than mortar. This paper provides an important contribution to study the failure analysis of concrete structures under dynamic loads. • Direct tensile dynamic stress–strain curves and failure modes of mortar were obtained using improved split Hopkinson tension bar. • Direct tensile dynamic increase factor of mortar was determined and compared with that presented in the FIB Model Code for Concrete Structures 2010. • Differences between the dynamic tensile mechanism of concrete and mortar in the direct tensile mode were analyzed. [ABSTRACT FROM AUTHOR]

• Detailed analysis of fracture initiation and propagation in intact, foliated and pre-cracked rocks were performed through simulation in particle flow code, highlighting the different behaviour in each rock type. • Variation in failure pattern and tensile strength of foliation rocks due to change in foliation angle was investigated. • Investigation of variation in the strength of pre-cracked rock due to change in crack angle and crack length. • Failure modes were developed on the basis of fracture initiation in rocks with pre-existing cracks. • Application of varying crack length on the degree of specimen anisotropy. A thorough numerical analysis was conducted to understand the failure mechanisms and behaviour in intact rocks, foliated rocks and rocks with pre-existing cracks using the Brazilian tensile strength tests. The dominant anisotropy in rocks, especially foliated rocks like phyllites, slates and schists, as well as sedimentary rocks like sandstone, limestones and shale, leads to complex failure mechanism. The presence of cracks leads to anisotropy causing different mechanisms of failure and variation in tensile strengths of rock mass. Numerical simulations were conducted based on experimental studies of foliated phyllite and dolomitic limestone from the Tejam Group, Lesser Himalaya. The variations in failure behaviour and strength of foliated rocks were studied for samples at different foliation angle using the particle distinct element model. The simulation results show that with increase in foliation angle to the loading direction (from 0° to 90°), the peak tensile strength of rocks remains almost same for specimens with θ = 0° to 30° and then increases linearly till 90°. The influence of cracks as anisotropy was also studied by changing crack length (from 5 mm to 30 mm) and angle (from 0° to 90°). The development of failure patterns in rocks with pre-existing cracks leads to a better understanding of the failure modes and makes it possible to interpret failure behavior, pattern, and strength parameters. With increase in crack length, the tensile strength of rocks decreases. Overall, this study depicts the influence of anisotropy and microparameters on failure modes and behavior in Brazilian tensile strength tests on foliated and pre-cracked rocks. [ABSTRACT FROM AUTHOR]

• The influence of layer thickness and mechanical parameters on the strength and failure patterns of layered rock-like materials is investigated. • The thickness of layers and mechanical properties has a significant impact on the failure patterns and tensile strength of these materials. • The study's results demonstrate that both numerical and direct tensile testing methods equally accurately determine tensile strength. • This research provides valuable insights for predicting the tensile strength and failure modes in layered rocks. Rocks generally exhibit less resistance to tension compared to shear or compression forces, and tension cracks often precede shear or compression failures. While the mechanical performance of rock layers under compression has been widely described, their tensile behavior is less known. The current study includes experimental approaches as well as computational testing with the three-dimensional Particle Flow Code (PFC3D) to evaluate the effect of layer thickness and mechanical parameters on the strength and failure patterns of layered rocks-like materials under continuous tension. The Brazilian tensile strength test was conducted on concrete and gypsum specimens. The concrete specimen measured 54 mm in diameter and 27 mm in thickness, resulting in a tensile strength of 1.35 MPa. The gypsum specimen, with the same measurements, had a tensile strength of 0.6 MPa. In addition, uniaxial compressive strength tests were performed on both materials, yielding compressive strengths of 18 MPa for concrete and 6 MPa for gypsum. Our findings indicate that layer thickness and mechanical properties considerably influence failure patterns, tensile strength, and progressive deformation of these materials. The failure modes seen in the layered specimens indicate that the tensile strength ascertained by numerical testing and direct tensile testing is equally accurate. Both the empirical and computational findings are in accordance with the analytical predictions of the failure criterion. In rock engineering, these failure criteria have a high degree of accuracy when it comes to predicting tensile strength and reflecting the failure modes of layered rocks, like layered sandstone, slate, and shale. [ABSTRACT FROM AUTHOR]

SiC fiber-reinforced SiC ceramic matrix composites (SiC f /SiC CMCs) hold potential as thermal structural materials. In this work, SiC nanofibres were coated with multilayer interfaces by magnetron sputtering with the aim to tailor the fiber-matrix interface of SiC nanofibre reinforced SiC composites for superior mechanical properties. The influence of multilayer interface coating and sintering temperature on the density, microstructure, and mechanical properties of SiC nf /SiC CMCs fabricated via a hot-press technique employing ultra-long single-crystal SiC nanofibers as reinforcement were investigated. The composites were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), Transmission electron microscopy (TEM), and a universal testing machine. The prepared CMCs were toughened and strengthened by the observed fiber pull-out and bridging. The multilayered SiC nf /SiC CMCs with multiple interface coatings display an identifiable saw-tooth-like pattern in the load-displacement test, suggesting a significant improvement in the toughness of prepared materials through a laminated structure with weaker interface binding brought on by the thicker, denser coating. In comparison to the SiC nf /SiC composites without interface coating, the prepared SiC nf /SiC CMCs with PyC/SiAlC/ZrC interface layers revealed optimum flexural strength (520 ± 28.88 MPa, ↑46.5 %) and fracture toughness (9.95 ± 0.44 MPa m1/2, ↑94.7 %) after an hour of hot pressing at 1800 °C under pressure of 30 MPa. Besides an increase in relative density at high sintering temperatures (1850 °C), further grain coarsening deteriorated mechanical properties. [ABSTRACT FROM AUTHOR]

• Efficient strain predictions are achieved with DeepLabv3+, enhancing the speed and accuracy of structural analysis. • Rapid and precise failure mode determinations are made possible by VGG-16, employing focal loss for efficient classification. • Accurate interpretability is ensured through Grad-CAM, aligning neural focus areas with fracture mechanics theory. • The method significantly improves efficiency, providing quick and confident results without the need for labor-intensive re-modeling during the FEA process. The joint is a critical component that facilitates force transmission across precast bridge slabs while maintaining structural integrity. Finite Element Analysis (FEA) is commonly used to examine the mechanical properties and load-bearing capacity of joints with different configurations. However, the repetitive process of "modeling-meshing-computing" consumes substantial manpower, time, and expertise. This study proposes an approach consisting of three key steps: (1) predicting strain distributions, (2) determining failure modes, and (3) analyzing interpretability of predicted results. Specifically, DeepLabv3+ is used to map the Finite Element (FE) model to strain distributions. A binary classification model based on VGG-16 predicts the failure state of the specimen. Interpretability analysis, using Gradient-weighted Class Activation Mapping (Grad-CAM), provides insights into the neural network's decision-making process. The optimized models achieve a Mean Intersection over Union (MIoU) of 0.5691 for strain distribution prediction on the cross-sectional surface and 0.6424 on the front surface. The failure detection model achieves an F1 score of 0.992 in determining failure states. The interpretability results align well with fracture mechanics theory, enhancing confidence in the model's predictions. This method serves as a surrogate to reduce the workload of finite element analyses, facilitating strain analysis and failure detection. [ABSTRACT FROM AUTHOR]

The failure process of the open-pored T300/1034-C carbon fiber composite laminate with a ply angle of [ 00 I ( ± 45°) /3 ( 90° ) 3]s under tensile load was studied by using 2-D shell elements and 3-D solid elements in the ABAQUS finite element software. First, the shell element and continuous shell element carbon fiber composite material models were established with the ABAQUS finite element software, and the internal failure of the layer was simulated using the built-in 2-D Hashin criterion and degradation model. However, the 2-D model did not consider the interaction between the failures of each layer, and by writing the material subroutine VUMAT, the 3-D Hashin criterion and the equivalent stress-strain bilinear degradation method based on the fracture energy were introduced, and the solid element was used to simulate the carbon fiber composite material failure behavior. Through the simulation of three element models, the results showed that the stress concentration caused by the opening will make the fiber and matrix of the laminate more likely to fail during the stretching process and become the source of cracks; during the failure process of laminates, they all show a failure development trend from " X-shape" to "hourglass-shape", and eventually break in the width direction; compared with the traditional shell element and continuous shell element, the simulation accuracy of the solid model is closer to the experimental value. The simulation limit failure loads of the three elements differ from the literature data by 26. 1%, 31. 1%, and 8. 64%, respectively. [ABSTRACT FROM AUTHOR]

Linear fracturing fluid (LFF) provides viscosity driven benefits of proppant suspensibility and fluid loss control, and with the use of a breaker agent, flowback recovery can be greatly enhanced. Shale tensile strength is critical in the prediction of fracture initiation and propagation, but its behavior under the interaction with LFF at reservoir temperature conditions remains poorly understood. This necessitated an in-depth investigation into the tensile strengths of Eagle Ford and Wolfcamp shales under thermally conditioned LFF and reservoir temperature controlled conditions. Brazilian Indirect Tensile Strength (BITS) testing was carried out for the quantitative evaluation of shale tensile strength, followed by extensive failure pattern classifications and surface crack length analysis. The thermally conditioned LFF saturation of shale samples led to average tensile strength (ATS) increases ranging from 26.33–51.33% for Wolfcamp. Then, for the Eagle Ford samples, ATS increases of 3.94 and 6.79% and decreases of 3.13 and 15.35% were recorded. The exposure of the samples to the temperature condition of 90 °C resulted in ATS increases of 24.46 and 33.78% for Eagle Ford and Wolfcamp shales, respectively. Then, for samples exposed to 220 °C, ATS decreases of 6.11 and 5.32% were respectively recorded for Eagle Ford and Wolfcamp shales. The experimental results of this research will facilitate models' development towards tensile strength predictions and failure pattern analysis and quantifications in the LFF driven hydraulic fracturing of shale gas reservoirs. [ABSTRACT FROM AUTHOR]

The paper focused on an experimental study on the microstructural, mechanical, and wear characteristics of 15 wt.% alumina (Al2O3) particulates with an average particle size of 20 µm, reinforced in Al2014 alloy matrix composite as-cast and heat-treated samples. The metal matrix composite (MMC)samples were produced via a novel two-stage stir-casting technique. The fabricated composite samples were subjected to evaluate hardness, tensile strength, fatigue behavior and wear properties for both as cast and T6 heat-treated test samples. The Al2014 alloy and Al2014-15 wt.% Al2O3 MMCs were in solution for 1 h at a temperature of 525 °C, quenched instantly in cold water, and then artificially aged for 10 h at a temperature of 175 °C. SEM and X-ray diffraction analyses were used to investigate the microstructure and dispersion of the reinforced Al2O3 particles in the composite and the base alloy Al2014. The obtained results indicated that the hardness, tensile and fatigue strength and wear resistance increased when an amount of Al2O3 particles was added, compared to the as-cast Al2014 alloy and it was observed that after subjecting the same composite samples to heat treatment, there was further enhancement in the mechanical and wear properties in the Al2014 matrix alloy and Al2014-15 wt.% Al2O3 composite samples. [ABSTRACT FROM AUTHOR]

The hollow Brazilian disc-type specimens of transversely bedded geo-materials were numerically modeled using the particle discrete element codes PFC2D for investigating the mechanical behavior and failure mechanism of the transversely isotropic rocks. The breakage mechanism and tensile strength of the transversely isotropic layered rocks were numerically studied using the hollow disc specimens. This numerical code was calibrated by the indirect tensile testing accomplished on the Brazilian disc specimens in the laboratory. Then, about 21 modeled hollow disc specimens with an outer diameter of 100 mm were considered. These specimens were established with two bedding layers in which the first one was the weakest layer with low mechanical characteristics and the second layer had relatively high mechanical parameters (close to those of the intact geo-material). In this study, the angle of the first (weak) layer relative to the applied loading direction varied. The angle of the second (stronger) layer was kept constant (i.e., 180° with respect to the loading direction). The numerical results showed that tensile cracks could develop in the weak layer, and their number decreased as the weak layer's thickness increased. On the other hand, the strong layer experienced no failure during the loading process. [ABSTRACT FROM AUTHOR]

Driven by the commitment of achieving peak carbon dioxide emissions before 2030 and carbon neutrality before 2060, China is promoting the optimization of its energy and industry structures. In the electricity supply industry, a large number of different types of sophisticated large and giant hydropower stations are planned or being constructed in western China. In future decades, hydropower may take the dominant position in China's electricity supply. Rock fracturing behavior plays a vital role in geotechnical hazard prevention and geotechnical engineering design. With the construction of hydropower stations, rock mechanics investigation will be of great concern. This study presents a hybrid model that coupled the finite element method and peridynamic theory to simulate the indirect tensile strength of marble. Sensitivity analyses of the loading rate, mesh size, and fracture energy release rate are performed. The numerical results indicate that both the loading rate and mesh size significantly affect the numerical representation of rock properties. After the calibration of the fracture energy release rate, Brazilian tensile strength modeling is successfully conducted, and the numerical results are consistent with the experimental results. [ABSTRACT FROM AUTHOR]

The issue of weld solidification cracking in fusion welding of highly alloyed aerospace aluminum alloys is eliminated in friction stir welding (FSW) because the base materials do not melt during welding. However, in FSW, the weld joint quality characteristics are found with highly sensitive for the variation of process variables. Therefore, this investigation deals with the analysis of the significance of FSW processing conditions, construction of stochastic tensile failure probability models for dissimilar AA6061-T6 with AA7075-T6 aluminum alloy friction stir welded joints, and postulation of their statistical predictive models. The experimental results have shown an effective mixing at the interface of both base alloys attributed to efficient bonding and resulted in the mechanical properties with the weld joints. A lowest tensile strength was achieved for the weld joint produced by the straight cylindrical profiled tool pin, which is 24.51% lower than the UTS of AA6061-T6 unwelded alloy while 59.09% lower than the AA7075-T6 unwelded alloy. The survival probability of the weld joints fabricated at 30 mm/min is 92% for 260 MPa applied stress, but the weld joints fabricated at 20 and 40 mm/min are 70 and 40%, respectively. For 50% reliability of the weld joint, the maximum allowable stress values suggested are 270, 288, and 255 MPa for processed at of 20, 30, and 40 mm/min welding speeds, respectively. The application stresses beyond 290 MPa, and the survival probability of the weld joints fabricated at 40 mm/min is zero. Empirical models postulated for tensile strength, ductility, and microhardness were fund with a reasonable agreement with their experimental measurements statistically. The derived reliability and empirical models can be used to estimate the reliability of the welded joints and predict their mechanical properties to estimate and enhance the functional performance of the welded structures in automobile and aerospace applications. [ABSTRACT FROM AUTHOR]

The trade-off between the safety and effectiveness of NiTi wire in practical applications has consistently hindered its advancement. This underscores the significance of adjusting its microstructure via appropriate heat-treatment techniques. This study systematically investigates the evolution of the constitution phases of the matrix and the grain size as the aging time increases from 3 min to 3 h at 550 °C for Ni 50.9 Ti 49.1 wire, and highlights the significant role of the R phase in static/cyclic tensile failure behavior. When aged for 30 min, the matrix consists mainly of the B2 phase, similar to the as-received wire, while it tends to transform into the R phase during loading (intermediate-R phase). In contrast, aging for 3 h leads to the formation of the R phase as the matrix phase (matrix-R phase). The two types of R phase are discussed and compared in detail with regard to their contribution to the static/cyclic tensile failure behaviour. The longest fatigue life was obtained in wires with the R phase as the matrix phase, which was due to the combined effect: (i) the rapid attainment of a stable state so as to minimise the extent of phase transformation; (ii) coordination deformation of twin and dislocation to alleviate stress concentration; (iii) and the strong bonding between Ti 2 Ni and the matrix that reduces the occurrence of the "stretching into the hole-coalescence-microcrack process". The enhanced flexibility observed in the wire with matrix-R phase is due to its reduced elastic modulus and lower transformation plateau. The increase in plasticity is linked to changes in the wire's fracture behavior resulting from grain growth. Such microstructural changes allow the alloy wire to exhibit a more uniform plastic deformation under stress, which in turn postpones the onset of significant fracturing. [ABSTRACT FROM AUTHOR]

We present a simple model of the mechanics of the transverse impact of a water droplet of finite size on a free-standing fiber. There are two major differences between the transversal impact of a liquid droplet and the impact of a solid projectile. The first difference is that the segment of the fiber interacting with the droplet is not required to move with the speed of the droplet as in the case of an impact of a solid projectile. The second difference is related to the duration of interaction between the fiber and impactor. In the case of a solid projectile, interaction is complete when either the fiber fails or the projectile is defeated. However, failure in the case of the impact of a droplet is governed particularly by the time of interaction with the liquid droplet, which is governed by the flow around the accelerating fiber that may lead to fiber failure. The analytical model assumes a droplet diameter much larger than the diameter of the fiber and predicts the transverse forces acting on the fiber at the impact site, transversal wave propagation, and associated tensile stress in the fiber. The model identifies dropletsize/velocity combinations that cause tensile failure of fibers with prescribed mechanical properties. [ABSTRACT FROM AUTHOR]

Pull-through(PT) is a unique failure mode of torque-controlled expansion(TCE) anchor after being pulled out from concrete. No universal design formula is available for predicting tensile bearing capacity of anchor of PT mode. In normal concrete(NC), PT failure usually occurs at large embedment depths(H ef), which is uncommon in the field and received less attention than the concrete breakout failure. However, due to the improved mechanical performance of the substrate, the PT mode dominates for anchors in high-performance steel fiber reinforced concrete(HPSFRC) substrate (even at small H ef). In this study, to study the PT mode in HPSFRC, the results of 34 PT failures from previous tests, including testing scenarios with different anchor diameters(D), H ef , and fiber contents(v f), are analyzed. The cracking morphology and load-bearing capacity distribution of PT mode are elaborated. Further, finite element models(FEM) of anchor pullout behavior in HPSFRC is established, which accurately identified different failure modes. The calculated N u by FEM agree well with the tested N u. The difference in damage domain between different failure modes is mainly reflected in the unloading stage. Parametric analyses were conducted on pre-tightening torque(T ini), H ef , D , sleeve length(L sleeve), anchor cone width, anchor cone length(L cone), and v f to study their influences on N u of PT mode. Except for L sleeve and L cone , which do not affect N u , changes in other factors can cause linear or nonlinear changes in N u. The non-linear relationship between N u and experimental parameters is formulated. Accordingly, a new prediction model that can accurately predict N u of PT mode for anchors in HPSFRC is developed, of which calibration factors are derived using probability functions. • Pull-out behavior of TCE anchors in high-performance steel fiber reinforced concrete(HPSFRC) is investigated. • Pull-out test mainly focuses on the crack morphologyand failure mechanism of pull-through(PT) mode. • Numerical simulation successfully identified different failure modes. • Based on parametric analysis on experimental and simulation results, an empirical model for PT mode in HPSFRC is proposed. [ABSTRACT FROM AUTHOR]

Manufacturing carbon nanotube (CNT) fibres on a large scale with properties that are a significant fraction of those measured for individual tubes or smaller bundles is crucial to achieving greater impact in industrial applications. We describe three macrostructured morphologies produced on a laboratory scale: CNT ribbons, ropes and tows, wherein tows are the most suitable for industrial scale-up, comprising a bundled structure of thousands of individual micro-fibres. For each morphology, we present the tensile failure mechanisms and mechanical performance observed over six orders of magnitude of strain rate. The tests were conducted on a conventional Hounsfield tensile tester (10─4 to 10─1 s─1 strain rate) and a modified split-Hopkinson tensile bar tester (30–150 s─1 strain rate). To avoid the problem of clamp failure, we present a novel method of testing loops, rather than uniaxial samples, as-produced from our chemical vapour deposition reactor. For material benchmarking and validation, we also tested unsized carbon fibre (Hexcel AS4) and Dyneema tows (SK25). All materials were used 'dry', i.e. not as a composite, for raw material and structure comparison. We show here that CNT tows exhibit both a mechanical performance and fracture behaviour which combines the ductility of Dyneema with the tenacity of carbon fibre. Image 1 [ABSTRACT FROM AUTHOR]

In slope stability evaluation, it is common that a potential tensile sliding surface is not accurately positioned. In this paper, the strength reduction method considering shear and tensile failure with a strain-softening model is adopted to simulate the deterioration of the strength parameters of geomaterials during failure. Based on the initial stress method, a new quantitative display index of the full sliding surface is proposed. This method was applied to the stability analysis of a heterogeneous slope and a homogeneous slope. The results show that the plastic zone determined with the strain-softening model is much smaller than that determined with the Mohr-Coulomb model, and the difference is 34–40%. The safety factor obtained without considering tensile failure is 3.1% larger than that obtained considering tensile failure. The index can be used to quantitatively display the shear failure zone and tensile failure zone of a sliding surface. [ABSTRACT FROM AUTHOR]

Highlights • Investigated intermediate strain rate tensile behavior of transparent polyurethane. • Large tensile deformation behavior and tensile failure behavior were analyzed. • Digital Image Correlation technique was adopted to acquire specimen strain. • Strain rate and temperature dependence and their equivalence were observed. • A phenomenological analysis of mechanical quantities was carried out. Abstract Transparent polyurethane has been widely applied in laminated windshield glasses as the interlayer material to enhance the reliability due to its outstanding impact resistance. Under impact loading such as bird strike, the interlayer undergoes large tensile deformation mainly at intermediate strain rates (at the order of magnitudes from 100 to 103, excluding 1000/s). In addition, the interlayer is on service over a wide range of temperatures for a plane traveling around the world. The mechanical behavior of transparent polyurethane under these conditions is not fully understood. In this study, systematical experiments were performed on transparent polyurethane. The viscoelasticity of the material was firstly verified by several quasi-static cyclic tests. Then a series of large tensile deformation and tensile failure experiments were conducted under intermediate strain rates and at temperatures of − 40 ° C to 40 ° C using a servo-hydraulic high-speed tensile machine. All strain data were acquired by the DIC technique. The experimental results show that tensile stress–strain curves and failure behaviors are significantly temperature and strain rate dependent. The rate-temperature equivalence was also observed. Finally, a phenomenological analysis of mechanical quantities of the material was carried out. [ABSTRACT FROM AUTHOR]

A fundamental study on the tensile failure of rock is conducted using the three-dimensional lattice spring model. The model covers three aspects: (1) the relationship between the mesoscopic tensile/shear failure and the corresponding macroscopic tensile failure; (2) the effects of the size, shape, and location of the initial defect on the macroscopic tensile failure; and (3) the effects of the porosity, heterogeneity, crystal structure, mesoscopic constitutive model, and model scale on its macroscopic tensile responses. Through investigation, this study reveals that the mesoscopic strength heterogeneity affects the macroscopic pre-peak response of rock, and the initial defect could control its macroscopic post-peak response. The post-peak characteristics of the mesoscopic constitutive model influence both the macroscopic pre-peak and post-peak responses, which are scale independent and scale dependent, respectively. Based on these investigations, a parameter-selection method for the mesoscopic constitutive model is established to fully utilize the macroscopic tensile experimental data. [ABSTRACT FROM AUTHOR]

Failure of steam-side oxide scales on boiler tubes can seriously influence the safety of coal-fired power plants. Uniaxial tensile tests employing acoustic emission (AE) monitoring were performed, in this work, to investigate the failure behavior of steam-side oxide scales on T22 alloy boiler superheater tubes. The characteristic frequency spectra of the captured AE signals were obtained by performing fast Fourier transform. Three distinct peak frequency bands, 100-170, 175-250, and 280-390 kHz, encountered in different testing stages were identified in the frequency spectra, which were confirmed to, respectively, correspond to substrate plastic deformation, oxide vertical cracking, and oxide spalling with the aid of scanning electronic microscopy observations, and can thus be used for distinguishing different oxide failure mechanisms. Finally, the critical cracking strain of the oxide scale and the interfacial shear strength of the oxide/substrate interface were estimated, which are the critical parameters urgently desired for modeling the failure behavior of steam-side oxide scales on boiler tubes of coal-fired power plants. [ABSTRACT FROM AUTHOR]

• A new phenomenological tensile failure criterion with an anisotropic coefficient was proposed. • Direct tensile test of the Kangding slate was carried out to verify the accuracy of the new criterion. • The tensile strength data of eight typical layered rocks were collected and compared with the other six typical tensile strength criteria to verify the universality and superiority of the new criterion. • Based on the sensitivity analysis of tensile rate, the loading rate of 0.01 m/s was recommended for the samples with various foliation angles. • Layer thickness has little effect on tensile strength, but a significant effect on tensile failure modes. The tensile strength is a key parameter for the design of many geotechnical engineerings such as tunnel support, slope support, and petroleum drilling. The tensile strength in layered rocks, however, is anisotropic due to the existence of bedding planes. In this paper, to study the anisotropic tensile behaviors, a series of direct tensile tests were conducted using Kangding slate with five different foliation angles (β = 0°, 30°, 45°, 60°, and 90°). Based on the N-Z criterion, a new tensile failure criterion with the anisotropic coefficient was proposed. The tensile strength data of nine typical layered rocks were collected to evaluate the prediction ability of seven anisotropic tensile failure criteria including the new criterion. Embedding the new criterion into FDEM, the loading rate-dependent and layer thickness-dependent tensile mechanism of layered rock under direct tensile test were simulated. The experimental and numerical simulation results showed that the foliation angle significantly affected the tensile strength and failure modes of the slate. With the increase of foliation angle (β), the tensile strength of nine typical layered rocks, including Kangding slate, presented a non-linear increase trend. Compared with the other six typical anisotropic tensile failure criteria, the new criterion has the best prediction capability on the tensile strength of rocks with four different anisotropic degrees, and therefore the new criterion was recommended. The new criterion was embedded in FDEM to carry out direct tensile simulation of slate with different β. The numerical simulation results were in good agreement with the experimental results, further verifying the accuracy of the new criterion. The loading rate sensitivity analysis indicated that a tensile rate of 0.01 m/s was recommended to assure quasi-static loading of the specimen. Through the sensitivity analysis of layer thickness, it is concluded that layer thickness has very little influence on tensile strength, but has a very significant influence on the final failure modes of the specimens. [ABSTRACT FROM AUTHOR]

In the present work, an attempt has been made to study the mechanical behavior and tensile fractography of 40- and 90-micron-sized boron carbide (B4C) particulate-reinforced light metal (LM) 29 alloy composites. LM29 alloy with 3, 6 and 9 wt. % of 40- and 90-micron-sized B4C composites was synthesized by liquid stir method. Microstructural analyses were obtained by using scanning electron micrographs and energy-dispersive spectrographs. Mechanical properties like hardness, ultimate, yield strength and ductility were evaluated as per American Society for Testing and Materials standards. Scanning electron microscope micrographs show the even dispersal of B4C particulates in the LM29 alloy, and this is confirmed by energy-dispersive spectroscopy analysis. Further, hardness, ultimate and yield strength of matrix LM29 alloy were enriched with the addition of B4C reinforcement and were more in the case of 40-micron-sized reinforced composites. There was small decrease in ductility of composites in both cases. [ABSTRACT FROM AUTHOR]

Edge-to-edge is the most common form of contact in a two-dimensional joint block system. Discontinuous deformation analysis (DDA) is a powerful tool for handling block systems and treats an edge-to-edge contact as two vertex-to-edge contacts with a couple of normal and shear springs at the extremes of the contact segment. However, this method is unsuitable for evaluating the tensile failure of a joint under asymmetrical tension conditions, even though it can simplify the contact type and increase computational efficiency. This is mainly because the distributed forces at an edge-to-edge contact are simplified as two couples of concentrated forces. To solve this problem, this paper proposes incorporating a multi-spring edge-to-edge contact model with DDA. In the model, several contact pairs with normal and shear springs on an edge-to-edge contact are set to simulate the distributed forces. Several benchmark tests were performed to demonstrate the discrepancy between the original and improved DDAs. The results revealed that the latter more accurately models the stress distribution across the edge-to-edge contact, providing a more reasonable acceleration required to topple a series of blocks resting on an inclined stepped base. [ABSTRACT FROM AUTHOR]