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This paper presents an approach for analytically solving gradient-enhanced damage (GED) models. The proposed approach provides rigorous proofs for essential phenomena observed in the traditional GED model, including damage widening, characteristic length sensitivity, and stress-locking. The derived cohesive law is a useful technique for accurately determining the material parameters of the GED model, significantly reducing the sensitivity to characteristic length. Furthermore, this study presents an isotropic damage model that considers both tensile and shear failures and can capture complex crack paths. Finally, a series of numerical examples is shown to demonstrate the efficacy of the suggested method. • This paper introduces a mathematical approach for the analytical solution of gradient-enhanced damage (GED) models. • The analytic solution alleviates the characteristic length sensitivity in the GED model. • The proposed damage evolution method can effectively capture complex crack paths. [ABSTRACT FROM AUTHOR]

In this paper, the effectiveness of reinforcements for flexible pavements is evaluated through an analysis of reflective cracking. Different stiffness and thickness reinforcements are considered for the rehabilitation of an already cracked pavement. The effect of the reinforcement is assessed from two different perspectives: (i) the ability to reduce stresses in the rehabilitated pavement layers, and (ii) the capacity to mitigate the crack propagation from deeper layers. A finite element model (FEM) is adopted to study the stress and strain state of the pavement layers. The pavement model has been properly validated, transitioning from a simply supported beam scheme to an elastic multilayer model. In addition, to represent crack propagation, fracture evolution is analyzed using Linear Elastic Fracture Mechanics (LEFMs) and Paris' law. The effect of different reinforcements on the pavement is then simulated. The results show that the reinforcement performance is strictly dependent on the interlayer thickness and stiffness. In particular, high stiffness reinforcements (geomembranes) show increasing effectiveness with stiffness, both in terms of reflective cracking and stress reduction. Conversely, low stiffness reinforcements (SAMIs) show a variable trend with the stiffness modulus. In fact, extremely low stiffness is effective in slowing down crack propagation but is detrimental to the wearing course's stress condition. However, as the stiffness increases, the likelihood of cracking in the wearing course decreases, though only a small beneficial effect is registered for crack propagation in the base layer. [ABSTRACT FROM AUTHOR]

In this paper, we propose a new approach for numerically simulating the growth of cracks in unidirectional composite materials, termed extended isogeometric analysis, evaluating the maximum stress intensity factor and T-stress. To validate our approach, we used a small anisotropic plate with two edge cracks, beginning with formulating the governing equations based on the energy integral method, Stroh's Formula, and the Elastic Law describing the behaviour of anisotropic materials, while considering boundary conditions and initial states. A MATLAB code was developed to solve these equations numerically and to post-process the tensile stress and the stress intensity factor (SIF) in the first mode. The results for the SIF closely match those obtained using the extended finite element method (X-FEM), with a discrepancy of only 0.0021 Pa·m0.5. This finding underscores the credibility of our approach. The extended finite element method has demonstrated robustness in predicting crack propagation in composite materials in recent years, leading to its adoption by several widely used software packages in various industries. [ABSTRACT FROM AUTHOR]

This paper presents a straightforward approach for determining the low-cycle fatigue (LCF) crack propagation rate in stiffened plate structures containing cracks. The method relies on both the crack tip opening displacement (CTOD) and the accumulative plastic strain, offering valuable insights for ship structure design and assessing LCF strength. Meanwhile, the LCF crack growth tests for the EH36 steel were conducted on stiffened plates with single-side cracks and central cracks under different loading conditions. The effects of stress amplitude, stress ratio, and stiffener position on the crack growth behavior were examined. Fitting and verifying analyses of the test data were employed to investigate the relationship between CTOD and the crack growth rate of EH36 steel under LCF conditions. The results showed that the proposed CTOD-based prediction method can accurately characterize the LCF crack growth behavior for stiffened plate of EH36 steel for use in ship structures. [ABSTRACT FROM AUTHOR]

Copyright of Atomic Energy Science & Technology is the property of Editorial Board of Atomic Energy Science & Technology and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

The key performance parameters of proppant are mainly the crushing rate and fracture conductivity, which are usually evaluated using physical experimental methods. However, the testing method for fracture conductivity has limitations, such as its long time-consumption, high testing costs, instability, and even the presence of large errors in testing results under the same conditions. The purpose of this paper is to propose a calculation method that can replace physical experiments. Firstly, we analyze the random and deterministic phenomena in the contact relationship between proppant particles from a microscopic perspective. Subsequently, we develop a physical model of the microscopic arrangement of these particles, enabling us to conduct further computer simulations of their microscopic configuration. Secondly, we conduct a microscopic mechanical analysis of the contact between proppant particles and between particles and boundaries and establish a corresponding mathematical model. Then, utilizing the simulation and mechanical analysis results of the proppant, we calculate the crushing rate. Considering the crushing rate of proppant, we improve the Kozeny–Carmen equation to determine the fracture permeability, and subsequently calculate the fracture conductivity. Finally, the calculated results are compared with the experimental results. The results show that the calculated values for the proppant crushing rate and fracture conductivity matched well with experimental data, and that the model's calculation values were more accurate. As the number of simulations increased, the accuracy of the calculation results became higher. Research shows that the fracture conductivity is influenced by factors such as the particle size, microstructure, and crushing rate. Numerical calculation methods can replace physical experiments and provide theoretical support for engineering applications of hydraulic fracturing proppant materials. [ABSTRACT FROM AUTHOR]

With the shift of coal seam mining to the deep, the in-situ stress of coal and rock mass increases gradually. High ground stress can limit the generation of rock cracks caused by blasting, and blasting usually shows different crushing states than low stress conditions. In order to study the blasting expansion rule of rock mass with cavity under high ground stress and the rock mass fracture state under different side stress coefficients. In this paper, the effective range of blasting and the stress distribution under blasting load are analyzed theoretically. The RHT (Riedel-Hiermaier-Thoma) model is used to numerically simulate the blasting process of rock mass with cavity under different ground stress, and the influence of ground stress and lateral pressure coefficient on the crack growth of rock mass is studied. The results show that when there is no ground stress, the damage cracks in rock mass are more concentrated in the horizontal direction and the fracture development tends to the direction where the holes are located, which confirms the guiding effect and stress concentration effect of the holes in rock mass, which helps to promote the crack penetration between the hole and the hole. The length difference of horizontal and vertical damage cracks in rock mass increases with the increase of horizontal and vertical stress difference. Under the same lateral stress coefficient, the larger the horizontal and vertical stress difference is, the stronger the inhibition effect on crack formation is. For blasting of rock mass with high ground stress, the crack formation length between gun holes decreases with the increase of stress level, and the crack extends preferentially in the direction of higher stress. Therefore, the placement of gun holes along the direction of greater stress and the shortening of hole spacing are conducive to the penetration of cracks between gun holes and empty holes. The research can provide reference for rock breaking behavior of deep rock mass blasting. [ABSTRACT FROM AUTHOR]

In response to the problem that the standard AT2 phase field model cannot effectively model quasi-brittle failure and the existence of length dependence, a new modified phase field model is presented in this paper. By introducing an additional energy, the competing relationship between elastic strain energy and dissipation energy during fracture is changed. A new crack dissipation functional is established using the energy equivalent approach. By introducing a novel rational degradation function, not only can the strength of material failure be effectively utilized, but the model can also reproduce the cohesive softening relationship. A multi-field finite element method is used to discretize the model governing equations, and the equations are solved by an efficient BFGS monolithic algorithm. Finally, some representative numerical examples are used to analyze the effects of parameters in degradation function, length scale and mesh size on the results. The presented numerical simulation results demonstrate length scale and mesh scale independence, and are in good agreement with the experimental results and previous numerical results. At the same time, the numerical results also exhibit cohesive softening properties similar to the current phase field cohesive zone model. These results verify the robustness and effectiveness of the modified phase field model presented in this paper for simulating quasi-brittle failure and brittle fracture. [ABSTRACT FROM AUTHOR]

(1) Modeling and characterization of ductile fracture in metals is still a challenging task in the field of computational mechanics. Experimental testing offers specific responses in the form of crack-mouth (CMOD) and crack-tip (CTOD) opening displacement related to applied force or crack growth. The main aim of this paper is to develop a phase-field-based Finite Element Method (FEM) implementation for modeling of ductile fracture in stainless steel. (2) A Phase-Field Damage Model (PFDM) was coupled with von Mises plasticity and a work-densities-based criterion was employed, with a threshold to propose a new relationship between critical fracture energy and critical total strain value. In addition, the threshold value of potential internal energy—which controls damage evolution—is defined from the critical fracture energy. (3) The material properties of AISI 316L steel are determined by a uniaxial tensile test and the Compact Tension (CT) specimen crack growth test. The PFDM model is validated against the experimental results obtained in the fracture toughness characterization test, with the simulation results being within 8% of the experimental measurements. (4) The novel implementation offers the possibility for better control of the ductile behavior of metallic materials and damage initiation, evolution, and propagation. [ABSTRACT FROM AUTHOR]

Wire and arc additive manufacturing (WAAM) offers promise in creating large complex structures due to its flexibility and high material deposition rates. The nickel-based alloy IN718 is favoured for WAAM due to its weldability and compatibility. However, WAAM can introduce issues like anisotropic grain structure, porosity, and residual stresses which can lead to directional variations in tensile, fatigue, and fracture behaviour. This paper studied the WAAM process of IN718, utilising cold metal transfer (CMT). The optimised CMT-WAAM parameters for IN718 were identified to as a wire feed speed of 8–10 m/min and a torch travel speed of 0.5–0.7 m/min, resulting in stable deposition and minimal defects. Nevertheless, columnar grain structures were observed in the build direction (BD), with coarse grains in the wall-length direction (WD). This anisotropic microstructure coupled with stress concentrators, contributes to the directional dependence observed in tensile properties, fatigue endurance, and crack growth. The investigation revealed superior ductility in the BD compared to the WD. Interestingly, the fatigue endurance testing showed a longer life in the WD compared with the BD, attributed to stronger stress concentrators in the BD specimens. However, when examining a cracked specimen, the fatigue crack propagated faster in the WD rather than the BD. [ABSTRACT FROM AUTHOR]

In the above referenced paper, misinterpretations led Martin to claim that there are errors in certain equations derived in our paper on the use of Frobenius’ method to solve curved crack problems. This note identifies the misinterpretations and shows that our results are the same as those derived by Martin. [ABSTRACT FROM AUTHOR]

Since the first paper on the fatigue of metallic materials by J. Albert in 1837, tremendous numbers of papers have been published in various journals by many researchers all over the world. Based on such a long history, several papers on the very high cycle fatigue (VHCF) in the life‐time longer than 107 cycles had appeared in some journals during the period of 1980's. One characteristic finding in these works is the fact that the metallic material can fail even at the stress level lower than the conventional fatigue limit. This fact means that the conventional fatigue design of mechanical structures cannot give the safety of the practical products in the very high cycle regime. Due to this fact, fatigue properties of structural materials in very long life regime has become an important subject; and a lot of studies have been carried out, and many important results have been accumulated until now. Typical aspects on VHCF property are summarized as follows: (1) the fatigue crack tends to occur around the interior inclusion, (2) fine granular area (FGA) is formed around such an inclusion, and (3) duplex S–N characteristics appear in the VHCF regime. In this paper, a brief historical review together with the future prospect on the very high cycle fatigue of metallic materials is attempted for the sake of reference to facilitate the research in this area. Highlights: Historical review and future prospect for researches on metal fatigue.Progress of researches on very high cycle fatigue of metallic materials.Review of interior crack initiation and growth mechanisms around inclusion.Quantitative formulation of interior crack growth around inclusion. [ABSTRACT FROM AUTHOR]

Abstract: The present paper gives comments on specimens to be considered for fracture toughness experiments. It is emphasized that the similarity between compact tension specimens, C(T), and cracks in real structures is often disregarded. [Copyright &y& Elsevier]

This paper reports on spall failure and damage modes in Laser Powder Bed Fusion fabricated Stainless Steel 316L (SS316L) with intentional levels of low-volume (1–5 vol. %) porosity and pore sizes of 200, 350, and 500 μm. The fabricated specimens were subjected to uniaxial-strain plate-impact loading at ∼4.5 GPa, to initiate incipient spall failure. Analysis of velocimetry profiles measured using multi-probe photon-Doppler velocimetry coupled with post-mortem analysis of soft-recovered samples reveals local suppression of spall failure (termed as spall-dominated) as a function of porosity, as the failure mechanism transitions from spall-centered tensile stress dominated to a pore-centered microstructure-dominated damage mode involving void/crack nucleation and growth at pre-existing pores. The critical porosity level where the suppression of spall failure is first observed, as well as the spall location, is dependent on both the volume fraction and the size of the initially fabricated pores. In samples of 500 μm pore size, the suppression of spall failure is observed with as little as 1 vol. % porosity, while samples with smaller pores (200 μm) still experience spall-centered tensile stress dominated failure with higher levels (5 vol. %) of porosity. In the case of pore-centered microstructure-dominated failure, spall damage can occur but the spall plane is shifted toward the rear free surface, or more generally in areas further away from the region with pores. Highly heterogeneous deformation twinning, shear banding, grain rotation, and cracking are observed in the vicinity of pre-existing pores and expected spall failure sites. [ABSTRACT FROM AUTHOR]

The article invites papers to be presented at the 10th annual meeting of the International Society of Mesomechanics to be held in Giza, Egypt from January, 14-18, 2008.

The size of wind turbine blades is increasing rapidly, and they are being installed in remote offshore locations. Consequently, it is essential to focus on improving the design and maintenance procedures in the blade industry to meet the growing demand. Of particular concern is the long-term operational performance of the wind turbine blade trailing edge. In this paper, we discuss the application of durability and damage tolerance analysis (DADTA) approaches to trailing edge service life prediction. DADTA is mandated in the aerospace sector to support airworthiness certification and to provide an updated life prediction of the structure based on the different stages of their service life. The DADTA framework has two main parts: durability and damage tolerance analysis. The durability part uses a structural fatigue approach based on a damage accumulation method during the initial design phase to predict the lifespan of a structure without defects. On the other hand, the damage tolerance analysis part uses a fracture mechanics approach and a damage growth method to update the lifespan prediction of a structure during the operation stages. This is achieved by utilizing sensors and inspection data as inputs while the structure is in service. Both these methods are comprehensive and have merits; however, their broad adoption in the wind turbine blade industry is still lacking. The current paper provides an extensive review of these methods and shows how these can be applied to the wind turbine blade industry, specifically for predicting the structural design life of the trailing edge of composite wind turbine blades. The review includes (a) defining wind turbine trailing edge failure modes, (b) trailing edge design procedures, and (c) a detailed discussion of the application of durability and damage tolerance analysis for trailing edge life prediction. Overall, this review paper would be of special interest to blade designers and would guide researchers and engineers interested in life prediction methodologies based on DADTA approaches for wind turbine blades. [ABSTRACT FROM AUTHOR]

This paper presents an extensive literature review focusing on the utilisation of crack tip plasticity as a crucial parameter in determining and enhancing crack growth models. The review encompasses a comprehensive analysis of various methodologies, predominantly emphasising numerical simulations of crack growth models while also considering analytical approaches. Although experimental investigations are not the focus of this review, their relevance and interplay with numerical and analytical methods are acknowledged. The paper critically examines these methodologies, providing insights into their advantages and limitations. Ultimately, this review aims to offer a holistic understanding of the role of crack tip plasticity in the development of effective crack growth models, highlighting the synergies and gaps between theoretical, experimental, and simulation-based approaches. [ABSTRACT FROM AUTHOR]

Copyright of Association of Arab Universities Journal of Engineering Sciences (JAARU) is the property of Association of Arab Universities and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Adhesively bonded doublers and adhesively bonded repairs are extensively used to extend the operational life of metallic aircraft structures. Consequently, this paper focuses on the tools needed to address sustainment issues associated with both adhesively bonded doublers and adhesively bonded repairs to (metallic) aircraft structures, in a fashion that is consistent with the building-block approach mandated in the United States Air Force (USAF) airworthiness certification standard MIL-STD-1530D and also in the United States (US) Joint Services Structural Guidelines JSSG-2006. In this context, it is shown that the effect of biaxial loads on cohesive crack growth in a bonded doubler under both constant amplitude fatigue loads and operational flight loads can be significant. It is also suggested that as a result, for uniaxial tests to replicate the cohesive crack growth seen in adhesively bonded doublers and adhesively bonded repairs under operational flight loads, the magnitude of the applied load spectrum may need to be continuously modified so as to ensure that the crack tip similitude parameter in the laboratory tests reflects that seen in the full-scale aircraft. [ABSTRACT FROM AUTHOR]

The heterogeneity of welded joints' microstructure affects their mechanical properties, which can vary significantly in relation to specific weld zones. Given the dimensional limitations of the available test volumes of such material zones, the determination of mechanical properties presents a certain challenge. The paper investigates X welded joint of S690QL1 grade high strength steel (HSS), welded with slightly overmatching filler metal. The experimental work is focused on tensile testing to obtain stress-strain properties, as well as fracture mechanics testing. Considering the aforementioned limitations of the material test volume, tensile testing is carried out with mini tensile specimens (MTS), determining stress-strain curves for each characteristic weld zone. Fracture mechanical testing is carried out to determine the fracture toughness using the characteristic parameters. The experimental investigation is carried out using the single edge notch bend (SENB) specimens located in several characteristic welded joint zones: base metal (BM), heat affected zone (HAZ), and weld metal (WM). Fractographic analysis provides deeper insight into crack behavior in relation to specific weld zones. The numerical simulations are carried out in order to describe the fracture behavior of SENB specimens. Damage initiation and evolution is simulated using the ductile damage material behavior. This paper demonstrates the possibility of experimental and numerical determination of fracture mechanics behavior of characteristic heterogeneous welded joint zones and their influence on crack path growth. [ABSTRACT FROM AUTHOR]

Investigating the constitutive relationship and the damage failure mechanism of solid propellants is of significance for improving the safety, storage period and use efficiency of solid rocket motors. This paper focuses on the complex mechanical response behavior of composite solid propellants under loads and introduces experimental research on quasi-static and dynamic mechanical properties. Limited by the accuracy of instruments and testing methods, the research progress of macroscopic constitutive models, mesoscopic mechanical models and microscopic molecular models is summarized from the perspective of numerical simulations based on model scale and modeling methods. This paper tracks the historical progress of key models and summarizes the main achievements and prospects in this field. The research in this paper has high scientific and theoretical significance and engineering application value. It can provide an important reference and guidance for the structural optimization and performance improvement of solid propellants and lay a solid foundation for the development of solid rocket motors. [ABSTRACT FROM AUTHOR]

Purpose: The purpose of this paper is to apply the concept of equivalent initial flaw size (EIFS) to the anisotropic nickel-based single crystal (SX) material, and to predict the fatigue life on this basis. The crack propagation law of SX material at different temperatures and the weak correlation of EIFS values verification under different loading conditions are also investigated. Design/methodology/approach: A three-parameter time to crack initial (TTCI) method with multiple reference crack lengths under different loading conditions is established, which include the TTCI backstepping method and EIFS fitting method. Subsequently, the optimized EIFS distribution is obtained based on the random crack propagation rate and maximum likelihood estimation of median fatigue life. Then, an effective driving force based on anisotropic and mixed crack propagation mode is proposed to describe the crack propagation rate in the small crack stage. Finally, the fatigue life of three different temperature ESE(T) standard specimens is predicted based on the EIFS values under different survival rates. Findings: The optimized EIFS distribution based on EIFS fitting - maximum likelihood estimation (MLE) method has the highest accuracy in predicting the total fatigue life, with the range of EIFS values being about [0.0028, 0.0875] (mm), and the mean value of EIFS being 0.0506 mm. The error between the predicted fatigue life based on the crack propagation rate and EIFS distribution for survival rates ranges from 5% to 95% and the experimental life is within two times dispersion band. Originality/value: This paper systematically proposes a new anisotropic material EIFS prediction method, establishing a framework for predicting the fatigue life of SX material at different temperatures using fracture mechanics to avoid inaccurate anisotropic constitutive models and fatigue damage accumulation theory. [ABSTRACT FROM AUTHOR]

This paper investigates the fracture mechanical properties of concrete, using crushed concrete aggregates (CCA) and granulated blast furnace slag (GGBS) for partial cement replacement. CCAs made from prefabricated concrete replace 100% of the fine and coarse fractions in concrete recipes with w/c ratios of 0.42 and 0.48. Two pre-treatment methods, mechanical pre-processing (MPCCA) and accelerated carbonation (CO2CCA), are investigated for quality improvements in CCA. The resulting aggregates show an increased density, contributing to an increase in the concrete's compressive strength. The novelty of this paper is the superposition of the effects of the composite parts of concrete, the aggregate and the cement mortar, and their contributions to concrete fracture. Investigations are directed toward the influence of fine aggregates on mortar samples and the influence of the combination of coarse and fine aggregates on concrete samples. The physical and mechanical properties of the aggregates are correlated with mortar and concrete fracture properties. The results show that CCA concrete achieves 70% of the fracture energy values of concrete containing natural aggregates, and this value increases to 80% for GGBS mixes. At lower w/c ratios, MPCCA and CO2CCA concretes show similar fracture energies. CO2CCA fine aggregates are the most effective at strengthening the mortar phase, showing ductile concrete behavior at a w/c ratio of 0.48. MPCCA aggregates contribute to higher compressive strengths for w/c ratios of 0.42 and 0.48. Thus, mechanical pre-processing can be improved to produce CCA, which contributes to more ductile concrete behavior. [ABSTRACT FROM AUTHOR]

A comparative study between two nano cementitious materials, i.e., Graphene Nanoplatelet (GNP) and Montmorillonite Nano Clay (MNC) cement matrix are considered in this paper. Nanofibers are introduced as an alternative to macro reinforcement to enhance the mechanical property and reduce the crack growth in the cement matrix at the nanoscale. Various analytical simulation has been carried out by ANSYS 15.0 to know the optimum percentage of water. A 3D Represent Volume Element (RVE) is used to simulate nano cementitious material as the material sizes differ. RVE is the minimum volume upon which a measurement can make, yielding an expected value of the entire. The GNPs and MNCs are added to the cement matrix with various percentages (0.02%, 0.08%, 0.1%, 0.15%, 0.17%, 0.22%, and 0.3%) by the weight of cement. After simulating the pullout models with proper boundary conditions, the behavior of nano-cementitious material is observed. A comparative study of all percentage variations revealed that the mechanical property increases up to 0.17% and 0.22% for GNPs and MNCs. It also observed that GNPs cementitious material performs better than MNCs cement matrix. [ABSTRACT FROM AUTHOR]

This paper introduces a comprehensive computational framework, comprising a finite deformation crystal inelasticity constitutive model and phase field model, for modeling crack growth in superelastic nitinol polycrystalline microstructures. The crystal inelasticity model represents crystal stretching and lattice rotation from elastic mechanisms, as well as local inelastic deformation due to austenite-martensite phase transformation. The phase field formulation decomposes the Helmholtz free energy density into stored elastic energy, phase transformation energy, and crack surface energy components. The elastic energy accounts for tension-compression asymmetry with the formation of the crack through a spectral decomposition. Kinetic Monte Carlo simulations generate equilibrium area fractions of different surface orientations, which serve as weights for the surface energy. An adaptive wavelet-enhanced hierarchical finite element (FE) model is introduced to alleviate high computational overhead in phase field crack simulations. Simulations with the coupled inelasticity phase field model are conducted under various loading conditions including Mode-I tension, a quasi-static Kalthoff experiment, and cyclic loading of polycrystalline microstructures. Crack propagation is effectively predicted by this model, providing valuable insights into the material mechanical behavior with growing cracks. [ABSTRACT FROM AUTHOR]

The paper presents the dynamic impact properties of laser-sintered polyamide PA2200 in accordance with the building orientation. The idea of deTermining the impact properties in relation to building orientation lays on orientation-property dependence founded in our previous studies of tensile, bending and fracture mechanics testing. The specimens were manufactured under the same energy density and temperature conditions, at four orientations, as described in the paper content. The experimental investigation was carried out on a pendulum impact testing machine to deTermine the impact energy and strength according to the building orientation. Brittle fracture was observed for all specimens, independent of building orientation, and a similar behavior was also observed in the elastic zone of deflection. However, impact strength and impact energy are influenced by orientation. [ABSTRACT FROM AUTHOR]

Packages made of corrugated paper are fundamental to the protection, transportation and handling of the appliance product market. During the storage and sales stages of a product, the package must resist compressive loads in different directions beyond moderate impacts. In this context, the objective of this work is to develop and implement a post-processor that allows the simultaneous analysis of two of the most common failure modes of packages made of corrugated paper: failure due to tensile or compressive stress limit, and failure due to local buckling, when the buckling of the faces of the corrugated paper between two peaks of the fluting waves occurs. It was realized that the current procedure proposed by the literature expend a series of operations, what became the failure analysis for corrugated boxes too lengthy for the immediacy of the industry. Thus, it was chosen to apply a procedure to simplify the failure limit surface. Tensile tests were performed for the characterization of corrugated material used in numerical simulations. Experimental tests were performed on corrugated boxes used on household appliance products. The Tsai-Wu criteria for the material failure evaluation was applied and a modified Nyman-Gustafsson criteria for the local buckling analysis on the numerical simulations was proposed. A good correlation between experimental tests and numerical results was obtained. This work brings high expectations to the agility requested by the industry in the launching of new products. [ABSTRACT FROM AUTHOR]

The microbial diversity in oligotrophic isolated crystalline Fennoscandian Shield bedrock fracture groundwaters is great but the core community has not been identified. Here we characterized the bacterial and archaeal communities in 12 water conductive fractures situated at depths between 296 and 798m by high throughput amplicon sequencing using the Illumina HiSeq platform. The great sequencing depth revealed that up to 95 and 99% of the bacterial and archaeal communities, respectively, were composed of only a few common species, i.e. the core microbiome. However, the remaining rare microbiome contained over 3 and 6 fold more bacterial and archaeal taxa. Several clusters of co-occurring rare taxa were identified, which correlated significantly with physicochemical parameters, such as salinity, concentration of inorganic or organic carbon, sulphur, pH and depth. The metabolic properties of the microbial communities were predicted using PICRUSt. The rough prediction showed that the metabolic pathways included commonly fermentation, fatty acid oxidation, glycolysis/gluconeogenesis, oxidative phosphorylation and methanogenesis/anaerobic methane oxidation, but carbon fixation through the Calvin cycle, reductive TCA cycle and the Wood-Ljungdahl pathway was also predicted. The rare microbiome is an unlimited source of genomic functionality in all ecosystems. It may consist of remnants of microbial communities prevailing in earlier conditions on Earth, but could also be induced again if changes in their living conditions occur. In this study only the rare taxa correlated with any physicochemical parameters. Thus these microorganisms can respond to environmental change caused by physical or biological factors that may lead to alterations in the diversity and function of the microbial communities in crystalline bedrock environments. [ABSTRACT FROM AUTHOR]

Surface preparation of engineering materials is necessary for preventing corrosion and subsequent failure of materials in service. There are different methods of surface preparations that can affect engineering materials in different ways. This study investigated the effect of surface preparation on the corrosion behavior of zinc sprayed and unsprayed mild steel. Quantitative analysis and potentiodynamic polarization techniques were used to evaluate the immersed samples of different surface preparations. The results indicated that the least corrosion rate was observed for the uncoated sample prepared with CC1200 grit paper at 0.041 mpy and successive samples in the order of CC220 grit paper at 0.047 mpy < P60 grit paper at 0.052 mpy < filing at 0.064 mpy and grinding at 0.074 mpy after 42-days of immersion. The prepared samples that were further coated with zinc spray demonstrated a similar trend. The sample prepared with CC1200 grit paper and further coated with zinc spray exhibited the lowest corrosion rate of 1.35 x 10-9 mpy. Potentiodynamic polarization results further suggested that the same behavior was observed in the quantitative analysis. [ABSTRACT FROM AUTHOR]

The HIDA-8 Conference held online on 20-22 April 2021 was the eighth in the series of the HIDA international conferences held in various countries since April 1998. Assessment of the behaviour of high temperature plant components containing incipient or service induced defects/cracks and operating under steady and/or cyclic load conditions has been an area of interest for some time. The EC and European high temperature industry jointly funded the project which was mainly aimed at unifying European defect assessment procedures with validation on a number of materials of interest to power and process plant. [Extracted from the article]

Rock mass is one of the most important load-bearing media in geotechnical engineering. It has been continually vulnerable to geological tectonic movements, natural calamities, and human excavation activities. Its inherent weak surfaces such as primary pores, joints, and fissures have resulted in varying damage degrees. In mining operations, the damaged rock mass has a variety of negative impacts on the stability of its overlying structures and is frequently disturbed by the load. To study the damage law of rock mass under cyclic loading, in this paper, an acoustic emission (AE) device was employed to monitor the rock under the action of two types of cyclic loads: the variable upper and lower pre-loads, and the fixed upper and lower pre-loads. The damage of the loaded rock was split into three stages in this research, based on the features of the AE signals of the rock under uniaxial load, and the damage evolution of the loaded rock was analyzed in distinct stages. The AE signals of the rock under cyclic loading were mainly emitted in the first loading stage. When the stress did not exceed the maximum stress value in the stress history of the loaded rock, few new AE event was generated in the loaded rock. After the low-frequency cyclic static load, the AE signals varied with the load-bearing stress of the rock during the whole process from initial loading to failure, which was consistent with the characteristics of the AE signals of the loaded rock. The research results can be adapted to rock mass in open-pit mines stability analysis and risk prediction while providing some references for the early warning and danger relief of rock masses in engineering. [ABSTRACT FROM AUTHOR]

In this paper, a series of low-temperature CVN (Charpy V-notch impact test) and DWTT (drop-weight tear test) experiments were carried out to deal with the intensifying contradiction of strength and toughness of ultra-high-strength pipeline steel. The fracture behavior and toughening mechanisms of ultra-high-strength pipeline steel were investigated using scanning electron microscopy, transmission electron microscopy and backscattered electron diffraction systems. The results show that DWTT fractures in ultra-high-strength pipeline steel had a variety of unconventional morphological features compared to CVN fractures, including ridge protrusion in ductile fracture conditions and a large-size fracture platform in brittle fracture conditions. Therefore, DWTT fractures contained more information about the material fracturing process, and could better reflect the actual process of material fracturing. In ultra-high-strength pipeline steel, fine-grained granular bainite caused cracks to undergo large deflections or frequent small transitions, which consumed additional energy and improved toughness. In contrast, large-sized granular bainite, which consisted of low-angle grain boundaries, did not effectively prevent crack propagation when it encountered cracks, which was not conducive to improved toughness. Moreover, the M/A constituents in large-sized granular bainite aggregated, cracked, or fell off, which could easily lead to the formation of microcracks and was also detrimental to toughening. [ABSTRACT FROM AUTHOR]

Competing risks models, also known as weakest-link models, are utilized to analyze diverse strength distributions exhibiting multi-modality, often attributed to various types of defects within the material. The weakest-link theory posits that a material's fracture is dictated by its most severe defect. However, multimodal problems can become intricate due to potential censoring, a common constraint stemming from time and cost limitations during experiments. Additionally, determining the mode of failure can be challenging due to factors like the absence of suitable diagnostic tools, costly autopsy procedures, and other obstacles, collectively referred to as the masking problem. In this paper, we investigate the distribution of strength for multimodal failures with censored data. We consider both full and partial maskings and present an EM-type parameter estimate for the Birnbaum-Saunders distribution under competing risks. We compare the results with those obtained from other distributions, such as lognormal, Weibull, and Wald (inverse-Gaussian) distributions. The effectiveness of the proposed method is demonstrated through two illustrative examples, as well as an analysis of the sensitivity of parameter estimates to variations in starting values. [ABSTRACT FROM AUTHOR]

In this paper, the distributed dislocation technique (DDT) is used to calculate the stress intensity factors (SIFs) at the tip of several moving cracks which are located at the interface between two dissimilar non-homogeneous half-planes. In this study, in-plane loading is considered and it is assumed that the properties of the non-homogeneous material change exponentially. First, by employing Fourier and Galilean transforms, the problem of Volterra type climb and glide edge dislocation is solved at the interface of two dissimilar materials, and then the DDT is used to obtain the singular integral equations of Cauchy type. The resulting singular equations are numerically discretized and solved to obtain dislocation density on the crack surfaces to determine the SIFs. Finally, the effects of change in parameters such as gradient non-homogeneous constant, Poisson ratio, crack growth rate and interaction between cracks on SIFs are shown graphically. [ABSTRACT FROM AUTHOR]

In recent years, many useful experimental results on the cracking behaviors of fractured rocks have been obtained via uniaxial, biaxial, triaxial, and Split Hopkinson Pressure Bar (SHPB) tests. In this paper, the influence of the inclination angle of flaws, number of flaws, and patterns of cracks on the mechanical properties during the failure process under static loading and dynamic loading conditions is introduced and reviewed. The results show that the presence of cracks can decrease the strengths of precracked specimens, and the inclination angles, numbers, and crack patterns of pre-existing flaws can change the mechanical properties and cracking behaviors of precracked specimens. Under static loading, the closer the inclination angle is to 90°, the greater the strength, the elastic modulus, and the peak strain of the precracked specimen. However, under dynamic loading, the influence of the inclination angle varies, and the strength can increase or decrease, possibly in a V-shaped manner. This change can be determined by multiple factors, such as the loading path, the materials of the precracked specimen, and the number of pre-existing cracks. Under dynamic loading, the precracked specimen usually exhibits an Xshaped conjugated failure. Additionally, some problems in the study of the cracking behaviors of fractured rocks and related future research are described and presented, and corresponding suggestions and solutions are given. In particular, excavation in deep rock engineering, support of the rock surrounding the tunnel, and mining engineering have important scientific and engineering significance. [ABSTRACT FROM AUTHOR]

This paper presents a probabilistic method to predict fatigue crack growth for surface flaws in pipelines using a particle filtering method based on Bayes theorem. The random response of the fatigue behavior is updated continuously as measured data are accumulated by the particle filtering method. Fatigue crack growth is then predicted through an iterative process in which particles with a high probability are reproduced more during the update process, and particles with a lower probability are removed through a resampling procedure. The effectiveness of the particle filtering method was confirmed by controlling the depth and length direction of the cracks in the pipeline and predicting crack growth in one- and two-dimensional cases. In addition, the fatigue crack growth and remaining service life with a 90% confidence interval were predicted based on the findings of previous studies, and the relationship between the fatigue crack growth rate and the crack size was explained through the Paris' law, which represents fatigue crack growth. Finally, the applicability of the particle filtering method under different diameters, aspect ratios, and materials was investigated by considering the negative correlation between the Paris' law parameters. [ABSTRACT FROM AUTHOR]

Plasma stimulation is a form of waterless fracturing as it requires that only the wellbore be filled with an aqueous fluid. The technique creates multiple fractures propagating in different directions around the wellbore. The intent of this paper is to present an experimental and numerical investigation of the degree of competitiveness of plasma stimulation with hydraulic fracturing, especially in the case of stimulating tight formation. Several cases were run experimentally. The samples included limestone and sandstone to investigate plasma fracturing in different rock types. In addition, the main goal of the experiments was to study the creation of fracture(s) under confining stresses, the type of rock, the amount of electrical energy used in the experiment, and the length of the wire to generate the plasma reaction. A laboratory plasma equipment was designed and used to accomplish the experimental work. The experiments were then numerically matched using a finite element numerical simulator, HOSS developed by LANL (Los Alamos National Lab). HOSS was developed to simulate high-strain-rate fractures such as those created by plasma stimulation. It accounts for mixed-mode fracture mechanics which are tensile and shear fractures. The simulator governing equations obey the conservation of mass and momentum in a solid-mechanics sense and account for the nonlinear deformation of rock material. The matching of the experiment allowed us to validate the HOSS simulation of the process and showed that the numerical results are in good agreement with the experimental work. Using the HOSS simulator, we also investigated the effect of higher energy levels and/or short release time on a cement rock model. The pressure profile that is developed due to the energy release can vary in the peak pressure and the release time. The results showed that the plasma fracturing technique is an effective stimulation method in sandstone and limestone. Plasma fractures were developed in the rock samples and extended from the sample wellbore to the outer boundaries. The shape of the pressure pulse has an impact on the developed fractures. Moreover, the effect of plasma stimulation on natural fractures was studied numerically. It was found that natural fractures can arrest the plasma-generated fractures that propagate from the wellbore to the outer boundaries. However, new fractures may develop in the rock starting from the natural fracture tips. [ABSTRACT FROM AUTHOR]

This paper investigates the influence of exposure to elevated temperatures on the fracture mechanics of polymer concrete (PC). The PC was synthesised using epoxy, silica sand, crushed basalt, and nanoclay. The prepared PC was exposed to temperatures of 24, 40, 60, 80, 100, 120 and 140°C for two hours, and the residual fracture toughness and fracture energy in mode I and mode II were studied. The three-point bending test was conducted on cracked semi-circular bend specimens with a crack angle of 0° (pure mode I) and 41° (pure mode II) to determine the fracture parameters. Subjection to high temperatures significantly increased the fracture toughness and fracture energy of the PC. The maximum fracture toughness and fracture energy were obtained after exposure to temperatures of 120°C and 140°C, respectively. Scanning electron microscopy was used to investigate the fracture surface of the PC. The type of fracture (brittle or ductile) of the PC before and after exposure to the target temperatures was evaluated. The mathematical relationships between modes I and II critical stress intensity factor (KIc and KIIc), as well as modes I and II fracture energy (GIf and GIIf) after exposure to high temperatures, were also determined. [ABSTRACT FROM AUTHOR]

This paper aims to study the Mode-I penny-shaped crack problem of an infinite body of one-dimensional hexagonal piezoelectric quasicrystal. The problem is transformed into a mixed-boundary value problem in the context of electro-elasticity of quasicrystals, and the corresponding integro-differential equations are analytically solved. Two extreme cases of electrically impermeable and permeable crack surface are considered. By virtue of the generalized potential theory method, the three-dimensional complete analytical solutions of three-dimensional crack problems under symmetric concentrated and uniform loads are expressed in terms of elementary functions. Important parameters in fracture mechanics are explicitly derived, such as crack surface displacements, the distributions of generalized stresses at the crack tip and the corresponding generalized stress intensity factors. The validity of the proposed solutions and the coupling effect of phonon-phason-electric fields are investigagted through numerical examples. [ABSTRACT FROM AUTHOR]

Purpose: This study aims to examine how the thickness of layers and printing speed impact the energy absorption capacity of honeycomb structures through drop-weight experiments. In addition, the effect of printing orientation on the resulting microstructure and mechanical performance was targeted to be examined. Design/methodology/approach: In this paper, after manufacturing test specimens using fused deposition modeling technique with three distinct layer thicknesses (0.16 mm, 0.20 mm and 0.28 mm) and printing speeds (40 mm/min, 50 mm/min and 70 mm/min), drop weight tests were carried out. Then to see the effect of printing orientation on mechanical performance, three-point-bending tests were performed and damage mechanisms were comparatively examined through scanning electron microscopy. Findings: An increase in layer thickness from 0.16 mm to 0.28 mm resulted in a notable 37% decrease in the impact resistance of the printed part. In addition, increasing the printing speed from 50 to 70 mm/min reduced the energy absorption capacity of the printed part by approximately 36.5%. Moreover, in terms of printing direction, transversely printed specimens showed 10% lower flexural strength than longitudinally printed specimens. Finally, scanning electron microscopy (SEM) observation showed that internal defects were more prominent in transversely printed specimens, resulting in premature failure. Furthermore, delamination was also detected in transversely printed specimens as another damage mechanism accelerating material failure. Originality/value: It is seen that the effect of printing parameters on the fundamental mechanical properties including tensile strength, strain at break, ductility and elastic modulus were studied by various researchers. However, to the best of authors' knowledge, the effect of printing speed and layer thickness on the energy absorption of polylactic acid based hexagonal honeycomb was not encountered. In addition, in-depth SEM analysis to discover the influence of printing direction significantly contributes to the literature. [ABSTRACT FROM AUTHOR]

The objective of this paper is to evaluate the dynamic stress intensity factors (DSIFs) of a cracked body using the bond-based peridynamics (BBPD) formulation. The peridynamics theory offers advantages over the classical continuum theory for solving partial differential equations in fracture mechanics. Nevertheless, some problems remain, such as its dispersion characteristics and constant micromodulus used in the classical BBPD. In this study, a Gaussian function is used to define the non-constant micromodulus. A wave dispersion analysis for a 1D problem was carried out and the influence of the horizon, mesh size and the kernel function on the dispersion properties were analyzed. On the other hand, a new approach to evaluate the DSIFs of a cracked body using the BBPD coupled with the displacement extrapolation technique is presented. Parameters that reduced the wave dispersion were kept for the DSIFs estimation. The proposed method is applied to analyze some benchmark examples. The obtained results are compared with the exact ones and they showed that the proposed approach can be used as an alternative method to evaluate DSIFs. [ABSTRACT FROM AUTHOR]

The analysis of critical states during fracture of wood materials is crucial for wood building safety monitoring, wood processing, etc. In this paper, beech and camphor pine are selected as the research objects, and the acoustic emission signals during the fracture process of the specimens are analyzed by three-point bending load experiments. On the one hand, the critical state interval of a complex acoustic emission signal system is determined by selecting characteristic parameters in the natural time domain. On the other hand, an improved method of b_value analysis in the natural time domain is proposed based on the characteristics of the acoustic emission signal. The K-value, which represents the beginning of the critical state of a complex acoustic emission signal system, is further defined by the improved method of b_value in the natural time domain. For beech, the analysis of critical state time based on characteristic parameters can predict the "collapse" time 8.01 s in advance, while for camphor pines, 3.74 s in advance. K-value can be analyzed at least 3 s in advance of the system "crash" time for beech and 4 s in advance of the system "crash" time for camphor pine. The results show that compared with traditional time-domain acoustic emission signal analysis, natural time-domain acoustic emission signal analysis can discover more available feature information to characterize the state of the signal. Both the characteristic parameters and Natural_Time_b_value analysis in the natural time domain can effectively characterize the time when the complex acoustic emission signal system enters the critical state. Critical state analysis can provide new ideas for wood health monitoring and complex signal processing, etc. [ABSTRACT FROM AUTHOR]

Shale gas, as an important unconventional oil and gas resource, plays an important role in energy supply. Due to the strong mechanical heterogeneity and compactness, which requires the use of fracturing to crush the formation to obtain industrial production capacity. Therefore, it is very important to analyze shale's mechanical properties and fracturing propagation laws. In this paper, the shale numerical model is established by adopting discrete element method (DEM). The mesoscopic constitutive parameters of shale with different matrix and bedding strength are determined based on rock samples tests. The reliability of the model is verified by finite element method. And the fracture propagation laws under the influence of shale beddings are studied. The results show that the existence of bedding fractures leads to the nonuniformity of fractures propagation in shale reservoirs. The stress difference of 5MPa and the approach Angle of 75° are the key factors affecting the interaction between hydraulic fractures and natural fractures. As the bedding number increases, the borehole pressure increases and the total number of fractures' propagation decreases. The results provide a theoretical basis for further understanding of fractures' propagation in deep shale reservoirs, and have important guiding significance for optimization and improvement of fracture complexity in the subsequent construction. [ABSTRACT FROM AUTHOR]

Detecting gear rim fatigue cracks using vibration signal analysis is often a challenging task, which typically requires a series of signal processing steps to detect and enhance fault features. This task becomes even harder in helicopter planetary gearboxes due to the complex interactions between different gear sets and the presence of vibration from sources other than the planetary gear set. In this paper, we propose an effectual processing algorithm to isolate and enhance rim crack features and to trend crack growth in planet gears. The algorithm is based on using cepstrum editing (or liftering) of the hunting-tooth synchronous averaged signals (angular domain) to extract harmonics and sidebands of the planet gears and low-pass filtering and minimum entropy deconvolution (MED) to enhance extracted fault features. The algorithm has been successfully applied to a vibration dataset collected from a planet gear rim crack propagation test undertaken in the Helicopter Transmission Test Facility (HTTF) at DSTG Melbourne. In this test, a seeded notch generated by an electric discharge machine (EDM) was used to initiate a fatigue crack that propagated through the gear rim body over 94 load cycles. The proposed algorithm demonstrated a successful isolation of incipient fault features and provided a reliable trending capability to monitor crack progression. Results of a comparative analysis showed that the proposed algorithm outperformed the traditional signal processing approach. [ABSTRACT FROM AUTHOR]

This paper describes a new arc-length control procedure for tracing the equilibrium curve of brittle fracture problems modeled with a phase field approach. The balance equations of this model are solved with a staggered strategy. The control equation of the arc-length procedure determines the displacement increments during the mechanical stage. The arc-length parameter is interpreted as imposing a given increment of the driving force appearing into the micro-force balance equation. The innovative technique consisting of applying the control equation to the displacement degrees of freedoms (DOFs) of the mechanical stage offers an enhancement over earlier arc-length strategies that focused on controlling the damage DOFs in the micro-force balance equation stage. This advancement enables the phase field approach to handle and simulate a broader range of problems, as demonstrated in this paper. The arc-length parameter is stepwise adjusted to yield a pre-established maximum damage increment in each staggered scheme step. As a consequence, the crack tip advance can be strictly controlled in every step holding bounded the pseudo-time integration error, even using an explicit staggered strategy. This procedure entails moderate computational costs for tracing the complete equilibrium curve, including unstable responses, limit points, snap-backs, etc., with the subsidiary advantage that lack of convergence has never been detected in the tests presented in this paper. Additionally, line search techniques have not been necessary. The proposed arc-length procedure is easily implemented in standard finite element codes, and according to our numerical experiments, it does not significantly increase the computational burden of the original explicit staggered strategy. [ABSTRACT FROM AUTHOR]