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Using the example of assessing the technical condition of the trunnions of drying cylinders in cardboard machines (CBM), the question of the possibility of ranking cyclically loaded elements of dynamic equipment according to the degree of damage to their material by fatigue cracks using acoustic emission (AE) measurements is discussed. As a result of special laboratory studies with varying loads in the cycle of loading and lubrication of crack edges, the features of AE due to the friction of crack edges and plastic deformation at the crack tip during its growth in a viscous material have been established. It is shown that during cyclic loading of the material, AE signals from the friction of its banks are detected more steadily than AE signals due to a crack jump with an increase in its length, and that tracking the former ensures the detection of fatigue damage in the material even under loading conditions insufficient for crack growth. Based on the data obtained, three AE signs of the presence of fatigue damage in the material of the elements of dynamic equipment were developed under the condition of cyclic activation of the movement of crack edges. As a result of industrial testing of the developed AE signs, their operability was confirmed, their boundary values on the operating trunnions of CBM drying cylinders were clarified, and a method for ranking trunnions by the level of damage due to fatigue cracks was proposed. By comparing the results of AE measurements with ultrasound testing, the reliability of the proposed approach was evaluated and showed the probability of detecting a fatigue crack in the trunnions of CBM drying cylinders at the level of 71%, with the probability of skipping and false rejection of the product of 12 and 17%, respectively. The developed technique is also transferable to other massive dynamic equipment after clarifying the boundary values of AE signs of fatigue damage in the material on this type of facilities. [ABSTRACT FROM AUTHOR]

Paper‐based friction materials with phenolic resin as the matrix are prone to thermal damage under harsh working conditions easily leading to materials failure. To satisfy the requirements of high speed and heavy load service situations, paper‐based friction materials with different polyimide resin content were prepared by wet forming technology to reveal the effect of polyimide resin on the properties of composites. And a paper‐based composite with phenolic resin was used for comparison. Results show that compared with the phenolic composite, tensile strength, and shear strength of the polyimide composite were increased by 50.5% and 36.4%, respectively. Due to the strong hydrogen bond in the imide ring of polyimide, the temperature of the polyimide composite at 2% weight loss was 292.7°C, which was 106.3°C higher than that of the phenolic composite. Moreover, the wear rate was reduced by 30.3% because the friction transfer film was produced during friction. To sum up, polyimide resin has the potential to replace phenolic resin under the condition of high speed and heavy load. Besides, the composite with polyimide resin content of 40.0 wt% demonstrated the best wear resistance and considerable strength attributed to the best interface combination. This research lays a theoretical foundation for the application of polyimide resin to paper‐based friction materials. [ABSTRACT FROM AUTHOR]

Biofiber is an extensive and renewable raw material, whose products meet the demands of constructing an environmental-friendly and resource-favorable society. As a typical biofiber assembly, paper inherits its characteristics and may lose its mechanical properties after prolonged contact with water, leading to a material failure. Here, we report an environment friendly waterproof composite by a simple surface treatment. This composite is creatively prepared via a formation of rough microstructures for ink micro-aggregates on the ink-brushed paper, of which this bio-inspired structure is beneficial to hydrophobic properties and light capture capability. Specifically, it possesses excellent hydrophobicity with a high contact angle over 150° and photothermal performance with a solar evaporation rate of 1.324 kg m−2 h−1 under 100 mW/cm2. In addition, it reveals superior waterproof and deicing performance, decreasing the icing adhesion time to 63 s under 100 mW/cm2. Additional advantages include durability, designability, and large-area production. In view of these excellent properties, this waterproof photothermal material holds a bright prospect in the fields of solar evaporation, deicing device, packaging, and so forth. [ABSTRACT FROM AUTHOR]

Graphene-based nanomaterials have found significant interest in the development of embedded sensors to monitor the fracture behavior in composite structures. In this work, in-situ crack propagation and fracture behavior within a glass fiber reinforced polymer composite (GFRP) was monitored using embedded reduced graphene oxide (rGO) coated fabrics and highly conductive graphene nanoplatelet (GnP) paper. All laminates were fabricated using the resin infusion process. The piezoresistive performance of both types of laminates was evaluated using in-plane and out-of-plane mechanical tests. The effect of GnP paper thickness (50/150/240 µm) and loading rate was also evaluated using tensile and Mode-I fracture loadings. Piezoresistivity of the sensors was reduced by increasing loading rate during tensile tests. All laminates with GnP paper exhibited poor mechanical performance under tensile loading. The laminates with 50 µm GnP paper showed highest sensitivity under Mode-I loading. In comparison to pristine laminates, the interlaminar fracture toughness of laminates with 50 µm GnP paper was reduced by 70%. Furthermore, laminates with rGO coated fabrics demonstrated stable crack propagation under Mode-I loading as compared to GnP based laminates. The fractured surfaces were analyzed using scanning electron microscopy to investigate the underlying fracture mechanisms of the sensors in the composite laminates. [Display omitted] • Composites with embedded GnP paper and rGO coated fabric sensors were manufactured. • Sensor based on thin GnP paper was found more sensitive than the thick GnP sensors. • Loading rate and thickness effects on the sensing behavior were characterized. • Increasing the load rate during in-plane tensile tests decreases the sensitivity. • rGO based sensor exhibited high mechanical properties than the GnP based sensors. [ABSTRACT FROM AUTHOR]

The mechanical properties of wood fiber-based, commercial papers and metal foils are qualitatively similar, and their plane stress, Mode I crack growth resistances have not been reliably correlated with single-valued fracture mechanics parameters for centimeter-scale specimens. Experimentally-measured crack tip strain fields of Mode I cracks growing in commercial paper were used to define a three-stage, steady-state crack growth mechanism. Immediately upon loading, the net sections ahead of the cracks yielded. As the cracks began to grow, well-defined zones of (incremental) active plasticity (ZAPs) formed within the yielded ligaments. Cracks transitioned to steady-state growth with an average characteristic stress, σ c , of 20.9 MPa. In contrast to metallic foils, the characteristic stress in steady-state cracks in paper was offset by 8.3 MPa due to a 1.9 mm fiber bridging zone that scaled with the average fiber agglomerate (floc) size. The fiber network structure also induced a large, reversed steady-state zone in the crack wakes. While reversed ZAPS were previously predicted by numerical models of plane strain Mode I and III cracks under small-scale yielding conditions, they were never observed experimentally and were neglected. The types and evolution of the cumulative and incremental plastic zones in paper defined appropriate paths for steady-state J -integral calculations. [ABSTRACT FROM AUTHOR]

B. Palmieri et al. in "Investigation on Stress Relaxation of Discontinuous Recycled/Repurposed Carbon Fiber Composites" investigate the thermo-mechanical and viscoelastic behavior of composites made at different recycled carbon fiber (rCF) content. These are similar in structure to carbon fiber composites, where the matrix features dielectric characteristics, making the structure capable of storing electric energy. This special issue focus is dedicated to the fourth edition of the "International Symposium on Dynamic Response and Failure of Composite Materials, Draf2022" held in Ischia, Naples, from June 21-24, 2022. [Extracted from the article]

In supporting the stable operation of high-penetration renewable energy grids, flywheel energy storage systems undergo frequent charge–discharge cycles, resulting in significant stress fluctuations in the rotor core. This paper investigates the fatigue life of flywheel energy storage rotors fabricated from 30Cr2Ni4MoV alloy steel, attempting to elucidate the material's mechanical properties, crack propagation behavior, and impact of internal defects on fatigue life. Tensile tests reveal that the material exhibited high yield (992 MPa) and tensile strengths (1130 MPa). The Paris formula is used to model crack growth rates, ending in good agreement with the experimental data. Fatigue tests at various stress conditions highlight the material's significant variability in fatigue life and emphasize the need for reliable design approaches. This paper also demonstrates that internal defect size and location critically affect fatigue life, calling for improvements in forging inspection standards. Overall, the present study provides a comprehensive analysis of 30Cr2Ni4MoV steel's suitability for flywheel rotors, balancing safety, and operational efficiency. [ABSTRACT FROM AUTHOR]

In this paper, an intelligent damage detection approach is proposed for steel-concrete composite beams based on deep learning and wavelet analysis. To demonstrate the feasibility of this approach, first, following the guidelines provided by relevant standards, steel-concrete composite beams are designed, and six different damage incidents are established. Second, a steel ball is used for free-fall excitation on the surface of the steel-concrete composite beams and a low-temperature-sensitive quasi-distributed long-gauge fiber Bragg grating (FBG) strain sensor is used to obtain the strain signals of the steel-concrete composite beams with different damage types. To reduce the effect of noise on the strain signals, several denoising techniques are applied to process the collected strain signals. Finally, to intelligently identify the strain signals of combined beams with different damage types, multiple deep learning models are constructed to train and to predict strain signals as denoised and not denoised, allowing for damage classification and localization in steel-concrete composite beams. In this experimental context, residual network-50 (ResNet-50) achieved the highest average accuracy compared to that of the other deep learning models. The average accuracy of the un-denoised and denoised signals is 96.73% and 97.91%, respectively, and wavelet denoising improved the prediction accuracy of ResNet-50 by 1.18%. The strain–time domain signals collected by sensors located farther from the damage zone also contain information about the damage to the composite beam. The deep learning models effectively extract damage features. The results of this experiment demonstrate that the approach used in this paper enhances the intelligence of structural damage identification. [ABSTRACT FROM AUTHOR]

In this paper, hip implants made of Ti-6Al-4V titanium alloy are analyzed numerically using Extended Finite Element Method XFEM. The combined effect of corrosion and fatigue was considered here since this is a common cause of failure of hip implants. Experimental testing of Ti-6Al-4V alloy was performed to determine its mechanical properties under different working environments, including normal, salty, and humid conditions. The integrity and life of the hip implant were assessed using the Linear Elastic Fracture Mechanics (LEFM) approach. For this purpose, the conditional fracture toughness Kq using CT specimens from all three groups (normal, humid, salty conditions) were determined. This provided insight into how different aggressive environments affect the behavior of Ti-6Al-4V alloy; i.e., how much its resistance to crack growth would degrade depending on conditions corresponding to the real exploitation of hip implants. Next, analytical and XFEM analyses of fatigue behavior in terms of the number of cycles were performed for all three groups, and the obtained results showed good agreement, confirming the validity of the integrity assessment approach shown in this work, which also represented a novel approach since fatigue and corrosion effects were investigated simultaneously. [ABSTRACT FROM AUTHOR]

Coal mining under the Quaternary thick loose layer affects key strata breakage, Bed-separations development, ground subsidence, and other studies. This paper presents a method for solving the deflection of a large-deflection inclined thin plate under a thick loose-layer cover with additional lateral loads and midplane forces. The methods presented are based on the principle of large-deflection of thin-plate, energy method, and fracture mechanics theory. The 7225 work face in Anhui Province, China, was studied. Combined with the large-deflection inclined thin plate model, the initial breakage distance within the main roof plate was calculated to be 33 m with the initial breakage angle of 61.2°, and the period breakage distance was calculated to be 21 m with the period breakage angle of 55.4°. The distribution range of "Vertical Three Zones" from 7225 working face to the ground, including the height of the caved zone is 38.07 m, the height of the fractured zone is 41.13 m, and the height of the curved zone with the thick loose layer removed is 187.56 m. During the dynamic development of the principal key strata (PKS), the deflection value develops from 0 mm to 2714 mm with 7225 working face mining, and the maximum value of the spatial volume is 56,485 m3, which is verified by Three-dimensional Discrete Element Code (3DEC) numerical simulation. The dynamic development of Bed-separation within the overlying strata, with a maximum development height of 545.2 mm and a maximum volume of 11,228.1 m3 of the Bed-separation cavity. The dynamic development of the Bed-separation height and the cavity under different mining length and width conditions of the working face are also discussed. The large-deflection inclined thin plate model proposed in this paper effectively explores the dynamic deflection and fragmentation law of the overlying strata induced by the inclined working face of Longwall mining and provides a theoretical basis and computational model for quantitatively evaluating the dynamic development of the Bed-separation cavity. [ABSTRACT FROM AUTHOR]

This paper forms part of an ongoing investigation into the tools required in linear elastic fracture mechanics (LEFM) for evaluating the durability of components designed for limited life replacement. In this study, we demonstrate that the USAF 'Characteristic K' method, when combined with the Hartman–Schijve adaptation of the NASGRO crack growth formula, can predict the impact of underloads on the propagation of small cracks in aluminum alloy AA7050-T7451 with reasonable accuracy. The published da/dN versus ΔK small crack growth curves associated with five specific underload spectra are examined. It is found that, in each case, there is reasonably good agreement between the predicted and the measured curves. To the best of the author's knowledge, this paper is the first to highlight the ability of the USAF Characteristic K approach, when coupled with the Hartman–Schijve equation, to reasonably accurately predict the growth of small cracks subjected to a range of underload spectra. [ABSTRACT FROM AUTHOR]

The design of cover landfill requires an optimum thickness of the compacted fine soil layer with small permeability. In general, the objective is to reduce the thickness of the landfill cover. However, for a thin layer, and under natural evaporation, denser crack network growths occur during the desiccation by drying. Cracks change the geometrical properties during the drying and wetting cycles and significantly compromise the role of the cover layer, by inducing an infiltration water flow and gas migration. An important differential flexure deformation occurs. The landfill cover, where stiffness and tensile and shear strengths were reduced is being progressively damaged. Thus, this paper aims 1) to quantify the flexural deformation and 2) to provide a methodology and a guideline for studying the integrity of a cover landfill. So, a mechanical model is proposed and implemented in Code Bright software. The methodology starts from the calibration and the validation of the mechanical model based on 1) four-point flexural beam tests and 2) on existing published results. A physical prototype was employed to demonstrate the flexure deformation, and the crack development. Moreover, short natural fibers were mixed and embedded in the soil to make the soil reinforcement and delay crack propagation. In addition to the experimental investigation, mathematical constitutive equations were proposed, in which the contribution of short fibers in terms of increase of tensile strength was introduced. Finally, a simple case study was considered to demonstrate the role of the fiber-soil composite on flexural deformation and tensile stress distribution across the cover layer. An analysis of the numerical results was conducted to support the use of short fibers as reinforcement, which is an environmentally friendly and sustainable solution. [ABSTRACT FROM AUTHOR]

This paper investigates the influence of fidelity on the capability of digital twins (DT) to detect two common material extrusion (MEX) failures: extrusion error and layer shift. Monitoring of the failures is first explored using an image-based DT to provide a benchmark. The fidelity-performance analysis of DTs with significantly different levels of fidelity ranging from low to high fidelity is then studied and presented. In this paper, digital twin fidelity is defined as the expression of the necessary levels of accuracy in different attributes of the twin. The basis for the DTs employed in this study is image comparison. Consequently, six attributes are selected to describe the fidelity, including image resolution, mesh number, shadow method, illumination model, light source and state threshold. The effects of varying the fidelity of the six attributes on the capability to detect printing failures are then analysed and discussed. It is shown that, for the two failure cases considered, lower-fidelity DTs can deliver comparable capability to what are considered DTs with high or ultra-high fidelity. In addition, benefits in terms of configuration cost, data storage, simulation time, and detection time are demonstrated. [ABSTRACT FROM AUTHOR]

This paper presents the results of an extensive investigation into the durability of cold spray repairs to corrosion damage in AA7075-T7351 aluminium alloy specimens where, prior to powder deposition, the surface preparation involved grit blasting. In this context, it is shown that the growth of small naturally occurring cracks in cold spray repairs to simulated corrosion damage can be accurately computed using the Hartman–Schijve crack growth equation in a fashion that is consistent with the requirements delineated in USAF Structures Bulletin EZ-SB-19-01, MIL-STD-1530D, and the US Joint Services Structural Guidelines JSSG2006. The relatively large variation in the da/dN versus ΔK curves associated with low values of da/dN highlights the fact that, before any durability assessment of a cold spray repair to an operational airframe is attempted, it is first necessary to perform a sufficient number of tests so that the worst-case small crack growth curve needed to perform the mandated airworthiness certification analysis can be determined. [ABSTRACT FROM AUTHOR]

Copyright of Structural Integrity & Life / Integritet i vek Konstrukcija is the property of University of Belgrade, Faculty of Mechanical Engineering 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.)

Fault slip will directly affect the technical performance of solid expandable tubular (SET). However, there are few researches on the mechanical behavior of shear failure when SET crosses the slip fault. In response to the above problems, this paper builds a three-dimensional dynamic tube-rock system numerical model that considers nonlinear frictional contact and fault slip based on the SET material constitutive model, Coulomb friction, and shale layer rock. The purpose is to reveal the influence of fault slip on the mechanical behavior of SET and to analyze the risk point of SET failure. The results of the study show that as the amount of fault slip increases, the maximum value of the Mises stress of SET appears in the direction perpendicular to the amount of fault slip (90°). With the increase in the number of faults, the shear stress distribution on the cross section hardly changes, and the shear stress distribution on the fault plane presents a "8" shape. When the included angle is 60°, the shear stress on the shear plane is the largest and the shear distribution is the most uneven. The research results of this paper provide a theoretical basis for the slip shear of SET. [ABSTRACT FROM AUTHOR]

It is crucial to propose an accurate fatigue life prediction method to ensure the structural integrity and operational reliability of engineering components in real-world service conditions. This paper considers how the uncertainty of fatigue failure in composite materials under variable amplitude loading conditions affects material fatigue life. It proposes an improved method to predict the residual fatigue life of a composite material by converting the number of loading cycles under different loading sequences. Firstly, the method suggests that the number of loading cycles for the same composite material, under variable amplitude loading conditions and at different stress levels, conforms to the assumptions of the Weibull cumulative distribution and the principle of probabilistic consistency. Using this assumption, a transformation model is established for the number of cyclic loading cycles in composite materials under variable amplitude loading conditions. Specifically, the model can convert the number of loading cycles under various loading sequences into an equivalent number of cycles under a uniform loading condition. Next, the residual fatigue life of the specimen at the final stress level was determined by analyzing fatigue test data under variable amplitude loading conditions. Finally, the proposed method is validated and compared using fatigue test data from the literature, which includes composites tested under two and three variable amplitude loading conditions. Validation results indicate that the proposed method for predicting residual fatigue life offers more accurate predictions, with all predicted life factors falling within ± 1.2 life factors. Additionally, compared to other existing models for predicting residual life, the proposed method effectively captures the impact of randomness and uncertainty in the fatigue failure process of composite materials using probabilistic statistical theory. This offers a more valuable reference for predicting fatigue life under variable amplitude load. [ABSTRACT FROM AUTHOR]

This document is a reference list for a research paper on fracture mechanics and structural integrity. The paper explores the effect of element size on fracture propagation stress using energy criteria. The research was funded by the Ministry of Higher Education Malaysia. The document also includes a Python code for an artificial neural network algorithm used in the research. The reference list contains other research papers on fracture mechanics, machine learning, and structural integrity. [Extracted from the article]

It is currently a challenge to accurately predict the deformation and fracture behavior of metal parts in automobile crashes. Many studies have shown that the deformation and fracture behavior of materials are significantly affected by the stress state during automobile crashes with complex stress state characteristics. In order to further promote the application of die-cast magnesium alloys in automobiles, it is particularly important to study the material deformation and fracture behavior of die-cast magnesium alloys. In this paper, the mechanical properties of the AM60B die-cast magnesium alloy sheet under four stress states (shear, tension, R10 notch tension, and cupping) were designed and tested. Based on the von Mises isotropic constitutive model and Swift weighted Hockett–Sherby hardening model, the plastic constitutive model of die-cast magnesium alloy was established. Based on the plastic model and the fracture model (JC, MMC, and DIEM) considering the influence of three stress states, the deformation and fracture behavior of the AM60B die-cast magnesium alloy front-end members in three-point bending were predicted by experiments and finite element simulation. The experimental results show that the deformation mode and loading–displacement curve trend of the AM60B die-cast magnesium alloy front members are the same, the crack initiation point and crack initiation time are the same, and the crack shape is similar. The results show that the complex stress state constitutive model parameters and the DIEM fracture model obtained in this paper can accurately predict the deformation and fracture failure behavior of the AM60B die-cast magnesium alloy sheet. [ABSTRACT FROM AUTHOR]

This paper reviews works on the dynamic analysis of flexible and rigid pavements under moving vehicles on the basis of continuum-based plane strain models and linear theories. The purpose of this review is to provide information about the existing works on the subject, critically discuss them and make suggestions for further research. The reviewed papers are presented on the basis of the various models for pavement-vehicle systems and the various methods for dynamically analyzing these systems. Flexible pavements are modeled by a homogeneous or layered half-plane with isotropic or anisotropic and linear elastic, viscoelastic or poroelastic material behavior. Rigid pavements are modeled by a beam or plate on a homogeneous or layered half-plane with material properties like the ones for flexible pavements. The vehicles are modeled as concentrated or distributed over a finite area loads moving with constant or time dependent speed. The above pavement-vehicle models are dynamically analyzed by analytical, analytical/numerical or purely numerical methods working in the time or frequency domain. Representative examples are presented to illustrate the models and methods of analysis, demonstrate their merits and assess the effects of the various parameters on pavement response. The paper closes with conclusions and suggestions for further research in the area. The significance of this research effort has to do with the presentation of the existing literature on the subject in a critical and easy to understand way with the aid of representative examples and the identification of new research areas. [ABSTRACT FROM AUTHOR]

The high-cycle bending fatigue experiment is one of the most important necessary steps in guiding the crankshaft manufacturing process, especially for high-power engines. In this paper, an accelerated method was proposed to shorten the time period of this experiment. First, the loading period was quickened through the prediction of the residual fatigue life based on the unscented Kalman filtering algorithm approach and the crack growth speed. Then, the accuracy of the predictions was improved obviously based on the modified training section based on the theory of fracture mechanics. Finally, the fatigue limit load analysis result was proposed based on the predicted fatigue life and the modified SAFL (statistical analysis for the fatigue limit) method. The main conclusion proposed from this paper is that compared with the conventional training sections, the modified training sections based on the theory of fracture mechanics can obviously improve the accuracy of the remaining fatigue life prediction results, which makes this approach more suitable for the application. In addition, compared with the system's inherent natural frequency, the fatigue crack can save the experiment time more effectively and thus is superior to the former factor as the failure criterion parameter. [ABSTRACT FROM AUTHOR]

In modern engineering application, enough high cycle bending fatigue strength is the necessary factor to provide the basic safety security for the application of the crankshaft in automobile engines (both diesel and gasoline types). At present, this parameter is usually obtained through the standard bending fatigue experiment process, which is time consuming and expensive. In this paper, a new accelerated crankshaft bending fatigue experiment was proposed step by step. First the loading procedure was quickened through the prediction of the residual fatigue life based on the UKF (unscented Kalman filtering algorithm). Then the accuracy of the predictions was improved based on the modified sampling range and the theory of fracture mechanics. Finally the statistical analysis method of the fatigue limit load was performed based on the above predictions. The main conclusion of this paper is that the proposed accelerated bending fatigue experiment can save more than 30% of the bending fatigue experiment period and provide nearly the same fatigue limit load analysis result. In addition, compared with the particle filtering algorithm method, the modified UKF can provide much higher accuracy in predicting the residual bending fatigue life of the crankshaft, which makes this method more superior to be applied in actual engineering. [ABSTRACT FROM AUTHOR]

Ultrasonic-assisted inner diameter machining is a slicing method for hard and brittle materials. During this process, the sawing force is the main factor affecting the workpiece surface quality and tool life. Therefore, based on indentation fracture mechanics, a theoretical model of the cutting force of an ultrasound-assisted inner diameter saw is established in this paper for surface quality improvement. The cutting experiment was carried out with alumina ceramics (99%) as an exemplar of hard and brittle material. A six-axis force sensor was used to measure the sawing force in the experiment. The correctness of the theoretical model was verified by comparing the theoretical modeling with the actual cutting force, and the influence of machining parameters on the normal sawing force was evaluated. The experimental results showed that the ultrasonic-assisted cutting force model based on the six-axis force sensor proposed in this paper was more accurate. Compared with the regular tetrahedral abrasive model, the mean value and variance of the proposed model's force prediction error were reduced by 5.08% and 2.56%. Furthermore, by using the proposed model, the sawing processing parameters could be updated to improve the slice surface quality from a roughness Sa value of 1.534 µm to 1.129 µm. The proposed model provides guidance for the selection of process parameters and can improve processing efficiency and quality in subsequent real-world production. [ABSTRACT FROM AUTHOR]

Mixed mode fracture is a widely studied topic, while the coupling effects of mixed mode cracking are unclear. In this paper, elastic fracture behaviors and the coupling effects of the mixed mode cracks are studied in detail based on the finite element method, experimental study and linear elastic fracture mechanics. Results show that there always exist II-III coupling effects at the crack tips of mixed mode cracks, which have many effects on the crack tip field and crack propagation behavior. It is found that a mode II component at the tip of a mixed mode crack is the main reason for crack deflection, while the mode III components show no effect. For any mixed mode crack, mode II components at the crack tip can be divided as that by mode II loading which causes plane crack propagation, and by the coupling effect which causes spatial crack propagation. On this basis, a new fracture criterion suitable for any mixed mode crack is proposed, combined with the coupling effect and the linear elastic superposition principle. The research in this paper provides a solution to the problem of an II-III coupling effect in mixed mode fracture research and further promotes the development of fracture mechanics. [ABSTRACT FROM AUTHOR]

The primary focus of this paper is to investigate the application of ANSYS Workbench 19.2 software's advanced feature, known as Separating Morphing and Adaptive Remeshing Technology (SMART), in simulating the growth of cracks within structures that incorporate holes. Holes are strategically utilized as crack arrestors in engineering structures to prevent catastrophic failures. This technique redistributes stress concentrations and alters crack propagation paths, enhancing structural integrity and preventing crack propagation. This paper explores the concept of using holes as crack arrestors, highlighting their significance in increasing structural resilience and mitigating the risks associated with crack propagation. The crack growth path is estimated by applying the maximum circumferential stress criterion, while the calculation of the associated stress intensity factors is performed by applying the interaction integral technique. To analyze the impact of holes on the crack growth path and evaluate their effectiveness as crack arrestors, additional specimens with identical external dimensions but without any internal holes were tested. This comparison was conducted to provide a basis for assessing the role of holes in altering crack propagation behavior and their potential as effective crack arrestors. The results of this study demonstrated that the presence of a hole had a significant influence on the crack growth behavior. The crack was observed to be attracted towards the hole, leading to a deviation in its trajectory either towards the hole or deflecting around it. Conversely, in the absence of a hole, the crack propagated without any alteration in its path. To validate these findings, the computed crack growth paths and associated stress intensity factors were compared with experimental and numerical data available in the open literature. The remarkable consistency between the computational study results for crack growth path, stress intensity factors, and von Mises stress distribution, and the corresponding experimental and numerical data, is a testament to the accuracy and reliability of the computational simulations. [ABSTRACT FROM AUTHOR]

Composite laminates have become increasingly popular in industries like aerospace and shipbuilding. In practical applications, the creation of notches in composite laminates is often necessary to enable assembly and modifications. This rise in the use of notched composite laminates highlights the need for reliable methods to predict potential failures in these components. With these predictions, the safety and reliability of composite structures can be ensured by preventing catastrophic failures. The present paper investigates the use of the Virtual Isotropic Material Concept (VIMC) combined with the Finite Fracture Mechanics (FFM) criterion to predict the Last Ply Failure (LPF) load in keyhole notched composite laminates and under mode I loading conditions. Experimental tests were conducted to measure the LPF load of E-glass/Epoxy keyhole notched specimens, and the results were compared with the predicted results using the VIMC-FFM criterion. The paper also derives an expression for the Stress Intensity Factor (SIF) function for a crack that emanates from the keyhole notch tip under mode I loading conditions. The derived equation matches very well with numerical data and have a mean absolute error about 2% in the studied domain. The study shows that the VIMC-FFM criterion predicts the LPF load of keyhole notched composite laminates with acceptable accuracy and in a simple and low-cost manner. [ABSTRACT FROM AUTHOR]

Before a new type of engine is introduced into civil aviation, it must comply with various safety regulations. These regulations include the analysis of secondary damage caused by the re-ingestion of a tooth fragment. The purpose is to prevent crack propagation through the gear rim, which would lead to catastrophic failure. In this context, identification of the initial crack location is crucial to determine the crack propagation path. Therefore, this paper presents a technique to determine and validate a constitutive material model and fracture locus for case-hardened spur gears. As the modelling of the surface-hardened layer is computationally intensive, it is necessary to homogenise the model. This paper comprehensively reviews and discusses the associated effects and errors. To determine the plastic behaviour of the case-hardened external gear (30CrNiMo8) and the nitrided internal gear (35CrAlNi7-10), the widely acknowledged Johnson–Cook material model is implemented using compression and Vickers indenter tests to define the necessary parameters. The fracture locus implementation is also based on the Johnson–Cook method and an axial shift of the fracture locus based on the hardness profile of the spur gears is determined by quasi-static pulsator tests. For validation, a project-specific gearbox test rig is used, enabling consistent ingestion of defined fragments. In addition, to check the likelihood of a tooth flank crack and to validate the results, a simplified ingestion experiment is performed. [ABSTRACT FROM AUTHOR]

This paper studies mechanical properties and energy damage evolution of fiber-reinforced cemented sulfur tailings (CSTB) backfill. The effects of fiber length and fiber content on the stress, toughness and failure properties of the CSTB were systematically revealed. In addition, the energy index evolution law was studied, and the energy damage evolution mechanism of CSTB was revealed. The results show that the deformation failure of fiber-reinforced CSTB mainly goes through four stages: initial crack compaction, linear elastic deformation, yield failure and post-peak failure. The peak stress and residual stress of the CSTB firstly increase and then decrease with the increase of fiber content and the addition of fiber can promote the change from brittle failure to ductile failure of the CSTB. Adding appropriate amount of fiber can improve the toughness of CSTB, and the influence degree of fiber length on the toughness index of CSTB is 6mm>12mm>3mm. The total strain energy increases linearly along the variation of fiber content, while the elastic strain energy and dissipated energy increase exponentially at the peak stress point. In the process of CSTB deformation and failure, "gentle—linear growth—slow growth—rapid decline" is for elastic strain energy, while "gentle—slow growth—rapid growth—linear growth" is for dissipation energy. The damage and failure of CSTB mainly experienced four stages: initial damage, slow growth of damage, accelerated damage and damage failure, and the damage evolution curve also showed the changing characteristics of "gentle—slow growth—rapid growth—linear growth". The CSTB without added fiber showed obvious "Y-type" and "linear-type" shear failure characteristics and the phenomenon of shear cracks penetrating the backfill appeared. No big shear crack occur when it is damaged, showing that the fiber addition restrain the crack growth and improve the overall crack resistance of the CSTB. Hydration products are obviously distributed on the surface of the fiber, which indicates that the fiber will be evenly dispersed in the CSTB and form a certain bonding force with the cement-tailings matrix, thus improving the overall mechanical properties of the CSTB. [ABSTRACT FROM AUTHOR]

This paper describes a numerical algorithm for solving the classic problem of a plane strain (KGD) fracture propagating in an impermeable elastic medium with zero toughness. The method, which takes advantage of the self-similar nature of the solution, combines a domain-based scheme to solve the elasticity equations and a finite volume method to solve the nonlinear lubrication equation. This work represents a first step towards developing a model able to account for pore pressure diffusion in the medium and corresponding poroelastic effects, noting that these processes are more efficiently solved using a domain-based rather than a boundary integral method. To enhance the efficiency and accuracy of the numerical scheme, the far-field crack asymptotics is embedded in the discretized elastic relationship between the fluid pressure and the crack opening, while the coupled fluid-solid tip asymptote is enforced in a weak form when solving the nonlinear lubrication equation. The proposed technique yields results that closely match the analytical solution, even with a coarse mesh. This approach offers potential for addressing more complex hydraulic fracturing problems in the future. [ABSTRACT FROM AUTHOR]

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]

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A better physical understanding of mesoscale and microscale mechanisms behind deformation and failure of paperboard material is important to optimize industrial packaging converting processes and decrease waste. In this study, these mechanisms were investigated using synchrotron X‐ray tomography during in situ continuous uniaxial tensile loading. High spatial and temporal data resolution enabled quantification of rapid changes in the material occurring before, during and after material failure. The evolution of 3D strain fields, fibre orientations and sample thickness showed that deformation and failure mechanisms differ significantly between samples tested in machine direction (MD), cross direction (CD) and 45° from the loading direction. In 45° and CD, gradual failure processes could be followed across several load steps. Immediately after failure, the in‐plane fracture region was significantly larger in both 45° and CD compared to MD. Both fracture characteristics and strain field distributions differed between the three material directions. Significant fibre reorientation was an active deformation mechanism in 45° already from the beginning of the loading, also present in CD after peak load but absent in MD. The MD‐dependent mechanisms interpreted and quantified at the scale of the fibre network in this study can help guide model development and likely have wider applicability to other paper‐based materials. [ABSTRACT FROM AUTHOR]

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, 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]

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 this paper, we present a robust exploration of the Gologanu–Leblond–Devaux (GLD) model, an advanced iteration of the Gurson model, designed to predict ductile fractures in porous metals. Going beyond the limits of the original Gurson model, the GLD model accounts for cavity shape effects and non-local strain localization, marking a significant leap in fracture mechanics. We also present a comprehensive exposition of the GLD model and its non-local extension, establishing their compatibility with the concept of GSMs. Notably, we emphasize the uniqueness of solutions in the numerical implementation, underlining the imperative need for a meticulously devised mixed implicit/explicit algorithm. Furthermore, we set out to validate the GLD model through rigorous comparisons of our numerical simulations with experimental data. Employing a damage delocalization approach rooted in the natural logarithm of porosity, our study provides compelling evidence of the model's performance. This approach mitigates issues observed with the original porosity rate, preventing excessive smoothing of porosity and maintaining the fidelity of stress–strain curves. In addition, we gave a profound theoretical elucidation of this phenomenon via Fourier's analysis of porosity rate. Through this work, we not only enhance our understanding of ductile fracture behavior but also establish a robust numerical framework for its predictive modeling. The GLD model emerges as a powerful tool for the accurate analysis and prediction of fracture phenomena in porous materials, further advancing the field of materials science and engineering. [ABSTRACT FROM AUTHOR]

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]

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]