Search

Purpose: The paper's goal is to examine and illustrate the useful uses of submodeling in finite element modeling for topology optimization and stress analysis. The goal of the study is to demonstrate how submodeling – more especially, a 1D approach – can reliably and effectively produce ideal solutions for challenging structural issues. The paper aims to demonstrate the usefulness of submodeling in obtaining converged solutions for stress analysis and optimized geometry for improved fatigue life by studying a cantilever beam case and using beam formulations. In order to guarantee the precision and dependability of the optimization process, the developed approach will also be validated through experimental testing, such as 3-point bending tests and 3D printing. Using 3D finite element models, the 1D submodeling approach is further validated in the final step, showing a strong correlation with experimental data for deflection calculations. Design/methodology/approach: The authors conducted a literature review to understand the existing research on submodeling and its practical applications in finite element modeling. They selected a cantilever beam case as a test subject to demonstrate stress analysis and topology optimization through submodeling. They developed a 1D submodeling approach to streamline the optimization process and ensure result validity. The authors utilized beam formulations to optimize and validate the outcomes of the submodeling approach. They 3D-printed the optimized models and subjected them to a 3-point bending test to confirm the accuracy of the developed approach. They employed 3D finite element models for submodeling to validate the 1D approach, focusing on specific finite elements for deflection calculations and analyzed the results to demonstrate a strong correlation between the theoretical models and experimental data, showcasing the effectiveness of the submodeling methodology in achieving optimal solutions efficiently and accurately. Findings: The findings of the paper are as follows: 1. The use of submodeling, specifically a 1D submodeling approach, proved to be effective in achieving optimal solutions more efficiently and accurately in finite element modeling. 2. The study conducted on a cantilever beam case demonstrated successful stress analysis and topology optimization through submodeling, resulting in optimized geometry for enhanced fatigue life. 3. Beam formulations were utilized to optimize and validate the outcomes of the submodeling approach, leading to the successful 3D printing and testing of the optimized models through a 3-point bending test. 4. Experimental results confirmed the accuracy and validity of the developed submodeling approach in streamlining the optimization process. 5. The use of 3D finite element models for submodeling further validated the 1D approach, with specific finite elements showing a strong correlation with experimental data in deflection calculations. Overall, the findings highlight the effectiveness of submodeling techniques in achieving optimal solutions and validating results in finite element modeling, stress analysis and optimization processes. Originality/value: The originality and value of the paper lie in its innovative approach to utilizing submodeling techniques in finite element modeling for structural analysis and optimization. By focusing on the reduction of finite element models and the creation of smaller, more manageable models through submodeling, the paper offers designers a more efficient and accurate way to achieve optimal solutions for complex problems. The study's use of a cantilever beam case to demonstrate stress analysis and topology optimization showcases the practical applications of submodeling in real-world scenarios. The development of a 1D submodeling approach, along with the utilization of beam formulations and 3D printing for experimental validation, adds a novel dimension to the research. Furthermore, the paper's integration of 1D and 3D submodeling techniques for deflection calculations and validation highlights the thoroughness and rigor of the study. The strong correlation between the finite element models and experimental data underscores the reliability and accuracy of the developed approach. Overall, the originality and value of this paper lie in its comprehensive exploration of submodeling techniques, its practical applications in structural analysis and optimization and its successful validation through experimental testing. [ABSTRACT FROM AUTHOR]

As a joints play a significant role in load transfer both in persistent and accidental situation an attempt to improve structural robustness under column loss situation was made. Based on previously conducted experimental tests of bolted double side steel end‐plate joints and numerical analysis a development to increase load‐capacity and rotational capacity of joints under column loss scenario was presented. Finite element method using Abaqus software with 3D numerical models were employed. Validated and complex models with geometrical and material non‐linearity with fracture simulation were applied. The application of additional double rings to bolted steel flush end‐plate joint lead to significant increase of load‐capacity and rotational‐capacity. The change of failure mode of joint were also obtained compared to the original specimen. [ABSTRACT FROM AUTHOR]

This paper presents a numerical approach for investigating fatigue delamination propagation in composite stiffened panels loaded in compression in the post-buckling field. These components are widely utilized in aerospace structures due to their lightweight and high-strength properties. However, fatigue-induced damage, particularly delamination at the skin–stringer interface, poses a significant challenge. The proposed numerical approach, called the "Min–Max Load Approach", allows for the calculation of the local stress ratio in a single finite element analysis. It represents the ratio between the minimum and maximum values of the stress along the delamination front, enabling accurate evaluation of the crack growth rate. The methodology is applied here in conjunction with the cohesive zone model technique to evaluate the post-buckling fatigue behavior of a composite single-stringer specimen with an initial delamination. Comparisons with experimental data validate the predictive capabilities of the proposed approach. [ABSTRACT FROM AUTHOR]

A finite element model (FEM) of the bracket arm of wrecker is developed and the mechanical behavior under six representative conditions is studied in this paper. Stress test experiment is carried out to validate the presented FEM. Comparison analyses show that results predicted from the FEM are in good agreement with those obtained from the test experiment. Moreover, the mechanical behavior analyses also give the danger working conditions for each component of the bracket arm. Based on the stress distributions under the danger working condition, structural improvement is conducted for the component which is prone to material failure. Mechanical behavior analyses of the improved structures are also carried out in this paper. Numerical analysis results show that the maximum stresses of each improved component of the bracket arm are all reduced to close or below the allowable stress. This indicted that the load bearing capacities of each component are improved effectively and meet the requirements of engineering applications. [ABSTRACT FROM AUTHOR]

Based on fracture mechanics theory, a finite element method was used to determine the stress intensity factors of the inclined crack on the inner surface of the pipe under axial compression load and external pressure. The effects of different influencing factors on the stress intensity factor along the crack front considering crack closure were systematically explored, which were different to those under internal pressure. The effects of high aspect ratio on KII, the crack inclination asymmetry caused by curvature and the effects of the friction coefficient on the stress intensity factors of the pipe with an inclined inner surface crack under axial compression load and external pressure were explored in this paper. To be fit for defect assessment, the solutions for stress intensity factors KII and KIII were derived, and new correction factors fθ and fμ were proposed in the empirical solutions to accommodate the crack inclination asymmetry and the friction coefficient, respectively. [ABSTRACT FROM AUTHOR]

Residual stress is an important factor that affects the properties of cold spray coatings. The study performed 2D single-, 3D single-, and 3D multiple-particle finite element simulations based on the Eulerian method, and hole drilling measurements to study residual stress in cold-sprayed copper coatings. The study examined how the basic modeling parameters affect residual stress in the 2D system. It found that the mesh size, substrate dimension, and simulation duration change the residual stress; while material failure does not have much effect because failure is localized. It also found that thermal softening, which occurs when the initial temperature and/or plastic deformation increase, helps to reduce the residual stress. In addition, the residual stress along the axisymmetric axis of the particle changes from being compressive at first to being compressive-tensile-compressive along the through-depth thickness direction with the interfacial stress being tensile that mainly originates from friction shear of the interfacial layers. For the 3D single-particle simulations, the average residual stress to the through-depth thickness shows tension to compression transition and is similar to the 2D cases. For the 3D multiple-particle simulations, the residual stresses in the coatings/substrate are all compressive because of the repeated and strong impact of the particles, which agree with the experimental measurements. The study also found that the compressive stresses decrease when the coating thickness increases because of more plastic deformation-induced thermal softening. This paper clarifies the effects of Eulerian-based finite element parameters on simulating residual stress in cold spray and will serve as a valuable reference for future studies. [ABSTRACT FROM AUTHOR]

Damage mechanics models exhibit favorable properties such as the intrinsic influence of stress triaxiality on damage evolution and the prediction of crack initiation as well as propagation leading to structural failure. However, their application requires advanced expertise hindering the transfer of these models into industrial practice, especially since the parameter calibration is a key obstacle. In this paper, a simplified procedure is proposed for a non-local extension of the Gurson–Tvergaard–Needleman model (GTN), which is a highly accepted model for ductile failure of metals. The procedure is iteration free and requires experimental input data from only two standardized tests. The parameters are determined using look-up diagrams created on the basis of systematic simulations and made available for different material behavior covering the majority of ductile metals. Benchmark tests for three different steels are conducted to evaluate the robustness of the proposed procedure. The reliability of the GTN model is validated for all investigated materials. [ABSTRACT FROM AUTHOR]

The paper develops a model based on the finite element analysis of the crack initiation and propagation in the generation IV structural materials due to the liquid metal embrittlement (LME) phenomenon. The stress-strain experimental curves obtained at 400 °C by testing in the liquid lead and air were converted as the Ramberg - Osgood constitutive equations by proposing a new method to obtain the strain hardening coefficient. To estimate the accuracy of prediction are used the residual and standardised residual in the context of regression analysis. Further, a model based on the Gurson-Tvergaard-Needleman approach (GTN) was set up to evaluate the crack initiation and propagation under the LME conditions. An application of the developed micro-mechanical model that predicts the crack initiation and propagation in the Compact -Tension (CT) specimen due to LME is performed. The model is practical in the structural integrity activities framework of the structural materials that will be used in the ALFRED demonstrator, which will be build-up at RATEN ICN, Romania. [ABSTRACT FROM AUTHOR]

Assessing the failure stability of engineering structures under service loadings by means of relevant crack growth concepts is one of key issues in damage tolerance analysis. Therefore, the behaviour of fatigue damages is theoretically examined through the crack growth rate. This paper describes a straightforward methodology to generate failure resistance under cyclic loading. To explore fatigue behaviour of two through--the--thickness cracks located at a hole, the stress intensity factor and life are estimated by means of developed analytical model. Stress state field is numerically analysed using the finite element method. Through relevant applications predictive capability of estimates is discussed. Relevant failure evaluations are performed in the case of complex--valued functions by employing the Euler's integration method, which is implemented in the software program developed. Whereas the type of cracks examined is taken into account through the stress intensity factor. [ABSTRACT FROM AUTHOR]

The modeling of the structural behavior of composite materials is an interesting but complex task since the response of the material to loading structural may be difficult to predict, and the failure may be manifested in different forms. In cross-ply fiber-reinforced composites, the major failure mechanisms include: (i) the failure of the matrix material (transverse cracking), (ii) delamination and (iii) the breakage of the fibers. The process of the transverse cracking is a well studied damage mechanism and can be used in numerical simulations, in order to study the effects of various parameters on the crack density. In this paper, the finite element modeling of a cross-ply composite under uniaxial loading in tension is performed using ABAQUS software, considering all the potential damage mechanisms. The model takes into account shear-lag effect for the determination of the stress transfer and furthermore it adopts a homogenization procedure for the calculation of elastic and viscoelastic material properties. Stochasticity is introduced by assigning various interfacial strengths that follow a Gaussian distribution, so as to predict the cracking sequence up to saturation in the transverse to the 0 ∘ layers. The results are directly compared with available experimental measurements showing reasonable agreement. Finally, a cross-ply RVE model was created and loaded in uniaxial tension and crack propagation is modelled with the Extended Finite Element Method (XFEM). The stress concentration calculations around the crack tips are in agreement with the mesoscale model. [ABSTRACT FROM AUTHOR]

In order to predict and assess creep life for plate structures with semi‐elliptic surface cracks under high temperature condition, the accurate calculation of the creep fracture mechanics parameter C* is a critical step. In this paper, the effects of crack sizes, plate geometries, and material creep properties on the parameter C* have been investigated under tensile and bending loads by extensive finite element analyses. Based on the results, the creep influence functions Hc for calculating C* values were obtained and fitted into equations for surface cracks in plates under both loads. The equations have been verified by finite element calculations. The C* solutions were obtained through these equations which are suitable for wide ranges of crack sizes, plate geometries, and materials. [ABSTRACT FROM AUTHOR]

The effect of support spans on single-hit ballistic limit and the effect of pre-existing ballistic damage on multi-hit ballistic limit for two S-2 glass/SC15 composite laminate thicknesses (i.e. 13.6 mm and 20.5 mm) using 0.50cal fragment simulating projectiles have been experimentally investigated in a companion paper. The main objective of this paper is to simulate and correlate the multi-hit ballistic experiments using finite element analyses. One multi-hit ballistic impact scenario on two different composite laminate thicknesses is considered in the present analyses. Finite element model of the impact scenario is developed using three-dimensional solid elements and are solved using LS-DYNA and the progressive composite damage model MAT162. The MAT162 properties and parameters of plain-weave S-2 glass/SC15 composites used in the present simulations were validated in our previous work. Multi-hit impact cases are simulated by sequentially impacting the composite laminate with five different fragment simulating projectiles at five different impact locations at an interval of 200 micro-seconds. Good correlations of ballistic limit velocities between experiments and finite element analyses are obtained. In addition, finite element analyses provided time histories of projectile and laminate dynamics, and damage evolution and interactions for the multi-hit impact cases. Detailed simulation results and comparison with the experiments are presented. [ABSTRACT FROM PUBLISHER]

The aim of the present paper was to explore the effect of initial lesions on the course of femoral head necrosis. A fracture mechanics model of the femoral head was developed and validated using the computed tomography (CT) scan images of a healthy volunteer and material mechanics test results of fresh femur samples. The dynamic development of stresses and fractures of the femoral head with various initial lesions were simulated under various loads. The results showed that the initial lesion of the femoral head spreads faster and collapses deeper as the load increases. The location of the initial lesion has a significant effect on the collapse of the femoral head. The lesions in the anterior and lateral areas of the femoral head are more likely to accelerate the collapse of the femoral head than the lesions in other areas. This study is helpful in predicting the collapse risk and guiding the daily activities of patients with femoral head necrosis. Additionally, this study helps doctors to make better decisions about treatment options. [ABSTRACT FROM AUTHOR]

The characteristics of thermomechanical fatigue life of complex electronic device system, micro-scaled design, is highly sensitive to changes in design factors. The solder ball, which acts as a linkage between the circuit board and the package, is a vital part to examine the performance of electronic device system. Repeated thermal loading causes the solder crack growth in models, eventually leads to the breakdown of devices. There have been lots of studies on investigating the fatigue life of solder joints employing well-established finite element procedure. However, generating a finite element model reflecting the whole device often requires unnecessarily large finite element matrices which may increase the computational cost and solder joint fatigue life can be highly dependent on the mesh resolutions. Recent studies suggest the sub-modeling method to handle the meshing process and alleviate the computational cost. In this paper, we delineate the methodology of two-step sub-modeling framework, aimed at improving the mesh fidelity of complex models while ensuring the efficiency of labor-intensive process of solder joint fatigue analysis. We employ the strain energy-based Darveaux's fatigue model to predict the fatigue life of solder joints. Through the investigation of the predicted fatigue life of solder joints across various sets of design parameters, it has been observed that the design factors of electronic devices exhibit a clear pattern in relation to the predicted fatigue life, even when only the second step of two-step sub-modeling framework is considered. Our findings suggest that it is efficient to utilize solely the second step of two-step sub-modeling framework to identify an appropriate reduced design space, where design parameters can be strategically selected for designing an optimal model. • Two-step sub-modeling enables efficient fatigue life prediction of DRAM modules compared to the conventional approach. • An efficient framework allows the geometric effect of solder ball to be quickly verified. • The proposed method aids in identifying appropriate design space guidelines to optimize subsequent model development. [ABSTRACT FROM AUTHOR]

This paper reports dynamic mechanical behaviors of 3-D rectangular braided composite with different braiding angles under multi-pulse impact load. The composite materials were prepared with braided preforms which have braiding angles of 15 °, 26° and 37 °, respectively. Impact compression tests were conducted in split Hopkinson pressure bar. High-speed camera system was used to capture damage growth process and a meso-scale finite element model was established to investigate failure mechanisms. We found that the braiding angle has significant effects on damage development, failure mechanisms and ultimate damage morphogenesis. The braided composite with 15° braiding angle shows a linear elastic response at the initial stage of stress–strain curves until the peak load. After the peak load, the composite has brittle failure behaviors, while the composites with 26° and 37° braiding angles exhibit non-linear elastic response at the beginning stage of stress–strain curves and ductile failure mode after yielding points. The composites with different braiding angles demonstrated both distinguished damage development and final fracture morphology. In addition, load-bearing ratio of yarns in composite was also affected by braiding angles. [ABSTRACT FROM AUTHOR]

In this paper, the extended finite-element method (XFEM) is employed to analyze electric field of insulating plate with crack. To begin with, both the approximation of XFEM and features of the enrichment functions for crack tip are presented. Then, XFEM is used to solve electric potential of an insulating plate with a middle crack, which proves the method can save computational time by comparison with classic finite-element method (CFEM) under the same computational accuracy. In addition, XFEM is also applied to calculate electrical field at crack tip of an insulating plate with an edge crack, which reveals that the relative error between XFEM and CFEM is small when the meshing size of CFEM around crack tip is smaller than that of XFEM. Therefore, electric field analysis of discontinuous and singular solutions can demonstrate the superior performance of XFEM. [ABSTRACT FROM PUBLISHER]

The honeycomb sandwiches are widely used in the transportation engineering for the realization of lightweight and crashworthy structures. However their application requires a better understanding of their impact response. Aims of this paper are the numerical investigation of aluminium honeycomb sandwiches subjected to low-velocity impact tests and the validation of finite element (FE) results. Before and after the low-velocity impact tests at different velocities, three dimensional (3D) reconstructions of the honeycomb panels have been carried out by a computed tomographic system in order to acquire exactly the dimension and the shape of the damage and to obtain information about geometry and cells defects. The FE models have been computed from CT data of the undamaged panels. The direct comparison has been done by superimposing the deformed images obtained from FE analyses and from 3D CT space reconstructions. The numerical model was also validated comparing the FE results with experimental data. [ABSTRACT FROM AUTHOR]

This discussion is based on the paper by Saviano and Pisanò (2017) (hereafter identified as “the original authors” or “the original paper”). The original authors employed a three-dimensional finite element analysis to investigate the effects of misalignment on the undrained capacity of suction anchors subjected to horizontal (H) and vertical loadings (V). In the original paper, various parametric studies including the misalignment angle, the anchor aspect ratio, the soil strength profile, and the interface adhesion factor on the HV failure envelope of suction anchors were comprehensively carried out. The discussion addresses the issues of the three-dimensional modelling approach for suction anchors using the model of the single anchor/plug rigid body employed in the original paper and questions the validity of the model if it corresponds to the most accurate representation of the numerical model for this type of offshore foundation. [ABSTRACT FROM AUTHOR]

Surface grinding is an effective method in the manufacturing process of silica glass. Study of grinding mechanism of optical glass in the ductile regime has been relatively mature, but the variation law of grinding force during brittle removal is still unclear. In this paper, a theoretical model of grinding force is presented based on fracture mechanics model to predict the influence of machining parameters on grinding force. Finite element analysis (FEA) is utilized to simulate the variation trend of grinding force and principal stress in single grain grinding. The experimental results of grinding force in the processing of single grain grinding are compared with theoretical model. The variation tendency of the FEA simulation and experimental results is in good agreement with the theoretical model. The observation of the surface topography also confirms it on the other hand. This model is reliable to predict the grinding force size and optimize the machining parameters. [ABSTRACT FROM AUTHOR]

Fracture toughness is an important parameter for measuring material properties in industry. In order to obtain data on the fracture toughness of a material it is often necessary to carry out a large number of fracture toughness experiments. The cost of the experiments is high and the experimental process is cumbersome. Moreover, in practice, there are often not a large number of materials that meet the requirements for the experiment. The relationship between different experimental ambient temperatures and fracture toughness can be determined by determining the reference temperature T 0 in the master curve method. In this paper the load-displacement curves of the specimens are obtained using finite element analysis. Determine the J integrals corresponding to the initiating load P int and the maximum load P c on the load-displacement curve using the Load Slope Compliance Changing Rate method. Determine the reference temperature T 0 in conjunction with the single temperature method. On the one hand, in order to validate the method, finite element analyses were performed on specimens of different thicknesses, temperatures, materials and types. This method was also applied to obtain fracture toughness data and to determine the reference temperature T 0. On the other hand, combining the master curve method and combining the experimental data of 16MnDR, 16MnR and 20MnMoNi55 ferritic steels were verified. The experimental results show that the results predicted by this method are in good agreement with the actual results. However, it has a certain conservative type. It provides a good solution for practical engineering. The accuracy of fracture toughness and reference temperature of ferritic steels of different thicknesses can be verified by few experiments. • The study found a Load Slope Compliance Changing Rate method for determining the specimen initiation load P int and critical load P c. • It is shown that φ in P int = P 0 + φ × (P c − P int) (0< φ <1) is not a fixed value. • The master curve for the predicted reference temperature works well and is able to include almost all experimental data for values less than K Jc(limit). • P int and Pc determined by CCR method have a quadratic relationship as the thickness changes. [ABSTRACT FROM AUTHOR]

• Shear bands' morphology in amorphous polymer under four-point bending is concerned. • Physical mechanisms of detour and strength decay of bands at intersections are analyzed. • Constitutive model can predict the morphology of shear bands under four-point bending. As a significant means of plastic deformation in polymers, shear bands play a crucial role in material failure and performance optimization. In this paper, the finite element method is utilized to numerically investigate the morphology of shear bands in an amorphous polymer plate under plane strain four-point bending. Amorphous polymers are characterized by the elastic-viscoplastic constitutive relationship that takes into account the effect of pressure on yielding, including intrinsic softening and subsequent orientation hardening. The impact of material parameters including intrinsic softening, orientation hardening, and initial imperfections on the evolution of shear bands and the undulations of the specimen's surface are explored in detail. In addition, the physical mechanisms responsible for the detour and strength decay of shear bands after passing the intersections are described. It appears that intrinsic softening is the driving force promoting the detour of shear bands at intersections, while orientation hardening is the driving force inhibiting the detour. By comparing the simulations with experimental observations, it is demonstrated that the model can qualitatively depict the morphology of the shear band during the four-point bending of amorphous glassy polymers. [Display omitted] [ABSTRACT FROM AUTHOR]

Following the current trend towards the lunar exploration and habitation, this study focuses on the development of efficient arch forms to be adopted for future long-span shielding structures on the lunar surface. More specifically, the static behaviour of the optimised, varying-thickness arches (VTAs), produced by a previously proposed iterative form-finding algorithm based on limit thrust-line analysis under gravitational and seismic loading is examined herein. These form-found arches are assumed to be constructed by laser-sintered additive manufactured lunar regolith. This paper starts with the visualisation of the limit thrust line using finite element analysis (FEA) on constant-thickness arches (CTAs). Subsequently, it presents the results from FEA on both VTAs and CTAs where it is observed that the original VTAs need to be geometrically enhanced, by thickening certain weak areas of their cross-section in order to minimise the local principal stresses and strain energy. The work proceeds with the quantification of the efficiency of the enhanced VTAs against their CTA counterparts, in both terrestrial and lunar gravitational environments. The most efficient enhanced VTAs are selected and recognised as the best structural forms for either terrestrial or lunar applications among all the arches examined in this research. Eventually, the real capacity of those most efficient arches against lateral loading is attested by means of pushover analysis. As expected, it is found that the geometric enhancement has significantly increased their structural capacity. • Enhanced varying-thickness arches (EVTAs) are more resilient than simple VTAs for a given lateral load. • EVTAs are structurally more efficient than their CTA counterparts in partial gravity environments. • Terrestrial EVTAs experience material failure before reaching their design load. • Lunar EVTAs can withstand up to 90% more load than their initial design load. [ABSTRACT FROM AUTHOR]

The objective of this work is to find out the stress intensity and load confrontation of the axially cracked ASME pressure vessels so that the condition of the vessel will be branded how much more the life of the vessel wall would come if the crack is generated during operating conditions. The background of this work is based on the failures often occurring in the oil, gas and chemical plant industries. Process equipments are having its own standard design procedures and operating life's according to its material properties. Some of the equipments need frequent refurbishment as well as proper maintenance during operations due to the various working conditions. The code practices that process equipments need to be designed for time span of 20 to 25 years. However failures occurring during operations are unpredictable but it is diagnosable. It may be due to various reasons such as malfunctioning of components and wrong operations. In this paper the work is such that if the crack is generated axially inside due to load or corrosion, how much more operation the vessel would sustain. If the cracks grow continuously due to frequent loads how long the un-cracked thicknesses would withstand the internal pressure loads. ASME based designed pressure vessel has been considered for this study. The typical pressure vessel crack has been modeled internally in axial directions. The operating load has been applied and the behavior of cracks and its load confrontations were simulated using finite element technology and the results were presented. [ABSTRACT FROM AUTHOR]

In this paper, a systematic and detailed observation was made of the crack extension behavior of thin 90° layers of cross-ply carbon fiber reinforced plastics (CFRP) laminates. The effect of ply thickness on the crack propagation mechanism was discussed with respect to the energy release rate of the intralaminar transverse crack, calculated using finite element analysis. In a laminate with a 40 μm-thick-ply, the crack gradually extended with increasing strain. Conversely, extreme crack extension was found at around 1.0% strain in a laminate with a standard thick ply. Based on the numerical analysis, the crack suppression effect is verified using a thin ply; the effect is apparently caused by a decrease in the energy release rate at the crack tip in the thin layer. [ABSTRACT FROM PUBLISHER]

mixed-mode fracture specimen was designed in this paper. This geometry is a judicious compromise between a modified Double Cantilever Beam specimen and Compact Tension Shear specimens. The main objective is to propose a specimen which traduces a stable crack growth during creep loading taking into account viscoelastic behaviour under mixed-mode loadings. The numerical design is based on the instantaneous response traduced by a crack growth stability zone. This zone is characterized by a decrease of the instantaneous energy release rate versus the crack length. In order to obtain a mixed-mode separation, the paper deals with the use of the M-integral approach implemented in finite element software, according to energetic fracture criterions. In these considerations, a numerical geometric optimization is operated for different mixed-mode ratios. Finally, a common specimen which provides to obtain fracture parameters, viscoelastic properties and creep crack growth process for different mixed-mode configurations is proposed. [ABSTRACT FROM AUTHOR]

The aim of this paper is to gain a better understanding of the impact different micro-geometries has on stress distribution in cutting tools. Both principal and effective stress distribution are studied. These quantities have a major impact on the occurrence of damages in the cutting tool such as crack formation, flaking, chipping, breakage and plastic deformation. The development of a stagnation zone is also investigated as well as the effect tool micro-geometries have on this zone. A finite element model is developed which enables the examination of these aspects, in detail. It was found that the model predicted these metal cutting phenomena with high accuracy. Cutting forces is within the standard deviation of experimental results. The experimental results also indicate that the stress distributions and the stagnation zone have been simulated correctly. This study has shown that the micro-geometries of the cutting tool have a great potential in reducing the maximal tensile/principal stress. This research work has also shown that the size of the stagnation zone can be controlled by micro-geometries on the cutting tool, which in turn can have an effect on the wear on the cutting edge. [ABSTRACT FROM AUTHOR]

The subsurface crack propagation is one of the major interests for gear system research. The subsurface crack propagation lifetime is the number of cycles remaining for a spall to appear, which can be obtained through either stress intensity factor or accumulated plastic strain analysis. In this paper, the heavy loads are applied to the gear system. When choosing stress intensity factor, the high compressive stress suppresses Mode I stress intensities and severely reduces Mode II stress intensities in the heavily loaded lubricated contacts. Such that, the accumulated plastic strain is selected to calculate the subsurface crack propagation lifetime from the three-dimensional FEA model through ANSYS Workbench transient analysis. The three-dimensional gear FEA dynamic model with the subsurface crack is built through dividing the gears into several small elements. The calculation of the total cycles of the elements is proposed based on the time-varying accumulated plastic strain, which then will be used to calculate the subsurface crack propagation lifetime. During this process, the demonstration from a subsurface crack to a spall can be uncovered. In addition, different sizes of the elements around the subsurface crack are compared in this paper. The influences of the frictional coefficient and external torque on the crack propagation lifetime are also discussed. The results show that the lifetime of crack propagation decreases significantly when the external load T increasing from 100 N m to 150 N m. Given from the distributions of the accumulated plastic strain, the lifetime shares no significant difference when the frictional coefficient f ranging in 0.04–0.06. [ABSTRACT FROM AUTHOR]

The paper presents a review of the developments in ship collision analysis over the last 10 years and the challenges to an Accidental Limit State (ALS) design method of ships based on collisions. It aims to discuss the technical difficulties in finite element analysis, especially the mesh-dependent material failure criterion, the accuracy of the analytical and semi-analytical formulae and the acceptance criterion in ALS design. In recent literature, various material failure criteria are proposed and validated in the fine-meshed models, but their accuracy is not clear in the applications of coarse-meshed models. The analytical calculations provide a relatively accurate prediction of the purely plastic responses of ship structures under impact loads, but a universal approach has not been found for fracture predictions. A semi-analytical method is a good approach in the ALS design, but the accuracy needs further improvements. The technical challenges are summarised in ship collision analysis for accurately assessing the structural damage with numerical and theoretical methods. • The paper presents a review of the developments in ship collision analysis in the recent 10 years. • It discusses the technical difficulties in conducting FE analysis, especially the mesh-dependent material failure criterion. • It covers the accuracy of the analytical and semi-analytical formulae and the acceptance criterion in ALS design. • The technical challenges in ship collision analysis are summarised. [ABSTRACT FROM AUTHOR]

The main cause of failure in bonded ceramic restorations is material fracture due to excessive stress concentration at the base of the prosthesis. The design of restorative functionally graded materials (FGM) could represent a major advance in dissipating mechanical stresses during occlusal contacts. The aim of this paper is to carry out a complete factorial design of finite element analyses to optimize a multilayer FGM introduced at the bottom of an overlay prosthesis. The number and thickness of layers vary within a spectrum compatible with ceramic shaping processes whereas Young's moduli variations are set in the range of dental tissues. For a 1.5-mm thick prosthesis, the optimal FGM configuration appears to be a 5 layers of 0.2 mm thickness with a linear distribution of Young's modulus from 30 to 70 GPa. This configuration was implemented in a 3D model of a restored tooth with realistic geometry to validate the proof-of-concept. [ABSTRACT FROM AUTHOR]

• Quantified the effect of Hill anisotropic plasticity on J-Q characterization of semi-circular surface cracks. • Demonstrated that the isotropic and anisotropic J – Q parameters can significantly diverge, especially, when crack planes are misaligned with respect to the material coordinate system. • The results are important for providing accurate predictions of failure in pipeline steels that often show significant plastic anisoptropy. In this paper, the J - Q two-parameter characterization of Hill-anisotropic elastic–plastic crack-front fields are examined for surface cracked plates under uniaxial tensile loadings. A method for two-parameter characterization crack-front field in anisotropic plastic materials is presented. Extensive three-dimensional elastic–plastic finite element analyses were performed for semi-circular surface cracks in a finite thickness plate, under remote uniaxial tension loading conditions. Surface cracks with relative depths a / t = 0.2, 0.6 were investigated. The loading levels spanned from small-scale to large-scale yielding. Different crack orientations with respect to the material coordinate directions were also considered. In topological planes perpendicular to the crack front, the crack-front stress fields were obtained. In order to facilitate the determination of Q -factors, modified boundary layer analyses were also conducted. The modified boundary layer analyses were adapted to account for plastic anisotropy. The J - Q two-parameter approach was then used in characterizing the elastic–plastic crack-front stress fields along these 3D crack fronts. Complete distributions of the J -integral and Q -factors for a wide range of loading conditions were obtained. The results indicate that the J – Q characterization is applicable to Hill-anisotropic plastic materials and provides good estimate for the crack-front constraint loss experienced under large-scale yielding. It was also observed that the isotropic and anisotropic J – Q parameters can significantly diverge, especially, when crack planes are misaligned with respect to the material coordinate system. This highlights the importance of the consideration of plastic anisotropy when performing constraint-based fracture mechanics analyses. [ABSTRACT FROM AUTHOR]

Structural integrity analysis for reactor pressure vessel (RPV) nozzles has been a vital issue due to the irradiation embrittlement and especially the discontinuity of geometry in RPV nozzles, which may cause a higher stress concentration and influence the structural integrity of RPV nozzles. For the linear elastic fracture mechanics (LEFM) analysis of the RPV nozzle, a postulated crack with a specific crack depth is presumed to evaluate the stress intensity factors (SIFs) whose crack depth does not grow during LEFM analysis. Thus, this paper would discuss the crack propagation for the postulated crack with a specific crack depth under the different reference temperature of nil-ductility transition (R T N D T ), and the SIFs on the specific crack depth are also calculated. In recent research, the extended finite element method (XFEM) was developed, which is based on the enrichment solution space to simplify the computational fracture mechanics with the crack propagation of various discontinuities, and can be used to evaluate the crack propagation of RPV nozzle with a specific crack depth under R T N D T of −23.89, −10.89, 0.89, 2.69, and 2.89 °C. To investigate the crack propagation and structural integrity of RPV nozzles, the finite element analysis of Taiwan domestic boiling water reactor (BWR) nozzles containing the postulated circular corner crack with depths of one-fourth and one-tenth thickness along the 45° path from the tip of the nozzle corner is engaged. The present result shows that the crack was growing when the R T N D T was 0.89 °C and. In addition, the XFEM calculation of the SIFs for the specific crack depth is similar to the LEFM results. • The RPV nozzles with postulated cracks were established to investigate crack propagation through XFEM. • The differences in RT NDT were used to evaluate the fracture toughness and discuss the crack propagation for RPV nozzles. • The stress intensity factors (SIFs) obtained by XFEM, LEFM, and the ASME BPVC were compared. • The XFEM analysis would overestimate SIFs more than the ASME BPVC and the LEFM. [ABSTRACT FROM AUTHOR]

This study investigates the thermal stress and bolt load distribution in a hybrid panel structure of an aircraft mechanical joint under extreme temperatures. The hybrid panel structure comprises two aluminum alloy splices, six T-shaped composite stringers, and two composite skins, secured together with 96 bolts. This study analyzed the strain induced by thermal stress on composite materials and metals within the structure across temperatures, employing temperature environment tests ranging from room temperature to −54 °C, alongside a carrying capacity test at −54 °C. Furthermore, a three-dimensional simulation model of the panel structure was developed, incorporating considerations for contact, metal elastoplasticity, and the progressive damage failure of composite materials. This model facilitated the determination of thermal stress and bolt load distribution patterns. The results indicate a strong consistency between the finite element analysis outcomes and the experimental data. Temperature variations exacerbate the uneven distribution of bolt loads, concentrating the load near the edges of the hybrid structure while diminishing it in the center. The bolt load distribution parallel to the mechanical load direction forms an "M" shape, with a maximum load magnitude of approximately 31 kN. Perpendicular to the mechanical load, the bolt load undergoes significant changes, especially at the edges, reaching a maximum of about 20 kN, which warrants attention. The bolt-load distribution of the structure with the increase in mechanical load at −54 °C tends to be consistent with that at room temperature. [ABSTRACT FROM AUTHOR]

This paper develops a three-dimensional damage plasticity based finite element model (FEM) to study the ultimate strength of the steel–concrete–steel (SCS) sandwich shell structure under patch loading. The FEM considers complex geometric nonlinearities of hundreds of stud connectors in the structure, complex interaction between the connectors and concrete, and material nonlinearities of steel and concrete used in the structure. In the developed FEM, the concrete core material adopts the concrete damage plasticity model to predict the post-peak softening and residual strength; the stud connectors and steel shells adopt a continuum damage model to phenomenologically describe the damage evolution in the steel material. The reasonable agreement between FE analysis and the quasi-static tests on the SCS sandwich shell structure confirms the accuracy of the FEM in predicting the ultimate shear resistance, load–deflection relationship, cracks in the concrete core, and punching shear failure of the top steel shell. A subsequence parametric study based on the validated FEM investigates the influence of the curvature on the first peak resistance of the SCS sandwich structure. Finally, the paper validates accuracy of an analytical model on the punching shear resistance of the concrete core of the SCS sandwich shell. [ABSTRACT FROM AUTHOR]

An overview of past research on T-stress is presented in this paper, we provides some critical review of the history and state of two elastic fracture mechanics and relationship to crack paths stability. The importance of the global approach with two parameters (K-T) or (K-A3) in the analysis of the linear elastic fracture mechanics, based on the effect of confinement according to the work of Williams, is presented in the field of CT specimen in mode I for the API X52 steel. The objective is to propose a numerical study, defining the T-stress, by applying the finite element method, in 2D, using the software ANSYS 15.0. Thereafter, we propose the method inspired from the volumetric approach developed by Pluvinage, this method is based on the determination of the effective stress Tef over an effective distance Xef ahead of the crack tip. Finally, it concludes with a discussion critical of methods of calculated the T-stress. [ABSTRACT FROM AUTHOR]

Beam-to-column welded joints in moment-resisting steel frames may undergo extremely low cycle fatigue in earthquake action. The aim of this paper is to investigate the fatigue failure behavior by means of experimental study and finite element analysis. Experiments were conducted on the six full scale beam-to-column welded joints. The seismic performance of welded joints with different weld access hole geometries was compared among them and the effect of crack initiation and growth on the load carrying capacity of welded joints was discussed. In addition, a continuum damage mechanics model used previously for monotonic loading was reformulated in order to account for the extremely low cycle loading condition. The model was implemented in a commercial nonlinear finite element software of ABAQUS, which was adopted to predict the fracture of beam-to-column welded joints subjected to monotonic loading and extremely low cycle loading. The predicted load displacement response agrees well with the test results. The distribution and evolution of damage in the welded joints were calculated during crack initiation and propagation. It is found that the methodology based on continuum damage mechanics proposed in the paper can successfully predict fracture behavior of beam-to-column welded joint with reasonable accuracy. [ABSTRACT FROM AUTHOR]

The behavior of materials and structures is strongly influenced by the loading rate. Compared with quasi-static loading structures loaded by high loading rate and impact acts in a different way. First, there is a strain-rate influence on strength, stiffness, and ductility, and, second, there are inertia effects activated. Both influences are clearly shown in experiments. Although steel does not exhibit significant strain rate sensitivity, the dynamic fracture of steel is highly sensitive on loading rates. In this paper, the static and dynamic fracture of steel is numerically studied on a compact tension specimen (CTS), which is loaded under loading rates up to 100 m/s. First, the proposed microplane model for steel is discussed and verified for monotonic and cyclic quasi-static loading. Subsequently, three-dimensional (3D) finite element dynamic fracture analysis is carried out. It is shown that the resistance of steel (apparent strength and toughness) increases progressively after the critical strain rate (approximately 100/s) is reached. Moreover, the crack branching phenomena and significant decrease of ductility are observed. The phenomena that are also well known from experimental evidence are attributed to the effect of structural inertia and inertia related to the high nonlinear behavior of steel at the crack tip and in the plastification zone. The numerical results indicate that maximum crack velocity of steel is much lower than the Rayleigh wave velocity, and for the investigated steel, it reaches approximately 400 m/s. [ABSTRACT FROM AUTHOR]

A mesoscopic, time-dependent finite element model for the simulation of dynamic fracture in laminated composite plates is presented. The computational model allows for the simulation of mesh-objective multiple matrix cracking and delamination in laminated composite plates. The analyses are performed with an emphasis on the quantification of the effect of the loading rate on interacting damage mechanisms, i.e. matrix cracking and delamination. In particular, rate effects on damage initiation, propagation, and interaction between matrix cracking and delamination under low and high velocity impact are studied. Moreover, the paper addresses computational issues related to time continuity in stress/strain and velocity fields, during dynamic simulation, at the time of incorporation of new degrees of freedom in a mesh-objective crack modeling approach. Illustrative numerical examples are presented to show the performance of the model. The model is validated with a fast crack growth simulation in a unidirectional laminate. An impact test on a cross-ply laminated plate is performed in order to study the rate effects on structural response and damage mechanics. [ABSTRACT FROM AUTHOR]

In this paper, the fracture toughness parameters of two types of dentistry cement have been investigated based on numerical and experimental analysis. Dentistry cements are largely applicable and useful when it comes to mending teeth and are used as resin and filler. Composite cement and adhesive resin cement are among the helpful cements in dentistry. As a result of production and the loading conditions in the mouth, the generation of micro-cracks is inevitable. In this research, by producing butterfly Arcan samples including crack and by loading those in different angles, pure mode-I, pure mode-II, and mixed-mode fracture data were obtained. The experiments were conducted by an Arcan fixture and loading device, which had the ability of investigating the fracture parameters of materials in different loading angles. By calculating the geometrical correction factors by using ABAQUS finite element software, fracture toughness and critical energy release rate have been obtained. Also, the effects of crack length, elasticity modulus, and Poisson's coefficient on the fracture parameters and energy release rate in different loading angles have been studied using numerical analysis. [ABSTRACT FROM PUBLISHER]

In the component-based method, the ductility characterisation of the tension component plays a primary role in accurately predicting the rotation capacity of the whole connection. In this paper, a refined finite element (FE) model is presented to assess the complete force–displacement response of the T-stub component, from the initial stiffness up to the fracture point. The refined FE model includes a non-linear continuum damage mechanics model that considers the onset of the damage, the damage evolution law, and the component failure. A parametric study was conducted to evaluate the influence of the damage parameters in the overall response of the T-stub component. The numerical results obtained from the refined FE model strongly agree with the experimental results of 18 test specimens. The comparison reveals the proposed FE model’s satisfactory accuracy, with an average fitting error below 9%. This paper constitutes the first part of a comprehensive methodology based on combining FE analysis and soft computing techniques. The ultimate goal of this methodology is to predict the key parameters that define the force–displacement response of the T-stub component. [ABSTRACT FROM AUTHOR]

This paper presents a numerical simulation technique which can be used to predict numerical creep crack growth (CCG) at elevated temperatures. The results of the numerical predictions are compared to experimental data taken from specimens with weld and parent properties. The experimental results consisted of uniaxial creep data and crack growth data taken from C-Mn steels and P22 welds tested at 360°C and 550°C, respectively. For C-Mn steels, compact tension (CT) specimen and internal pressurised shallow cracked pipe were tested for creep crack growth. Whilst, for P22 welded, HAZ CT specimens were used. The constitutive behaviour for these materials is described by a power law creep model. A damage-based approach combined with a crack tip constraint model based on void growth is used to predict the crack propagation rates in the pipe component using a 2D finite elements (FE) mesh. Elastic-plastic-creep analyses are performed using a damage based node de-bonding criteria to simulate and predict crack extension under plane stress and plane strain conditions. It has been found that CCG the experimental data lies within the plane stress/strain range of 2D-FE model predictions irrespective of material and geometry. [ABSTRACT FROM AUTHOR]

[Display omitted] • New ring tensile specimen for pipeline material fracture testing is examined. • Specimens (ring and plane) produced by selective laser sintering from polymer PA12. • Determined dependence on specimen geometry and stress concentrator length. • PRNT specimen enables good assessment of pipeline material fracture properties. • Simple fabrication from pipe; Pressure simulated by contact with the testing tool. In order to develop a non-standard method for determining the resistance to fracture and damage of pipeline materials, a new geometry of ring-shaped specimens with sharp notches or cracks has been defined. The need to develop a new method for testing of the specimens cut from the pipes arises due to the difficulties in determination of fracture mechanics parameters on thin-walled pressure pipelines, especially those with a smaller cross-section, by application of the standard procedures/specimens. Previous studies dealing with the topic of pipeline testing by non-standard methods are presented in the introductory part of the paper. In the experimental part of the research, tests on PRNT (Pipe Ring Notched Tension) and SENT (Single Edge Notched Tension) specimens are performed. Samples of these specimens were produced by SLS (Selective Laser Sintering) technique of additive production from PA12 (polyamide PA 2200) material. For the purpose of this study, a tool that is protected at the national level (in Serbia) as intellectual property is used for testing of the ring-shaped PRNT specimens. Tensile testing of both types of specimens is monitored by Aramis GOM 2M system; its operation is based on the method of digital image correlation, DIC. Additionally, finite element analyses are conducted on the PRNT and SENT geometries, enabling the calculation of the fracture mechanics parameter – Stress intensity factor K. It is concluded that the presented procedure based on the PRNT specimen has a good potential for use as a non-standard method for fracture resistance examination of pipeline materials. It can be performed on the specimens cut directly from the pipes (new or from exploitation). The dependence of the fracture resistance on the stress concentrator size is not pronounced, which means that the results depend dominantly on the material properties, rather than on geometry. [ABSTRACT FROM AUTHOR]

The J‐integral approach manifests itself in an efficient way to determine the crack growth and failure mechanism of tread and sidewall compounds used in tyres. Therefore, for a pure shear (PS) specimen of carbon black filled natural rubber, the J‐integral formula was vivisected, and the material parameters were defined using the concepts of solid mechanics considering the planar stress conditions. Theoretical calculations, experimental observations, and finite element analysis were executed to calculate the J value for different strain percentages. Different hyperelastic material models were used to understand the hyperelastic behavior of the test compound, but Yeoh model was found to be the best fit with the least error against the experimental test data. The frequency sweep dynamic mechanical analyzer test was done to observe the viscoelastic response of the material. It was observed that the J value decreased with decreasing contour radius and had exhibited stark difference with the global tearing energy values, indicating the effects of stress softening and the dependence of J value on the elastic characteristics of the material. Further, the J value attained from finite element methods for a random strain 22% was used to predict the crack growth rate of the pre‐notched PS specimen. Highlights: J‐integral formula for pure shear specimen using solid mechanics approach.J value comparison of theoretical, experimental, and finite element methods.Dependence of J value on the elastic characteristics of the material.Different hyperelastic models compared and Yeoh model chosen for analysis.Prediction of crack growth rate at a random strain percentage. [ABSTRACT FROM AUTHOR]

Purpose – The early detection of cracks, corrosion and structural failure in aging structures is one of the major challenges in the civil, mechanical and aircraft industries. Common inspection techniques are time consuming and hence can have strong economic implications due to downtime. The paper aims to discuss these issues. Design/methodology/approach – As a result, during the past decade a number of methodologies have been proposed for detecting crack in structure based on variations in the structure's dynamic characteristics. This work showcases the efficacy of particle swarm optimization (PSO) and genetic algorithm (GA) in damage assessment of structures. Findings – Efficiency of these tools has been tested on structures like beam, plane and space truss. The results show the effectiveness of PSO in crack identification and the possibility of implementing it in a real-time structural health monitoring system for aircraft and civil structures. Originality/value – The methodology presented establishes the PSO as robust and competent tool over GA for crack identification using changes in natural frequencies. [ABSTRACT FROM AUTHOR]

This paper reports the results of elastic-creep finite element (FE) analyses of a P91 steel pipe weld with two external 'type IV' circumferential cracks, subjected to internal pressure and end (system) load using creep properties obtained at 650°C. Numerical contour integral calculations have been performed to obtain both transient and stationary high temperature fracture mechanics parameters. A mesh sensitivity analysis was performed in order to ensure the accuracy of FE analyses in the transient creep stage. The effects of load magnitude, the material mismatch near the crack surfaces and the crack depth on the stationary creep C* contour integrals have been investigated, and corresponding analytical correlations are presented. [ABSTRACT FROM AUTHOR]

We have shown that a significant creep occurs at the concrete-fiber reinforced polymer (FRP) interface based on double shear long-term test. The primary test parameters were the shear stress to ultimate shear strength ratio, the epoxy curing time before loading as well as the epoxy thickness. The test results showed that when the epoxy curing time before loading was earlier than seven days the shear stress level significantly affected the long-term behavior of epoxy at the interfaces, and in particular the combined effect of high shear stress and thick epoxy adhesive can result in interfacial failure if subjected to high-sustained stresses. In this paper, based on the previous experimental observations, an improved rheological model was developed to simulate the long-term behavior of epoxy adhesive at the concrete-FRP interfaces. Furthermore, the newly developed rheological creep model was incorporated in finite element (FE) modeling of a reinforced concrete (RC) beam strengthened with FRP sheets. The use of rheological model in FE setting provides the opportunity to conduct a parametric investigation on the behavior of RC beams strengthened with FRP. It is demonstrated that creep of epoxy at the concrete-FRP interfaces increases the beam deflection. It is also shown that consideration of creep of epoxy is essential if part or the entire load supported by FRP is to be sustained. [ABSTRACT FROM AUTHOR]

Abstract: This paper presents an advanced method for the estimation of air-spring fatigue life. Furthermore, the paper presents the influence of the cord angle on the air-spring external characteristic and fatigue life. To calculate the damage and respectively the fatigue life, experimental fatigue data, together with the finite element analysis in ABAQUS is used. The research shows that cord angle has a great effect on the air-spring life and external characteristic as well. As a result of the research, it can be concluded that at larger cord angles the damage is caused by the stress that acts in the air-spring axial direction (X-stress). Therefore, the crack at cord angles greater than 40° appears on the plane that is perpendicular to the air-spring axis. On the other hand, at smaller cord angles the damage is caused by the stress that acts perpendicular to the air-spring axial direction (Y-stress). Therefore, the crack at cord angles smaller than 40° appears on the plane that is parallel to the air-spring axis. The optimal cord angle is the one that assures an appropriate ratio between X-stress and Y-stress. For the air-spring discussed in this research, the optimal cord angle is between 40° and 45°. Since a cord angle also affects the air-spring external characteristic, it has to be chosen in a way to assure an acceptable compromise between the fatigue life and the external characteristic. [Copyright &y& Elsevier]

A numerical model of ballistic impact on a two-dimensional Kevlar KM2® plain-woven fabric has been validated by experiment. This paper shows that it is necessary to experimentally measure material constants of yarns for having good input parameters of the model. Effects of yarn Poisson’s ratio, transverse and shear modulus on impact behaviors of a simple crimped yarn and a complete fabric have been carried out. The effect of the Poisson’s ratio can be negligible in both impact cases: on a single crimped yarn and a complete fabric. The same conclusion has been proven for the effect of the transversal modulus except the cases of its so low values that can cause yarn early damage. The shear modulus of a yarn appears to be an important material parameter that mainly influences the ballistic performance of a two-dimensional plain-woven fabric. When using a very high value of a shear modulus of yarn, a crimped single yarn is broken immediately after contact with projectile in pure shearing mode. [ABSTRACT FROM PUBLISHER]

This paper developed 3D elastoplastic finite element analysis (FEA) models to investigate non-axisymmetric tubes neck spinning. The three-roller mandreless neck spinning process was simulated by commercial FEA software, MSC. Marc. The distribution of the transient von Mises stresses in the contact zone between the roller and the blank, and the equivalent plastic strains after spinning were obtained. The locations and causes of fractures were analyzed. The thickness distribution of the spun workpiece was investigated numerically and experimentally. It shows that during 3D non-axisymmetric tubes spinning, diametral elongation and fractures mostly occur at the opening end of workpiece, which considered as the primary location of defects. Fractures may also occur easily at the initial spinning area, which may be considered a secondary location of defects. The distributions of equivalent stresses and strains are non-uniform during both offset and oblique 3D non-axisymmetric tubes spinning. The maximum stress and strain values occur at the location where the biggest offset or inclination is induced, while the minimum values occur at the opposite location of 180° away from the maximum values. For the oblique tube, however, the strain distribution changes gradually along the axial direction, which is different from that of the offset tube. Thinning occurs during forward path spinning and thickening occurs during backward path spinning. Therefore, for multipath neck spinning processes, forward and backward paths should be applied alternately to avoid excessive thinning or thickening of workpiece. [ABSTRACT FROM AUTHOR]

Highlights • Constrained and unconstrained 3D elastic-plastic crack tip stress fields. • The proximity of plane strain along 3D crack front tip. • A new parameter (J / z σ o) to characterize three-dimensional constraint. • Explicit expressions for crack tip constraint at θ = 0°, 0< z / t < 0.5, 2 ≤ r σ o J ≤ 10. • Modification of two-parameter J - Q fracture mechanics for 3D crack problems. Abstract Crack tip constraint can be used as a means to relate the stresses at the crack tip to a measure of fracture toughness of a material. Current technique to determine crack tip constraint demonstrated in structural integrity standards are based on two-dimensional plane strain approach. This paper explores the possibility of extending the current two-dimensional crack tip constraint solutions to three-dimensional crack problems through an investigation of the asymptotic structure of three-dimensional crack tip stress fields under elastic-plastic non-hardening responses. Analysis was based on three-dimensional boundary layer formulations, combined with full-field solutions of single edge notched bend bars and centre cracked tension panels having a range of thicknesses. The fields along the crack front were examined as a function of load level and thickness. From the results, it is demonstrated that, at the crack tip (r = 0), a family of asymptotic fields develop which feature a constant stress sector directly at the crack tip. Within this sector the fields differ hydrostatically while being similar in respect of the maximum stress deviator. At the intersection with the free surface, an elastic perfectly-plastic corner field which differs from the plane stress field is shown to develop. It is shown that in these fields the level of constraint is parameterised by J / z σ o , where z is the distance from the free surface. J / z σ o unifies both the change in the maximum principal stress and the mean stress, as a function of thickness and deformation level from all sections of different geometry and thickness specimens. An explicit expression has been developed which demonstrated the constraint loss due to in-plane and out-of plane crack tip constraint effects, allowing a two-parameter fracture mechanics methodologies in a modified form to be extended to fully three-dimensional fields. [ABSTRACT FROM AUTHOR]