The ductile failure predictions have been an issue in many engineering applications. It begins with a design of machines and tools, continues with an evaluation of manufacturing processes, and last but not least ends with the assessment of various structures. The paper deals with a predictability of used criteria for a random structure of aluminum alloy 2024-T351, which was performed under the conditions of room temperature three-point bending. The bi-failure mode creates a space for the numerical studies of various approaches and gives an insight into the model performance. The plasticity was described by Lode-dependent yield criterion, which was coupled with several pressure and Lode-dependent fracture models to form a continuum damage mechanics approach via the material weakening. It was incorporated through a nonlinear damage accumulation, which was finally implemented using Fortran 77 subroutine into abaqus/explicit . All the models exhibited a good ability of crack onset prediction in terms of the force responses and realistic predictability of the crack propagation. The field of deformations was successfully compared with experimental data obtained by an optical method.

The effects of two temper conditions (T4 and T6 heat treatments) upon the stress corrosion cracking (SCC) of AA6061 plates have been investigated in this work. AA6061 alloys were double-side-welded by the tungsten inert gas (TIG) welding method. SCC behavior of both the as-welded and as-received alloys was reported. Optical microscopy (OM) and scanning electron microscopy (SEM) were used to determine the precipitate structure of the thermal-altered zones and the base metal (BM), and also the hardness variations were examined using microhardness testing (Vickers hardness). The small-size precipitate structures in the T6 tempered alloy and the coarser precipitate structures in the T4 tempered alloy were found by microstructural investigations. As a result, T4 temper heat treatment of this alloy considerably reduced its susceptibility to stress corrosion cracks due to relatively coarse and more separate precipitate morphology. In welded specimens, SCC failure occurred in the area between the heat-affected zone (HAZ) and the base metal. Stress corrosion resistance in the fusion zone was strong in both temper conditions. The aim of this work was to obtain the effects of heat treatment and welding on SCC behavior of the age-hardenable aluminum alloy. The authors conclude that a deep insight into the SCC resistance of AA6061 alloy indicates the precipitate particle distributions and they are the key point for AA6061 alloy joints in chloride solution.

Al 7068-T651 alloy is one of the recently developed materials used mostly in the defense industry due to its high strength, toughness, and low weight compared to steels. The aim of this study is to identify the Johnson–Cook (J–C) material model parameters, the accurate Johnson–Cook (J–C) damage parameters, D 1 , D 2 , and D 3 of the Al 7068-T651 alloy for finite element analysis-based simulation techniques, together with other damage parameters, D 4 and D 5 . In order to determine D 1 , D 2 , and D 3 , tensile tests were conducted on notched and smooth specimens at medium strain rate, 10 0 s −1 , and tests were repeated seven times to ensure the consistency of the results both in the rolling direction and perpendicular to the rolling direction. To determine D 4 and D 5 further, tensile tests were conducted on specimens at high strain rate (10 2 s −1 ) and temperature (300 °C) by means of the Gleeble thermal–mechanical physical simulation system. The final areas of fractured specimens were calculated through optical microscopy. The effects of stress triaxiality factor, rolling direction, strain rate, and temperature on the mechanical properties of the Al 7068-T651 alloy were also investigated. Damage parameters were calculated via the Levenberg–Marquardt optimization method. From all the aforementioned experimental work, J–C material model parameters were determined. In this article, J–C damage model constants, based on maximum and minimum equivalent strain values, were also reported which can be utilized for the simulation of different applications.

Johnson–Cook (JC) strength and failure models have been widely used in finite element analysis (FEA) to solve a variety of thermo-mechanical problems. There are many techniques to determine the required JC parameters; however, a best practice to obtain the most reliable JC parameters has not yet been proposed. In this paper, a genetic-algorithm-based optimization strategy is proposed to calibrate the JC strength and failure model parameters of AISI/SAE 1018 steel. Experimental data were obtained from tensile tests performed for different specimen geometries at varying strain rates and temperatures. FEA was performed for each tensile test. A genetic algorithm was used to determine the optimum JC parameters that best fit the experimental force-displacement data. Calibrated JC parameters were implemented in FEA to simulate the impact tests of standard V-notch Charpy bars to verify the damage mechanism in the material. Considering good agreement of the experimental and FEA results, the current strategy is suggested for calibration proposes in other kind of materials in which plastic behavior could be represented by the JC strength and failure models.

Mechanical properties of additive manufactured metal components can be affected by the orientation of the layer deposition. In this investigation, Ti–6Al–4V cylindrical specimens were fabricated by electron beam melting (EBM) at four different build angles (0 deg, 30 deg, 60 deg, and 90 deg) and tested as per ASTM E8 Standard Test Methods for Tension Testing of Metallic Materials. With the layer-by-layer fabrication suggesting granting anisotropic properties to the builds, strain fields were recorded by digital image correlation (DIC) in the search for shear effects under uniaxial loads. For the validation of this measuring method, axial strains were measured with a clip extensometer and a virtual extensometer, simultaneously. Failure analysis of the specimens at different orientations was conducted to evidence the recording of shear strain fields. The failure analysis included fractography, optical micrographs of the microstructure distribution, and failure profiles displaying different failure features associated with the layering orientation. Additionally, an experimental study case of how the failure mode of components can potentially be designed from the fabrication process is presented. At the end, remarks about the shear effects found, and an insight of the possibility of designing components by failure for safer structures are discussed.

The focus in this work is toward an investigation of the fracture response of brittle materials with different specimen size loaded in diametral compression using different boundary conditions. The compacted zone underneath the loading points is assumed to be limited and only responsible for the load transition to the rest of the material. Therefore, the theory of elasticity is used to define the stress state within a circular specimen. A tensile failure criterion is used, and the final load capacity is related to the formation of a subsurface crack initiated in a probabilistic manner in a region in the vicinity of the loaded diameter of the specimen. This process is described by Weibull theory, and it is assumed here that the growth of the subsurface crack occurs in an unstable manner. Therefore, the assumption in Weibull theory that the final failure occurs as soon as a macroscopic fracture initiates from a microcrack is fulfilled. The concept of disk effective volume used in Weibull size effect is presented in a convenient way that facilitates the application of the model to transfer the tensile strength obtained from different methods such as three point bending and Brazilian test. The experimental results for Brazilian test on a selected hard rock are taken from the literature and a fairly close agreement is obtained with the model predictions.

This overview/survey assesses the state of the discipline for the failure of homogeneous and isotropic materials. It starts with a quick review of the many historical but unsuccessful failure investigations. Then, it outlines the dysfunctional current state of the field for failure criteria. Finally, it converges toward the technical prospects that can and very likely will bring much needed change and progress in the future.

A comprehensive study has been conducted to develop proper test methods for accurate determination of failure strengths along different material directions of closed-cell polymer-based structural foams under different loading modes. The test methods developed are used to evaluate strengths and failure modes of commonly used H80 polyvinyl chloride (PVC) foam. The foam's out-of-plane anisotropic and in-plane isotropic cell microstructures are considered in the test methodology development. The effect of test specimen geometry on compressive deformation and failure properties is addressed, especially the aspect ratio of the specimen gauge section. Foam nonlinear constitutive relationships, strength and failure modes along both in-plane and out-of-plane (rise) directions are obtained in different loading modes. Experimental results reveal strong transversely isotropic characteristics of foam microstructure and strength properties. Compressive damage initiation and progression prior to failure are investigated in an incremental loading–unloading experiment. To evaluate foam in-plane and out-of-plane shear strengths, a scaled shear test method is also developed. Shear loading and unloading experiments are carried out to identify the causes of observed large shear damage and failure modes. The complex damage and failure modes in H80 PVC foam under different loading modes are examined, both macroscopically and microscopically.

This paper presents the energy absorption of target materials with combinations of polyurethane (PU) foam, PU sheet, SiC inserts, and SiC plate bonded to glass fiber reinforced composite laminate backing during impact loading. SiC inserts and SiC plates are bonded as front layer to enhance energy absorption and to protect composite laminate. The composite laminates are prepared by hand lay-up process and other layers are bonded by using epoxy. Low-velocity impact is conducted by using drop mass setup, and mild steel spherical nosed impactor is used for impact testing of target in fixed boundary conditions. Energy absorption and damage are compared to the target plates when subjected to impact at different energy levels. The energy absorbed in various failure modes is analyzed for various layers of target. Failure in the case of SiC inserts is local, and the insert under the impact point is damaged. However, in the other cases, the SiC plate is damaged along with fiber failure and delamination on the composite backing laminate. It is observed that the energy absorbed by SiC plate layered target is higher than SiC inserts layered target.

In this paper, the authors present an internal state variable (ISV) cap plasticity model to provide a physical representation of inelastic mechanical behaviors of granular materials under pressure and shear conditions. The formulation is dependent on several factors: nonlinear elasticity, yield limit, stress invariants, plastic flow, and ISV hardening laws to represent various mechanical states. Constitutive equations are established based on a modified Drucker–Prager cap plasticity model to describe the mechanical densification process. To avoid potential numerical difficulties, a transition yield surface function is introduced to smooth the intersection between the failure and cap surfaces for different shapes and octahedral profiles of the shear failure yield surface. The ISV model for the test case of a linear-shaped shear failure surface with Mises octahedral profile is implemented into a finite element code. Numerical simulations using a steel metal powder are presented to demonstrate the capabilities of the ISV cap plasticity model to represent densification of a steel powder during compaction. The formulation is general enough to also apply to other powder metals and geomaterials.

The use of lightweight materials in the automotive industry for structural parts has been increasing in recent years in order to reduce the overall vehicle's weight. New innovative lighter materials are being developed nowadays to accomplish that objective. In order to keep or even increase passenger's safety, structural parts made of these materials need to withstand static and impact loads within a range of different temperatures along the vehicle's life. The effect of these conditions when joining these dissimilar lighter materials is a critical issue to be considered when designing the car's body. In this paper, the strength under real car conditions of single lap joints (SLP) made of aluminum alloy (AA) bonded to carbon fiber reinforced polymer (CFRP) adherends was studied. A new crash-resistant epoxy adhesive was used to bond these lightweight materials and an extended characterization of its cohesive properties was carried out. The single lap joints were tested at temperatures of −30, +23, and +80 °C under quasi-static and impact loading. The data obtained was used to perform simple numerical models of the single lap joints under static and impact loads. The experimental results showed an expected increase of the joints strength with the strain rate. The joints behavior was highly influenced by the adherends, especially by the aluminum yielding at high and room temperatures. Delamination of the composite was obtained at low and room temperatures, which explained the strain rate dependence of the failure load. The numerical models predicted with good accuracy the strength of the joints under both static and impact loads.

Increasing interest in using aluminum as the structural component of light-weight structures, mechanical devices, and ships necessitates further investigations on fatigue life of aluminum alloys. The investigation reported here focuses on characterizing the performance of cruciform-shaped weldments made of 5083 aluminum alloys in thickness of 9.53 mm (3/8 in.) under constant, random, and bilevel amplitude loadings. The results are presented as S/N curves that show cyclic stress amplitude versus the number of cycles to failure. Statistical procedures show good agreements between test results and predicted fatigue life of aluminum weldments. Moreover, the results are compared to the results obtained from previous experiments on aluminum specimens with thicknesses of 12.7 mm (1/2 in.) and 6.35 mm (1/4 in.).

A new peridynamic (PD) formulation is developed for cubic polycrystalline materials. The new approach can be a good alternative to traditional techniques such as finite element method (FEM) and boundary element method (BEM). The formulation is validated by considering a polycrystal subjected to tension-loading condition and comparing the displacement field obtained from both PDs and FEM. Both static and dynamic loading conditions for initially damaged and undamaged structures are considered and the results of plane stress and plane strain configurations are compared. Finally, the effect of grain boundary strength, grain size, fracture toughness, and grain orientation on time-to-failure, crack speed, fracture behavior, and fracture morphology are investigated and the expected transgranular and intergranular failure modes are successfully captured. To the best of the authors' knowledge, this is the first time that a PD material model for cubic crystals is given in detail.

A relatively low-temperature carbon nanotube (CNT) synthesis technique, graphitic structure by design (GSD), was utilized to grow CNTs over glass fibers. Composite laminates based on the hybrid CNTs–glass fibers were fabricated and examined for their electromagnetic interfering (EMI) shielding effectiveness (SE), in-plane and out-of-plane electrical conductivities and mechanical properties. Despite degrading the strength and strain-to-failure, improvements in the elastic modulus, electrical conductivities, and EMI SE of the glass fiber reinforced polymer (GFRP) composites were observed.

Microstructurally informed macroscopic impact response of a high-manganese austenitic steel was modeled through incorporation of the viscoplastic self-consistent (VPSC) crystal plasticity model into the ansys ls-dyna nonlinear explicit finite-element (FE) frame. Voce hardening flow rule, capable of modeling plastic anisotropy in microstructures, was utilized in the VPSC crystal plasticity model to predict the micromechanical response of the material, which was calibrated based on experimentally measured quasi-static uniaxial tensile deformation response and initially measured textures. Specifically, hiring calibrated Voce parameters in VPSC, a modified material response was predicted employing local velocity gradient tensors obtained from the initial FE analyses as a new boundary condition for loading state. The updated micromechanical response of the material was then integrated into the macroscale material model by calibrating the Johnson–Cook (JC) constitutive relationship and the corresponding damage parameters. Consequently, we demonstrate the role of geometrically necessary multi-axial stress state for proper modeling of the impact response of polycrystalline metals and validate the presented approach by experimentally and numerically analyzing the deformation response of the Hadfield steel (HS) under impact loading.

In this study, a new magnesium (Mg) alloy containing 0.4% Ce was developed using the technique of disintegrated melt deposition followed by hot extrusion. The tensile and compressive properties of the developed Mg–0.4Ce alloy were investigated before and after heat treatment with an intention of understanding the influence of cerium on the deformation and corrosion of magnesium. Interestingly, cerium addition has enhanced the strength (by 182% and 118%) as well as the elongation to failure of Mg (by 93% and 8%) under both tensile and compressive loadings, respectively. After heat treatment, under compression, the Mg–0.4Ce(S) alloy exhibited extensive plastic deformation which was 80% higher than that of the as-extruded condition. Considering the tensile and compressive flow curves, the as-extruded Mg–0.4Ce and the heat treated Mg–0.4Ce(S) alloys exhibited variation in the nature and shape of the curves which indicates a disparity in the tensile and compressive deformation behavior. Hence, these tensile and compressive deformation mechanisms were studied in detail for both as-extruded as well as heat treated alloys with the aid of microstructural characterization techniques (scanning electron microscope (SEM), transmission electron microscope (TEM), selective area diffraction (SAD), and X-ray diffraction (XRD) analysis. Furthermore, results of immersion tests of both as-extruded and heat treated alloys revealed an improved corrosion resistance (by ∼3 times in terms of % weight loss) in heat treated state vis-a-vis the as-extruded state.

This study was conducted to investigate the stress, strain, and strength ratio distributions in the composite flywheel rotor for high-energy density storage applications. Symmetric laminate design was used to avoid shear and extension–bending coupling and to minimize torsion coupling. The rotor studied consists of four anisotropic unidirectional plies. The continuity conditions of the radial stresses and displacements between plies were used to obtain a local stiffness matrix for each ply and develop the global stiffness matrix for the rotor due to the different ply orientations. The Tsai–Wu three-dimensional (3D) quadratic failure criterion in stress space was used to evaluate the strength ratio of the rings. Analysis was done for ply orientations between [±5 deg] S and [±85 deg] S . Three specific ply orientations were reported for discussion. The results show how the stress, strain, and safe rotational speed of the flywheel change as the ply orientations are varied. The circumferential stress was found to be the dominant stress. It increases as the ply angle increased in the circumferential direction while the axial stress decreased. Due to significant improvements in composite materials and technology, the results from this study will contribute to further development of the flywheel which has recently re-emerged as a promising application for energy storage.

Gas tungsten arc (GTA) welding of Ti alloy Ti6Al4V is carried out in vertical-up direction. Weld parameters for the Ti6Al4V alloy were developed using Ti6Al4V (ELI) alloy filler wire and following two pass welding process. X-ray radiography was carried out to ensure the soundness of the weld. Tensile strength of the weldment was evaluated and microstructure characterization was carried out. It is observed that specimens mostly failed in heat affected zone (HAZ) area toward parent material with occasional failure at the weld. Microhardness mapping and microstructural analysis revealed HAZ as the weaker zone, where dissolution of α and formation of β have initiated. Due to moderate cooling rate at this zone, microstructure remained α–β , whereas weld microstructure is found to have martensitic α ′ resulting in an increase in the microhardness. Yield strength (YS) of weldment is found to be more than 90% of parent metal (PM) and also reduction in elongation is noted. Fractography observations of failed specimen away from the weld show mainly ductile failure. Weldment failure fractography shows the presence of dendrite indicating failure near the fusion line.

The contemporary approach of utilizing uniaxial tests data for prediction of failure in composite materials, that are anisotropic and inhomogeneous under multi-axial loading has witnessed to be inadequate. Consequently, biaxial and multi-axial tests appeared obligatory to enhance our perceptive about the performance of these complex materials. The present paper is focused on selection of suitable geometry for the test coupons required under biaxial loading. The specimen with (1) uniform stress about the gauge section, (2) failure in the gauge section, and (3) preventing the undesired nonuniform strain distribution due to stress concentration is selected. Finite element analysis (FEA) is implemented on the cross shape (╬) specimen with different undercuts and holes with different stress ratios ranging from ( σ x : σ y ) = 1:1, 1:0.5, 1:0.75, 1:−0.25, 1:−0.5, and 1:−0.75 are applied on the four edges of the specimen for selection of suitable geometry.

Fatigue analysis of a simply supported composite plate with laminate configuration of [0n/90n]s under central patch impulse loading is presented using an analytical method. The method mainly consists of two steps, one, evaluation of vibration induced stresses for the given central patch impulse loading using modal analysis, and two, fatigue analysis using S–N curve approach, residual strength approach as well as failure function approach. The stress state in the plate was evaluated using viscous damping model as a function of time. The stress-time history was converted into block loading consisting of many sub-blocks. In the present study, the block loading consisted of four sub-blocks and a total of 175 numbers of cycles. The block loading was repeated after every 5 s. Next, fatigue analysis was carried out based on the block loading condition evaluated. Number of loading blocks for fatigue failure initiation and the location of failure were obtained. Studies were also carried out using two-dimensional (2D) finite element analysis (FEA). Number of loading blocks required to cause fatigue failure initiation under central patch impulse loading was found to be 3120 and 3170 using the analytical method and 2D FEA, respectively.