Through-thickness Shear Research Articles

Investigation of the effect of anisotropy on Generalized Forming Limit Diagram

In contemporary industrial practices, various methods are employed to subject raw metal sheets to deformation in order to fabricate requisite components. These sheets exhibit a defined capacity for deformation during the forming process. Over recent decades, a plethora of experimental and numerical methodologies have emerged to ascertain these forming limits. Initially, a forming limit diagram (FLD) was devised, predicated on the phenomenon of necking, under the assumption that forming takes place under plane-stress conditions. However, in certain complex processes like hydroforming and incremental forming, necking can manifest at sites where normal and through-thickness shear stresses act upon the sheet in addition to the in-plane stresses, rendering the plane-stress assumption inadequate for predicting forming limits in such scenarios. Thus, it becomes imperative to derive a diagram that can accurately forecast forming limits in these processes. This study aims to establish a Generalized Forming Limit Diagram (GFLD) through numerical means. GFLDs were constructed utilizing two distinct yield functions, namely Von-Mises and Hill48, for isotropic and anisotropic states, respectively. The findings reveal that normal compressive stress and through-thickness shear strain augment the formability of sheet metals. Furthermore, the outcomes illustrate that accounting for anisotropy introduces variances between diagrams in some regions of the FLD curve while the discrepancies are minor within the central regions.

Vibration-induced crack tip flipping: A closer look at an unfamiliar phenomenon in pipeline failure analysis

Fracture propagation control is an essential strategy to avoid a catastrophic event involving both economic losses and environmental damage. The Dynamic Tensile Tear Test (DT3) was introduced as an alternative tool to characterise dynamic fracture behaviour of high-strength pipeline steels. Mimicking the in-service loading conditions by imposing a dynamic tensile load, the obtained fracture surfaces closely resemble those observed in full-scale pipeline burst tests. A phenomenon called Crack Tip Flipping (CTF) could also be observed in combination with the formation of Arrowhead Markings (AHMs). The mechanisms provoking these phenomena and their effect on the fracture resistance of the pipeline material have not yet been investigated with respect to pipeline failure. Therefore, a high-speed stereo DIC setup was used to study the fracture behaviour of ×70 grade pipeline steel. The DIC setup identified a mechanical out-of-plane vibration that resulted in an additional torsional loading component. Numerical models were constructed with implementation of the Modified Bai-Wierzbicki (MBW) damage model to validate the experimental observations. Imposing a vibration-induced out-of-plane component resulted in a nearly identical fracture behaviour as observed during experiments. Both the crack path and the final fracture surface could be reproduced. Based on the obtained data, it is suggested that this oscillation causes a rotation of the stress tensor controlled by the through-thickness shear component. As a result, the stress state at the crack front is oriented towards the plane of maximum shear, forming a slanted fracture surface. Notably, the additional torsion load did not affect the load-displacement curve, as the value of the effective stress remains unaffected. Consequently, the fracture resistance, computed from energy values extracted from the load-displacement curve, are not influenced by the occurrence of CTF or the formation of AHMs. Conversely, based on the discussed mechanism of CTF, its presence could indicate the conditions under which pipeline failure occurred.

Free Vibration of Rectangular Composite Cantilever Plate and Its Application in Material Degradation Assessment

Many composite cantilever plate-like structures have found engineering applications in different industries. For attaining a meaningful assessment of the plate vibration characteristics, it is important to have efficient and effective methods for determining the natural frequencies/mode shapes of composite cantilever plates. In this paper, a method formulated on the basis of the Ritz method and a simple first-order shear deformation theory (SFSDT) is presented to analyze the free vibration of thin as well as thick rectangular composite cantilever plates for determining their natural frequencies. In the SFSDT, the total deflection is the sum of two deflection components, namely, bending and through-thickness shear-deformation-induced deflections. The successful application of the Ritz method together with the SFSDT for the free vibration analysis of thick composite plates relies on the selection of two independent sets of characteristic functions for the bending and through-thickness shear-deformation-induced deflections, respectively, to satisfy the requirements for the displacement and force conditions at the fixed edge of the plate. The novelty of the proposed method is that two independent sets of characteristic functions, namely, polynomials and trigonometric functions, which satisfy the displacement and force conditions at the fixed edge have been identified and used in the variational method to construct the eigenvalue problem for extracting the modal characteristics (natural frequencies and mode shapes) of the plate. It has been shown that the uses of the selected characteristic functions can produce excellent natural frequencies for both thin and thick composite cantilever plates. Some existing theoretical and experimental natural frequencies of thin as well as thick composite plates have been used to demonstrate the accuracy of the proposed method in predicting natural frequencies. The significant effects of through-thickness shear deformation on the natural frequencies of composite cantilever plates are studied to show the merit of the present method. Finally, for illustrating the application of the proposed method in free vibration analysis, a novel procedure established on the basis of the sensitivity analysis of natural frequencies is presented to assess the material degradation of composite cantilever plates. The numerical examples have shown that fewer than 10 iterations are required in the identification process to produce a good estimation of the current value for each material constant.

A novel method for the characterization of through-thickness shear constitutive behavior of composites

This work presents a novel experimental method to characterize the through-thickness shear response for fiber-reinforced polymer composite materials. A sandwich short-beam shear specimen with a thin 0° laminated face sheet bonded with a thick 90° laminated core is proposed. A combination of a finite element model-based stress calculation and a full-field surface strain measurement in a custom sandwich specimen under bending is used in the method. An entire interlaminar shear response in the 2–3 principal material plane has been generated using a regression of FEM-calculated shear stress and DIC-measured shear strain. The measured 23-plane interlaminar shear stress–strain response was very close to the 23-plane Iosipescu test and the plate-twist shear test, but a higher ultimate shear strain was achieved. Transverse tensile failure with a 45° fracture angle originated from the transverse shear stress on the neutral surface. A full set of the three-dimensional stress–strain constitutive relations has been assessed using one short-beam-shear test method, and identical nonlinear shear stress–strain responses with distinct ultimate shear strengths have been observed in the three principal material planes for the generic FRP tape material in this work for the first time.

Rheological response of compressible SMCs under various deformation kinematics: Experimental aspects and simple modelling approach

Flow conditions during compression moulding of Sheet Moulding Compounds (SMCs) govern the microstructure and the resulting mechanical properties of composite parts. Low-density and high-fibre content SMCs were subjected to simple compression, œdometric compression and through-thickness shear loadings, using dedicated rheometers. Simple compression and œdometric compression experiments revealed the compaction behaviour of both types of SMCs. During simple compression experiments, the compaction of low-density SMCs was accompanied by in-plane elongational flow phenomena, whereas the high-fibre content SMCs exhibited compaction below a characteristic axial strain and elongation and shear above. Shear tests showed that shear stress did not vary over a wide range of shear strain while being accompanied by axial compression stress. Both SMCs exhibited a shear-thinning behaviour with compression viscosities that depended on the fibre volume fraction. Finally, a transversely isotropic tensorial model for SMCs seen as compressible materials was proposed. Its predictions are consistent with the experiments.

Evaluation of design equations for out-of-plane shear strength of deep concrete sections in nuclear power plant buildings

Reinforced concrete walls in nuclear power plant buildings, which are generally more than one-meter thick, are typically designed to resist out-of-plane shearing force using concrete resistance only, namely, through-thickness shear reinforcement is not provided. Standard ASCE 43, which addresses design of safety-related nuclear facilities in the United States, references ACI 349 for design of reinforced concrete nuclear structures and components, with exceptions as deemed necessary. The code ACI 349–13, assumes, identically to ACI 318–08 and ACI 318–14, that the nominal shear stress capacity of longitudinally reinforced concrete sections is independent of cross-section depth: an assumption not supported by data. In the last revision cycle of ASCE 43, the ACI 349–13 design equation for concrete shear stress capacity was evaluated for conformance with the performance target of the standard, namely, a 98% or higher probability of exceedance, and found to be inadequate. A correction to the ACI 349–13 equation was developed and implemented in ASCE 43–19 to account for the effects of effective depth and longitudinal reinforcement ratio on concrete shear stress capacity. In parallel with the revision of shear provisions in ASCE 43, a size-effect modification factor, λs, was introduced in ACI 318–19 to account for the reduction in concrete shear stress capacity with increasing effective depth. In this paper, the technical basis for the correction factor included in ASCE 43–19 is developed and the ACI 318–19 equation is assessed to judge whether it achieves the ASCE 43 performance target. The assessment utilized the test data of longitudinally reinforced beams assembled by Reineck and his co-workers for slender sections (ratio of shear span-to-effective depth greater than or equal to 2.4) and non-slender sections (ratio of shear span-to-effective depth less than 2.4). For slender sections, the probability of exceedance of the ASCE 43–19 (ACI 318–19) design strength is greater than 98% (99%). For non-slender sections, the exceedance probabilities are greater than 99%. Because the ACI 318–19 equation meets the ASCE 43 performance target for both slender and non-slender sections, the correction invoked in ASCE 43–19 could be retired once ACI 349 adopts the shear provisions of ACI 318–19 for longitudinally reinforced concrete.

A novel computational framework for exact stress analysis and bending behavior of sandwich panels with non-homogeneous cores

A novel computational framework is proposed for accurate stress analysis of sandwich panels with any non-homogeneous cores based on the quadrature element method (QEM). To solve the problem of inaccurate assumption of through-thickness shear strain distribution for the non-homogeneous core, existing in engineering theories, the core is modeled by a quadrature plate element. Due to the non-homogeneity of the core, however, its stiffness matrix cannot be accurately obtained by the nodal quadrature which is widely used in QEM. Therefore, an explicit formulation for an arbitrary number of nodes and nodes of any type is worked out to get an accurate stiffness matrix. Numerical solutions of sandwich panels with different cores subjected to various loads are presented. Results are verified by the conventional finite element method and existing analytical solution. It is found that the deformation and all stress components can be accurately predicted by the present method with a small number of nodes and thus the method is efficient in analyzing any type of sandwich panels under general loads and boundary conditions. The influence of power-law index and loading type on the deflection, through-thickness distributions of stresses and shear strain as well as the location of the neutral surface is analyzed. An important outcome of this investigation is that the existence and location of the neutral surface of a sandwich panel with a soft core are highly dependent on the loading conditions, which should be remarkedly noted in sandwich theories and engineering design.

A Comparative Evaluation of Third-Generation Advanced High-Strength Steels for Automotive Forming and Crash Applications.

While the third generation of advanced high-strength steels (3rd Gen AHSS) have increasingly gained attention for automotive lightweighting, it remains unclear to what extent the developed methodologies for the conventional dual-phase (DP) steels are applicable to this new class of steels. The present paper provides a comprehensive study on the constitutive, formability, tribology, and fracture behavior of three commercial 3rd Gen AHSS with an ultimate strength level ranging from 980 to 1180 MPa which are contrasted with two DP steels of the same strength levels and the 590R AHSS. The hardening response to large strain levels was determined experimentally using tensile and shear tests and then evaluated in 3D simulations of tensile tests. In general, the strain rate sensitivity of the two 3rd Gen 1180 AHSS was significantly different as one grade exhibited larger transformation-induced behavior. The in-plane formability of the three 1180 MPa steels was similar but with a stark contrast in the local formability whereas the opposite trend was observed for the 3rd Gen 980 and the DP980 steel. The forming limit curves could be accurately predicted using the experimentally measured hardening behavior and the deterministic modified Bressan–Williams through-thickness shear model or the linearized Modified Maximum Force Criterion. The resistance to sliding of the three 3rd Gen AHSS in the Twist Compression Test revealed a comparable coefficient of friction to the 590R except for the electro-galvanized 3rd Gen 1180 V1. An efficient experimental approach to fracture characterization for AHSS was developed that exploits tool contact and bending to obtain fracture strains on the surface of the specimen by suppressing necking. Miniature conical hole expansion, biaxial punch tests, and the VDA 238-100 bend test were performed to construct stress-state dependent fracture loci for use in forming and crash simulations. It is demonstrated that, the 3rd Gen 1180 V2 can potentially replace the DP980 steel in terms of both the global and local formability.

Constitutive, Formability, and Fracture Characterization of 3rd Gen AHSS with an Ultimate Tensile Strength of 1180 MPa

<div class="section abstract"><div class="htmlview paragraph">The superior formability and local ductility of the emerging class of third generation of advanced high-strength steels (3rd Gen AHSS) compared to their conventional counterparts of the same strength level offer significant advantages for automotive lightweighting and enhanced crash performance. Nevertheless, studies on the material behavior of 3rd Gen AHSS have been limited and there is some uncertainty surrounding the applicability of developed methodologies for conventional dual-phase (DP) steels to this new class of AHSS. The present paper provides a comprehensive study on the quasi-static and dynamic constitutive behavior, formability characterization and prediction, and the fracture behavior of two commercial 3rd Gen AHSS with an ultimate strength of 1180 MPa that will be contrasted with a conventional DP1180. The hardening response to large strain levels was determined experimentally using tensile and shear tests and then validated with 3-D simulations of tensile tests. In general, the strain rate sensitivity of the two 3rd Gen AHSS was significantly different as one grade exhibited larger transformation-induced behavior. The in-plane formability of the three 1180 MPa steels determined using Marciniak tests was similar but with a stark contrast in the local formability for the 3rd Gen AHSS. The forming limit curves could be accurately predicted using the experimentally measured hardening behaviour and the modified Bressan-Williams through-thickness shear model. An efficient experimental approach to fracture characterization for AHSS was developed that exploits tool contact and bending to obtain fracture strains on the surface of the specimen by suppressing necking. Miniature conical hole expansion and biaxial punch tests are used along with the VDA 238-100 bend test.</div></div>

Buckling and postbuckling behavior of shell type structures under thermo mechanical loads

The thermo mechanical buckling and post-buckling behavior of layered composite shell type structure are considered with the finite element method under the combination of temperature load and applied mechanical loads. To account for through-thickness shear deformation effects, the thermal elastic, and higher-order shear deformation theory is used in this study. The refined higher order theories, that takes into account the effect of transverse normal deformation, is used to develop discrete finite element models for the thermal buckling analysis of composite laminates. Attention in this study is focused on analyzing the temperature effects on buckling and post-buckling behavior of thin shell structural components. Special attention in this paper is focused on studying of values of the hole in curved panel on thermal buckling behavior and consequently to expend and upgrade previously conducted investigation. Using finite element method, a broader observation of the critical temperature of loss of stability depending on the size of the hole was conducted. The presented numerical results based on higher-order shear deformation theory can be used as versatile and accurate method for buckling and post-buckling analyzes of thin-walled laminated plates under thermo mechanical loads.

Through-thickness shear texture of the twin-roll cast AA6016 sheet after asymmetric rolling and its recrystallization behavior

In this study, we investigate the through-thickness shear texture F{111}<112> and r-cube {001}<110> of the AA6016 twin-roll cast sheet under asymmetric rolling (ASR) via simulation and experiments and its recrystallization behaviors after annealing at 330 °C for 60 min. ASR can be achieved by controlling the velocity ratio of the upper and lower rollers to 2.0. Finite element (FE) simulations in case of ASR are used to determine the shear strain through the sheet thickness. Polycrystal simulations are conducted based on the FE results to predict the shear texture. Subsequently, the crystallographic texture of the sheet obtained with unidirectional ASR processes is evaluated. The experimental results show that the F-texture is obtained and that the inhomogeneity was distributed. The F-texture intensity of the sample near the lower roller (sample A) was greater than that of the sample near the upper roller (sample B). The simulation results are in good agreement with the measured results. However, the simulation results obtained with respect to the r-cube texture are greater than the measured results, resulting in considerable deviation. Further, the different recrystallization behaviors of the F-oriented grains (F-grains) are determined based on the sheet thickness. The F-grains associated with sample A can be obtained based on the rolling texture contributed by continuous recrystallization, whereas those associated with sample B can be achieved via discontinuous recrystallization. A considerably inhomogeneous microstructure and texture are observed through the sheet thickness after annealing.

Texture and Microstructure Evolution During Single-Point Incremental Forming of Commercially Pure Titanium

In the present investigation, the evolution of texture and microstructure during incremental sheet forming was investigated. Hot-rolled sheets of commercially pure titanium were subjected to single-point incremental forming to obtain truncated pyramid geometries. It was observed from texture measurements that there was splitting of basal poles along the transverse direction. Moreover, a significant number of twins was observed in the deformed microstructure with the fraction of extension twins being highest compared to other variants. The crossing of deformation twins, formation of twin lamellar structure and formation of secondary extension twins within primary contraction twins were additionally observed. The state of deformation in the pyramid walls was analyzed via finite element method which in turn was used as input for carrying out crystallographic texture simulations via visco-plastic self-consistent simulations. It was observed that the state of deformation in the wall regions is plain strain compression plus through-thickness shear.

Determination of the material model and damage parameters of a carbon fiber reinforced laminated epoxy composite for high strain rate planar compression

The progressive failure of a 0°/90° laminated carbon fiber reinforced epoxy composite was modeled in LS-DYNA using the MAT_162 material model, including the strain rate, damage progression and anisotropy effects. In addition to conventional standard and non-standard tests, double-shear and Brazilian tests were applied to determine the through-thickness shear modulus and the through-thickness tensile strength of the composite, respectively. The modulus reduction and strain softening for shear and delamination parameters were calibrated by low velocity drop-weight impact tests. The rate sensitivities of the modulus and strength of in-plane and through-thickness direction were determined by the compression tests at quasi-static and high strain rates. The fidelity of the determined model parameters was finally verified in the in-plane and through-thickness direction by the 3D numerical models of the Split Hopkinson Pressure Bar compression tests. The numerical bar stresses and damage progressions modes showed acceptable correlations with those of the experiments in both directions. The composite failed both numerically and experimentally by the fiber buckling induced fiber-matrix axial splitting in the in-plane and the matrix shear fracture in the through-thickness direction.

Experimental Characterization and Deterministic Prediction of In-Plane Formability of 3rd Generation Advanced High Strength Steels

The objective of the current study is to develop a practical, deterministic approach to the prediction of the in-plane formability of two third generation advanced high-strength steels (AHSS) of 980 and 1180 MPa ultimate tensile strength using only quasi-static mechanical property data. The hardening response to large strains was experimentally measured with the use of simple shear and tensile tests and validated in tensile simulations. The process-corrected limit strains in the Nakazima and Marciniak tests were compared to various analytical Forming Limit Curve (FLC) models for in-plane stretching. It was observed that the widely-used Marciniak–Kuczynski model can adequately predict the experimental FLC in biaxial stretching but significantly underestimated the limit strains in uniaxial stretching for both third generation AHSS. The observed through-thickness shear fracture mode in biaxial stretching was reasonably well-captured by the Bressan–Williams (BW) instability model for the 1180 MPa steel. A proposed extension of the BW model to uniaxial tension by adoption of the maximum in-plane shear stress criterion (BWx model) provided superior experimental correlation relative to the zero-extension model of Hill that was too conservative. Finally, a linearized version of the modified maximum force criterion (MMFC) was proposed that markedly improved the correlation with the process-corrected FLC for in-plane stretching of AHSS. The developed framework for FLC prediction was then applied to a DP980 AHSS and an AA5182 aluminum alloy from the literature. The DP980 corroborated the observed trend for the two third generation AHSS whereas the MK and the BWx models performed best for the AA5182 with its saturation-type hardening behavior and non-quadratic yield surface.

High temperature rise dominated cracking mechanisms in ultra-ductile and tough titanium alloy

Extensive use of titanium alloys is partly hindered by a lack of ductility, strain hardening, and fracture toughness. Recently, several β-metastable titanium alloys were designed to simultaneously activate both transformation-induced plasticity and twinning-induced plasticity effects, resulting in significant improvements to their strain hardening capacity and resistance to plastic localization. Here, we report an ultra-large fracture resistance in a Ti-12Mo alloy (wt.%), that results from a high resistance to damage nucleation, with an unexpected fracture phenomenology under quasi-static loading. Necking develops at a large uniform true strain of 0.3 while fracture initiates at a true fracture strain of 1.0 by intense through-thickness shear within a thin localized shear band. Transmission electron microscopy reveals that dynamic recrystallization occurs in this band, while local partial melting is observed on the fracture surface. Shear band temperatures of 1250–2450 °C are estimated by the fusible coating method. The reported high ductility combined to the unconventional fracture process opens alternative avenues toward Ti alloys toughening.

Fundamental differences between plane strain bending and far-field plane strain tension in ductile plate failure

The objective of this paper is to investigate the ductile fracture behavior of thin metal plates under nominally plane strain conditions, with an emphasis on the differences between far-field plane strain tension and plane strain bending. Recent experimental results show that the fracture strain obtained using far-field plane strain tension tests is significantly lower than that obtained under plane strain bending conditions. Investigating the source of these differences is of critical importance for multiple industries since it affects formability, crashworthiness and ductile failure of thin metal plates. The present work provides critical insights into this issue based on the results of a detailed numerical investigation of both tests to failure, using the micro-mechanics based Gurson material model. The numerical simulations reveal many similarities between plane strain bending and far-field plane strain tension until the onset of localization. In the far-field plane strain tension case, after Considère thinning, a through-thickness shear localization occurs, followed by a micro-crack formation in the center of the plate. This is accompanied by an increase of the stress triaxiality well above the nominal plane strain tension level (i.e., ~ 0.57 for thin plates). In contrast, the absence of thinning in plane strain bending yields a stress triaxiality that equals nominal plane strain tension, which results in a significantly lower void growth rate (in reference to far-field plane strain tension). A surface instability (undulations) eventually forms on the tension side of the plate in plane strain bending, followed by multiple shear bands. The crack initiates inside the dominant shear band and propagates from the surface into the plate. These differences in the localization mechanisms and local stress states are responsible for the difference in the macroscopic fracture strain obtained under far-field plane strain tension and plane strain bending.

Elucidating the deformation modes in incremental sheet forming process: Insights from crystallographic texture, microstructure and mechanical properties

This study investigates the exact state of deformation in single point incremental forming (SPIF) and double-sided incremental forming (DSIF) techniques using experimental observations of texture evolution coupled with a multiscale simulation of the processes. The texture evolution was investigated for different sets of forming parameters such as vertical displacement, wall angle and tool diameter. It was observed that difference in crystallographic texture due to change in tool diameter and vertical displacement was marginal. However, significant difference in texture evolution was observed upon changing the wall angle. Further analysis of crystallographic texture revealed that role of through thickness shear (TTS) is limited in case of DSIF process compared to SPIF process. Numerical simulation of SPIF process via finite element method was successful in capturing the contribution from TTS in SPIF process. Based on insights obtained from finite element calculations, Visco-Plastic Self-Consistent simulations were carried out which were successful in predicting the experimental texture. Finally, the effect of different incremental forming techniques on the mechanical properties of the formed components was studied. The observed anisotropy in yield strength was explained based on the inverse of average Schmid factor. Lankford parameter and yield locus were also estimated from the experimental textures to understand the feasibility of incremental forming at different wall angles.

Influence of hornification on the physical and flexural properties of Moso bamboo

This work aims to investigate experimentally the improvements on the physical and flexural properties of Moso bamboo species (Phyllostachys pubescens) associated to the hornification phenomenon, widely used as a treatment in wood pulps or paper to reduce porosity, absorption capacity and water retention of the fibers, as well as to increase their stiffness. To accomplish this task, bamboo samples subjected up to ten wetting and drying cycles had their flexural characteristics such as stiffness, strength, neutral axis, deflection at failure and through-thickness shear modulus compared with untreated samples. The moisture content was monitored during cycles and image analysis was performed to determine the distribution of vascular bundles throughout the wall thickness of the culm’s cross-section. The experimental program showed a reduction in water retention capacity of bamboo and in the deflection at failure, as well as an increment in the modulus of elasticity up to 70% after treatment. The tests also reveal a major influence of shear deformation on the overall deflection and appropriate strain measurement techniques must be used for a more accurate moduli determination. Finally, a simplified micromechanical approach was used along with fiber content distribution to estimate the influence of hornification on the moduli under compression and tension of the constituents.

Numerical study on through thickness shear capacity of insulated sandwich panels

In the world with ever decreasing natural resources and ever increasing need for structures along with global warming compel us to go for a less consuming and more environment friendly approach one of such is wall panel construction using precast sandwich panels. Precast concrete sandwich panels (PCSP) are as name suggests a type of precast wall panels with an insulated core sandwiched between two wire mesh reinforced concrete wythes. The core can be of any insulated material, in this study the core material used is Expanded Polystyrene (EPS). These panels can be used as both wall panels and roof panels. The two wythes are associated by the shear connectors through the EPS centre for transference shear forces (hence called as through-thickness shear) between the wythes and accomplishing composite activity in the panels. The shear connector that is considered for this study is a discreet truss shaped shear connector that are proven to be effective by previous experimental studies. Though various experimental studies are conducted in those panels the numerical study in this is scanty. In this paper the numerical study is conducted for the through thickness shear capacity of the sandwich panels using ABAQUS-CAE software (Finite Element Analysis software). The parameters varied in this numerical study include the effect of absence of EPS core and thickness of the EPS core. From the numerical model the stress strain relationship along with the load deflection curves are plotted and the results are discussed. The results from the numerical studies are similar to that of the experimental studies and are compared.

Secondary buckling and failure behaviors of composite sandwich panels with weak and strong cores under in-plane shear loading

The secondary buckling and failure behaviors of composite sandwich panels (CSPs) subjected to in-plane shear loading are studied via a self-developed quasi-conforming finite element method. The influences of key material and geometry parameters on postbuckling and failure behaviors are investigated. Numerical results show that (1) postbuckling failure is dominated by the ratio of two strengths, i.e. the through-thickness shear strength of the core and the transverse tensile strength of the lamina. In addition, two constant thresholds for this strength ratio exist in the relationship between the load bearing capacity of CSPs and the ratio, which can be used to define “weak” or “strong” core and the status of postbuckling load bearing capacity (PLBC); (2) local failures of the core and face sheets (FSs) can lead to a drastic decrease in the local stiffness of CSPs, a singularity of the tangent stiffness matrix and the occurrence of secondary bucklings of CSPs; (3) secondary bifurcation identification, branch switching and convergence improvement are all necessary to obtain reasonable paths during the path-following.