In-plane Uniaxial Compression Research Articles

Some Unfamiliar Structural Stability Aspects of Unsymmetric Laminated Composite Plates.

It is widely recognized that certain structures, when subjected to static compression, may exhibit a bifurcation point, leading to the potential occurrence of a secondary equilibrium path. Also, there is a tendency of deflection increment without a bifurcation point to occur for imperfect structures. In this paper, some relatively unknown phenomena are investigated. First, it is demonstrated that in some conditions, the linear buckling mode shape may differ from the result of geometrically nonlinear analysis. Second, a mode jumping phenomenon is described as a transition from a secondary equilibrium path to an obscure one as a tertiary equilibrium path or a second bifurcation point. In this regard, some non-square plates with unsymmetric layer arrangements (in the presence of extension-bending coupling) are subjected to a uniaxial in-plane compression. By considering the geometrically linear and nonlinear problems, the bucking modes and post-buckling behaviors, e.g., the out-of-plane displacement of the plate versus the load, are obtained by ANSYS 2023 R1 software. Through a parametric analysis, the possibility of these phenomena is investigated in detail.

Modified lap shear test for intralaminar shear failure of fiber reinforced composites

This work presents a modification of the lap shear test for application to the intralaminar shear failure of fiber reinforced composites. The proposed method involves an S-shaped double-cracked specimen loaded under uniaxial in-plane compression. The resulting loading is akin to a lap shear test but inducing intralaminar shear failure (not interlaminar). Elastic stress analysis confirms a shear dominated stress state in specimen ligament, and numerical contour-integral confirms a mode II dominance in the near tip region. Experimental results for an epoxy/carbon twill woven composite are presented, demonstrating the ease of the test method. Nonlinear quasi-ductile behavior is observed, as expected, and necessitates the use of elastoplastic fracture mechanics to interpret the fracture toughness. The estimated initiation toughness values are successfully verified via cohesive crack simulations. The presented test represents a simple and repeatable method to characterize the intralaminar shear failure of fiber-reinforced composites.

Numerical studies of the energy absorption capacities and deformation mechanisms of 2D cellular topologies

This paper investigates the energy absorption capacities of selected cellular topologies under quasi-static loading conditions. Twenty topologies with nearly identical relative densities belonging to 4 groups were examined: honeycomb, re-entrant, bioinspired and chiral. The topologies were modeled using an experimentally validated numerical ABSplus model and subsequently subjected to in-plane uniaxial compression tests. The findings revealed the topologies with the most favorable energy absorption parameters and the main deformation mechanisms. The topologies were classified by mechanism, and a parametric study of basic material properties, namely modulus of elasticity, yield stress, and ductility, was performed for a representative topology from each mechanism. The results indicated that the honeycomb group topologies were characterized by the largest average absorbed energy, and yield stress was found to have the greatest impact on energy absorption efficiency regardless of the main deformation mechanism.

Experimental and numerical study of in-plane uniaxial compression response of PU foam filled aluminum arrowhead auxetic honeycomb

PurposeAuxetics metamaterials show high performance in their specific characteristics, while the absolute stiffness and strength are much weaker due to substantial porosity. This paper aims to propose a novel auxetic honeycomb structure manufactured using selective laser melting and study the enhanced mechanical performance when subjected to in-plane compression loading.Design/methodology/approachA novel composite structure was designed and fabricated on the basis of an arrowhead auxetic honeycomb and filled with polyurethane foam. The deformation mechanism and mechanical responses of the structure with different structural parameters were investigated experimentally and numerically. With the verified simulation models, the effects of parameters on compression strength and energy absorption characteristics were further discussed through parametric analysis.FindingsA good agreement was achieved between the experimental and simulation results, showing an evidently enhanced compression strength and energy absorption capacity. The interaction between the auxetic honeycomb and foam reveals to exploit a reinforcement effect on the compression performance. The parametric analysis indicates that the composite with smaller included angel and higher foam density exhibits higher plateau stress and better specific energy absorption, while increasing strut thickness is undesirable for high energy absorption efficiency.Originality/valueThe results of this study served to demonstrate an enhanced mechanical performance for the foam filled auxetic honeycomb, which is expected to be exploited with applications in aerospace, automobile, civil engineering and protective devices. The findings of this study can provide numerical and experimental references for the design of structural parameters.

Compression-Induced Dehydrogenation of Graphene: Insight from Simulations

In this work, we reported the results of systematic studies of various configurations of chemically adsorbed hydrogen atoms on the surface of corrugated graphene induced by in-plane uniaxial compression. Different magnitudes of the substrate corrugations have been considered. Results of the calculations demonstrate the visible difference in the electronic structure of corrugated non-hydrogenated graphene, contrary to the absence of a visible effect of corrugation of graphene. The reciprocal effect of corrugation and local hydrogenation on the permeation of protons (H+) throughout the graphene membrane is also discussed. Results of the periodic DFT calculations demonstrate that binding energy between graphene and large hydrogen clusters drastically decreases with increasing the magnitudes of the corrugation graphene substrate. A similar effect of decreasing hydrogen binding energies was also observed for corrugated graphane. The obtained results can be used to control the release of hydrogen from graphene by switching mechanical stress on and off without applying additional heat.

Numerical modelling of DMLS Ti6Al4V(ELI) polygon structures

Numerical modelling is particularly advantageous for analysing structures with complex behaviour. It is used to predict the mechanical properties of structures. Analytical modelling, on the contrary, has limited capacity for predicting the behaviour, particularly of structures, because it is based on mathematical equations that do not always exactly represent the geometry of the model. In such cases, numerical modelling is used for predicting structural bending, axial deformation, and buckling behaviour. This study documents numerical modelling of different types of polygon structures. To reduce computation costs, planar and extruded Ti6Al4V(ELI) hexagonal shell structures were used to predict stresses in the out-of-plane and in-plane directions. This was followed by numerical modelling of different types of planar polygon structures to predict their load-bearing capacity and stiffness. Thereafter, the hexagonal polygon was subjected to out-of-plane and in-plane uniaxial compression loads. This was done to compare the bending and buckling behaviour of finite element (FE) models to analytical models. The numerical and analytical results were then compared to determine how the ratio (t/L) of the wall thickness (t) and length of the polygon members (L) influenced the effective stiffness of the hexagonal polygon. The triangular polygon was seen to have the greatest load-bearing capacity and stiffness of all polygons that were modelled. The hexagonal model was observed to generate deformations due to compression, similar to those reported in literature. The critical buckling loads for the analytical honeycomb (HC) models were found to be below the yield stress for (1-, 1.125-, and 1.25-mm wall thicknesses) and above the yield stress for all FE HC models, respectively. The effective stiffness of the HC models were observed to increase with the increasing (t/L) ratio, for both the numerical and analytical models.

Hierarchy of Lifshitz Transitions in the Surface Electronic Structure of Sr_{2}RuO_{4} under Uniaxial Compression.

We report the evolution of the electronic structure at the surface of the layered perovskite Sr_{2}RuO_{4} under large in-plane uniaxial compression, leading to anisotropic B_{1g} strains of ϵ_{xx}-ϵ_{yy}=-0.9±0.1%. From angle-resolved photoemission, we show how this drives a sequence of Lifshitz transitions, reshaping the low-energy electronic structure and the rich spectrum of van Hove singularities that the surface layer of Sr_{2}RuO_{4} hosts. From comparison to tight-binding modeling, we find that the strain is accommodated predominantly by bond-length changes rather than modifications of octahedral tilt and rotation angles. Our study sheds new light on the nature of structural distortions at oxide surfaces, and how targeted control of these can be used to tune density of state singularities to the Fermi level, in turn paving the way to the possible realization of rich collective states at the Sr_{2}RuO_{4} surface.

Development of a unified design buckling curve for fibre reinforced polymer plates subjected to in-plane uniaxial and uniform compression

Presented are 24 non-dimensional buckling curves to estimate the strengths of Fibre-Reinforced Polymer (FRP) square plates having four simply supported edges and subjected to in-plane uniaxial and uniform in-plane compression. The curves are constructed by the authors from a parametric numerical analysis using ABAQUS® software with changing variables for: material properties; initial geometrical imperfections; laminate lay-ups; and plate thicknesses. These strength curves express relationships for the buckling reduction factor with plate slenderness, and account for post-buckling strength. We observe that regardless of the laminate lay-up (except for purely unidirectional), the choice of FRP material and the magnitude of the initial geometrical imperfection the predicted buckling reduction factors display a meaningful correlation with plate slenderness. Presented is a proposed unified buckling design curve, defined as the lower bound to 18 of the 24 ABAQUS®-generated buckling curves. This new curve is benchmarked by the authors against experimental test results extracted from the literature and it is found that there is a reasonable agreement. The authors recommend that the proposed buckling design curve has the potential to be introduced into structural design standards as a procedure to design the buckling strengths of FRP plates.

Mechanical Properties of Semi-Regular Lattices

The mechanical properties of seven semi-regular lattices were derived analytically for in-plane uniaxial compression and shear. These analytical expressions were then validated using Finite Element simulations. Our analysis showed that one topology is stretching-dominated; two are stretching-dominated in compression but bending-dominated in shear; and four are bending-dominated. To assess their potential, the properties of these seven semi-regular topologies were compared to regular lattices. We found the elastic buckling strength of the stretching-dominated semi-regular tessellation to be 43% higher than a regular triangular lattice. In addition, three of the four bending-dominated semi-regular topologies had a higher elastic modulus than a regular hexagonal lattice. In fact, one of these bending-dominated topologies was 85% stiffer and 11% stronger than a hexagonal lattice. This topology would be ideal for applications requiring a high stiffness and high energy absorption.

Strong strain gradients and phase coexistence at the metal-insulator transition in VO2 epitaxial films

The proximity of a thermodynamic triple point and the formation of transient metastable phases may result in complex phase and microstructural trajectories across the metal-insulator transition in strained VO2 films. A detailed analysis using in-situ synchrotron X-ray diffraction unveils subtle fingerprints of this complexity in the structure of epitaxial films. During phase transition the low-temperature monoclinic M1 phase is constrained along the {111}R planes by the coexisting high-temperature R phase domains, which remain epitaxially clamped to the substrate. This geometrical constraint induces counteracting local stresses that result in a combined tilt and uniaxial in-plane compression of M1 domains, and a concomitant anomalous cR-axis elongation. This mechanism progressively transforms the M1 phase into the transitional triclinic phase (T), and ultimately into the monoclinic M2 phase, generating strong strain and tilt gradients that remain frozen after the complete transformation of the R phase upon cooling to RT. The transformation path of VO2 films, the complex competition between stable and metastable VO2 polymorphs and its impact on the structure of the low temperature monoclinic state, provide essential insights for understanding the electronic and mechanical properties of the films at the nanoscale, as well as to control their use in functional devices.

Atomistic and continuum modeling of 3D graphene honeycombs under uniaxial in-plane compression

Using large-scale molecular dynamics (MD) simulations in conjunction with continuum modeling, the deformation behaviors of three-dimensional (3D) graphene honeycomb structures under uniaxial in-plane compression have been systematically investigated. The stress-strain responses of graphene honeycombs were found to be dependent on the loading direction, prism size and lattice orientation, but little affected by the junction type. Two critical deformation events, i.e., elastic buckling and structural collapse, were identified, with the associated local and global structural changes associated at these critical events clarified. Continuum models accounting for the effect of lattice orientation and size-dependent yielding have been developed to quantitatively predict the threshold stresses for those critical deformation events. In addition, it has been demonstrated that the overall stress-strain curve of graphene honeycomb can also be reasonably well predicted via continuum modeling, albeit deviation at large strains due to effect of junction on cell wall bending. The present study provides critical mechanistic understanding and predictive tools for optimizing and designing 3D graphene honeycombs in small-scale applications.

In-plane compression behavior of FDM-manufactured hierarchical and hybrid hierarchical hexagonal honeycombs for infrastructural safety applications

The infrastructure safety and response to the natural or man-caused calamities has always been a top consideration for any modern project. Impact energy absorption is one such area where advanced measures are being adopted to prevent any damage to the infrastructure from any impact caused by vehicles or other elements. Honeycomb structures have been primarily used in such high impact energy absorption applications. With the advent of modern additive manufacturing practices, drastic modifications to the simple honeycombs generally used are possible, thus expanding the reach and capability of these structures. In this article, in-plane uniaxial compression performance of hybrid and hierarchical hexagonal honeycombs has been studied in the context of strain energy absorption for in-plane impact such as the case of vehicle collision to the pillars of flyover or bridges. The polylactic acid (PLA) filament has been used to manufacture the honeycombs through fused deposition modeling (FDM) additive manufacturing technique. Simple hexagonal honeycombs have been studied first at low deformation speed to understand the deformation mechanics under uniaxial compression and its dependence on the unit cell dimensions and cell wall thickness. The effect of transition to the hybrid and hierarchical hexagonal honeycombs on the compression deformation has been highlighted next. While the hierarchical structures show better energy absorption capabilities and plateau stress, the hybrid hexagonal honeycombs show their high loadresistance. Dependence of the mechanical performance of such structures on the unit cell dimensions, orientation and wall thickness has also been examined through detailed experimental analysis.

Multiscale based finite element modeling for the nonlinear bending and postbuckling analyses of some noncarbon nanomaterials

Multiscale based finite element model developed in the framework of the Cauchy–Born rule is employed to investigate the nonlinear response of some noncarbon nanosheets considering geometric and material nonlinearities. The Tersoff–Brenner type interatomic potentials with newly calibrated empirical parameters are employed to model the atomic interactions. The quadratic-type Cauchy–Born rule is used to couple atomic entities with entities at the continuum scale. A four-node Kirchhoff-type finite element is used for the continuum approximation of the different nanosheets. The governing finite elemental equations are derived through the principle of minimum potential energy and Newton–Raphson method is used to linearize the nonlinear algebraic equations. The nonlinear bending response of the noncarbon nanosheets, with clamped boundary conditions, subjected to uniformly distributed and central concentrated load is reported in detail. The present results obtained from the multiscale based finite element method are also supported with molecular static simulations for some cases. The postbuckling response of the nanosheets subjected to uniaxial in-plane compression is also reported. The effect of initial strain on the central deflection of nanosheets under distributed and central point load is also investigated in detail and few interesting findings are revealed.

A detailed finite element investigation of the effects of local lateral high-velocity impacts on the ultimate strength of unstiffened steel plates subjected to uniaxial in-plane compression

In this paper, the ultimate strength of unstiffened steel plates under uniaxial in-plane compression is numerically studied considering the local lateral impact of a rigid-body impactor. The plates are made of mild steel, where its behaviour is modelled by using the Johnson-Cook material model. The material parameters of the Johnson-Cook material model calibrated by the authors were employed for predicting the behaviour of the target in order to numerically reproduce the impact tests. The value of average in-plane stress of the plates is determined accounting for the collision of rigid-body impactor with masses of 50–150 gr and velocities of 400–1200 m/s. Moreover, the effects of stress waves induced as a result of lateral impact of the rigid-body impactor on the ultimate strength of the plates under uniaxial in-plane compression are also assessed. The results indicate that the ultimate strength of the plate decreases due to stress-wave creation and thus, it is required to take that into account. Besides, it is revealed that assuming the final damaged state of the plate after being laterally impacted by the rigid-body impactor as an initial condition, does not yield a correct response when evaluating its ultimate compressive strength under uniaxial in-plane compression.

Deformation and instability of three-dimensional graphene honeycombs under in-plane compression: Atomistic simulations

While monolayer graphene is known strong and brittle, its three-dimensional (3D) scaleup to architected assemblies, such as graphene aerogels, leads to superior compressibility and resilience. 3D graphene assemblies feature nanoscale characteristic dimensions, and their constitutive mechanical behaviors arise from complex deformation modes. However, whether 3D graphene assemblies exhibit deformation mechanisms widely observed in conventional foams is unclear. Using molecular dynamics simulations, we explore the deformation and instability mechanisms in a 3D graphene honeycomb subjected to uniaxial in-plane compression. Our simulations capture the orientation-dependence of stress–strain response and deformation mode. Compression along the armchair direction causes progressive buckling and results in a structural transformation. In contrast, compression along the zigzag direction results in localized shearing. These findings demonstrate that deformation and instability mechanisms in 3D graphene honeycombs are very similar to those identified in hexagonal honeycombs at the macro-scale level, both experimentally and theoretically.

Toward development of optimum specimen designs and modeling of in-plane uniaxial compression testing of aluminum alloy 2024 and AISI 1008 steel sheet material

Tension-compression testing is commonly conducted to understand and predict springback during a stamping process. However, large strains are generally difficult to achieve during the in-plane compression portion of the test. Proper specimen design and control of frictional forces are necessary for obtaining large strains. This paper describes extensive finite element analyses (FEA) and optimization studies (Phase 1) that were conducted to calibrate the model test assembly for three different buckling modes obtained in uniaxial compression tests of aluminum alloy 2024 and American Iron and Steel Institute (AISI) 1008 steel specimens. In addition to obtaining these three buckling modes correctly, calibrated FEA model predicted forces matched measured forces reasonably well. Also, a good agreement between computed and measured stress-strain data was demonstrated for one compression experiment. In the Phase 2 optimization study, optimum specimen geometries will be developed by using these verified, optimum FEA model test assemblies in three types of compression buckling experiments.

A New Method to Investigate the Progressive Damage of Imperfect Composite Plates Under In-Plane Compressive Load

Numerous studies have been conducted for failure criteria of fiber reinforced composites.The aim of this study is to present a new computational and mathematical method to analyze theprogressive damage and failure behavior of composite plates containing initial geometric imperfectionsunder uniaxial in-plane compression load. A new methodology is presented based on collocation methodin which the interested domain is discretized with Legendre-Gauss-Lobatto nodes. In order to avoid anexcessive number of nodes, an appropriate weight coefficient is considered for each node. The method isbased on the first order shear deformation theory and small displacement theory. Several failure criteria,including Maximum stress, Hashin and Tsai-Hill, are used to predict the failure mechanisms. The stiffnessdegradation is carried out by instantaneous and complete ply degradation model. Two different types ofboundary conditions are considered in this study. The effects of thickness, initial imperfections, andboundary conditions are studied, as well. The results are compared with the previously published data.It is found that the boundary conditions have significant effects on the ultimate strength of imperfectcomposite plates.

On buckling of a thin plate on an elastomeric foundation

We study analytically the case of cylindrical buckling of a plate resting on an incompressible, elastomeric foundation, which is subjected to in-plane uniaxial compression. Our analysis differs from the classical Hetényi solution for a plate resting on a Winkler foundation in that we consider the incompressibility and the continuity of the elastomer foundation. The critical buckling force is derived in terms of the flexural rigidity and the length of the plate, and the modulus and the thickness of the elastomer foundation. The critical buckling force scales with these parameters in a different manner than in the case of a Winkler foundation. The ratio of the critical buckling load in the present problem to that predicted for its Winkler counterpart is shown to depend strongly on the lateral confinement of the elastomer foundation.

Buckling Behavior of Composite Plates with a Pre-central Circular Delamination Defect under in-Plane Uniaxial Compression

Delamination is one of the most common failure modes in composite structures. In the case of in-plane compressional loading, delamination of a layered flat structure can cause a local buckling in delaminated area which subsequently affects the overall stiffness of the initial structure. This leads to an early failure of the overall structure. Moreover, with an increase in load, the delaminated area may propagate in the post-buckling mode; and consequently, to predict this behavior, a combination of failure modes will be used to predict failure. In this work, the proposed analysis will predict the delamination shape and load carrying capacity of a composite laminated plate during delamination process in post-buckling mode. For this purpose, it is assumed that the composite laminate contains an initial circular delaminated (defected) area. The analysis is performed through a numerical scheme based on finite element method. Results show that in most cases, the onset of crack growth is affected by the first opening mode while it is well probable that during the delamination growth, the effects of other modes dominate the initial primary opening mode. Consequently, during progression of any delamination which may occur as a result of further loading, a jump in failure mode which is predicted in this analysis, may occur. Moreover, the induced results show that the stacking sequence of the delaminated composite plate has a significant effect on the delamination growth and the load carrying capacity of the overall structure.

Work principle in inelastic buckling analysis of axially compressed rectangular plates

PurposeThe purpose of this paper is to analyze the inelastic buckling of a rectangular thin flat isotropic plate subjected to uniform uniaxial in-plane compression using a work principle, a deformation plasticity theory and Taylor–Maclaurin series formulation.Design/methodology/approachThe non-loaded longitudinal edges of the rectangular plate are clamped, whereas the loaded edges are simply supported (CSCS). Total work error function is applied to Stowell’s plasticity theory in the derivation of the inelastic buckling equation. Mathematical formulation of the Taylor–Maclaurin series deflection function satisfied the boundary conditions of the CSCS rectangular plate. The critical inelastic load of the plate is then derived by applying variational principles.FindingsValues of the plate buckling coefficient are calculated using various values of moduli ratio for aspect ratios ranging from 0.1 to 1.0, in intervals of 0.1. The accuracy of the proposed technique is validated by comparing the results obtained in the present study with solutions from a previous investigation. The percentage differences in the values of the buckling coefficient ranged from −0.122 to −4.685 per cent.Originality/valueThe results indicate that the work principle approach can be used as an alternative approximate method for analyzing inelastic buckling of rectangular thin flat isotropic plates under uniform in-plane compressive loads.