In-plane Compression Research Articles

Energy absorption analysis of origami structures based on small number of samples using conditional GAN

Origami-inspired metamaterials are increasingly being applied to the fields of science and engineering owing to their unique mechanical characteristics. Geometric and material arrangements of the panels and creases can lead to different mechanical properties of origami structures, such as energy absorption and multi-stability. The actual folding processes of the origami structures usually include crease rotation and panel deformation. However, the traditional analytical or empirical solutions based on rigid folding assumptions cannot sufficiently reflect the folding process precisely. Finite element analysis can provide detailed origami folding information, but it is a highly time-consuming cycle, including modeling and computing. Typically, conventional data-driven approaches necessitate a considerable amount of data samples to analyze the energy absorption of origami structures. The unavailability of extensive datasets poses a major impediment in employing data-driven methods to explore the authentic behavior of origami structures. Based on the situations above, a new data-driven framework with conditional generative adversarial networks with tabular data (CTGAN) is proposed in this study. To verify the feasibility of the framework, two study cases are presented herein: a Miura-ori structure in-plane quasi-static compression and the square-twist (Type 1) folding process. Energy absorption properties are predicted accurately and efficiently by the framework based on small number of samples, which are highly consistent with predicted results based on a large dataset. The framework not only provides a promising solution for energy absorption analysis of origami structures but also overcomes the bottlenecks (small number of sample datasets and a mixture of data types) associated with machine learning methods in origami structure area.

Fracture characteristics and in-situ damage mechanism of PIP-C/SiC composites to various temperatures and loading velocities

C/SiC composites prepared by polymer infiltration and pyrolysis (PIP) are among the most promising materials for application in ultrahigh-temperature conditions. However, the mechanical properties and damage mechanisms of PIP-C/SiC composites at different loading velocities and temperatures have not been systematically studied. In this study, in-plane compression, bending, and in-plane shear experiments were systematically performed at different loading velocities and temperatures in an inert atmosphere. The ultimate strengths of the PIP-C/SiC composite were determined under different conditions, and the failure modes were revealed. In addition, in-situ X-ray microtomography tension experiments were conducted to study the failure mechanism of the PIP-C/SiC composite. The results showed that the ultimate strengths were considerably affected by the temperature and loading velocity, and the failure modes were dependent on experimental types. The fracture location of the PIP-C/SiC composite is affected by the defect. And the direction of crack propagation is toward the existing cracks and voids.

Study of the effect of strain rate on the in-plane shear and transverse compression response of a composite ply using computational micromechanics

The use of composite materials for structures subjected to impacts requires a deep understanding about the dynamic behaviour of the material. To this end, a physically-based computational micromechanics simulation tool has been developed to predict failure initiation in a composite ply over a wide range of strain rates. The computational micromechanics framework incorporates constitutive models for the fibre, matrix and fibre-matrix interface, which are partly calibrated with novel micromechanical testing techniques. The simulation tool was applied to two matrix-dominated deformation modes of the ply: transverse compression and in-plane shear. The comparison of simulation and experimental results at coupon level have revealed a change in failure initiation mechanism of the composite ply with strain rate, which was then corroborated through observation of the fracture surfaces on the samples.

Ultimate Shear Strength of Pitted Plates with Crack Using Finite Element Method

_ Ultimate strength of thin steel plates was studied under shear loading when pitting corrosion and cracking occur simultaneously. Nonlinear finite element method was used and the effects of different geometrical parameters, such as crack position, crack length, pit depth, pit diameter, number of the pits, and the inclination angle of the crack, were investigated. It was found that the degree of the pitting (DOP) significantly reduces the ultimate shear strength of the pitted plates when the corrosion is low. For high amount of corrosion, the reduction of the ultimate shear strength remains the same regardless of the amount of the DOP. In plates with short cracks, the crack length has no influence on the reduction of the ultimate shear strength. Also, it was found that the position of the crack is more effective than the length of the crack on the reduction of the ultimate shear strength of the cracked plates. In the cracked-pitted plates, there was no interaction between crack and pit for extremes value of DOP. For low value of DOP, the ultimate shear strength of the cracked-pitted plate was the same as the cracked plate, and for large value of DOP, it is the same as pitted plate. Introduction According to a study performed between 2002 and 2008 by American Bureau of Shipping (ABS) (“Review of Current Practices of Fracture” 2012), majority of reported fractures of the ships were structural failures, such as weld defect, buckling, fracture, and cracking. Cracks and corrosion are two more common defects, which are the main reasons of the failure of the aged steel structures. Plates and stiffened plates are the main structural elements in many structures, including airplanes, bridges, offshore structures, and ships. Ultimate strength evaluation of these structural elements is crucial for rational design of structures, such as Load Resistance Factor Design (LRFD) methods in civil engineering and Ultimate Strength (UTS) evaluation in ship structure. Many studies are carried out to evaluate ultimate strength of intact and damaged plates/ stiffened plates under in-plane compressive stress. Ranji (2012) studied ultimate strength of plate with general corrosion under in-plane compression. He proposed a spectrum for random generation of corroded surface and ultimate strength of corroded plate was evaluated using computer code ANSYS. Ranji and Zarookian (2015) analyzed ultimate strength of cracked stiffened plates with cracks having different stiffeners numerically.

Strength of mortar reinforced with geogrid

The iron in ferrocement is susceptible to corrosion when exposed to severe environmental conditions, use of an alternate non-corrosive mesh type reinforcement is more appropriate and suggested in future construction. In this study, polypropylene geogrids were used as the reinforcement in mortar. Study deals with the strength characteristics of mortar reinforced with geogrid. Biaxial geogrids have high tensile strength in two directions and this property can be beneficially used in mortar and concrete. The mortar specimens containing with and without polypropylene geogrid panels were tested. In-plane tension, in-plane compression and flexure tests were conducted. The effect of number of layers and orientation of geogrid was investigated. A total of 96 specimens were tested in the study. From the experimental results, geogrid reinforcement was found to be useful to enhance the unidirectional tensile strength and flexural strength of the mortar. Variations in the number of layers have a significant effect on tensile strength of composite. While in case of flexural strength, increasing the number of layers beyond a limit has negligible effect. The test results showed that tensile strength and flexural strength of composite is influenced by the orientation of geogrid. The tensile stress and flexure stress values of specimens were compared with theoretical values based on Voigt model. The results were comparable and hence validated.

Effects of different joint wall lengths on in-plane compression properties of 3D braided jute/epoxy composite honeycombs

To comply with the trend in the development of engineering materials towards lightweight, high strength, eco-friendly, sustainable, and multi-functional, a three-dimensional braided integrated composite honeycomb is designed. The effects of geometrical parameters particularly joint wall lengths on the in-plane mechanical behavior of the honeycombs were investigated. The results show that the in-plane mechanical properties are related to the number of cell walls, and the angle between the cell wall and the loading direction. Increasing the number of cell rows to double and triple at similar areal density lead to an improvement of the maximum load up to 2.5, and 3.8 times, respectively. Similarly, the total absorbed strain energy increased up to 2.6 and 5.9 times, respectively. The displacement at the maximum load is increased by 1.6 and 2.7 times as a result of increasing the cell row number. The total absorbed strain energy increased to 1.7 and 1.3 times, respectively. The failure angle of the 3D braided composite honeycomb is about 4°–7°. This investigation presents the geometrical factors of a 3D braided composite honeycomb can be further designed and optimized, but it also provides a reference for the development and design of a new composite honeycomb.

In-plane compressive response of composite sandwich panels with local-tight honeycomb cores

In the present study, honeycomb cores with periodic tight zones were proposed for carbon-fiber and aluminum-honeycomb sandwich panels by flattening hexagon-shaped cells of honeycomb walls. In-plane compression tests were performed for sandwich panels with three types of local-tight honeycomb cores to evaluate the effects of the local-tight configurations on mechanical properties and failure modes. Experimental results indicated that the mechanical properties of sandwich specimens were effectively increased by using the proposed local-tight honeycomb cores. In particular, the specific energy absorption of sandwich specimens with a local-orthogonal-tight core was increased by 400.46%. In addition, Digital Image Correlation (DIC) technique was employed to further investigate the compressive behaviors of the sandwich specimens with and without local-orthogonal-tight honeycomb cores. The experimental measurements and detailed DIC observations indicated that the local-orthogonal-tight honeycomb core sandwich structures, which provided improved load transferring paths and reduced mismatch between the high-stiffness face sheets and low-stiffness core, exhibited progressive crushing failure modes.

In-plane compression performance of additively manufactured honeycomb structures: a review of influencing factors and optimisation techniques

PurposeHoneycombs enjoy wide use in various engineering applications. The emergence of additive manufacturing (AM) as a method of customisable of parts has enabled the reinvention of the honeycomb structure. However, research on in-plane compressive performance of both classical and new types of honeycombs fabricated via AM is still ongoing. Several important findings have emerged over the past years, with significance for the AM community and a review is considered necessary and timely. This paper aims to review the in-plane compressive performance of AM honeycomb structures.Design/methodology/approachThis paper provides a state-of-the-art review focussing on the in-plane compressive performance of AM honeycomb structures, covering both polymers and metals. Recently published studies, over the past six years, have been reviewed under the specific theme of in-plane compression properties.FindingsThe key factors influencing the AM honeycombs' in-plane compressive performance are identified, namely the geometrical features, such as topology shape, cell wall thickness, cell size and manufacturing parameters. Moreover, the techniques and configurations commonly used for geometry optimisation toward improving mechanical performance are discussed in detail. Current AM limitations applicable to AM honeycomb structures are identified and potential future directions are also discussed in this paper.Originality/valueThis work evaluates critically the primary results and findings from the published research literature associated with the in-plane compressive mechanical performance of AM honeycombs.

In-plane compression behavior of a novel 3D auxetic honeycomb

The star-triangular honeycomb (STH) has a unique deformation mode and mechanical properties, especially under low-velocity impact load. This study proposes a novel 3DSTH based on 2DSTH. 3DSTH specimens were manufactured by the 3D printing process, and quasi-static compressive tests were implemented to verify the reliability of the established finite element model. Numerical results show that 3DSTH exhibits a typical negative Poisson’s ratio effect under in-plane compression, and the cells near the platens bend and collapse in the out-of-plane direction. The theoretical analytical formulas of elastic modulus and Poisson's ratio were derived according to the deformation mechanism of the typical cell. The theoretical prediction results match the numerical simulation results accurately. In addition, the parameter analysis shows that the elastic modulus decreases firstly and then increases with the increase in the inclined angle, showing a quadratic parabolic relationship. However, the Poisson’s ratio only increases monotonically with the increase in the inclined angle. Subsequently, the angle and thickness gradients of 3DSTH with different distribution patterns were constructed. The influences of gradient distribution on deformation mode and energy-absorbing characteristics of 3DSTH were studied by performing a comparative analysis. The bidirectional gradient distribution is more conducive to improving the deformation stability and energy absorption characteristics of 3DSTH than the unidirectional gradient distribution. Moreover, 3DSTH exhibits more excellent deformation mode and energy absorption characteristics, approximately 25.45% higher than that of 2DSTH with the same geometric parameters. This study is mainly expected to create some new ideas for the design of the auxetic structure.

Experimental study and modeling analysis of planar compression of composite corrugated, lattice and honeycomb sandwich plates

Experimental study and modeling analysis of planar compression of composite corrugated, lattice and honeycomb sandwich plates

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.

Calibration of strapdown magnetic vector measurement systems based on a plane compression method

The strapdown magnetic vector measurement system, which can measure the magnetic vector and the attitude of a magnetometer simultaneously, has wide applications in geophysical prospecting, etc. Calibration of systematic errors, including magnetometer errors and misalignment errors, is essential for this system. Traditional methods calibrate these two errors separately, with the problem of cumbersome steps and being dependent on special data acquisition methods, such as rotation. An original method that combines a plane compression method with an ellipsoid fitting method is proposed in this paper, which can simultaneously complete the calibration calculation of magnetometer error and misalignment error in one experiment. The calculation can be performed using the spatial scatter point data required by the traditional attitude-independent magnetometer calibration method, and no additional mechanical equipment is required. A mathematical analysis of this method is performed to study the elements decreasing the measurement accuracy of the system, and numerical simulation and field experiments are performed to validate the analysis. The results indicate that the method can contribute to the accuracy improvement of magnetic vector measurement systems.

Energy Absorption of 3D Printed ABS and TPU Multimaterial Honeycomb Structures.

Advances in multimaterial 3D printing are enabling the construction of advantageous engineering structures that benefit from material synergies. Cellular structures, such as honeycombs, provide high-energy absorption to weight ratios that could benefit from multimaterial strategies to improve the safety and performance of engineered systems. In this study, we investigate the energy absorption for honeycombs with square and hexagonal unit cells constructed from acrylonitrile butadiene styrene (ABS) and thermoplastic polyurethane (TPU). Honeycombs were fabricated and tested for out-of-plane and in-plane compression using ABS, TPU, and a combination of ABS with a central TPU band of tunable height. Out-of-plane energy absorption for square honeycombs increased from 2.2 kN·mm for TPU samples to 11.5 kN·mm for ABS samples and energy absorption of hexagonal honeycombs increased from 2.9 to 15.1 kN·mm as proportions of TPU/ABS were altered. In-plane loading demonstrated a sequential collapse of unit cell rows in square honeycombs with energy absorption of 0.1 to 2.6 kN·mm and a gradual failure of hexagonal honeycombs with energy absorption of 0.6 to 2.0 kN·mm. These results demonstrate how multimaterial combinations affect honeycomb compressive response by highlighting their benefits for controlled energy absorption and deformation for tunable performance in diverse engineering applications.

An Approximately Isotropic Origami Honeycomb Structure and Its Energy Absorption Behaviors

Honeycomb structures have a wide range of applications owing to their light weight and promising energy absorption features. However, a conventional honeycomb structure is designed to absorb impact energy only in the out-of-plane direction and demonstrates unsatisfactory performance when the impact energy originates from a different direction. In this study, we proposed an origami honeycomb structure with the aim of providing an approximately isotropic energy absorption performance. The structure was created by folding a conventional honeycomb structure based on the Miura origami pattern, and it was investigated using both numerical and experimental approaches. Investigations of the structural behaviors under both out-of-plane and in-plane compressions were conducted, and the results revealed significantly different deformation modes in comparison with those of a conventional honeycomb structure. To determine the influences of geometries, we conducted a series of numerical studies, considering various structural parameters, and analyzed the response surface of the mean stress in three directions. Based on the numerical and experimental results, a parameter indicating the approximate isotropy of the origami honeycomb structure was introduced. The proposed structure is promising for absorbing energy from any direction and has potential applications in future metamaterial design work.

Wrinkles, Ridges, Miura-Ori, and Moiré Patterns in MoSe2 Using Neural Networks.

Effects of lateral compression on out-of-plane deformation of two-dimensional MoSe2 layers are investigated. A MoSe2 monolayer develops periodic wrinkles under uniaxial compression and Miura-Ori patterns under biaxial compression. When a flat MoSe2 monolayer is placed on top of a wrinkled MoSe2 layer, the van der Waals (vdW) interaction transforms wrinkles into ridges and generates mixed 2H and 1T phases and chain-like defects. Under a biaxial strain, the vdW interaction induces regions of Miura-Ori patterns in bilayers. Strained systems analyzed using a convolutional neural network show that the compressed system consists of semiconducting 2H and metallic 1T phases. The energetics, mechanical response, defect structure, and dynamics are analyzed as bilayers undergo wrinkle-ridge transformations under uniaxial compression and moiré transformations under biaxial compression. Our results indicate that in-plane compression can induce self-assembly of out-of-plane metasurfaces with controllable semiconducting and metallic phases and moiré patterns with unique optoelectronic properties.

Discerning perturbed assembly of lipids in a model membrane in presence of violacein: Effects of membrane hydrophobicity

For the lack of effective antibiotics towards antibiotic resisting bacteria, it is required to discover new antibiotics and to understand their antimicrobial mechanism. Violacein is a violet pigment found in several gram-negative bacteria possessing antimicrobial properties to gram-positive bacteria. This present article investigates the insertion ability of this molecule into a model membrane composed of zwitterionic phospholipids. Thermodynamic characterization of lipid monolayers in the presence of violacein was carried out using a single lipid layer formed at air-water interface. The molecule inserts into the layer altering the area occupied by each lipid and the in-plane compressibility of the film. This insertion increases with the hydrophobic chain length of the lipid. The perturbed self-assembly of lipids in a bilayer is quantified using a lipid multilayer system applying the X-ray reflectivity technique. The electron density profile from the reflectivity data shows that the molecule inserts into the fluid phase creating a relatively ordered chain conformation. Further, the insertion into the gel phase is observed to increase with the increased thickness of the hydrophobic core of a bilayer.

Effect of openings on the behaviour of rammed earth structures under quasi-static loading

Rammed earth (RE) is a centuries-old construction technique that uses renewable resources found in the surrounding environment. As for concrete or timber houses, doors and windows are mandatory. Until date, the effect of openings on the mechanical behaviour of RE structures has received little attention. The primary contribution of this research is to assess the impact of opening on the behaviour of RE structures. A three-dimensional finite element models of RE walls were developed and calibrated against three experimental tests by Lilley and Robinson (1995). In the experimental study, RE walls with the geometrical dimensions 2285 mm × 1220 mm × 305 mm (length × height × thickness) were constructed from unstabilized soil and evaluated under in-plane compression loading. The considered walls have two types of openings: arch-type and rectangular shape. The numerical results obtained through non-linear finite element method analysis demonstrate the pertinence of the proposed model for quantifying bearing capacity and failure modes. Using the verified numerical model, a parametric study was carried out to investigate the effects of material characteristics, the geometrical characteristics of the opening and finally the improvement options using lintel reinforcements.

Multi-objective bulk scale optimisation of an auxetic structure to enhance protection performance

This paper aims to optimise a bulk scale design of a novel auxetic structure, the hourglass structure (HGS), through a multi-objective optimisation model to improve its protection performance. A 3D numerical model of the HGS under an in-plane quasi-static compression was developed and validated with experimental results. Based on the validated numerical model, a series of numerical analyses were conducted by automating the HGS design process with randomly generated design variables. The automated numerical analyses built a dataset of the selected protective performance indicators (namely, peak elastic stress, plateau stress, and energy absorption capacity). Then, the dataset was used to develop a high-accuracy surrogate model using a radial basis function (RBF) neural network. Afterward, the Pareto optimal solutions were searched with the non-dominated sorting genetic algorithm (NSGA-II). The best compromise design out of the Pareto optimal set was determined with the ideal point method. The performance of the optimum design was simulated under both quasi-static and blast loadings to comprehensively explore the protective performance. In addition, a correlation matrix was constructed to investigate the effects of each design parameter on the protective performance indicators quantitatively. The results showed that the obtained optimum design outperformed the baseline structure under both quasi-static and blast loadings. The optimum HGS design displayed a higher and more stable negative Poisson’s ratio along with two deformation modes leading to two plateau stress levels. The optimised HGS design is applicable as the core of high-performance protective sandwich structures.

Type I size effect and failure behavior of woven composites under biaxial flexure

This study presents an experimental investigation into the failure and size effect exhibited by woven composites under biaxial flexure, induced via the ring-on-ring plate bending test. Square-shaped, epoxy/carbon twill woven composite plates of various sizes, scaled in three dimensions are considered. The biaxial flexural response of all specimens is found to be ductile and nonlinear with failure initiation at the top surface edges under combined in-plane compression and out of plane shear. These combined compression/shear cracks propagate towards the plate center, exhibiting a four-fold symmetry, and causing the plate to deform into a cone. Elastic stress analysis is presented to interpret and support the observations. The nominal stress at the onset of non-linearity is found to obey a type I size effect law, exhibiting a marked decrease with increased plate size but approaching a constant value. This size effect must be accounted for when designing woven composite parts to be subjected to biaxial flexure.

Characterizing the biaxial compressive deformation behavior of epoxy polymer through cruciform experiment and finite element analysis

The multiaxial deformation behaviors of amorphous epoxy polymers were characterized using planar biaxial compression tests and finite element (FE) analyses of cruciform specimens. The multiaxial limit of elastic deformation was investigated considering buckling instability of the planar biaxial compression tests. An offset-based yield criterion was proposed to determine the initial yield surface considering the nonlinear elastic deformation characteristics observed in the deformation tests. An FE analysis confirmed using the results of the tests revealed that the proposed method captured the initial multiaxial yielding in the central gauge of the specimen, demonstrating that existing pressure-dependent classical yield functions, such as the paraboloidal and conical yield functions, cannot appropriately describe the initial yield surface of the epoxy polymer. The yield function previously customized from molecular dynamics (MD) data exhibited a relatively good agreement with the initial yield surface. The determined shape of the initial yield surface and its agreement with the MD data–driven yield function were not consistently maintained during subsequent yielding. The results indicate that a new customized yield function properly describing the broader initial yield surface than those of the classical yield functions and its shape transition to plastic behavior is necessary to accurately reflect the entire multiaxial deformation behavior.