In-plane Compression Research Articles

Compressive properties and energy absorption of 4D printed auxetic mechanical metamaterials

Auxetic mechanical metamaterials contract or expand laterally when subjected to compressive or tensile load in the axial direction and offer potential benefits in areas such as flexible electronics, aerospace, and soft actuators. Nevertheless, when metamaterials are fabricated using conventional methods, their configurations and properties are fixed, which prohibits adaptation to the specific geometric requirements of their application environment. This limits their further development. This paper proposes an auxetic mechanical metamaterial with a negative Poisson's ratio and energy absorption capability. Compression specimens are fabricated with LCD photo-curable printing technology. The deformation mechanism and in-plane compression characteristics are examined through experimental and numerical simulation methods. The influence of unit cell geometrical control parameters on Poisson's ratio and energy absorption are also explored. The results indicate the dominant deformation mechanism of metamaterial during in-plane compression is bending deformation. The negative Poisson's ratio behavior is more pronounced when compressing along the X direction than along the Y direction, and the specimens also exhibit energy absorption capacity. In addition, the metamaterials prepared by 4D printing technology can be transformed from one configuration to another under external stimuli stimulation and force, and exhibit different mechanical properties, realizing programmable and reconfigurable, further expanding their application range.

Energy absorption and piezoresistive characteristics of 3D printed honeycomb composites with hybrid cell architecture

ABSTRACT This paper introduces a novel hybrid honeycomb (HC) design achieved by continuously blending non-auxetic hexagonal and auxetic re-entrant cell geometries along the out-of-plane direction. These novel hybrid HCs are additively manufactured via fused deposition modelling (FDM) using PA12 polymer reinforced with 15 wt.% of discontinuous carbon fibres. We study the mechanical and piezoresistive performance of hybrid HCs under quasi-static in-plane and out-of-plane loading performed at temperatures ranging between 25-125°C. The results demonstrate significant in-plane compression performance enhancements in the hybrid configuration, achieving up to 43% increase in the collapse strength and 119% in absorbed energy. The incorporation of multiple hybrid layers in the honeycomb structure further enhanced the in-plane properties, ultimately achieving a 181% enhancement in energy absorption. The hybrid honeycombs also showed a pronounced piezoresistive response with gauge factors in the range of 18–37 within the elastic regime, making them suitable for a wide range of multifunctional applications.

Large-ratio stiffness switching via harnessing the in-plane buckling and bi-stability of high-load capacity composite laminates

Stiffness tuning is crucial in developing many advanced engineering systems such as morphing aircraft, soft robotics, etc. Achieving a significant stiffness change while maintaining a high load-bearing capacity in compression is a challenging task. This study addressed this challenge by exploiting the in-plane buckling and bistability of asymmetric carbon fiber composite laminates. Due to the inverted curvatures of these laminates at their two stable states, they showed two distinct in-plane compression behaviors—stiff response where the laminate behaved like a thin curved column (with a stiffness coefficient near 68 N mm−1), and compliant response where the laminate acted like a soft non-linear spring (with stiffness near 0.7 N mm−1). As a result, a simple snap-though between these two stable states offered a significant stiffness change, with a high/low stiffness ratio of ≈97. By using extensive finite element simulations, experimentation, and a semi-empirical curved plate buckling model, this study examined the mechanics underpinning the laminate’s 3-step buckling and the influences of asymmetric boundary contacts with friction. Additionally, three strategies to enhance the laminate’s performance—adjusting the aspect ratio, applying lateral loads, and parallel stacking were examined. It also demonstrated cellular structure concepts using these bistable laminates. Remarkably, by simply adding a small lateral in-plane force (e.g., a rubber band), one could substantially increase the stiffness ratio of the composite laminates to ≈200 and load-bearing capacity at the stiff configuration, outperforming the state-of-art variable stiffness methods.

Enhancing crashworthiness characteristics of modified hexagonal honeycomb structural panels through stretching and bending of ribs

The effects of stretching and bending of concave, convex, and horizontal ribs on the energy absorption characteristics of modified hexagonal honeycomb structural panels are investigated under in-plane quasi-static compression loading conditions. In this regard, five hierarchical modified structural panel configurations were fabricated using polylactic acid material (PLA) via a fused filament 3D printer, ensuring uniform wall thickness in the 1.5–2 mm range. The panels included the regular hexagonal panel (RHP), regular hexagonal panel with concave rib (RHCP), regular hexagonal panel with convex rib (RHXP), regular hexagonal panel with concave and horizontal ribs (RHCRP), and regular hexagonal panel with convex and horizontal ribs (RHXRP). In-plane quasi-static compressive loading tests were conducted to analyze crush resistance characteristics, and buckling modes of the modified honeycomb panels were examined through experimental and finite element analysis procedures. The result indicates that the specific energy absorption capacity (SEA) of RHXRP is increasing significantly compared to the SEA capacity of other categories of the structures. The changes in failure modes and increased crush energy absorption characteristics of modified RHP with the introduction of concave, convex, and horizontal ribs are elaborated.

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.

Structural routes to stabilize superconducting La3Ni2O7 at ambient pressure

The bilayer perovskite La3Ni2O7 has recently been found to enter a superconducting state under hydrostatic pressure at temperatures as high as 80 K. The onset of superconductivity is observed concurrent with a structural transition which suggests that superconductivity is inherently related to this specific structure. Here we perform density functional theory based structural relaxation calculations and identify several promising routes to stabilize the crystal structure which hosts the superconducting state at ambient pressure. We find that the structural transition is controlled almost entirely by a reduction of the b-axis lattice constant, which suggests that uniaxial compression along the [010] direction or in-plane biaxial compression are sufficient as tuning parameters to control this transition. Furthermore, we show that increasing the size of the A-site cations can also induce the structural transitions via chemical pressure and identify Ac3Ni2O7 and Ba-doped La3Ni2O7 as potential candidates for a high temperature superconducting nickelate at ambient pressure. Published by the American Physical Society 2024

Design of multifunctional polymethacrylimide foam sandwich with excellent radar absorption capability and compressive performance

A composite multifunctional radar absorption polymethacrylimide (RAPMI) foam sandwich (MRAPS) was constructed. Analytical models for out-of-plane and in-plane compression of the MRAPS were established. Three-dimensional failure mechanism maps and specific strength cubic cloud maps were drawn. Finally, a multiobjective particle swarm optimization (MOPSO) algorithm was used to achieve an integrated design, and a specific calculation example was tested and verified through experiments. The resulting sandwich with a 43.0 mm thickness core and 0.13 g/cm3 density achieves 90% effective absorption above broadband (RL ≤ −10 dB) in the 2–18 GHz range. As a radar absorption absorber, the MRAPS increased the engineering value and strategic importance of PMI foam for structural components in the military and aerospace sectors.

Evaluation of Post Tension Runway Plate as Retrofitting Simulated with Compression In-Plane Force in Numerical Approach

The swelling of soil can result from fluctuations in its moisture content, causing it to expand and contract. To mitigate this, structures in direct contact with the soil may require retrofitting. Post-tensioning is one such method that can enhance the stiffness of the structure without altering its properties, thereby helping to prevent damage from expansive soil. This research presents a novel methodology for the design of retrofitting runway pavements using post-tension plates, employing a numerical approach that considers various influencing factors. The methodology integrates the use of differential and Kerr foundation equations, employing the Levy method to ascertain the deflection of the plate structure. Soil parameters are derived from soil sampling and laboratory tests, while loads are determined based on prior research findings and governmental regulations. The findings of the study indicate that the thickness of the plate structure influences its deflection, as greater thickness results in increased stiffness within the structure. Increasing the thickness of the plate enhances stiffness and diminishes deflection. Regarding the direction of post-tensioning, employing tension in both directions proves most effective, resulting in a reduction of deflection by 22.11%. However, this model demands higher costs compared to others due to the increased requirement for tendon post-tensioning. As an alternative, aligning the direction of post-tensioning with the direction of load movement can lead to a reduction of 15.14% in plate deflection, while incurring lower costs compared to applying post-tensioning in both directions.

Predicting the post-bifurcated patterns of architectured materials using group-theoretic tools

Extensive studies on hexagonal honeycombs under in-plane compression have demonstrated that the structure’s symmetry plays a decisive part in the emergence of deformation patterns in post-bifurcated configurations. In this work, the aim is to take advantage of this property by presenting a new group-theoretic approach to list the various attainable post-bifurcated patterns of periodic architectured materials.As of today, some group-theoretic approaches have been elaborated for determining the post-bifurcated paths and thus patterns of a symmetric system submitted to specific loading conditions. However, the application of these approaches requires knowledge of the system’s governing equations. By making use of another group-theoretic tool, this work predicts the various possible post-bifurcated configurations of a periodic architectured material a priori of any non-linear computation by simply assessing the symmetry group of its undeformed configuration.This approach is applied, as an example, to the buckling of regular hexagonal honeycombs but can be easily transferred to any periodic architectured material. This work is a first step towards the elaboration of a more general process for the design of architectured materials when harnessing post-bifurcated behaviour is essential.

Comparison of in-plane compression of additively manufactured Ti6Al4V 2D auxetic structures: Lattice design, manufacturing speed, and failure mode

The metal-based 2D auxetic lattice structures hold the potential for multifunctional tasks in aerospace applications. However, the compression response of those manufactured by powder bed fusion process is underexplored. This study proposes a comprehensive comparison of in-plane quasi-static compression performance of 2D auxetic lattice structures, utilizing three designs (anti-tetrachiral (ATC), double arrow-headed (DAH), and tree-like re-entrant (TLR)), manufactured with stiff Ti6Al4V by the electron beam powder bed fusion process (PBF-EB) with various manufacturing speeds. The results revealed unique failure patterns and superior energy absorptions among 2D lattice structures in the literature. TLR design enhanced energy absorption by overcoming failures between DAH columns and exhibited the lowest standard deviations in specific energy absorption (SEA) values (9.75 %–12.62 %). Besides, Kernel average misorientation (KAM) values followed the order of DAH, TLR, and ATC, and inversely correlated with SEA values. ATC structures with the lowest KAM outperformed DAH and TLR by 47.5 % and 6.44 %, respectively. Scan speed variations affected SEA and porosity values differently for each lattice design while exhibiting similar microstructure characteristics. The findings in this study propose a significant contribution to the development of aerospace sandwich structures where harsh environments exist and employment of 2D topologies are required.

Theoretical and numerical analysis of period-doubling bifurcation in sandwich systems

Period-doubling bifurcation will appear when a stiff film is embedded into a compliant matrix or constrained to a soft substrate and undergoes in-plane compression. Though period-doubling bifurcation in bilayer systems have received extensive investigation, the mechanism of intricate post-buckling phenomena in sandwich systems remains an open question due to the inherent high nonlinearity. In this paper, a theoretical model for period-doubling bifurcation in sandwich systems is established and verified by finite element simulations. The proposed theoretical model is generalized to neo-Hookean materials and transformed into an equivalent nonlinear oscillator through an internal-to-external force transformation. Theoretical analysis reveals that an increase in the degree of up-down symmetry suppresses period-doubling bifurcation. Especially, when both the substrate and superstrate are identical, the influence of nonlinear deformation partly reflected by even high terms on the pressure difference on the film disappears, as a result, a novel period-doubling-like pattern appears due to the competitive effects from both sides strike a balance.

Fabrication of micro/submicron hierarchical structures on ceramic sheet surfaces combining 2-step imprinting and in-plane compression processes

Many organisms have functional microstructured surfaces. Particularly, lotus leaves have hierarchical dual-scale micro/nanostructures on their surface and exhibit highly water repellent properties. We have developed techniques to fabricate patterns on inorganic material surfaces such as ceramics. Applying these techniques to fabricate hierarchical structures can make ceramic surfaces even more promising. In this paper, we prepared 2 kinds of mold with line-and-space patterns with pitches 50 μm and 2 μm and fabricated micro (rough patterns)/submicron (fine patterns) hierarchical structures on sintered ceramic sheets using a newly developed imprinting process with in-plain compression method. We proposed processes for the fabrication of such hierarchical structures, discussed the possibility of higher resolution of the patterns by comparison with the analytical results.

Numerical Investigation of an Experimental Setup for Thermoplastic Fuselage Panel Testing in Combined Loading

The main purpose of this study comprises the design and the development of a novel experimental configuration for carrying out tests on a full-scale stiffened panel manufactured of fiber-reinforced thermoplastic material. Two different test-bench design concepts were evaluated through a numerical modeling strategy, which will be validated at the next stage using a targeted series of mechanical tests. A baseline experimental setup was developed after a number of candidate configurations were numerically investigated. The supporting elements along with the load introduction systems were defined in such a way as to represent the stiffness of a fuselage barrel section and its representative loading scenarios. The test rig and the investigated thermoplastic panel were numerically simulated to acquire valuable data pertaining to deformations and stresses when subjected to different loading combinations. Two distinct load cases were numerically examined: the first case was the in-plane compression of the thermoplastic panel, while the second case consisted of an internally applied pressure load introduced via an inflatable airbag, installed under the panel. Both loading scenarios were recreated inside the numerical virtual environment in order to examine two distinct stiffening configurations as well as to determine the maximum/limit loads to be used in the planned future experimental campaign. It was concluded that the designed test rig could successfully be used for the structural evaluation of fuselage panels under representative loading conditions.

Machine learning assisted prediction and analysis of in-plane elastic modulus of hybrid hierarchical square honeycombs

In this study, experimental, finite element (FE) simulation, machine learning (ML), and theoretical techniques are employed to investigate the in-plane elastic modulus (EHHSH) of hybrid hierarchical square honeycombs (HHSHs). First, HHSHs with different configurations were fabricated using a 3D printer, and in-plane quasi-static compression tests were conducted on them. Then, 234 FE models are simulated to determine the EHHSH of HHSHs with various configurations, and the results are used to train 11 ML models. Comparative analysis demonstrates that the Extreme Gradient Boosting (XGBoost) model has the best predictive capability. Moreover, a modified theory for EHHSH is established based on the XGBoost model and existing theory, and its exceptional predictive capability is verified by comparing with experimental, FE, and existing theoretical results. Finally, the upper and lower bounds of EHHSH are determined by the modified theory, and the Shapley Additive Explanation (SHAP) method is used to identify the importance of different geometric parameters on tailoring EHHSH. The combination of theoretical and ML techniques provides a promising approach for developing a robust prediction model of material properties.

Experimental Comparative Analysis of the Through-Thickness and In-Plane Compression Moduli of Unidirectional CFRP Laminates

This study explores the experimental characterization of the through-thickness compression properties in unidirectional laminates using cube compression tests. Cubical specimens, each with an edge length of 10 mm, were symmetrically outfitted with biaxial strain gauges and subjected to a compression test. While similar methodologies exist in the literature, this work primarily addresses the potential biases inherent in the testing procedure and their mitigation. The influence of friction-induced non-uniform deformation behavior is compensated through a scaling of the stiffness measurements using finite element (FE) analysis results. This scaling significantly enhances the accuracy of the resulting parameters of the experiments. The ultimate failure of the specimens, originating from stress concentrations at the edges, resulted in fracture angles ranging between 60° and 67°. Such fracture patterns, consistent with findings from other researchers, are attributed to shear stress induced by friction at the load introduction faces. The key findings of this research are the comparisons between the through-thickness modulus (E33c) and strength (X33c) and their in-plane counterparts (E22c and X22c). The results indicate deteriorations of E33c and X33c from E22c and X22c by margins of 5% and 7%, respectively. Furthermore, the results for E22c and X22c were compared with the results obtained through a standard test, revealing a 12% enhancement in strength X22c and 4% underestimated stiffness E22c in the cube compression test.

In-plane compression of bi-laterally confined layered structure: Plastic model and parametric study

Discrete layered structures are commonly used in various functional configurations, such as power batteries. However, the mechanical behavior of the discrete layered structure in the in-plane direction is not well understood due to the complexity of inter-layer interactions. In this study, we investigated the behavior of layered structure under in-plane compression with fixed boundary conditions using theoretical analysis, FE simulations and material tests.In FE simulations, a layered structure could exhibit a specific stable compression deformation pattern until local collapse occurs. To understand the underlying mechanisms, we identified two secondary behaviors, referred to as squeeze elements, during the in-plane compression process. By properly recognizing crucial parameters, we modeled and analyzed the mechanical behaviors of the squeeze elements using plastic theory. The primary behaviors of the layered structure are then explained by examining the mechanical relationship between the squeeze elements and the entirety of the structure. Additionally, the impact of the lateral constraints and the layer numbers on the layered structure is analyzed and verified.Significantly, we discovered a non-monotonic influence of lateral constraints on the maximum energy absorption of the layered structure before local collapse. This finding is further supported by in-plane compression tests conducted on pouch cell batteries. From a structural integrity standpoint, we emphasize the importance of integrated design in the lateral direction to enhance the safety tolerance of functional layered structures subjected to in-plane compression.

Hydrodynamic instabilities in a two-dimensional sheet of microswimmers embedded in a three-dimensional fluid

A collection of microswimmers immersed in an incompressible fluid is characterised by strong interactions due to the long-range nature of the hydrodynamic fields generated by individual organisms. As a result, suspensions of rear-actuated ‘pusher’ swimmers such as bacteria exhibit a collective motion state often referred to as ‘bacterial turbulence’, characterised by large-scale chaotic flows. The onset of collective motion in pusher suspensions is classically understood within the framework of mean-field kinetic theories for dipolar swimmers. In bulk two and three dimensions, the theory predicts that the instability leading to bacterial turbulence is due to mutual swimmer reorientation and sets in at the largest length scale available to the suspension. Here, we construct a similar kinetic theory for the case of a dipolar microswimmer suspension restricted to a two-dimensional plane embedded in a three-dimensional incompressible fluid. This setting qualitatively mimics the effect of swimming close to a two-dimensional interface. We show that the in-plane flow fields are effectively compressible in spite of the incompressibility of the three-dimensional bulk fluid, and that microswimmers on average act as sources (pushers) or sinks (pullers). We analyse the stability of the homogeneous and isotropic state, and find two types of instability that are qualitatively different from the bulk, three-dimensional case: first, we show that the analogue of the orientational pusher instability leading to bacterial turbulence in bulk systems instead occurs at the smallest length scale available to the system. Second, an instability associated with density variations arises in puller suspensions as a generic consequence of the effective in-plane compressibility. Given these qualitative differences with respect to the standard bulk setting, we conclude that confinement can have a crucial role in determining the collective behaviour of microswimmer suspensions.

Secure most significant bit plane compression based reversible data hiding in encrypted image technique using Huffman Ciphersystem

Secure most significant bit plane compression based reversible data hiding in encrypted image technique using Huffman Ciphersystem

In-plane compression behavior of meta-tetrachiral and common auxetic structures

Meta-tetrachiral structure, as a novel negative Poisson’s ratio auxetic materials, combines the topological features of tetrachiral and anti-tetrachiral structures. Under the in-plane compression, a comparative study on the mechanical properties of the meta-tetrachiral and the common tetrachiral and anti-tetrachiral structures is investigated experimentally and numerically. Three types of specimens are fabricated by using Stereo Lithography Apparatus (SLA) technology; numerical models are established by using FEA software and verified by quasi-static compression tests. The simulated and experimental results together indicate that the in-plane deformation patterns of the meta-tetrachiral are limited by the different loading directions. The deformation mechanism of the meta-tetrachiral loaded along different directions is summarized by the deformation behavior of the specimens. The Young’s modulus of the meta-tetrachiral loaded along different directions is larger than that of the anti-tetrachiral structure. The auxetic properties (NPR) of the meta-tetrachiral structures loaded along different directions are superior to that of the tetrachiral structure. In addition, it is found that the meta-tetrachiral loaded along the Y-direction shows a better performance in terms of energy absorption compared to the other structures. The effect of the meta-tetrachiral structures with different wall thicknesses on energy absorption was investigated.

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.