In-plane Compression Tests Research Articles

In-plane crashworthiness study of bio-inspired metallic lattice structure based on deep-sea glass sponge

Inspired by the double-diagonal reinforced configuration of deep-sea glass sponges, a metallic bio-inspired lattice structure (BLS) was fabricated using additive manufacturing (AM) techniques. In-plane quasi-static compression tests demonstrated the energy absorption (EA) of BLS was improved by about 60 % compared to conventional lattice designs. Subsequent experimental and numerical investigations examined the effects of wall thickness, elucidating the corresponding variations in crashworthiness indicators. The study revealed that when the wall thickness increased from 0.40 mm to 0.60 mm, the EA and mean crushing force (Pm) exhibited a substantial increment of 58.1 % and 91.1 %, respectively. The finite element (FE) simulations underwent experimental validation, exhibiting satisfactory agreement. Parametric studies using the validated FE model explored the effects of geometric factors, such as diagonal distance, unit size, unit number and graded thickness on the crushing performance of BLS. Results indicated that enhancing the EA performance of BLS was achievable by concurrently reducing the unit size and increasing the unit number. The maximum EA achieved was 3535.5 J, representing a 62.9 % improvement compared to the initial configuration, which exhibited an EA of 2170.7 J. Additionally, the introduction of graded thickness facilitated a controllable collapse pattern, thereby improving the crashworthiness performance. Lastly, the in-plane dynamic crushing simulations were conducted, identifying three distinct collapse patterns, where the U-Mode exhibiting a negative Poisson's ratio (NPR) behavior. A deformation mode map and rigid-perfectly plastic-lock (R-PP-L) model were developed to evaluate the dynamic response of BLS under varying relative density (RD) and impact velocity (V). These findings provided valuable insights for designing sponge-inspired structures with enhanced crashworthiness performance.

Bidirectionally graded honeycombs under quasi-static loading: Experimental and numerical study

Density-graded cellular solids possess tailorable mechanical properties through variable localized densities, made possible with design freedom offered by additive manufacturing. In this paper, a novel design strategy is proposed to generate bidirectionally graded honeycombs where the gradient direction is both parallel and perpendicular to the loading direction. A gradient function is developed to design three density gradient honeycombs having three different thickness gradients. The graded honeycombs along with their uniform density regular honeycomb counterparts of similar relative density are manufactured using material extrusion process. In-plane compression tests are carried out to perform a comparative study of the honeycombs. Unlike the regular honeycombs, graded honeycombs show layer-by-layer deformation, in addition to cell-wise collapse in lateral direction. Graded honeycombs show better energy absorption characteristics in low and high energy compressions, and high strain regime. Also, graded honeycombs have similar or higher specific energy absorption, densification strain, mean crushing force, and peak crushing force. The compressive responses of the honeycombs are simulated with finite element analysis and the simulation results agree well with the experimental results. The results substantiate the significance of thickness gradient in controlling the density gradation, and effectively tailoring the load-bearing capacity, deformation behavior, and energy absorption characteristics of cellular structures.

In-Plane Compressive Responses of Non-Homogenous Re-Entrant Honeycombs Fabricated by Fused Deposition Modelling.

Auxetic structures, with re-entrant (inverted hexagonal or bow tie) unit cells, have received considerable interest due to their negative Poisson's ratio property that results in superior mechanical properties. This study proposes a simple method to create non-homogeneous re-entrant honeycombs by modifying the size of chevron crosslinks. The various structural designs were conceived by changing the geometrical dimensions of the crosslinks, namely the length (lcl) and the thickness (tcl), while maintaining the parameters of the re-entrant cell walls. The influence of the design parameters of chevron crosslinks on the mechanical behaviour of additively manufactured re-entrant honeycombs was investigated experimentally and numerically. The structures were fabricated using the Fused Deposition Modelling (FDM) technique from polylactic acid (PLA) plastic. In-plane quasi-static compression tests were conducted to extract the elastic, plastic, and densification properties of the structures. Furthermore, a Finite Element (FE) model was developed via LS-DYNA R11.0 software, validated experimentally, and was then used to obtain a deeper insight into the deformation behaviour and auxetic performance of various designs. The obtained results revealed that the mechanical performance of re-entrant honeycombs can only be tuned by controlling the geometrical configuration of chevron crosslinks.

In-plane crushing behavior and energy absorption of sponge-inspired lattice structures

Novel energy-absorbing structures were a crucial requirement for the structural crashworthiness design in the automotive and aerospace industries. Inspired by the unique double-diagonal reinforced configuration of deep-sea glass sponge, we proposed a bionic lattice structure (BLS) fabricated by additive manufacturing (AM). In-plane quasi-static compression tests and numerical simulations were conducted on BLS with varying wall thicknesses (t), and two distinct deformation modes were observed: layer-by-layer mode with zero Poisson's ratio (ZPR) and uniform deformation mode with negative Poisson's ratio (NPR). The effects of structural parameters on the crushing behavior of BLS were investigated by numerical method. It was found that BLS with wall thickness (t) of 1.2 mm exhibited better energy absorption performance than 0.45 mm, with the energy absorption (EA), specific energy absorption (SEA), and mean crushing force (Pm) increased by 745.0%, 216.5%, and 744.3%, respectively. The change in crushing mode was caused by the ‘+’ shaped joints changing from buckling to rotation, and the crushing behaviors of BLS could be effectively controlled by adjusting unit size and unit number. Finally, theoretical prediction models were developed using simplified super folding element (SSFE) theory to gain deeper insights into crushing behavior and performance of BLS. The present study provided valuable insights into the in-plane crushing and energy absorption capabilities of BLS. Moreover, it highlighted the potential of the double-diagonal reinforcement design in developing innovative energy-absorbing structures.

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.

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.

Point-fixed connections in structural glass with injection mortar infill. experimental investigation and numerical simulations

This paper focuses on the experimental and numerical study of the performance of point-fixed connections in structural glass panels. For that purpose, an experimental program of in-plane uniaxial compressive tests was conducted on small-scale specimens. The specimens were manufactured using monolithic and laminated heat-strengthened glass (HSG). The point-fixed connections were realized using two infill products: (a) fischer FIS V Plus and (b) Hilti Hit HY270. A Digital Image Correlation (DIC) based measurement system in combination with strain gauges is used for tracking kinematics and deformations of the investigated specimens. It was found that the performance of the two infill products is comparable. The tests demonstrate that the failure mode of the monolithic panels is governed by infill failure, whereas the failure of the laminated panels is controlled by glass fracture. The numerical study was performed to assess the stress distribution around the hole in laminated glass. A 3D Finite Element (FE) model built in Abaqus is validated based on DIC and strain gauge measurements. A sensitivity analysis was performed on the eccentricity in the laminated glass panels and the friction coefficient between infill and glass/steel. It was observed that the eccentricity in the laminated panels has a significant influence on the stress amplification in the panels. Also, it was found that the value of the friction coefficient can significantly change the distribution of the principal stresses around the hole.

Investigating the effect of recycled irregular metallic particles embedment on the interlaminar strength of polyamide-based composites

ABSTRACT In this research, for the first time, the effect of embedding irregular and jagged steel particles of recycled milling dendritic chips on the improvement of compressive and interlayer strength of thermoplastic polyamide6 (PA6)-based, 200 g/m2 plain weave E-glass-fabric-reinforced composite laminates was investigated. The goal here is to examine whether the sharp spikes on the particles can penetrate adjoining laminate layers to provide superior interface toughness compared to spherical toughening particles. In-plane compression tests, according to ASTM D695-15 standard, show that through thickness expansion leads to delamination and subsequent failure. Consequently, theoretical considerations suggest that enhancements in interface toughness should lead to an increase in compression strength. For this purpose, steel particles with three size ranges, 300–600 µm, 150–300 µm, and 75–150 µm, were prepared and embedded into the composite laminates using film-stacking and hot-pressing process, in four different volume fractions. The particle distribution, impregnation, and bonding with the PA6 matrix were analyzed using optical and scanning electron microscopy imaging. Overall, results demonstrate a very good mechanical bonding between the particles and the thermoplastic matrix. Some interlocks between the particles and composite laminates were observed which has led to an improvement in the compressive strength of the composite laminate.

Structural comparison of conventional and chiral auxetic morphed aircraft rib

Abstract Tri-chiral structures are auxetic structures that show negative Poisson’s ratio. This effect is due to their microstructure and geometric sequence. They are used in the development of novel products as they show improved damping and energy absorption properties. While traditional manufacturing methods remain dysfunctional, the development of additive manufacturing technology provides opportunities for new studies in various industries such as aviation, textile, and automotive. In this study, passive airfoil morphing application was applied and a comparative study was carried out. A two-stage study was conducted. First, the tri-chiral pattern was fabricated by an FDM 3D printer with PLA+ and subjected to the in-plane compression test. Stress–strain curves of the tri-chiral structure were generated. Then, it was used in airfoil morphing applications. Morphed airfoil was also manufactured and a compression test was applied. Secondly, the aerostatic loads of the aircraft were calculated. Both conventional and chiral morphed ribs’ behaviors under flight loads were examined using the FEM and results were compared. The weight difference was calculated. In addition, eigenfrequency and eigenvectors of traditional and chiral ribs were computed and transverse vibration frequencies were expressed. Despite being more than 50 % lighter, chiral morphed rib was found to be stiffer than conventional rib.

Ultrahigh-temperature mechanical behavior and failure mechanisms of SiCf/SiC composites

SiCf/SiC composites are potential candidates in the aerospace fields for application as high-temperature structural components. Their mechanical properties and failure behaviors at ultra-high temperatures (above 1473 K) are important to obtain systematically. This work performed the in-plane compressive, bending, and interlaminar shear tests at 1573 K and 1773 K in an inert atmosphere. The results showed dramatically that the in-plane compressive and interlaminar shear strengths increased with the temperature increment from 1573 K to 1773 K. In contrast, a reduction in flexural strength was noticeable. To reveal the failure mechanisms, fracture surface microstructures of these SiCf/SiC samples were characterized. It was found that the fiber surfaces for the samples tested at 1773K were rougher than the samples tested at 1573K. It meant that, with the temperature increasing, the fiber-matrix interfaces enhanced, which resulted in increasing compressive and interlaminar strengths. For the bending tests, serious delamination occurred when the temperature increased to 1773K, which induced the flexural strength reduction. The numerical simulations of bending samples were developed to reveal the mechanism of strength degradation as the temperature elevated.

Investigation of energy absorption performances of a 3D printed fiber-reinforced bio-inspired cellular structure under in-plane compression loading

This article proposes glass-fiber-reinforced bone-inspired cellular structures to enhance energy absorption capability. The elastic modulus of the bone-inspired unit cell is obtained analytically based on the energy method and then employed in Particle Swarm Optimization algorithm to get optimized cellular structures. In the optimized cellular structure, the stiffness is optimized and the energy absorption capacity is investigated. A Fused Filament Fabrication 3D printing process is used to fabricate the cellular structures with continuous glass fiber-reinforced polylactic acid (PLA). In-plane compression tests are performed to investigate the mechanical performance of cellular structures. Finite Element Modeling (FEM) is conducted to analyzed the mechanical performance of the structures. In FEM, the failure criterion is determined using the maximum stress and VUSDFLD subroutine, and the damage growth is modeled by decreasing the mechanical properties. A good agreement between numerical and experimental results was observed. Results demonstrated that the energy absorption in glass-fiber-reinforced PLA is ∼250% higher than in the un-reinforced structure. The optimized cellular structure exhibits a stable prolonged plateau stress region and very high specific energy absorption parameters.

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.

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.

A New Technique for Determining the Shape of a Paper Sample in In-Plane Compression Test Using Image Sequence Analysis

The article presents a new technique for analyzing phenomena occurring during the measurement of the strength properties of paper in the conditions of compression of the tested samples with forces acting in the paper plane. The technique is based on collecting data on the current distance of the clamps holding the tested sample and the force exerted on the sample using a universal testing machine and on the simultaneous recording of image sequence of the sample during the measurement. Next, the resulting images are subjected to processing and analysis, the purpose of which is to extract information about the shape of the sample edge in all phases of the measurement. Its advantage is the ability to determine the deflection arrow of the sample and describe its shape using the selected function given by the analytical parametric formula. It will be helpful in further research on the development of an analytical model describing the phenomena occurring during paper compression, and a method to determine the mechanism of paper destruction and the corresponding maximum force that destroys a paper sample.

Failure progression and toughening mechanism of 3D-printed nacre-like structures under in-plane compression

Nacre (also called mother-of-pearl) is known to have a delicate balance of stiffness, strength, and toughness, which originates from its ‘brick-and-mortar’ structure. In this study, nacre-like structures are fabricated using a high-resolution, multi-material 3D printer, where two different polyurethane acrylates (one that is hard and another that is soft) are used to represent the tablets and matrix. Six nacre-like structures are designed and fabricated to explore the influence of geometric parameters on the mechanical behaviors. Quasi-static in-plane compression tests and simulations are carried out to explore the failure mechanism of the nacre-like structures. The results show that the quasi-static compression responses of nacre-like structures have four stages: elastic, plateau, fragmentation, and densification. It is found that tuning the nacre architecture can optimize the mechanical performance of the specimen, including the peak load, ductility and stress reduction behavior et al. As the results of the numerical model show good agreement with the stress–strain response observed in the experiments, the model is applied to further investigate the strain distributions of the nacre-like structures. The patterns of the strain distribution suggest that synergistic deformation is the key toughening mechanism for the nacre-like structures.

Compressive property and shape memory effect of 3D printed continuous ramie fiber reinforced biocomposite corrugated structures

The present work aimed to study the quasi-static compression behaviors of 3D printed continuous ramie fiber reinforced biocomposite corrugated structures (CFCSs) with excellent shape memory effects. The in-plane compression test was conducted to evaluate the effects of cell shapes, fiber volume fraction (f v) and addition of fiber on the compression behaviors and energy absorption (EA) characteristics of the corrugated structures. The results showed that the compression property and EA capacity of the 3D printed CFCSs increased with decreasing f v and the addition of continuous ramie yarn. The 3D printed continuous ramie fiber reinforced biocomposite with inverted trapezoid cell shape corrugated structures (CFITCSs) outperformed other cell shapes in the compression strength and specific EA. The analytical model for the in-plane compression strength of CFITCSs was derived, and predictions were in good agreement with measurements. In addition, continuous natural fiber reinforced composite structure for shape memory was proposed for the first time. The shape recovery testing results demonstrated that 3D printed CFCSs had the potential to be a key element of lightweight programmable smart systems.

Mechanical performance of bio-inspired hierarchical honeycomb metamaterials

Natural materials with hierarchical structures usually have superior mechanical properties. Herein, inspired by the macro–micro coupling deformation characteristics of biomaterials, novel hierarchical auxetic-hexagonal honeycombs (AuxHex) metamaterials with various substructures, including equilateral triangles and double arrowheads lattice cells, were constructed. A universal analysis model of the plastic collapse stress was first established, considering the deformation behavior of both the primary and secondary structures. This mechanism-based method gets rid of redundant numerical fitting parameters, and is applicable to different hierarchical lattice structures. Typical hierarchical AuxHex specimens were prepared using selected laser melting and stainless steel. In-plane compression tests and finite element simulation results demonstrated that, in contrast to the regular structures, hierarchical honeycombs exhibit enhancement in their load-bearing capacities and energy absorption ability. The specific modulus of T-AuxHex and A-AuxHex were increased by about 180% and 45%, the specific strength rose by approximately 50% and 15%, and the specific energy absorption was improved by about 160% and 50%. The effects of geometrical parameters were systematically discussed to reveal the mechanisms underlying the enhancement of the above mechanical characteristics. The proposed theoretical model provides a new method for designing the mechanical properties of hierarchical metamaterials by tailoring the type and distribution of secondary structures.

Characterization and modeling of continuous carbon fiber-reinforced polycarbonate under multiaxial loads

The presented work considers the characterization of a continuous fiber-reinforced thermoplastic (FRTP) with unidirectional plies under quasi-static, multiaxial loading conditions and the modeling of the non-linear mechanical behavior. For the experimental investigation, hoop wound tubular specimens fabricated from carbon fiber-reinforced polycarbonate (CF-PC) tape were tested on an electromechanical static testing machine with an axial and torsional drive. The multiaxial material response was determined for an extensive set of tests performed at several load ratios of in-plane shear to transverse stress. For modeling the non-linear mechanical response, an elasto-plastic framework is used which is kept preferably simple in order to facilitate the application in numerical analysis. Based on the generated experimental data, suitable criteria for fracture and yielding are proposed. The defined yield criterion respects the special characteristics of a FRTP such as the different mechanical behavior under transverse tensile and compressive loading as well as a linear material response in the direction of the fiber reinforcement . Furthermore, the implementation of the proposed model as a user-defined material (UMAT) routine for implicit finite element analysis (FEA) using Abaqus /Standard is described and the calibration of the plasticity approach using only the data of the in-plane shear and transverse compression tests is discussed. The model predictions for multiaxial loads are validated using the determined biaxial material data. • Multiaxial experimental data for a continuous fiber-reinforced thermoplastic • Full dataset of the arithmetic mean stress–strain curves is provided • Selection of a suitable fracture criterion and definition of a yield criterion • Development and implementation of a non-linear elasto-plastic material model • Calibration and validation of the material model using the determined multiaxial data

Influence of Moisture Diffusion on the Dynamic Compressive Behavior of Glass/Polyester Composite Joints for Marine Engineering Applications

Thermoset polymers offer great opportunities for mass production of fiber-reinforced composites and are being adopted across a large range of applications within the automotive, aerospace, construction and renewable energy sectors. They are usually chosen for marine engineering applications for their excellent mechanical behavior, including low density and low-cost compared to conventional materials. In the marine environment, these materials are confronted by severe conditions, thus there is the necessity to understand their mechanical behavior under critical loads. The high strain rate performance of bonded joints composite under hygrothermal aging has been studied in this paper. Initially, the bonded composite specimens were hygrothermal aged with the conditions of 50 °C and 80% in temperature and relative humidity, respectively. After that, gravimetric testing is used to describe the moisture diffusion properties for the adhesively bonded composite samples and exhibit lower weight gain for this material. Then, the in-plane dynamic compression experiments were carried out at different impact pressures ranging from 445 to 1240 s−1 using the SHPB (Split Hopkinson Pressure Bar) technique. The experimental results demonstrated that the dynamic behavior varies with the variation of strain rate. Buckling and delamination of fiber are the dominant damage criteria observed in the sample during in-plane compression tests.

A new method to evaluate the in-plane compression behavior of paperboard for the deep drawing process

To evaluate the influence of different normal pressures and the fiber orientation on the in-plane compression behavior of paperboard during the deep drawing process, a new method was developed. In addition, the influence of the wrinkle formation on the dynamic coefficient of friction and the bending resistance was examined. To evaluate the eligibility of the in-plane compression testing method, a validation strategy was developed to compare the results from the new alternative tests with the punch force profiles from the deep drawing process within an empirical model.