Quasi-static Compression Experiments Research Articles

Mechanical properties of diamond-type triply periodic minimal surface structures fabricated by photo-curing 3D printing

Triply periodic minimal surface (TPMS) structures have attracted significant attention owing to their smooth surface configuration and parametric modeling properties. In this study, photo-curing 3D printing was employed to generate diamond-type TPMS structures, and micro-CT scanning revealed the presence of internal defects within the 3D printed TPMS structures. Two key design variables were explored: volume fraction and unit cell size. Quasi-static compression experiments were conducted to delve into the compression properties and energy absorption capabilities of the 3D printed TPMS structures. The findings reveal that increasing the volume fraction significantly enhances the compressive modulus, ultimate strength, and energy absorption capacity of TPMS structures. Additionally, increasing the cell size improves compression properties and energy absorption per unit volume. To predict the coupling effect of volume fraction and unit cell size on the compression performance of TPMS structures, a bivariate quadratic regression model was established. In addition, TPMS structures were subjected to load-unload cyclic experiments, shedding light on the evolution patterns of residual strain and hysteresis energy during cyclic loading. It provides insights into the design of reusable and fatigue-resistant diamond-type TPMS structures for various engineering applications.

Study on crashworthiness of square frustum lattice structure under in-plane compression load

The direction of load on the component in engineering applications is often uncertain, so the excellent crashworthiness and smooth load transfer of energy-absorbing structures in various directions is of great application value. Square frustum lattice structure (SFLS) was proposed based on the control of cell deformation mode and the improvement of in-plane strength without increasing the overall mass. Compared with multi-cell tubes commonly used in engineering and origami-patterned structure with excellent performance in research, it is found that the SFLS shows high and stable energy absorption capacity with the same structural parameters. The SEA and CFE of SFLS are 1.7 times and 3.5 times of origami structure and multi-cell tube, respectively, and the fluctuation indicator of the force displacement curve of origami structure and multi-cell tube are 1.7 times and 2.7 times of that of SFLS. In-plane quasi-static compression experiment was carried out and the finite element model was verified. The results of parametric analysis and sensitivity show that, compared with the change of cell number and cell height, the crashworthiness of SFLS under in-plane compression was most sensitive to the ratio of side length, in the range of parameters studied, the maximum SEA value of SFLS can reach 79.35 J/g for k value equal to 0.3, while the best indicator of smoothness of force-displacement curve of SFLS is found at k equal to 0.5.

Enhanced energy absorption and mechanical properties of porous Ti-6Al-4 V alloys with gradient disordered cells fabricated by laser powder bed fusion

Additive manufacturing (AM) has revolutionized the production of porous metals, greatly improving control over their structural properties and offering unprecedented advantages in lightweight applications and energy absorption. Balancing energy absorption and compressive strength in ordered and disordered porous structures is challenging due to shear deformation and deformation mechanisms. This study investigates the mechanical and energy absorption properties of porous Ti-6Al-4 V alloys with gradient disordered cells fabricated using laser powder bed fusion (LPBF). The compressive response of samples with different regularities (R) and varying layers of disordered cells was analyzed through quasi-static compression experiments and finite element simulations. The results indicate that introducing a disordered cell gradient significantly enhances energy absorption by preventing the formation of shear bands observed in porous structures with ordered cell structures. When the regularity (R) is 0.8, 0.4, and 0.2 with one or two layers of disordered cells, mechanical properties are optimized and characterized by a balance between compressive strength and energy absorption. It is significant that, while preserving or enhancing compressive strength, the energy absorption of the material can be augmented substantially. Specifically, porous Ti-6Al-4 V (R = 0.8, L4) achieves an energy absorption increase of up to 154.9kJ/m³, which represents a dramatic enhancement of approximately 245.0 % over the regular porous structure (R = 0 or L0), which absorbs only 44.9 kJ/m³. Compared to ordered and disordered porous structures, the disordered cell gradient demonstrates significant potential in tuning the mechanical properties of porous metals, thereby advancing their applications in aerospace, biomedical, and protective fields.

Failure mechanism and crashworthiness optimization of variable stiffness nested origami crash box

In recent years, the study of the crashworthiness of lightweight and efficient thin-walled energy-absorbing structures has received increasing attention. In this work, 3D printing technology was adopted to create a nested origami crash box with stiffness variation, which was made of short carbon fiber reinforced nylon material. The structure effectively inhibits the development of failure behavior of short carbon fiber-reinforced nylon origami crash box due to material brittleness. The quasi-static compression experiment results indicate that compared to origami crash box, nested origami crash box improves by 40% in specific energy absorption and 50% in crash force efficiency, while the initial peak crushing force remains unchanged. The effects of three key geometrical parameters, namely dihedral angle, distance between tubes, and height difference on the damage mechanism of the nested origami crash box are discussed in detail using the finite element method, and the response surface model combined with the non-dominated sorting genetic algorithm II is used for multi-objective optimization. In this work, the concepts of origami theory and nested systems are integrated for the first time, aiming to achieve a stable and efficient energy-absorbing deformation mode by precisely modulating the stress transfer path of the structure and its stiffness. This work provides new ideas for the design and fabrication of novel lightweight energy-absorption boxes.

Study on influencing factors of controllable mechanical behavior of rock-like porous materials.

Due to the discrete and non-homogeneous of similar materials and the inability to realize large-size and original scale modeling, it is difficult to restore the structure and stress state of underground coal and rock mass in similar simulation tests. To solve this problem, a lightweight and suitable for large-scale modeling similar material, rock-like porous material has been developed. The quasi-static uniaxial compression experiment was carried out by using the large tonnage multi-module electronic control test system. And the influencing factors of controllable mechanical behavior of rock-like porous materials were studied. The results showed that, under uniaxial compression conditions, the material stress-strain curve exhibits three phases: elastic stage, failure stage, and platform stage. The uniaxial compressive strength, elasticity modulus, stress drop, and softening modulus of rock-like porous materials basically increase with the increase of density. The stress after peak strength changes from a slow decrease to a "stepped" or even "cliff like" downward trend. Polypropylene fibers have the effect of enhancing the uniaxial compressive strength, elasticity modulus, stress drop, softening modulus, shear deformation, and residual strength stability of rock-like porous materials. The rock-like porous material has a critical loading velocity, and it increases with density. At the critical loading velocity, the material shows obvious shear failure, and the shear inclination angle is the largest, and so is the uniaxial compressive strength. Through the experimental research, the influence laws of density, polypropylene fiber, and loading velocity on the failure mode, mechanical parameters, and mechanical behavior of the material are clarified, and the quantitative relationship between density and each mechanical parameter is obtained. The research is helpful to realize the accurate control of mechanical behavior of rock-like porous materials and further inverts the deformation and failure mechanism of underground coal and rock structures through indoor similar simulation tests.

Vibration suppression of a meta-structure with hybridization of Kresling origami and Yoshimura origami

In recent years, the deployment and vibration suppression capabilities of spacecraft have become one of the prominent research topics. Considerable effort has been dedicated to studying the deployability and vibration suppression performance of origami structures. However, traditional origami types severely limit their application in aerospace engineering due to their unique deployment behavior. This study introduces a novel meta-structure with hybridization of Kresling origami and Yoshimura origami (MHKYO), designed to suppress low-frequency vibrations. The band structure and transmission rate of the proposed metastructure were studied to evaluate its vibration suppression performance. The adjustment of the bandgap of the metastructure was achieved through geometric parameter variation. Quasi-static compression experiments and transmission rate experiments were carried out, and the results obtained were almost consistent with those obtained by finite element methods. During the compression process, the origami metastructure exhibited quasi-zero-stiffness (QZS) behavior. The influence of the metastructure’s stiffness on the band structure was analyzed. It is also proved that the hybrid origami metastructure improves the vibration suppression performance of the traditional origami metastructure. This work proposes a new origami-inspired metastructure, providing a certain theoretical basis for the application of origami technology in aerospace engineering.

Inverse design of cellular structures with the geometry of triply periodic minimal surfaces using generative artificial intelligence algorithms

Triply periodic minimal surfaces (TPMS) exhibit excellent mechanical and energy absorption properties due to their structural advantages. However, existing porous TPMS structural design methods are constrained to a forward process from structural parameters to mechanical properties. This study proposed an inverse design method that combines bidirectional generative adversarial networks (BiGAN) and mechanical performance targets, resulting in a combined TPMS structure of Primitive and IWP types with superior buffering and energy absorption capabilities. The results show that under a single load value target condition of the designed structure, the minimum deviation index (R2) between the load value corresponding to the displacement point and the target load value is only 0.987, and the maximum mean absolute percentage error (MAPE) is only 5.92 %. When considering the elastic modulus target, the approach successfully conducts two sets of combined structural designs meeting the requirements of both high and low elastic moduli. When targeting the specified load-displacement curve conditions, specifically when combining high elastic modulus with ascending plasticity, the designed structures exhibit an error of only 2.2 % compared to the target property. Moreover, the quasi-static uniaxial compression experiments conducted on additively manufactured designed structures confirm that the experimental curves match the target curves in terms of deformation trends and load value ranges. The success of this inverse design approach for cellular TPMS structures has the potential to expedite new structural material development processes.

Effects of corrosion on mechanical properties of bolted porous structural panel

In this paper, polylactic acid materials combined with fused deposition molding technology were used to prepare porous structural panels. A combination of quasi-static compression experiment and finite element simulation analysis was adopted to explore effect of pitting time and concentration of dichloromethane solvent on the compression properties of porous structural panels. Results showed that surface of 100 % solvent became smooth and flat, while surface of 80 % solvent only formed a dense covering film. When specimens continues to suffer from corrosion, the single-layer specimens changed its deformation directions to a certain extent, while the instability of the two layers bolted porous structural panels gradually decreased when the corrosion damage increased. Mass concentration of 90 % was the critical point for local mechanical performance of specimens.

Research on the shear band suppression mechanism in strut-based lattice structures by oblique graded design

Under compressive loads, shear band formation in lattice structures can lead to stress fluctuations, resulting in a decrease in energy absorption capacity. To specifically suppress shear bands, it is necessary to expound the formation mechanisms. This study used theoretical analysis, experiments, and finite element (FE) simulations to elucidate the mechanism underlying shear band formation in strut-based lattice structures. It was determined that stress concentration at strut joints along the 45° diagonal plane induced shear deformation. Shear bands were most pronounced along the four body diagonals, and their existence diminished as the distance from the diagonal increased. Therefore, a design of oblique graded lattice structure (OGLS) was proposed, and quasi-static compression experiments were performed using FE method. The results showed that the main internal stress of OGLS is combined with the original 45° shear stress and the annular staggered stress produced by the oblique graded design, which constrains each other and avoids mutual dislocation deformation, thus realizing shear band suppression. However, an excessively large graded coefficient excessively weakens the 45° shear stress and results in the appearance of an annular compact band. By optimizing the graded coefficient based on the deformation consistency of the outer contour, the optimized OGLS exhibited significant improvements in yield strength, plateau stress, and energy absorption, which are increased by 36.06%, 39.29%, and 34.41%, respectively. This research offers novel perspectives on how lattice structures can attain stable compression deformation and a high energy absorption capacity.

A failure model for bulk metallic glass based on strain rate-correlated softening mechanism

Due to the amorphous nature of the bulk metallic glasses (BMGs), catastrophic fractures occur once the nucleation and propagation of shear bands occur, which is quite different from crystal materials. So far, the underlying mechanism of BMG failure behavior and its strain rate effect are still controversial. In this work, the quasi-static and dynamic compression experiments of Vit-1 BMG were carried out in a wide range of strain rates from 0.001 s−1 to 5000 s−1. The results show that the variation tendency of failure stress with strain rate can be divided into three stages. The quasi-static failure stress is insensitive to the change of strain rate with only almost constant free volume softening effect inside the material during the failure process. When entering dynamic loading stage, the failure stress decreases significantly, which is caused by a combination of increasing thermal softening and free volume softening effects. When the strain rate increases to the third stage, that is, over 2000 s−1, the failure stress and the softening effects basically remain unchanged. The transformation of failure mechanism is well confirmed by the micromorphology of fracture surfaces. Based on the experimental results, a concise empirical failure model is established, in which the failure stress is decomposed into softening and non-softening parts. The verification experiments show that the model can effectively predict the compression failure stress of BMG under different strain rates.

Rigid–flexible coupling design and reusable impact mitigation of the hierarchical-bistable hybrid metamaterials

Mechanical metamaterials with multistable unit cells featured by negative stiffness or quasi-zero stiffness is attracting increasing attention owing to their unique mechanical properties and reusable potential. In this paper, a hierarchical-bistable hybrid metamaterial with rigid–flexible coupling design is proposed, demonstrating excellent mitigation performance and protection against multiple impacts. The metamaterial consists of a multi-layer bistable beams with a central honeycomb and is manufactured by 3D printing. Firstly, the negative stiffness characteristics of the curved beams in the metamaterial are theoretically determined, and the convergence of the finite element model under different mesh sizes is analyzed. And the quasi-zero stiffness characteristics of the metamaterial have been confirmed, along with its more stable and uniform deformation pattern, through the quasi-static compression experiment. Then the buffering performance of the metamaterial is studied in ball impact tests, showing an average improvement of about 65% compared to the rigid control group, while verifying the accuracy of the finite element model. With the analysis of the deformation modes and strain energy, the mitigation mechanism of metamaterials is demonstrated to extend the contact time and disperse the impact load through the layered deformation to reduce the peak response, instead of relying on plastic strain. Finally, the reusability of the metamaterial is explored by the ten-times plate impacts simulation. The results demonstrate that the metamaterial decreases the plastic strain of its structure by 60% while reducing impact response, thereby preventing the premature failure of core components. These results demonstrate the great potential of the proposed metamaterials for various engineering applications, including aircraft or spacecraft landing protection, vehicle pedestrian protection, and the transportation protection of fragile objects or precision instruments.

A filling lattice with actively controlled size/shape for energy absorption

This study unveils a groundbreaking development: the chain lattice structure (CLS), a unique lattice with the capability to actively adjust its size and shape for filling diverse thin-walled structures, thereby enhancing their energy absorption characteristics. Traditional lattice structures, known for excellent energy absorption, are constrained by fixed sizes and shapes post-fabrication, limiting their adaptability to various energy-absorbing structures. The CLS introduces a revolutionary lattice structure dynamically modifying dimensions and shape. Employing selective laser sintering (SLS), we craft CLS prototypes using nylon 11 material, followed by rigorous quasi-static compression experiments. The congruence between experimental and simulation analyses validates our model's accuracy. CLS actively adjusts within varying cross-sectional thin-walled square tubes, demonstrating substantial improvements in energy absorption and compression stability compared to empty tubes (ETs). Additionally, CLS adapts to diverse cross-sectional shapes, including circular, hexagonal, and triangular tubes. Comparative assessments reveal significant enhancements in energy absorption and compression stability for CLS-filled tubes. Moreover, the pre-deformed CLS model was filled with different shapes of front rails, and its axial crashworthiness and deformation pattern stability were significantly improved compared with the unfilled front rails. In summary, CLS's flexibility in adjusting to thin-walled structures of varying dimensions and shapes holds immense promise for enhancing their performance across a wide range of applications.

Quasi - static and impact performance study of a three-dimensional negative Poisson's ratio structure with adjustable mechanical properties

The mechanical properties of most materials with a negative Poisson's ratio (NPR) cannot be flexibly adjusted after being designed to meet complex engineering requirements. To ensure the changes of those materials’ relative density are minimal when overcoming these limitations, this study proposes a novel method that adjusts the mechanical performance by grooving the structure and adjusting the angle of the diagonal support rod. Unlike traditional methods that involve adding 'ribs' to the structure for adjustability, this approach focuses on the design of the structure itself. To analyze the large deformation behavior of unit-cell lattices, we established a theoretical model based on plastic deformation theory and derive the relationship between the number of unit-cell lattices and the relative density of multi-cell lattices. Experimental samples were fabricated by using selective laser melting (SLM). Meanwhile, the accuracy of the finite element results was verified by quasi-static compression experiments and impact experiments. Then the validated finite element model is then utilized to discuss the influence of structural parameters on mechanical properties. In addition, we also studied the influence of medium and low-speed impact loads on the deformation characteristics, mechanical properties, and energy absorption (EA) of the structures. The results demonstrate the reliability of the design method, showcasing its potential to achieve on-demand adjustability of stress, stiffness, and strength to meet complex engineering requirements. Notably, the adjustment range of peak load is from 24.55 MPa at the lower limit α = 60° to 48.29 MPa at the upper limit α = 90°, with an adjustment range of 23.74 MPa. The adjustment range of the average platform stress is from 10.8 MPa at the lower limit of α = 60° to 24.34 MPa at the upper limit of α = 80°, and the adjustment range reaches 13.54 MPa. This study provides new insights on intelligent protection engineering and the adjustable mechanical properties of metamaterials.

3D-printed polymer-derived ceramics with tunable cellular architectures

Ceramic materials possess high mechanical strength and environmental stability, but their brittleness limits their suitability for structural applications. A solution lies in using polymer-derived ceramics (PDCs), which offer enhanced toughness and versatility in shaping unlike traditional ceramic processing methods. This study explores tunable ceramic cellular architectures based on triply periodic minimal surface (TPMS) designs, fabricated via stereolithography (SLA) using a silicon oxycarbide precursor formulated for vat photopolymerization. By combining the preceramic polymer with a photoinitiator, crosslinkers, and other additives, intricate shapes are 3D-printed and then pyrolyzed under nitrogen, resulting in PDCs with complex TPMS geometries. The toughness, strength, and stiffness of the 3D-printed structures are evaluated through quasi-static compression experiments. Comprehensive material and microstructural characterizations of the PDCs are performed pre- and post-pyrolysis, employing visual inspection, X-ray micro-tomography, thermogravimetric analysis, energy dispersive X-ray spectroscopy, density, and rheological measurements. Optimization of 3D printing and pyrolysis parameters yields ceramic structures with 2.2 MPa compressive strength and 330 MPa stiffness with a lattice density of 0.5 g cm-3. The ceramic material, including porosity, had a maximum density of 1.63 ± 0.01 g cm-3. This low-cost SLA 3D printing technique is ideal for creating thin features and customized structures of bio-inspired, architectured ceramics. Furthermore, the process exhibits excellent printability, being compatible with common and cost-effective SLA, DLP, and LCD 3D printers.

Establishing a unified viscoplastic constitutive equation for EA4T steel: Comparative analysis with Arrhenius model

Quasi-static and impact compression experiments were conducted on EA4T steel using a Gleeble-3800 thermal simulation machine. The study aimed to investigate the complex microstructural evolution and thermal deformation behavior of EA4T steel under various experimental conditions, including temperatures ranging from 970 °C to 1170 °C and strain rates ranging from 0.01s−1 to 1s−1. To precisely elucidate these phenomena, we meticulously constructed a unified visco-plastic constitutive model using the internal variable methodology. The model's parameterization was achieved through the effective application of genetic algorithm optimization techniques. Rigorous validation of the model was performed by meticulously comparing its outputs with experimental data, including key metrics such as average grain size, recrystallized fraction, and effective flow stress. In addition,a comparative analysis with the improved Arrhenius model highlights the superior performance of the unified visco-plastic constitutive equation in capturing the intricate microstructural evolution and thermal deformation behavior exhibited by EA4T steel.

Evaluation of quasi-static and dynamic compressive properties of Ti-6Al-4 V functionally graded shell lattices with minimal surfaces

Functionally graded shell (FGS) lattices have recently captivated enormous research interest in engineering applications for their outstanding mechanical and energy-absorbing performances. This paper designs FGS lattices featuring I-WP triply periodic minimal surfaces using implicit functions. FGS and uniform shell (US) samples made of Ti-6Al-4 V powder are manufactured utilizing laser powder bed fusion technology. Quasi-static compression and drop-weight impact experiments are conducted to evaluate the mechanical and energy-absorbing performances as well as deformation mechanism of FGS and US samples. The results demonstrate that the deformation modes of the samples under both loading conditions are similar, which is basically attributed to the drop-weight impact velocities being lower than the critical speeds calculated by the rigid-power-law hardening (RPLH) model. Additionally, the effects of loading velocity on the deformation mechanisms of US and FGS lattices are simulated, and homogenization, transition, and shock deformation models are predicted by the RPLH model. The FGS sample exhibits distinct layer-by-layer failures and eliminates the abrupt shear band under dynamic and quasi-static loadings. Compared to the quasi-static results, a notable strain rate hardening effect is observed under the dynamic condition, mainly due to the hardening of the row material. Consequently, the elastic modulus, yield strength, compression strength, and cumulative energy absorption of the US sample under drop-weight impact loading improved by 18.74 %, 56.52 %, 45.31 %, and 6.62 %, respectively. However, the FGS sample shows less sensitivity to strain rate owing to the layer-by-layer deformation mechanism, and their elastic modulus, yield strength, compression strength, and cumulative energy absorption only increased by 11.84 %, 34.72 %, 36.85 %, and 3.86 %, respectively. The FGS lattices exhibit a low peak stress during the compression process, which is favorable for industrial applications in crashworthiness and energy absorption.

Inspiring nested modular structure for axial compression performance

Modular structures can adapt to different energy absorption scenarios by changing the assembly form. In this work, inspired by Chinese window frames, four-leaf clovers, cotton rose hibiscus, and maze, a variety of nested modular (NM) structures are proposed with aluminum square tube as base platform. The finite element model of aluminum square tube (AST) is verified through quasi-static compression experiments. Building upon the above, a hierarchical aluminum square tube (HAST) structure is further proposed for enclosing multi-module nested modular (M-NM) structures. Five nested components, namely plum octagonal nested modular structure (PONM), square fluted tube nested modular structure (SFTNM), floral layered nested modular structure (FLNM), square spiral nested modular structure (SSNM), square spiral distributed nested modular structure (SSDNM), are combined with these two platforms, thus generated ten typical NMs. These NM models exhibit two deformation modes, namely the progressive folding of multilobe flaps and the hybrid of outward expansion and progressive folding. M-PONM looks like "jackfruit" after being compressed. Furthermore, the effects of reducing nested components and employing hybrid assembly techniques are further explored. The results indicate that the proposed NM structures significantly enhance the compressive resistance and stability of AST. It is noteworthy that reducing nested components weakens the coupling effects, while hybrid assembly has the opposite effect. In summary, this work provides a series of novel NM structures, providing new ideas for the design of energy absorbing structures.

Mechanical and thermal property analysis and optimization design of hybrid lattice structure based on triply periodic minimal surfaces

Hybrid lattice structures have significant potential in engineering applications owing to their outstanding mechanical and thermal properties. In this paper, an innovative design strategy for hybrid lattice structures is proposed involving the integration of primitive surfaces with truss lattice configurations. This approach allows for the full exploitation of the mechanical and thermal properties inherent in each component, leading to the development of new hybrid lattice structures. Firstly, the quasi-static compression and fluid-solid coupling heat conduction analysis of the hybrid lattice structure is carried out by numerical simulation. Then the effects of surface wall thickness, and truss diameter on the mechanical and thermal properties of the lattice structure are discussed. Additionally, the mechanical performance of the array hybrid lattice structure is evaluated through quasi-static compression experiments. These experimental results are compared with those from the numerical simulations, validating the accuracy of the simulation model. Finally, a multi-objective optimization model targeting specific elastic modulus and heat dissipation performance (indicated by Nusselt number) is established, in response to the demand of aviation and aerospace industries for lightweight, load-bearing, and heat-dissipating multi-functional integrated lattice design. The non-dominated sorting genetic algorithm is utilized to solve the optimal model, and the distribution of feasible solutions and Pareto front are obtained. The results show that the interpenetrating hybrid lattice structure has a greater improvement in mechanical and thermal properties than the primitive surfaces. This research holds significant implications for the design of multi-performance hybrid lattice structures.

Compression properties and energy absorption of Gyroid lattice cylindrical shells filled thin-walled tubes fabricated by selective laser melting

In recent years, lattice cylindrical shells (LCSs) based on the triply periodic minimal surfaces (TPMS) have been researched in the energy absorption (EA) field due to their distinctive mechanical properties. However, LCS structures will generate severe lateral expansion and localized fragmentation during compressive deformation, resulting in a significant decrease on compression performance. To further improve EA properties, Gyroid LCS filled thin-walled tubes (LCS-T) are proposed and produced by selective laser melting (SLM). In this work, the influence of the interaction (hollow thin-walled tubes + LCSs core) of the Gyroid LCS-T with different filling radii on the compressive properties and EA were investigated by the quasi-static compression experiments and finite element simulation systematically. The results showed that the Gyroid LCS-T based on AlMgScZr alloy fabricated by SLM had high connection strength and no obvious defects. The specific EA (SEA) of Gyroid LCS-T with radius of 3, 6, and 9 increased by 42.1%, 49.3%, and 53.3%, respectively, compared to thin-walled tubes. Compared to the sum of all components individually, the Gyroid LCS-T achieved superior performance in both compressive properties and EA by transferring stresses from the LCS interior to the thin-walled tube. Furthermore, the gradient design realized adjustment of the structural deformation and improved EA with about 1.24 times compared to uniform structure. This research offered visionary insights into designing energy-absorbing structures and optimizing parameters for LCS-T.

Strain rate effects on fragment morphology of ceramic alumina: A synchrotron-based study

Dynamic (600–1000 s−1) and quasi-static (0.001–0.01 s−1) compression experiments are conducted on a high-purity alumina ceramic using a split Hopkinson pressure bar and a material test system, respectively. The postmortem fragments of ceramic samples at different strain rates are then characterized via synchrotron micro computed tomography (CT). The three-dimensional (3D) morphologies of fragments are quantified using the gyration tensor analysis after proper segmentation of CT images. The mean fragment size decreases in a power-law form while the mean shape indices (sphericity, elongation index and flatness index) increase in a logarithmic-linear form, with increasing strain rates. In addition, the fragment size and shape distributions are all found to follow the Weibull probability distribution. To reveal the underlying mechanisms of such strain rate effects, high-speed optical and X-ray imaging are implemented to capture the fracture process of ceramic samples under quasi-static and dynamic compression. Primary and secondary wing cracks (PWCs/SWCs) control the fracture and fragmentation of the ceramic under both loading conditions. Compared to quasi-static loading, a considerably larger number of SWCs are produced under dynamic loading, and pronounced branching and bridging occur among the PWCs, which prevent the PWCs from coalescing into axial splitting cracks. Consequently, crack networks composed of high-density wing cracks break the sample into finer and more isotropic fragments, consistent with CT characterizations. Scanning electron microscopy is utilized to analyze the micro damage modes of ceramic samples. Transgranular fracture dominates the grain-scale damage and contributes to the higher dynamic fracture resistance of the alumina under dynamic loading, as a result of more homogeneous nucleation and growth of micro cracks.