International Journal of Impact Engineering最新文献

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.

Steel wire reinforced ultra-high performance concrete (SWRUHPC) offers exceptional resistance to impacts and blast, making it a promising construction material for infrastructure with blast-resistance demands. However, limited research has been conducted on the blast-resistance characteristics and design of SWRUHPC elements under blast loading, particularly in considering multiple influencing parameters and levels. Therefore, this study employed finite element simulation methods to investigate the influence of scaled distance (Z), reinforcement ratio (ρ) and slab thickness (D) as well as slab length (L) on the failure mode and maximum deflection of SWRUHPC slabs. Range analysis and variance analysis methods were used to quantitively analyze the effects of various factors on the blast resistance performance, culminating in the proposal of a design formula for SWRUHPC slabs. The results demonstrated that SWRUHPC exhibits superior blast resistance compared to ordinary concrete, effectively reducing the occurrence of concrete spalling and splashing, thus enhancing overall structural resilience in blast scenarios. Among the four factors analyzed, their influence on maximum deflection follows this order: D > Z > ρ > L. Notably, the maximum deflection decreases by 82 % when the slab thickness increases from 40 mm to 90 mm. Additionally, the established design formula for SWRUHPC slabs under different scaled distances shows good agreement with the numerical simulation results, offering valuable design guidelines for SWRUHPC slabs in protective engineering structures.

The axial crushing behavior of natural bamboo culms with various growth ages under quasi-static and low-velocity impact was experimentally investigated in this study. First, the macro- and micro- structural features of bamboo culms were observed, and the tensile mechanical properties of bamboo materials were measured. And then the typical crushing responses and deformation/failure patterns of dynamically-loaded bamboo culms were presented, compared with those under quasi-static load. Whereafter, the strain field distribution and energy absorption characteristics of bamboo culms were analyzed, and the crashworthiness of tested bamboo culms under impact load was evaluated. Finally, the energy absorption capacity of bamboo culms was compared with typical metallic circular tubes (made of Q235 steel and AA6061-T6 aluminum alloy) and other widely-used engineering materials/structures. The results indicate that the brittle fracture is the dominant failure mode of bamboo culms, which includes the splitting mode for internodal specimens and the bulging mode for nodal specimens. The nodal bamboo culms have a superior energy absorption capacity and crashworthiness compared to internodal bamboo culms, attributed to the dense distribution of vascular bundles and high anti-split strength of bamboo nodes. The energy absorption capacity of 1-year-old nodal bamboo culms is better than that of aluminum or steel tubes, and the corresponding SEA value of nodal bamboo culms has reached 11.8 J/g, while it is 10.65 J/g of the aluminum tube and 6.65 J/g of the steel tube, respectively.

Prefabricated ultra-high-performance concrete (UHPC) target has the advantages of prominent anti-penetration capability and good construction quality. However, the interfaces in the prefabricated target would inevitably reduce its penetration resistance. To deal with this problem, a new prefabricated technique with the use of wet joints and rebars is proposed. To demonstrate the effectiveness of the proposed technique, two sets of projectile penetration tests on prefabricated targets assembled by prefabricated UHPC blocks, wet joints and rebars were firstly conducted and compared with corresponding experimental results of monolithic targets, demonstrating the comparable penetration resistance between prefabricated targets and corresponding monolithic targets. Then, based on the Kong–Fang model and SPG method, the numerical models of the two tests were developed and validated against the experimental data. The validated numerical models were further used to investigate the influences of interfaces, wet joints and rebars on the penetration resistance of prefabricated targets. The numerical results found that the horizontal interfaces have a limited influence on the penetration resistance while the vertical interfaces have a strong influence. It also numerically demonstrated the effectiveness of the proposed technique using wet joints and rebars to connect prefabricated blocks. The research results can provide an important reference for the use of prefabricated targets in protective engineering.

In this work, we provide a hydrocode simulation model for high-velocity projectile impact against ultra-high-performance concrete targets and establish a methodology to extract damage quantities from the simulation results. In the parameter derivation process, published and own data stemming from material experiments, such as uniaxial, triaxial, and planar plate impact tests, are used as a starting point. To fill the systematic gaps of strength data for pressures of 1 GPa to 5 GPa and for fractured concretes, residual velocities of projectiles and qualitative target damage information from ballistic experiments with high-hard steel spheres are additionally used as a reference in parametric simulations. All criteria from the comparatively broad data basis are successfully reproduced by the simulation model simultaneously. The simulated damage quantities derived by the proposed extraction procedure are reasonable counterparts to the corresponding experimental measures from earlier published works, allowing a new quality of comparison between both worlds.

Orbital debris impacts on spacecraft are an emerging threat to space missions due to the exponential increase in the number of satellites orbiting the Earth. Debris characteristics (size, material, velocity, etc.) are not well known for the size range of 10 mm or less that is undetectable using Earth telescopes or radar observation. The objective of this research was to determine wether a concept designed to detect impact of particles in the ∼1 to 5 mm range, find the location of the impact, and characterize the impacting projectile (velocity, size, angle, density), is feasible.

The paper describes the design, fabrication, and tests performed on “witness plates” (the concept) made of two parallel layers of additively manufactured aluminum and instrumented with sixteen gages, eight on each layer. Laboratory experiments have shown that the waves can be recorded and properly interpreted to find location of impact, sound speed in the plate, and to estimate impact velocity. It was shown analytically that the amplitude of the first strain wave that propagates from the impact point is expected to decay as 1/r. This was observed as well in the signals recorded in the experiments. CTH computations were performed during the pre-test design phase and the post-test analysis phase. In fact, the numerical simulations have been key and pervasive in this research effort as they provided invaluable insight for the initial design and the correct interpretation of signal anomalies seen during the tests. Additionally, the computations confirmed the 1/r law derived analytically, i.e. that the assumptions for the derivation were justified. The main conclusions of the research are that, for a normal impact, the 1/r law for front gages can be easily used to determine the diameter of the impactor. It is possible that the back gages could be used to determine the density of the impactor as well. Finally, it was shown that oblique impacts generate an expected assymetry in the signals recorded. Though this aspect should be investigated further, the assymetry is probably uniquely related to the impact angle, which could provide the angle information.

Structural impact often accompanies large amounts of contacts and leads to complex mechanical phenomena. In solid mechanics, the numerical manifold method (NMM) is proposed to address problems featuring continuous-discontinuous transitions by utilizing a dual coverage system encompassing both mathematical and physical covers. In the present work, a penalty contact algorithm for 3DNMM based on cover-based contact theory is programmed and applied to impact mechanics problems. The accuracy of the developed contact algorithm is firstly calibrated through free-falling blocks and collision blocks. The influence of contact parameters on contact convergence is systematically studied, and three preliminary criteria for how to set contact parameters are provided. The effectiveness of the contact algorithm is verified by conserving system momentum during block collisions. Subsequently, the contact algorithm is applied to Taylor rod and car-streetlight impact simulation, further confirming its effectiveness in modeling high-speed collisions, large displacements, and large deformations of structures. By comparing the 3DNMM results with those from Abaqus, the contact algorithm developed here performs exceptionally well in solving collision problems and produces results consistent with commercial software. The research results in the present work verify the applicability and accuracy of the proposed contact algorithm in solving structural dynamic impact problems. The present work also provides guidance for contact parameter setting in impact problems.

The study on dynamic shear behavior of fiber reinforced polymer (FRP)-concrete interface is of great significance for the performance evaluation and design of FRP externally strengthened concrete structures. Firstly, the quasi-static and dynamic single shear test on the interfacial shear behavior between carbon fiber reinforced polymer (CFRP) sheet and concrete substrate was carried out. The corresponding failure modes of CFRP-concrete interface, CFRP strain-time histories, load-displacement curves, and interfacial shear stress-slip relationships under loading rates of 8.33 × 10⁻⁶–10 m·s⁻¹ were obtained. It was indicated that the dynamic interfacial shear behaviors, i.e., interfacial failure mode, debonding load, interfacial shear stress, etc., were sensitive to loading rates. Then, a 3D mesoscale modeling approach of concrete with random shaped, sized, and spatially distributed convex polyhedron aggregates was proposed, in which the volume fraction of aggregates was adjustable within the range of 0–50 % through gravitational drop and size scaling of aggregates. Furthermore, based on the established 3D mesoscale concrete model and the zero-thickness cohesive elements for adhesive layer, numerical simulations for FPR-concrete interfacial shear behavior were conducted and validated by comparing with the present and existing quasit-static and dynamic single shear tests. The experimental phenomenon of the failure location transferring from concrete substrate to adhesive layer at high loading rates was numerically reproduced. Finally, the influences of strain rate enhancing effects of aggregates and mortar on the interfacial failure modes were discussed. It was revealed that the failure location transferring from the concrete substrate to the adhesive layer was significantly affected by the strength enhancement of mortar and aggregates with the loading rate increasing.

Glass mat thermoplastic tubes are potential materials for improving crashworthiness owing to their excellent crash energy absorption capability due to their splaying failure mode of glass mat thermoplastic tubes, which must be considered in the crash analysis to accurately predict their crash performance. This study investigates the crash analysis of glass-mat thermoplastic composite tubes to realize the splaying failure mode and crash energy absorption capability. We evaluated the mechanical properties and fracture toughness of advanced glass mat thermoplastics, termed multi-layered hybrid mats, and employed the result in a 3D Hashin-type continuum damage model implemented with a user material subroutine. For the crash analysis of glass mat thermoplastic tubes, a three-dimensional finite element (FE) model, including cohesive elements in the middle layer of the tube to simulate the splaying failure mode, was constructed. In addition, in the process of the efficient FE modeling of the crash tube, the fracture toughness correction factor was proposed and optimized to calibrate the energy absorption in conjunction with crash test results, as interlaminar fracture modeling causes a difference in energy absorption between the actual test and simulation. As a result, the proposed crash analysis predicted the energy absorption capacity and a splaying failure mode of glass-mat thermoplastic tubes, demonstrating strong concordance with experimental results.

This study investigates the effectiveness of Lightweight Expanded Clay Aggregate (LECA) as a novel cushion material mitigating repeated rockfall impacts on reinforced concrete (RC) slabs in rock sheds. Small-scale impact tests and finite element simulations analyze LECA particle size, cushioning material, block shape, and impact energy level influence on the dynamic response and damage. Results show LECA outperforms sand in attenuating impact forces and transmitted loads under successive impacts, which indicates a better protection effect on the substructure. Smaller LECA particles lead to wider stress distribution angles, longer impact durations, and lower peak forces. Block shape significantly influences impact force, with higher unified nose factors increasing forces. LECA cushions exhibit a dynamic amplification factor less than 1, indicating reduced transmitted loads compared to sand. Under high-impact energy conditions, the LECA cushion limits RC slab deflection within the elastic limit across all block shapes, while sand exceeds the elastic limit, potentially leading to structural failure. LECA mitigates flexural cracking and redistributes loads more uniformly, reducing overall RC slab damage compared to sand. However, localized failure modes require further optimization. This study highlights LECA's potential for enhancing rock shed structural safety and resilience against severe rockfall events, providing insights for optimal mitigation strategies.