International Journal of Impact Engineering最新文献

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.

Damage determination and quantification are critical issues in conducting damage assessment and performance-based design for RC columns under low-velocity impact loads. An impediment in these issues lies in defining reasonable damage criteria. To this end, a framework inspired by existing experimental results is proposed to quantify the damage of RC columns. The core concept of this framework is to establish the relationship between the engineering demand parameter (i.e., drift ratio) and the damage index based on residual axial capacity and to convert the damage index threshold to the drift ratio threshold using a reliability-based method. According to the proposed framework, damage criteria are developed for RC columns in two typical impact scenarios, including the mid-span and near-base impacts. During this process, linear relationships between the maximum drift and the residual one at the impact location are developed by statistically analyzing the existing experimental data (a total of 212 test samples). Based on experimentally validated numerical models, empirical formulas for estimating the residual axial capacity of RC columns are established. The maximum drift, the residual drift, and the axial capacity degradation are interrelated in the proposed damage criteria, overcoming the limitation that the current deformation-based damage criteria used for low-velocity impact loads lack physical significance.

The safety of Li-ion batteries (LIB) has become an important issue with the continuously increased use of electric vehicles (EV) in the world. In a survivable vehicle crash, when the vehicle needs to maintain structural integrity, crash-induced shock may damage EV's LIB. Therefore, an evaluation of commonly used mechanical shock test standards for EV battery module and pack is performed in this study against the crash-induced shock signals collected from National Highway Traffic Safety Administration (NHTSA) New Car Assessment Program (NCAP) tests. Various shock analysis methods including signal characteristics in time domain, power spectral density (PSD) and shock response spectrum (SRS) in frequency domain, and the acceleration/velocity-change diagram are used for the evaluation. It is found that most peak accelerations of NCAP shock signals significantly exceed the peak accelerations specified in shock testing standards. Crash-induced shocks cannot be fully represented by the half-sine pulse adopted in shock testing standards. In both time and frequency domains, the existing shock testing standards generally underestimate the severities of the crash-induced shocks, and therefore, are non-conservative. It also shows that the correct selection of a filter for the processing of the original crash-induced shock signal is crucial for the specification of EV battery shock environment and shock response analyses. The results obtained in this research can support the development of more reliable shock testing standards for EV batteries.

Due to the unique design requirements for high load-bearing capacity of ship structures, composite materials used in the marine industry are gradually being developed with the characteristics of multi-layer sandwich structures with large thickness and cross-section, which are different from thin-walled composite materials widely applied in the aeronautical industry. However, sandwich composite materials used in marine structures have high susceptibility to impact event during in-service applications. The impact induced damage may seriously affect their mechanical performance and structural safety. Therefore, a comprehensive investigation in this paper on the failure mechanisms of composite sandwich panels with orthogonal woven GFRP facesheets and a PVC foam core layer is carried out with a series of single and repetitive low-velocity impact tests. The variations of impact force, dent depth, structural stiffness, failure modes, energy absorption and so on of composite sandwich panels against impact energy levels and impact numbers were explored. The results demonstrate that the delamination damage threshold at the first impact, the sudden drop of peak force and the slow descent process of impact force are the three typical characteristics of impact responses that corresponded to delamination initiation and fibre breakage of the upper panel, and compression damage of the core layer, respectively. The accumulated impact-induced damage has a significant negative effect on load-bearing and energy-absorption capabilities of composite sandwich panels. Moreover, an approximate theoretical analytical method is presented to solve the impact resistance of composite sandwich panels. The analytical results are compared well with experimental results. This research provides a detailed understanding of the damage mechanisms of composite sandwich panels under impact loadings and a guidance for impact resistant design of ship protective structures.

A pressing issue for reinforced concrete walls, which are commonly used as building structures, is how the fragments and shock waves generated by the explosion of a cased charge affect the concrete structure. In this paper, the damage modes of reinforced concrete walls (RC walls) and reinforced concrete-steel composite walls (RCS walls) under the combined loading of fragments and shock waves are investigated by experimental methods, and the effects of wall thickness, strength, stand-off distance, and thickness of the steel plate on the back on the damage modes of the walls are discussed. Based on the experimental data, the damage modes of the walls were classified into three classes. In comparison, the installation of steel plates on the back of concrete walls was found to be a significant means of protection, effectively preventing the penetration of metal fragments and the splashing of concrete fragments.

In this experimental study, the scaled double-layer containment structure represented by 1000 mm × 1000 mm targets of outer reinforced and inner prestressed concrete of thickness 200 mm has been subjected to ballistic impact by 10 and 20 kg rigid missiles at incidence velocities, close to 100 m/s. The inner layer of prestressed concrete was cast with and without a monolithic rear steel liner of thickness 1.5 mm. The prestressing force was induced in the vertical and horizontal directions with respect to 15 % of the characteristic compressive strength of concrete (M45). In double-layer tests, the 20 kg missiles perforated the outer layer target with significant residual velocities, while the 10 kg missile just perforated the outer layer. The 20 kg missile, when impacted the inner layer prestressed concrete target with a rear steel liner, experienced no damage. However, when impacted, the prestressed concrete target without a rear steel liner suffered significant rear surface cracking but no scabbing of concrete. This concludes that steel liner plays a substantial role in mitigating rear surface cracking and minimizing damage to the inner layer target. The ballistic tests were also performed on single independent prestressed concrete targets with and without steel liner against 20 kg missiles. In single-layer tests, the target with the rear surface steel liner restricted the perforation phenomena, however, significant damage occurred to the concrete and the steel liner. On the other hand, the target without a steel liner underwent complete failure through perforation. Hence, steel liners not only controlled the rear surface cracking (in double-layer) but also effectively controlled the perforation phenomena (in single-layer). No loss of prestressing force was observed in the case of the double-layered configuration, however, when the missile impacted the single-layered prestressed concrete target, a noticeable loss of prestressing force was observed. The perforation limit velocities calculated using Modified NDRC, BRL-NDRC, CEA-EDF, UMIST, and Modified UMIST empirical models for reinforced and prestressed concrete targets were compared with the experimental results.

In Split Hopkinson Pressure Bar (SHPB) tests, the stress wave effects during the elastic phase of the stress-strain curve and their influence mechanisms are crucial. Due to the extremely short duration of the elastic deformation phase, the stress wave effects on the specimen during this stage cannot be ignored. This leads to significant errors in the obtained elastic stress-strain curves. However, the dynamic compressive elastic stress-strain relationship forms the basis for studying the viscoelastic behavior of materials. Accurate determination of elastic yield stress and yield strain is also essential for deriving accurate plastic stress-strain relationships. Quantitative research on the stress wave effects during the elastic compression phase of SHPB tests is fundamental for decoupling and obtaining accurate material elastic curves. This paper conducts a quantitative theoretical analysis of the structural effects caused by stress wave evolution during the elastic compression phase, based on the assumption of plane waves. It studies the deviation characteristics and main factors of the phenomenological engineering stress-strain curves of the specimen compared to the actual material stress-strain curves under different conditions, revealing the influence rules and mechanisms of this deviation. The maximum stress deviation value and its corresponding dimensionless time, as well as the variation trend of the maximum stress deviation value within different fluctuation intervals, are calculated. Additionally, the study investigates the cases where the incident wave is arc-shaped or a combination of arc and linear waves. The findings provide theoretical references for the precise design and accurate data processing of SHPB tests.

Dynamic brittle fracture and shear banding are two typical failure modes of metals, and the transformation of the brittle-ductile failure mode has been observed in the Kalthoff test. This paper establishes a thermo-elastic-plastic coupled three-dimensional phase field model to simulate brittle-ductile failure mode transition of metals. The expression for the variation of the Taylor-Quinney coefficient with stress triaxiality is adopted, and the critical energy release rate is automatically adjusted using the Taylor-Quinney coefficient. Then, the Kalthoff test is simulated using the proposed model. The brittle-ductile failure mode transformation phenomenon is reproduced, which agrees well with the experimental results. It can be well proved that impact velocity is crucial in determining the transition to failure mode. At low-velocity impact, the energy is insufficient to drive the plastic accumulation of the shear band, resulting in brittle tensile fracture. At high-velocity impact, the energy is sufficient to drive the formation of adiabatic shear bands, resulting in tensile shear failure. In addition, three-dimensional simulations show that the tip of the shear band exhibits a crescent-shaped non-two-dimensional extension state under finite thickness. This numerical framework provides a predictive tool to understand the evolution of the dynamic failure of metals under impact loading.

In this study, the experimental and numerical investigations are performed to explore the enhanced energy-absorption performance of hybrid polyurethane(PU)-foam-filled lattice metamaterials subjected to low-velocity impact (LVI). Initially, three types of lattices are prepared by additive manufacturing technique, and then filled with the PU foams using freeze casting technique. Experimental and numerical LVI tests have been performed to characterize the energy-absorption performance of pure and hybrid lattice structures. These experimental and numerical results indicate that the hybrid structures possess the longer elastoplastic and damage evolution stages than the pure ones. The overall absorbed energy of the hybrid structures is distinctly higher than the sum of pure lattices and PU foams, disclosing the enhancement of the energy-absorption capacity induced by the PU-foam-filling. Besides, the pure and hybrid hyperbolic lattice structures exhibit the better energy-absorption capacity than two other types, due to the compression-twist effect. As the foam collapse occurs, the lattice damages are significantly inhibited in the hybrid ones. It reveals that the filled foams protect the embedded lattices via causing foam collapse to dissipate impact energy. Meanwhile, foam-filling prevents the excessive twisting behavior of the hyperbolic lattice and makes the stress distribute more evenly.

Experiment and numerical simulation were conducted to investigate the penetration performance of shaped charge jet into block stone concrete targets. The experiment has shown that the jet undergoes deflection and other phenomena during its penetration of block stone concrete. Improvements have been made to the methods used by previous scholars for constructing aggregate particles, resulting in a particle model that more closely resembles the true shape of the aggregate. A novel method for judging the intersection of aggregate particles based on the Plucker coordinate system was proposed. In comparison with traditional methods, this method is not constrained by the shape of aggregate particles. By utilizing dynamic simulation software to replicate aggregate settlement during the production process of concrete targets, a 3D meso-scale model of concrete was successfully established. Numerical simulations were conducted according to the experimental settings, with the results demonstrating good consistency between the experimental and numerical simulations, thus confirming the reliability of the model and methodology presented in this article. Additionally, the numerical simulation results suggest that the aggregate content significantly influences the degree of interference, penetration depth, and damage zone range of the jet, while the impact position primarily affects the deflection of the jet. This article provides a numerical simulation method for future research on the penetration and damage mechanism of shaped charge jet considering the 3D meso-scale model of concrete.