International Journal of Impact Engineering最新文献

A non-ordinary state-based peridynamics (NOSB-PD) model is proposed to simulate the projectile penetration into concrete targets. In this model, the Kong-Fang concrete material model recently proposed is firstly implemented into the NOSB-PD framework to describe the complex dynamic behavior and failures in concrete material subjected to penetration loading, and then an improved point-to-volume discrete frictional contact model is proposed to simulate the physical interaction between projectile and target. After the mesh-free discretization and explicit time integration, the proposed NOSB-PD model is used to numerically predict two sets of projectile penetration experiments into low-strength and high-strength concrete targets. And numerical predictions are found to be in good agreements with corresponding test data including penetration depth, projectile deceleration, deformation of projectile and failures in concrete targets.

In this study, metakaolin-based foam geopolymer (MKFG) with densities of 400 kg/m³, 600 kg/m³, and 800 kg/m³ were prepared. The effect of weak links on the dynamic mechanical behavior, damage morphology, and energy absorption capacity (SEA_p) of the MKFG was studied by X-CT analysis, Split Hopkinson Pressure Bar (SHPB) test, and fractal analysis. The results show that the connected porosity of MKFG rises with decreasing density. The sensitivity of the damage level to strain rate decreases with elevated connected porosity, which is because the stress concentrations caused by weak links. The amplifying effect of strain rate on the dynamic compressive strength of MKFG diminishes as the connected porosity increases. The sensitivity of SEA_p to the damage level rises with a decrease in the connected porosity. Finally, the simulation results corroborate that the distribution of connected pores has a significant influence on the damage process of the MKFG.

Most impact tests of reinforced concrete (RC) structures are small-energy and reduced-scale tests. Due to the size effects under strain rate, there are large differences in the dynamic responses between reduced-scale and full-scale tests, which makes it inappropriate to design full-scale structures under impact loading based on reduced-scale test results. This paper presents the first results to compare the effects of drop weight impact tests on reduced and full-scale reinforced concrete (RC) beams. The experimental results are used to identify limits of applicability of the similarity laws that have been developed based on low-energy impact tests on reduced-scale structures. Due to low stiffness of the reduced-scale specimens, their failure mode is typical of bending. In contrast, the full-scale specimens have much higher bending stiffness and therefore are more prone to shear failure. Since the ratio of impact force to reaction force decreases as the geometric dimensions of RC beams increase, it is likely that the reaction forces of full-scale RC beams inferred from theories based on the reduced-scale impact test will be lower than in real situation, which could lead to unsafe design. The existing effective length analysis method only considers the stage before the impact force reaches the peak value and cannot deal with the change in effective length of full-scale RC beams with nonlinear deformation. The current theory of energy for impact test that considers the total mass of the structure cannot accurately reflect the effect of full-scale tests in which the loss of energy of the structure is much higher than the absorbed energy. The energy analysis method for full-scale structures is more reasonable when considering the effective mass. The guidance of reduced-scale test is not applicable in full-scale test, and the large deviation of forces between the reduced-scale and full-scale structures by using the DLV systems. To rectify these problems, this paper proposes a similarity law for GVH systems.

Peridynamic (PD) has a unique advantage in describing the crack growth and fragmentation of brittle materials. Concerning the dynamic behaviors and failure patterns of concrete slabs under projectile perforations, a modified bond-based PD approach maintaining both the easy implementation and computational stability characteristics was firstly developed from the following three aspects, (i) a rate-dependent PD constitutive model was proposed for describing the dynamic behaviors of concrete; (ii) a progressive damage criterion considering the tension-compression anisotropy, softening behavior, and strain rate effect of concrete was incorporated to more accurately reproduce the damage and failure of concrete; (iii) an improved micro-modulus function related to bond length was introduced to reveal the internal length effect of bond force. Then, numerical simulations of projectile perforation on concrete slabs by utilizing the developed modified bond-based PD approach, as well as the corresponding sensitivity analyses of discretization parameters including horizon size and particle spacing were performed. Based on the recommended horizon size and particle spacing, the predicted residual velocity of projectile and failure patterns of concrete slabs exhibited an excellent agreement with the test data. Furthermore, by comparisons of the traditional bond-based PD and classical finite element methods, the superiority of developed approach in describing the perforation damage of concrete targets against projectile impact was demonstrated. Finally, the modified bond-based PD approach was employed to blind simulate the projectile normal and oblique perforating multi-layered spaced concrete target plates. It was found that the modified PD model reasonably predicted the terminal ballistic trajectory, deflection angle, and residual velocity of projectile, as well as the failure patterns of target plates. The present work provides a new way to predict the terminal ballistic effect of projectile and dynamic behaviors of concrete slabs.

Epoxy polymers are extensively used in various engineering applications such as aerospace, defence, sports, automotive etc. This article focuses on the in-depth mechanical characterisation of EPOFINE®-1564, a Bisphenol-A-based liquid epoxy resin under various loading conditions. To predict the tensile and compressive behaviour of the representative epoxy resin, quasi-static experiments were performed in the range of 10⁻⁴ to 10⁻² s⁻¹ on Universal testing machine (UTM) while the dynamic experiments were conducted using Split Hopkinson Pressure Bar (SHPB) for high strain rates (1136–2833 s⁻¹). In this study, 3D Digital Image Correlation (DIC) was also used to evaluate the specimen's full-field displacement profile over a wide range of strain rates. Analysis of various mechanical properties such as elastic modulus, yield strength, and ultimate strength, revealed that the epoxy polymer is strain rate dependent within the considered strain rate range. For understanding the fracture behaviour, three-point bend (TPB) experiments were also carried out for both quasi-static (1–10 mm/min) as well as dynamic (10–15 m s^-1) regimes. Dynamic fracture experiments were performed using the modified Hopkinson Pressure Bar (MHPB). The fracture toughness was determined through load vs crack mouth opening displacement (CMOD). Fracture toughness was found to increase with the displacement rate due to the significant plastic deformation under quasi-static range. Conversely, it was found to decrease under dynamic loading because of absence of plastic deformation resulting in brittle fracture. The fracture surface of the specimen was examined through a high magnification digital microscope.

Fiber-metal laminates (FMLs), known for their lightweight and high strength, are widely used in structural protection in the fields of shipbuilding, military, and aerospace. Experiments were conducted using 12.7 mm hard spherical projectiles at speeds ranging from 915.7 – 1290 6 m per second to study the high-speed impact on FMLs composed of titanium and Ultra-high Molecular Weight Polyethylene(UHMWPE). The primary failure modes of the fibers were tensile failure and compressive shear failure. With increasing impact velocity, the proportion of tensile failures in the fibers gradually decreased, transitioning to shear plug failure as the main failure mode, while the titanium alloy primarily experienced erosive perforation and petal-shaped tearing. At a speed of 1290 6 m/s, the titanium alloy began to exhibit significant adiabatic shear tearing in four directions. Further, a three-dimensional numerical model was established, which, through theoretical analysis and experimental validation, proved to be highly reliable. Using this theoretical model, a deeper analysis of the dynamic response and penetration mechanism of the structure was conducted, explaining the energy distribution mechanism and dynamic response mechanisms of various parts. Based on this model, improvements and optimizations were made to the laminar structure of the UHMWPE/titanium alloy FML. Placing metal at the back maximized energy absorption but led to more pronounced bulging.

Scaling effects on the resistance response of RC components have been found under impact, penetration, and blast. To investigate the mechanism and origins of the scaling effect on the impact response of RC beams, numerical models of geometrically similar beams were established on the ABAQUS platform by considering the strain rate effect. The influence of material properties such as elasticity, plasticity, and strain rate effect on the similarity of beam impact response was accessed and analyzed. Then, the scaling effects of impact characteristics such as time history, damage, effective mass, and span length of RC beams were discussed and compared from the local and global stages. The numerical findings revealed that material properties influence the scaling effect on the impact response and strain rate distribution. The inhomogeneity of strain rate distribution and the difference in dynamic strength caused by the non-uniform scaling for the strain rate effects (DIFs) contribute to the scaling effect. In addition, the two-stage analysis results indicated that the scaling effects exhibited in the local and global responses of RC beams are not entirely consistent. As the scale factor increases, for the large-sized beams, the normalized deformation profile shrinks, the equivalent mass factor decreases, the effective span length changes slower, and the moving velocity of the plastic hinge slows down. Several impact performance characteristics, such as strain rate distribution within the beam and the damage and deformation curve of the beam, will reflect localization as the scale factor increases. It is expected that the preliminary mechanism analysis of this study could provide a reference for analyzing the impact response of prototype beams.

The interaction of projectile and target in a penetration process is key for precise prediction and safety design. However, this interaction is instantaneous and varying with complex physical phenomena, that induces a challenge of panoramically illustrating the penetration process. This work develops a new numerical model that can capture the penetration process of a deformable projectile impacting ductile target plate and meanwhile the interaction of projectile and target is considered. Here, physical mechanisms are explored and accordingly mathematical derivations for theoretical analysis are carried out. The issues of plastic stress wave, contact stress, shear perforation and energy dissipation are involved. Both the deformation of projectile and failure of target plate are addressed which include the upsetting deformation of projectile, pit-opening performance of target plate and perforation of target plate. This model presents the history of the deformation of projectile and target, velocity evolution, penetration resistance and shear perforation with timing. The modelling results show a high-precision prediction by comparing with experimental data of a flat-ended projectile penetrating Weldox 460E steel target plate [54] and other developed models of plugging failure model [13] and plastic wave model [48] for both cases of 16mm- and 20 mm-thickness target plates. This work offers the comprehensive calculation and analysis of penetration process and reveals the insights of the transient phenomena for impact engineering.

An analytical model is presented herein on the penetration of a flat-nosed long rod into a semi-infinite concrete target based on the previous theoretical studies and experimental observations. The nose shape of the flat-nosed long rod in deformable penetration state is assumed to be a circular arc and the length of plastic region of the long rod in hydrodynamic penetration is taken into account. The behavior of an erosive penetrator is further divided into two penetration stages (namely semi-hydrodynamic penetration and hydrodynamic penetration) and a new critical impact velocity (i.e. erosive velocity) is derived to characterize the beginning/incipient erosion in accordance with plastic wave propagation theory. According to the new theoretical considerations, the relationship of dimensionless instantaneous mushrooming head radius versus impact velocity is rewritten and the method for predicting semi-hydrodynamic penetration tunnel radius is proposed. It transpires that the present model predictions are in good agreement with available experimental results for the penetration of flat-nosed long rods into semi-infinite concrete targets in terms of penetration depth, penetration modes, penetration tunnel size, residual mass and residual length.

By incorporating the plastic deformation and Puck damage criteria law, a three-dimensional elastic-plastic-damage model has been established to predict the behavior of carbon fiber reinforced thermoplastic (CFRTP) composites under low-velocity impacts. The model has been integrated into ABAQUS/Explicit, and off-axis tensile test were conducted to ascertain appropriate parameters for the elastic-plastic model. Additionally, finite element modeling of off-axis tensile were employed to assess the precision of the model parameters and to contrast the variance of accounting for plastic deformation against neglecting it. The effectiveness of the elastic-plastic-damage model, incorporating damage considerations, was confirmed through an analysis of the mechanical response and progressive damage of CFRTP during low-velocity impact tests. Compared to the elastic-damage model that does not consider plastic deformation, the elastic-plastic-damage model, which takes plastic deformation into account, exhibits higher prediction accuracy. Both simulation and experimental results indicate that delamination and matrix cracking are the dominant damage patterns observed in CFRTP at relatively low impact energies (≤16.20 J).