Simulation Of High-speed Impact Research Articles

A hierarchical multiscale strategy for analyzing the impact response of 3D braided composites

A hierarchical multiscale framework has been developed to predict the impact response of 3D braided composites, in which a bridging model(unit cell model), was employed as a bridge between micro- and macro- scale. A paraboloidal elastic-to-plastic damage model for the epoxy, including the hydrostatic effect, was conducted, where a robust algorithm has been implemented to enhance the convergence and accuracy. At the microscale, nine RVEs (representative volume elements) with different fibers distributions were generated in order to enhance reliability and to reduce the size effect for the micromechanical analysis; At the macroscale, firstly, a unit cell model was proposed as a virtual meso-scale based on the geometric topology of 3D braided composites, and then the unit cell model was implicitly introduced into the macromodel based on the transformation matrix. The homogenization method was adopted for transferring the mechanical properties between scales. These constitutive models were implemented by two user defined subroutines (UMAT and VUMAT) in ABAQUS/Standard and ABAQUS/Explicit for micromechanical analysis and impact simulation, respectively. Furthermore, the failure envelop was carried out for matching a better strength criteria for the braiding yarn. Finally, the high-speed impact simulation was employed to validate the effectiveness of the multiscale framework. The results show that the numerical results are agreed with the experiments well.

Simulation of CFRP/aluminum foam sandwich structure under high velocity impact

To profoundly reveal the protective performance of CFRP/aluminum foam sandwich structure, the high-speed impact simulation models of CFRP, aluminum foam and their sandwich structures are built by ABAQUS/Explicit module. The VUMAT user material subroutine is written for CFRP panel, and Hashin damage criterion is introduced. The elastic constitutive model and macro modeling method for the aluminum foam are chosen. The impact process under different working conditions is numerically simulated and the reliability of the model is verified by one-stage light gas gun loading experiment at the corresponding simulation conditions. At the same time, the protective performance of CFRP/ aluminum foam sandwich structure under different steel projectile shapes, impact velocities and impact angles (the angle between the ballistic and the target normal line) are simulated. The results show that the Mises stress nephogram of CFRP panel is peanut-like with obvious directivity. The stress wave propagates fastest in the direction perpendicular to the fiber. In the impact velocity range of 172−450 m/s, with the increase of impact velocities, the loss of kinetic energy will increase, but the increase of kinetic energy loss will decrease with the increase of impact velocities, and the contact force between the projectile and the sandwich structure will also increase. Thus the sandwich structure will have more serious delamination and fiber breakage, which will consume more kinetic energy. When the velocity of the projectile is greater than 300 m/s, the impact capability of the sandwich structure tends to the upper limit of impact capacity. In the impact velocity range of 170∼300m/s, the sandwich structure has stronger protective performance than ball-nosed projectile when the flat-nosed projectile impact, and the difference of the residual velocity between the two kinds of projectiles is larger. The shape of the projectile has a great influence on the protective performance of the CFRP/ aluminum foam sandwich structure. When the impact velocity is greater than 300m/s, the residual velocities of the two kinds of projectiles are almost the same, and the shapes of the projectile have a gradual effect on the performances of the CFRP/ aluminum foam sandwich structure. The anti-shock performance of sandwich structure under oblique impact is stronger than that of vertical impact. With the increase of impact angles, the transverse deformation of sandwich structure increases, and the anti-shock performance of sandwich structure also increases.

Experimental Study on Dynamic Compression Mechanical Properties of Aluminum Honeycomb Structures

In this paper, dynamic compression tests are developed to investigate the dynamic compression mechanical properties of the aluminum honeycomb structures at different strain rates, especially at the high strain rates. The difficulties at the high strain rates exist due to the large deformation, the low wave resistance and the size effect of the honeycomb structures. The Split Hopkinson Pressure Bar (SPHB) test method is carried out and special measures such as the adoption of waveform shaper, the size optimization of the impact bar and the specimen, and employment of the semiconductor strain gauge, etc. are taken to overcome the difficulties. It is discovered that the dynamic compression mechanical properties possess a stress hardening effect at a high strain rate from 1.3 × 103 s−1 to 2.0 × 103 s−1, but then a stress softening effect at a high strain rate of 4.6 × 103 s−1. It is also discovered that the yield strength and the average plateau stress at the strain rate of 2.0 × 103 s−1 is higher than that at the strain rate of 1.3 × 103 s−1. However, the yield strength and the average plateau stress at the strain rate of 4.6 × 103 s−1 is lower than that at the strain rate of 2.0 × 103 s−1 and 1.3 × 103 s−1, but higher than that at a quasi-static state. This indicates that the aluminum honeycomb structure is sensitive to the strain rate. Additionally, the damage mode of the aluminum honeycomb structure is plastic buckling, collapse and folding of the cell wall, which is carried out using dynamic compression tests. The folding length of the cell wall at a higher strain rate is found to be longer than that at a lower strain rate. The test results can also be used as the stress–strain curves of the honeycomb constitutive model at the high strain rates to carry out the numerical simulation of high-speed impact.

An improved technique for verification of high-speed impact simulation

The risk of strange objects impacts that can decrease local strength properties must be taken into account in the design of primary airframe structures in the aeronautics, energy and space industries. Damage that may occur as a result of high-speed impacts can affect the structure load carrying capacity of the structure. Testing all impact scenarios on real structures is expensive and impractical. This paper integrates numerical analyses with high-speed impact tests of hail stones on flat metallic and composite panels. A new technique for displacement measurements using a laser triangulation sensor during impacts were proposed and used for a quantitative analysis and for precision verification of a numerical model results. A comparison between the testing and simulation results reveals consistent predictions of damage initialization on the composite material and plastic deformation on the metallic material. The application of flat test panels for verification and tuning of the numerical models allows an optimized final design of a real structure and decreases the risk of non-compliance of the structure during verification tests.

Multiscale cohesive zone modeling and simulation of high-speed impact, penetration, and fragmentation

In this work, a multiscale cohesive zone model (MCZM) is developed to simulate the high-speed penetration induced dynamic fracture process such as fragmentation in crystalline solids. This model describes bulk material as a local quasi-continuum medium which follows the Cauchy–Born rule while cohesive zone element is governed by an interface depletion potential, such that the cohesive zone constitutive descriptions are genetically consistent with that of bulk element. This multiscale method proved to be effective in describing material inhomogeneities and it is constructed and implemented in a cohesive finite element Galerkin weak formulation. Numerical simulations of high-speed penetration with different shape of penetrators, i.e., square, circle and parabola nose penetrators are performed. Results show that the proposed MCZM can successfully capture spall fracture, the penetration process and different characteristics of fragmentation under different shape of penetrators.

Numerical Simulation of High-Speed Impact on Regolith Using Compressible and Non-Expanding Fluid Model

Numerical Simulation of High-Speed Impact on Regolith Using Compressible and Non-Expanding Fluid Model

Two-stage light-gas magnetoplasma accelerator for hypervelocity impact simulation

The development of macroparticles acceleration methods for high-speed impact simulation in a laboratory is an actual problem due to increasing of space flights duration and necessity of providing adequate spacecraft protection against micrometeoroid and space debris impacts. This paper presents results of experimental study of a two-stage light- gas magnetoplasma launcher for acceleration of a macroparticle, in which a coaxial plasma accelerator creates a shock wave in a high-pressure channel filled with light gas. Graphite and steel spheres with diameter of 2.5-4 mm were used as a projectile and were accelerated to the speed of 0.8-4.8 km/s. A launching of particle occurred in vacuum. For projectile velocity control the speed measuring method was developed. The error of this metod does not exceed 5%. The process of projectile flight from the barrel and the process of a particle collision with a target were registered by use of high-speed camera. The results of projectile collision with elements of meteoroid shielding are presented. In order to increase the projectile velocity, the high-pressure channel should be filled with hydrogen. However, we used helium in our experiments for safety reasons. Therefore, we can expect that the range of mass and velocity of the accelerated particles can be extended by use of hydrogen as an accelerating gas.

Analytical Simulation of High-speed Impact onto Hybrid Glass/Carbon Epoxy Composites Targets

Recently, the authors developed an analytical model, which has been shown valid to simulate accurately high-speed penetration onto composite materials targets. In this paper, the analytical model has been modified to analyse the impact onto hybrid composite material targets. Several equations have been corrected, although the basic structure of the model has been kept intact. The model has been utilized to analyse impact of steel balls, 5.56 mm diameter onto hybrid carbon/glass laminates at impact speeds ranging between about 200 and 600 m/s. Two different S2 glass fibre contents have been analysed, namely 12 and 21%. Analytical results of both ballistic limit (maximum speed for no perforation) and residual velocity of penetrator after full perforation vs. impact velocity show acceptable agreement with experimental results. We may conclude that modified analytical model is a valuable tool to simulate high-speed impact onto hybrid composite targets, being useful for a first stage design optimization.

Analytical simulation of high-speed impact onto composite materials targets

This article presents a relatively simple analytical model aimed at simulating high-speed penetration into composite materials targets. The model is based on a set of basic hypotheses common to other previous analytical models developed in our department and elsewhere. However, this new model is of a more refined nature acquisition that allows for reliable results without requiring the use of parametric data needed in previous models. For the first time, the model provides a qualitative explanation of the sudden drop of energy absorbed by the target with impact velocities slightly higher than the ballistic limit. A qualitative explanation, experimentally observed, of the shape of woven fabric laminates after impact is also noted. The model predictions of both ballistic limit and residual velocity after perforation reasonably agree with experimental results, in spite of the use of static data of the target material. Thus, this model may serve as a useful tool for a primary stage of composite armour design, permitting a large number of parameters to be screened before using higher cost numerical and experimental approaches.

Simulation of high speed impact, penetration and fragmentation problems on locally refined Cartesian grids

Techniques are presented to solve problems involving high speed material interactions that can lead to large deformations followed by fragmentation. To simulate such problems in an Eulerian framework on a fixed Cartesian mesh, interfaces (free surfaces as well as interacting material interfaces) are tracked as levelsets; to resolve shocks and interfaces, a quadtree adaptive mesh is employed. This paper addresses issues associated with the treatment of all interfaces as sharp entities by defining ghost fields on each side of the interface. Collisions between embedded objects are resolved using an efficient collision detection algorithm and appropriate interfacial conditions are supplied. Key issues of supplying interfacial conditions at the precise location of the sharp interface and populating the ghost cells with physically consistent values during and beyond fragmentation events are addressed. Numerous examples pertaining to impact, penetration, void collapse and fragmentation phenomena are presented along with careful benchmarking to establish the validity, accuracy and versatility of the approach.

Simulation of high speed impact into ceramic composite systems using cohesive-law fracture model

A numerical study for the analysis of oblique metal/ceramic/metal three layer composite systems against a long-rod has been performed. The study was done using a three-dimensional dynamic program NET3D, which uses the finite element Lagrangian method with explicit time integration. To model the discrete nature for fracture and damage of brittle materials, we implemented cohesive-law fracture model with a node separation algorithm for the tensile failure and Mohr–Coulomb model for the compressive loading. A tetrahedral element implemented in the code provides more potential fracture surfaces than a hexahedral element. As a verification of the scheme, an oblique impact into the composite system was conducted and the calculated penetration depth and propagating crack paths were found to be in good agreement with experiment. Next a series of three-dimensional numerical simulations have been conduced to examine the ballistic performance of three layer composite systems. The residual velocity and residual length of the rod were computed for different plate thickness ratios of equal areal density. The impact velocities considered are 1.5, 1.8 and 2.2 km/s. The oblique angle of the plate is 0° and 45°. The optimum thickness ratios of ceramic to metal are very similar to those obtained from the previous experiment.

Lagrangian 기법에 의한 충돌 해석 시 접촉처리의 병렬화 및 병렬효율 평가

The evaluation of parallel performance of a high speed impact simulation is not an easy task because not only the development of parallel explicit code is difficult but also a large number of processors is not easily accessible. In this paper, the parallel performance of a new Lagrangian FEM impact code carried out on cluster supercomputer has been described in high speed range. In the case of metal sphere impacting to oblique plate, the overall speed-up continuously increases even up to 128 CPUs. Investigation of elapsed time of each part reveals that most of the inefficiency comes from the load imbalance of contact.