Low Velocity Impact Simulations Research Articles

Modeling damage induced plasticity for low velocity impact simulation of three dimensional fiber reinforced composite

An elasto plastic damage model for three dimensional Fiber Reinforced Plastic (FRP) composite is proposed to simulate the progressive damage and damaged induced inelastic deformation in case of low velocity impact. Exponential softening model is implemented for damage growth prediction and a three dimensional plastic potential is used for plastic surface growth. An explicit code, VUMAT is written and implemented in ABAQUS/Explicit. The material softening parameter, m is determined from the finite element simulation of a single element model. Low velocity impact simulations are performed with graphite/epoxy laminate. Delamination behavior is simulated using surface based cohesive interaction between the two adjacent plies. The results show that the predicted behavior matches well with experimental observations. The model is successfully able to capture the central deflection of the laminate plate and permanent indentation on the surface.

A damage evolution study of E-glass/epoxy composite under low velocity impact

To predict the behavior of composites in case of low velocity impact, various material models are available in the literature. Damage evolves exponentially or linearly with strain in these models. These models are using either characteristic length ‘Lc’ or material exponent parameters, ’m’ to solve the problem of strain localization. A method to relate these parameter to each other is suggested here. The choice of material exponent, ‘m’ for a particular mesh size is also discussed. Low velocity impact simulations for E-glass/epoxy composite are performed using continuum damage mechanics based material model and compared with the experiments. The damage observed through the light projected area on the laminate, contact forces and displacement plots with respect to time were studied and compared with finite element analysis results to demonstrate the effectiveness of the model. Digital Image Correlation (DIC) technique is used for experimentation to obtain displacement on the surface of the plate.

Finite element implementation of an orthotropic plasticity model for sheet metal in low velocity impact simulations

A finite element (FE) implementation of an orthotropic plasticity model for sheet metal in impact simulations is performed. An accurate description of anisotropic plasticity model is presented for obtaining reliable predictions in FE simulations of low velocity impact processes. The elasto-plastic model includes isotropic elasticity, anisotropic yielding, associated plastic flow and mixed non-linear isotropic/kinematic hardening. The material model is implemented into a user-defined material (VUMAT) subroutine for the commercial finite element code ABAQUS/Explicit to predict the numerical response of circular aluminum plate subjected to low velocity impact. The impact energy was imposed by the definition of the impactor initial velocity. The numerical results of the impact force history and impact velocity are in good agreements with the LDA experimental data. The anisotropy effect of aluminum plate under low velocity impact is studied.

NUMERICAL SIMULATIONS OF QUASI-STATIC INDENTATION AND LOW VELOCITY IMPACT OF ROHACELL 51 WF FOAM

Numerical simulations of quasi-static indentation and low velocity impact of low density polymethacrylimide (PMI) Rohacell 51 WF foam using indenters with different nose shapes (conical, truncated-conical, hemi-spherical and flat) were carried out using the finite element code LS-DYNA. A 2D axisymmetric model was generated. A strain-rate dependent material model and r-adaptive remeshing were used for low velocity impact simulations. Numerical predictions matched the available experimental data very well. Moreover, the predicted resistance force closely matched the empirical results. The results demonstrated the ability of the model to reproduce the deformation mechanisms of the penetration process of Rohacell 51 WF foam.

Modelling the simulation of impact induced damage onset and evolution in composites

This paper presents two modelling strategies for the simulation of low velocity impact induced damage onset and evolution in composite plates. Both the strategies use a global–local technique to refine the mesh in the impact zone in order to increase the accuracy in predicting the impact phenomena without affecting the computational cost. Cohesive elements are used to simulate the inter-lamina damage behaviour (delaminations) and Hashin’s failure criteria are adopted to predict the intra-lamina failure mechanisms. The two modelling strategies differ in terms of input parameters for the inter-lamina and intra-lamina damage evolution laws and in terms of modelling solutions in the impacted area. Comparisons between numerical and experimental results on composite plates subjected to different impact energies, according to the ASTM D7136 requirements, have been used to assess the peculiarities and the fields of application for the two proposed modelling strategies. Both the strategies have been tested by adopting the finite element code ABAQUS®. The different approaches to set the parameters of cohesive elements’ constitutive laws and Hashin’s criteria and the different choices made in quantifying the dependence of failure criteria on the finite elements’ average size have been taken into account.

Progressive damage modeling of plain weave E-glass/phenolic composites

An optimized set of material properties and parameters for E-glass/phenolic composites is determined for use in the rate dependent composite damage model MAT162 in LS-DYNA. The model requires 39 material properties and parameters, and is able to capture the seven different damage modes and post damage softening behavior of composites. The unknown MAT162 parameters were determined by conducting parametric simulations of low velocity impact (LVI), depth of penetration (DOP), and ballistic impacts. The modulus reduction parameter OMGMX is found by simulating LVI tests and varying the values of OMGMX to find the best agreement with LVI experimental data. The limit of compressive volume strain for element eroding was found by simulating DOP experiments and comparing the results to the experimental data. Then the element eroding axial strain E_LIMT and EEXPN were determined by simulating ballistic impact experiments. When the optimized values were determined, analysis of ballistic experiments were conducted and compared to the experimental impact versus residual velocity curve. The results of the simulations were in excellent agreement with the experimental data.

Inclusion of Strain-Rate Effects in Low Velocity Impact Simulation of Laminated Composites

Composite materials are widely used in aircraft, automotive, marine and railway applications and are exposed to impact loads, in particular low velocity impact. As material properties of composites are affected by strain-rate [, finite element analysis (FEA) by using static properties would not predict their impact behaviour accurately. Thus, the objective of this study was to include strain-rate effects in the simulation of composite laminates under low velocity impact. This was achieved using ABAQUS anisotropic damage model (ADM) by taking account of material properties changes as a function of log strain-rate using user-defined ABAQUS/VUSDFLD subroutine Strain-Rate Dependent ADM (SRD ADM). Results obtained from SRD ADM were validated using simple tensile test done by Okoli [. Subsequently a three-point bending impact event of a simple composite laminate beam by a cylindrical steel impactor was simulated using both the original ABAQUS Static ADM and the user-defined SRD ADM, and compared with experimental impact test results done by [. The results show that reductions in errors of predicted maximum impact reaction force (compared to experimental data) were achieved from 29% using Static ADM to 14% using SRD ADM and from 35% using Static ADM to 15% using SRD ADM respectively for impactor speeds of 2 ms-1 and 5 ms-1.

Permanent indentation characterization for low-velocity impact modelling using three-point bending test

This paper deals with the origin of permanent indentation in composite laminates subjected to low-velocity impact. The three-point bending test is used to exhibit a non-closure of matrix crack which is assumed as a cause of permanent indentation. According to the observation at microscopic level, this non-closure of crack is produced by the blocking of debris inside matrix cracking and the formation of cusps where mixed-mode delamination occurs. A simple physically-based law of permanent indentation, “pseudo-plasticity”, is proposed. This law is qualitatively tested by three-point bending finite element model and is lastly applied in low-velocity impact finite element model in order to predict the permanent indentation. A comparison between low-velocity impact experiments and simulations is presented.

Impact Resistance Research of Composite Laminate Structure

The composite material has been widely used in aircraft structures. But this kind of material has some shortage such as poor impact resistance, low residual compressive strength, which have a negative influence on the performance of aircraft structures. In this paper, simulations of low-velocity impact and compression process of composite laminates with AL ply and different core material has been done. The simulation results show that softer core materials and AL ply with certain thickness can improve the residual compressive strength

Impact Damage Research of Composite Laminates with AL Ply

The composite material has been widely used in aircraft structures. But this kind of material has some shortage such as poor impact resistance, low residual compressive strength, which have a negative influence on the performance of aircraft structures. In this paper, simulations of low-velocity impact and compression process of composite laminates with AL ply has been done. Finite element software ABAQUS/Explicit has been adopted to simulate the 3.5J impact and compression. A certain number of composite laminates with different thickness of AL ply has been tested, equal weight traditional composite laminates also been simulated as comparison. The simulation results show that AL ply with certain thickness can improve the residual compressive strength.

An experimental investigation into localised low-velocity impact loading on glass fibre-reinforced polyamide automotive product

In the automotive industry, more and more engineered parts are shifting from metals to engineering plastics. However localised impact loading and long term ageing effects of under-the-hood plastic components is not well understood. In this paper, localised low velocity impact experiments and simulations were conducted on glass fibre-reinforced polyamide sump to investigate typical flying stones impact scenarios. Complete components were manufactured by injection moulding techniques for the experimental samples. The samples were then subjected to a range of low velocity impact using drop weight tower and flying projectiles from an air gun. Damage assessments were then performed following the experiments. In parallel, finite element analysis using LS DYNA was carried out to virtually benchmark and to predict the strength and fracture behaviour of stressed plastic parts. This has permitted to perform numerous impact tests in different situations with varying parameters. The study results show the significant contribution of the design in terms of shock absorption. The specific sump design with a protective ribbing combined with a superior material increases considerably the impact resistance. The paper will provided detailed discussions and results from both the experiments and finite element analysis investigations.

Simulation of low velocity impact on composite laminates with progressive failure analysis

The impact is particularly damaging in the case of composites where the fibers are elastic and brittle as well as the matrix when compared with conventional ductile metals. This paper deals with the prediction of the delamination damage induced by low velocity impact in a laminated composite performed using the progressive damage model MAT162 implemented in the transient non-linear finite element code LS-DYNA. Good agreement with the experimental result was observed, especially for shape and orientation of the delaminations.

The Simulation of Low-Velocity Impact on Composite Laminates with the Damage Model Based on Strain

This paper proposed a composite damage model including the damage initiation and evolution based on strain to predict the composite intralaminar damage under impact loading. In the numerical simulation, the user material subroutine VUMAT and the cohesive-zone model are chosen to describe the composite damage model and the delamination of interfaces between different plies. ABAQUS software is used to simulate the low-velocity impact of different thickness composite laminates. It is found that the delamination shape and area, the contact force and the deflection of the impactor obtained by the numerically simulation agree well with the experimental results.

Low-velocity impact behavior of fiber metal laminates

The low-velocity impact response of a range of fiber metal laminate (FML) panels was investigated through testing and finite element simulations. The objective of this study was to understand the impact-damage resistance of these novel composites, so that they can be designed optimally for impact-resistant aircraft applications. The FML panels were made up of aluminum alloy 7475 T761 and unidirectional S2 glass/epoxy oriented in a cross-ply configuration. Experimental tests were performed using a free-fall drop dart testing machine. The plate specimens were constrained on a circular edge by the clamping fixture. The shape and the nature of the damage inflicted by impact were evaluated using both destructive cross-sectional microphotography and nondestructive ultrasonic techniques. The tests showed that FML laminates are capable of absorbing energy through localized plastic deformation and through failure at the interface between the layers. In particular, delaminations occurred in the back face of the aluminum-alloy sheet and its adjacent fiber-reinforced epoxy layer and in between adjacent fiber-reinforced epoxy layer. The finite element code, LS-DYNA3D, was used to perform numerical simulations of low-velocity impact to predict the complex damage propagations. The computed post-impact deformed shapes and damage patterns were found to be fairly close to experimental results.

Numerical Simulation of Mechanical Behavior of Composite Structures by Supercomputing Technology

This paper will examine the possibilities of the virtual tests of composite structures by simulating mechanical behaviors by using supercomputing technologies, which have now become easily available and powerful but relatively inexpensive. We will describe mainly the applications of large scale finite element analysis using the direct numerical simulation (DNS), which describes composite material properties considering individual constituent properties. DNS approach is based on the full microscopic concepts, which can provide detailed information about the local interaction between the constituents and micro-failure mechanisms by separate modeling of each constituent. Various composite materials such as metal matrix composites (MMCs), active fiber composites (AFCs), boron/epoxy cross-ply laminates and 3-D orthogonal woven composites are selected as verification examples of DNS. The effective elastic moduli and impact structural characteristics of the composites are determined using the DNS models. These DNS models can also give the global and local information about deformations and influences of high local in-plane and interlaminar stresses induced by transverse impact loading at a microscopic level inside the materials. Furthermore, the multi-scale models based on DNS concepts considering microscopic and macroscopic structures simultaneously are also developed and a numerical low-velocity impact simulation is performed using these multi-scale DNS models. Through these various applications of DNS models, it can be shown that the DNS approach can provide insights of various structural behaviors of composite structures.

Dynamic Direct Numerical Simulation of Woven Composites For Low-velocity Impact

This article describes a numerical low-velocity impact simulation with finite element models based on direct numerical simulation (DNS) on 3D orthogonal woven composites. The DNS approach is based on the concept that composites can be directly modeled considering their microscopic structures and each constituent's material property inside composite materials. Comparison studies with the classical approach based on the homogenized material property are carried out and these show that the DNS approach can cope with the limits of the classical approach which has difficulties in considering the inner microscopic structures. A few 3D DNS models are proposed in order to obtain intense understanding of the micro-geometrical effects of the matrix and yarns on the dynamic behaviors under impact. Deformation and internal stresses due to impact are investigated in detail at a microscopic level inside the materials. Furthermore, the multiscale model based on DNS concepts is also developed and analyzed taking into account micro and macroscopic structures of materials together.

Finite element simulation of low velocity impact on shape memory alloy composite plates

Delamination of composite materials due to low velocity impacts is one of the major failure types of aerospace composite structures. The low velocity impact may not immediately induce any visible damage on the surface of structures whilst the stiffness and compressive strength of the structures can decrease dramatically. Shape memory alloy (SMA) materials possess unique mechanical and thermal properties compared with conventional materials. Many studies have shown that shape memory alloy wires can absorb a lot of the energy during the impact due to their superelastic and hysteretic behaviour. The superelastic effect is due to reversible stress induced transformation from austenite to martensite. If a stress is applied to the alloy in the austenitic state, large deformation strains can be obtained and stress induced martensite is formed. Upon removal of the stress, the martensite reverts to its austenitic parent phase and the SMA undergoes a large hysteresis loop and a large recoverable strain is obtained. This large strain energy absorption capability can be used to improve the impact tolerance of composites. By embedding superelastic shape memory alloys into a composite structure, impact damage can be reduced quite significantly. This article investigates the impact damage behaviour of carbon fiber/epoxy composite plates embedded with superelastic shape memory alloys wires. The results show that for low velocity impact, embedding SMA wires into composites increase the damage resistance of the composites when compared to conventional composites structures.

Simulation of low velocity impact on fiber laminates using a cohesive zone based delamination model

An existing delamination model is further developed for use in transverse impact simulations. An algorithm is developed making it possible to determine the propagation direction of the delamination front. Using this it is possible to determine relative orientation of the delamination front with respect to the fibers above and below the interface. In a qualitative evaluation it is shown that the present delamination model can be used for modeling delamination initiation and growth in transverse impact simulations.

Numerical simulations of low-velocity impact on an aircraft sandwich panel

The potential hazards resulting from a low-velocity impact (bird-strike, tool drop, runway debris, etc.) on aircraft structures, such as engine nacelle or a leading edge, has been a long-term concern to the aircraft industry. Certification authorities require that exposed aircraft components must be tested to prove their capability to withstand low-velocity impact without suffering critical damage. This paper describes the results from experimental and numerical simulation studies on the impact and penetration damage of a sandwich panel by a solid, round-shaped impactor. The main aim was to prove that a correct mathematical model can yield significant information for the designer to understand the mechanism involved in the low-velocity impact event, prior to conducting tests, and therefore to design an impact-resistant aircraft structure. Part of this work presented is focused on the recent progress on the materials modelling and numerical simulation of low-velocity impact response onto a composite aircraft sandwich panel. It is based on the application of explicit finite element (FE) analysis codes to study aircraft sandwich structures behaviour under low-velocity impact conditions. Good agreement was obtained between numerical and experimental results, in particular, the numerical simulation was able to predict impact damage and impact energy absorbed by the structure.

The use of r-adaptivity with local, intermittent remesh for modeling hypervelocity impact and penetration

An explicit, r-adaptive finite element method is described for application to hypervelocity impact and penetration problems. Here, r-adaptivity refers to a numerical scheme in which the nodes of the mesh are moved to improve the quality of the mesh. The r-adaptive scheme implemented here is similar to ALE, in that the physical and mesh velocities are independent; however, in this application the mesh is constrained to follow the physical boundaries of the material. Thus, interfaces do not flow through the mesh. The advantage of this treatment is that the original contact conditions are preserved. The r-adaptive scheme is very effective in controlling the time step in the calculation; however, it is not sufficient to completely control the topology of elements. At that stage an automatic remesh is performed and is confined to a region local to the distorted elements. To illustrate the applicability and robustness of the method, results from low-velocity and hypervelocity Taylor anvil impact simulations are presented. The results for hypervelocity represent the first near-Lagrangian calculations with traditional finite elements ever successfully performed for this application (here, near-Lagrangian implies that the mesh motion is typically everywhere close to the material motion). Strengths and weaknesses of the approach are highlighted.