Finite element modeling of impact, damage evolution and penetration of thick-section composites

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Abstract

Impact, damage evolution and penetration of thick-section composites are investigated using explicit finite element (FE) analysis. A full 3D FE model of impact on thick-section composites is developed. The analysis includes initiation and progressive damage of the composite during impact and penetration over a wide range of impact velocities, i.e., from 50 m/s to 1000 m/s. Low velocity impact damage is modeled using a set of computational parameters determined through parametric simulation of quasi-static punch shear experiments. At intermediate and high impact velocities, complete penetration of the composite plate is predicted with higher residual velocities than experiments. This observation revealed that the penetration-erosion phenomenology is a function of post-damage material softening parameters, strain rate dependent parameters and erosion strain parameters. With the correct choice of these parameters, the finite element model accurately correlates with ballistic impact experiments. The validated FE model is then used to generate the time history of projectile velocity, displacement and penetration resistance force. Based on the experimental and computational results, the impact and penetration process is divided into two phases, i.e., short time Phase I – shock compression, and long time Phase II – penetration. Detailed damage and penetration mechanisms during these phases are presented.

Introduction

Impact, damage and penetration modeling of thick-section composites are of great importance to many industrial, automotive, aerospace and defense applications. A large number of material properties and model parameters are required in damage modeling of composites using finite element analysis (FEA) techniques. A systematic model-experiment methodology is required to validate the finite element model (FEM) from static to impact loading conditions. A validated FEM should predict the evolution of impact damage, the rebound velocity of the projectile, and the impact-contact or resistance force for non-penetrating projectiles. For penetrating projectiles, the prediction of projectile residual velocity and displacement, evolution of damage, and penetration resistance force on the projectile with significant accuracy is needed to predict the post-ballistic residual strength of the composite laminate and multi-hit performance. For low velocity impact experiments one can measure the impact-contact force as a function of time to validate the FE model. On the other hand, high speed flash-X-Ray and photography can be used to measure the impact and residual velocities of the projectiles, ejection velocities of debris, and the dynamic deflection of the impact plate. However, in most commercial ballistics facilities, the impact and residual velocities of the projectile are measured at a minimum. It is thus important to validate a FEM which can accurately model the impact and residual velocities of the projectiles over a wide range of projectile impact velocities. The validated FEM then can be used to predict the time histories of projectile velocity and penetration resistance force with confidence. This is the main goal of the present study.

A fair amount of work can be found in literature addressing different aspects of composite impact and damage modeling under low velocity impact [1], [2], [3], [4], [5], [6], [7], [8] and high velocity impact on fabrics [9], [10], [11], [12], [13], [14], [15], [16], [17], soft laminates [18], [19], and fiber reinforced composites [20], [21], [22], [23], [24], [25], [26], [27], [28], [29], [30], [31], [32], [33], [34]. This includes our original work [34] on the development of a quasi-static punch shear test (QS-PST) methodology to study the quasi-static penetration mechanics behavior of thick-section composites. This methodology established a series of model validation experiments to determine rate independent mechanical properties and damage parameters for quasi-static penetration modeling of plain-weave 814 gsm (gm/m2) (24 oz/yd2, 5 × 5 tows/inch) S-2 glass/SC15 laminates. Our modeling parameters were used to successfully model impact, damage and penetration of relatively thin composite plates [20], [21], [22], [23], [35]. Advanced theoretical models which explain experiments on fabrics or body armor exists in literature [36], [37], [38], however, similar models are not available for thick-section composites. Theoretical impact models treat fabrics as a membrane and consider transverse impact induced 1D elastic–plastic stress wave propagation along the fiber axis, and uses tensile failure criteria for the fiber. Membrane models have been further modified to model impact on thin-composites [39], however, neglects the through-thickness stress wave propagation. In our previous work [35], we have shown that impact damage, and penetration of thick-section composites occurs under different phases and damage modes, e.g. (a) shock compression (b) compression–shear (c) tension–shear (d) and structural vibration. While theoretical models for different phases of penetration will be presented elsewhere, the present work focuses on FE analysis to gain insight.

The present work builds upon our previous quasi-static penetration model of ballistic penetration [35] and extends it to develop a combined experimental and computational methodology for modeling the high velocity impact, damage and penetration mechanics of thick-section composites under a wide range of impact velocities. In the present FEA work, the Lagrangian explicit finite element analysis code LS-Dyna 971 is used in conjunction with the progressive composite damage model used in our previous studies to model the rate sensitive progressive damage and penetration behavior of thick-section composites. Validated FE model parameters are then used for detailed analyses of impact, stress wave propagation, damage, and penetration mechanics of composites plates of different thickness and impact velocities.

Section snippets

Modeling progressive damage and penetration of thick-section composites

Computational penetration mechanics modeling of composites is a relatively complex subject, which requires defining several fiber and matrix dominated damage modes, rate effects on material properties, and one or more element erosion criteria. One such progressive composite damage model is MAT_COMPOSITE_DMG_MSC (MAT162), developed by Materials Sciences Corporation and implemented in LS-Dyna 971 [36]. MAT162 is specially designed to model ballistic penetration of thick-section composites in

Ballistic experiments

The impact, damage and penetration modeling will be performed by simulating the ballistic experiments on baseline twenty two layer (22L) plain-weave S-2 Glass/SC15 composite plates of dimension 178 mm × 178 mm, and thickness HC = 13.2 mm and impacted with a right circular cylinder of mass, diameter and height of MP = 13.8 gm, DP = 12.7 mm and HP = 14.02 mm, respectively [34]. Test specimens were bolted between a steel support plate of dimension 178 mm × 178 mm and thickness 50.8 mm and a cover

Finite element modeling of ballistic impact, damage and penetration

In order to accurately simulate the ballistic experiments presented in Figs. 1b and 2a, a square composite plate of dimension 178 mm × 178 mm × 13.2-mm is modeled with 753k solid elements in 3D. A full 3D model is used instead of a quarter-symmetric model to avoid computational difficulties related to element erosion at the symmetric boundaries. A total of 36 elements are placed in the through-thickness direction in 12 material layers with 11 predefined delamination interface definitions. The

Summary and conclusions

Modeling the ballistic impact, damage, and penetration of thick-section composites is complex in nature, and requires modeling and tracking the evolution of different composite damage modes in time and space. We present here the explicit dynamic finite element analysis (FEA) technique, where the equations of motion are solved in incremental time steps and the time history of deformations, tractions, and damages are calculated based on the conditions of earlier time steps. We use the

Acknowledgments

Research was sponsored by the Army Research Laboratory and was accomplished under Cooperative Agreement Number W911NF-06-2-011. The views and conclusions contained in this document are those of the authors and should not be interpreted as representing the official policies, either expressed or implied, of the Army Research Laboratory or the U.S. Government. The U.S. Government is authorized to reproduce and distribute reprints for Government purposes notwithstanding any copyright notation

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