Numerical Study On The Penetration Resistence Of Fibre Reinforced Plastic Laminates

Numerical study on the penetration resistance of fiber-reinforced plastic (FRP) laminates has been conducted in this paper. Dynamic continuum damage constitutive models for fiber-reinforced plastic laminates subjected to impact loading have been proposed and incorporated into ABAQUS as user subroutines through ABAQUS/VUMAT. The constitutive models have been used in the numerical simulations of the reponse and failure of FRP laminates and structures subjected to projectile impact. The main contents of this paper are summarized as follows:1. Continuum damage mechanics (CDM) models have been proposed to predict the response and failure of fiber-reinforced plastic laminates subjected to impact loadings. The CDM models basically consist of two stages, i.e. linear elastic stage before damage and strain softening stage after damage initiation. The quadratic form of various stress parameters is taken to formulate the failure criteria for different failure modes of FRP laminates, such as tensile/shear failure and compressive failure along in-plane principle directions, in-plane shear failure, compressive failure in the through thickness direction as well as inter-laminar delamination. The influence of shear and normal stresses in the through thickness direction on different failure modes are considered. The delamination is assumed to occur not only when the inter-laminar normal stress is tensile but also when the inter-laminar normal stress is compressive and the inter-laminar shear stress is sufficiently high.It is assumed in the present constitutive CDM models that once a failure criteria is satisfied, the corresponding damage will begin to accumulate and the stiffness of material will be reduced gradually until the complete failure. Different damage variables are introduced to describe the reductions of material stiffness with the development of damage for different failure modes. Two different froms of strain softening are given in the thysis, one is exponential form, the other has linear form. The stress-strain constitutive relationship is adopted for the former one whilst the stress-displacement relationship combined with the fracture energy approach for the latter one to reduce the mesh dependency due to strain concentration. Comparisons of mesh dependency are made and analyzed by examples.Furthermore, the strain rate dependency to strength and modulus of FRP laminates is also considered by introducing the dynamic enhancement factor in a unified framework.2. The newly proposed two constitutive models are incorporated into Abaqus/Explicit as user subroutines through ABAQUS/VUMAT. Numerical study has been conducted on the response and failure (perforation) of FRP laminates under projectile impact. Comparisons are made between numerical results and experimental data for different laminated material systems, such as CFRP, GFRP, KFRP, which were perforated by projectiles with different nose shapes, i.e. flat, conical, hemispherical and ogival, in terms of deformation profiles, ballistic limit, residual velocity and force-displacement curve. It is shown that the numerical simulations are in good agreement with the experimental observations and that the constitutive models proposed in the thysis are reliable and predictive.3. The continnum damage mechanics constitutive models for FRP laminates are employed to study the influence of curvature on the ballistic performance of FRP laminates. It is demonstrated that the ballistic limits of FRP laminates are improved slightly due to the existence of curvature and that the FRP laminate has the highest ballistic limit when its curvature is5.0. It is also demonstrated that the composites which are laminated as the sequence of Aluminum-GFRP-KFRP have the highest ballistic limit.4. Numerical simulations have been performed to investigate the response of PASGT helmet struck by a fragment simulating projectile (FSP) impact. A detailed finite element model of head is constructed which includes the main parts of human’s head, such as scalp, skull, cerebrospinal fluid and brain system. The responses of the PASGT helmet and the head are studied when the helmet is subjected to impact by the fragment simulation projectile (FSP) on the different locations (front, top, side and back sites) of the helmet. It is found that the maximum stress and pressure in the head are the lowest when the helmet is impacted on its frontal site whilst the maximum stress and pressure the highest when the helmet is struck on its top site. It is also found that the maximum stress in the skull and the maximum pressure in the brain tissue increase with increasing impact angle which is defined as the angle between the axis of FSP and the tangent of helmet surface.