COMPUTATIONAL STUDY OF INTERFACE EFFECT ON IMPACT LOAD SPREADING IN SiC MULTI-LAYERED TARGETS

Abstract

The effect of finite strength interface with friction on lateral load spreading and phenomena of interface crack initiation and propagation in bonded multi-layered targets under high velocity impact are presented through axisymmetric finite element simulations. The finite element code DYNA2D, developed at the Lawrence Livermore National Laboratory, was augmented with a phenomenological damage model for the silicon carbide ( SiC ) ceramic and contact/cohesive interface model. Simulations were carried out for four target configurations under varying interface strength (Tm), critical strain energy release rate (Gc), and inter-layer friction coefficient (μL). It is shown that the high wave speed SiC remains a potential material for enhanced load spreading if the confinement is ensured to reduce/delay its damage. The load spreading also increases with the increase in μL that comes into play after the interface failure. However, the μL of unity or more needed to approach the upper bound of load spreading found in the perfectly bonded target layers is not practical. It is shown that the resilience of the multi-layered targets depends on Tm as well as the Gc. But, the lateral load spreading depends dominantly on Tm and reaches the upper bound with its increase. It is further shown that the interface cracks initiate and propagate in shear, mode II. The crack speed is invariably the maximum at initiation and is of the order of the longitudinal wave speed of materials on either side. The maximum initiation speed of 11.29Cs and 7.79Cs are predicted at the SiC -aluminum and steel- SiC interfaces for the frictionless case, where Cs is the shear wave speed of the more compliant aluminum or steel. The crack speed reduces monotonously after initiation, but it remains in the intersonic region for more than 150 ns. Whether the propagating crack tip attains the steady state speed depends on the available driving energy. The steady state crack speed of 0.86Cs to 1.21Cs is predicted only at the steel- SiC interface at 2 mm depth from the impact surface, lasts for more than 3 μs, is shown to be independent of the interface strength upto 300 MPa, and is also independent of the friction coefficient.