Failure of Frp Under Bi-Axial Load

Introduction

The use of composite material is increasing more and more as we are heading towards new technology. As we know that in Aerospace Field, weight saving plays great role but we cannot afford to have less strength and yet be light and durable so its demand on current airplane is increasing more and more. A recent aircraft Boeing 787 (Dream liner) has 50% (by weight) use of composite materials, also airbus A380 comprises more than 20% of the composite materials.

Composite Materials are widely used in some major aircraft structures like wing and fuselage. In our paper we shall study the failure modes of Fiber Re-inforced Polymers (Plastics) under bi-axial loading condition. Composites are often subjected to complex multi-axial loading in service and consequently, experimental investigation should consider bi-axial tests. Composites Laminates are developing multi-axial stress states and consequently testing closer to reality is needed. Even though large demand exists for experimental multi-axial test data, there is little existing experimental capability to evaluate the multi-axial response of composite Materials.

In the past, some analysis has been conducted by various researchers. John T. Wang, Christine G. Lotts and David W. Sleight (1999) has written an AIAA paper 99-1336 about the analysis of discrete source damage progression in the tensile stiffened composites panel using Langley’ COMET-AR Finite Element Analysis Codes. They have compared two types of crack tip model, one being a sharp crack tip and other being as a slit with round tips. They found that with the finer meshing, damage initiation is much earlier in round model compared to the sharp crack tip model. They also have compared the effect of different failure criteria. They found that for same amount of damage growth, the applied load level predicted by the Maximum Stress Criterion is higher than that predicted by the Hashin and Hashin-Rotem Criteria. They found that Hashin-Rotem Criterion provides the closest match with the experimental result.

Also Du Kai et al has done some analysis about tensile properties of stiffened composite panels with discrete source damage. In their analysis, they have compared the different stress states of Fiber and matrix at different laminates with fiber at different fiber angles. They have used ABAQUS FEM solver for their analysis. The failure criterion was Hashim-Rotem Criterion.

In the failure analysis of laminated composite pinned joints done by the Buket Okutan , the author has compared the different types of failure criterion and selected the best criteria. The author has also stated that Hashin’s Criterion was the most matching criteria with the experimental result. The author has also compared the stress state of various fibers at different angles. He concluded that the fibers facing the direction of force applied hold the maximum stress. He has used the ANSYS solver to solve these complex simulations.