An FEA model for understanding the effectiveness of fastener as crack arrest mechanism has been constructed. The effect of the fastener in the sliding direction (Mode II) is modeled using fastener flexibility approach. The FEA results show that the fastener provides significant crack retardation capability in both Mode I and Mode II conditions. The analyses provide insights into the problem of disbond/delamination arrest using fastener or similar mechanisms. An analytical model for the problem is developed. The model consists of a splitbeam with a fastener attached; the fastener is modeled as a system of springs. An elastic layer is placed between the beams on the cracked faces to resolve contacts. The problem is solved using energy principles. The mode-decomposed strain energy release rates (SERR) at the crack tip are solved analytically 11-13. The primary goal of the current work is to enhance the safety of bonded composite structures by providing analysis methods for arrest mechanism.

Deployable structures are new prefabricated frames that can be transformed from a closed stage or compact configuration to a predetermined, stable expanded form. The structure is very convenient for transportation and recycling because it can be stretched out, drawn back and disassembled into pieces easily. This paper describes a new deployable structure composed of scissor composite members, each of which consists of universal scissor components, connected by bolts, and braced by pre-tensioned ropes out-of-plane, conforming a stable system. An aluminum-alloy deployable model was fabricated and a test program was carried out under vertical load to evaluate the capacity of the structure. Numerical analysis using FEM was conducted for validation purpose. By studying the stability and capacity of the structure, comprehensive evaluations of the structure were made. Possessing several advantages stated in this paper, deployable structures can be used as semi-permanent and temporary large spatial buildings.

A FEA model for analyzing effectiveness of fastener as crack arrest mechanism has been established. The effect of the fastener is modeled using fastener flexibility approach consisting of linear springs. It is shown that the fastener provide significant crack retardation capability in Mode I, but has limited resistance for Mode II propagation. The development of analytical solution for the crack arrest problem is important to the design of bonded/co-cured/co-bonded composite aircraft structures. A procedure for assessing the reliability of the fastener arrest mechanism has been demonstrated. A probabilistic approach is used because traditional damage tolerance methods for metallic structures are not generally applicable to composite structures. Probabilistic method can provide a more quantitative evaluation of reliability and safety of a structure. Analytical method for analyzing the crack arrest problem is being developed. The method consists of two parts: 1) crack-tip stress analysis; and, 2) nonlinear split-beam analysis with fastener. The analytical method makes possible accurate and efficient solution of crack arrest problems and is useful for structural design and optimization.

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