Failure Initiation Predictors for Reliability-Based Design of Hybrid Composite Materials

ABSTRACT: This proposal is concerned with the development of a novel failure initiation and progressive failure analysis modeling method for advanced composite structures, including the analysis of selected structural joints utilizing a statistically based micromechanics model embedded in a 3D non-linear finite element code. The method accounts for the interaction between out-of-plane failure and in-plane failure and also the material microstructure. The proposal utilizes a fundamental physics based approach that is devoid of empirical formulas that have dominated failure prediction tools in composites. The results to be obtained will provide the necessary guidance in selecting the most robust methodology to achieve the desired goal of combining initial design with reliability based tools to re-design and evaluate existing designs of composite structures. In the proposed approach, designated as a “progressive failure analysis tool”, computations will be simultaneously carried out in parallel at three length scales, as needed (the laminate level, the lamina level and at the level of a fiber/matrix unit cell representation of the lamina), with strong coupling between the three scales. BENEFIT: This effort is expected to result in industry standard reliability prediction and reliable structure design tools for safe life design of military air vehicles. Commercial application includes the application of this reliability prediction and reliable structure design tools for safe life design of land, sea and air commercial vehicles. Reliability based analysis will help to move to reliability based certification, which is a long term drive to improve certification process, and eliminate overlapping conservative design factors. Improved analysis tools like the present development can aid with subcomponent certification testing, as better analysis helps to understand the tests. Progressive damage analysis is needed for many detailed joint configurations, as well as damage tolerance assessments of new unitized composite bonded assemblies. Current bonded pi-joints require certification testing for each new size and shape; this analysis tool could allow great reduction in the certification testing through the use of a combination of analysis developed as part of the proposed project and testing to develop pi-joint allowables.