SBIR-STTR Award

Conventional damage tolerance assessments of metallic structures based on crack growth generally do not apply to composites. The current practice of residual strength assessment based on small BVID (barely visible impact damage) and large CDT (critical damage threshold) damage is known to increase service repair costs of thin composite honeycomb panels. There is, therefore, a need to develop better damage tolerance assessment analysis methodologies. KaZaK Composites, Incorporated proposes to utilize their expertise and experience in damage tolerance assessment, mechanical property modeling and life prediction of polymer matrix composites to develop an advanced damage evaluation tool for the USAF. In the proposed work, analysis and tests will be performed to determine the structural strength and integrity of a traditional composite material with controlled defects. A new constituents and micromechanics-based (MMF) and element-failure method (EFM) approach to failure initiation and progression for composites will be employed in the analysis methods for both cases. This advanced numerical tool will begin to be used in association with commercial finite element software to provide the Army with an obvious transition path to assessing composites durability for current applications.

Keywords:
Thin Ply, Damage Progression, Composite Durability, Mmf, Structural Integrity, Residual Strength, Damage Tolerance, Composites

In the design of fiber reinforced polymer (FRP) composite materials, the preeminent concerns are typically: progressive failure and life prediction especially when subjected to fatigue loading. Fatigue experiments are usually very expensive and take a long time to complete. Furthermore, there could be thousands of test cases depending on the material system and layup sequences envisioned for a particular design. So this conventional procedure can hardly satisfy the need for a fast design cycle and cannot guarantee an optimal final design. Here we propose a method based on micro-mechanics. Starting from the constituents, i.e., fiber, matrix and interface, we proceed to predict the behavior of individual plies, bulk laminates and eventually total structures. Through the micromechanics approach, it is possible to predict progressive failure or life of composite structures. The Phase II program proposed anticipates developing a validated, long-term durability prediction methodology for FRP composite materials that can be used to strengthen, repair, and upgrade existing FRP structures on vehicles. This methodology will also be applicable to the design of new composite structures. This Phase II effort will also strive for integration into software tools for the implementation and integration with commercial finite element analysis software.

Keywords:
Thin ply, damage progression, composite durability, MMF, structural integrity, residual strength, damage tolerance, composites.