Analytical Tools for Composite Material Damage Evaluation

Large unitized composite structures significantly reduce part count and cost of manufacture. Damage tolerance assessments of unitized structures are essential to ensure known damage threats will not compromise the safe operation of aircraft. The current practice of residual strength assessment and tests based on small BVID (barely visible impact damage) and large CDT (critical damage threshold) damage is known to increase in-service repair costs of thin composite honeycomb panels. There is therefore a need to develop accurate damage tolerance assessment analysis methods and efficient repairs. This proposal aims to develop analytical and computational tools for quantitative damage tolerance assessment of traditional composites based on progressive damage modeling. Analysis and tests will be performed on the residual strength and integrity of representative damaged components and adhesively bonded repairs. A constituents- and micromechanics-based failure approach (MMF) to damage initiation and progression for traditional composites will be employed. This will extend the considerable analysis capability and concept, hitherto successfully applied to conventional CFRP structures, to repaired composites and optimized repair processes. The development of tools under Phase I will enable the selection of the most promising candidate concepts for further testing and verification under Phase II. BENEFIT: Ensuring the survivability of hybrid composite structures against various levels of damage threats by embedding damage-tolerant features will increase the margin of confidence in the design of large unitized aircraft structures. The developed rational quantitative methodology and analytical tools are applicable whenever damage tolerance assessment and knowledge of need-to-repair are critical, such as in military and civil aviation overhaul and maintenance services. The tools will also enable the assessment of the effectiveness of various proposed repair schemes in restoring structural integrity.