Fatigue Life Modeling of Composite Bonded Joints in Rotorcraft Structure

Hoyt, D.M., Ward, S.H., Bau, H.

NSE Composites Phase I Final Report to US Army for SBIR A98-029 (USAAMCOM TR 99-D-12, ADB248414), July 1999.

The rotorcraft industry lacks a validated analysis tool that enables engineers to confidently predict the strength and durability of composite bonded joints in primary structures. NSE Composites (NSE) is developing such a tool for this SBIR program. In Phase I, NSE successfully demonstrated the feasibility of a state-of-the-art analysis approach that predicts static strength and fatigue life, and accounts for rotorcraft certification issues.

NSE teamed with Bell Helicopter, Boeing, and Sikorsky to define three high priority composite bonded joint configurations that represent a broad range of joint types and materials found in rotorcraft structure: a tee-stiffened panel, a lap joint, and a tapered repair joint. Non-linear 2-D finite element models were successfully used with strength-of-materials failure criteria to predict damage initiation, and fracture mechanics to predict static strength and fatigue life. Fatigue life under spectrum loading was predicted using damage accumulation methods. Design and damage tolerance criteria were also addressed in the analyses. The results of Phase I have laid the foundation for successful follow-on development of an automated, validated software tool for the strength and fatigue analysis of composite bonded joints, which has the potential to enable significant cost and weight savings in composite aerospace structures.