Methodology for Predicting the Onset of Widespread Fatigue Damage in Lap-Splice Joints

NASA has conducted an Airframe Structural Integrity Program to develop the methodology to predict the onset of widespread fatigue damage in lap-splice joints of fuselage structures. Several stress analysis codes have been developed or enhanced to analyze the lap-splice-joint configuration. Fatigue lives in lap-splicejoint specimens and fatigue-crack growth in a structural fatigue test article agreed well with calculations from small-crack theory and fatigue-crack-growth analyses with the FASTRAN code. Residual-strength analyses of laboratory specimens and wide stiffened panels were predicted quite well from the critical crack-tip-opening angle (CTOA) fracture criterion and elastic-plastic finite-element analyses (twoor three-dimensional codes and the STAGS shell code). INTRODUCTION In the past decade, NASA in collaboration with the Federal Aviation Administration (FAA) and aircraft industry has conducted a program to develop the methodology to predict the onset of widespread fatigue damage (WFD) in lap-splice joints of fuselage structures [1]. The onset of WFD is defined as the life at which fatigue cracking has developed to such an extent that residual strength is reduced below structural requirements. Each aircraft manufacturer has developed in-house durability and damage-tolerance analysis methods that are based on their product development history. To enhance these methods, NASA has adopted the concept of an analytical “tool box” that includes a number of advanced structural analysis codes which represent the comprehensive fracture mechanics capability to predict