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 a...

The growth of slant cracks by fretting fatigue of a half plane in contact with a flat rounded pad was studied. The mode I and mode II stress intensity factors for cracks of various lengths and directions were calculated using the semi-analytical method of the distribution of dislocations, and their cumulative effect on the crack growth was investigated using the strain energy density criterion....

The aim of this study is to evaluate the microstructures, tensile lap shear strength, and fatigue resistance of 6022-T43 aluminum alloy joints welded via a solid-state welding technique-ultrasonic spot welding (USW)-at different energy levels. An ultra-fine necklace-like equiaxed grain structure is observed along the weld line due to the occurrence of dynamic crystallization, with smaller grain...

Estimating and tracking crack growth dynamics is essential for fatigue failure prediction. A new experimental system— coupling structural and crack growth dynamics—was used to show fatigue damage accumulation is different under chaotic (i.e., deterministic) and stochastic (i.e., random) loading, even when both excitations possess the same spectral and statistical signatures. Furthermore, the co...

This paper presents the results of a combined experimental and theoretical study of the fatigue crack initiation in LIGA Ni thin films with a thickness of 270 mm. The potential roles of surface oxide thickening and slip bands are explored for fatigue crack initiation. Surface oxides and roughness are characterized using X-ray photoelectron spectroscopy (XPS) and atomic force microscopy (AFM). T...

A large area electronics in the form of a soft elastomeric capacitor (SEC) has shown great promise as a strain sensor for fatigue crack monitoring in steel structures. The SEC sensors are inexpensive, easy to fabricate, highly stretchable, and mechanically robust. It is a highly scalable technology, capable of monitoring deformations on mesoscale systems. Preliminary experiments verified the SE...