Influence of controlled depth abrasive water jet milling on the fatigue behavior of carbon/epoxy composites

Conventional milling during aircraft structural composite repair encourages defect generation and distortion, causing hindrance in milling depth control and thereby adversely affecting their mechanical behavior. Abrasive water jet (AWJ) milling can be an alternative to avoid these problems. In this study, carbon/epoxy laminates are milled using AWJ and machined surfaces are characterized at micro (surface texture) and macro (damage size) scales. Defects in the form of craters, ridges-valleys and broken fibers are identified and quantified. A new parameter crater volume (C-v) is proposed to quantify and qualify the machining quality in terms of induced damage. This introduces a novel approach to characterize the machined surface without ignoring the machining damage. Milled specimens with different damage levels are subjected to tensile and tension-tension fatigue tests instrumented with thermography and acoustic-emission transducers. Machined specimens with high C-v exhibited inferior fatigue behavior and X-ray tomography revealed that crack/fracture initiation occurred from the crater edges.