Propagation of Hole Machining Defects in Pin-Loaded Composite Laminates

Abstract

The propagation of hole machining defects in pin-loaded carbon/epoxy laminates subjected to uniaxial tension fatigue loading was investigated using two non-destructive examination (NDE) techniques. The KTH-method, a new method which gives defect-free1 holes, was used to machine holes in specimens. For comparison, holes were also machined using two traditional methods (DIXI and Dagger drills) causing varying extent of damage. X-ray radiography and computerised tomography were used to give two- and three-dimensional images, respectively, of defect propagation after 50,000-250,000-500,000-cycles, and after failure. Permanent hole elongation was monitored during cyclic loading. The results showed that the propagation of defects occurred in a controlled and stable phase until a sharp fatigue limit was reached (about 400,000 cycles for the DIXI specimen and about 500,000 cycles for both the KTH and Dagger specimens). During the stable phase, the global structural response of the specimens was affected very little by the damage propagation. At the fatigue limit, extensive damage development and defect propagation occurred, resulting in similar large permanent hole elongations in all specimens.

Drilling of fiber reinforced plastics: A review

“…The influence of defects generated after hole making on the strength and fatigue life of composite laminates subjected to static and fatigue loading were studied by Tagliaferri et al [26], Persson et al [27], Ramkumar et al [28] and Xu et al [29]. In general, the results indicated that tool material and geometry slightly affect the fatigue life of composites.…”

Modeling and tool wear in drilling of CFRP

“…Delamination and surface finish in drilling composite materials have been found to be influenced by a number of factors such as feed rate, cutting speed, drill geometry, tool wear and tool material. Delamination remains the most serious damage mode as it reduces severely the load carrying capacity of laminated composite structures and, therefore, must be avoided (Abrate [8], Persson et al [9,10]). The importance of tool geometry in delamination reduction is evidenced by several authors.…”

The Influence of Selected Local Phenomena in CFRP Laminate on Global Characteristics of Bolted Joints

“…The properties of laminate around the hole can be weakened/deteriorated compared to their nominal values. This deterioration can be a result of the drilling technology, and on the other hand, the cyclic load during the service of the structure [32][33][34]. Analysis of the hole machining effects can be found in refs.…”