Failure mechanisms in compression-loaded composite laminates containing open and filled holes

Filled hole-based compression allowable strengths for carbon/epoxy laminate s are not widely used in airframe design, due to a lack of understanding of geometry-related effects and failure mechanisms. The effects of fastener h ole-filling, hole clearance, and clamp-up torque upon the filled hole compr ession strength of composite laminates were investigated experimentally and analytically. Tests were conducted using open and filled hole specimens wi th defined hole clearances spanning the range permitted in Class 1 structur al holes (nominal bolt diameter +0.003/-0.000 inch). All filled hole specim en configurations demonstrated compression strengths in excess of those for open hole specimens, due to the development of a load path through the fas tener. Hole clearance was found to be the primary factor governing filled h ole strength; fastener torque had relatively little effect. A semiempirical strength prediction methodology was developed using 2-D finite element ana lysis and ply-level quadratic failure theory. Good agreement between experi mental data and predictions was demonstrated for T800/3900-2 tape laminates .