Impact of Nd-YAG laser drilling on the fatigue characteristics of APC-2A/AS4 thermoplastic composite material

Both carbon fiber thermoset and thermoplastic materials can be drilled using a laser. This, however, results in significant damage to the material, but the extent to which this would reduce the fatigue life was not known. Studies have been conducted to evaluate this for an aerospace application, which required a light-weight, but perforated, skin panel through which air could be sucked. The objective has been to determine the impact on the fatigue life of quasi-isotropic APC-2A/AS4 due to Nd-YAG laser-drilled holes (∼120 μm diameter, spaced ∼500 μm apart). Static tensile tests indicate a 29% reduction in strength. The maximum stress versus cycles to failure (S-N) relationship is represented by a power law function: S=KN^m. The laser drilling has been seen to reduce the value of K (coefficient of fatigue strength), but the value of m (fatigue strength degradation exponent), which was determined from nonperforated specimens, was unchanged.