Imminent fracture detection in graphite/epoxy using acoustic emission

An experiment designed to detect incipient failure in graphite/epoxy tensile specimens is described. Tests using eighteen samples of six different graphite/epoxy compositions in six-ply balanced [0/+45/?45], laminates indicate that a failure precursor does exist. This precursor takes the form of a sudden reduction in the acoustic-emission output at 99 percent of the ultimate tensile load, and evidence indicates that the reduction is the result of a change in the fundamental failure mechanism. The shape of the acoustic-emission countrate curve is analyzed and found to correlate well with micro-mechanical fracture activity.