Porosity is a known detrimental material condition that includes a plurality of voids in the composite material caused by trapped or evolved gases which may be caused by improper processing, such as improper curing of the composite material.
The ultrasonic inspection of composite laminates takes advantage of the fact that porosity does not block ultrasound, like, for example, a delamination does, but scatters and attenuates the ultrasound. Consequently, by measuring the amount of attenuation an estimate of the degree of porosity can be obtained for correlation with manufacturing specifications. Typically, attenuation curves are produced to match ultrasonic attenuation on the inspected composite laminate part with actual porosity levels. Or else, the backwall is simply monitored for loss of attenuation below a fixed value.