Nondestructive Residual Stress Measurements in Composites

An ultrasonic Rayleigh surface wave method is proposed to evaluate residual stresses in composites. The Rayleigh wave method has several distinct advantages, including the ability to eliminate the effect of fiber orientation on the residual stress determination. Also, the Rayleigh wave approach can discriminate between tensile and compressive residual stresses and obtain a residual stress depth profile by altering the penetration depth of the Rayleigh wave. The Rayleigh wave is bound to the surface of the composite, enabling measurements on curved and other irregularly shaped surfaces. This program emphasizes composites; our previous experience will help the Navy address measurement needs in metals. This program will lead to an enhanced understanding of residual stress fields that exist in composites. A residual stress evaluation system, consisting of a field portable inspection system based on a portable computer that can be operated remotely by a single user, will also be developed. This will enable the stress levels to be determined rapidly and the data to be stored for later analysis. The results obtained from this instrument will be used for manufacturing process control and in-service inspections. Preliminary contacts with commercial users have demonstrated significant interest in this proposed system, simplifying the commercialization process.