An inverse acoustical phased array technique for impact detection and location

Due to the complex failure modes associated with composites, a structural health monitoring system capable of accurately locating the source of strength-reducing events is desirable in order to reduce inspection time and time out of service. Various active and passive inspection techniques exist but most require large footprints and extensive cabling to monitor full scale structures. This work derives various location techniques by coupling modal acoustic emissions with phased array techniques to detect and accurately locate the source of strength-reducing events such as impacts. Phased array techniques provide a method to more accurately track phase points for determining arrival times used to back-calculate the source, as well as providing a method that can incorporate anisotropic wave speeds. To increase accuracy by neglecting local to global material changes, the local velocity profile per component was found and built into the derived location algorithms. The location algorithms were then tested on two full scale composite structures based on strength and stiffness critical design considerations. It was found that with two arrays, each with dimensions of 1 inches in width and 8 inches in length and consisting of four sensors each, events could be accurately located over a 65 ft2 region on the stiffness critical structure with an average error of 10 inches and over a 100 ft2 region on the strength critical structure with an average error of 9 inches.