Current research at NIST has proven that ultrasonic signals from a scanning acoustic microscope can be used to map residual stress patterns in engineering materials. Previously, no direct method existed for displaying stress. Knowing a materials residual stress is important in determining the integrity of that material, and how it may respond in service. The existing NIST method relies on measuring the amplitude of shear waves produced by mode conversion from a defocused ultrasonic transducer. This method works well except for the fact that the return signals can be corrupted by an additional component of the longitudinal wave. This proposal seeks to improve the usefulness of the NIST method of stress mapping by using digital filtering techniques to eliminate the unwanted longitudinal component of the ultrasonic waveform. Filtering techniques have a high probability of success since the shear wave component exists at about twice the frequency of the longitudinal wave. In this Phase 1 effort, Sonix will: (1) design digital filters; (2) embed the filter algorithms into an existing acoustic microscope; (3) test the filtering algorithms on engineering materials provided; and (4) deliver and install a working prototype of the improved microscope software at the NIST facility in Gaithersburg. COMMERCIAL APPLICATIONS: Sonix has an existing customer base of several hundred acoustic microscope users. Upon successful completion of Phase 1, Sonix will poll its users to determine a marketing strategy. It is very likely that digital filtering capabilities added to the acoustic microscope will be a desirable upgrade feature to the system
