Enhanced , lightweight material systems , such as 17 - 4PH stainless steel sandwich panels are being developed for use as fan blades and fan containment material systems for next generation engines . In order to improve the production for these systems , nondestructive evaluation ( NDE ) techniques , such as ultrasonic spectroscopy , are being utilized to evaluate the brazing quality between the 17 - 4PH stainless steel face plates and the 17 - 4PH stainless steel foam core . Based on NDE data , shear tests are performed on sections representing various levels of brazing quality from an initial batch of these sandwich structures . Metallographic characterization of brazing is done to corroborate NDE findings and the observed shear failure mechanisms .