|Problem: The notch sensitivity of a new material system needed to be characterized, the failure mechanisms identified, and peak strains measured. Bounding cases were required to validate the test techniques and to provide qualitative comparisons. Only the data for the bounding cases can be presented here.
Solution: The surfaces of a brittle steel and a ductile aluminum test coupons were painted with a white base and black paint was misted on the surface to generate speckles that were about 0.01 inches in diameter. The VIC3D system was used to sample 30 images per minute during a slow ramp to failure. Full-field displacements were extracted for the 0.75 inch wide coupons. Double edge notches had been machined into each coupon to provide known stress concentrations. The strain at failure was quantified and compared to the results from the new material.
The steel material exhibited a low amount of ductility and the aluminum material exhibited large ductility before failure. Contour plots of the strain in the direction of loading (eyy) were extracted (note: the maximum contour strain levels were 4,000 and 60,000 microstrain for the steel and aluminum materials, respectively. Strains were also extracted for a small region that was near the notch (Local), over a strain gage size area halfway between the two notches (Center), and averaged across the entire notch region (Average).
|Brittle Steel Prior to Failure
|Ductile Aluminum Prior to Failure