Problem: The validation of a progressive damage model for composite materials needed the local strain at crack initiation and the load when cracks advanced. Strain gages only provided averages over small areas that might not be where cracks nucleate or could obscure the visual confirmation of nucleation location.
Solution: The surface of the composite material was painted with a white base and black paint was misted on the surface to generate speckles that were about 0.004 inches in diameter. The VIC3D system was used to sample 120 images per minute. Full-field displacements were extracted for a 1 inch by 1 inch area around an open hole and strains calculated from the displacements. The crack length was determined using techniques that were developed to automatically determine the load at crack extension and validated from VIC3D visualizations of the crack.
|Maximum Tensile Strain
at Crack Nucleation
|Visualization of Crack Lengths|
|Measured Crack Growth|