NDE OF INTERFACIAL BONDS BY MICRO-SCANNING GAMMA BACKSCATTERING

ADHESIVELY BONDED STRUCTURAL MATERIALS REQUIRE NONDESTRUCTIVE METHODS OF INSPECTION AND EVALUATION (NDI/E) TO DETECT CRACKS, VOIDS, AND INCLUSIONS WHICH DIRECTLY AFFECT BOND STRENGTH. LACK OF RELIABLE NDI/E, PARTICULARLY DURING MANUFACTURE, WILL FORCE RELIANCE ON LARGE DESIGN MARGINS OF SAFETY AND EXPENSIVE DESTRUCTIVE TESTING. PHASE I WILL ADDRESS THESE NEEDS WITH GAMMA-RAY BACKSCATTER RADIOMETRY USING A COLLIMATED DETECTOR TO ACHIEVE NEAR MICROSCOPIC RESOLUTION. THIS IS SIMILAR TO BACKSCATTER TOMOGRAPHY (BOTH REQUIRE ACCESS TO A SINGLE SURFACE), BUT INSTEAD OF CREATING AN INTEGRATED IMAGE, INTERSECTING DETECTOR AND SOURCE VIEWS MEASURE DENSITY IN ONE PIXEL AT A TIME. FINER RESOLUTION IS ACHIEVED USING STACKS OF CONVERGING PLANAR VANES OR OTHER CONFIGURATIONS TO FOCUS THE VIEW TO A SMALL REGION. INSPECTION WOULD SCAN THIS REGION AT VARIOUS DEPTHS BELOW THE SURFACE OR COULD MAP A LARGER VOLUME AND THUS ENABLE DETAILED IMAGING. RECENT APPLICATIONS TO COMPOSITES SUGGET IT SHOULD BE POSIBLE TO ADJUST THE SENSITIVE VOLUME TO LESS THAN 1 MM(3), ENABLING DETECTION OF DEFECT SIZES ON THE ORDER OF A FEW MICROMETERS. PHASE I WILL DETERMINE FEASIBILITY OF SUCH MICROSCOPIC SCANNING IN REPRESENTATIVE COMPOSITE MATERIALS. PENDING THE OUTCOME OF THESE TESTS, A PROTOTYPE INSPECTION SYSTEM WILL BE DEVELOPED IN PHASE II AND CALIBRATED WITH APPROPRIATE DESTRUCTIVE TESTS.