Innovative Concepts for Rapid and Inexpensive Testing for Threshold Stress Intensity (KISCC) under Stress Corrosion Cracking (SCC) Conditions of Alumi

Report developed under SBIR contract for topic OSD09-C05. SCC of aluminum is of particular concern in the chloride containing environments that are typical for naval operations and is increasingly investigated as part of the system design process for naval aircraft structures and subsystems. However, modern test methods that determine KIscc of aluminum require expensive long duration testing (10,000 hours). The feasibility of developing a reliable accelerated test method to measure KIscc for aluminum alloys has been demonstrated by obtaining accelerated test results of a 7075 T6 aluminum alloy that corresponds to the published values of KIscc. The Phase I project demonstrated 1) that the RSL test method developed for steels does, in fact, measure the Stress Corrosion Cracking (SCC) threshold for the onset of crack growth in aluminum alloys, 2) that the sensitivity to detect the onset of crack growth is enhanced by an analytical method that defines crack initiation, 3) that specimen design enhanced notch acuity and localized the crack initiation site increases sensitivity to SCC and 4) that the test method significantly reduced both the time of test (less than 100 hours) and the number of test coupons compared to ASTM E1681. Phase II will pursue advanced development of a testing system and method for measuring SCC resistance of aluminum alloys. The system will be based on the RSL test system presently used for measuring SCC resistance of steel alloys. The system and method used will be developed, optimized, fabricated and validated against representative alloys.