Continuing efforts to develop environmentally acceptable materials and processes are constrained by the timeconsuming nature of qualification testing. Us ers who must make their decisions under conditions of uncertainty want to minimize risk. Frequently, substantial testing is conducted in support of the initial product qualification decision or in support of requalification for design modification to improve performance or solve problems. The present qualification test process is both time-consuming and costly and is often preempted by environmental compliance or enforcement requirements. There is a need to develop accelerated and less costly means for qualification testing of alternate, substitute, and emerging new materials and processes in order to introduce environmentally acceptable materials rapidly into the military inventory and force structure.
The technical objective of this project is to create combined environmental and reliability testing techniques with a 20:1 time compression ratio for evaluating adhesive bond durability. The goal is to develop low-risk, fast-track methodologies and techniques for military qualification of new, modified, environmentally-benign (low in volatile organic compounds and nonchromated) adhesive and adhesive primer materials as well as environmentally-benign metal prebond surface preparations.
Testing was conducted to determine the strength retention of lap shear specimens in accelerated aging environments. The results were correlated with the actual 10-year exposure lap sheer data which form the baseline for the program. Adhesive bonded components removed from flying or retired aircraft were obtained. Good and debonded areas were c haracterized, with good areas being machined into specimens for testing. Correlations were made between accelerated testing and actual service history. Significant inservice durability data available for existing bonding processes were correlated with accelerated testing conducted using a specimen prepared with the processes. Additionally long-term exposure specimens were obtained from industry and their results compared to the accelerated test data generated during this program. Additional specimens were placed in long-term exposure so future direct comparisons also will be possible with the new accelerated test techniques. The major technical risks were (1) duplicating the end effect and mechanisms of long-term aging on bonded joints and (2) determining and generating the amount of empirical evidence required to support configuration change decisions.
Lockheed Martin Vought Systems (formerly Loral Vought Systems) believes the test correlates well with the actual long-term testing baseline. However, end users believe more data may be required to prove this. Several organizations have sent specimens to be tested and compared to their data. Specimens fabricated for correlation with Navy exposure testing were tested aboard the USS Kittyhawk. Several potential end users reaffirmed their interest in the accelerated tests and provided specimens for testing. Results of the tests still support the original conclusions about the aging mechanism and the theoretical bridge between the accelerated test and actual performance. This project was completed in FY 1997.
The development of an acceptable accelerated testing technology will reduce the time needed for testing, reduce the cost of testing, and eliminate costs for environmental compliance and hazardous material/waste management. These efficiencies and economies will result in the elimination of unnecessary or redundant tests and the promotion of earlier implementation of clean technology. The project will provide a method of accelerating the qualification of technology development projects involving the development of substitutes for materials with hazardous or toxic manufacturing wastes.