Background
The ability to perform construction and fabrication activities such as welding is critical to future activities in space. As on the ground, welds on critical space components will require inspection. The purpose of this project is to investigate adaptation of conventional nondestructive testing techniques and procedures to the space environment. While there are various characteristics of the space environment such as near-vacuum pressures, increased radiation, low gravity, and (on the moon) the presence of regolith that make application of conventional nondestructive evaluation (NDE) techniques different in space, the focus of this work is on the wide variations in temperature under which inspections will have to be performed. The target operational temperature range is -130○C to +150○C.
This project is part of a cost-sharing agreement with NASA that supplies funding as well as in-kind labor to the program. The focus of the program is the inspection of laser weld joints in aluminum panels.
Approach
The objective of this project is to evaluate the use of Electromagnetic Acoustic Transducers (EMATs) and eddy current testing (ET) transducers for the NDE of welds in the space environment. Both EMAT and ET transducers can operate without contact to the inspected parts surfaces, and neither transducer requires material on the part surface to couple energy during inspection.
SwRI designed and fabricated custom EMAT and ET transducers using designs suitable for the expected temperature extremes. To test the sensors, SwRI constructed a temperature-controlled chamber that allows one-dimensional scanning of both transducers. The functionality of each transducer type will be determined over the temperature range. NASA is fabricating the weld samples to be used in testing. The samples will be 0.25-inch-thick, aluminum plates with a laser-produced weld and introduced defects.
Accomplishments
The temperature-controlled test chamber has been designed and bult. The chamber was shown by testing to be able to reach and maintain the required temperature extremes. Both the EMAT and ET transducers have been designed, built, and tested at room temperature. At room temperature, the sensors have functioned as expected. NASA delivered an initial set of two aluminum plates containing various void and porosity defects in the welds. NASA will deliver a third test plate which will have machined notches to simulate crack-like defects. Once that plate is received, testing over the temperature range will begin and the ability of the transducers to detect the various defects of the range will be measured.