Crack Detection - Commercialization Status
Prof. Reinhold Ludwig, Prof. Diran Apelian
The nondestructive detection of hairline cracks poses a significant problem to the P/M part producers. Identifying faulty components early in the manufacturing cycle is of paramount importance to assure quality and reduce cost.
In response to this industry problem PMRC launched a crack detection program with the objective to inspect green-state compacts. Since none of the traditional nondestructive evaluation methods and the associated instruments proved suitable for green-state inspection, research focused on developing a new testing approach of exploiting the idea of electrostatic current flow through the compacts. The typically high electric resistivity of the metallurgical structures permits the creation of substantial electric field distributions inside and on the surface of the samples in response to an applied current. The resulting voltage patterns on the surface carry sufficient information to detect both surface-breaking and sub-surface defects.
The inspection system developed by PMRC relies on a novel array sensor concept consisting of up to 100 spring-loaded probes in contact with the green-state sample. Current is injected in various directions, and voltages are measured over the surface area of the part. Although the method is most sensitive to surface breaking flaws as small as 20 microns in size, subsurface flaws can be detected to a depth of approximately 7.5 mm. The developed inspection apparatus is inexpensive and allows for flexible sensor configurations for parts of different geometries.
The research program started in early 1996 and a first prototype system was delivered in 1998. Additional modifications and enhancements resulted in a stepper motor driven press with foot paddles and indicator lights to enable an operator to make go/no-go part evaluations within 1 to 2 seconds. Testing with controlled and industry supplied production samples have underscored the success of this testing methodology. A U.S. patent has been issued (US 6,218,846 - Multi-ProbeImpedance Measurement System and Method for Detection of Flaws in Conductive Articles) and commercialization efforts are solicited to bring this technology to market.
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