Prediction of wrinkling in sheet metal by using modified Yoshida test and coordinate measuring machine (CMM) for wrinkle height measurement

摘要

Yoshida test is generally used to assess the influence of material properties on wrinkling behavior of sheet materials in forming processes. A standard Yoshida test specimen however, tends to fail near the grips when it is stretched to maximum wrinkle height values. Moreover, conventional dial gauges and height gauges used in the past for measurement of a maximum wrinkle height of deformed specimen provided information only at the central location of the specimen. This approach did not provide any information about distribution of wrinkles over the entire surface of deformed Yoshida specimen. The present research was focused on a modified Yoshida specimen with extension arms for better gripping, and measurement of initiation of wrinkles with strain gauges. Also a coordinate measuring machine (CMM) was used to measure wrinkle height over the entire surface of deformed specimen. A wide range of sheet thickness of a typical strain ageing deep drawing steel material was used in the experimental phase. It provided higher repeatability of results and marked reduction in specimen failure near the grips. It was also possible to measure the wrinkle height at equal interval on the lateral axis of deformed specimen. These results were used to predict influence of parameters like sheet thickness, material rolling direction, yield strength, work hardening coefficient and anisotropy on initiation and subsequent development of wrinkles. Relationship between wrinkle height vs. wrinkling initiation and maximum applied loads were also developed. Design engineers for selection of materials, adjusting corner radii and part profiles of sheet metal parts at early design stages, could use the wrinkling behavior result. It would also assist manufacturing engineers in development of sheet metal forming processes to avoid part failure due to wrinkling.