Determining Forming Limit Diagrams of Annealed 304 Stainless Steel at Multiple Strain Rates Using Digital Image Correlation
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Abstract
Forming Limit Diagrams are an essential tool in the metal forming industry. They accurately estimate the overall deformation a material can endure without ripping or wrinkling. Obtaining and modeling these curves can be a difficult process, especially with rate-sensitive material. Rate-sensitive material may affect the Forming Limit Diagram and limit the speed at which metal forming can occur. Nakajima Testing is a prominent method of obtaining a Forming Limit Diagram, as per ISO 120004-2. This paper aims to examine the behavioral changes of the Forming Limit Diagram of annealed 304 Stainless Steel at two different strain rates, quasi-static and dynamic. Quasi-static tension testing is performed and localized strain data is used in LS-DYNA to simulate future Nakajima Testing. Nakajima Testing is performed using a fixture that is used on a hydraulic load frame at a quasi-static rate, and on a drop tower apparatus at a dynamic rate. The quasi-static test results and dynamic test results are compared with each other, as well as the simulated results. The dynamic testing resulted in a higher FLD than the quasi-static testing. More testing needs to be performed to solidify the results.