The goals of this Grant Opportunities for Liaison with Industry (GOALI) research project are to experimentally and analytically characterize the stress based failure criterion for sheet materials; to incorporate the criterion into finite element models of the sheet metal forming process; and to exploit the material phenomenon through process innovations. Past research has shown that the stress based failure criterion is path independent or at least less sensitive to the deformation path than the commonly used strain based failure criterion. First, a biaxial test apparatus will be used to characterize the stress based failure criterion for advanced alloys. Using this experimental data, analytical and numerical models will be developed to assist designers determine the correct process variation in order to prevent tearing concerns. Finally, process innovations for both deep drawing and stretch forming will be implemented to exploit this material behavior. This research will add significantly to the scientific knowledge base for this emerging material characteristic. There are several broader impacts from this research. First, improved failure prediction methods will benefit society at large through a reduction in the time to market of new products and more aggressive product designs, which will decrease the weight and cost of components. Graduate students will also benefit from the potential to work with industrial partners as summer interns. Furthermore, the results of this research will be directly integrated into course material thus impacting the education of students. Finally, to ensure that the results of this research are effectively disseminated to industries, a set of workshops will be conducted at Alcoa.
The goals of this research project were to experimentally and analytically characterize the stress based failure criterion for sheet materials; to incorporate the criterion into finite element models of the sheet metal forming process; and to exploit the material phenomenon through multiple step process innovations. Past research has shown that the stress based failure criterion is path independent or at least less sensitive to the deformation path than the commonly used strain based failure criterion. In this research, numerical simulations were used to determine the element type in numerical simulations which most accurately capture the failure (Hasan et al., 2011), to demonstrate the path independence of a stress based failure criterion (Sakash et al., 2006) and to understand shifting effects of the strain based approach (Derov et al., 2009). Other projects included: predicting forming severity during multiple step operations (Kinsey et al, 2006), assessing key assumptions in analytical models and comparing experimental results to the simulations (Hasan et al., 2012). An essential research tool (i.e., a Digital Imaging Correlation system) to generate full field strain data from experiments for these comparisons was obtained from a separate NSF Major Research Instrumentation grant (#0821517). Furthermore, a device was fabricated to apply the bi-axial loading and experimentally characterize the stress based failure criterion. Finally, the design of a cruciform specimen to use in the process has been analyzed. This research resulted in six journal/transaction publications (and another one in preparation) and seven peer-reviewed conference papers. One Ph.D. student and five Master’s degree students (with an additional current student) have worked on this research topic. There are several broader impacts from this research. First, improved failure prediction methods will benefit society at large through a reduction in the time to market of new products and more aggressive product designs, which will decrease the weight and cost of components. Graduate students also benefited from the real world importance of the research and the interaction with industrial partners. Furthermore, the results of this research were integrated into course material thus impacting the education of students. Several Research Experience for Undergraduates and Research Experience for Teachers participants were involved in the work thus extending the educational benefits, including outreach to K-12 education. Finally, to ensure that the results of this research are effectively disseminated to industries, a set of workshops are being planned with Alcoa, the industrial partner on the grant.
