On the failure characteristics of superplastic sheet materials subjected to gas pressure forming

• Published in: Scripta materialia Vol. 42; no. 3; pp. 257 - 263
• Main Author: Khraisheh, Marwan K
• Format: Journal Article
• Language: English
• Published: New York, NY Elsevier Ltd 17.01.2000; Elsevier Science
• Subjects: Applied sciences; Bulge forming; Condensed matter: structure, mechanical and thermal properties; Deformation and plasticity (including yield, ductility, and superplasticity); Exact sciences and technology; Failure characterization; Mechanical and acoustical properties of condensed matter; Mechanical properties of solids; Metals. Metallurgy; Physics; Superplastic deformation; Bulge forming; Failure characterization; Superplastic deformation; Constitutive equation; Forming processes; Strain rate sensitivity; Explosive forming; Superplastic forming; Ruptures; Theoretical study; Plastic deformation; Strain rate
• ISSN: 1359-6462; 1872-8456
• DOI: 10.1016/S1359-6462(99)00359-0

In order for the superplastic forming process to become widely acceptable as an efficient forming technique, the issue of predicting thinning and failure during deformation must be addressed. Limited results are available in the literature regarding this issue. The objective of the present study is to shed some light on this critical subjects. The preliminary results reported here on the Pb-Sn superplastic alloy can be very useful in developing general guidelines and procedures to be used by the SPF industry. However, more tests on different engineering superplastic materials (Al and Ti alloys) and using different process parameters (e.g. die geometry and dimensions) are needed to develop the general guidelines. The following can be concluded from this study: Different failure modes were observed for different forming rates. When forming under constant effective strain rate, it was observed that failure occurs at a time near the peak value of the forming pressure profile constructed based on the assumptions of balanced biaxial stretching and isotropy. Hence, forming time to failure can be accurately estimated. Following a simple instability analysis using uniaxial-based stress-strain rate relation did not succeed in predicting actual thinning at failure.