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A Viscoplastic Model Based on a Variable Strain Rate Sensitivity Index for Superplastic Sheet Metals

Omid.Majidi's picture

In recent years, superplastic forming (SPF) technology has been used for producing complex sheet components in automotive and aerospace industries. Under the SPF conditions, i.e. low strain rates and elevated temperatures, a superior elongation is achieved.

A reliable constitutive equation is essential for finite element analysis of the SPF products. The available viscoplastic constitutive equations are either too simple to capture all characteristics of the flow behavior of the superplastic metals or too sophisticated to be characterised and implemented in FE codes. Nevertheless, almost all of these models are based on assumption of a constant (average) strain rate sensitivity index (m-value).

It has been shown that m-value is not constant and could vary with plastic strain rate and strain. Thus, a novel model for predicting the uniaxial flow behavior of superplastic metals at different strain rates was proposed based on the variation of the m-value with a strain rate and plastic strain. The proposed model, hereafter named VmV model, requires minimum experimentation and calculations for determination of the constants, yet could give very accurate prediction of hardening, softening and damage behaviors of the studied superplastic metals.

The VmV model was published on the International Journal of Material Forming:

https://link.springer.com/article/10.1007/s12289-018-1443-2

https://www.researchgate.net/publication/328030900_A_Viscoplastic_Model_...

 

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