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A general forming limit criterion for sheet metal forming

A general forming limit criterion for sheet metal forming,10.1016/S0020-7403(98)00113-1,International Journal of Mechanical Sciences,Thomas B. Stought

A general forming limit criterion for sheet metal forming   (Citations: 91)
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The forming limit of sheet metal is defined to be the state at which a localized thinning of the sheet initiates during forming, ultimately leading to a split in the sheet. The forming limit is conventionally described as a curve in a plot of major strain vs. minor strain. This curve was originally proposed to characterize the general forming limit of sheet metal, but it has been subsequently observed that this criterion is valid only for the case of proportional loading. Nevertheless, due to the convenience of measuring strain and the lack of a better criterion, the strain- based forming limit curve continues to play a primary role in judging forming severity. In this paper it is shown that the forming limit for both proportional loading and non-proportional loading can be explained from a single criterion which is based on the state of stress rather than the state of strain. This proposed criteria is validated using data from several non-proportional loading paths previously reported in the literature for both aluminum and steel alloys. In addition to significantly improving the gauging of forming severity, the new stress-based criterion is as easy to use as the strain-based criterion in the validation of die designs by the finite element method. However, it presents a challenge to the experimentalist and the stamping plant because the state of stress cannot be directly measured. This paper will also discuss several methods to deal with this challenge so that the more general measure of forming severity, as determined by the state of stress, can be determined in the stamping plant.
Journal: International Journal of Mechanical Sciences - INT J MECH SCI , vol. 42, no. 1, pp. 1-27, 2000
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    • ...If a prestrain leads to an initial strain state (e1i, e2i) , and a secondary forming operation results in a final strain state (e1f, e2f), then the principal stresses at the end of the secondary stage are given by [13]:...
    • ...The related formulation is presented in appendix (d) of reference [13]...
    • ...According to the investigations of Arrieux [10], Stoughton [13, 14] and other researchers [9, 11, 16], the most significant characteristic of stress-based forming limit curves (SFLC) is their strain-path independence...
    • ...As mentioned in “Stress-based froming limit curves”, the theoretical SFLCs were obtained by using Stoughton’s method [13] to translate the limiting strains into stress space, using the same constitutive assumptions as in the MK model...
    • ...Finally, Stoughton’s method [13] was subsequently employed to translate limit strains into limit stresses, using the same constitutive assumptions as in the MK analysis...

    Morteza Nurcheshmehet al. Investigation on the strain-path dependency of stress-based forming li...

    • ...Stoughton (2000) made a convincing case for the use of the FSLC...
    • ...Stoughton & Yoon (2005), proposed FSLCs that account for the orientation dependence of strength...

    K ANKAMMAet al. In-plane anisotropy in tensile deformation and its influence on the dr...

    • ...Experimental evidence for paths independent FLSD has been reported that the path dependence of the strain-based approach arises from the path dependent constitutive laws governing the relationship between the stress and strain tensors [9, 12]...

    Seong-Chan Heoet al. Formability evaluation of dimple forming process based on numerical an...

    • ...Arrieux et al. [2] and Stoughton [3] proposed a path-independent stress-based FLD...

    Ravindra K. Saxenaet al. Numerical simulation of fracture in cup drawing

    • ...In this work, the FLSC for a given tube material was determined from the experimental strain-based FLC by following the mapping procedure outlined by Stoughton [28]...

    Honggang Anet al. Multi-objective optimization and sensitivity analysis of tube hydrofor...

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