Characterization of forming limits at fracture with an optimized cruciform specimen: Application to DP600 steel sheets

Song, Xiao; Leotoing, Lionel; Guines, Dominique; Ragneau, Eric

doi:10.1016/j.ijmecsci.2017.03.023

Cited by 47 publications

(29 citation statements)

References 34 publications

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“…Figure shows the forming limit strains at fracture under linear and nonlinear strain paths (Type 2‐A and Type 2‐B). As described in previous study, the forming limit strains at fracture under linear strain paths is fitted by a straight line with k =−0.39 and A =0.63, while those under nonlinear strain paths is fitted by a straight line with k =−0.49 and A =0.68. For linear strain paths, the experimental results are in accordance with the ones of Gruben et al., especially for uniaxial and equibiaxial loadings.…”

Section: Experimental Procedures and Resultsmentioning

confidence: 98%

“…As shown in Figure , an optimised cruciform specimen was proposed by the authors to identify the FL strains at fracture of DP600 sheets under linear strain paths . This specimen is designed for sheets with an initial thickness of 2 mm and the shape is not specific to DP600 sheets since its performance was also validated for other materials, like aluminium alloys.…”

Section: Experimental Procedures and Resultsmentioning

confidence: 99%

“…The time‐dependent method is relatively efficient for identifying the beginning of fracture. The FL strains at fracture of DP600 sheets under linear strain paths have been identified by the presenting authors …”

Section: Experimental Procedures and Resultsmentioning

confidence: 99%

“…The critical ratio method was successfully used to identify the FL strains at necking of DP600 sheet metal under linear strain paths . The same method is adopted to determine the FL strains at necking under the two types of nonlinear strain paths.…”

Section: Experimental Procedures and Resultsmentioning

confidence: 99%

“…For linear strain paths, the correlation between results from conventional Marciniak tests and biaxial tensile tests is rather good for FLCN . Recently, a new shape with an initial thickness of 2 mm was optimised by the authors and validated for linear strain paths . The initial thickness reduction from 4 to 2 mm permits to study metal sheets with a larger range of applications.…”

Section: Introductionmentioning

confidence: 99%

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Effect of continuous strain path changes on forming limit strains of DP600

Song

Leotoing

Guines

et al. 2019

Strain

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The strain path may change in actual sheet metal-forming processes, so the determination of formability of sheet metal should consider the nonlinear strain path. For identifying the forming limit (FL) strains under nonlinear strain path, a conventional two-step procedure with unloading is classically used to produce the strain path change, which results in no continuous measure of strain. The in-plane biaxial tensile test with a cruciform specimen is an interesting alternative to overcome the drawbacks of conventional method.The strain path change can be made without unloading during a single test. In this work, the experimental FL strains of DP600 sheets under two types of nonlinear strain path are investigated and then compared with those under linear strain paths. The Oyane ductile fracture criterion is used in the finite element simulation to predict the experimental results. KEYWORDS FLCF, FLCN, in-plane biaxial tensile test, nonlinear strain path | INTRODUCTIONMost of the forming limit curves at necking (FLCNs) and the forming limit curves at fracture (FLCFs) have been experimentally determined using methods that produce proportional loading with insignificant changes in strain paths. However, in some innovative forming processes, such as single point incremental forming, complex strain paths with several changes have been identified by different authors. As an example, Figure 1 shows the evolution of the strain path during an incremental forming operation of a truncated aluminium cone with a wall angle of 60°. [1] As can be seen, drastic changes in the strain path are observed during the forming operation, without unloading, and a very high level of deformation can be achieved, well beyond the conventional forming limit strains at necking. In addition, it has been demonstrated that strain path change has an influence on the FLCN and more specifically on the high level of forming limits (FL). [2] Because the strain path change obviously affects the FL strains at necking, no unified FLCN exists in the strain space to represent the formability of sheet metal. [3] The strain paths in sheet metal forming are classically divided into two types: Linear strain path and nonlinear strain path. Traditionally, the identification of strain-based FLCN or FLCF is limited to the sheet metal undergoing linear strain paths. Three types of experimental FLCN (Figure 2) are concluded by Barata da Rocha et al. [2] to investigate the effect of strain path change on the FL strains at necking. For Type 1, the FLCN is determined under proportional loading. Every point of the FLCN is defined by major and minor strains at necking. As shown in Figure 2a, the whole FLCN (ABCD) is produced by different strain paths from biaxial stretching (OA) to uniaxial tension (OD) through plane-strain tension (OC). The red dash line shows the FLCF, which is higher than the FLCN. [4] For Type 2, the FLCN is identified under two steps of proportional loading. Different prestrain levels

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Section: Experimental Procedures and Resultsmentioning

confidence: 98%

Section: Experimental Procedures and Resultsmentioning

confidence: 99%

Section: Experimental Procedures and Resultsmentioning

confidence: 99%

Section: Experimental Procedures and Resultsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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