The bending dependency of forming limit diagrams

Neuhauser, Felix M.; Terrazas, Oscar; Manopulo, Niko; Hora, Pavel; Tyne, C. J. Van

doi:10.1007/s12289-018-1452-1

Cited by 16 publications

(11 citation statements)

References 12 publications

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“…According to the bending theory [27,38], the larger the radius of curvature, the smaller the decrease in sheet thickness in the bending region and, consequently, the higher the capacity of the sheet to stretch or deform longitudinally. Several researchers [17][18][19][20][46][47][48][49] have investigated the effect of the radius of curvature on the limit wall stretch of other materials and observed the same trend. Ma and Welo [50] explained that for most metallic materials during bending, the neutral line (NL) that separates the tensioned region from the compressed region moves away from the center of the sheet as the radius of curvature increases.…”

Section: Limit Wall Stretch (𝑳 𝒎𝒂𝒙 𝑳 𝟎 ⁄ )mentioning

confidence: 73%

Failure analysis of AISI 430 stainless-steel sheet under stretching and bending conditions

Luiz

Rodrigues²

2022

Preprint

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Ferritic stainless steels have been widely used to substitute austenitic steels because of their lower cost and higher deep drawing capacity. However, failures, such as shear fracture, have been observed in parts with small radii during the drawing process in applications where both bending and stretching occurs. Conventional techniques, such as failure criterion consideration, finite element method, and forming limit diagram, are unable to predict this type of fracture, which has hampered the development of new processes and products. To overcome this limitation, herein, we investigated the effects of tool radius, direction, and test speed on the formability to fracture of an AISI 430 stainless-steel sheet under bending and stretching conditions. An equipment was used to perform the draw-bend fracture (DBF) test based on the bending under tension test. The DBF test efficiently reproduced the tensile, mixed, and shear fractures. Furthermore, we determined the fracture limit strain on the outer surface, thickness, and sidewall of the sample, as well as the coefficient of friction. The data showed that the radius to thickness ratio related to the process parameters had a direct impact on the experimental results. In addition, the results can be utilized for setting design guidelines and failure prevention.

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Section: Limit Wall Stretch (𝑳 𝒎𝒂𝒙 𝑳 𝟎 ⁄ )mentioning

confidence: 73%

Failure analysis of AISI 430 stainless-steel sheet under stretching and bending conditions

Luiz

Rodrigues²

2022

Preprint

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“…For example, for an application towards rotary draw bending (RDB) was conducted by KHODAYARI with the conclusion that in RDB the tubular material might even fail above the NAKAJIMA FLC [27]. For three point air bending, NEUHAUSER and TERRAZAS suggest to implement a third dimension to the FLD to capture the impact of bending strain on failure which underlines the relevance of these considerations [28]. However, compared to free form profile bending, a significant superposition of bending stress over sheet metal thickness ranging from full compression to full tension is present in over-thickness bending.…”

Section: Discussionmentioning

confidence: 99%

A Critical Evaluation of Forming Limit Curves Regarding Layout of Bending Processes

Frohn-Sörensen

Nebeling

Reuter

et al. 2022

KEM

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Forming limit curves (FLCs) are important to predict failure against biaxial deformation in sheet metal forming. Particularly crucial is the detection and evaluation of the stable/instable transition which indicates necking and ultimately leads to rupture. In the past, it has been observed that specific processes, in particular free-form bending processes, might not be predicted well by conventionally evaluated FLCs, i.e. the Nakajima experiment, where tapered sheet metal specimens are stretched over a hemispherical punch until material failure. In the present study, FLCs are evaluated from such Nakajima tests and from notched tension tests (NTT) highlighting large differences in between both results. The differences in between the evaluation methodologies are discussed with respect to contact and bending strain in the forming zone. The FLCs of three tested sheet metal materials are compared to fracture strain resulting from an incremental bending process with free forming zone demonstrating an increased failure prediction accuracy by the NTT FLCs than by the conventional ones. In the light of these results, it is therefore encouraged to critically assess the application of FLCs obtained from NTTs to various free-form bending processes.

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“…It is very well known that bending induced by forming tools has a beneficial effect on formability because it enables higher strains at the sheet surface before the onset of localized necking. The bending effect and its contribution in the enhancement of formability in press-working (see, e.g., Vallellano et al [26,27], Luo and Wierzbicki [28], Morales-Palma et al [29] and Neuhauser et al [30]) and incremental sheetforming processes (see, e.g., Silva et al [31] and Centeno et al [32]) have been widely discussed in this research field.…”

Section: Bending Effectmentioning

confidence: 99%

Analysis of formability in conventional hole flanging of AA7075-O sheets: punch edge radius effect and limitations of the FLC

et al. 2019

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Hole flanges are commonly manufactured in mass production by conventional press-working. In an industrial context, the process limits are usually evaluated by means of the Limiting Forming Ratio (LFR), which defines the maximum attainable diameter of the flange related to the initial pre-cut hole. Nevertheless, the LFR does not provide enough information about material deformation, thickness distribution or the expected onset and type of failure. In this sense, a systematic investigation using the Forming Limit Diagram (FLD) is needed. Under these circumstances, the aim of this work is to provide a better understanding of the deformation process in conventional hole flanging, analysing the effect of the punch edge radius as well as the influence of the strain distribution along the hole flange on formability. An experimental campaign on 1.6 mm thickness AA7075 annealed sheet was completed using cylindrical punches with different profile radii. In addition, numerical modelling of the process using finite elements was developed. The results allow better understanding of the physical mechanisms governing material deformation and process formability in very ductile materials. In this regard, this research work contributes to the current state of the art in conventional hole flanging by establishing the modes of failure that prevail in the process and the influence of the bending induced by the tool radius in the flange formability. In addition, the limitations of using conventional FLD for providing a limiting threshold for the strain states attained in the flanges deformed with different punch profiles are also identified.

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The bending dependency of forming limit diagrams

Cited by 16 publications

References 12 publications

Failure analysis of AISI 430 stainless-steel sheet under stretching and bending conditions

Failure analysis of AISI 430 stainless-steel sheet under stretching and bending conditions

A Critical Evaluation of Forming Limit Curves Regarding Layout of Bending Processes

Analysis of formability in conventional hole flanging of AA7075-O sheets: punch edge radius effect and limitations of the FLC

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