The forming limit curve for bending processes

Marciniak, Z.; Kuczyński, K.

doi:10.1016/0020-7403(79)90081-x

Cited by 21 publications

(6 citation statements)

References 5 publications

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“…When localized necking occurs the deformation concentrates in narrow area which is inclined to the tensile direction and fracture occurs soon after. In the studied material localization appears faster and slightly stronger in the specimen cut in the transversal direction which indicates lower ability to spread the deformation out to wider area also in bending [1,4,5].…”

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confidence: 84%

FEM - Modeling of Bendability of Ultra-High Strength Steel

Arola

Mäntyjärvi

Karjalainen

2013

KEM

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Ultra-high strength steels have been widely used in different industrial applications. It is necessary to understand the behavior of these materials in common forming processes such as air bending. It is known that the bendability of ultra-high strength steels is lower than other high-strength steels but what are yet to be discovered are the parameters that define the limits of bendability of these steels. The aim of this study was to investigate the factors affecting the bendability of ultra-high strength steel using optical strain measurements and FEM-modeling of the bending process. By using the true stress-strain relation measured by optical strain measuring system the bendability of ultra-high-strength steel was modeled fairly accurately. As a result, it was noted that the strain distribution at the bend of a steel possessing better uniform strain was more widely distributed and there were no highly localized strains. On the other hand as the failure occurred the strains were considerably smaller than the true failure strain of the material in uniaxial tension. As a conclusion it was stated that the ability to withstand the localization of deformation might describe the bendability of ultra-high-strength steel better than the values of the uniform or true failure strain in uniaxial tension test.

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confidence: 84%

FEM - Modeling of Bendability of Ultra-High Strength Steel

Arola

Mäntyjärvi

Karjalainen

2013

KEM

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“…Also, the space is limited for placement of camera for continuous recording of images of deforming grid pattern. In some cases, good designs are available, but they have not been utilised to assess the bending models .…”

Section: Literature Reviewmentioning

confidence: 99%

“…Specifically, most of the advanced bending theories are formulated for plane strain deformation mode, which prevails only in the mid‐width region of the bend specimen and not at the edges. Also, while many bend test methods have been available in the literature , only few have been utilised to assess the available analytical or finite element (FE) models. The present work attempts to fill this gap by comparing the results from bending experiments based on a new design concept and those from an analytical model and an FE simulation of the bend experiments for an automotive aluminium sheet.…”

Section: Introductionmentioning

confidence: 99%

Assessment of Analytical Models of Pure Bending of Sheet Materials Using the Digital Image Correlation Method

Govindasamy

Jain

2016

Strain

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Bending of sheet materials is a common forming mode for shaping sheet components. Although many numerical models of bending, both analytical and numerical simulations based, are available in the literature, extensive experimental validations have been rather limited. A new bend test method and complementary three-dimensional finite element (FE) simulation of the experiments are employed to assess the predictions from an advanced analytical and FE model of pure bending of aluminium sheet materials. The experimental set-up developed and utilised is an open concept design that allows access to the tensile surface and through-thickness region in the vicinity of the specimen bend line to continuously record images of the deforming specimen with two cameras. The specimen images are analysed for strains using an online strain mapping system based on digital image correction method. Tangential strain distribution results from the models in terms of material thinning in the bend region are compared with those from the experiments on AA2024 aluminium sheet material by considering the responses from the specimen edges and mid-width regions at the bend line. Furthermore, the tangential and radial stress distributions on the through-thickness section of the specimen from the analytical model are compared with those from the FE model. The results from experiments, FE model and analytical model are compared and discussed in the light of the experimental data and the assumptions involved in the development of the models.

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“…The role of geometry is particularly apparent when thin sheet materials undergo forming processes with significant bending. There is a large body of literature on the combined stretching and bending of metallic sheets for automotive and other applications [2], but the relevant bending-dominated processes tend to be geometrically constrained, so that forming limits and localization are discussed with respect to thinning or shear banding [3,4]. In contrast, the topic of the present study is an instability in which the bending deformations themselves are highly localized, and can be described as a curvature blowup or runaway crease formation in either a desired or undesired location in a sheet.…”

Section: Introductionmentioning

confidence: 99%

Avoiding localization instabilities in rotary pleating

Tian¹,

Hanna²

2022

Preprint

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Rotary pleating is a widely used process for making filters out of nonwoven fabric sheets. This involves indirect elastic-plastic bending of pre-weakened creases by continuously injecting material into an accordion-shaped pack. This step can fail through a localization instability that creates a kink in a pleat facet instead of in the desired crease location. In the present work, we consider the effects of geometric and material parameters on the rotary pleating process. We formulate the process as a multi-point variable-arc-length boundary value problem for planar inextensible rods, with hinge connections. Both the facets (rods) and creases (hinges) obey nonlinear momentcurvature or moment-angle constitutive laws. Some unexpected aspects of the sleeve boundary condition at the point of material injection, common to many continuous sheet processes, are noted. The process, modeled as quasistatic, features multiple equilibria which we explore by numerical continuation. The presence of, presumably stable, kinked equilibria is taken as a conservative sign of potential pleating failure. Failure may also occur due to localization at the injection point. We may thus obtain "pleatability surfaces" that separate the parameter space into regions where mechanical pleating will succeed or fail. Successful pleating depends primarily on the distance between the injection point and the pleated pack. Other factors, such as the crease stiffness and strength relative to that of the facets, also have an influence. Our approach can be adapted to study other pleating and forming processes, the deployment and collapse of folded structures, or multi-stability in compliant structures.

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The forming limit curve for bending processes

Cited by 21 publications

References 5 publications

FEM - Modeling of Bendability of Ultra-High Strength Steel

FEM - Modeling of Bendability of Ultra-High Strength Steel

Assessment of Analytical Models of Pure Bending of Sheet Materials Using the Digital Image Correlation Method

Avoiding localization instabilities in rotary pleating

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