Problems in creep testing under biaxial stress systems

Kelly, D A

doi:10.1243/03093247v111001

Cited by 30 publications

(12 citation statements)

References 3 publications

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“…The load bearing capacity of sheets under uniaxial tension is smaller than that under biaxial tension so that failure usually occurs in the arms of a cruciform specimen in a biaxial testing. It has been found that thickness reduction in the central region and slots in the arms of a cruciform specimen are beneficial for both inducing localised necking to occur in the central gauge region and improving the uniformity of strain and stress distribution [48][49][50]. In this case, only the central zone is considered as the gauge section where biaxial loading condition is fulfilled.…”

Section: Dimensions Of Specimensmentioning

confidence: 99%

Formability evaluation for sheet metals under hot stamping conditions by a novel biaxial testing system and a new materials model

Shao

Lin

et al. 2017

International Journal of Mechanical Sciences

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Published: Z. Shao, N. Li, J. Lin, T. Dean, 2017, Formability evaluation for sheet metals under hot stamping conditions by a novel biaxial testing system and a new materials model, Int. J. Mech. Sci., 120, pp149-158. AbstractHot stamping and cold die quenching has been developed in forming complex shaped structural components of metals. The aim of this study is the first attempt to develop unified viscoplastic damage constitutive equations to describe the thermo-mechanical response of the metal and to predict the formability of the metal for hot stamping applications. Effects of parameters in the damage evolution equation on the predicted forming limit curves were investigated. Test facilities and methods need to be established to obtain experimental formability data of metals in order to determine and verify constitutive equations. However, conventional experimental approaches used to determine forming limit diagrams (FLDs) of sheet metals under different linear strain paths are not applicable to hot stamping conditions due to the requirements of rapid heating and cooling processes prior to forming. A novel planar biaxial testing system was proposed before and was improved and used in this work for formability tests of aluminium alloy 6082 at various temperatures, strain rates and strain paths after heating, soaking and rapid cooling processes. The key dimensions and features of cruciform specimens adopted for the determination of forming limit under various strain paths were developed, optimised and verified based on the previous designs and the determined heating and cooling method [1]. The digital image correlation (DIC) system was adopted to record strain fields of a specimen throughout the deformation history. Material constants in constitutive equations were determined from the formability test results of AA6082 for the prediction of forming limit of alloys under hot stamping conditions. This research, for the first time, enabled forming limit data of an alloy to be generated at various temperatures, strain rates and strain paths and forming limits to be predicted under hot stamping conditions.

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Section: Dimensions Of Specimensmentioning

confidence: 99%

Formability evaluation for sheet metals under hot stamping conditions by a novel biaxial testing system and a new materials model

Shao

Lin

et al. 2017

International Journal of Mechanical Sciences

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“…6. It has been shown that a reduced thickness in the central zone of a cruciform specimen and slots in the arms are beneficial for both inducing failure to occur within the gauge zone and improving the uniformity of strain distribution [39,40].…”

Section: Development Of Specimen Designmentioning

confidence: 99%

Development of a New Biaxial Testing System for Generating Forming Limit Diagrams for Sheet Metals Under Hot Stamping Conditions

Shao

Lin

et al. 2016

Exp Mech

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Conventional experimental approaches used to generate forming limit diagrams (FLDs) for sheet metals at different linear strain paths are not applicable to hot stamping and cold die quenching processes because cooling occurs prior to deformation and consistent values of heating rate, cooling rate, deformation temperature and strain rate are not easy to obtain. A novel biaxial testing system for use in a Gleeble testing machine has been adopted to generate forming limits of sheet metals, including aluminium alloys, magnesium alloys and boron steel, under practical hot stamping conditions in which heating and cooling occur. For example, the soaking temperature is about 900°C and the deformation temperature range is 550-850°C for boron steel [1] and the soaking temperature is about 535°C and the deformation temperature range is 370-510°C for AA6082 [2]. Resistance heating and air cooling were introduced in this pioneering system and the thermal analysis of different heating and cooling strategies was investigated based on a type of cruciform specimen. FE models with a UAMP subroutine were used to predict temperature fields on a specimen in ABAQUS 6.12. Digital image correlation (DIC) system was used to record strain fields of a specimen by capturing images throughout the deformation history and its postprocessing software ARAMIS was used to determine forming limits according to ISO standards embedded in the software. Heating and cooling strategies were determined after the analysis. Preliminary results of forming limit curves at the designated temperatures are presented in order to verify the feasibility of this new method.

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“…Deng et al [2], Kuwabara et al [3] and Makinde et al [4] optimized specimens for metals. Demmerle and Boehler [5] compared different proposed specimen designs and chose the specimen of Kelly [6] with slits and a thickness reduced area to perform an optimization for isotropic materials. Boehler et al [7] investigated anisotropic sheet metals with this specimen type.…”

Section: State-of-the-artmentioning

confidence: 99%

Cruciform Specimen Design for Biaxial Tensile Testing of SMC

Schemmann¹,

Lang²,

Helfrich

et al. 2018

J. Compos. Sci.

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This paper presents an investigation of different cruciform specimen designs for the characterization of sheet molding compound (SMC) under biaxial loading. The considered material is a discontinuous glass fiber reinforced thermoset. We define various (material-specific) requirements for an optimal specimen design. One key challenge represents the achievement of a high strain level in the center region of the cruciform specimen in order to observe damage, at the same time prevention of premature failure in the clamped specimen arms. Starting from the ISO norm for sheet metals, we introduce design variations, including two concepts to reinforce the specimens' arms. An experimental evaluation includes two different loading scenarios, uniaxial tension and equi-biaxial tension. The best fit in terms of the defined optimality criteria, is a specimen manufactured in a layup with unidirectional reinforcing outer layers where a gentle milling process exposed the pure SMC in the center region of the specimen. This specimen performed superior for all considered loading conditions, for instance, in the uniaxial loading scenario, the average strain in the center region reached 87% of the failure strain in a uniaxial tensile bone specimen.

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Problems in creep testing under biaxial stress systems

Cited by 30 publications

References 3 publications

Formability evaluation for sheet metals under hot stamping conditions by a novel biaxial testing system and a new materials model

Formability evaluation for sheet metals under hot stamping conditions by a novel biaxial testing system and a new materials model

Development of a New Biaxial Testing System for Generating Forming Limit Diagrams for Sheet Metals Under Hot Stamping Conditions

Cruciform Specimen Design for Biaxial Tensile Testing of SMC

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