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Material responses to the laboratory simulation of complex cyclic loadings

100%

Szymczak T. , Kowalewski Z. L. , Rutecka A.

tom Vol. 15, No. 3

509-516

The paper presents investigations identifying an influence of complex cyclic loading controlled by the strain signals on the selected mechanical properties of the 2024 aluminium alloy. Investigations of proportional and non-proportional loading paths in the form of square and circle were carried out at room temperature using thin-walled tubular specimens enabling realisation of complex stress states due to acting of axial force and twisting moment. The hardening effect of the material due to cyclic loading was observed on the basis of: stress responses into the strain controlled loading programme; hysteresis loop variations and amounts of stress amplitude. In the case of the non-proportional cyclic loading an additional hardening effect was identified. Second-order effects, which allow better understanding of the influence of proportional and non-proportional loading paths on mechanical behaviour of engineering materials, were identified. In the case of the circular loading path a delay of the maximum stress signals with respect to strain ones is demonstrated. For the square loading path a softening effect was observed. It is reflected by the rapid stress drop on this direction, which is perpendicular to that where the stress level begins to turn back. The yield surface approach is also applied in order to assess the mechanical properties variations due to cyclic loading of the material.

Yield surface characterization for lightweight alloy sheets via an improved combined shear–tension experimental method

72%

Zheng L. H. , Wang Z. J. , Wan M. , Meng B.

Archives of Civil and Mechanical Engineering

2022

tom Vol. 22, no. 2

art. no. e96, 1--17

Combined shear and tension (CST) tests are important experimental methods for characterizing yield surfaces for metal sheets, which is vital to ensure the effectiveness of the constitutive models employed in finite element simulation. However, the existing CST experimental method with a reduced thickness specimen, designed for advanced high strength steel sheets, is not suitable for accurately characterizing yield surfaces for lightweight alloy sheets, such as aluminum alloy sheets. In this paper, an improved experimental method employing CST loading along with an appropriate full-thickness specimen is proposed to address the problem. To establish the proposed experimental method, an appropriate full-thickness specimen is presented through finite element method and combined with a newly developed biaxial testing machine. To verify the effectiveness and feasibility of the improved experimental method, virtual simulations and real experiments on the proposed full-thickness specimen obtained from 6K21-T4 aluminum sheets under different CST loading cases are conducted. Research results show that the yield surfaces of the aluminum alloy sheets between simple shear and plane strain (SSPS) can be described accurately by employing the improved experimental method. In addition, according to the experimental results, the prediction capability of the Yld2000 and Hill48 yield criteria is studied. It is found that the commonly used Yld2000 yield criterion cannot accurately predict the yield behavior of the aluminum alloy sheets under shear-dominant loading.

A graphical approach to yield and boundary surfaces of selected hypoplastic constitutive equations

72%

Sikora Z. , Cieśla P.

nr 2

An engineering methodology taking into account the effect of local damage on the global behavior of surface cracked shell structures

58%

Chiesa M. , Ostby E. , Skallerud B. , Thaulow C.

tom Vol. 7, no 1

267-291

The line spring finite element is a versatile numerical tool for performing engineering fracture mechanics analysis of surface cracked shells. An accurate yield surface of plane strain single-cracked (SEC) specimens having shallow, as well as deep, cracks is presented here. The meaning of the J-integral when crack growth occurs is discussed. The J-integral is regarded as a sort of accumulated measure of the global deformation in the ligament. The complete Gurson is used in order to support our observations. Furthermore a crack propagation law relating a local criterion for crack growth to the global deformation field is outlined. A methodology to link micro-mechanically based crack growth simulations with line spring analysis is proposed by suggesting an alternative way to calculate the J-integral from the line spring framework. Some details of the numerical implementation of the backward Euler integration scheme at the integration point of the line spring element in order to account for plasticity are presented here for a bilinear material model. An efficient numerical procedure, based on a proposed crack growth law, is also presented in order to account for ductile crack propagation. A numerical case is considered in order to show that the proposed procedure is suited to the purpose.