Biaxial tensile testing of cruciform slim superalloy at elevated temperatures

The identification of the post-necking strain hardening behavior of metal sheet is important for finite element analysis procedures of sheet metal forming process. The inverse modeling method is a practical way to determine the hardening curve to large strains. This study is thus focused on the evaluation of the inverse modeling method using a novel material performance test. In this article, hot uniaxial tensile test of a commercially pure titanium sheet with rectangular section was first conducted. Utilizing the raw data from the tensile test, the post-necking hardening behavior of the material is determined by a FE-based inverse modeling procedure. Then the inverse method is compared with some classical hardening models. In order to further evaluate the applicability of the inverse method, biaxial tensile test at elevated temperatures was performed using a special designed cruciform specimen. The cruciform specimen could guarantee that the maximum equi-biaxial deformation occurs in the center section. By using the inverse modeling procedure, the hardening curves under biaxial stress state are able to be extracted. Finally the stress-strain curves obtained from the two experiments are compared and analysis studies are provided.2 of 15 point. However, many sheet forming processes usually involve large deformation and can generate strains far beyond the necking point, so the stress-strain curve up to the necking point is not sufficient for numerical simulation procedures. Generally, the available pre-necking stress-strain curves are extrapolated to large strains using different hardening models [5]. It is obvious that the predicted post-necking hardening curve greatly depends on the choice of phenomenological constitutive models and one model that is best fitted to a certain material may not suits for another [6].Recently, numerous investigations have been made to acquire the hardening curve beyond diffuse necking by many researchers [7][8][9][10][11]. The initial attempt was made by Bridgman [7], who derived a set of analytical models for the distribution of stress and strain across the diffuse necking region for a round bar. However, the correction and compensation for stress and stress values of Bridgman's method is based on the measurement of evolving geometrical parameters of the necking area, which requires much experimental effort. Ling [8] and Zhang et al. [9] extended the research of Bridgman by proposing new models for determining the post-necking hardening behavior of strip specimen with rectangular section. Other researchers [10,11] further studied the necking problem experimentally based on Bridgman's work in more sophisticated ways. Currently, a new optical-numerical measurement techniques, i.e., the Digital Image Correlation (DIC) method, is used widely for obtaining full-field information for both in-plane displacements and strains of the test specimen and has been applied by many researchers for determining the post-necking hardening curve of uniaxial test [12,13], Scheider et al. [14] investigat...

Section: Experimental Details Of the Biaxial Tensile Testmentioning

confidence: 99%

Section: Experimental Details Of the Biaxial Tensile Testmentioning

confidence: 99%

Evaluation Study on Iterative Inverse Modeling Procedure for Determining Post-Necking Hardening Behavior of Sheet Metal at Elevated Temperature

Mei

Lang

Liu

et al. 2018

“…Kuwabara et al [18,19] determined the yield surface of a cold-rolled steel sheet and an aluminum alloy sheet using abrupt strain path change in biaxial tensile tests. Xiao et al [20,21] performed biaxial tensile tests on TA1 titanium alloy at different angles, with respect to the material rolling direction and found that the limit strain was anisotropic in nature. In addition, Srinivasan et al [22] carried out equi-biaxial tensile tests on CP-Ti and showed that the ductility decreases and the strength increases under biaxial loading.…”

Section: Introductionmentioning

confidence: 99%

Biaxial Tensile Behavior of Commercially Pure Titanium under Various In-Plane Load Ratios and Strain Rates

Zhang

Zhu

Zhou

et al. 2021

The aim of the present work is to contribute to the characterization of the biaxial tensile behavior of commercially pure titanium, under various in-plane loading conditions at room temperature, by a non-contact digital image correlation system. Several loading conditions, with load ratio ranging from 4:0 to 0:4 and displacement rate ranging from 0.001 to 0.1 mm/s, are examined. It is found that the yield strength and ultimate tensile strength of biaxial sample are greater than that of uniaxial sample, where the equi-biaxial sample shows the highest strength. It is also observed that increase in strain rate leads to remarkable improvement of tensile strength. Fractographic analysis indicates that the shape and size of dimples are load ratio and strain rate dependent. Additionally, a modified Johnson–Cook constitutive model was proposed to account for the effect of strain rate on biaxial tensile deformation. The experimental results are in good agreement with the simulated results, indicating that the proposed model is reliable to predict biaxial tensile deformation of commercially pure titanium at different strain rates.

“…It is at least worth noting, however, that the thinning of the central gauge was not proposed in this standard. Meanwhile, other strategies for specimen design have also been suggested [10][11][12][13][14][15][16], such as multistage thinning, unilateral thinning, etc., but these specimen designs never gained wide acceptance. In addition, the Wu research group [17][18][19][20][21] have also studied the stress-strain distribution of cruciform specimens designed with several previous, mature strategies, such as "slitting on the arm", "central thinning", and "fillet".…”

Section: Introductionmentioning

confidence: 99%

Optimal Design of a Miniaturized Cruciform Specimen for Biaxial Testing of TA2 Alloys

Zhu

Zhang

et al. 2019

The biaxial tensile testing of cruciform specimens is an effective way to create complex loading, and is a feasible experimental method for studying the subsequent yield behavior. However, relevant knowledge gaps still exist in the geometric design of miniaturized cruciform specimens which are applicable to test machines with maximum load less than 5000 N. The present work outlines the systematic investigations of the optimal design of the miniaturized cruciform specimen of a commercial pure titanium TA2 for biaxial tensile testing. Finite element modeling (FEM) coupled with the orthogonal design is employed to explore the influence of various geometric parameters, i.e., the thickness of the central gauge region, the width, the length, and the number of the slit, and the radius of the inner chamfer, on the stress distribution of the central gauge region. The optimal geometric design of the miniaturized cruciform specimen is successfully obtained, simultaneously considering the stress uniformity in the central gauge region and economic factors. The full-field strain distributions are also determined via the digital image correction (DIC) technique, which confirm the accuracy of the results achieved from FEM. This work provides a complete and reliable procedure for optimizing the geometry of miniaturized cruciform specimens, whose application can be expanded to other metals in the future.