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Stress measurement errors in the tension-shear tests using a cruciform specimen are evaluated. The tension-shear test method was proposed by Minki et al (2022). A servo-controlled biaxial tensile testing apparatus is used as the testing machine. The gauge area (GA) of the tension-shear specimen receives normal stress, σxx, and shear stress, σxy; however, the stress distribution in the GA is not uniform. Therefore, the average stress, σave, is calculated by dividing the testing force by the average cross-sectional area of the GA. The average cross-sectional area is obtained by measuring the strain distribution of the GA with DIC. On the other hand, the deformation of the cruciform specimen is analyzed by finite element analysis to calculate the stress distribution at the GA, and the stress components at the strain measurement position by DIC is determined as the true value, σt. We can evaluate the stress measurement error, as (σt-σave)/σt. Next, various linear stress paths (σx/σxy=const.) are applied to the cruciform test piece made of a cold-rolled mild steel sheet, and the stress points forming the contours of equal plastic work in the σxx-σyy-σxy stress space were investigated. Then, we identify the Yld2000-2d yield function that can approximate these stress points. Furthermore, by comparing that with the Yld2000-2d yield function identified by conventional biaxial and uniaxial tensile tests, the effect of the tension-shear test on improving the accuracy of material modeling is investigated.