13th International Conference on Fracture June 16–21, 2013, Beijing, China 5 were listed in the table 8. Table 8 The uniaxial tensile experimental results of the Welding seam center The type of the steel The position of the specimen Yield Stress (Mpa) Tensile Stress (Mpa) EQ70/56 Welding seam center 728.8 828.2 According to the uniaxial tensile stress-strain curve, the true stress expression was as follow: σt = (1 +ε)σ(3) while the true strain expression was as follow: εt=ln (1+ε)(4) Plot the true stress-strain curve from the equations (3) and (4), and then the true stress-strain curve of the welding seam center could be plotted as figure 2. Figure 2 True stress-strain curve of EQ70/56 Under the guidance of the Standard <Metallic materials Tensile testing at ambient temperature>, it measured the elastic modulus with electrometric method. As the elastic modulus was independent of the thickness of the specimens, there was no elastic modulus distinction in the same position of the specimen. The elastic modulus E was determined by the equation (5) as follow: 0S F E ε = (5) Here, F denotes the load increment, while the S0 denotes the cross section area. Table 9 The results of Elastic modulus test Position E(Gpa) Welding seam center 215.5 4 The FADs of welding seam center of EQ70/56
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