13th International Conference on Fracture June 16–21, 2013, Beijing, China -2- 2 Mechanical properties of materials and stiffened plate construction The hull steel used for skin plate and stiffener of stiffened plate structure is a low alloy steel in this paper, and its mechanical properties of the hull steel are listed in Table 1, Table 1 The mechanical properties of hull steel material s (MPa) b (MPa) δ(%) φ(%) hull steel 480 580 21.4 74 weld metal 400 505 28 74 The Charpy impact specimens were used in experiments, which firstly were cut notch ~3mm by EDM (electrical charge machine), and then pre-fatigue for achieving a relative crack length a/W≈0.5. The dynamic fracture toughness of hull steel under different loading rate conditions were tested by pendulum impact test ( MPa m s/ ~105 ) and Hopkinson bar apparatus ( MPa m s/ ~106 ), respectively. The experimental results are shown in Table 2. The impact energy tested by pendulum impact experiment can be used to calculate the dynamic fracture toughness by the following Equation [3]: 1290.17 108.03CVN 2 d ⅠK (1) It can be seen from Equation (1) that the dynamic fracture toughness under loading rate MPa m s/ ~105 can be obtained using the value of CVN. The dynamic fracture toughness of tested material under higher loading rate MPa m s/ ~106 can be gained using Hopkinson bar loading apparatus, details for testing procedures can be found elsewhere [4]. Table 2 The dynamic fracture toughness and dynamic strength of hull steel loading rate MPa m s/ ~105 MPa m s/ ~106 Temperature (K) 273 293 273 293 KⅠd (MPa m) 119 128 64 74 Kd (MPa m) 282 343 71 89 Yd (MPa) 567 565 640 638 b(MPa) 691 678 774 768 As the dynamic yield strength of tested material is a necessary parameter in next analysis, the dynamic yield strengths under different strain rate and temperature were carried out using dynamic compression test in Hopkisnon bar apparatus in order to investigate the rate sensitivity of this material. Thus the dynamic compression test was carried out on the Hopkinson pressure bar test for determining the dynamic yield strength of hull steel. The relationship between dynamic yield strength and strain rate and temperature can be established as following according to our experimental data: (2) Where T is the experimental temperature, sis the yield strength under quasi-static, is the strain
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