13th International Conference on Fracture June 16–21, 2013, Beijing, China -3- rate. Using the Equation (2), the dynamic yield strengths of hull steel under different strain rate and temperature were evaluated and listed in Table 2. The data listed in Table 2 and the thickness of skin were confirmed to be meet the plane strain condition in terms of ASTM E-399 standard. Therefore, it needed to use the Irwin Equation to transform the data listed in table 2 to plane stress fracture toughness Kd [5, 6]: dⅠ 2 ( ) 1 yd d K B Ⅰ , ) (1 1.4 2 d 2 2 d Ⅰ Ⅰ d K K (3) The value of plane stress fracture toughness Kd transformed were also listed in Table 2. The simple stiffened plate construction with two stiffeners was analyzed, as shown in Figure 1. The stiffeners are symmetrically distributed at both sides of central crack 2a, and the crack plane passes through the rivet hole. The stiffener and skin plate are connected by rigid rivet. The corresponding construction parameters are as following: thickness of the skin plate B=24mm, sectional area of stiffener As=20mm×80mm, interval of stiffeners b=600mm, interval of rigid rivet p=b/12=50mm, modulus of elasticity Es=E=2.1×10 5MPa, Reinforcement ratio [7]: μ=AsEs/(AsEs+EbB) （4） where Es is elastic modulus of stiffeners, E is elastic modulus of skin plate. The value of μ is calculated using Equation (4) to be 0.1. Figure1. Construction diagram of stiffened plate construction 3 The residual strength of stiffened plate construction According to linear-elastic fracture mechanical theory, the relationship between stress and plane strain fracture toughness is following for the infinite wide plate with a penetrated central crack that bears the average tensile stress in both surface [8]. c c c a K / Ⅰ (for infinite width plate, a<<w, 1＝ ) (5) Here, cis fracture stress, ac is the half length of critical crack and cⅠK is quasi-static plane strain fracture toughness. If the dynamic fracture toughness does not meet the plane strain condition, the equivalent value must be calculated by Equation (3). According to the Equation (5), the curve of
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