13th International Conference on Fracture June 16–21, 2013, Beijing, China -5- the related data listed in table 2 and Equations (3)-(8), as shown in Figures 2 and 3. Whether Figure 2(a) and (b) or Figure 3(a) and (b), all of them indicate that for stiffened plate construction with penetrable crack in center, the residual strength curve nearly coincides with that of non-stiffened plate construction when the crack length is small, which shows that reinforcement effect of stiffener is not obvious. When the crack propagated near the stiffener, the amplitude decrease of stress intensity factor become larger due to the load beard by stiffeners increasing, and the stress intensity factor reaches to maximum value while the crack propagates to the central line of stiffeners. At the same time, the residual strength curve of stiffened plate construction is much higher than that of non-stiffened plate construction. The reinforcement effect of stiffener decreases again and the residual strength curve of stiffened plate construction falls with increasing crack According to the relative position between the failure curve of stiffeners and the residual strength diagram of stiffened plate construction, the crack arrest behavior of the stiffened plate construction includes a stiffener critical construction (Figure 2) and a skin critical construction (Figure 3). In skin critical construction (Figure 3), the unstable expansion of crack is arrested when the lengths reaches 1a under stress state of σ1 and the initial length of crack satisfying a0<a1< as. Under this condition, the crack is in stable state. That is to say, any expansion of crack would lead to further increase of the fracture resistance. It can be concluded that crack is in controlled state or crack arrest state. As the stress increased to σ0, crack would steadily spread to as and then unsteadily propagate. Following, the stiffener would fracture because of the high stress applied, which results in structural failure. However, in the skin critical construction, as shown in Figure 2, when crack spread to as, since the stress of stiffener reaches its fracture stress, fracture would occur and the reinforced influence of stiffener released. As a result, crack of skins spread instability and led to structural failure. 0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0 100 200 300 400 500 600 700 800 failure curve of stiffener residual strength of stiffened plate structure residual strength of non-stiffened plate structure stiffener as=0.279m a 0=0.225m 0=363MPa , MPa a, m b (a) 0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 100 200 300 400 500 600 700 800 failure curve of stiffener residual strength of stiffened plate structure residual strength of non-stiffened plate structure as=0.248m b 0=434MPa stiffener , MPa a, m (b) Figure2. Residual strength diagram of stiffened plate construction of the hull under loading rate MPa m s/ ~105 and temperature 273K (a) and 293K (b)
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