Fracture Characteristic Analysis For Shipbuilding Stiffened Panels Under Dynamic Loading

The static and dynamic mechanical properties of a shipbuilding steel and its weld metal have been obtained by using Instron4050 tester, pendulum tester and Split Hopkinson Pressure Bar. The results indicate that the shipbuilding steel and its weld metal present better low-temperature toughness without brittle tendency. But under dynamic loading they all present obviously tendency of brittle which is more obvious as the loading rate increases and the temperature decreases.Transition temperature (T_k) for a shipbuilding steel and its weld metal has been obtained by the criterions of energy and 50FATT under dynamic loading. Compared with Fracture Characteristic Analysis Map (FCAM), adaptability to dynamic loading for the shipbuilding steel and its weld metal has been evaluated. The results indicate that the welded structure of the shipbuilding steel can satisfy working requirement with higher safe tolerance under the condition of middle loading rate and the series of temperature, while they present obviously maladjustment under the condition of higher loading rate. So it is necessary to take arresting or defending measures for the safety of marines under limited working conditions.In the second section of the thesis, residual strength figures have been founded for stiffened structures of a shipbuilding steel and its weld metal according to the arrest principle of the stiffened structure and linear elastic fracture mechanics. It has obtained the residual strength lower-limit level and the range of crack sizes which can be arrested effectively under the condition of loading rates K|·≈10⁵ and 10⁷MPam^1/2/s and at the temperature of -20℃0℃and 20℃. The characteristic of fracture and arrest, effects of stiffening ratio and strength of stiffeners have also been discussed.The stress intensity factor reduction coefficient C has been calculated for a cracked sheet with welded and uniformly spaced stringers on the base of Poe's riveted force method. The calculations indicate that the computed value of C is hardly effected when the size of rivet spacing is less than b/20, where b means stiffener spacing. Then the value of C can be used as the stress intensity factor reduction coefficient of welded stiffened panels when the rivet spacing equals to b/20. Using the computed value of C, residual strength figures have been founded for welded stiffened panels of the shipbuilding steel and its weld metal under the condition of loading rates K|·≈10⁵ and 10⁷ MPam^1/2/s and at the temperature of -20℃0℃and 20℃. The differences of fracture and arrest characteristic between riveted and welded stiffened panels have also been discussed.