Discussion On J_IC Test Method And Fracture Behavior Analysis For Welded Joint Of Steel 907A

Reasonable valid data couldn't be obtained by applying validity criterion of current J-integral testing methods (GB2038-80, GB2038-91) to higher tearing resistance metals, so J_IC -value of material cannot be measured conveniently. The crack initiation process of commercial tough metal has been analyzed. It's suggested that this process is one process of transition from crack blunting and stretch dominated by plastic deformation to fracture with micro-voidcoalescence, and it is also a continuous developing process from quantitative change to qualitative. As a property used to evaluated crack initiated resistance of materials, the crack initiation point is practically special value when above transition has been completed. At the same time, the stretched zone has saturated at front of the crack.A new testing method of J_IC has been proposed, and it is as follows: J-Δα relationship may be fitted by power function form with measured all data situating at front and back of the crack initiation point; Substituting Δα=SZW_c in J-Δα equation gives a J-value, and it may be regarded as the ductile fracture toughness J_IC -value of material measured. Applying above method, the J_IC -value of steel 907A has been measured to be 196.75 KJ/m², which is in accordance with result measured using England standard BS7448 Part4.Local instable fracture occurred in the process of weld specimen suffering applied load for steel 907A welded joint has been analyzed. It's indicated that local brittle zones existed at front of the crack is the reason why local instability of weld specimen takes happen. There are two reasons leading to produce local brittle zone: The one is big block composite nonmetallic inclusion which mainly contains carbon and oxygen with little iron, silicon, sulphur, chromium, manganese and so on; The another is carbide (similarly cementite or alloy cenentite).By ANSYS EF software, J-integral conservation of TPB specimen has been validated, its plastic zone size has been calculated, and effect of strength match on J-integral has also been studied for welded joint of shipbuilding steel 907A. It's...