DIC Experimental Study Of The Effect Of Welding Conditions On Crack Characteristics

Welded structures are widely used in pressure vessels and piping industry, engineering machinery, ships, automobiles and other industrial areas, but welding will inevitably generate residual stress in welded structure. With the increase of service time, the microscopic defects in the in service welded structure will germination and expanded into a crack. Crack reduces the carrying capacity of the structure, causing stress concentration, the further propagation of crack will even lead to sudden and catastrophic accidents. Therefore, the study of crack properties especially crack characteristic of welded structure is very important.This research study the variation of stress intensity factor, J integral and crack tip opening displacement when the welding conditions change. In this paper, crack fracture parameters will be studied by the experimental method. This paper uses digital image correlation for technical support and compact tension (CT) specimens for research object, studying crack properties by comparing the fracture parameters of welding and no welding specimens.Firstly, doing tensile test of no welding CT specimen at room temperature, using digital image correlation measurement system to measure and calculate the fracture parameters of specimens, we get each value of fracture parameters and the tendency of each value changing with the load. The results show that:during elastic stage, with the increase of load, stress intensity factor increase linearly; J integral and crack tip opening displacement will increase.Secondly, changing the distance between welding line and crack tip, the interval time between two welds, the direction of two welds, and then welding of CT specimens, we get different welding residual stress distribution under different welding conditions. Doing tensile experiment of welding specimens, we obtain crack fracture parameters under the different welding residual stress distribution by digital image correlation measurement system.Finally, comparing each fracture parameter of no welding CT specimen and the CT specimen under different welding conditions, we obtain fracture parameters changing law after changing welding conditions. The results show that:each fracture parameter of welding CT specimen is smaller than the no welding one; When the welding direction of the front and back change from same to different, each fracture parameter value decreases; When the distance between welding line and crack tip change from 8mm to 30mm, each fracture parameter value decreases; When the interval time between two weld change from 0 minute to 30 minutes, each fracture parameter value decreases.