Study Of Magnetic Signal For Typical Structural Steel And Weldment

With the development of society and economy, the working load on the machinery equipment is more and more complex, and more than80%metal components damage are caused by fatigue failure. Metal magnetic memory technology, as one of the nondestructive testing technologies, can diagnose the stress concentration and damage of ferromagnetic components in the early stage by online and offline testing. It has a strong research significance and application value.This paper focused on Q345steel commonly used in the industry firstly. Tensile and compressive fatigue experiments were undertaken on the prefabricated notch specimen. Magnetic memory signals on the different lines of specimen were captured by EMS2000+intelligent magnetic memory detector. The effect of experimental instrument clamp, tensile stress and compressive stress on the magnetic signals was studied; the impact of fatigue cycles on magnetic signals of different testing points was explored; magnetic signal characteristic parameters were used to show stress concentration degree in the materials, and the variation regularity of magnetic signal on the testing points in the fatigue cycle is explained.Then Q235was chosen to manufacture weldment with no defect, and the magnetic signals were observed before and after heat treatment. The influence of different bending fatigue loads on weldment magnetic memory signal characteristics was discussed; changes of weldment magnetic memory signal under different cycles were analyzed; magnetic signals above different testing lines were compared; and the fatigue cycle of different loads such as elasticity, yield point and plastic effect on the magnetic signal characteristic were studied.At last, three types of Q235steel weldment, including crack, unfused and no defect, were prefabricated. Their magnetic signals under fatigue bending load were studied; the magnetic signal characteristics when the weldment fractured were analyzed; magnetic signal feature parameters were used to locate the fusion area defects of different types weldment; and the crack propagation characterized by the magnetic memory technology is discussed.