Metal fatigue test test method

Metal fatigue test refers to the method of measuring σ-1 of the metal material through metal material experiments, drawing the S-N curve of the material, and then observing the fatigue failure phenomenon and fracture characteristics, and then learning to determine the fatigue limit of the metal material under symmetrical cycles. Experimental equipment generally includes fatigue testing machines and vernier calipers.
Under the action of a sufficiently large alternating stress, microscopic cracks may occur in parts such as sudden changes in the appearance of the metal component, surface marks or internal defects, etc. Dispersed microcracks will form macrocracks after assembly and communication. The formed macro cracks gradually expand slowly, the cross-section of the component gradually weakens, and when a certain limit is reached, the component will suddenly break. The above failure phenomenon caused by metals due to alternating stress is called metal fatigue. Materials with good plastic properties under static load often break suddenly when the stress is lower than the yield limit and there is no obvious plastic deformation. The fatigue fracture is obviously divided into two areas: the smoother crack expansion zone and the rougher fracture zone. After the crack is formed, the alternating stress causes the two sides of the crack to open and close, and squeeze and grind each other repeatedly. This is how the smooth area is formed. The interruption and change in size of the load leave multiple crack fronts in the smooth zone. As for the rough fracture zone, it is formed by sudden fracture. Statistics show that about 70% of the failure of mechanical parts are caused by fatigue, and most of the accidents caused are catastrophic. Therefore, it is of practical significance to study the fatigue resistance of metal materials through experiments.