High-precision on-line measurement method of metal tension-tension fatigue crack growth rate based on infrared displacement sensor

In order to solve the problem of accurately measuring fatigue crack growth rate in the field of international material fatigue research, a new method of measuring fatigue crack growth rate with infrared displacement sensor was designed. Three pearlite rails were taken as examples of tensile-tensile fatigue crack growth tests. The open end of the compact tensile (CT) fatigue standard specimen was designed as a kitchen knife. So that the open end and the prefabricated crack were on the same plane, and then two high-precision infrared displacement sensors were arranged at the extended end. In the process of fatigue crack propagation of CT standard specimen, at any moment when the aperture is maximum, the displacement difference of the extended end were recorded by the sensor in time, and then the crack growth was calculated by similar triangles. This new on-line measurement method can dynamically measure a-N curve and the fatigue crack initiation process of CT standard specimens, and the accuracy of a-N curve can reach 0.1 mu m. The trend of crack initiation of pearlite rail is that the crack tends to be steep, then becomes slow. The zone II is straighter and closer to the theory. The view that reducing the thickness of pearlite lamellae is beneficial to improve fatigue life is well supported. The difficult problem of crack initiation measurement in fatigue field has been filled and perfected.