Experimental Research On Crack Length Measurement Method Of Three Point Bending Specimen

In fatigue crack growth rate test and fracture toughness test, the fatigue crack length measurement is very important, many experts and scholars have conducted a lot of research, and achieved fruitful results. Based on the BFS method, the electrical measuring method was applied to monitor three-point bending specimen crack length in this paper, namely in the case of a known load, according to the strain on the front end face of the three point bending specimen would be to get crack length. Through the experimental study on the analysis, the method has reached the experiment purpose, can get a good "average" crack length. The specific content of this paper is as follows:The first part:the test scheme design. This part draws on a lot of research methods and scientific achievements of predecessors to carry out experimental study on the fatigue crack propagation. Method of COD, unload compliance method and the BFS method give a lot of enlightenment in this paper. On this basis, combining with the existing experimental experience, this article try to design the test scheme from the perspective of the finite element method, and then three fatigue crack propagation length measurement testing schemes were proposed.The second part:the screening of the test schemes. We researched on the fatigue crack propagation test for 25 mm thick of three-point bend specimens, and then test results of three test schemes were discussed. Finally, we believed in that fatigue crack propagation length measurement test scheme on â…¢ area of the three point bending specimen is feasible, and preliminarily determined the relationship between the strain on the front end face of the three point bending specimen and fatigue crack length.The third part:the induction of experimental law. On the basis of preliminary experiment research, we again conducted fatigue crack propagation test of four groups of different sizes.Through the analysis and comparison of the result of the test data processing,the specimens of five kinds of dimensions were link up by using a power function. Finally we can get a curve that descriped the relationship between the fatigue crack length and the strain on the front surface of the specimen at the fatigue crack growth.