Experimentation Study Of Low-cycle Fatigue Life Of Tension Steel Bars

Fatigue is the most important reason of structural failure, fatigue failure is also the project of a very common phenomenon, especially in shipbuilding, aviation, transportation, marine engineering,and mechanical manufacturing industry. It is a serious threat to the safe of engineering structures. The steel in the service process is often subject to strong winds, earthquakes, etc. The role of repeated load may lead to structural members repeatedly into the plastic state, so the plastic fatigue damage or even rupture. Therefore, the description of steel structure in the strong wind, earthquake damage under the criteria to become a very important field of steel structure. From the 1820s began,in the world, some scholars have started studying the fatigue of metal components, has been on the structure from different angles, in different forms and other aspects of the different failure criteria, has established different plastic damage models. However, these models still exist some limitations and shortcomings.This thesis detailed described the fatigue failure theory,and studyed the component under cyclic loading in the fatigue properties, summed up the characteristics of fatigue and factors affecting the performance. In fact, many engineering components experienced throughout the life of the limit cycles are not many. In this short-lived under the premise of the design can increase stress or strain levels, give full play to the potential of materials to make components of high stress or high strain in the plastic yield. Particularly for well ductile materials, changes into a larger post-yield strain, while relatively small changes in stress, so the strain fatigue can be more appropriate to describe the fatigue properties of materials.In order to study low-cycle plastic steel rod failure mechanism, this article in accordance with the "GBT 15248-1994 amplitude axial fatigue of metal materials, test methods", with a group of Q235-A cylindrical steel members in the INSTRON 1341 servo material testing machine low-cycle fatigue failure tests of plastic, its for axial deformation level being given repeated loading until the fracture destroyed. Measured the limit cycle times at different strain amplitude,then deal with the experimental results, consistent with the distribution of fatigue life obtained curve, that is, pieces of steel rod low-cycle fatigue under plastic, "the plastic strain rate-number of cycles" (s-n) curves, and by Matlab software, curve fitting data results to arrive at a more reasonable "response rate-fatigue" curve. Then, the curve with symmetric displacement amplitude under cyclic loading fatigue life curve of comparative analysis, find the differences, and to analyze the causes, comparing two curves of the applicable types and conditions. Made a more resonable low-cycle fatigue damage model finally.