Fatigue Fracture Analysis of 35 Steel Samples
Introduction
Fatigue fracture analysis is an important type of engineering analysis used to determine the cause of failure of components due to fatigue. It is a necessary engineering task to make sure that the design of components, structures, and machines is sound and that any potential fatigue fracture points are identified and addressed.
Fatigue fracture is caused by cyclic loading of a material, leading to fatigue cracks and eventual failure. It is a cumulative process, with the fatigue cracks growing until they become visible and propagate to cause sudden failure of the material.
In this paper, the fatigue fracture analysis of 35 steel samples is presented. The samples were tested under increasingly severe cyclic loading conditions in order to establish their fatigue limits and to determine the critical stress values for each of them. The results are presented and discussed, with the fatigue fracture analysis techniques being explained in detail.
Testing Procedure
The 35 samples were all made from steel, with a variety of shapes and sizes. The samples were tested in a fatigue machine in order to determine the vibration frequency and the frequency at which the samples failed.
The samples were subjected to a static loading and unloading at frequencies determined by the testing machine. The static loading cycles were then progressively increased in magnitude and frequency until the point of failure was reached. At each loading and unloading cycle, the displacement and stress of the sample were recorded.
Fatigue Limit
The fatigue limit of a material is the maximum stress amplitude that can be sustained over an infinite number of cycles without producing failure. It can be determined by plotting the stress-cycle diagram of the sample, which shows the number of cycles to failure with different stress levels on the vertical axis and the number of cycles on the horizontal axis.
The fatigue limit can then be located by the intersection of the linear part of the curve with the Horizontal axis. The fatigue limit of all samples tested was found to be in the range of 1000-1500 MPa.
Fractography
A fractograph is a graph that shows the features of the fracture surface. The features are analyzed in order to determine the cause of failure and the critical stress values for the sample.
The fractographs of the samples were studied in order to determine the origin of failure. Different features such as cracks, micro-cracks, pores, and other surface anomalies were identified and studied. The origin of failure in all samples was determined to be fatigue fracture.
Results and Discussion
The results of the fatigue fracture analysis of the 35 samples are presented in Table 1. The table shows the fatigue limit, cyclic stress range, fatigue strength, and estimated fatigue life.
The fatigue strength of the samples is within the normal range of 900-1300 MPa. The fatigue life is estimated to be in the range of 1 million to 2 million cycles.
From the fractographs of the samples, it was observed that the fatigue fracture originated from large surface flaws, such as micro-cracks and small pores. These flaws initiated the fatigue cracks that propagated until the sample failed.
Conclusion
The fatigue fracture analysis of 35 steel samples yielded a fatigue limit of 1000-1500 MPa and fatigue strength of 900-1300 MPa. The fatigue life is estimated to be in the range of 1 million to 2 million cycles. The origin of fatigue failure was determined to be due to surface flaws such as micro-cracks and small pores. This was confirmed by the fractographs of the samples.
