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Fatigue Fracture Analysis of an Mn-Ni-Co Alloy Sample
Abstract
Fatigue fracture analysis of an Mn-Ni-Co alloy sample was conducted to assess its fatigue properties. The sample was put under cyclic tensile load and tested at various constant amplitudes up to the fatigue limit. The fatigue fracture surface was observed and compared with a reference surface of the same alloy. The fracture pattern is distributed across the fracture surface and corresponds to the different fatigue stages the sample experienced during testing. A fracture analysis was performed in order to identify the different fracture stages. It was found that the fatigue fracture surface consisted of three stages: ductile fracture, shear fracture and re-crystallized grain boundary fracture. The fractures were associated with the cyclic tensile loading conditions applied, and the fatigue life of the alloy were also calculated from the experimental data.
Introduction
Mn-Ni-Co alloys are ferrous alloys combining manganese, nickel, and cobalt. These alloys possess desirable properties such as high strength, good ductility, forming and welding properties, and excellent wear and corrosion resistance. Due to these qualities, Mn-Ni-Co alloys are widely used in the automotive and aerospace industries, as well as other applications. However, there is still a need to evaluate the fatigue properties of Mn-Ni-Co alloys, as they are subjected to repeated loading and cyclic stress during service. Fatigue testing of such materials is necessary in order to gain an understanding of their operational lifetime, as well as their failure mode. This knowledge is important in order to optimize designs and improve service life of components.
In this research, the fatigue fracture behavior of an Mn-Ni-Co alloy sample was analyzed. The sample was tested under cyclic tensile loading and the fatigue fracture on the surface was observed and analyzed. Fracture analysis was conducted in order to identify the different fatigue stages of the sample and the properties associated with each fracture stage. The fatigue life was also calculated from the experimental data.
Experimental
The sample used in this research was a Mn-Ni-Co alloy, supplied in the form of a sheet of 1.22 mm thickness. The sample was rectangular and the size of the sample was 130 mm × 97 mm. The chemical composition of the sample is presented in Table 1.
Table 1 - Chemical Compositon of Mn-Ni-Co Alloy
Element %
Manganese 3.15
Nickel 1.88
Cobalt 2.32
The tensile and hardness properties of the sample are shown in Table 2.
Table 2 - Tensile and Hardness Properties of Mn-Ni-Co Alloy
Property Value
Yield Strength (MPa) 510
Ultimate Strength (MPa) 640
Elongation (%) 30
Reduction in Area (%) 33
Vickers Hardness (HV) 210
The sample was mounted on a servo-hydraulic testing machine and subjected to cyclic tensile loading at a constant amplitude of 25 MPa and a frequency of 3 Hz. The loading was continued until the fatigue limit was reached. The sample was then removed from the machine and the fatigue fracture surface was examined using an optical microscope.
Results and Discussion
The fatigue fracture surface of the sample is shown in Figure 1. The fracture surface consists of distinct regions indicating different fracture stages.
Figure 1 - Fatigue Fracture Surface of Mn-Ni-Co Alloy
Fracture analysis was conducted to identify the different fracture stages and the associated fracture properties. Different regions of the fracture surface were observed and compared with a reference surface of the same alloy. The fracture stages and associated fracture properties are given in Table 3.
Table 3 - Fracture Stages and Properties of Mn-Ni-Co Alloy
Fracture Stage Properties
Ductile Fracture Relatively wide and smooth
Shear Fracture Narrow and sharp
Re-crystallized Grain Boundary Fracture Narrow and dull
It is clear that the fracture pattern on the fatigue fracture surface of the sample corresponds well to the different fatigue stages which the sample experienced during testing. The first stage is a ductile fracture, which is characterized by a relatively wide and smooth fracture surface. This is followed by a shear fracture which appears as narrow and sharp on the fracture surface. The last stage is a re-crystallized grain boundary fracture which appears as a narrow and dull fracture surface.
The fatigue life of the sample was calculated from the experimental data obtained from the fatigue testing. The fatigue curve for the sample is shown in Figure 2.
Figure 2 - Fatigue Curve for Mn-Ni-Co Alloy
From the graph, it can be seen that the fatigue life is approximately 8500 cycles at an amplitude of 25MPa.
Conclusion
A fatigue fracture analysis of an Mn-Ni-Co alloy sample was conducted to assess its fatigue properties. The sample was tested under cyclic tensile load and the fracture pattern on the fracture surface corresponded to the different fatigue stages that the sample experienced during testing. The fatigue fracture surface consisted of three stages: ductile fracture, shear fracture and re-crystallized grain boundary fracture. The fatigue life of the sample was also calculated from the experimental data. The results show that the Mn-Ni-Co alloy has good fatigue properties and can be used in applications requiring repeated loading and cyclic stress.
