Metal Fatigue Numerical Simulation

Abstract: The metal widely used in the production of life, so metal fatigue has gradually to be known. Using the finite element software (Fatigue) of metal material at different axial load fatigue performance under conditions of simulated and analyzed, the analysis showed, alternating stress amplitude is constant stress, fatigue life with mean stress decreases, and the tensile stress is more prone to fatigue failure; in alternating load average stress certain circumstances, with the increase of stress amplitude , fatigue life decreases.

Keywords:: metal materials; fatigue performance; numerical simulation

As people's living standards increasing, more and more widely used in metal industries, and thus the fatigue performance of metal more and more attention. What is metal fatigue? The reference to the American Society for Testing and Materials (ASTM ) in the "Statistical Analysis of fatigue test and the standard definition of the relevant terms" (ASTM E206-72) in the definition: a point or some point in the disturbance under stress, and in a sufficient number of cycles after the disturbance or the formation of cracks complete rupture of the material occurs in the partial, permanent structural changes in the development process, known as fatigue. [1] present experimental simulation fatigue test is mainly due to relatively high cost of fatigue testing, finite element modeling provides a A new method of calculation of fatigue.

Metallic materials in use are known as alternating load fatigue load, the corresponding stress is called fatigue stress, and the change of load and stress with time course load spectrum and stress are known as Spectrum. When the load or stress spectrum spectrum The constant amplitude and frequency as constant amplitude loading. [2], the situation discussed in this article belong to this situation. and compared to static damage, fatigue damage is characterized mainly in the following points: �� time sex. Static damage is the destruction of one-time maximum load to bear, short duration; fatigue failure is repeatedly load to bear the damage caused, it happened to go through a fairly long period of time. �� stress size. When the static pull extension (compression) when the static stress intensity is less than the yield limit, or limit, static damage does not occur; and when the alternating stress is less than the ultimate strength or yield limit, the fatigue failure may occur. �� failure modes. metal structure Static damage depends on the material itself; But whether it is brittle or plastic material, they fatigue were no significant deformation is brittle failure. �� cross section features. static damage to components of the sections usually show features of coarse granular or fibrous; The fatigue failure of components of the sections, always showing characteristics of the two regions, some are smooth, the other is coarse granular or fibrous. �� factors. static damage resistance depends on the material itself; the fatigue damage and material The microstructure, component shape and size, surface condition, the use of conditions and the external environment have a relationship. Therefore, for the same material, static performance data are concentrated, and fatigue data are quite dispersed, need to use the knowledge of mathematical statistics analysis.

1 size and simulation parameters
Simulation with a thickness of 5 mm, a width of 10 mm plate specimens, shown in Figure 1. The basic mechanical properties in Table 1.

During the simulation, consider the following two aspects: �� the stress amplitude alternating stress must, cyclic stress, respectively, the average stress of -40 MPa, -20 MPa, 0,20 MPa, 40 MPa when the survival rate was 50% fatigue life; �� must mean stress, stress amplitude was 100 MPa, 110 MPa, 120 MPa, 130 MPa, 140 MPa, 150 MPa, 160 MPa when the survival rate was 50% of the fatigue life. Based on the symmetry relations, taking 1 / 4, modeling, shown in Figure 2. the material fatigue curve (SN curve) is the tensile strength of the material through the Fatigue software generated.

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When the alternating load, the average stress is not zero, the process to use in calculating the correction to the Goodman or Gerber amendment Goodman correction method used here, when the average stress is zero, not using any method of correction. Figure 3 the stress amplitude 140 MPa, tensile stress 120 MPa, compressive stress 160 MPa, average stress -20 MPa, the survival rate of 50% of the fatigue life contours. other cases the fatigue life shown in Table 2, Table 3.


From Table 2 can be mean stress and fatigue life of the diagram, Figure 4. From the figure we can see that the alternating stress amplitude is constant stress, fatigue life with mean stress increases. Also It can be seen, the metal material by alternating load, the tensile stress and compressive stress on fatigue is different, if the alternating load
Compressive stress than tensile stress, the material will adversely affect the life, which tensile stress is more prone to fatigue. In general, material cracks under tensile stress by the compressive stress will hinder the crack propagation Effect of crack closure effect even so, in normal use, as far as possible the material to reduce the impact by this load.

Figure 3 Fatigue life contours
Table 3 can be the life of stress amplitude and fatigue diagram, shown in Figure 5. The figure can be seen alternating load in some cases, the mean stress, amplitude increased with stress, fatigue gradually decreases . reduce the speed and the size of a certain stress amplitude relationship, when the stress amplitude is greater than 120 MPa, the decrease in the rate of increase, if the fatigue life time, compared to static damage, that damage to the static fatigue damage limit state.


3 Conclusion
Through the numerical simulation of metal materials, we can draw the following conclusions: �� alternating stress amplitude is constant stress, fatigue life with mean stress decreases, and the tensile stress is more prone to fatigue failure; �� in the delivery variable load average stress certain circumstances, with the increase of stress amplitude, fatigue life decreases.


References
1 week pass month, ZHENG Hong-xia, Luo Huiqiang. MSC.Fatigue Fatigue Analysis and a Case [M]. Beijing: Science Press, 2005.1
2 Chengyu Ren, Miao Longxiu, Hou Binglin. Fatigue strength [M]. Beijing: China Railway Press, 1990:21
3 Xinsu Min .316 L stainless steel after surface nanocrystallization mechanism of fatigue [D]. Guiyang: Guizhou University, 2009

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