Metal Fatigue Life** Method.
There are many ways to fatigue life**. According to the basic assumptions and control parameters of fatigue crack formation life, it can be divided into nominal stress method, local stress-strain method, energy method, field strength method, etc.
Nominal stress method.
The nominal stress method is a method to estimate the fatigue life of a structure according to the linear cumulative damage theory by taking the nominal stress of the structure as the basis of the test and life estimation, using the rain flow method to extract the independent and unrelated stress cycles, and combining the s-n curve of the material. The basic assumption is that for any member (or structural detail or element), as long as the stress concentration coefficient kt is the same and the load spectrum is the same, their lifetime is the same. In this method, the nominal stress is the control parameter. The method is simple and easy to implement considering the influence of load sequence and residual stress.
However, this method has two main shortcomings: first, because it studies the fatigue problem in the elastic range, it does not consider the influence of the local plastic deformation of the notched root, and the calculation error is large when calculating the fatigue life of the structure with stress concentrationSecond, it is very difficult to determine the equivalent relationship between the standard sample and the structure, which is related to the geometry of the structure, the loading mode and the size of the structure, materials and other factors. It is precisely because of the above defects that the formation ability of fatigue cracks in the nominal stress method is low, and this method requires S-N curves under different stress ratios r and different stress concentration factors kt, and it takes a lot of money to obtain these material data. Therefore, the nominal stress method is only suitable for calculating the fatigue life of high-cycle fatigue and notch-free structures with low stress levels. In recent years, the nominal stress method has also been continuously developed, and the stress severity coefficient method (S.) has appeared one after anotherST), effective stress method, rated coefficient method (DRF), etc.
So let's find outParameters of Inconel706 alloy material:
incone706（n09706)
Inconel706 is a Fe-Ni-Cr based precipitation hardening deformed superalloy with a service temperature of 550 -650 °C. This alloy is a modified alloy of GH4169 alloy, and its properties are similar to GH4169 alloy. Due to the reduction of niobium content in the alloy, it has better production process performance, hot and cold processing performance and welding performance. The alloy below 700 has high strength, good oxidation resistance and corrosion resistance. The alloy can be used to produce large-size and oversized superalloy products, suitable for the manufacture of parts such as aero-engine casings, diffuser housings, turbine discs and fasteners, and can also be used to manufacture large-diameter chucks for gas turbines for combined cycle power generation. The main products are bars, forgings, rings, sheets and strips.
Inconel706 Chemical Composition:
Chemical composition
Physical properties
Inconel706 heat treatment system
The standard heat treatment regime for forged bars and rings is:
(925-980) *30min) (cooling on demand) +845 10 *3h AC+720 10 *8h FC(55 h) 620 10 *8h AC;hbs≥285
Corrosion resistance properties
The chromium element in the alloy is supplied with an antioxidant medium, and the nickel element is not only supplied with an anti-reducing environment, but also has a strong resistance to stress corrosion cracking of two chloride ions and hydroxyl ions.