Metal Fatigue No Cd [WORK] Crack
Download File --->>> https://ssurll.com/2tqiGr
Abstract:The influence of the electrodeposition of cadmium and zinc-nickel and the stress concentration effect on the fatigue behavior of AISI 4140 steel threaded components were studied. Axial fatigue tests at room temperature with a stress ratio of R = 0.1 were performed using standard and threaded specimens with and without nut interface under base material, cadmium, and zinc-nickel-coated conditions. Finite element analysis (FEA) was used, considering both elastic and elastoplastic models, to quantify the stress distribution and strain for threaded specimens with and without a nut interface. The numeric results were correlated to the experimental fatigue data of threaded components with and without the nut interface, to allow the oil & gas companies to extrapolate the results for different thread dimensions, since the experimental tests are not feasible to be performed for all thread interfaces. Scanning electron microscopy (SEM) was used to analyze the fracture surfaces. The stress concentration factor had a greater influence on the fatigue performance of threaded components than the effect of the Cd and Zn-Ni coatings. The fatigue life of studs reduced by about 58% with the nut/stud interface, compared to threaded components without nuts. The elastoplastic FEA results showed that studs with a stud/nut interface had higher stress values than the threaded specimens without a nut interface. The FEA results showed that the cracks nucleated at the regions with higher strain, absorbed energy, and stress concentration. The substitution of Cd for a Zn-Ni coating was feasible regarding the fatigue strength for threaded and smooth components.Keywords: fatigue; AISI 4140 steel; finite element method; stud; FEA
Fatigue is a failure mechanism that involves the cracking of materials and structural components due to cyclic (or fluctuating) stress. While applied stresses may be tensile, compressive or torsional, crack initiation and propagation are due to the tensile component. One of the intriguing factors about fatigue development is that fatigue cracks can be initiated and propagated at stresses well below the yield strength of the material of construction (these stresses are usually thought to be related to elastic deformation, not plastic deformation.
Some engineers dedicate their careers to specializing in fatigue mechanics in order to better predict the life expectancy of a component. These engineers are concerned with answering the following questions:
Several processes may be used to extend the fatigue life of a metal component. These processes focus of enhancing the surface properties of a component. This includes case hardening using a carburizing or nitriding process or shot peening the surface in order to induce residual compressive stresses. Smoothing and/or polishing are also used to minimize stress risers.
Fatigue strength and fatigue life are two parameters used to describe fatigue behavior. Tests that show the relationship between stress (S) and number of cycles to failure (N) can be performed on a component. The data is represented on what is known as the S-N curve. The S-N curve exhibits two distinct behaviors for materials:
Iron and titanium alloys typically display the former conditions while nonferrous alloys typically display the latter. The fatigue limit is observed on the plot as a horizontal line, as shown in Figure 1, representing the largest value of stress that will not cause failure and becomes independent of the number of cycles.
The relationship for the latter curve (Figure 2) shows the number of cycles a metal can endure before failure for a range of applied stress levels. In general, metals can sustain high loads for a low number of cycles (i.e. low-cycle fatigue), or they can sustain low loads for a large number of cycles (i.e. high-cycle fatigue) before failure.
Vibration fatigue is a type of mechanical fatigue caused by vibration of equipment or piping during operation. As an example, vibration fatigue could occur as a result of operating equipment beyond designated integrity operating windows. Vibration-induced fatigue damage is typically caused by poor design, lack of support (or dampeners), or excessive support or stiffness. The amplitude and frequency of vibration are critical factors for vibration fatigue damage that leads to crack initiation and crack propagation.
Corrosion fatigue occurs from the simultaneous actions of chemical attack and mechanical fatigue. Corrosive environments are known for deteriorating metal. As corrosion develops, the area of damage serves as a point of stress concentration and results in the initiation of a crack. Thin films and coatings are applied to protect equipment from corrosion; however, mechanical fatigue will frequently damage these films and expose the equipment to the surrounding conditions.
Thermal fatigue is simply a failure that is induced by cyclic temperature changes. This mechanism is most often encountered in the tube assemblies of fired heaters. Mechanical fatigue may or may not be present. In most services, thermal fatigue is caused by start-ups and shut-downs. Sudden temperature changes are referred to as thermal shock and result in immediate failure.
Start-ups and shut-downs increase the susceptibility to thermal fatigue. Rapid heating and cooling rates also increase susceptibility. One rule-of-thumb indicates that thermal fatigue is likely to develop if the temperature swing between exceeds 200F operating temperature and shut-down.
Conventionally, three primary fatigue analysis methods have been used to estimate fatigue life; these are the stress-life (S-N) approach, the strain-life (ε-N) approach, and the fracture mechanics (crack growth) approach.
There are many sources and occurrences of metal fatigue in the chemical and refining industries. They range from low-cycle thermal stresses in an FCCU, to the relentless pressure cycling of a PSA, to the ultra-high cycles of a rotating pump.
Few of us have not experienced or heard about vibration fatigue (cracking) failures, especially around pumps and compressors. Typically small branch connections, equalizer lines, vents and drains are susceptible, especially if they are screwed...
This eBook offers practical guidance for, and real examples of, in-service degradation attributed to thermal fatigue. It provides a detailed discussion on thermal fatigue detection, characterization and evaluation, and mitigation or remediation.
Metallic materials are extensively used in engineering structures and fatigue failure is one of the most common failure modes of metal structures. Fatigue phenomena occur when a material is subjected to fluctuating stresses and strains, which lead to failure due to damage accumulation. Different methods, including the Palmgren-Miner linear damage rule- (LDR-) based, multiaxial and variable amplitude loading, stochastic-based, energy-based, and continuum damage mechanics methods, forecast fatigue life. This paper reviews fatigue life prediction techniques for metallic materials. An ideal fatigue life prediction model should include the main features of those already established methods, and its implementation in simulation systems could help engineers and scientists in different applications. In conclusion, LDR-based, multiaxial and variable amplitude loading, stochastic-based, continuum damage mechanics, and energy-based methods are easy, realistic, microstructure dependent, well timed, and damage connected, respectively, for the ideal prediction model.
Fatigue damage is among the major issues in engineering, because it increases with the number of applied loading cycles in a cumulative manner, and can lead to fracture and failure of the considered part. Therefore, the prediction of fatigue life has an outstanding importance that must be considered during the design step of a mechanical component .
The fatigue life prediction methods can be divided into two main groups, according to the particular approach used. The first group is made up of models based on the prediction of crack nucleation, using a combination of damage evolution rule and criteria based on stress/strain of components. The key point of this approach is the lack of dependence from loading and specimen geometry, being the fatigue life determined only by a stress/strain criterion .
Bhattacharya and Ellingwood  predicted the crack initiation life for strain-controlled fatigue loading, using a thermodynamics-based CDM model where the equations of damage growth were expressed in terms of the Helmholtz free energy.
A very interesting fatigue life prediction approach based on fracture mechanics methods has been proposed by Ghidini and Dalle Donne . In this work they demonstrated that, using widespread aerospace fracture mechanics-based packages, it is possible to get a good prediction on the fatigue life of pristine, precorroded base, and friction stir welded specimens, even under variable amplitude loads and residual stresses conditions .
In the present review paper, various prediction methods developed so far are discussed. Particular emphasis will be given to the prediction of the crack initiation and growth stages, having a key role in the overall fatigue life prediction. The theories of damage accumulation and continuum damage mechanics are explained and the prediction methods based on these two approaches are discussed in detail.
A power law formulated by Paris and Erdogan  is commonly used to model the stable fatigue crack growth:and the fatigue life is obtained from the following integration:where is the stress intensity factor range, while and are material-related constants. The integration limits and correspond to the initial and final fatigue crack lengths.
Fatigue cracks have been a matter of research for a long time . Hachim et al.  addressed the maintenance planning issue for a steel S355 structure, predicting the number of priming cycles of a fatigue