Papers by Keyword: Fatigue Life Prediction

Abstract: This paper investigates the growth behavior of fatigue cracks initiated at corrosion pits in laboratory coupons of LC9 aluminum alloy subjected to a transport aircraft loading spectrum. Corrosion pits were introduced by exposing the coupons to EXCO solution for a variety of periods to produce corrosion damage varying from mild to severe. In general, the presence of corrosion damage reduced the fatigue lives of components to a severe extent. It was found that the depth of the corrosion pit was a suitable parameter for characterizing the corrosion damage and for predicting the fatigue life of the coupons using commercial fatigue crack growth software

Abstract: Fatigue is the most common failure mechanisms in structures of construction machinery with inherent defects under variable amplitude loading, which have to endure for a long term cycle loadings in the actual service. In the present investigation an exponential model is proposed for fatigue life prediction with retardation caused by a single spike under constant amplitude loading. Comparisons between the predicted life and the experimental data are provided to demonstrate the utility and robustness of the proposed model.

Abstract: Aiming at the demand of remanufacturing mechanical parts fatigue life prediction, the main methods of fatigue life prediction are reviewed and summarized. The finite element and dynamics combined simulation method has been widely used at present, whose advantages are that it is suitable for most of the mechanical parts, and the forecast cycle is short, and it can be analyzed combining with the parts actual working condition, but the prediction accuracy depends on the comprehensive degree to the service condition. The experimental method is the most traditional method, and the fatigue life value obtained by the method is reliable, but the method is entirely depend on experience, and the cost of experiments is expensive, so the feasibility is bad. The fatigue life analysis method can lower the dependence on large number of experiments, but there is a great distance between the predicting fatigue life and actual fatigue life in working environment. The metal magnetic memory non-destructive testing method doesnt damage the testing objects, but the method is still in the stage of further research at present. Finally, taking the number of experiments, prediction cycle, prediction accuracy, prediction cost and the complex degree of the principle involved in the prediction process as evaluation indexes, the finite element and dynamics combined simulation method is the best fatigue life prediction method according to the score values of each method calculated by the quantitative scores based on the expert evaluation method.

Abstract: In this paper, a fatigue life prediction method for fiber reinforced polymer composite lamina is proposed. Based on two independent introduced damage variables, the damage degree of fiber and the damage degree of matrix, the issue of lamina fatigue is transformed into the study of damage evolution for fiber and matrix. Subsequently, the damage driving force and the damage evolution equations for the fiber and the matrix are constructed, respectively. Then, a novel parameter identified method is conducted. Finally, with the failure criterion for the lamina presented, the fatigue life prediction method of the composite lamina is proposed.

Abstract: A novel method based on damage line is put forward to improve the prediction accuracy of fatigue life under variable amplitude loads. According to fatigue strength change before and after the damage line, mechanical parts service processes are divided into undamaging and damaging process. Undamaging process life, damaging process life and fatigue life are calculated by the novel method. The prediction results are closer to the actual situation. In order to simplify calculation, the damaging process is regarded as linear process. The results are more accurate than traditional fatigue life prediction method. The novel method can be widely used in light-weight constructions, reduction of time-to-market period, product safety, reliability design and so on.

Abstract: Planetary cage in caterpillar is designed with the static strength theory. While the dynamic characteristics of planetary parts in different working condition is difficult to obtain with the limit of traditional method, so research on reliability and fatigue life prediction of planetary cage is very difficulty which result that designed life is much longer than practical life. The reliability of caterpillar is affected deeply. The dynamic loads suffered by planetary cage in different working condition is obtained based on running simulation with MSC.ATV, and then the fatigue life of planetary frame is calculated with fatigue life prediction system of planetary cage. The study case proves the new method is feasible. Research on planetary cage in caterpillar based on running simulation test resolve not only the technical problem of loads in different work condition but also close connection with engineer, so the research have very important utility significance.

Abstract: Gear box in caterpillar is designed with the static strength theory. While the dynamic characteristics of planetary parts in different working condition is difficult to obtain with the limit of traditional method, so research on reliability and fatigue life prediction of gear box is very difficulty which result that designed life is much longer than practical life. The reliability of caterpillar is affected deeply. The dynamic loads suffered by gear box in different working condition is obtained based on running simulation with MSC.ATV, and then the fatigue life of planetary frame is calculated with fatigue life prediction system of gear box. The study case prove the new method is feasible.

Abstract: One approach to limiting CO₂ emissions from oxidation of carbon-based fuels is to capture the CO₂ and store it, possibly in onshore or offshore subsurface geologic formations. From the CO₂ transportation structure perspective, a critical component of this approach is the pipeline transportation of supercritical or dense CO₂. In CCS, the pipelines undertaking a CO2 transportation task suffer various loads, the effects of which is easily aggravated due to the existence of a high working pressure (above 7.4MPa) and inner corrosion. For the application of anthropogenic CO₂ pipe transportation technique, this paper will address a LEFM-based finite element method which can evaluate fatigue life for a CO₂ transmission pipeline containing a semicircle inner defect. Specifically, a portion of welded round steel pipeline is selected as the object of our analysis. Under the inner pressure fluctuation scenarios, an FRANC2D finite element procedure is generated to simulate mode-I crack extension from a given inner edge crack, which initiates from the half circle defect,and the corresponding stress intension factors(SIFs), , and its increment, , varied with different cracking depths, are calculated and compared. Afterwards, the fatigue lives for the pipeline with the defects of different sizes are obtained by using a modified Paris formula which can analyze the influence of crack closure and stress ratio. Thus, the relation between the fatigue life of CO₂ pipelines and the dimension of the inner defect can be determined by performing the proposed fatigue crack growth analysis.

Abstract: Fatigue life estimation of notched components is mostly dependent on notch stress and strain calculation with non-linear finite element analysis (FEA). For multiaxial cyclic loading, the stress-strain analysis of notch root is rather complex and the non-linear FEA is also very time-consuming. In this paper, a new fatigue life prediction method for notched components under multiaxial loading is proposed. First, a linear elastic solution needs to be solved for notched components under multiaxial cyclic loading. Then, an elastic equivalent parameter is computed using the linear elastic solution. On the basis of the elastic equivalent parameter combined with the Neuber’s rule, an elastic-plastic equivalent parameter is obtained. Finally, the elastic-plastic equivalent parameter is used to estimate fatigue crack initiation life of notched components. The proposed method needs only elastically calculated notch strain history as the basic input and is convenient for engineering application. The method is verified with experimental data of SAE 1045 notched shaft specimens under proportional and non-proportional loading. The results showed that the method can provide good life estimates.

Abstract: The most important characteristics for service safety of complex metal structures are those describing crack initiation and growth caused by static or dynamic, variable loading. Crack initiation and growth is subject of numerous investigations by different methods. The paper shows the possibility of applying infrared thermography to the problems of fracture mechanics. The main aim of testing was to qualitative relate the temperature changes of the spacemen measured by infrared thermography with the evaluation of fatigue cracks in steel specimen. Based on the distribution of temperature on the surface of the sample, during the action of force, the spread of plastic zones and crack tip are determined. The increase of temperature produced by the plastic deformation at the crack tip has been measured by infrared camera Thermal CAM SC640, FLIR Systems. SE(B) specimens were tested in three-point bending (TPB), following the procedures of ASTM E1820, on electrical mechanical testing machine with crack tip opening displacement (CTOD) control, at room temperature. Numerical simulation of stress distribution on the same model under same condition is presented, too. The results showed that thermography is a method suitable for monitoring and prediction of crack initiation and growth, as well as critical stress in elastic and elastic-plastic deformations. Fatigue crack growth behaviour of cracked TPB specimen made of S355 J2 G3 steel using Paris relation is considered.