Fatigue Life Analysis Research Articles

Fatigue life analysis based on the groove angle reduction in the butt welding of excavator booms

This study analyzes the effect of changes in groove angle on the fatigue strength of the V-groove butt weld joint made of SM490A steel used in excavators. Butt-type specimens with different groove angles of 40° and 30° were manufactured by CO2 welding at a speed of 300 mm/min on a 13.5 mm thick steel plate. Four-point bending fatigue tests were conducted at room temperature with a frequency of 5 Hz and stress ratio of R = 0.1, and fatigue limits were set to 2 × 106 cycles. The high-cycle fatigue life of VG40 was approximately 7% higher than that of VG30. The stress concentration coefficient calculated using the effective notch stress method was 1.62 for the VG40, and 1.78 for the VG30, with an approximate difference of 9%. This decrease in fatigue life was caused by stress concentration due to the notch effect at the weld root, which was attributed to the adjacent backplate. Although the fatigue life decreased slightly owing to the improvement angle of the welded part, no difference was observed in microstructure and hardness. Therefore, it was confirmed that a sound weld was formed. The results of this study can be used as important basic data for determining the V-groove angle.

Fatigue Life Analysis of Hydrogen Production Reactor Welds Under Thermal-mechanical-chemical Coupling

Hydrogen production reactor are subject to performance degradation problems in the complex environment of high temperature, high pressure and exposed to hydrogen atmosphere. The welds, being weak parts, are susceptible to fatigue damage under the influence of loads such as temperature, pressure and hydrogen penetration. In this paper, we focus on the fatigue life analysis of welds in hydrogen production reactor, taking into account the complex working conditions of thermal-mechanical-chemical coupling. Based on the Fe-safe fatigue analysis software, the stress variation of the welds under multi-field coupling was used as a cyclic load and the fatigue life was predicted using the stress-life method. Respectively, the fatigue life variation law of the weld region was studied at different temperatures, pressures, and hydrogen penetration conditions. The results show that the lowest fatigue life of the welds are concentrated in the vicinity of the fusion zone, with hydrogen penetration and temperature variations having a larger impact on the fatigue life, followed by pressure.

Effect of cathodic protection on the corrosion fatigue crack growth behavior and fatigue life of XS-grade shipbuilding steel

Shipbuilding steels are subjected to corrosion fatigue damage phenomena due to conjoint effects of cyclic loading by sea waves and corrosive seawater environment, which often leads to premature failure of ship hull structures. In practice, the impressed current cathodic protection (ICCP) technique is applied to mitigate ship hull corrosion by electrochemically making it cathodic. It is implemented by impressing a direct current to minimize the electrode potential to a predefined protection potential. It is significant to study the effect of ICCP on the corrosion fatigue crack growth rate (CFCGR) behavior and fatigue life assessment of ship hull structures. In this study, CFCGR behavior of high-strength XS-grade shipbuilding steel was investigated in unprotected freely corroding (FC) and protected ICCP (at – 800 mV) conditions using compact-tension specimens at 0.1 Hz frequency in artificial seawater (3.5 wt.% NaCl solution). After crack-closure corrections, it was found that the ICCP-protected specimen (∆KTH = 18 MPa √m) exhibited higher sub-critical or threshold corrosion fatigue crack propagation resistance as compared to the FC specimen (∆KTH = 14 MPa √m). Fractography of the FC specimen revealed the debonding of non-metallic inclusions and formation of micro-pits/secondary cracks as dominant damage mechanisms. ICCP-protected specimen exhibited a signature pattern of parallel secondary cracks and a proportional increase in their density with increasing stress intensity levels during primary crack growth. This fracture morphology indicated the primary-crack branching and further arrest, leading to retarded crack growth rates under ICCP-protection. Fatigue life analysis also confirmed this finding, where the beneficial ICCP-protection effect resulted in at least two times enhancement in fatigue lives from the unprotected FC condition.

Analysis and Optimization of Random Vibration Fatigue Life for Stacked Solder Joints Based on Orthogonal Experimental Design

Analysis and Optimization of Random Vibration Fatigue Life for Stacked Solder Joints Based on Orthogonal Experimental Design

Fatigue life analysis of deep rolled bearing inner rings

The deep rolling process can influence the surface and subsurface of hardened steels, such as the bearing steel AISI 52100, due to mechanical loading and elastoplastic deformation. By intentionally adjusting the surface and subsurface properties, the fatigue life of bearing inner rings can be increased. This is among others attributed to the strengthening of surface and subsurface. Residual stresses induced by deep rolling and modifications of the material microstructure also contribute to this effect. In the investigations presented the deep rolling process parameters of rolling pressure, overlap ratio, and ball diameter were specifically selected based on previous works. Fatigue life investigations were conducted on honed and deep rolled bearing inner rings to enhance the understanding of failure mechanisms and to quantify the influence of the deep rolling process on fatigue life. It was found that the deep rolled bearing inner rings exhibit higher compressive residual stresses in the subsurface than honed rings and also showed longer fatigue life under rolling loads. Optical analyses of bearing rings that failed due to fatigue were performed to detect the failure mechanisms. The tested bearings showed classical fatigue, where cracking is initiated below the surface and propagates to the surface under further stress. Residual stresses can influence both the crack initiation and propagation.

Static stress and fatigue life analysis of rocket trolley leaf spring using numerical simulation

Static stress and fatigue life analysis of rocket trolley leaf spring using numerical simulation

Material characterisation of anodising effects on small fatigue crack nucleation in AA7XXX alloys

The precursor cleaning steps in the anodising surface finish process for aluminium alloy aircraft parts are known to lead to etching of surface-breaking intermetallic particles and grain boundaries, which in turn leads to preferential sites for fatigue crack nucleation. Type 1C anodising per MIL-A-8625F, is a favoured aircraft aluminium part corrosion protection treatment meeting modern health and environmental requirements. Type 1C anodising uses electrolysis in a non-chromic acid bath (typically based on sulphuric, boric-sulphuric or phosphoric acid formulations) to develop a thick aluminium oxide surface layer. In previous studies the equivalent initial damage sizes of these nucleation sites was calculated from near surface fatigue crack growth measurements using quantitative fractography in both Type 1C anodised aluminium alloy 7050-T7451 and 7085-T7452. A notable difference was observed in the values for these two materials with AA7085-T7452 equivalent initial damage sizes being significantly smaller. Since these values are critical crack starting size assumptions in fatigue life analysis for aircraft fleets, the observed differences must be investigated and explained for notionally similar alloys under identical conditions.In this work, the material surrounding the population of crack nucleation sites in several Type 1C anodised fatigue tested specimens manufactured from AA7050-T7451 and AA7085-T7452 materials has been characterised using precise surface preparation methods and scanning electron microscopy techniques. It has been demonstrated that there is a statistically significant difference in the number, size, aspect ratio and distribution of surface breaking Al7Cu2Fe intermetallic particles beneath the anodising layer that, when etched out during the anodising process, are responsible for fatigue crack nucleation in 7050-T7451 over 7085-T7452 material. The increased size, angular shape and coverage of these intermetallics in AA7050 serves to increase their effectiveness as preferential locations for fatigue crack nucleation through two mechanisms, as a highly localised stress concentrating feature, as well as through their ability to sample more of the material's microstructural features ensuring a discontinuity is present in the most favourable orientation and location for fatigue crack nucleation.

Numerical Analysis and Experimental Validation of Temperature Induced Creep and Fatigue life of Inconel 740H and Haynes 282

The Nickel based super-alloys have gained lot of importance in the last decade or so owing to their applications in areas like power generation, military aircrafts, marine propulsion and nuclear reactors. Utilities worldwide are facing increased demand for additional electricity, reduced plant emissions and greater plant efficiency. To meet this challenge, it requires materials with very high temperature creep and fatigue strength and better coal ash corrosion resistance. For the realization of advanced ultra-supercritical (A-USC) thermal plant operating at service temperature and pressure about 700oC to 760oC and 24 MPa respectively, the use of Nickel based super alloys are indispensable. The two A-USC qualified alloys include Inconel 740H and Haynes 282. This study focus on improving the creep and fatigue life of the A-USC qualified alloys by predicting the optimum operating parameters through finite element modeling for temperature induced creep and fatigue analysis of the said A-USC alloys. The influence of various operating parameters like temperature, machining induced residual stress, surface finish, creep duration and fatigue loadings on output parameters like creep strain, elongation, creep and fatigue life were studied. Abaqus/Standard was used for the numerical simulation. Using ANOVA, the most influencing operating parameters were identified. It was observed that the machining induced residual stress and surface finish have greater influence on creep and fatigue life of alloys. Alloy with lower value of machining induced residual stress and better surface finish will have better creep and fatigue life. The proper validation of model was performed by comparing the results with relevant literature.

Fatigue life analysis of spinning bearings for roller-guided bushing special machines considering creep-slip characteristic

In order to ensure the longer working life of rolling guide bushing, this work proposed a fatigue life prediction model of spinning bearings based on the Hertzian contact distribution and creep-slip characteristic. The influence of different parameters on the fatigue life of spinning bearings was analyzed according to the damage parameter theory of the critical plane method and the L-P theory. Finally, the fatigue life prediction model of spinning bearings was verified through the finite element simulation combined with the experiments. The reliability results show that creep-slip characteristic and deformation lead to the contact zone stress of the spinning bearing firstly increases, decreases subsequently to zero and then increases to the peak value. The increase of rotational speed will make the fatigue life of the spinning bearing firstly increases and then decreases. With the increase of friction coefficient, its fatigue life will become smaller and smaller, and the increase of the external load will decrease its fatigue life. Meanwhile, the prediction error rate of the fatigue life prediction model proposed in this study is 4.60%, which is within the error tolerance. This study provides certain methods and ideas for fatigue life prediction of spinning bearings, and lays a theoretical foundation for the design of highly reliable spinning bearings.

Fatigue Life Analysis of Remanufactured Radial Rolling Bearing with the Replaced Loading Zone

The replacement of the loading zone is not considered in the active calculation method on fatigue life of remanufactured bearings. In practical application, when the radial bearings are reinstalled after remanufacturing, it is required to replace the loading zone, which results in a large deviation between the calculated fatigue life according to the active calculation method and the actual life. In this paper, the fatigue life factors of radial bearings with different remanufacturing levels are calculated according to the actual application condition. The results of case studies show that with the improvement of the remanufacturing level, regardless of whether the loading zone is replaced or not, the remanufacturing bearing life factor is gradually increased and the maximum can reach 1. Considering the replacement of the loading zone, the life factors of remanufactured bearings with different fixed rings are also very different, among which the remanufacturing deviation of fixed outer-ring level II is the largest, reaching 11.3%. However, with the increase of the remanufacturing level, the deviation decreases gradually. The life factors by the method presented in this paper of remanufactured radial bearings with the replaced loading zone are significantly higher than those of the active calculation method. The research results of this paper provides a more accurate calculation scheme for the fatigue life of remanufactured radial rolling bearings, which is a supplement to the active calculation method and has important practical significance for the practice of bearing remanufacturing engineering.

Fatigue life analysis model of crankshaft under uncertain working conditions based on physical-data collaboration

The uncertainty of working conditions often affects the fatigue life of the crankshaft. In order to study the impact of uncertain working conditions on the fatigue life of the crankshaft, the fatigue life analysis model of crankshaft under uncertain working conditions was established based on the engine working process model, equivalent stress calculation model, fatigue life calculation model and surrogate model. The engine working process model was established based on the filling and empty method to simulate engine performance under different working conditions, and the accuracy of the model is verified by experimental data. The equivalent stress calculation model under uncertain working conditions was established by combining the performance data with the equivalent stress calculation model. Based on the fatigue life curve, the transformation from equivalent stress to fatigue life can be realized, and the fatigue life of crankshaft under uncertain working conditions can be obtained. Finally, the relationship model between working condition and fatigue life was established based on the Kriging surrogate model. Through comparative analysis, the calculation errors of the established equivalent stress calculation model and fatigue life calculation model are 2.6% and 1.9% respectively. This study not only establishes the relationship between fatigue life and working conditions of crankshaft based on physical-data collaboration, but also provides an effective model basis for follow-up crankshaft reliability analysis.

A new exhaustive semi-analytical method to calculate stress distribution on the surface of a curved beam with circular cross section, with an application to helical compression springs

In mechanical and in civil engineering, stressed curved beams are found in many applications involving failure and fatigue analysis. However, stress formulas of straight beams cannot be applied to curved beams with any reasonable degree of accuracy. Hence, curved beam theory is yet to be properly defined and is only established for particular sets of loads, particular applications, and particular cross-section geometries. This work proposes the first exhaustive solution of stress field calculation on the surface of a curved beam with a circular cross section, computed with an open-access databank preliminary built with FE simulations and considering every kind of static mechanical load applied and any curvatures. Such data are an important prerequisite for probabilistic fatigue life analysis. A numerical campaign was executed with different relative curvatures and was gathered in an open-access stress coefficient databank to facilitate data use. For any given curvature and wire diameter, the method can obtain the distribution of each stress on the surface of the circular curved beam, calculated with any combination of forces and momenta applied on its centroidal line. This calculation method was successfully verified with an application to a cylindrical compression spring. As a result, the present semi-analytical model has a 99.9% accuracy on the maximal Tresca stress calculation, being more than 43,000 times faster than the most realistic FE model. This is a significant breakthrough for researchers and engineers looking to save industrial time, optimization process or fatigue estimations.

Numerical analysis on mechanical and fatigue behaviors of aviation electrical connector considering structural effect

AbstractThis work is motivated by the fact that the reliability of electrical connectors influenced by their mechanical behavior and fatigue life directly affects the working performance of the whole equipment system. In this paper, theoretical analyses of insertion force, maximum stress, and fatigue life in an aviation electrical connector are presented and the corresponding mathematical models are firstly derived. Then, to numerically investigate its mechanical behavior and fatigue life, a simplified 3D FE model is developed by using ABAQUS and FE‐SAFE software and verified by experiments and theoretical analysis. Finally, the distribution and evolution characteristics of contact forces, stress and fatigue life considering the influences of reed thickness and slot width are quantitatively analyzed in details. The results indicate that the insertion force first increases and then stabilizes at the level of 0.16 N as the pin head is fully inserted into the jack, which shows an opposite to the evolution of extraction force. Moreover, the maximum value of stress and the minimum value of fatigue life are all located at the root of the jack reed. Besides, unlike the small effect of slot width, the Fimax and σmax values obviously increase and the Nf value decreases with the increment of reed thickness.

Effect of different roller end-flange constructions on the fatigue life of the cylindrical roller bearings: A novel flange deformation formula

This paper performs the fatigue life analysis of the radial Cylindrical Roller Bearings (CRBs) with consideration of various roller end-flange shapes such as toroidal-toroidal, spherical-toroidal, and spherical-conical. A novel formula for each flange contact deformation in cylindrical roller bearing with different roller end-flange geometry including toroidal geometry is developed. Inner ring misalignment angle and radial deflection results obtained from the present study are verified with numerical and experimental results from the literature. The results approach to that of literature when the flange is changed from toroidal geometry to conical geometry. Using formulas developed in the present study, the effect of various roller end-flange geometries on the bearing life is investigated for different external loadings. It is observed that the bearing life increases when the roller end and flange are changed to toroidal geometry.

Research on the dynamic characteristics of wind turbine gearboxes under the spatiotemporal inhomogeneous in the wake

In response to the problem of increasing fatigue load and frequent faults caused by the wake effect, the dynamic characteristics and fatigue life analysis of wind turbine gearbox under the Spatial-temporal non-uniformity of wake region were carried out in this paper. A rigid-flexible coupling model of gears transmission system for a 2 MW wind turbine was established. Based on the three-dimensional Station-temporal inhomogeneous wake model proposed in our previous work, the wind speed distribution of six typical locations in the wake region was obtained. Results show that, the spatiotemporal inhomogeneous effects of the wake expansion have great impact on the dynamic characteristics of the gearboxes for the downwind turbines located in different positions. Vibration energy representing the magnitude of impact energy during the operation of the gearbox is significantly higher under wake conditions than under upstream conditions; meanwhile, the gearbox vibration signal contains more impact component in the wake. The velocity deficit and increased turbulence intensity results in less intense but more complex vibration non-smoothness in the turbine transmission system. As the downwind distance downwind increases, the vibration frequency distribution of the transmission system at each moment is larger, but the vibration energy is reduced. Under the 3D spatiotemporal inhomogeneous effects of the wake expansion, the downstream turbine with staggered arrangement is less affected by wake and has a smoother vibration than the tandem arrangement. At the same downstream distance, the gear life is better in a tandem arrangement than in a staggered arrangement (a maximum value happens at the downstream distance of 6D). Research in this paper can provide references for the study of the dynamic characteristics of large wind turbine transmission systems under the wake effects as well as for the micro-siting of wind farms.

Fatigue life analysis of high-pressure seamless steel cylinder for hydrogen using autofrettage design

The seamless steel gas cylinders remain widely used for hydrogen refueling stations due to its intrinsic safety, especially for the situations with high pressure over than 60 MPa. When the internal pressure thick wall cylinder is subjected to high pressure even ultra-high pressure, autofrettage process is usually adopted to improve its bearing capacity and fatigue life. In this paper, fatigue life analysis was performed on the seamless steel cylinder for hydrogen using the autofrettage design approach. The stress distribution along the wall thickness direction before and after the autofrettage process were analyzed. Based on the ideal elastic-plastic material, the residual stress caused by the autofrettage pressure were obtained. On this basis, the expressions of residual stress and total stress along the cylinder wall in elastic-plastic deformation region were obtained, which will affect the fatigue crack growth rate (FCGR). Therefore, the fatigue crack growth tests of 34CrMo4 steel under different stress ratios (R) were carried out, especially for R < 0 to simulate the residual stress. Using the FCGR corrected with stress ratio, the fatigue life of the autofrettage high-pressure seamless steel cylinder was estimated and compared with the conditional cylinder. The results showed that fatigue life can be improved using the autofrettage design approach.

Application of multiaxial fatigue criterion in critical plane to determine lifetime of composite laminates

This paper analyzes the results of fatigue tests of samples made of composite laminate. These samples were cut out from a previously produced laminate with different fiber-orientated layers at different angles. Thus, various variants of the complex stress state were obtained for the material with anisotropic properties. The samples cut out at 0° angle was taken as a reference point for the calculations. In order to perform the calculations, three popular stress criteria used in the case of statics were modified: maximum stress, Azzi-Tsai-Hill and Norris. Then, it was proposed to apply to the analysis of fatigue life of composites the fatigue criteria known from the analysis of isotropic materials, defined in the critical plane. The definition of the critical plane was considered as the plane in which the maximum normal stress or maximum shear stress occurs – obtaining two different versions. As a result of the calculations, it turned out that the best compliance of the calculations with the experiment was obtained using the criterion defined in the critical plane determined by the shear stresses, where the normal and shear stresses were included in it as the sum of their linear combination with weighting factors.

Fatigue life analysis of welded joints in the frequency plane in a structure designed for the defense industry

Welded joints are used in many industrial products and evaluations against static and dynamic stresses are important in terms of structure and life safety. It is very difficult to predict and model the vibration fatigue life of welded joints in the frequency plane under dynamic stresses. In this study, fatigue life estimation was made in the welded joint on a structure under vibration stresses in the frequency plane. Vibration characteristics for modes up to 1000 Hz were determined by modal analysis of the structure. In the MIL-STD 810G standard, power spectral density (PSD) is offered for composite wheeled vehicles, which are products of the defense industry. Random vibration analyzes were performed by defining PSD data as analysis input. With the effective notch stress approach, geometry and material S-N definitions were made and evaluations were carried out according to the Dirlik method. As a result of this study, the fatigue life of welded joints was determined as 4.582e+11 seconds. Approaches for structural reliability in a welded joint structure designed for the defense industry are proposed.

Multiaxial Fatigue Analysis of Connecting Bolt at High-Speed Train Axle Box under Structural Subharmonic Resonance.

Based on the dynamic characteristics of the axle box front cover of high-speed trains in the subharmonic resonance state, the nonlinear single-degree-of-freedom (SDOF) model was proved to be reasonable, and reasons for the ineffectiveness of the common prevention methods for preventing bolt failure were analyzed firstly. Then, dynamic stress of the bolt was simulated by innovatively adopting the linear method based on frequency response analysis. The stress simulation method was verified to be practical under the subharmonic resonance state by analyzing and comparing the experimental and numerical results of the bolted front cover. It was proved that the linear method was accurate enough to simulate the dynamic stress of bolts, which is of great engineering significance. In addition to the transverse resonance stress of bolts caused by drastic vertical vibration of the front cover, the tensile resonance stress at the root of the first engaged thread was too large to be neglected on account of the first-order bending modes of bolts. Next, equivalent stress amplitude of the multiaxial stresses was obtained by means of the octahedral shear stress criterion. Finally, fatigue life of bolts was predicted in terms of S-N curve suitable for bolt fatigue life analysis. It argued that the bolts were prone to multiaxial fatigue failure when the front cover was in subharmonic resonance for more than 26.8 h, and the fatigue life of bolts could be greatly improved when the wheel polygonization was eliminated by shortening the wheel reprofiling interval.

Fatigue life analysis of fillet weld with root gap in bogie tie rod seat under road traffic load

The results of failure analysis on the fillet welds of the tie rod seat in HDX2 type vehicle showed that size of root gap around cracks was usually larger than that observed in the region without cracks. Dynamic strain gauges were used to measure the time-strain curve of the zone surrounding the fillet weld in the locomotive traveling process. Then, a transfer matrix was utilized to calculate the time-strain curve of fillet welds and then a rainflow counting method was adopted to obtain hierarchical load spectra in the traveling process, which was used for predicting fatigue damage of fillet welds and safe service mileage. To reveal the influence of the root gap on the fatigue life of fillet welds, a three-factor and five-level orthogonal scheme was designed by taking the height, width and length of the root gap as variables. The calculation results based on road traffic loads indicated that: (1) When there is no gap at the root of fillet weld, the safe service mileage can meet standard requirements; when there is a gap at the root of the fillet weld, the safe service mileage is significantly shortened; (2) When the width, height or length of the root gap of fillet weld increases, the safe service mileage decreases monotonously. Given the same change in size, effect of the change in height of root gap on safe service mileage is the most significant among the three variables considered; (3) The maximum stress at straight line section of weld path was significantly greater than that at the corner section; (4) An inspection and maintenance program for root gaps of various sizes was developed.