Fatigue Lifespan Research Articles

Tangential contact modeling to seal considering elastic-plastic for lubrication transition mechanism

Researches on the reciprocating seals lubrication under elastic-hydrodynamic lubrication (EHL) are mature, and leakage of failure criterion has been described with Couette flow for more than 30 years, which could not reflect to leakage mechanism in multiscale. Thus, it is necessary to explore seal leakage failure to focus on micro convex bodies of asperities model under contact pressure and cycle tangential friction stress in mixed lubrication. This is because convex bodies behaviors determine sealing effect and lubrication behaviors in microscale with subjecting to the dominant pressure. Interaction between convex bodies fatigue hysteresis curve and elastic-plastic strain are also calculated to explore sealing effect with leakage rate mechanism. We then design water seal at high pressure of 100 MPa with the speed of 0.1–1 m/s and medium temperature from 5 ℃ to 40 ℃. IWAN model of the convex bodies are calculated. Probability density function and Jenkin’s elements critical slip displacement are obtained. Convex bodies of radial and tangential deformation are also calculated through loading of contact pressure and friction stress with cycle strength coefficient to obtain seal fatigue lifespan. Ratio to seal stick and slip friction is calculated for evaluating the loading boundary. Seal leakage failure mechanism with fatigue characteristics is illustrated with macro lubrication parameters and micro convex bodies mechanics performance.

Enhancing Sustainable Afforestation through Innovative Earth Auger Design: A Simulation Study in Hilly Regions

The objective of this study was to advance sustainable forestry development through the creation of mechanical equipment, taking into account forestry operational methods. A suspended automatic feeding and retracting excavation device for tree pits was engineered, and its interaction with soil was investigated by integrating the Discrete Element Method (DEM) with Multi-Flexible Body Dynamics (MFBD). Based on simulation results, the research explored the impact mechanisms of the machine on soil transportation, working load, and fatigue lifespan of the spiral blades for different terrains and operating conditions. The coupling simulation method demonstrated the potential for designing and testing forestry equipment in specific operating environments, reducing time and resource consumption for field testing. Terrain significantly influenced soil disturbance variability, while the effect of operating direction was minor. Operational parameters should consider soil and water conservation, favoring the formation of fish-scale pits. Field tests in forested areas validate the practicality of the apparatus, providing valuable insights for the operation and equipment design of earth augers in hilly regions.

Dynamic cyclic fatigue resistance of RACE EVO in S-shaped canal with different angles of access: An in vitro study

Abstract Introduction: Nickel–titanium instruments annually undergo improvements to enhance the cyclic fatigue lifespan, especially with challenging canals. This study examines RACE EVO instrument in an S-shaped double-curvature canal in different angles of insertion 0°, 20°, and 40° to investigate the behavior of the heat-treated instruments in challenging canals. Materials and Methods: A total of 30 instruments were assigned to three groups (Group 0°, Group 20°, and Group 40°). RACE EVO instruments were tested in artificial canals. The canals had two curvatures: an apical one which its parameters are 70° angle and 2 mm radius and a coronal one which its parameters are 60° angle and 5 mm radius. The test was done using a cyclic fatigue apparatus. A statistical study was done by one-way analysis of variance groups, and Tukey’s honestly significant difference/Tukey–Kramer with a level of significance (α) was adjusted to 0.05. Results: The time until failure was reduced by the increase in the angle of insertion; however, Group 20° and Group 40° were not significantly different. All the instruments were broken apically. The scanning electron microscopic analysis showed typical characteristics of cyclic fatigue failure. Conclusions: Increasing the inclination during the insertion reduced the resistance of the RACE EVO instruments to cyclic fatigue failure despite the surface heat treatment of the instrument.

Low-Cycle Fatigue Behavior of Hydrostatic Extruded AZ80 Mg Alloy

The fatigue properties of conventional and hydrostatic extruded AZ80 Mg alloy were fully studied under strain-controlled mode. The hydrostatic extrusion can effectively increase the tensile strength, but decrease the elongation. Consequently, the low cycle fatigue lifespan of the hydrostatic extruded specimens was shorter than that of the conventional extruded ones. The Manson-Coffin-Basquin relationship was adopted to describe the fatigue lifespan of the extruded AZ80 alloys. Finally, the fracture surfaces were observed by scanning electron microscope. The fatigue crack stable propagation zone of the hydrostatic extruded sample has decreased significantly compared with that of the conventional extruded sample. The hydrostatic extruded specimen has small reverse plastic zone size, which leads to microscopically rough fatigue crack propagation zone.

Microstructure analysis and life prediction of DD6 superalloy under 760 °C combined high and low cycle fatigue conditions

The impact of high and low cycle combined loads on the fatigue performance of DD6 alloy was investigated in this work. Specifically, the combined high- and low-cycle fatigue response of DD6 alloy was examined at a temperature of 760 °C under different low cycle stress amplitudes (960, 1000, and 1040 MPa). The findings revealed that higher low cycle stress amplitudes result in shorter combined high and low cycle fatigue life and less dispersion in life. Correlations between the microstructural features (crystal plane distribution, fracture elevation difference, and the area proportion of crack propagation zone) and fatigue performance were accurately established, demonstrating a linear relationship between these microstructural features and the logarithm of fatigue life. The study also uncovered the evolution rule of microstructural features in high- and low-cycle combined fatigue. Furthermore, the fracture mechanism was analyzed and the distribution of high and low cycle combined fatigue life of DD6 alloy at 760 °C was statistically validated using the dual-parameter Weibull distribution theory. Building upon the crystal plasticity theory, a fatigue life prediction model was developed, and the combined cycle fatigue lifespan under various low cycle stress amplitudes was compared. The comparison between the predicted life and actual fatigue life indicated that the predicted lifespan falls in three times the scatter band.

Data-driven prediction of the fatigue performance of corroded high-strength steel wires

Corrosion damage determines the fatigue performance and intensifies the fatigue lifespan scatter of high-strength steel wires. Many experimental studies have been performed on corroded wires to quantify the correlation between fatigue life and corrosion. However, accurate analysis and fatigue performance prediction of various types of corrosion are still insufficient. This study proposes a predictive machine learning-based model to explore the quantitative influence of corrosion degree, stress ranges, loading ratio, loading frequency and other factors on the fatigue life of corroded high-strength steel wires. The proposed model is trained using the adaptive boosting algorithm on the basis of a collected database containing 323 samples from corrosion fatigue tests. A cross-validation method with the grid-search approach is applied to accelerate the optimisation of the hyperparameters. The performance of model is thoroughly compared with the empirical models and the common utilized machine learning algorithms. The prediction performance of the proposed model is considerably good, with a coefficient of determination of 0.96. The generalisation ability of the proposed model is superior to that of two common machine learning algorithms. Additionally, the physical meaning of the model is proven to be reasonable through a weight analysis of the input features. The stress range, corrosion rate and loading stress ratio dominate the fatigue performance of corroded high-strength steel wires.

Prediction of Synchronous Generator Fatigue Life in Islanded Microgrids With Harmonic Loads

This paper investigates the prediction of Synchronous Generators (SG) fatigue life span regarding current harmonic distortion in islanded microgrids. An analytical approach is proposed to calculate the harmonic components in the oscillating electromechanical torque of SGs feeding nonlinear loads in these microgrids. Moreover, a procedure is proposed to determine the damage of torsional vibration caused by these harmonics to the shaft of SGs. The proposed approach considers the cumulative effect of torque harmonics to predict the fatigue life. In a case study, the fatigue life span is calculated for an SG feeding a typical microgrid involving rectifier loads considering different loading and harmonic distortion conditions. Results show that harmonic distortion can consume the fatigue life of SGs significantly. Moreover, various effects of positive, negative, and zero sequence harmonics in the stator currents on the fatigue life of SGs are highlighted. The sensitivity of SG fatigue life to harmonic distortion magnitude, harmonic order, the shaft diameter, and windings parameters are also investigated.

Self‐healing natural rubber based on dynamic disulphide exchange towards fatigue lifetime extension

AbstractDynamic disulphide exchange mechanism was introduced to promote self‐healing characteristics to natural rubber compound and the corresponding healing mechanism and mechanical properties are presented. The formation of reversible dynamic disulphide bonds within rubber molecular chains was evidenced via FTIR and the total crosslink density of dynamic disulphide crosslinks was quantitatively measured by equilibrium swelling test. Scanning Electron Microscopy (SEM) results revealed that the healed area of the fractured surface adhered well with minor scar on the contact surface, suggesting that intermolecular diffusion occur at the fracture surface. It was also found that the tensile strength and tear strength of the broken samples able to recover 91% and 103%, respectively, under thermal healing at 150°C for 10 min. The fatigue lifespan of the materials increased 154.9% compared with the conventional rubber. The successful fabrication of self‐healing natural rubber through dynamically reversible disulphide exchange mechanism would be expected to open up new opportunities for development of sustainable rubber products.

Experimental study of temperature effect on the mechanical tensile fatigue of hydrated lime modified asphalt concrete and case application for the analysis of climatic effect on constructed pavement

Previous experimental studies have suggested that hot mixed asphalt (HMA) concrete using hydrated lime (HL) to partially replace the conventional limestone dust filler at 2.5% by the total weight of all aggregates showed an optimum improvement on several key mechanical properties, fatigue life span and moisture susceptibility. However, so far, the knowledge of the thermal response of the modified asphalt concrete and thermal influence on the durability of the pavement constructed are still relatively limited but important to inform pavement design. This paper, at first, reports an experimental study of the tensile fatigue life of HMA concrete mixes designed for wearing layer application. Tests were conducted under three different temperatures for five mixes of different HL contents and one with no use of HL. On the experimental data, temperature effect on material fatigue was characterized in terms of the S-N curve modelling parameters. At last, numerical modelling, set at a climatic scenario in the UK, was performed to analyse and compare the seasonal climatic thermal influence on the fatigue life of two pavement structures using and not using the HL modified HMA concrete. Both the experiment and modelling have demonstrated that the 2.5% HL HMA concrete largely enhances the fatigue life of the material and the constructed pavement.

Experimental study on the nonlinear dynamic characteristics of a kind of hinged connection structure

The hinged connections are widely used in mechanical structures, such as the expandable structures and truss structures in spacecraft and the three-point hitch device in agricultural machinery. The hinged connections allow relative rotations between the connected members so that the positions of mechanical structures can be adjusted. Thus, the hinged connections are always subject to large and complex forces during working operation, and these will lead to complicated nonlinear vibrations which have a significant impact on the working performance and fatigue lifespan of the mechanical structures. Therefore, the nonlinear dynamics characteristics of the hinged connection are studied. Firstly, the experimental platform of a typical hinged connection is established according to the mechanical structure characteristics and loading features of the hinged connection structure. Then the vibration experiments of the hinged connection structure are carried out respectively under different working conditions. Finally, the effect of hinge clearances and excitation frequencies on the nonlinear dynamics of the hinge connection structure is studied by the vibration response of the hinge connection structure under different working conditions. The results of this study can provide a reference for the optimal design of the hinged connection structure.

Evaluation of Fatigue Life of Recycled Opaque PET from Household Milk Bottle Wastes.

Polyethylene terephthalate (PET) is among the most used thermoplastic polymers in large scale manufacturing. Opaque PET is increasingly used in milk bottles to save weight and to bring a glossy white aspect due to TiO2 nanoparticles. The recyclability of opaque PET is an issue: whereas the recycling channels are well established for transparent PET, the presence of opaque PET in household wastes weakens those channels: opaque bottles cannot be mixed with transparent ones because the resulting blend is not transparent anymore. Many research efforts focus on the possibility to turn opaque PET into resources, as one key to a more circular economy. A recent study has demonstrated the improvement of the mechanical properties of recycled PET through reactive extrusion. In the present work, the lifespan of recycled opaque PET has been evaluated throughout tensile–tensile fatigue loading cycles at various steps of the recycling process: The specimens are obtained from flakes after grinding PET wastes (F-r-OPET), from a subsequent homogenization step (r-OPET-hom) and after reactive extrusion (Rex-r-OPET). Virgin PET is also considered as a comparison. First, tensile tests monitored by digital image correlation have been carried out to obtain the elastic modulus and ultimate tensile stress of each type of PET. The fatigue properties of reactive REx-r-OPET increase, probably associated with the rise of cross-linking and branching rates. The fatigue lifespan increases with the macromolecular weight. The fracture surface analysis of specimens brings new insight regarding the factors governing the fatigue behavior and the damaging mode of recycled PET. TiO2 nanoparticles act as stress concentrators, contributing to void formation at multiple sites and thus promoting the fracture process. Finally, the fatigue life of REx-r-OPET is comparable to those of virgin PET. Upcycling opaque PET by reactive extrusion may be a relevant new route to absorb some of the growing amounts of PET worldwide.

Regulating lithium-ion flow by piezoelectric effect of the poled-BaTiO3 film for dendrite-free lithium metal anode

Dendritic growth is regarded as the intrinsic cause of failure for the lithium metal rechargeable batteries, which blame on the uneven lithium-ion flux induced by the fragile native solid electrolyte interface (SEI) film. Herein, a functional SEI film is composed of BaTiO3 (BTO) dipole in polyacrylonitrile (PAN) matrix, to regulate lithium-ion flux through piezoelectric effect. It is found that, piezoelectric effect of the poled BTO film will induce a reversed local electric field on the dendrites bulge, thus reducing the aggregation of lithium-ion flow and slowing down dendrite growth. Moreover, the PAN matrix of the BTO film exhibited outstanding mechanical property of toughness and long fatigue lifespan, buffering volume change of lithium metal electrode during the plating/striping process. Under the effect of the poled BTO film, the lithium electrode achieved a flatter and smoother surface than that of native SEI film even after depositing a large area capacity of 10 mA h cm−2. Consequently, The Li||Poled-BTO-Cu half-cell delivered 94% coulombic efficiency over 180 cycles. Furthermore, the Poled-BTO-Li||FeLiPO4 could maintain the capacity at 110 mA h g−1 after 350 cycles.

Fatigue lifespan of a planetary roller-screw mechanism

Electro-mechanical actuators including planetary roller screw (PRS) support cyclic loads in aeronautical conditions. PRS multiple thread contacts between screw, rollers and nut allow the mechanism to support large loads. However, aeronautical accreditation requires fine prediction of fatigue lifespan. In this paper, a fatigue design strategy for PRS mechanisms is proposed combining Hertz contact model and a multi-axial fatigue criterion. The method is applied on two examples, one standard and one inverted PRS.The lifespan of PRS mechanism depends on maximal Dang Van stress. The Hertz sliding angle (Hertz contact main direction/sliding velocity) was introduced to analyze PRS performances. For both examples, the maximum stress at thread contact were located in bulk material but not at the surface. Dang Van stress mainly depended on curvature ratio, Hertz sliding angle and loads. Based on this analysis, Dang Van criterion was implemented to derive the loading domain of infinite lifespan of the mechanism. Critical contact was not always on the roller-screw side.

The deformation modes and transferability during low-cycle fatigue of Mg and Mg–3Y alloy

Mg–Y alloys show distinctly different slip/twinning activity under quasi-static monotonic loading at room temperature compared with pure Mg, as extensively reported. In this work, the influences of 3% Y addition on the deformation modes and transferability during strain-controlled tension-compression low-cycle fatigue (LCF) at room temperature of Mg sheets were studied quantitatively and statistically. The activity of various slip systems and twinning-detwinning were measured at desired fatigue stages via quasi-in-situ EBSD observations together with slip trace analysis. The results indicate that the activation of deformation modes in pure Mg was featured by the cyclic transition, i.e., tension twinning (at the compressive reversal) → detwinning + basal slip (at the tensile reversal). In Mg–3Y alloy, basal slip dominated the cyclic deformation throughout the fatigue life span. Compared with pure Mg, Mg–3Y alloy displayed the enhanced activity of various slip systems, including basal, prismatic, and pyramidal slip systems, but lower twinning-detwinning activity. For deformation transferability, mk, which is the product of the Schmid factor (SF) and the geometric compatibility factor (m’) values of the adjacent grains, was used to evaluate the slip transferability and twinning transferability at grain boundaries. Mg–3Y alloy showed a higher likelihood of slip transfer but lower twinning transferability than pure Mg. The underlying mechanisms affecting the activity of various slip systems and twinning, as well as deformation transferability and mechanical behavior, were discussed.

Application of machine learning algorithms for the optimization of the fabrication process of steel springs to improve their fatigue performance

Machine Learning algorithms are aimed at building generalizable models to provide accurate predictions or to find patterns from noisy data. These characteristics are potentially beneficial for the fabrication of steel products. In this research, 529 rotating bending fatigue tests (R = -1 and σa = 400 MPa) were carried out on steel suspension spring bars fabricated using different combinations of manufacturing parameters. A reliable regression model (R2 = 0.877 on the test dataset) based on the Gradient Boosting algorithm was obtained. The interpretation of the model was carried out through the Permutation Importance algorithm, revealing the relevance of the temperature in the tempering treatment applied after quenching on the fatigue lifespan. This pattern was quantitatively described by means of the Partial Dependence Plot of this feature. Besides, a specific study was carried out to obtain a reliable interpretation of the results derived from the Machine Learning analysis. In this sense, it has been observed that specimens subjected to high temperature tempering display a lower surface hardness that provokes a higher surface roughness after shot peening; this, in turn, facilitates the initiation of surface cracks during the fatigue tests reducing the fatigue lifespan. This study provides a reliable framework to optimize the suspension spring manufacturing conditions to increase their fatigue lifespan as well as an example, generalizable to other manufacturing processes, of the potential benefits of Machine Learning.

Property Evaluation of Cement-Stabilized Macadam Modified via Phosphorus Slag Materials

Phosphorus slag, known as the waste product of the phosphate ore industry, is causing critical environmental issues due to its direct exposure to natural spaces. In this article, a partial replacement of the natural fine aggregate ordinarily used in cement-stabilized macadam (CSM) base by phosphorus slag was explored to be an effective solution for phosphorus slag waste. CSM specimens were fabricated by adding various dosages of phosphorus slag particle and fine powder, whereas the optimum moisture content and maximum dry density were analyzed through compaction tests. Compressive strength, bending tensile strength, fatigue life span, dry shrinkage, and temperature shrinkage performance at different curing durations were investigated to evaluate the properties of modified macadam. Results show that phosphorus slag reduced the early compressive strength of CSM to a small extent, but the compressive strength finally increased at 90 days’ curing. The modified slag particles and slag fine powder exhibited different behaviors to repeated loading, moisture loss, and temperature difference. Finally, according to the strength change, fatigue performance comparison, and shrinkage strain caused by the incorporation of phosphorous slag materials into the CSM, it was verified that 25% of the particles to 40% of the fine powder is the best replacement ratio.

Experimental Investigation of the Fatigue Lifespan of Anchor Bolts with Consideration of Loading History

Preloaded bolted connections are one of the most used approaches for anchoring steel structures and equipment. Preload is induced by a mechanical tightening of the nut with the required torque. In the case of anchor bolts embedded in a concrete base, the prescribed tightening procedure has to be followed for safe and reliable operation. The present paper addresses the problem of anchoring a new casting pedestal using the original anchor bolts. The aim was to verify the original anchoring system’s reliable and safe operation, taking into account the current condition of the bolts. The analysed anchoring bolts are subjected to cyclic (disappearing) stress during the rotation of the casting pedestal. If the interplays between the anchor bolt and the concrete foundation were damaged, production would shut down, resulting in high economic losses. For this reason, the authors used a modified nut with a lightened first thread when investigating the actual state of the anchoring and setting the required preload. The shape and dimensions of the nut were determined based on the results of numerical modelling. The experimental measurements consisted of two phases. In the first phase, the values of axial forces in the anchor bolts at the required preload were set using the designed dynamometers. The second phase was focused on the operational measurements. The methodology of measuring the axial forces and the interpretation of the results obtained, including a comprehensive view of the anchoring safety, provides relevant evidence of the functionality and effectiveness of the proposed solution. Based on the results of the operational measurement and the prescribed handling of the casting pedestal, the lifespan of the anchoring was determined to be 3650 days under the loading cycles to date.

Fatigue lifespan assessment of stay cables by a refined joint probability density model of wind speed and direction

Stay cables are crucial load-bearing components of long-span cable-stayed bridges. Because they are sensitive to wind, the wind load is an important control load in their safety and fatigue evaluation. To consider the effects of variations in the wind speed and direction, a joint probability density model of wind speed and direction is proposed for evaluating the fatigue lifespan of a stay cable. For this purpose, an angular–linear model is introduced to coordinate the marginal distribution of wind speed and direction. The marginal distribution of wind speed comprises a Gumbel model, while that of the direction comprises a refined mixture of a von Mises distribution model. Subsequently, based on the dynamic simulation of a coupled wind–vehicle–bridge system, an assessment method for fatigue lifespan is developed by considering the variation of traffic flow with four load levels and variations in wind speed and direction. The results indicate that the refined angular–linear distribution model yields considerable fitting results for the measured data with respect to the wind speed and direction. Although the response and fatigue damage of a stay cable mainly depend on its length and location, the effect of the direction variation of the wind load is also not negligible. Additionally, the results from the assessment method show that the fatigue lifespan of a stay cable on the windward side of the local prevailing wind direction is relatively shorter than that of the leeward side.

High cycle fatigue behaviour of autoclave-cured woven carbon fibre-reinforced polymer composite gears

The high cycle fatigue behaviour of autoclave-cured carbon fibre-reinforced polymer (CFRP) composite gears is investigated. The CFRP gears were milled from a composite plate and tested in mesh with a steel drive gear under five torque loads ranging between 0.4 and 0.8 Nm in unlubricated conditions. A detailed gear damage analysis is conducted by employing scanning electron microscopy and high-resolution optical microscopy. Epoxy matrix microcracking is found to be the damage mechanism that leads to the final delamination failure. CFRP gears exhibited a significantly improved performance and a longer fatigue lifespan in comparison with the polymer and polymer composite gears.

Micro Solder Joint Reliability and Warpage Investigations of Extremely Thin Double-Layered Stacked-Chip Packaging

Abstract To overcome the limited operational speed for nanoscaled transistors, scaling electronic devices to small and thin packaging and high-density arrangements have become the technological mainstream in designing versatile packaging architectures. Among these, a promising candidate is a three-dimensional integrated circuit (3D-IC) package due to its excellent capability of heterogeneous integration. However, sequential reliability is a troublesome concern given the complex packaging structure, especially for the assembly of microsolder joints. To address this issue, we propose a double-layered, thin stacked chip package under the application of temperature cycling load. The packaging warpage and creep impact of SnAg microsolder joints on their fatigue lifespan are examined separately. Nonlinear material/geometry finite element analysis (FEA) is used on important designed factors, including the elastic modulus of underfill, chip thickness, and the radius and pitch of through silicon via (TSV). The simulated results indicate that the best fatigue lifetime of SnAg microsolder joint can be achieved at 10 μm of each chip thickness, 230 μm and 5 μm for TSV pitch and radius within the examined designed extent. Moreover, a hard underfill material requires consideration when the mounted chips thicken. Consequently, reliability significantly improves by dispersing thermomechanical stress/strain of the SnAg microjoints to neighboring underfill and related packaging components, especially for large TSV array spacing.