Mechanical Fatigue Life Research Articles

Study of the effect of crystal orientation on the mechanical response and fatigue life of solder joints under thermal cycling by crystal plasticity

Electronic products are subjected to thermal cycling caused by power cycling in service processes. Owing to the difference in the coefficients of thermal expansion (CTEs) of solder joints and other packaging materials, solder joints suffer from thermomechanical fatigue, and cracks appear at their bonding interfaces. Solder joints are usually a single grain or three grains with Beachball morphology, and their composition is Sn-based Pb-free SAC305 (96.5Sn–3.0Ag–0.5Cu wt.%) solder, which exhibits obvious anisotropic mechanical behavior. This study investigated a thermal cycling simulation of Plastic Ball Grid Array (PBGA) packaging, in which the Anand model was used for solder joints, and the outermost solder joint was found to be a dangerous point. Sub-models were then established for this solder joint with several typical crystal orientations. The effect of crystal orientation under thermal cycling was simulated using thermomechanical crystal plasticity. When the c-axis of Sn crystal was perpendicular to the substrate, the deformation resistance was the largest, and the accumulation of equivalent plastic strain and strain energy dissipation was the slowest; hence, the fatigue life was the longest. As the angle between the c-axis and the substrate decreased, the deformation accumulated faster. When the c-axis was parallel to the substrate, the deformation of the solder joint was the fastest, and thus this joint was the first to fail and had the shortest fatigue life. In addition, the simulation of three grains indicated that orientations and their distributions had an influence on the shear strain accumulation of slip systems and fatigue life.

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.

Performance evaluation of asphalt mixture reinforced by lignin and ceramic fiber

A single-adding fiber technology only plays a role in improving one performance of asphalt mixture such as high temperature or low temperature or water damage performance. Although double-adding fiber-reinforced asphalt mixtures are expected to improve overall road performance, existing research still only focuses on the analysis of a single performance. In this study, two representative fibers including lignin fiber (LF) and ceramic fiber (CF) were selected including to investigate the role of double-adding fibers in asphalt mixtures. The effect of different fiber proportions on the overall road performance of stone matrix asphalt (SMA-13) mixtures was analyzed via wheel tracking tests, low temperature bending test, moisture susceptibility test and fatigue test, etc. The results revealed that the combined addition of LF and CF exhibited superior improvements in mechanical strength, anti-rutting performance, moisture susceptibility, and fatigue life as compared to that of using either fiber alone. Specifically, compared to that of SMA mixtures using LF, the SMA mixtures using both two fibers improved in 11% dynamic stability, 8.6 % low-temperature bending stress, 2.1 % moisture susceptibility and 20 % fatigue life, respectively. And compared to that of SMA mixtures using CF, the mixtures using both two fibers increased in 11 % low-temperature bending strain and 8 % fatigue life, while improving slightly in dynamic stability, low-temperature bending stress, and moisture susceptibility respectively. Based on the results of efficiency coefficient method, the recommended ratio of LF to CF in the asphalt mixture is 1:2, providing a more balanced and comprehensive enhancement of road performances. This study provides a theoretical reference for the engineering application of improving the road performance of asphalt mixture through composite fiber blending, which can effectively enhance the service life of asphalt pavement.

Numerical analysis and experimental investigation of residual stress and properties of T-joint by a novel in-situ laser shock forging and arc welding

A novel technique, referred to as Weld-LSF, has been proposed for the low-stress manufacturing of T-joints through in-situ synchronous assisted arc welding, employing laser shock forging. This innovative process introduces plastic deformation in the deposited weld seam at elevated temperatures, effectively reducing the tensile residual stresses (TRS) associated with welding. The thermal-mechanical coupling finite element model for Weld-LSF has been established, combining the classical bar-frame model and the inherent strain theory. The mechanism behind achieving low-stress welding of T-joints through in-situ LSF has been analyzed. Subsequently, experimental investigations were conducted using Q345 base metal and ER60–5 welding wire to study the influence of in-situ LSF on the microstructure and mechanical properties of the specimens. The results demonstrate that by introducing in-situ LSF at higher temperatures in the weld seam, tensile residual stresses are transformed from high to low levels, with the average TRS reduced from 342 MPa to 185 MPa, representing a significant reduction of 45.9 %. In-situ LSF forms a hardened layer with a depth of approximately 0.5 mm on the surface of the weld seam, albeit with certain depth limitations. Furthermore, the in-situ LSF treatment addresses the issue of poor ductility caused by stress concentration at the weld toe of T-joints, achieving a desirable combination of strength and ductility. The feasibility of in-situ LSF technology in welding fabrication has been established. In comparison to traditional welding techniques, the in-situ LSF treatment offers promising prospects for achieving low-stress welding, thereby enhancing the mechanical performance and fatigue life of the welding process.

Fatigue characteristics of nano-SiO2 cemented soil under coupled effects of dry-wet cycle and seawater corrosion

In the marine environment, cement soils are subject to a variety of adverse conditions, including seawater corrosion, dry and wet cycles, and dynamic loading. These environmental conditions pose a significant threat to the structural integrity of these engineered soils. The addition of Nano-SiO2 particles to these cement-treated soils is offered as an engineering solution to extend their service life. It has been shown that the incorporation of Nano-SiO2 into the Cemented soil can significantly increase the static strength and improve the microstructure of the Cemented soil. Four different Nano-SiO2 particles, which have been extensively studied in the literature, are used as admixtures in the cemented-soil. Optimal dosages of these Nano-SiO2 particles are determined based on unconfined compressive strength (UCS) and scanning electron microscopy (SEM) data. Wet-dry cycles are applied to the cement-treated soil samples to simulate tidal rise and fall relevant to the marine environment. Nuclear magnetic resonance (NMR) and X-ray diffraction tests are also performed to complement the SEM study. The incorporation of Nano-SiO2 into cement-treated soils in a marine environment improved the mechanical strength and fatigue life of the cement-treated soils. It also reduced the corrosion rate of the cemented soils in the sea, and the improvement in mechanical stability was also quite remarkable. The fatigue life of Nano-SiO2 cemented soils was 1.35 times longer than that of conventional cemented soils, and the peak dynamic modulus of elasticity of the added Nano-SiO2 cemented soils increased by 29%, when subjected to 60 cycles of seawater. The improved fatigue life of Nano-SiO2 Cemented soils is a function of their structural filling tropism and distribution tropism. The improved fatigue of Nano-SiO2 is a result of the combined effect of particle effect, volcanic ash effect, and nucleation effect.

Analysis of Prior Ultrasonic Impact Peening Treatment on Fatigue Behaviour of AA6063-T6

The mechanical and fatigue – ultrasonic impact peening interaction of AA6063-T6 were examined at room temperature (RT). This aluminum alloy is typically used in aerospace structural components such as wing spores of aircraft. The experimental results of un peened and peened samples were compared in both mechanical and fatigue tests. It was observed that the ultrasonic impact peening (UIP) treatment influenced the mechanical fatigue life and fatigue strength due to strain hardening of the surface and to the high compressive residual stresses. It was revealed that the improvement percentage (IP) due to application of (UIP) is recorded to be 6.8 for (UTS), 5.9 for (YS) and 6.25 for elongation. While for fatigue strength the IP was obtained to be 2.77. A comparison of the results was made with other researchers and the comparison was satisfactory

Mechanical damage characteristics of CR/PPA composite modified asphalt pavement under multi-factor coupling effect in the seasonally frozen region

Asphalt pavements are inevitably affected by coupled effects of dry-wet/freeze-thaw cycles, UV radiation, temperature, and loading during service, resulting in degradation of their road performance and reduced service life. Therefore, this study used crumb rubber (CR) and polyphosphoric acid (PPA) as modifiers to prepare CR/PPA composite modified asphalt mixtures for testing. To investigate the mechanical properties of the composite modified asphalt mixtures under the action of multi-factor coupling. Meanwhile, the performance analysis of matrix asphalt and SBS modified asphalt mixtures were carried out as a comparison. Density and water penetration tests, splitting tests, beam bending tests, and four-point bending fatigue tests reveal the evolution of asphalt mixture road performance. Finally, regression fitting was performed on the test data to establish the mechanical damage model of each type of asphalt mixture. The results show that with the increase of wet-dry/freeze-thaw cycles and the increase of UV radiation time, the void ratio and water permeability coefficient increase and the splitting strength, bending and tensile strain, and fatigue life decrease for all types of asphalt mixtures. When the number of wet-dry/freeze-thaw cycles reached 8, the mechanical properties of the asphalt mixture decreased significantly, while the changes leveled off after the number of cycles reached 15. When the UV radiation time is less than 4 months, the mechanical properties of the asphalt mixture decay more slowly. However, with a further increase in radiation time, the mechanical properties decay rapidly. The water-saturated specimens have a more significant effect on the mechanical damage of each type of asphalt mixture. Compared with the other two mixtures, the composite modified asphalt mixtures have superior mechanical properties and fatigue life. The mixture performance damage model based on the least squares Levenberg-Marquardt method (L-M method) was able to simulate the experimental data well, with a minimum correlation coefficient R2 of 0.9285. In summary, the road performance of all types of asphalt mixtures under the coupling of multiple factors has deteriorated, while the composite modified asphalt mixtures have better anti-damage characteristics, with good prospects for promotion.

Study on mechanical behavior and fatigue life of defective ropes in HTHP gas well with high-sulfur content

As demand for energy increases, the number of “three-high” (high-pressure, high-yield, high-sulfur) gas Wells has doubled, the severe stress fluctuation of pipe string caused by downhole high-pressure environment leads to the failure of rope fracture is particularly prominent. It is easy to cause pipeline blockage and large amount of high-pressure toxic gas leakage caused by tool string accidental falling. Therefore, based on the theory of Love and elastoplastic contact theory, and considering the influence of Poisson’s ratio effect, this article establishes a calculation model for tensile fatigue of interaction between rope strands to study the influence of key structural parameters and breaking wire position on stress distribution and fatigue life of rope. The results show that: the core strand of the rope is the main force position, the overall stress shows the trend of decreasing with the increase of winding radius; when the rope is stretched, the axial deformation near the core of the rope is smaller than the deformation far from the core; under the same number of broken wires, the fatigue life of different ropes is related to the location of broken wires, the farther the location of broken wires from the core of the rope, the higher the fatigue life. The research work in this article provides theoretical guidance for the safe operation of ropes in “three-high” gas wells.

Comparative Assessment of Mechanical Properties and Fatigue Life of Conventional and Multistep Rolled Forged Connecting Rods of High Strength AISI/SAE 4140 Steel

This paper aims to improve the mechanical properties and fatigue life of AISI/SAE 4140 alloy steel connecting rods (CRs). Conventional CRs are typically manufactured through open die forging/hammering, blocking, and hot forging processes. In the present work, a modification to the process route has been proposed such that the open die forging/hammering was completely replaced with a multistep asymmetrical reducer rolling technique. Four rolling passes were introduced to achieve the desired preform shape and size. The effect of each rolling pass on grain size, mechanical properties, and fatigue life was investigated. Samples from each multistep rolling, blocking, and forging stage were subjected to impact, hardness, tensile, and fatigue testing. Metallography using optical and scanning electron microscopes was also conducted to reveal metallurgical changes. Fatigue testing and fractography were performed using the R.R. Moore Rotating-Beam Fatigue testing machine and scanning electron microscope, respectively, to evaluate the fatigue life and the fracture behavior of both the conventional and multistep rolled forged CRs. It was observed that, unlike the conventional forging process, multistep asymmetrical rolling gradually reduces grain size as the rolling progresses and improves yield, tensile, and impact strengths, hardness, and ductility. In comparison to conventional forging, multistep rolling led to an almost 33% and 29% increase in yield and tensile strengths, respectively. Moreover, the fatigue life of multistep rolled CR increased by more than five times compared to conventional CR.

Friction Stir Welding of Non-Heat Treatable Al Alloys: Challenges and Improvements Opportunities

Friction stir welding (FSW) is an effective solid-state joining process that has the potential to overcome common problems correlated with conventional fusion welding processes. FSW is used for the joining of metallic materials, in particular Al alloys (non-heat-treatable and heat-treatable). The heat produced by the friction between the rotating tool and the workpiece material generates a softened region near the FSW tool. Although the heat input plays a crucial role in producing a defect-free weld metal, it is a serious concern in the FSW of work-hardened non-heat-treatable Al alloys. In this group of alloys, the mechanical properties, including hardness, tensile properties, and fatigue life, are adversely affected by the softening effect because of grain growth and reduced dislocation density. Considering this challenge, work-hardened Al alloys have been limited in their industrial use, which includes aerospace, shipbuilding, automotive, and railway industries. The current comprehensive review presents the various approaches of available studies for improving the quality of FSW joints and expanding their use. First, the optimization of welding parameters, including the tool rotational and traverse speeds, tool design, plunge depth, and the tilt angle is discussed. Second, the incorporation of reinforcement particles and then underwater FSW are stated as other effective strategies to strengthen the joint. Finally, some supplementary techniques containing surface modification, bobbin tool FSW, copper backing, and double-sided FSW in relation to strain-hardened Al alloys are considered.

Investigating the effects of shroud and blade thickness profiles on aeromechanical behavior and fatigue-life of 17-4PH impellers

In the present study, effects of blade and shroud thickness profiles on the stress distribution and fatigue life of centrifugal compressor impellers are investigated. Impeller geometry is generated based on an available data of a single-stage centrifugal compressor and is simulated in actual operating conditions. Pressure distribution on the impeller blades is obtained using Computational Fluid Dynamics (CFD) simulation which is then incorporated into Finite Element (FE) structural analysis. Equivalent stress and total deformation contours on the impeller are employed to pinpoint critical areas and maximum stress values. Simulations are performed for multiple cases with various shroud and blade thickness values to capture the role of these important parameters in aeromechanical behavior of the structure. Furthermore, fatigue stress amplitude limit and fatigue-life are evaluated based on the results of the FE analyses. It will be demonstrated that semi-open configuration is the most desirable design from mechanical stress and fatigue-life viewpoints. For shrouded impellers, it is shown that the mechanical stress increases and fatigue life decreases with increasing the blade thickness while for the shroud thickness, there exist an optimal point with minimum stress level and maximum fatigue life. The methodology and results of this paper can be employed for other impellers with different geometries and operating conditions to find the optimal design points from the structural mechanics perspective.

A Hybrid Deep Generative Network for Pore Morphology Prediction in Metal Additive Manufacturing

AbstractMetal additive manufacturing (AM) has been receiving unprecedented attention for its transformational role in extending the AM materials from polymers to various metals. However, various quality issues, especially porosity, significantly impacts the mechanical properties and fatigue life of the final products, which imposes barriers for the widespread adoption of metal AM processes. In this study, we use the deep learning (DL) techniques to comprehensively investigate the relationships between pore microstructure and processing parameters. Specifically, a novel hybrid deep generative prediction network (HDGPN) that leverages both variational autoencoder and generative adversarial network is proposed to characterize the complex pore microstructure with in-depth representations and predict pore morphology under arbitrary processing parameters. By visualizing the predicted pore morphology, the complicated interaction dynamics between the processing parameters and pore microstructure are directly revealed, which may guide the optimization of metal AM manufacturing processes to fabricate defect-free products. A case study of a selective laser melting (SLM) process is conducted to validate the proposed modeling and prediction framework.

Engineered origami crease perforations for optimal mechanical performance and fatigue life

Perforating crease lines has been widely adopted as a practical method for designing thick engineering origami structures. Perforations inevitably reduce crease stiffness and thus affects the mechanical characteristics and fatigue performance of origami structures. It is therefore important to understand the effect of perforations on the performance of origami creases. The purpose of this study is to propose a perforated crease with desirable folding response and fatigue performance for engineering origami structures. Drawing on the literature on engineering origami, ten perforated creases are proposed, including single- and double-sided slots, oblong holes, elongated holes, moon holes, and barbell holes. Next, finite element analysis is used to assess their folding and unfolding responses, and to predict their fatigue lives combined with FE-SAFE. It is demonstrated that the crease with three rows of oblong holes is the optimal design, which has excellent mechanical characteristics and fatigue performance. A parametric analysis is then carried out to investigate the effect of sheet thickness, hole size, and holes arrangement on the performance of the optimal perforated crease. It is revealed that increasing sheet thickness, hole distance, or row distance exerts a positive effect on reaction forces, while increasing hole length or hole width produces a negative effect. Additionally, the fatigue life is severely reduced as sheet thickness or hole length increases, while it enhances with increasing hole width or hole distance. On the other hand, variations in row distance have an insignificant effect on the fatigue life. The parametric analysis presented in this study can provide guidance for the application of optimal perforated creases to engineering origami structures.

A COMPARATIVE STUDY ON THE FATIGUE STRENGTH AND SERVICE LIFE OF LOWER LIMB ARTERIAL STENT AT DIFFERENT STENOSIS RATES

In order to study the influence of different stenosis rates of blood vessels on the fatigue strength and service life of lower limb arterial stent, numerical simulation was conducted for the mechanical behavior of four types of nickel-titanium alloy lower limb arterial stents (Absolute Pro, Complete SE, E-luminexx-B and Pulsar-35) under the action of radial compression, release and pulsating loads, so as to predict the fatigue life and safety of stents at different stenosis rates (0%, 30%, 50% and 70%). The study found that with increased vascular stenosis rate, both the elastic stress and strain of stent tend to increase, while the fatigue strength, service life and safety tend to decrease. When a stent is implanted in a normal blood vessel, its fatigue strength satisfies the requirement of a 10-year service life requirement, with maximum elastic stress and strain occurring on both sides of the connecting ribs at the end of stent. When the vascular stenosis rate is greater than 30%, the fatigue strength of the stent does not meet requirement of a 10-year service life, and fatigue fracture is likely to occur at the most stenotic part of the blood vessel. With increased vascular stenosis rate, the E-luminexx-B stent with the largest width of support had a significant decrease in its service life. The stent whose supporting unit is of symmetric wave peak structure has a longer service life compared with that whose supporting unit is of offset wave peak structure. The revealing of the influence of vascular stenosis rate on the mechanical properties and fatigue life of stents provides theoretical reference for the fracture failure mechanism of stents.

Effect of Boron on Mechanical Properties and Fatigue Life of Spring Steel for Automobile Suspension

Three Si-killed 55SiCrA suspension spring steels with different boron contents (0, 23 ppm and 43 ppm) were obtained by vacuum induction levitation melting furnace. Through hot tensile, torsional Bauschinger and rotating bending fatigue tests, the microstructure, precipitate, tensile strength, percentage of area reduction, elastic sag resistance and fatigue life of spring steel were analyzed, respectively. Boron accelerated the dynamic recrystallization at 800 ºC and prevented the formation of reticular proeutectoid ferrite and coarse pearlite in steel, then made the tempered troostite of heat-treated spring steel become fine and uniform. However, much BN and boron carbide formed along prior austenite grain boundaries in spring steel containing 43 ppm boron and was retained after quenching and tempering, leading to the decrease of ductility and fatigue life of spring steel. Therefore, 23 ppm boron was the best content for increasing hot ductility and ductility at room temperature of spring steel, and improved its tensile strength and elastic sag resistance, finally, the fatigue life increased from 5.3 × 107 cycles to 8.2 × 107 cycles.

Three-dimensional mechanical properties analysis and fatigue life prediction of G105 drill pipe

Three-dimensional mechanical properties analysis and fatigue life prediction of G105 drill pipe

A Review on Fatigue Mechanisms and Approaches for Hard metals

In this study, fatigue lifemechanisms and approaches for hard metals commonly known as cemented carbides that are supported by literature are reviewed on development of fatigue life technology methods. The hard metals materials are mainly used in engineering systems and failure due to fatigue is common phenomenon in engineering materials.The fatigue crack growth therefore plays very important role towards fatigue failure mechanisms and this remains a setback to engineering fraternity as far as usage of these hard metals are concerned. The fatigue process occurs when a material is subjected to fluctuating stress and strain, this may lead to failure when it accumulates loading due to cumulative damage, multiaxial and variable loading. The Crack initiation growth and micro-mechanisms of damage during fatigue growth with optimization of fatigue life technology approaches and fracture growth resistance are main focus of this review article. Thee review of this paper is based on fatigue life mechanisms adoption methodsfor hard metals with novelty of Crack Tip opening displacement technologyand its implementation in various systems will ought to assist technologists in extraordinary broad programs.In conclusion cumulative damage, fatigue mechanisms, multiaxial amplitude loading and fatigue crack growth mechanics techniques are important andan appropriate fatigue life technology mechanisms methods. Eventually these review article will give potential information on fatigue life technology adoption methods and this helps future researcher and technologists to consider the fatigue life models and these ideas will impact on future application of fatigue life failure mechanisms.

Dynamic stress characteristics and fatigue life analysis of a slanted axial-flow pump

The shaft of the slanted axial-flow pump device is inclined, so, the stress on the impeller is complex, which leads to the prominent problem of structural reliability. In order to study the mechanical characteristics and fatigue life of the slanted axial-flow pump, the stress-strain characteristics and variation law of impeller under different flow rate conditions are analyzed by fluid-structure interaction method, at the same time, the stress-strain characteristics of impellers with geometrically similar and five different structural sizes when nD value is equal are solved, finally, the fatigue analysis of blades is carried out based on Miner’s linear fatigue cumulative damage theory to predict the fatigue life of impellers. The results show that under different flow rate conditions, the maximum equivalent stress of the impeller blade is concentrated at the blade root and gradually attenuates to the blade flange. The maximum deformation of the blade is located at the blade rim and moves from the inlet side to the outlet side with the increase of flow rate. When the nD value is constant, the maximum equivalent stress and maximum deformation displacement of the blade increase with the increase of the impeller size. Under various flow rate conditions, the service life of the impeller reaches 108, and the safety factor of each part of the blade is greater than 15, when operating within the working condition range of 0.8 Qbep∼1.2 Qbep, the impeller can operate continuously for 14 years without fatigue damage.

Study on gear bending fatigue considering gradient characteristics: Numerical analysis and experiments

The bending fatigue of the case hardened gear, one of the essential components used in high-end equipment such as helicopters, wind turbines and automobiles, significantly limited the safety, reliability and service life of such equipment. In this work, we proposed a novel gear bending fatigue model incorporating gradient characteristics of hardness and residual stress based on the continuum damage theory to evaluate the bending fatigue behavior of case hardened wind turbine gear. The damage equations involving the residual stress and hardness gradients and damage coupled constitutive equations are derived. This model is then experimentally validated on the bending stress, bending fatigue failure position, mechanical properties deterioration and bending fatigue life. The evolutions of damage, stress response and mechanical properties are investigated. Results show that the predicted gear bending fatigue lives of different case hardened gears are within the 1.5 scatter factor bond.

Effect of Infill Density in FDM 3D Printing on Low-Cycle Stress of Bamboo-Filled PLA-Based Material.

In this paper, the fatigue behavior of polylactic acid (PLA) material with bamboo filler printed by 3D additive printing using fused deposition modelling (FDM) technology at different infill densities and print nozzle diameters is investigated. The mechanical test results are supported by the findings from SEM image analysis. The fatigue behavior was tested at four consecutive 250 cycles at loads ranging from 5 to 20, 30, 40, and 50% based on the limits found in the static tensile test. The results of the static tensile and low-cycle fatigue tests confirmed significant effects of infill density of 60%, 80%, and 100% on the tensile strength of the tested specimens. In particular, the research results show a significant effect of infill density on the fatigue properties of the tested materials. The influence of cyclic tests resulted in the strengthening of the tested material, and at the same time, its viscoelastic behavior was manifested. SEM analysis of the fracture surface confirmed a good interaction between the PLA matrix and the bamboo-based filler using nozzle diameters of 0.4 and 0.6 mm and infill densities of 60%, 80%, and 100%. Low-cycle testing showed no reductions in the mechanical properties and fatigue lives of the 3D printed samples.