Prolonged Fatigue Life Research Articles

Fatigue behavior of friction stir welded AA6061 alloy using brass insert

Aluminum alloys, broadly used in aerospace and automotive, are particularly susceptible to fatigue failures. The grain refinement characteristics can improve the fatigue behavior of aluminum alloys, which can be achieved using friction stir welding (FSW). The primary aim of this study is to examine how incorporating a brass insert influences the fatigue crack growth behavior of AA6061-T6 alloy welded through FSW, comparing welds with and without the insert. Microstructural analysis showed fine recrystallized grains are obtained for both welds. However, welding with the insert exhibited smaller grains. Moreover, robust intermetallics are formed for welding with insert due to the intermixing reaction at FSW temperature, which improves mechanical properties such as hardness and tensile strength. The findings on fatigue indicate that the fatigue resistance of the weld with insert is significantly high, which can be attributed to the increased grain boundaries and development of strong intermetallic compounds, which hindered the crack propagation. Fractographic analysis of the fracture surfaces indicated the presence of striation marks in the weld with the insert, which slowed crack propagation and prolonged fatigue life. The findings suggest real-world applications in industries, where improving the fatigue life and structural reliability of welded aluminum components is critical.

Deformation and microregion fracture mechanisms in type 316L welded joint under isothermal and thermo-mechanical fatigue loadings

Deformation and microregion fracture mechanisms in type 316L welded joint under isothermal and thermo-mechanical fatigue loadings

Fatigue Life Analysis and Equal Life Optimization Design of Fluid End of Septuple Fracturing Pump

Abstract To determine the cause of failures phenomenon of fatigue cracks in the crossbore area of septuple fracturing pump 4 inch fluid end, optimal design the fluid end based on the idea of equal fatigue life to reduce non-uniformity and prolong fatigue life. Firstly, the static finite element analysis under 14 design conditions and 1 test condition are calculated, the results fulfill the static strength requirements. Next, based on the static of 14 actual working conditions, find cycle peaks through constant amplitude alternating load, the fatigue life and distribution rule were calculated. Then, increase the single side width increment e to 75mm, non-uniformity between 7 cylinders is reduced from 26.6% to 1.35%, the fatigue life is prolonged by 98.2%. Finally, by parameter optimization of the crossbore fillet radius Ru to 15mm and reducing the distance from the central axis of the suction cylinder to the top 25mm, the non-uniformity of the cylinder 4 is reduced from 20.07% to 7.67%, the fatigue life is prolonged by 40.9%, and it is prolonged by 179.4% totally. The results show that the analysis method by finding cycle peaks can accurately calculate the fluid end fatigue life. The equal fatigue life parameter optimization approach has obvious consult significance for reduce non-uniformity and prolong fatigue life of septuple fluid end.

Fatigue Life Estimation under High Temperature and Variable Loading of AA7001-T6 Using Shot Peening

In this study, the fatigue life of aluminum alloys (7001-T6) was predicted with shot peening at various temperatures. Surface treatment with shot peening steel balls is a mechanism for reducing damage. An experimental investigation was conducted to find the degree of fatigue accumulation for AA7001-T6 under rotational bending loading and stress ratio R = −1. The experiments were conducted at RT (25 ℃), 330 ℃, and SP + 330 ℃ temperatures. A modified damage stress model that considers damage at various load levels was recommended for forecasting the fatigue life under high temperatures. The model and experimental results were compared to determine the most damage (Miner’s rule). The experimental results of the fatigue life indicated that the increased testing temperature reduced the fatigue life. However, using shot peening at high temperatures increased the fatigue life by 8% when loading sequence L-H and 10% when loading sequence H-L. The results showed a satisfactory degree of safety for the present model. Nevertheless, Miner’s model featured two models: one for low–high loading and high-low loading. The results were proper for prolonging fatigue life.

Very high cycle fatigue of laser powder bed fused Al-Cu-Mg-Ag-TiB2 (A20X) Alloy: Stress relief and aging treatments

Very high cycle fatigue of laser powder bed fused Al-Cu-Mg-Ag-TiB2 (A20X) Alloy: Stress relief and aging treatments

Development of porous asphalt mixture based on the synthesis of PTEMG and MDI polyurethane asphalt

Development of porous asphalt mixture based on the synthesis of PTEMG and MDI polyurethane asphalt

Experimental investigation on fatigue life and tensile strength of carbon fiber-reinforced PLA composites based on fused deposition modeling

Fused deposition modeling (FDM) is a widely used additive manufacturing (AM) method that offers great flexibility in fabricating complex geometries without requiring expensive equipment. However, compared to other manufacturing methods, FDM-produced parts generally exhibit lower strength and fatigue life. To overcome this limitation, researchers have explored the use of fibers and reinforcements to enhance the mechanical properties of FDM parts. Nevertheless, the performance of FDM-produced parts can be significantly affected by various manufacturing parameters, including infill density, which is a key factor in balancing time and cost. In this study, the tensile strength and fatigue life of carbon fiber-reinforced polylactic acid (PLA) composites produced by FDM were investigated by varying the infill density (50 and 75%) and raster angle (0°, 45°, and 90°). The effects of 100% filling density, raster width, and nozzle diameter on mechanical properties were also examined. The experimental results demonstrated that increasing the infill density and decreasing the raster angle can enhance the tensile strength, although the fatigue behavior was found to be more complex and dependent on the infill density. The optimal parameters for producing FDM parts with improved mechanical properties were identified based on the analysis of the tensile strength and fatigue life data. This research has yielded significant findings concerning the diverse fatigue behavior associated with the raster angle at different infill densities. Specifically, noteworthy observations reveal that a raster angle of 45 degrees at 50% infill density, and a raster angle of 0 degrees at 75% infill density, exhibited the most prolonged fatigue life. This outcome can be ascribed to the specific loading conditions and the inherent strength of the sediment layer at the critical point of stress concentration.

Contribution of overload-induced residual stress to fatigue retardation pertinent to notch geometry

Contribution of overload-induced residual stress to fatigue retardation pertinent to notch geometry

Numerical prediction of warm pre-stressing effects for a steam turbine steel

In warm pre-stressing (WPS), the fracture resistance of cracked steel components is raised when subjected to certain temperature-load histories. WPS’s beneficial effects enhance safety margins and potentially prolong fatigue life. However, understanding and predicting the WPS effects is crucial for employing such benefits. This study utilised pre-cracked compact tension specimens made from steam turbine steel for WPS and baseline fracture toughness testing. Two typical WPS cycles were investigated (L-C-F and L-U-C-F), and an increase in fracture resistance was observed for both cycles. The WPS tests were simulated using finite element analysis to understand its effects and predict the increase in fracture resistance. A local approach was followed based on accumulative plastic strain magnitude ahead of the crack tip. Since cleavage fracture is triggered by active plasticity, the WPS fracture is assumed when accumulated plasticity exceeds the residual plastic zone formed at the crack tip due to the initial pre-load.

High Cycle Fatigue and Very High Cycle Fatigue of Orthorhombic (O + α<sub>2</sub>)-Type Ti–27.5Nb–13Al Alloy with and without B and Fatigue Striation Analysis in Comparison with (α + β)-Type Titanium Alloys

The lightweight and high strength Ti–27.5Al–13Nb intermetallic alloy, based on the orthorhombic Ti2AlNb phase (O phase) and the α2 phase incorporated, was previously developed by the authors. This alloy would seem to have good potential for applications where fatigue behavior is a main concern, such as automobile and aircraft engine parts. The minor addition of boron (B) is known to refine the ingot grain size and thus to improve the subsequent mechanical properties. For these reasons, the high cycle fatigue (HCF) and very high cycle fatigue (VHCF) properties of B-free and 0.1 pct B-modified Ti–27.5Al–13Nb alloy were examined in the present study. HCF tests were performed at room temperature (RT) in tension-tension mode at an R of 0.1 and a frequency of 10 Hz, while VHCF tests were performed using an ultrasonic resonance fatigue test machine at an R of −1 and a frequency of 20 kHz. In both fatigue tests, hourglass-shaped specimens were used. With the addition of 0.1 pct B, the prior B2 grain size of an ingot was reduced drastically, from 600∼1000 µm for the B-free alloy to 100∼250 µm. The 0.1 pct B-modified Ti–27.5Al–13Nb alloy with a duplex microstructure consisting of a globular α2 phase and a lamellar microstructure exhibited superior elongation of 6.1 pct at RT. The HCF curve for this alloy with a duplex microstructure was almost the same as that for a Ti–6Al–4V alloy with a fully lamellar microstructure. Although prolonged fatigue life was previously reported in the HCF region in the 0.1 pct B-modified Ti–6Al–4V alloy, the addition of 0.1 pct B to the Ti–27.5Al–13Nb, Ti–6Al–4V and Ti–4Al–2.5V–1.5Fe alloys had no such effect in the VHCF region. VHCF strength for a lamellar microstructure was ranked in the order of Ti–4Al–2.5V–1.5Fe, Ti–6Al–4V and Ti–27.5Al–13Nb from the highest. Well-defined striations were observed at the propagation stage area of the fatigue fracture surface of B-free Ti–27.5Al–13Nb, and the measured striation spacing kept a constant of 0.29 µm through the propagation distance of 300 µm. The calculation based on this observation showed that the fatigue life spent in the propagation stage was very short and thus almost 100 pct of HCF life was thought to be spent in the fatigue initiation stage. For the B-free Ti–6Al–4V alloy with an equiaxed microstructure, the striation spacing increased from 0.06 µm to 4 µm as the fatigue crack propagated for a distance of 1,000 µm. Calculation based on the striation spacing revealed that, similar to the case with the Ti–27.5Al–13Nb alloy, the fatigue initiation stage consumed almost 100 pct of fatigue life regardless of the B addition.

Experimental investigation on mechanical properties and characterization of steel fibre concrete with Bacillus subtilis

Building cracks spoil the aesthetic view of the structure along with degrading the strength of the structure. It leads to the failure of the structure as a whole. Propagation of cracks in the concrete surface increases the chance of permeability due to moisture content in the atmosphere which might corrode the internal reinforcements. To overcome this situation, a solution in the form of fibre-reinforced self-healing concrete was suggested in this research work. Steel fibre was added by varying 0%,1%,2%,3%,4% and 5% interms of volume of concrete to prolong fatigue life and decrease the crack width under fatigue loading. Bacteria (Bacillus subtilis) are used to heal the cracks by producing calcium carbonate (CaCO3) as a result. Bacterial concrete with fibre (BCF) was cast by M30 mix as per Indian Standard Code. Studied concrete's mechanical and microstructural properties like compression strength test, flexural strength test, split tensile strength test, SEM images, EDS, XRD and FTIR methods. From microstructural studies, it is clear that there is sufficient self-healing material in broken concrete, hence the efficiency of BCF's self-healing property is commendable and the ability of the generated BCF concrete to regain strength.

On Nonlinear First Ply Failure Study of Laminated Composite Thin Skewed Hypar Shell Roofs

The skewed hypar shells have gained immense popularity in practical civil engineering fields due their highly aesthetic look. Light weight laminated composite material has increased its wide acceptance day by day in practical structures by virtue of superior material properties like high strength, high stiffness to weight ratio, prolonged fatigue life etc. Different types of bending as well as free and force vibration studies of laminated composite skewed hypar shells were done by earlier researchers. In some literatures, the first ply failure was also investigated using geometric linear strains only. So, the present paper aims to study the first ply failure behaviour of laminated composite skewed hypar shell roofs considering geometric nonlinearity. An eight noded isoparametric curved finite element having five degrees of freedom at each node is used here for finite element method. To establish the correctness of the present approach different benchmark problems are solved in this paper. Various types of lamina stacking sequences are taken up by the authors’ problems for first ply failure analysis of symmetric and antisymmetric skewed hypar thin shells with practical boundary condition. Along with the maximum stress and maximum strain failure criteria the authors use interactive failure criteria like Hoffman, Tsai-Hill and Tsai-Wu criteria as well as failure mode based criteria like Hashin and Puck criteria for the present study. The results obtained from this numerical investigation are analysed and post processed from different engineering standpoints to extract meaningful conclusions regarding first ply failure behaviour of the composite skewed hypar thin shells and to arrive at important practical guidelines which are expected to be beneficial for practicing civil engineers.

Simulation Analysis with Randomly Distributed Multiple Projectiles and Experimental Study of Shot Peening

Shot peening technology is used to improve the fatigue strength of materials and parts, and is one of the most effective surface engineering techniques to prolong fatigue life. In this paper, according to the finite element simulation analysis of shot peening, a randomly distributed multiple-shot finite element model was established. The superimposed effects of multiple projectile impact craters in shot peening are fully considered. The effects of shot velocity, shot peening angle and shot coverage on the residual stress field and surface roughness were studied. The alloy steel 20MnTiB, widely used in the automotive industry, was used as the raw material to process the specimens. The shot peening tests of different process parameters were carried out. The test results verified the correctness and accuracy of the random distribution model of multiple-shot. The shot-peening simulation model proposed in this paper allows a more accurate analysis of the effect of shot-peening parameters on the surface residual stress field and helps to quickly set the correct shot-peening process parameters. This paper further investigates the effect of shot peening parameters on fatigue life, providing a basis for the rational development of shot peening solutions.

Prolonged fatigue life in aluminum clad steel by electropulsing treatment: Retardation of interface-microcrack formation

• Back stress strengthening increased the mechanical properties of the ACS. • Cracks initiate at Al grains near interface due to preferred pile-up of the GNDs. • Fatigue life of the ACS was significantly prolonged by electropulsing treatment. • Damage recovery is due to diminished GNDs and retarded microcrack formation. The prolonged fatigue life of aluminum clad steel (Al clad steel, ACS) using electropulsing treatment is systematically investigated by characterizing the microstructural change at different fatigue cycles. The microstructural changes associated with fatigue damage evolution show that cracks are prone to initiate at Al grains of the interface and propagate toward the Al side in the fatigue test due to a preferred accumulation of geometrically necessary dislocations (GNDs) in the soft Al grains near the interface. The electropulsing treatment with a subsecond duration is proved to be efficient in healing the fatigue damage and significantly prolonging the fatigue life of the ACS. The increased fatigue life by electropulsing treatment is attributed to the diminished density of piled GNDs and the retardation of microcrack formation at the interface. The present study elucidates the failure mechanism of ACS and proves that electropulsing treatment is an efficient method to prolong the fatigue life of laminated metal composites by healing the accumulated damage during the fatigue test.

Low cycle fatigue behavior of near-alpha titanium alloys used in deep-driving submersible: Ti-6Al-3 Nb-2Zr-1Mo vs. Ti-6Al-4 V ELI

The low cycle fatigue (LCF) of Ti-6Al-3Nb-2Zr-1Mo and Ti-6Al-4V ELI with a bimodal structure were compared at different total strain amplitudes ( ∆ ε t / 2 ) from 0.5% to 1.0%. Because the Ti-6Al-3Nb-2Zr-1Mo exhibited a higher tensile elongation, but a lower yield strength than Ti-6Al-4V ELI, it displayed a slightly longer fatigue life than Ti-6Al-4V ELI when ∆ ε t / 2 was larger than 0.7% (plastic deformation predominated), while its fatigue life became shorter when ∆ ε t / 2 was less than 0.7% (elastic deformation predominated). Both Ti-6Al-3Nb-2Zr-1Mo and Ti-6Al-4V ELI showed a continuous cyclic softening behavior due to the rearrangement or mutual annihilation of initial dislocations during cyclic deformation, and the variation of cyclic softening rate depended on ∆ ε t / 2 was consistent with the variation of fatigue life depended on ∆ ε t / 2 . In cyclic deformation, the prismatic and basal slips were easier to activate, and the dislocation bands were denser and more homogeneous in the Ti-6Al-3Nb-2Zr-1Mo than that in the Ti-6Al-4V ELI due to the actual Al content in former was smaller than that in latter, which was beneficial to reduce local stress concentration and prolong fatigue life. • The LCF properties of Ti-6Al-3Nb-2Zr-1Mo and Ti-6Al-4V ELI depend on ∆ ε t / 2 , when ∆ ε t / 2 is larger than 0.7%, the former fatigue life is slightly longer than the latter. However, when ∆ ε t / 2 is less than 0.7%, the former fatigue life becomes shorter than the latter. • The work provided data for the material selection of the pressure hull of deep-diving submersibles.

Mechanism for superior fatigue performance of warm laser shock peened IN718 superalloy after high-temperature ageing

The high cycle fatigue properties of IN718 alloy treated by warm laser shock processing (WLSP) were studied after high-temperature ageing at both room temperature and 600 ℃. The strengthening and toughening mechanism of WLSP on the hardened surface layer of IN718 alloy was elucidated to reveal the highly stable strengthening effects at high temperature. It was found that the thermally assisted surface hardening techniques had more obvious advantages in maintaining fatigue resistance and prolonging fatigue life of the alloy with the hardened surface layer during long-term service at elevated temperature, comparing with the conventional laser shock peening (LSP). After WLSP treatment, complex structures of γ″ phase/high-density dislocation with stacking faults (SFs) and nano-sized twins in γ″ phases surrounded by the more stable and higher density of geometrically necessary dislocations (GNDs), formed in the hardened surface layer. Therefore, a remarkable strengthening effect in the hardened surface layer was achieved due to the production of more stable hetero-deformation induced (HDI) stress. Meanwhile, the substructure evolution, compressive residual stress reduction and γ″ phase growth in the hardened layer of WLSP alloy were also inhibited during high-temperature ageing, owing to the existence of the special structure, contributing stability of microstructure and strengthening effect under conditions of high-temperature ageing and subsequent cyclic loading at high temperature. Thus, both the fatigue crack initiation resistance and initiation time of WLSP alloy can be improved in the surface of specimen. This is the main reason why after high-temperature ageing the fatigue resistance of WLSP sample can be kept stably and the median fatigue strength can be improved at both room temperature and 600 ℃. • The mechanism of WLSP alloy with excellent properties stability at high temperature was studied. • Fatigue resistance was retained to a large degree for WLSP alloy after long term ageing. • Complex structure of γ″ phase/high-density dislocation with stack faults and nano-twins in γ″ phases were observed. • WLSP provided the hardened layer with high GND density and strong HDI strengthening effect. • The complex structure contributed to the good stability of microstructures and properties.

Duplex treatment of arc plasma nitriding and PVD TiN coating applied to dental implant screws

In modern dentistry, surface modification technology is critical for the long-term service of dental implants. The purpose of this study was to evaluate the effects of the duplex treatment of arc plasma nitriding and TiN coating on the mechanical behavior of implant systems. The Ti6Al4V screws of dental implants were treated by physical vapor deposition (PVD), arc plasma nitriding (APN), and arc plasma nitriding-physical vapor deposition (APN-PVD). The surface characteristics , loosening properties, and fatigue performance of different treated screws were analyzed. The results showed that APN-PVD duplex treatment produced a gradient surface structure, reduced the surface roughness , and improved the TiN coating adhesion. Compared with the PVD-treated screws alone, APN-PVD-treated screws improved anti-loosening performance, reduced surface wear, and prolonged fatigue life . Duplex treatment by arc plasma nitriding and TiN coating may be a method suitable for dental applications. • APN-PVD duplex treatment method was applied to dental implant screws. • APN-PVD with a gradient composite layer reduced the surface roughness and improved the TiN coating adhesion. • APN-PVD improved the anti-loosening performance of the screw and the wear resistance of the screw. • APN-PVD prolonged the fatigue life of implant systems.

Fatigue properties of plasma nitriding for dental implant application

Fatigue failure of implant components is a common clinical problem. Plasma nitriding, an in situ surface-strengthening method, may improve fatigue properties of dental implants. The purpose of this invitro study was to evaluate the effect of plasma nitriding on the fatigue behavior of implant systems. The preload and friction coefficient of plasma nitrided abutment screws, as well as settlement of the implant-abutment interface, were measured. Then, the reverse torque values and pullout force were evaluated after cyclic loading. Finally, the fatigue properties of the implant system were investigated with static fracture and dynamic fatigue life tests, and the morphology of the fracture on the surface of the implant system was observed. The plasma nitriding treatment reduced the friction coefficient; increased the preload, settlement value, reverse torque values, pullout force, and static fracture load; and prolonged fatigue life. Furthermore, abutment screws with plasma nitriding treatment showed a different fatigue fracture mode. Plasma nitriding improved mechanical performance and may be a suitable way to optimize the fatigue behavior of dental implants.

Effect of central screw taper angles on the loosening performance and fatigue characteristics of dental implants

Biomechanical performance plays an important role in the long-term service of dental implants. Loosening and fatigue damage of the central screw are the most common problems. This research investigated the effect of the central screw taper angle on the loosening performance and fatigue characteristics of dental implants. Central screws with four taper angles, 30°, 60°, 90° and 180°, were processed and tested. The loosening performance of the screws under initial and postload conditions was compared. Then, the fatigue characteristics of dental implants was measured. Finally, the wear and fracture modes of the screws were observed. The damage locations were verified by finite element analysis (FEA). The results showed that the central screws with 30° taper had substantially better anti-loosening performance and less fretting wear. The central screws with 180° taper had a higher preload, resulting in a longer fatigue life. Furthermore, the fatigue fracture of the central screw occurred at the level of the first thread position, consistent with the FEA results. In the future clinical applications, central screws with a 30° taper angle may improve anti-loosening performance and prolong fatigue life by increasing the tightening torque.

Effect of stress-relief annealing on isothermal fatigue life of a new hot stamping die steel 4Cr2Mo2V

For 4Cr2Mo2V hot stamping die steel, the isothermal fatigue test was suspended at different cycles, and the stress-relief annealing was carried out in situ. After annealing, the fatigue tests were continued. The stress-relief annealing was carried out at 30%, 50% and 70% of the cycle life when the total strain amplitude was 0.5%, and the fatigue life was increased by 30.27%, 23.84% and 10.24% respectively. On the basis of Basquin-Coffin-Manson life prediction model, by adding the influence of stress-relief annealing on life, obtained the stress-relief annealing life prediction model. The dislocation density, microstructure and pole figure were analyzed by TEM and XRD to explore the mechanism of stress-relief annealing on prolonging fatigue life. After stress-relief annealing, the full width at half maximum (FWHM) decreased, and the dislocations originally piled up at the grain boundary moved into the grain, delayed the time of dislocation cell or wall formation. At the same time, it could also eliminate the trend of consistent orientation of most grains in the fatigue process. This is the main reason why stress-relief annealing prolongs fatigue life.