Superior Fatigue Life Research Articles

Biomechanical Comparison of Three Locking Compression Plate Constructs from Three Manufacturers under Cyclic Torsional Loading in a Fracture Gap Model.

The aim of the study was to compare the stiffness and cyclic fatigue of locking compression plate constructs from three manufacturers, DePuy Synthes (DPS), Knight Benedikt (KB), and Provet Veterinary Instrumentation (Vi), under cyclic torsion. The constructs of DPS, KB, and Vi were assembled by fixing a 10-hole 3.5-mm stainless steel locking compression plate 1 mm away from a validated bone model with a fracture gap of 47 mm. The corresponding drill guides and locking screws were used. Three groups of six constructs were tested in cyclic torsion until failure. There was no significant difference in initial stiffness between DPS constructs (28.83 ± 0.84 N·m/rad) and KB constructs (28.38 ± 0.81 N·m/rad), and between KB constructs and Vi constructs (27.48 ± 0.37 N·m/rad), but the DPS constructs were significantly stiffer than the Vi constructs. The DPS constructs sustained the significantly highest number of cycles (24,833 ± 2,317 cycles) compared with KB constructs (16,167 ± 1,472 cycles) and Vi constructs (19,833 ± 4,792 cycles), but the difference between KB and Vi constructs was not significant. All constructs failed by screw damage at the shaft between the plate and the bone model. DPS constructs showed superior initial torsional stiffness and cyclic fatigue life than Vi constructs, whereas KB and Vi constructs shared comparable results. Further investigation is required to assess the clinical significance of these biomechanical differences.

Investigation of the Impacts of Solder Alloy Composition and Temperature Profile on Fatigue Life of Ball Grid Array Solder Joints Under Accelerated Thermal Cycling

Abstract This study investigated the thermal fatigue reliability of ball grid array (BGA) solder joints under accelerated thermal cycling, considering the impacts of solder alloy and temperature profile. Applying the Darveaux solder joint reliability assessment, simulations consider lead-based (63Sn37Pb and 62Sn36Pb2Ag) and lead-free (SAC105, SAC305, and SAC405) solder alloys under temperature profiles: 0°C (Tmin) to 100°C (Tmax), −40°C to 85 °C, −40 °C to 125 °C, and −40 °C to 150 °C. Results indicate that SAC305 exhibited the highest equivalent stress, while 63Sn37Pb demonstrated the highest plastic strain and creep strain energy density. SAC105 displayed the lowest stress and strain parameters. Moreover, increasing the thermal cycling temperature range intensifies stress, strain, and damage parameters, with −40 °C to 150 °C showing the highest magnitudes. SAC405 exhibited superior thermal fatigue life compared to other alloys, with its cycles to failure outperforming 63Sn37Pb, SAC105, 63Sn36Pb2Ag, and SAC305 by 16832, 11992, 6218, and 3601 cycles, respectively. Lower temperature ranges enhance thermal fatigue life, with 0 °C to 100 °C recording 8%, 33%, and 53% higher life than −40 °C to 85 °C, −40 °C to 125 °C, and −40 °C to 150 °C, respectively. Notably, higher silver content and lower temperature ranges were associated with increased thermal fatigue life, providing valuable insights for BGA solder joint reliability enhancement.

Fatigue behavior of polymethyl methacrylate/acrylonitrile butadiene styrene blends including blend composition, stress ratio, frequency, and holding pressure effects

In engineering applications, polymer materials are expected to exhibit superior fatigue life and balanced mechanical properties as essential performance criteria. The blending method is an important alternative in improving the performance criteria of ABS polymer in service. Thermogravimetric Analysis (TGA), Differential Scanning Calorimetry (DSC), Fourier Transform Infrared Spectroscopy (FTIR), and Dynamic Mechanical Analysis (DMA) methods were used for characterization. The effects of the PMMA fraction on the mechanical and fatigue behavior of PMMA/ABS blends were investigated by tensile and fatigue tests. Also, the influence of blend composition, stress amplitudes, stress ratio, holding pressure, and loading frequency on fatigue life is considered. The study improved yield strength, tensile strength, and elongation at break values of blends compared to ABS. In addition, 115 % and 75 % improvements were achieved in fatigue cycles at high and low-stress amplitudes with blends, respectively, for tension/tension loading. Similar improvements were obtained for fully reverse loading at 218 %. Thus, it was determined that the PMMA/ABS blend exhibited superior fatigue life in both tension/tension and fully reverse loading situations. Finally, it has been understood that PMMA/ABS blends can be designed to have mechanical properties and fatigue life behavior that can meet different requirements in conditions for engineering applications.

Comparison of fatigue life behavior between 4-point and uniaxial loading for L-PBF Ti–6Al–4V after HIP treatments

The present study investigated the effects of Hot Isostatic Pressing (HIP) on the fatigue performance of Laser Powder Bed Fusion (L-PBF) Ti–6Al–4V alloy under both 4-point bending and uniaxial testing. Three HIP-cycles were examined: standard, low temperature/high pressure (LTHP), and super beta. Moreover, an annealed heat treatment group was incorporated to compare against the HIP groups. The material microstructure was analyzed and compared across the heat treatments during the study, which showed the presence of α′ martensites, α+β Widmanstätten, and coarse equiaxed grains. Similarly, tensile and hardness testing were implemented to study the mechanical properties, where due to the effects of the HIP treatments, higher ductility but lower hardness values were recorded. Furthermore, fracture morphologies and stress-life (cycles-to-failure) (S–N) curves of the Ti–6Al–4V specimens concerning the fatigue behavior were analyzed. The HIP treatment groups behaved similarly during 4-point bending and uniaxial testing, with the LTHP obtaining a superior fatigue life behavior, followed by the standard and super beta HIP groups. In addition, the efficacy of HIP to reduce pores showed better results in the 4-point bending specimens, leading to few defects as fatigue initiators in contrast to the uniaxial specimens. Fractography results suggested that defects and microstructural features acting as fatigue crack initiators (FCI) govern the fracture behavior of uniaxial specimens. In contrast, only the presence of microstructural features controls the 4-point bending failure behavior.

Analysis of Environmental Impact and Mechanical Properties of Inconel 625 Produced Using Wire Arc Additive Manufacturing

Inconel 625 is a nickel-based superalloy widely used in industries such as energy, space, and defence, due to its strength and corrosion resistance. It is traditionally time- and resource-intensive to machine, leading to increased environmental impact and material waste. Using additive manufacturing (AM) technology enables a reduction in resource consumption during the manufacture of high value components, as material is only deposited where it is required. This study compares the environmental impact of manufacturing an Inconel 625 impeller through machining and wire arc additive manufacturing (WAAM) by employing established life cycle assessment methods. WAAM shows significant advantages, cutting energy consumption threefold and reducing material waste from 85% to 35%. The current work also evaluates the mechanical properties of WAAM-produced components through tensile and axial fatigue testing, in addition to the use of optical and electron microscopy for metallurgical analysis and fractography. This demonstrates yield and ultimate tensile strengths exceeding industrial standards, with comparable or superior fatigue life to other AM methods. The improved fatigue performance extends the service life of components, bolstering sustainability by reducing the need for frequent replacements, thereby lessening associated environmental impacts. These findings underscore the promise of WAAM in enhancing both environmental sustainability and mechanical performance in manufacturing Inconel 625 components.

Full scale testing of fatigue resistant composite joints for offshore wind Jacket and Floating structures

Complex welds in the joint region reduce the fatigue resistance of structural joints of circular hollow sections with factors that results in increased wall thicknesses of the tubes and overspending of steel in the multi-membered part of the jacket and floating support structures for offshore wind turbines. The wrapped composite joint is a breakthrough technology utilising bonding and fatigue resistant composite material to connect steel tubular members instead of welding. The main technical advantage is that the superior fatigue life of wrapped composite joints. Full-scale wrapped composite joint is tested by cyclic out-of-plane bending loading in resonance-based Cronos testing rig at OCAS N.V. in Belgium. Results reveal exceptional fatigue life of wrapped joints to combined loading when compared to welded joints, showcasing a potential that can radically reduce steel use for offshore structures.

Comparative fatigue analysis of wrought and laser powder bed fused Ti-6Al-4V for aerospace repairs: Academic and industrial insights

Additive manufacturing (AM) holds great promise for delivering benefits in repair of aerospace components. To fully exploit the benefits of AM, it is crucial to demonstrate that AM-produced components satisfy the performance criteria specified by the aerospace industry relative to conventional wrought material. This research assesses the performance of laser-powder bed fused (L-PBF) and wrought Ti-6Al-4V coupons following the aerospace method of manufacture (MoM), which ensures that the material undergoes both surface and sub-surface enhancement to meet fatigue requirements. The results reveal that the aerospace MoM-treated L-PBF Ti-6Al-4V coupons exhibit superior fatigue life compared to their wrought counterparts. Furthermore, it is understood that the vibratory polishing process retains the beneficial compressive residual stress from shot peening, while simultaneously enhancing the surface finish and fatigue life. Finally, a life-cycle cost model assessment highlights that the L-PBF coupons have superior fatigue life and are cost-effective particularly for low-volume repairs, while the use of wrought material is economical for large-volume repair but may compromise fatigue life.

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.

Effect of In-trough and Out-of-trough fixturing in vibro-polishing

Advanced compressor design with superior aerodynamic and fatigue life performance demands superior surface quality, typically Ra≤0.25 µm. Vibro-polishing is media finishing technology which is commonly employed to mass finish aerospace engine components such as blisks. Frequency of vibration, location, and orientation of workpiece, media size, lubrication etc. are known tuneable knobs to optimize the performance of Vibro-polishing. However, longer cycle times in vibro-polishing still pose a challenge. In this study, effect of In-trough (IT) and Out of trough (OOT) fixturing at various depths of immersion into the media is studied. Workpiece used was made of Ti-6Al-4V with a geometry representative of a blisk blade. OOT fixturing was observed to yield better surface quality than IT fixturing irrespective of the depth of immersion. Further, a very low Ra of about 0.10 µm was achieved with 1 h of processing at highest depth of immersion into the media in OOT fixturing, resulting in significant reduction in cycle time to reach aerospace component surface roughness of Ra≤0.25 µm. Further, uniform vibro-polished surface topography with no alterations in the as received microstructure was observed in both IT and OOT fixturing.

Tailoring microstructure with special bimodal structure to improve the ductility and fatigue life of laser powder bed fused Ti6Al4V alloy

Achieving the high strength and ductility, as well as the excellent fatigue life, was the primary consideration for aerospace application of the additively manufactured (AM) titanium alloys, but it was limited to the high residual stress, huge columnar β grains arising from the severe directional heat flow and temperature gradient. To address these challenges and then improve the comprehensive mechanical properties, this work newly designed heat treatment schedules to tailor the microstructure to improve tensile/fatigue properties in the laser-powder bed fusion (L-PBF) of Ti6Al4V. The optimized schedule (920 °C/1 h/water cooling + 800 °C/2 h/furnace cooling) obtained the special bimodal structure, including the thin lamellar α+β phases (thickness of 1.8 μm) and the discontinuous equiaxed grain boundary α phases (GB-α) (diameter in ∼6 μm), achieving the good combination of tensile strength (1025 MPa) and ductility (17.2%). The heated-treated Ti6Al4V parts with thickness of 2∼10 mm exhibited the good stability of strength and eliminated the strength anisotropy. The dimensional effect of specimen resulted in the significant discrepancy in ductility. The tailored Ti6Al4V exhibited the superior low-cycle fatigue life equivalent to the wrought counterpart due to the refined α phases, whereas presenting the relatively low stability in the high cycle fatigue life. The fracture morphology showed the crack initiation and propagation resulting from the aligned pores and uncontrollable defects.

Enhanced cyclic stability and enlarged working temperature window of NiFeGa elastocaloric refrigerant via introducing strong texture and ductile interfacial precipitate

The poor mechanical properties will result in low fatigue life and limited working temperature window of elastocaloric effect (eCE) for ferromagnetic shape memory alloys with lower critical stress. In this work, a microstructure design strategy, i.e., simultaneously introducing strong texture and ductile interfacial γ-phase, was adopted to reduce the strain discontinuity near the grain boundary and enhance the grain boundary cohesion, further improving the mechanical properties and eCE performance. With this strategy, the compressive strength and strain of the prototype Ni54Fe19Ga27 alloy can exceed 1.5 GPa and 30.0% at room temperature, respectively. Furthermore, a wide working temperature window of 120 K with an adiabatic temperature change of −8.5 to −1.2 K and superior eCE fatigue life of 2 × 104 cycles with an adiabatic temperature change of ∼3 K have been achieved. This work is expected to provide an effective strategy to enhance the eCE performance of ferromagnetic shape memory alloys.

High cycle fatigue behaviour of Invar 36 alloy fabricated by laser powder bed fusion

ABSTRACT The Invar 36 alloy was additively manufactured by laser powder bed fusion (PBF-LB), and systematical observations and experiments for microstructure, defects, metallography, especially high cycle fatigue behaviour and fractography were conducted. Inadequate laser energy density results in hardly overlapping melting traces, generating numerous defects. Accordingly, the fabricated Invar 36 alloy presents an inferior high cycle fatigue life, as it failures from the rapid aggregation of the defects. In contrast, an adequate laser energy density remarkably enlarges the overlapping between adjacent melting traces. The large molten pools with steady boundaries are beneficially to generate favourable microstructures and low porosity. Consequently, the Invar 36 alloy shows superior high cycle fatigue life, completely generated from small crack propagation, long crack propagation and final fracture stages. Above experimental results and analysis primarily link up the PBF-LB process, microstructures (defects) and high cycle fatigue performance for PBF-LB Invar 36 alloy.

Fatigue Repair of Cracked Steel Plates Using Small-Patch Ultrahigh-Modulus CFRP Governed by Bond Failure

This study evaluates the effectiveness of externally bonded small-patch ultrahigh-modulus (UHM) carbon fiber–reinforced polymer (CFRP) plates of 460 GPa modulus in extending fatigue life and slowing crack propagation in steel plates with simulated fatigue cracks. The study investigates a range of very short bond lengths for applications where bonding space may be limited or accessibility restricted, together with the effect of single- versus double-sided application, on fatigue performance. It also compares short UHM CFRP plates with similar length normal modulus (NM) (165 GPa) CFRP plates with regard to extending fatigue life and reducing stress concentration at the crack tip. Distributed fiber-optic sensors (DFOS) and digital-image correlation (DIC) are used to capture the full strain field and track crack growth. Results showed that fatigue life was increased by up to 2.0 and 2.34 times for single- and double-sided UHM CFRP repairs. As bond length increased from 25 to 100 mm, fatigue life increased from 1.36 to 2.0. UHM CFRP more effectively reduced stress concentration at the crack tip, by 60% compared with 37% for NM CFRP, indicating that it has the potential for superior fatigue life gains, relative to NM CFRP if the necessary bond length to prevent or delay debonding is provided. As debonding failure governed in this study, NM CFRP plates achieved comparable fatigue life extension. DIC tracking of crack growth matched the traditional “beach marking” technique with less than 6% difference.

Correlation of residual stress, hardness and surface roughness with crack initiation and fatigue strength of surface treated additive manufactured AlSi10Mg: Experimental and machine learning approaches

Post-processing methods are widely used to address the issues caused by surface imperfections and bulk defects in additive manufactured materials. In our previous studies, we analysed the effects of different peening-based treatments of shot peening (SP), severe vibratory peening (SVP) and laser shock peening (LSP) on fatigue performance of V-notched laser powder bed fusion AlSi1Mg samples. Herein, the fracture surfaces of failed samples were further analyzed and obtained experimental data were further elaborated by machine learning (ML)-based approach to identify the correlation between residual stress, hardness and surface roughness (all affected by the applied post-treatments) with the depth of crack initiation site and fatigue life of the post-treated samples. ML-based model was developed via a six layer deep neural network (DNN) as well as using stacked auto-encoder (SAE) for pre-training of the used data set. Taking the advantages of SAE, the accuracies of more than 0.96 were obtained for the predicted results. Correlations were obtained by performing parametric analyses and the importance of each input factor was assessed through sensitivity analyses. The obtained results revealed that by enhancing surface hardening and inducing higher compressive residual stresses as well as more efficient surface roughness reduction, deeper crack initiation site and superior fatigue life can be obtained. In addition, it was found that the depth of sub-surface crack initiation had direct relation with fatigue life improvement in the samples.

Effect of the microstructure of suspension plasma-sprayed thermal barrier coatings on their thermal cycling damage

The suspension plasma spray (SPS) technique has recently attracted attention due to the variety of microstructures achievable using submicron spray particles mixed with a solvent to form a suspension. Thermal barrier coatings (TBCs) with a columnar microstructure can be obtained using SPS. Because of its unique columnar microstructure achieving high strain tolerance, a top coat sprayed using this technique can efficiently suppress thermal cycling damage in SPS–TBCs. However, there are few reports on the effect of microstructure on the damage behavior of SPS–TBCs with a columnar structure. In this study, the effect of the top coat microstructure on the thermal cycling fatigue of SPS–TBCs was investigated. The size of the complex oxide formed on the top coat–bond coat interface and the length of the cracks at the interface (formed as a result of thermal cycling) increase with the column diameter in the top coat of SPS–TBCs. The thermal spray conditions affect the thermal cycling fatigue life of SPS–TBCs. The SPS–TBC with fine columnar structure exhibits superior thermal cycling fatigue life.

Low‐cycle fatigue characteristics and fracture behavior of the die‐forged 2014 aircraft wheel

AbstractIn order to provide a sufficient theoretical basis for the fatigue‐resistant design of the aircraft wheels, strain‐controlled low‐cycle fatigue (LCF) tests were carried out on specimens machined in the extrusion direction (ED) and transverse direction (TD) of die‐forged 2014 aluminum alloy wheels. Although the TD specimens have lower tensile strength and yield strength, the fatigue test results show that the TD specimens have superior fatigue life compared with the ED specimens at total strain amplitudes of 0.5–0.8%. This is predominantly caused by the coarse Al12(MnSi)2(FeCu) intermetallic particles close to the surface layer, which results in a relatively short crack initiation stage for the ED specimens. In contrast, TD specimens with finer and more uniform recrystallized grains exhibit more excellent resistance to fatigue crack initiation (FCI) and propagation (FCP). Moreover, the fatigue life of alloys could be accurately predicted via a Manson–Coffin–Basquin (MCB) model based on total strain.

Origin of superior low-cycle fatigue resistance of an interstitial metastable high-entropy alloy

In this study, the deformation behaviors and related microstructural evolutions were investigated in either monotonic or cyclic deformation modes in an interstitial metastable high-entropy alloy. These investigations aimed to reveal the mechanisms underlying the superior low-cycle fatigue (LCF) life of this alloy. A thermomechanical process was applied to induce fine-grained (FG) and coarse-grained (CG) microstructures in Fe–30Mn–10Co–10Cr–0.4C (atomic percentage) alloy. Their superior combination of strength and ductility was attributed to the appearance of deformation-induced ε-martensite and the presence of carbon. The CG alloy showed a greater volume fraction of ε-martensite than the FG alloy in the monotonic deformation mode, and vice versa in the cyclic mode. Such a disparity was interpreted in light of the back-stress effect of the relaxed γ-grain boundaries in the latter mode. Meanwhile, the γ-to-ε phase transformation under cyclic loading at low strain amplitudes (0.4%) barely led to an improved fatigue life as compared with that at higher strain amplitudes (≥ 0.55%). The high reversibility of partial dislocation motions under cyclic loading and delaying the formation of dislocation cells through the martensitic transformation could explain why the alloys investigated in this study exhibited a superior LCF life compared with high-entropy alloys reported in previous studies.

Experimental investigation of the shear behaviour of concrete beams with CFRP strip stirrups under static and fatigue loading

Existing reinforced concrete (RC) structures often decrease in safety and service life owing to reinforcement corrosion or fatigue. Therefore, there are urgent requirements to propose new structures for engineering applications. This study investigates the static and fatigue shear behaviours of concrete beams using carbon fibre reinforced polymer (CFRP) strips instead of steel stirrups. The study mainly conducted the shear tests on nine statically loaded beams and six cyclically loaded beams with varied shear span ratios (a /d = 1.0, 2.5 and 3.5) and configurations of CFRP strip stirrups. The results reveal that concrete beams with CFRP strip stirrups have similar static shear behaviour to RC beams. Nevertheless, the CFRP strip stirrup beams exhibit superior fatigue life compared to that of RC beams, which significantly restrain the development of deflection, concrete cracks, and stirrup strain. Using CFRP strip stirrups instead of steel stirrups can effectively improve the shear resistance of the concrete beams under static and fatigue loading.

Cyclic deformation behavior and fatigue life modeling of CNT-reinforced heterogeneous aluminum-based nanocomposite

Heterogeneous materials are regarded as an emerging class of structural materials with superior balanced performance relative to the conventional unimodal counterparts. In the present study, the cyclic deformation behavior of carbon nanotube (CNT)-reinforced 2009Al nanocomposite with a bimodal-grain structure was studied via strain-controlled fatigue tests. Both bimodal-grained base alloy and nanocomposite exhibited basically cyclic stabilization during cyclic deformation. A higher cyclic stress level was observed to sustain by the nanocomposite at all strain amplitudes applied, along with a superior fatigue life at lower strain amplitudes due to its higher monotonic strength. However, at higher strain amplitudes, the base alloy exhibited better fatigue properties because of its higher ductility. A strain-energy density based approach integrated with accumulative damage process was used to predict fatigue life via a modified method for the evaluation of intrinsic fatigue toughness, which is defined as the sum of all hysteresis loop areas from the first cycle to the number of cycles to failure. The application of the proposed method for the intrinsic fatigue toughness was observed to give a better fatigue life prediction.

Moisture susceptibility and fatigue performance of asphalt binder modified by bone glue and coal fly ash

The main purpose of incorporating waste into asphalt binder is due to their excellent properties and low cost as binder modifiers, in contrast to the impracticability of typical binder in the current flexible asphalt pavement by the increase of heavy traffic loads and volumes. The focus of this study is to use coal fly ash (CFA) with bone glue modified asphalt to check the effect of coal fly ash (CFA) towards fatigue resistance and moisture sensitivity. This study combined 60/70 penetration grade binder with optimum percentage of bone glue (10%) and 2%, 4%, 6% and 8% of fly ash. After conducting consistency tests and some mixture tests, it is concluded that fly ash gives superior fatigue life to flexible asphalt pavement and the effect towards moisture sensitivity is slightly good.