Search

This study focuses on the creation of high degree biocomposite with the utilization of renewable resources, including cardanol oil, palm kernel fiber and chitosan biopolymer. The principal aim of this research was to achieve high degree ratio of biocomposite for safe and eco-friendly application. The chitosan biopolymer was extracted from marine waste sea urchin spikes via deproteination. The biocomposites were prepared via hand layup technique following testing via ASTM standards. According to results, among the composites fabricated, PC5 exhibits exceptional mechanical strength with tensile strength of 88.2 MPa, flexural strength of 133.35 MPa and impact energy of 3.92 J. Therefore, PC6 composite performs better wear resistance with reduced coefficient of friction of 0.399 and Sp. wear rate of 0.01 mm3/Nm, respectively. And also, PC6 provides good thermal resistance with initial decomposition temperature of 345 °C. Similar to mechanical properties, in fatigue behavior also PC5 exhibits high fatigue life cycle counts with 19,647 for 25% UTS, 18,799 for 50% UTS and 17,571 for 75% UTS. The obtained results show that the inclusion of palm kernel fiber and chitosan significantly enhances the mechanical properties, wear and thermal resistance of the composites, while the cardinal oil binder ensures proper adhesion. However, thermal aging conditions were implemented to assess the material's ability to withstand harsh environmental factors. Notably, among the composite materials tested, the designations with chitin (such as PC4, PC5, and PC6) exhibited lesser susceptibility to the effects of thermal aging. This resilience is attributed to the presence of NH2 functional groups within chitin, which play a role in reducing the impact of thermal aging. These discoveries highlight the promising qualities of the developed polyester biocomposites, suggesting their suitability for a wide array of industrial applications requiring materials capable of enduring high-temperature environments such as automotive door panels, structural, space, defense and sports applications. [ABSTRACT FROM AUTHOR]

The notch effect significantly influences the fatigue response of components and is particularly relevant for parts produced with additive manufacturing (AM) processes, characterized by complex geometries and possible geometric discontinuities inducing local and critical peak stresses. Moreover, the low surface quality, as well as manufacturing defects and residual stresses, interacts with the local peak stress induced by geometric discontinuities, complicating the assessment of the notch effect for AM parts and requiring extensive experimental fatigue investigations. In the present paper, the notch sensitivity of as‐built AlSi10Mg specimens produced with the laser beam powder bed fusion in the Very High Cycle Fatigue regime is investigated. Ultrasonic fatigue tests up to 109 cycles have been carried out on rectangular bars and rectangular bars with a central through‐thickness hole. The notch effect has been found to significantly affect the fatigue response of the investigated AlSi10Mg specimens, with surface defects having a main role and pointing out the influence of the surface quality on the crack formation. Highlights: Notch sensitivity on the very high cycle fatigue (VHCF) response of AlSi10Mg specimens is investigated.The AlSi10Mg VHCF fatigue response is strongly influenced by the notch.The experimental fatigue notch factor is close to that computed with literature models.Experimental tests are recommended to account for the large experimental scatter. [ABSTRACT FROM AUTHOR]

ABSTRACT A combined high and low cycle fatigue (CCF) life prediction model, considering creep, low‐cycle fatigue (LCF), high‐cycle fatigue (HCF) at the maximum LCF nominal stress (HLCF) damages, and the interaction damage between LCF and HLCF, is proposed. The proportions for these four types of damage in total CCF damage are quantified. Compared with the existing CCF models, the CCF model proposed in this paper considers creep damage in CCF and has higher accuracy. The escalation in HCF stress amplitudes leads to reduced CCF life owing to the augmentation of HLCF and interaction damages. The increase in the cycle ratio of HCF to LCF, causing a reduction in CCF life is ascribed to elevated HLCF and creep damages. The calculated damage proportion results from the proposed model are consistent with the observations of the fracture characteristics using a scanning electron microscope (SEM), indicating the necessity of considering creep damage in CCF life prediction at high temperatures. [ABSTRACT FROM AUTHOR]

ABSTRACT Components in aero‐engine are likely excited in multiple resonance models in dynamic loads. This paper proposes an accelerated fatigue testing method that combines the vibration test with ultrasonic loading to develop a feasible experimental system for combined cycle fatigue (CCF) and explore the CCF characteristics in the high cycle fatigue (HCF) associated with very high cycle fatigue (VHCF) conditions. A thin plate specimen of 7075‐T6 aluminum alloy with two natural frequencies of 2 and 20 kHz is designed for the experiment. The stress waveform and distribution during real‐time monitoring provide validation for the method. Finally, the influences of composite loads are demonstrated by exploring the characteristics of the S–N curves and fracture morphology. The results suggest that the increase in both axial and bending stress markedly diminishes fatigue life, while the difference in stress levels under combined loading is revealed through variations in fatigue striation morphology. [ABSTRACT FROM AUTHOR]

ABSTRACT X‐ray computed tomography (XCT) is extremely useful for the non‐destructive analysis of additively manufactured (AM) components. AM components often show manufacturing defects such as lack‐of‐fusion (LoF), which are detrimental to the fatigue life of components. To better understand how cracks initiate and propagate from internal defects, we fabricated Ti‐6Al‐4V samples with an internal cavity using electron beam powder bed fusion. The samples were tested in high‐cycle and very high‐cycle fatigue regimes. XCT was used to locate crack initiation sites and to determine characteristic properties of cracks and defects with the aid of deep learning segmentation. LoF defects exposed to the outer surface of the samples after machining were found to be as detrimental to fatigue life as the internal artificial defects. This work can benefit industries that utilize the AM of high‐strength, lightweight alloys, in the design and manufacturing of components to improve part reliability and fatigue life. [ABSTRACT FROM AUTHOR]

ABSTRACT High and very high cycle fatigue tests were performed to examine the microstructure and fracture mechanism of GH4169 superalloy in combination with techniques including electron‐backscatter diffraction (EBSD). Fractographic analysis revealed that surface failures are induced by surface flaws, whereas internal failures are caused by pores, facets, and inclusions. The three‐dimensional observation shows that fracture surfaces exhibit an irregular texture due to crystallographic mismatch of grains and plastic deformation at the crack tip. Based on EBSD analysis, Euler angles exhibited a complex geometry of grain orientation at the crack tip area, hindering crack propagation as evidenced by lower values of the Schmid factor and misorientation at the crack tip. Furthermore, the threshold values of small and long cracks decrease, whereas the transformation sizes from small to long crack growth increase from surface to internal failure. Finally, a novel microstructure defect‐based life prediction model is established, and the predicted results demonstrate a close resemblance to experimental outcomes. [ABSTRACT FROM AUTHOR]

To assess the contribution of residual stress to the improvement of high‐cycle fatigue (HCF) properties, HCF tests are performed on Ti‐6Al‐4V specimens with different residual stress levels but no other evident surface state modification induced by machining. Results indicate that compressive residual stress induced by machining significantly improves the HCF performance of Ti‐6Al‐4V specimens. Of all the specimens, the fatigue strength of specimens with a surface residual stress level of −400 MPa is increased by approximately 16.4%. Furthermore, to accurately predict the fatigue life based on three mean stress correction equations (e.g., Walker, Goodman, and Smith–Watson–Topper), the method of reducing surface residual stress by a reduction factor and then adding to the mean stress is proposed. A reduction factor of 0.55 is found to be appropriate for the alloy under the test condition, with majority of the predicted data falling within a factor of three scatter band. Highlights: Isolate residual stress from other surface integrity parameters by machining.Compressive residual stress improves both the fatigue life and strength.Effect of residual stress is considered by introducing a reduction factor in mean stress.Develop a life prediction method based on mean stress correction model. [ABSTRACT FROM AUTHOR]

The very high cycle fatigue (VHCF) strength of welded joints made of high-strength structural materials is generally poor, which poses a serious threat to the long life and reliability of the structural components. This work employs an ultrasonic vibration fatigue testing system to investigate the biaxial fatigue failure mechanism of the welded joints. The results revealed that under uniaxial loading conditions, the propensity for fatigue failure in plate specimens was predominantly observed at the specimen surface. Regardless of whether under uniaxial or biaxial loading, the initiation of fatigue cracks in cruciform joints was consistently traced back to unfused flaws, which were primarily located at the interface between the solder and the base material. Concurrently, it was noted that the fatigue strength of cruciform joints under biaxial loading was merely 44.4% of that under uniaxial loading. The geometric peculiarities of the unfused defects led to severe stress concentrations, which significantly reduced the fatigue life of the material under biaxial loading conditions. [ABSTRACT FROM AUTHOR]

Aluminium alloys have been one of the leading materials used in aircraft structural components due to their mechanical performance, low density, and different manufacturing and inspection techniques. The mechanical, chemical, and electrical properties of metallic alloys relate to the microstructural arrangement, which depends on the alloying elements and manufacturing parameters. Therefore, this study aims to experimentally develop an Al-2wt.%Ni-0.5wt.%Co alloy as an alternative for aerospace applications, evaluating the main metallurgical aspects influencing mechanical strength. The samples were solidified in brass moulds with four different diameters, allowing four different cooling rates. A statistical analysis of the correlation between microstructural parameters and mechanical properties is proposed to optimise the conditions for obtaining the best mechanical strength. A microstructure with an essentially cellular matrix of the α-Al phase was observed. The tensile strength limit values (σU) of 117 MPa, specific elongation (δ) of 13.8%, and average microhardness of 33 HV were obtained. The Al-2wt.%Ni-0.5wt.%Co alloy exhibits impressive high cycle fatigue performance, with an endurance limit of 91 MPa at 107 cycles, driven by the synergistic effects of Al3Ni for strength and Al9Co2 for enhanced ductility and toughness. [ABSTRACT FROM AUTHOR]

High-speed ballistic impact tests were conducted at room temperature and 500 °C on nickel-based superalloy GH4169 simulated blade specimens containing leading-edge features. The microscopic characteristics of the impact notch at room temperature versus 500 °C were observed by electron backscatter diffraction (EBSD), and it was found that the grains on the notched subsurface were ruined, while in more distant regions, the impact energy was mainly absorbed by grain boundaries. Internal damage is more concentrated in the notched subsurface region at 500 °C compared to room temperature. The high cycle fatigue strength of the damaged specimens under different conditions was tested. The results showed that the high cycle fatigue strength of the damaged specimens increased with the increase in the notch depth, and the fatigue strength of the damaged specimens at 500 °C was higher than the fatigue strength at room temperature. Both the 48 h post-impact holding time at 500 °C and the preload during impact at 500 °C increased the fatigue strength of the damaged specimens. [ABSTRACT FROM AUTHOR]

The issues of the high-cycle fatigue resistance of notches and the role of non-propagating short cracks in defining the fatigue notch sensitivity and fatigue limit of the configuration are addressed. A fracture mechanics approach is employed to determine the threshold configuration that defines the associated fatigue limit. The influence of notch sharpness, notch size, intrinsic fatigue limit, microstructural dimensions, and the threshold for crack propagation is examined. A simple expression is proposed to estimate the maximum fatigue notch factor, kfMax, which incorporates the influence of these non-propagating cracks. The fatigue limits for both blunt and sharp elliptical notches are analyzed and predicted based on experimental results reported in the literature. Additionally, shallow notches or small defects are analyzed, where it is found that the same hypothesis may not be applicable. [ABSTRACT FROM AUTHOR]

Due to variations in chemical composition and production processes, homonymous austenitic stainless steels can differ significantly regarding their initial microstructure, metastability, and thus, their fatigue behavior. Microstructural investigations and fatigue tests have been performed in order to evaluate this aspect. Three different batches and production forms of nominally one type of steel AISI 347 were investigated under monotonic tensile tests and cyclic loading under total strain and stress control in low and high cycle fatigue regimes, respectively. The deformation induced α'-martensite formation was investigated globally by means of in situ magnetic measurements and locally using optical light microscopy of color etching of micrographs. The investigation showed that the chemical composition and the different production processes influence the material behavior. In fatigue tests, a higher metastability and thus a higher level of deformation induced α'-martensite pronounced cyclic hardening, resulting in significantly greater endurable stresses in total strain-controlled tests and an increase in fatigue life in stress-controlled tests. For applications of non-destructive-testing, detailed knowledge of a component's metastability is required. In less metastable batches and for lower stress levels, α'-martensite primarily formed at the plasticization zone of a crack. Furthermore, the formation and nucleation points of α'-martensite were highly dependent on grain size and the presence of δ-ferrite. This study provides valuable insights into the different material behavior of three different batches with the same designation, i.e., AISI 347, due to different manufacturing processes and differences in the chemical composition, metastability, and microstructure. [ABSTRACT FROM AUTHOR]

The very high‐cycle fatigue (VHCF) fractographies of high‐strength steel AISI 4340 with tensile strength ranging from 1285 to 2363 MPa fabricated by tempering were systematically observed and quantitatively analyzed. It is found that the fatigue crack initiation sites were gradually transferred from the specimen surface to the interior with increasing the tensile strength or decreasing the stress amplitude. Such phenomenon has become common rule in the high‐cycle fatigue (HCF) or VHCF regimes of high‐strength steels. Based on the fracture mechanics, a simplified transition mechanism for fatigue crack initiation sites is established in terms of the influence of applied stress amplitude and microstructure, which is beneficial to enhance our understanding on the variation of fatigue strength increasing the tensile strength. [ABSTRACT FROM AUTHOR]

The fir‐tree tenon/mortise structure in areo‐engine suffers from the combined high and low cycle fatigue (CCF) loads during service. The structural integrity of the tenon/mortise structure is significantly affected by the local strain distribution, while the strain value under the CCF loads is difficult to acquire. In this study, a simulated specimen of tenon/mortise structure is designed, and the CCF test is carried out using a divided‐path loading fixture to avoid interference between the high cycle fatigue (HCF) loads and the low cycle fatigue (LCF) loads. The high speed digital image correlation (DIC) method is adopted to acquire the real‐time strain distribution during CCF test. According to the strain results, the critical position of the mortise and its strain variation are determined. The high cycle strain of the mortise is proportional to the vibration amplitude of the tenon. The experimental results can provide basis for strength and life assessment. Highlights: A combined high and low fatigue test system is designed to study the strain variation.The real‐time strain distribution is obtained by high speed digital image correlation (DIC) method.The strain exhibits sinusoidal variations when applied to the combined high and low cycle fatigue (CCF) loads. [ABSTRACT FROM AUTHOR]

This review explores uniaxial ultrasonic fatigue (USF) testing as a common and dependable method for quantifying the extended fatigue life of fiber‐reinforced polymer (FRP) composites. The objective is to explain the complexities governing the fatigue life behavior of FRPs, particularly in the realm of very high cycle fatigue (VHCF) where the number of loading cycles exceeds 107. To this end, this review encompasses the analysis of VHCF behavior, including the derivation and interpretation of stress–life (S–N) data, the evaluation of various fatigue damage mechanisms (i.e., controlling mechanisms of crack initiation and propagation) exhibited in FRP composites, and a thorough investigation of the frequency‐dependent effects on fatigue responses. Furthermore, this review tries to analyze the microscopic intricacies intrinsic to the VHCF failure of FRP composites, encompassing aspects such as fiber‐matrix de‐bonding, matrix cracking, and delamination, unveiling their modes and effects in a detailed manner. This review also underscores the pivotal integration of simulations, machine learning, and modeling techniques, emphasizing their crucial role in explaining both macroscopic and microscopic interactions governing the VHCF of FRPs. Highlights: CFRPs' very high cycle fatigue (VHCF) is poorly understood but critical in many sectors.Testing CFRPs' VHCF using ultrasonic fatigue (USF) addresses long, complex procedures.Environment‐dependent USF testing shows how conditions like corrosion impact CFRPs.Advanced modeling and machine learning enhance understanding of CFRPs' VHCF behavior. [ABSTRACT FROM AUTHOR]

In this paper, the mechanical properties and microstructures of bearing steels with arsenic contents of 30, 40, and 120 ppm have been investigated. The results show that As‐40 steel has the highest tensile strength but lower fatigue strength than As‐120 steel. The fatigue crack propagation rate of As‐120 steel is relatively low, mainly due to the increase in ΔKth. After quenching and tempering, As‐120 steel has larger prior austenite grains and more undecomposed, elongated carbides appear, reducing the uniformity of the steel. For carbides with an aspect ratio greater than 2, they cannot grow by the Oswald mechanism of spontaneous migration but are spheroidized by self‐cracking. The undissolved elongated carbides have a lower chemical potential, which increases the diffusion tendency of arsenic in the matrix. SIMS and EPMA analyses show that there is no significant distortion of the trace element arsenic. Highlights: The arsenic content in bearing steel has property advantages within the optimal range.Trace element arsenic will diffuse near low chemical potential strip carbides.A certain amount of arsenic coarsening grains can improve the fatigue strength of steel [ABSTRACT FROM AUTHOR]

This study aimed to investigate the failure mechanism of Ti60 titanium alloy in the high cycle fatigue (HCF) and very high cycle fatigue (VHCF) at 500°C. Ti60 specimens were characterized before and after the 500°C VHCF test, and the fracture surfaces were observed. The results show that there are three different fatigue failure mechanisms at 500°C: (i) equiaxed primary α phase (αp) cleavage, forming small unsmooth facets and rough fracture area (RA), and fusion of non‐adjacent facets to grow into the main crack. (ii) αp grains gather into large grain with triple junction, and large grain slip to form large fusion facet. (iii) Oxide shedding and then cracks form. A dynamic recurrent neural network model is used to predict the fatigue life of Ti60 alloy, 91% of the overall predictions were within the scatter band of 3.0, and 100% were within the scatter band of 5.0. Highlights: Characterization yields three fatigue fracture mechanisms of Ti60 alloy at 500°C.Haigh diagrams evaluate the empirical formulas and constant life curves.Characterization reveals multiple triple junctions within the large αp grains after fatigue test.A dynamic recurrent neural network model predicts the fatigue life. [ABSTRACT FROM AUTHOR]

Copyright of Acta Materiae Compositae Sinica is the property of Acta Materiea Compositae Sinica Editorial Department and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

The inadequate fatigue performance of Laser Powder Bed Fusion (L-PBF) Ti-6Al-4V alloy, primarily due to intrinsic defects, poses a significant challenge for industrial applications. Internal defects often serve as initiation sites for fatigue cracks, significantly impacting the fatigue life of L-PBF Ti-6Al-4V components. Accurate evaluation of the role of internal defects in fatigue performance and quantitative analysis of influential parameters are crucial for guiding optimal L-PBF manufacturing design. This study aims to critically review recent notable contributions focusing on high-cycle fatigue (HCF) in these alloys, with many of the presented insights being easily transferred to other types of AM alloys. Efforts have been made to identify correlations between fatigue life at various stages and critical internal defects. Key aspects, including microstructure and post-processing treatments, and their effects on HCF have been thoroughly analyzed. The findings enhance the scientific understanding of fatigue performance of L-PBF Ti-6Al-4V alloy and open new avenues for future research. [ABSTRACT FROM AUTHOR]

Compared to the traditional alloys, high entropy alloys exhibit exceptional strength and outstanding ductility, making them highly attractive for use in demanding engineering applications. However, the atomic-scale deformation behavior of HEAs with precipitate under the low-cycle loading conditions has not been well studied. Here, we utilize molecular dynamics simulations to investigate the low cycle fatigue behavior of AlCoCrFeNi HEAs with AlNi-rich phase, in order to better understand the cyclic deformation, work hardening, and damage mechanisms. In the stress-strain hysteresis loops, the stress in the elastic stage exhibits a gradual linear increase, followed by fluctuations at yielding and plastic deformation. The strain hardening depends on the cycle number after the yielding stage. With an increase in the number of cycles, the activation mode of stacking faults gradually transitions from a multi-slip system to a single-slip system, attributed to the gradual phase transformation. A thorough examination of dislocation evolution is crucial in understanding the strengthening and plastic behavior of materials under cyclic loading. The generation of more stair-rod dislocations further suppresses the movement of dislocations. The combined effects of element diffusion, structural transformation, and incoherent precipitation play a critical role in enhancing the mechanical properties of AlCoCrFeNi HEAs. The strength of high entropy alloys is improved through interface strengthening caused by element diffusion and structural transformation, along with dispersion induced by incoherent precipitation. This work provides a detailed atomic-level understanding of the cyclic deformation-induced strengthening mechanism, in order to design highstrength and ductile HEAs with specific desired properties. [ABSTRACT FROM AUTHOR]

More and more often, semi‐precast reinforced concrete slabs with lattice girders are employed for industrial buildings or bridges, where they are exposed to high cycle fatigue loading. Despite research in recent years that has led to the formulation of an S–N curve for lattice girders, the effects of cyclic loading on semi‐precast slabs have not yet been sufficiently clarified. Moreover, research has so far been limited to single‐span slabs. The effects of continuous slab systems, which are mainly realized in buildings and bridges, cannot be considered in the calculation of fatigue resistance yet. To improve the fatigue design concept for shear and interface shear, theoretical and experimental investigations were conducted at the Institute of Structural Concrete, RWTH Aachen University. In addition to the fatigue behavior of 16 tests under cyclic loading, particular attention is paid to the increase in shear and interface shear resistance at the inner support of continuous slabs. Furthermore, the influences of the support detailing were investigated. The findings illustrate further potential for optimization of the design under cyclic loading. [ABSTRACT FROM AUTHOR]

AbstractIn this study, the progress of surface crack and high cycle fatigue of the surface piercing propellers (SPPs) are investigated numerically using the finite element method. The cyclic load is calculated from the hydrodynamic pressure on the blade by simulating the fluid around the blade using the computational fluid dynamics software STAR-CCM+. The initial cracks are assumed to be created near the blade root. The fatigue life is calculated from the Paris-Erdogan equation. The results show that the crack close to the root has a shorter life and the stresses at the crack front depend on the blade-water interaction duration. [ABSTRACT FROM AUTHOR]

Standard non-local gradient damage methodology for fatigue analysis has an intrinsic drawback of unusual widening of the damage zone. This causes a rapid growth of crack in the simulations which often violate experimental evidences. In order to tackle this undesirable behaviour, the localizing gradient damage methodology has been formulated for high cycle fatigue crack growth simulations. The framework comprises of coupling damage and elasticity through continuum mechanics, a fatigue damage law and an interaction function which reduces the influence of damaged regions on the surrounding locality. The present scheme prevents the spurious widening of the damage-band around the critically damaged area and therefore the non-physical growth of fatigue crack in the simulations is successfully countered. The developed framework is tested on various standard specimens under mode-I and mixed-mode high cycle fatigue loads. Nonlinear finite element analysis is used for this purpose. The discretized form of solver equations for the localizing framework is mathematically derived. Numerical examples show that the simulated crack-growth curves using proposed localizing framework agree closely with the experimental data and has a higher accuracy than the standard non-local framework. [ABSTRACT FROM AUTHOR]

The fatigue behaviors of high-strength bearing steel were investigated with rotating bending fatigue loading with a frequency of 52.5 Hz. It was revealed that the high-strength steel tended to initiate at interior non-metallic inclusions in a very high-cycle fatigue regime. During fractography observation, it was also seen that the inclusion acting as a failure-originating site was seldom smaller than 10 μm. Moreover, prior austenite grains could also act as the originating source of failure when inclusion was absent. The crystal plasticity finite element method (CPFEM) was adopted to simulate the residual stress distribution around non-metallic inclusions of different sizes under different loading amplitudes. The accumulated plastic strain around the inclusion suggested that the existence of inclusion may reduce material strength and lead to more fatigue damage. The value of accumulated plastic strain around different inclusion sizes also resembled the crack nucleation or propagation of the materials. The simulation results also indicated that inclusions smaller than 5 μm had little influence on fatigue lifetimes, while inclusions larger than 10 μm had a significant influence on fatigue lifetimes. [ABSTRACT FROM AUTHOR]

This paper presents a pioneering experimental investigation of the fatigue behavior of a full-scale (15.24 m × 3.89 m) concrete bridge deck reinforced with glass fiber–reinforced polymer (GFRP) rebar under rolling (R)-load cycles applied using the Rolling Load Simulator (ROLLS) at Queen's University, Canada. The study compares this type of fatigue with conventional fixed-point pulsating (P)-loads. The deck is supported by two Steel I-girders spaced at 3.05 m. A 3.81-m-long section on one end was subjected to R-loads and a similar section on the other end, to P-loads, both up to 3 million (M) cycles. Monotonic tests were performed periodically. The study showed that R-load results in far more fatigue damage than P-load, as reflected by 71% and 54% stiffness degradation (k/ko), respectively. This suggests that cumulative damage of one R-cycle is equivalent to 120 P-cycles. Live load deflection limit of span/800 was reached in the R-loading section after 0.78M cycles, and at 3M cycles was exceeded by 15%, but the P-loading section remained below the limit. GFRP reinforcement performed very well, with maximum strain remaining below 10% of the guaranteed tensile strain. The R-load section showed far more extensive and dense grid-pattern cracking with concrete pitting at the soffit, while the P-load section showed minor longitudinal and some radial cracks. A conversion factor (ξ) is established to enable researchers and designers convert (k/ko) from readily and easily available P-loading to an equivalent R-loading of GFRP-reinforced deck at any number of cycles, since P-loading is not conservative and R-loading capabilities are not easily available. In this study, ξ is 0.59 at 3M cycles and is projected to be 0.5 at 10M cycles. Practical Applications: It has been well-established that fixed-point pulsating loads cannot accurately replicate the fatigue damage resulting from traffic loads on bridge elements. The degradation behavior of bridge decks' stiffness should be studied using rolling loads. However, conducting a rolling load fatigue experiment often requires a specialized apparatus that is not readily available. This paper presents the establishment of a conversion factor (ξ) that can be used to convert the normalized stiffness data of bridge decks tested under traditional pulsating loads into real stiffness degradation data under rolling loads. [ABSTRACT FROM AUTHOR]

Axial loading fatigue tests were conducted for α + β titanium alloy with two stress ratios to elucidate the microstructure-based interior cracking behavior at 150 °C temperature. The interior failure is attributed to the cleavage of the large primary α-grains (αp) and facet–facet cluster zone–fisheye formation, which is the primary failure mode in the very high-cycle fatigue regime. Furthermore, microcracks are generated through soft-oriented large αp-grains along the {0001} slip plane in the direction of maximum shear stress, forming the crystallographic facets. Moreover, due to the variation in the grain orientation, significant plastic deformation is produced within the facet-cluster zone. The low-angle grain boundaries offer limited resistance in the propagation of the formed crack, which can pass through neighboring grains easily, exhibiting characteristic transcrystalline failure. Based on the analysis above, the interior fracture mechanism was summarized as related to the microstructure characteristics. In addition, dislocation configurations, slip bands, and stacking faults indicate that the deformation behavior with faceting-induced fracture occurs by joint action of dislocation bypassing, stacking fault shearing, and increasing thermal activation energy at intermediate temperature. The microstructure-based interior failure mechanism is presented based on electron backscatter diffraction, focused-ion beam, and transmission electron microscopy. [ABSTRACT FROM AUTHOR]

The additive manufacturing (AM) is a relative new manufacturing process that belongs to the fourth industrial revolution, thus yielding new challenges that are worth the study in terms of reliability. In that sense, this work presents a comparative study of as printed and optimally heat-treated 1.2709 maraging steel manufactured by laser powder bead fusion (LPBF) AM process. The results suggest that parts were sound in terms of visual inspection and microstructural analysis. In the case of mechanical properties, the results suggest that the highest variability occurred after the heat treatment. The high cycle fatigue samples revealed a fracture without exhibiting a considerable amount of plastic deformation. On the other hand, the low cycle fatigue results revealed that at 1% strain the optimally heat-treated specimens have lower fatigue life due to the presence of surface discontinuities and the reduction of ductility after the heat treatment. [ABSTRACT FROM AUTHOR]

The combined high and low cycle fatigue (CCF) loading condition and random uncertainty exert a considerable impact on the design of turbine shafts. To enhance the fatigue life and reliability, this research proposes a CCF reliability analysis and optimization method for turbine shafts. A CCF fatigue reliability analysis framework is established, which focuses on the quantification of CCF loading characteristics and random uncertainty. The consideration of CCF loading characteristics contain the loading frequency ratio of high cycle fatigue (HCF) to low cycle fatigue (LCF), the stress amplitude ratio of HCF to LCF, as well as their interaction. The consideration of random uncertainty contains material, geometry and load, and a surrogate model‐based method is introduced to improve the quantification efficiency. Through the validation by comparing with experimental data and traditional methods, the proposed method is with higher accuracy and efficiency. By integrating the proposed fatigue reliability analysis method with design optimization, optimal design values for the turbine shaft were identified. This method theoretically extends the shaft's CCF life and provides practical engineering guidance for its reliability analysis and design. [ABSTRACT FROM AUTHOR]

This study presents an experimental investigation of the high-cycle fatigue behaviour of an Al–Si–Cu alloy. The test specimens were fabricated via semisolid metal processing, namely thixoforming. High-cycle fatigue testing was conducted on an hourglass specimen subjected to T6 heat treatment with a stress ratio of R = 0.1 and a uniform-amplitude load of 20 Hz up to the final failure of the specimen. Result showed the S–N curves for the T6 heat-treated thixoforming alloy specimens improved by 50 MPa fatigue strength at 106 cycles compared with that of the T6 heat-treated as-cast specimens. SEM examination of the fracture surface reveals that fatigue damage was governed by porosity, which served as the main cause for the initiation of cracking in the as-received alloy. By contrast, fatigue failure in the thixoformed alloy was governed by the inclusion of impurities such as carbon and an oxide film. Therefore, this study confirmed that the thixoformed T6 alloy has 19% greater resistance to fatigue failure and 0.25 quality index (QT) as compared with the as-received T6. [ABSTRACT FROM AUTHOR]

This article explores the behavior of short beam specimens made from a titanium/fiber-reinforced polymer (FRP) hybrid sandwich material. The study compares the flexural characteristics of specimens with FRP skins and titanium skins, which were manufactured using additive manufacturing processes. Three-point bending tests were conducted to evaluate the mechanical properties of the specimens. The results provide insights into the fracture mechanisms and performance of the hybrid sandwich material. The study found that titanium-skinned specimens had the highest strength, while aramid and carbon fiber skins had comparable mechanical characteristics. The article also includes micrographs of the fracture surfaces and compares the performance indexes of the different specimens. [Extracted from the article]

To investigate the low-cycle fatigue properties of flexure-shear critical columns, nine reinforced concrete (RC) columns were subjected to monotonic and constant-amplitude cyclic loading. The effects of loading displacement amplitudes and shear span ratios on failure modes, load-displacement response, strength degradation, and energy dissipation capacities of RC flexure-shear columns were explored. Test results indicated that the low-cycle fatigue and damage properties of column specimens were dependent on the displacement amplitudes. The cumulative damage effects and shear effects induced by cyclic loading were intensified with increasing displacement amplitudes and decreasing shear span ratios, respectively, resulting in flexure-shear failure. The maximum loading cycles (i.e., fatigue life) of low-cycle fatigue specimens decreased apparently as displacement amplitudes increased, with a maximum variation range of 98.8%. Meanwhile, the low-cycle fatigue characteristics of flexure-shear columns were also relevant to energy dissipation capacities. The normalized energy dissipation capacity of specimens diminished exponentially with increases in loading cycles due to the cyclic effects, and the cumulative energy dissipation decreased significantly as displacement amplitude increased. Test columns had a maximum degradation rate of energy dissipation up to 0.43 times that of the first hysteresis cycle. Furthermore, a new fatigue-life model was proposed based on the cumulative damage properties of cyclic loading columns. This model considered the effects of deformation and energy dissipation on low-cycle fatigue properties, providing a basis for evaluating the damage properties of flexure-shear critical columns subjected to low-cycle fatigue loading. [ABSTRACT FROM AUTHOR]

This article predicts bending very high cycle fatigue (VHCF) life of three typical nickel‐based alloys SM2550, BG2532, and G3 used for completion strings. Fatigue tests were conducted on the three alloys using an ultrasonic fatigue system at a frequency of 20 kHz. The results showed that the fatigue strength ranges of the three alloys were markedly different, reflecting their different sensitivities to fatigue loading. Scanning electron microscope observations revealed numerous fatigue crack origins with internal decohesion in the fatigue source region. To achieve unified prediction of the fatigue life for the three alloys, a prediction model based on deep learning was built with inputs including fatigue initiation quantity, cleavage facet size, and other fatigue fracture characteristics. It was found that single source feature was insufficient to obtain satisfactory prediction accuracy for all alloys, while multifeature coupling integration could significantly improve the prediction precision, enabling reliable prediction of alloy fatigue life. This study provides new insights into bending VHCF life prediction. Highlights: This article predicts bending VHCF life for three completion strings.Bending VHCF life model utilizing deep wise separable convolution was established.Deep learning can effectively integrate with bending VHCF analyses. [ABSTRACT FROM AUTHOR]

Rolling can result in anisotropy in the microstructure and mechanical properties of the sheet material. This study focuses on the very high cycle fatigue (VHCF) performance of magnesium alloys in the rolling direction (RD), normal direction (ND), and the bisecting angle between the ND and RD (ND–RD). The findings reveal that RD specimens demonstrate superior fatigue performance, while the ND specimens exhibit the lowest fatigue resistance. During the crack initiation stage, the primary influential factor is the maximum shear stress. Due to c‐axis alignment with ND direction in grains, the deformation mode for ND and RD specimens primarily involves first‐order pyramidal slip, while ND–RD specimens primarily undergo basal slip and prismatic slip. In early stable crack propagation, grain size and texture cause variations in the morphology of the rough area among the three directional specimens. Notably, the RD specimens show faster crack propagation during crack initiation than early stable propagation stage. Highlights: The rolled Mg alloys have the highest very high cycle fatigue strength along rolling direction.Texture and grain boundaries significantly affect crack initiation and early propagation.Maximum shear stress dominates slip‐induced crack initiation within primary grains. [ABSTRACT FROM AUTHOR]

The microstructure, mechanical properties, and high/very‐high cycle fatigue behaviors of 9Cr3W3Co turbine rotor steel and its welded joint were investigated. The welded nugget zone (WNZ) exhibited the highest microhardness value, followed by the heat‐affected zone (HAZ), while the base material (BM) showed the lowest hardness value. The WNZ exhibited a higher yield strength compared to the BM with reduced elongation, while maintaining similar ultimate tensile strength. The fatigue strength of the BM at 5 × 107 cycles is roughly 53.7% of the yield strength, whereas that of the WNZ increases to approximately 55.0%. In comparison to the fatigue strength of the BM at 5 × 107 cycles, the WNZ exhibits a notable increase of 10.5%. Smaller grain size and higher dislocation density were observed in the WNZ, which contributed to improved microhardness, yield strength, and fatigue resistance through grain boundary strengthening and dislocation hardening. Highlights: Microstructure and mechanical properties of 9Cr3W3Co steel welded joints were studied.Microhardness values of various zones are non‐uniform and the maximum value in WNZ.Dislocation and grain boundary strengthening contributed to strengthening in WNZ. [ABSTRACT FROM AUTHOR]

In this article, the life of metals under fatigue loading with variable amplitude has been investigated. For this purpose, the continuum damage mechanics method is used to model the damage parameter, in which the amount of dissipated energy in each cycle per volume is known as the damage index. The damage model introduced in this article has the ability to be used in problems with variable amplitude, therefore, in this study, a specimen of Q235 steel was simulated in Abaqus software and from two subroutines UMAT and UMATHT to simultaneously extract dissipated energy in Each cycle and its corresponding temperature were used. In order to investigate the fatigue life under variable amplitude loading, Two blocks with different amplitudes have been considered. Different types have been considered for these two blocks, and their results show that the introduced damage model has a high sensitivity to the loading history and sequence; Also, there is a good agreement between the results of this research and the experimental results. [ABSTRACT FROM AUTHOR]

High-Density Polyethylene (HDPE) like other thermoplastics has low mechanical properties which limits its range of applications, especially under the influence of dynamic loads and high temperatures. Therefore, as one of the highly attractive approaches for improving mechanical properties, nanomaterials have been used as reinforcement materials in polymer matrix composite. The present study focuses on the role of nanomaterials on the mechanical properties and fatigue resistance of high-density polyethylene reinforced with (1, 2, and 3%) nano alumina oxide at a range of testing temperatures between 20 and 60ºC. The results manifested that the addition of nano alumina oxide improves the strength of base polyethylene and increases the fatigue resistance by (63.7%, 146.5%, and 228.4%), (69.25, 163.5 and 202.8) and (94%, 214.8% and 290.3) at (20. 40 and 60°C), respectively in cooperation with the pure high-density polyethylene. In addition, as the applied testing temperature increases, the fatigue resistance in all test specimens decreases. It was found that the highest fatigue resistance occurred at (HDPE+3%Al2O3) composite due to the good distribution of nano Al2O3 within the HDPE base which led to a better crack propagation prevention than other composites. [ABSTRACT FROM AUTHOR]

Copyright of Journal of Aeronautical Materials is the property of Editorial Board of Journal of Aeronautical Materials and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

As the reliability and lifespan requirements of modern equipment continues to escalate, the problems with very high cycle fatigue (VHCF) has obtained increasingly widespread attention, becoming a hot topic in fatigue research. Titanium alloys, which are the most extensively used metal materials in the modern aerospace industry, are particularly prone to VHCF issues. The present study systematically reviewed and summarized the latest (since 2010) developments in VHCF research on titanium alloy, with special focus on the (i) experimental methods, (ii) macroscopic and microscopic characteristics of the fatigue fractures, and (iii) construction of fatigue fracture models. More specifically, the review addresses the technological approaches that were used, mechanisms of fatigue crack initiation, features of the S–N curves and Goodman diagrams, and impact of various factors (such as processing, temperature, and corrosion). In addition, it elucidates the damage mechanisms, evolution, and modeling of VHCF in titanium alloys, thereby improving the understanding of VHCF patterns in titanium alloys and highlighting the current challenges in VHCF research. [ABSTRACT FROM AUTHOR]

The prediction of mechanical behavior and fatigue life is of major importance for design and for replacing costly and time-consuming tests. The proposed approach for polymers is a combination of a fatigue model and a governing constitutive model, which is formulated using the Haward–Thackray viscoplastic model (1968) and is capable of capturing large deformations. The fatigue model integrates high- and low-cycle fatigue and is based on the concept of damage evolution and a moving endurance surface in the stress space, therefore memorizing the load history without requesting vague cycle-counting approaches. The proposed approach is applicable for materials in which the fatigue development is ductile, i.e., damage during the formation of microcracks controls most of the fatigue life (up to 90%). Moreover, damage evolution shows a certain asymptote at the ultimate of the low-cycle fatigue, a second asymptote at the ultimate of the high-cycle fatigue (which is near zero), and a curvature of how rapidly the transition between the asymptotes is reached. An interesting matter is that similar to metals, many polymers satisfy these constraints. Therefore, all the model parameters for fatigue can be given in terms of the Basquin and Coffin–Manson model parameters, i.e., satisfying well-defined parameters. [ABSTRACT FROM AUTHOR]

Resistance spot welding (RSW) is the most commonly used method for joining sheet metals structures in the automotive industry. The cyclic loading conditions on RSW joints can lead to fatigue failure, hence, affecting their reliability and durability. The comprehension of the fatigue strength for the RSW is very critical, especially for the dissimilar RSW joints. This study presents analyses to characterize the fatigue behavior of these joints. Therefore, the crack propagation, and fatigue life under specific loading conditions have been studied. The fatigue strength of similar aluminum Al-1050, and dissimilar copper with aluminum Cu-Al RSW joints was examined experimentally and numerically. The lap-sheet materials were spot welded using optimum welding parameters to ensure a consistent range for the produced weld nugget. In this work, the experimental test rig has been designed and established to have an axial fatigue load. The high cycle fatigue tests were performed, and the P-N curves were obtained. The work was analyzed numerically using finite element (FE) analysis, in conjunction with experimental results. Aluminum sheet joint has the highest fatigue limit as compared to dissimilar Cu-Al joints. The crack growth rate of the similar RSW joint is slower than those of dissimilar joints because it has higher stress intensity factor (SIF). The coefficients of the Paris' constants, C and m, have been determined. [ABSTRACT FROM AUTHOR]

This paper investigates the fatigue behaviour of laser powder bed fusion (LPBF) processed Ti6Al4V samples under three build orientations. The post-heat treatment (PHT-1050 °C) was carried out. The microstructural characterization was performed using optical microscopy, X-ray diffraction SEM and EDS techniques. The tensile test and high cycle fatigue tests were performed. The PHT performed at 1050 °C exhibited Widmanstatten microstructure consisting of a higher volume fraction of elongated β and a small amount of α. PHT samples' ductility was ~ 67%, 40% and 177% higher than the as-printed samples under horizontal, inclined and vertical orientations. Interestingly, the fatigue lives of PHT samples at higher stress levels were higher and nearly isotropic in all three build orientations than the as-printed samples due to enhanced ductility and fewer critical pores. Further strong correlation between PHT samples and ductility was established. Moreover, there was a marginal improvement in fatigue limit due to PHT at 1050 °C compared to as-printed samples. [ABSTRACT FROM AUTHOR]

This study investigates the profound influence of multi-axial forging (MAF) on the microstructural characteristics, high cycle fatigue properties, and impact toughness behaviour of the bulk ultrafine-grained aluminum-lithium (Al–Li) 8090 alloy. The solution-treated Al–Li 8090 alloy was subjected to MAF at both liquid nitrogen temperature (LNT) and room temperature for 2, 4, and 6 forging cycles, resulting in cumulative true strains of 1.2, 2.4, and 3.6, respectively. The MAFed sample at LNT after 6 cycles displayed a well-defined ultrafine-grained microstructure, exhibiting grain sizes ranging from 100 to 400 nm. Detailed electron backscatter diffraction analysis confirmed significant grain refinement with increasing MAF cycles for various conditions. The high-cycle fatigue strength exhibited a progressive enhancement with the increasing number of cycles and was observed to be maximum for the CF cycle-6 condition (131 MPa), attributing to the effective suppression of dynamic recovery at cryogenic temperatures. [ABSTRACT FROM AUTHOR]

The present study deals with the fatigue behavior of a wrought nickel‐based superalloy René 41. Uniaxial, fully reversed low‐cycle fatigue tests were conducted at room and elevated (800°C) temperatures under total strain control. Cyclic response was analyzed using the statistical theory of the hysteresis loop, and scanning and transmission electron microscopies were employed to study relevant damage mechanisms. At room temperature, cyclic deformation was found to localize to slip bands since the first cycle, and most slip bands were formed very early in the fatigue life. Hence, shearing of the strengthening phase, coherent γ′ precipitates, was found to be significant only in the first few cycles. At 800°C, fatigue life was affected by an environmental attack resulting in a surface oxide layer. Cyclic deformation was less localized; nevertheless, cyclic slip localization in persistent slip bands and resulting γ′ shearing contributed to cyclic softening throughout the fatigue life. Highlights: Cyclic slip is localized in persistent slip bands since the first cycle.Majority of slip bands are formed very early in the fatigue life.At room temperature, γ′ shearing is only significant early in the fatigue life.At 800°C, γ′ shearing occurs all over the fatigue life due to weaker slip localization. [ABSTRACT FROM AUTHOR]

The investigation of fatigue behavior typically involves time‐consuming tests, leading some researchers to explore methodologies based on self‐heating tests to reduce the process. For composite materials, the conventional approach involves piecewise linear approximations of the self‐heating curve and the stress transition between the first and second regimes is arbitrarily associated with a fatigue lifetime equal to 106 cycles. This paper proposes a novel methodology to address these simplifications. First, a non‐linear viscoelastic model is used to describe the self‐heating curve. Based on the mechanisms established in the literature, a link is proposed between the dissipation and the fatigue limit. The load leading to a significant contribution of non‐linear mechanisms is associated with an infinite life time. It allows the identification of an S– N curve and prediction of fatigue behavior through a minimal number of tests. The comparison with fatigue results is satisfactory. Highlights: A link is proposed between dissipation and fatigue.Modeling of the dissipation in laminated composites subjected to cyclic loadings.A criterion is proposed to identify the fatigue limit based on the dissipation.A S– N curve is identified and extrapolated up to high cycles fatigue. [ABSTRACT FROM AUTHOR]

The deposition of combustion residues in the nozzle ring (NR) of a turbocharger turbine stage changes the NR geometry significantly in a random manner. The resultant complex and highly asymmetric geometry induces low engine order (LEO) excitation, which may lead to resonance excitation of rotor blades and high cycle fatigue (HCF) failure. Therefore, a suitable prediction workflow is of great importance for the design and validation phases. The prediction of LEO excitation is, however, computationally expensive as high-fidelity, full annulus CFD models are required. Previous investigations showed that a steady-state computational model consisting of the volute, the NR, and a radial extension is suitable to reduce the computational costs massively and to qualitatively predict the level of LEO forced response. In the current paper, the aerodynamic excitation of 69 real contaminated NRs is analyzed using this simplified approach. The results obtained by the simplified simulation model are used to select 13 contaminated NR geometries, which are then simulated with a model of the entire turbine stage, including the rotor, in a transient time-marching manner to provide high-fidelity simulation results for the verification of the simplified approach. Furthermore, two contamination patterns are analyzed in a more detailed manner regarding their aerodynamic excitation. It is found that the simplified model can be used to identify and classify contamination patterns that lead to high blade vibration amplitudes. In cases where transient effects occurring in the rotor alter the harmonic pressure field significantly, the ability of the simplified approach to predict the LEO excitation is not sufficient. [ABSTRACT FROM AUTHOR]

Labyrinth seals are commonly used in turbomachinery in order to control leakage flows. Flutter is one of the most dangerous potential issues for them, leading to High Cycle Fatigue (HCF) life considerations or even mechanical failure. This phenomenon depends on the interaction between aerodynamics and structural dynamics; mainly due to the very high uncertainties regarding the details of the fluid flow through the component, it is very hard to predict accurately. In 2014, as part of the E-Break research project funded by the European Union (EU), an experimental campaign regarding the flutter behaviour of labyrinth seals was conducted at "Centro de Tecnologias Aeronauticas" (CTA). During this campaign, three realistic seals were tested at different rotational speeds, and the pressure ratio where the flutter onset appeared was determined. The test was reproduced using a linearised uncoupled structural-fluid methodology of analysis based on Computational Fluid Dynamics (CFD) simulations, with results only in moderate agreement with experimental data. A procedure to adjust the CFD simulations to the steady flow measurements was developed. Once this method was applied, the matching between flutter predictions and the measured data improved, but some discrepancies could still be found. Finally, a set of simulations to retain the influence of the external cavities was run, which further improved the agreement with the testing data. [ABSTRACT FROM AUTHOR]

Monitoring physical demands during task execution with exoskeletons can be instrumental in understanding their suitability for industrial tasks. This study aimed at developing a fatigue level prediction model for Back-Support Industrial Exoskeletons (BSIEs) using wearable sensors. Fourteen participants performed a set of intermittent trunk-flexion task cycles consisting of static, sustained, and dynamic activities, until they reached medium-high fatigue levels, while wearing BSIEs. Three classification algorithms, Support Vector Machine (SVM), Random Forest (RF), and XGBoost (XGB), were implemented to predict perceived fatigue level in the back and leg regions using features from four wearable wireless Electromyography (EMG) sensors with integrated Inertial Measurement Units (IMUs). We examined the best grouping and sensor combinations by comparing prediction performance. The findings showed best performance in binary classification of leg and back fatigue with 95% (2 EMG + IMU sensors) and 82% (single IMU sensor) accuracy, respectively. Tertiary classification for back and leg fatigue level prediction required four sensor setups with both EMG and IMU measures to perform at 79% and 67% accuracy, respectively. The efforts presented in our article demonstrate the feasibility of an accessible fatigue level detection system, which can be beneficial for objective fatigue assessment, design selection, and implementation of BSIEs in real-world scenarios. [ABSTRACT FROM AUTHOR]