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Copyright of Journal of Materials Engineering / Cailiao Gongcheng is the property of Journal of Materials Engineering Editorial Office 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.)

Nowadays, material extrusion (ME) is one of the most popular additive manufacturing technology, which offers a new way of manufacturing parts with specific complex geometry and mechanical properties. However, with the expansion of the application range of ME products, it is urgent to investigate their fatigue property so as to ensure the reliability and safety. In this paper, the damage mechanical fatigue life prediction model of ME products considering void defects was established. Fatigue test specimens built with different processing parameters were then fabricated, and tensile fatigue tests were carried out under different stress levels. In addition, a novel method, utilizing vibration during ME process, was proposed to improve the built products' fatigue property, and corresponding theoretical and experimental investigations were performed to reveal the influencing mechanism of the vibration utilized. The results showed that the proposed model was validated by comparing the theoretical predictions with the experimental measurements. As layer height and printing speed were increased, the fatigue life of ME specimens dropped, while it rised with the increasing extrusion temperature. The built products' fatigue life could be improved obviously by using vibration. [ABSTRACT FROM AUTHOR]

Quantitative characterization on fatigue properties of SMA490BW welded components with annealing heat treatment is very significant for steel structure service. In this work, the relief of residual stress during welding and the subsequent annealing heat treatment process of plate and tube-to-plate components is simulated using the finite element method with the Norton-Bailey creep model. Traction structural stress is used to evaluate the fatigue life of SMA490BW plates and tube-to-plate components under two annealing heat treatment processes by considering residual stress. It is found that the residual stress distribution state of welded components keeps the same tendency by annealing heat treatment, while the peak value of longitudinal and transverse residual stress is decreased significantly due to the increase of equivalent creep strain with the width of the welded plate exceeding 6 times the thickness. The fatigue data for two annealing heat treatment processes and welding of plate and tube-to-plate components are within a 95% confidence interval of the ASME Master S N curve. The influence of load range on fatigue life is more significant than that of welding residual stress. By quantifying the residual stress in the load ratio correction, the standard deviation of fatigue data for different full-scale components more convergent. • The fatigue life of welded components w and w/o AHT are unified in Master S N curve. • The accumulation of equivalent creep strain caused the relief of residual stress. • The role of stress range on fatigue damage is more significant than residual stress. [ABSTRACT FROM AUTHOR]

Aiming at typical connection structure of the bolt holes errors on edge strip of front spar of central wing,this paper analyzes the fatigue property of the structure. The fatigue life of the structure is analyzed by means of structure durability analysis theory. The detail fatigue rating is worked out by finite element analysis and through experimental verification; this paper studies the changes of fatigue life and detail fatigue rating between structure with manufacturing errors and the original structure.Through theoretical and experimental analysis,this paper judges the validity of repair methods for the fastening holes error in the current aviation industry and provides theoretical and experiment data support for repairing methods.

The article will be focused on monitoring the influence of the structure on the fatigue properties of aluminium alloys for the casting of type Al-Mg. As an experimental material were used aluminium alloys EN AC 51200 and EN AC 51500, supplied in a cast state without a heat treatment. They were produced by the continuous casting method. These alloys were selected on the basis of the chemical composition, where the content of most alloying elements is comparable, only in the case of the concentration of magnesium are these alloys significantly different. Fatigue properties of aluminium alloys were tested by three-point bending cyclic loading. The fracture surface of the testing sample was examined using scanning electron microscopy (SEM), where samples were observed on various stages of the fatigue process, their characteristics and differences of fracture surfaces.

The modeling air-cooled turbine blades specimens of DD6 single crystal superalloy with different distributions of cooling film holes were used to study the high cycle fatigue properties at room temperature. The SEM fracture observation was carried out. The results indicate that the cooling holes have significant effects on the high fatigue life of DD6 single crystal superalloy. The average life of non-hole specimens is four times of that of the three-row holes specimens under the same testing conditions. However, the distribution of cooling film holes has relatively less influence on fatigue life. The fracture of the specimens with non-hole is linear source by SEM analysis, but the cracks are found around the cooling film holes and the fracture of the specimens with single row to three rows is a typical multi-source rupture, and cracks all initiate from near film holes. According to fracture and crystallography theoretical conjecture, the cracks propagate along the {001} slip plane for non-hole, single-row holes and the middle location of the multi-row holes specimens. However, the cracks around the holes grow along the {111} slip plane for upper and lower holes of the specimens with multi-row holes. In addition, the distribution of stress field along cooling holes of four different specimens was analysed by FEM method. The results show that the fracture location and morphology of specimens are consistent well with numerical simulation analysis.

Various bonding materials have been developed for power semiconductor products. However, the fatigue characteristics of many of these materials are difficult to evaluate uniformly using a conventional test, and this difficulty represents an obstacle to ensure proper material selection. In this report, we developed a new experimental method that can evaluate the fatigue properties of thin bonding layers. The conclusions of this report are shown below. (a) In developed method, the specimen with bonding layer is subjected to a two-way, four-point bending load. This method enables an evaluation even for a bonding material that can form only a thin layer. Furthermore, our method enables carrying out a fatigue test without any additional deformation even when substantial creep or ratchet deformation occurs in the bonding material. The high-speed examination is also possible to obtain high-cycle fatigue strengths. (b) We conducted a fatigue test on a Sn3.5Ag0.75Cu solder bonding layer. The results were that the fracture mode was good agreement with an actual joining structure. Moreover, the fatigue life obtained by our method in this test range followed the Coffin-Manson rule with high accuracy. (c) We found the relationship between the strain of bonding layer and the fatigue life using finite element analysis. The result was that the fatigue life curve of bonding layers was good agreement with that of bulk materials.

The stress states of a crankshaft under founding moment loading were analyzed by using fire element method, and the stress distributions of a crankshaft were calculated by interpolation method. Then,the critical distance method and different strength criterions were chosen to predict the structural fatigue properties of crankshafts with the same maternal and different met radius. Corresponding experimental were also conducted. The results show that the agues; characteristics of the crankshafts with different fillet radius are predicted based on the first strength fettered and the critical distance method, both of the critical point method and fine method will cause some fine naively apparent errors. While the are based on the third, fourth strength criterion and critical distance method, the critical line method has higher accuracy than that of the critical point method, which is caused by the damage types of the crankshafts. [ABSTRACT FROM AUTHOR]

The test of compression fatigue property of high ductile concrete (HDC) after freeze-thaw cycles of 75 times and 150 times is used to study the fatigue deformation characteristics and fatigue life under different stress level and load frequency.The HDCS-N curve model suitable for different freeze-thaw conditions was established by comparing the fatigue performance of the specimens under normal temperature curing with that after freeze-thaw cycle.The results show that the fatigue life is directly proportional to the loading frequency and inversely proportional to the stress level. After the freeze-thaw cycle, the fatigue life was significantly reduced compared with the normal temperature curing. The maximum decrease was 95.3% after 75 freeze-thaw cycles and 97.3% after 150 freeze-thaw cycles. The specimens have good integrity and ductility after fatigue failure.Based on the analysis of test results, the S-N curve model of HDC under different freezing-thawing conditions was established with loading frequency and freezing-thawing times as reference values, and the fatigue reduction coefficient of HDC material was calculated:0.660~0.674 under normal curing conditions, 0.589~0.612 after freezing-thawing cycle, which decreased by 9.2%~12.6%. It can provide reference for practical engineering. [ABSTRACT FROM AUTHOR]

In order to study the fatigue properties of basic Magnesium Sulfate cement reinforced concrete beams, specimens of the basic magnesium sulfate cement (BMSC) and ordinary portland cement (PO·C) were in strength grade of C40 and C50 were prepared, respectively. Response surface methodology is applied to this study. The results show that under the fatigue load, the deflection value of the specimen decreases with the increase of the number of fatigue cycles. The fatigue cycle life of the BMSC specimens with higher strength grades is more than that of the PO·C specimens, and the higher the strength grade, the more obvious. Under the fatigue load, the development of the midspan deflection of the specimen showed an S-shaped trend, and the deflection in the BMSC specimen was smaller than that of the PO·C specimen. The spacing of the cracks in BMSC columns was smaller than that of PO·C columns because of the better bond performance between the reinforcing bars and the surrounding BMS concrete. But the crack widths of BMSC columns were close to the width of PO·C columns. It shows that the BMSC specimen has a high rigidity and good resistance to deformation. [ABSTRACT FROM AUTHOR]

To obtain a better understanding of the mechanical properties and failure characteristics of the single-crystal Fe-3%Al alloy (SC), tensile and fatigue properties of the SC and polycrystalline Fe-3%Al alloy (PC) have been investigated. The tensile strength and fracture strain for the SC samples were different depending on the loading direction, i.e., 〈111〉, 〈110〉 and 〈100〉, which could be explained by the Schmid factor. Fatigue strength for the SC samples was basically correlated with their tensile strength. Different fatigue properties were obtained for the PC sample, e.g., the high fatigue strength was obtained in the early fatigue stage, and significant reduction in the fatigue strength was appeared in the later fatigue stage, e.g., low endurance limit at 107 cycles. The reason for this was caused by the material brittleness due to the accumulated dislocation at the grain boundaries. Because the high ductile SC samples made severe plastic deformation ahead of the crack tip, the crack growth rate did not enhance even if the high stress intensity factor range was applied in Region II (da/dN versus ΔK). The crack growth rate dropped just before the final fracture. Effective stress intensity factor range was estimated using the crack closure model, but the crack growth rate is found to be affected strongly by the slip system of SC sample. [ABSTRACT FROM AUTHOR]

• CCF life of blades decrease after aluminizing while increase after strengthening. • Element migrations lead to the generation of defects in the aluminized region. • Cracks are easy to initiate and propagate into the matrix in the aluminized blade. • A hardened region with residual compressive stress form on strengthening blades. • Crack initiation and growth resistances increase obviously in strengthening blades. Fatigue properties of K403 superalloy blades were tested using a combined high cycle fatigue (HCF) and low cycle fatigue (LCF) loading. Samples were tested in the as-cast, as-aluminized, and as-strengthened conditions. The strengthening treatment was wet sand blasting the blade root, followed by shot peening, and vibratory polishing. Metallographic and scanning electron microscope (SEM) fractographic examinations were conducted on the blades, including detailed characterization of the layered structures formed by aluminizing using energy dispersive spectroscopy (EDS). It has found that aluminizing created a surface which was brittle at the test temperature. Fatigue cracks initiated in the aluminized coating and propagated into the substrate, which reduced the fatigue life of the blades. However, the strengthening treatment improved the fatigue life by creating a compressive residual stress and removing a portion of the brittle outer layer of the aluminized coating. [ABSTRACT FROM AUTHOR]

Copyright of Rare Metal Materials & Engineering is the property of Northwest Institute for Nonferrous Metal Research 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.)

Copyright of Rare Metal Materials & Engineering is the property of Northwest Institute for Nonferrous Metal Research 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.)

In order to study the fatigue behavior of steel-concrete composite beams with corroded stubs under negative bending moment, one specimen was tested under static loading while five specimens were tested under fatigue loading. In the static test, the bearing capacity of the composite beam under negative bending moment was obtained as a reference for the fatigue tests. In the fatigue tests, the load-strain curves, load-mid span deflection curves, the residual deformation and stiffness were obtained. The test results indicate that the fatigue life of test specimens decreases with the increases of corrosion rate of studs while the residual deformation increases with the increases of corrosion rate of studs. The stiffness of test specimens decreases during the fatigue loading process but has no relationship with the corrosion rates. The slip stiffness decreases significantly with the increases of corrosion rate of the studs. [ABSTRACT FROM AUTHOR]

Copyright of China Mechanical Engineering is the property of Editorial Board of China Mechanical Engineering 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.)

Abstract The fracture resistance of nanoscale MEMS films under high frequency impact seriously influences its service life. Nano impact test is a reliable technique to evaluate the fatigue fracture resistance of films by simulating the dynamic cyclic loading conditions. In this paper, a kind of Cu film was prepared by magnetron sputtering. The effects of loading parameters and indenter size on the fatigue damage behavior were studied for the Cu films during by nano impact test technique. The dislocation propagation and crack initiation during the nano impact process were also analyzed by molecular dynamics simulation. The results show that: Nano impact failure of Cu film can be divided into three stages and the main failure forms are cracks and delamination. The increase of the indenter radius leads to the increase of fatigue indentation size. The deformation range and damage accumulation degree of thin film material also increased correspondingly. With the increase of nano impact loading rate, the film material suffered more momentum from the indenter. The fatigue damage energy accumulation accelerates the damage. Highlights • Fatigue property of Cu Film was tested by nano-impact technology. • The nanometer impact fatigue process is simulated by molecular dynamics. • The damage mechanism of nanometer impact fatigue is analyzed. • Relationships between indenter size and loading rate and fatigue property are explained. [ABSTRACT FROM AUTHOR]

Highlights • The fatigue mechanism was analyzed from macroscopic to microscopic scales. • Effect of porosity on fatigue performance of Al foams was investigated. • The deformation process under quasi-static and cyclic compression was comparatively analyzed. Abstract The compression-compression fatigue properties of open-cell Al foams fabricated by space-holder method with different porosities were investigated. The ε–N curves of the Al foams show two types based on the stress levels (k). The first type shows a three-stages for low stress level (k < 0.9), while the second type only presents stage I and stage III for high stress level (k ≥ 0.9). The quasi-static compression tests were performed to determine the yield strength (σ s) of Al foams. The fatigue strengths of Al foams with porosities of 50%, 60% and 70% are 12.77 MPa (0.75 σ s), 7.61 MPa (0.68 σ s) and 3.02 MPa (0.66 σ s) respectively, showing a linear decrease with the increment of porosity. The macroscopic deformation observation shows that the local deformation regions during fatigue tests emerge earlier than those during quasi-static compression tests. The initiation and propagation of fatigue cracks are the main failure mechanism of Al foams subjected to compression fatigue loading. [ABSTRACT FROM AUTHOR]

• Gigacycle fatigue behavior of a high-entropy alloy is firstly studied. • Fatigue micro-cracks trend to initiate near a triple junction grain boundary. • The {1 1 0} slip planes may also lead to the fatigue crack initiation, not only preferential {1 1 1} slip planes. Widespread interest has been generated by the high-entropy alloys (HEAs) due to their exceptional ability to combine high plasticity and high strength. However, there is still no comprehensive explanation for their fatigue behavior and crack initiation mechanism in the very high cycle fatigue region up to 109 cycles to the author's best knowledge. This work studied the gigacycle fatigue behavior of a single-phase CoCrFeMnNi HEA. It is found that fatigue failure is caused by casting defects and crystallographic facet. For the case of crystallographic facet just originating from matrix, the fatigue micro-cracks tend to initiate near a triple junction grain boundary. The activation of the {1 1 0} slip planes may also lead to the fatigue crack initiation, not only preferential {1 1 1} slip planes for this alloy. [ABSTRACT FROM AUTHOR]

Porosity defects are the main issues faced by aluminum alloys manufactured by wire-arc directed energy deposition (WA-DED), which seriously affect the mechanical properties of WA-DED aluminum alloys, especially the fatigue properties. Thus far, there is still no effective solution for the elimination of porosity in high-strength WA-DED aluminium alloys. In this study, an innovative hybrid WA-DED + interlayer friction stir processing (FSP) method was applied to successfully fabricate thick-walled Al-Zn-Mg-Cu-Sc-Zr aluminum alloy component with enhanced strength-ductility and fatigue properties by utilizing a custom 7B55-Sc wire. The porosity defects caused by the WA-DED process were significantly reduced in the FSP effective zone, and the original continuous grain boundary eutectic structures were broken up and dispersed along the grain boundaries. The grains were also further refined with an average size of about 1.1 ± 0.2 μ m in the stirring zone (SZ) and 1.6 ± 0.3 μ m in the overlapping SZ. The nanoscale intragranular precipitates (IGPs) were mostly composed of both rod-like η Mg (Zn , Cu , Al) 2 phases and secondary Al 3 (Sc, Zr) phases. The yield strength (YS), ultimate tensile strength (UTS) and uniform elongation (EL) in the horizontal and vertical directions were all substantially improved comparing with the WA-DED 7B55-Sc component, especially in the horizontal direction, reaching 387 ± 7 MPa, 511 ± 15 MPa and 14.6 ± 0.5%, respectively. The fatigue property after 1 × 107 cycles for the WA-DED + interlayer FSP 7B55-Sc sample was significantly increased by 81%, reaching 170 MPa in vertical direction compared to 100 MPa of the WA-DED 7B55-Sc component. [ABSTRACT FROM AUTHOR]

With the improvement of steel production technology, different grades of high-strength steel have been developed and widely applied in engineering, however the fatigue properties of high-strength steel need to be further studied. In this research, regarding the fatigue properties of Q690D high strength steel butt welds, experimental investigation and numerical simulation were carried out. Experimental investigations of Q690D high strength steel butt welds were performed, and properties including the basic mechanical behaviors, metallographic structure, fatigue crack growth rate and fatigue performance were obtained. The fatigue test results were compared with fatigue data from existing studies of butt welds and the Eurocode3 fatigue design S-N curve. The fatigue life prediction was performed and the fatigue crack propagation process was simulated based on the platform combining ABAQUS and Franc3D. The results show that the tested butt-welded joints specimen includes more initial defects, its fatigue properties are comparable to those of 355 MPa grade steel butt-welded joints, and the fatigue resistance advantages of high strength steels are not obvious. The simulated results are in good agreement with the fatigue test results, indicating the proposed simulation method is applicable in the fatigue life assessment of engineering structures with known initial defects. The proposed simulation method provided a numerical analysis approach to the fatigue assessment of engineering structures, thereby reducing the cost of fatigue tests and bringing significant economic and social benefits. • Experiments of Q690D butt welds were performed, high cycle fatigue performance were obtained. • The fatigue test results were compared with fatigue data from existing studies and Eurocode3 fatigue design S-N curve. • Fatigue life prediction was performed and the fatigue crack propagation process was simulated. • Different approaches of considering welding residual stress were analyzed. [ABSTRACT FROM AUTHOR]

The property of the surface layer of twice hole expansion Ti1023 alloy was analyzed by TEM, X-ray and roughness tester, and the strengthen mechanism of the bushing hole expansion was discussed. The results indicate that the roughness(Ra1.722→0.349 μm), hardness(Hv32→38) and residual stress distribution of the hole are improved by twice hole expansion techniques,and the fretting wear fatigue(fatigue limits 385→619MPa) of Ti1023 alloy is improved.

Through investigating the effect of parameters on the fatigue properties and crack propagation behavior of friction stir crack repaired 2024 aluminum alloy, we demonstrated that the fatigue strength of friction stir repaired Al2024 was sensitive to the repairing parameters and had a “V” type discipline with the rotating speed or advancing velocity. The fatigue crack growth rates of the repaired specimens were higher than the base material counterpart, and the crack propagation mechanism in the repaired zone was mainly intergranular. When the improper repairing parameters were adopted, the delamination defect would form at the interfaces between the repaired layer and base material

MnS inclusions in bearing steel have long been considered to significantly affect the fatigue life of bearing steel. In this paper, the sizes of inclusions in bearing steel with different sulfur contents were analyzed and the precipitation behavior of MnS was calculated using thermodynamics. Furthermore, the positive role of MnS in bearing steel was discussed. Results showed that when the size of inclusions in bearing steel was increased, the proportion of MnS components in composite inclusions gradually decreased. When the sulfur content was increased, the shape of inclusions changed from a particle shape to a strip shape. With increasing MnS content, the inclusion ratio of Al2O3 was significantly reduced in the Al2O3–CaO–MgO–MnS quaternary inclusion system, particularly for MnS proportions greater than 20%. The content of sulfur in bearing steel significantly affects the precipitation temperature of MnS. When sulfur content increases from 0.001% to 0.007%, the precipitation temperature of MnS increases from 1493 K to 1633 K as the precipitation of MnS moves from the austenite solid phase to the liquid and solid phases, and the precipitation size of MnS inclusions significantly increases. The size of oxide inclusions should be controlled to improve MnS wrap oxide inclusions in steel. Based on these results, a composition control with high sulfur levels and low oxygen levels should be adopted to improve the fatigue performance of steel.

Highlights • The fatigue properties of a new rib-to-deck welded joint linking the longitudinal U-rib and deck plate of orthotropic steel deck (OSD) were investigated in this study. • Seven large-scale OSD specimens, including three conventional OSDs and four OSDs utilizing the new type of rolled U-ribs, were tested under static and cyclic loadings. • Fatigue tests were carried out to investigate the fatigue damage propagation process, failure mode, and fatigue resistance; and the initiation and propagation of fatigue cracks were studied in terms of the morphology. • The effective notch stress method was employed to investigate the fatigue failure mechanism of the full-scale OSD specimens. Abstract This study investigates the fatigue performance of an innovative rib-to-deck welded joint linking the longitudinal U-rib and deck plate of orthotropic steel deck (OSD). The welded joint has an increased weld depth due to the rolled U-rib with thickened edges. Seven large-scale OSD specimens, including three conventional OSDs and four OSDs with the rolled U-ribs, were tested under static and cyclic loadings. The static loading tests indicate that the welded joint may significantly change the stress distribution around the rib-to-deck joint. Fatigue tests were carried out to investigate the damage propagation process, failure mode, and fatigue resistance. The effective notch stress method is employed to evaluate the fatigue properties and failure mechanism. For both types of the OSD specimens, the predominant failure mode was cracking at the deck weld root. The fatigue resistance of the specimens that had different U-ribs were comparable, indicating that the use of the rolled U-ribs did not significantly increase the resistance to the fatigue cracking initiated at the deck weld root. This study suggests that the evaluation of fatigue resistance must be performed based on the specific failure mode. [ABSTRACT FROM AUTHOR]

Abstract For decades, VO 2 -based smart windows have aroused much interest in energy efficient materials. To meet the practical requirements, VO 2 -based thin films should exhibit a high quality performance in equilibrating the solar modulation ability (Δ T sol) and the luminous transmittance (T lum) simultaneously. More importantly, durability and fatigue performance, which determine the life-time in actual use, have rarely been properly explored and obviously cannot be neglected. Herein, SiN x /VO 2 , VO 2 /SiN x and SiN x /VO 2 /SiN x multilayer structures were proposed and prepared by reactive magnetron sputtering in this work. The amorphous SiN x not only acts as the antireflection layer for promoting optical performance, but also serves as the ions diffusion barriers or passivation layers on the bottom and/or top of VO 2. As expected, the optimized composite structures successfully enhanced the solar modulation ability (from 10.8% to 14.5%, 34% maximum increase rate of Δ T sol) and luminous transmittance (from 36.1% to 40.4%, 12%maximum increase rate T lum-L) compared with single-layer VO 2 , in accordance with our optical modeling. More significantly, fatigue property had been unprecedentedly proposed and measured in about 2 years, demonstrating an ultra-long heating-cooling cycling times (104 cycles) in ambient atmosphere for SiN x /VO 2 /SiN x structure, exhibiting a dramatic life-time of 27 years, while the single layer VO 2 could only provide the life-time of 4 years (1.6 × 103 cycles). Moreover, SiN x /VO 2 /SiN x structure also presented excellent durability on hot and wet condition, which is three times as the VO 2 film without SiN x. Complementally, the improvement of the hydrophobicity with SiN x surface was found by contact angle test, which would make it possible to form an unobstructed view on rainy day. In conclusion, our works can provide facile structures and novel assessment method on fatigue performance for VO 2 -based films, and promote the industrial application for smart windows. Highlights • Two years fatigue performance was studied in VO 2 -based films. • SiN x /VO 2 /SiN x (SVS) structures exhibit an excellent optical performance. • SVS structures exhibit an elongated life-time in hot and wet environment. • Improved hydrophilicity is obtained by overlying SiN x on VO 2 films. [ABSTRACT FROM AUTHOR]

Ultra‐high molecular weight polyethylene (UHMWPE) is the most popular material used for the articulating surface of joint replacements. Delamination is a common fatigue‐related failure mode in UHMWPE components; however, the relationship between delamination resistance and fatigue crack growth has not been reported. Here, the delamination resistance of contemporary UHMWPE materials, including highly cross‐linked UHMWPE (HXLPE), vitamin E blended UHMWPE (VEPE), and vitamin E blended HXLPE (VEXLPE), was measured to verify a previously proposed accelerated test method using a U‐shaped sliding motion; the results were compared with those of fatigue crack growth tests. The oxidative stability of each material was estimated using Fourier transform infrared analysis. UHMWPE sterilized by gamma irradiation in an inert atmosphere and annealed HXLPE had lower delamination resistance than virgin UHMWPE after artificial aging. This was consistent with previous findings from retrieval studies, and in vitro knee simulator and ball‐on‐flat unidirectional reciprocation wear studies. In contrast, remelted HXLPE, VEPE, and VEXLPE showed excellent delamination resistance after artificial aging. The results of the delamination tests were not consistent with those of fatigue crack growth tests, indicating the complex delamination mechanism and importance of evaluating these factors separately. © 2018 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 107B: 65–72, 2019. [ABSTRACT FROM AUTHOR]

Abstract Porous titanium scaffolds with different unit cell type (tetrahedron and octahedron) and pore size (500 µm and 1000 µm) were fabricated by selective laser melting (SLM), and the effects of unit cell type and pore size on their fatigue properties and cell affinity were studied. The fatigue properties were performed by static and dynamic mechanical testing, while the cell affinity was evaluated in vitro with mouse osteoblast cells. It was found that octahedron scaffolds exhibited superior static mechanical properties, longer fatigue lives and higher fatigue strength in comparison to those of tetrahedron ones. As expected, scaffolds with 1000 µm pore resulted in lower compressive properties and shorter fatigue lives compared to those with 500 µm pore. The differences were analyzed based on the unit cell structure, porosity, and manufacturing imperfections. Scanning electron microscopy (SEM) and immunofluorescence showed that cells spread better on octahedron scaffolds than those on tetrahedron ones. Meanwhile, the scaffolds with 1000 µm pore were more suitable for cell attachment and growth within the same unit cell owing to higher porosity. The comparison of different pore geometry on the mechanical and biological property provided further insight into designing an optimal porous scaffold. Graphical abstract fx1 Highlights • The unit cell and pore size were estimated to affect the fatigue behavior and cell affinity of porous titanium scaffolds. • Octahedral scaffolds perform better than tetrahedral ones in fatigue properties that increase with decreasing pore size. • Cell proliferation was superior in the lattices with bigger pore size, and specifically in the octahedral unit cell. [ABSTRACT FROM AUTHOR]

Highlights • Heat treatment reduces fatigue property due to the separation and coarsening of Si. • Fatigue property is closely related to yield strength. • Surface or subsurface pores are sources of crack initiation. Abstract The fatigue property of selective laser melting AlSi10Mg samples with different heat treatments was investigated. The samples were tested in the state of as-built condition, stress relief treatment, solution treatment and solution + artificial aging treatment. It is found that the as-built sample displays the highest fatigue property, and the solution treatment samples exhibit the lowest fatigue property. Heat treatment reduces the fatigue property. The fatigue cracks originate from the surface or subsurface of all the samples, surface or subsurface pores have quite important effect on fatigue property. It is found that the fatigue property is closely related to the yield strength other than ultimate tensile strength or elongation. The change in fatigue property and static mechanical properties is mainly due to the microstructural transformation. Heat treatment changes the size and morphology of Si, which leads to a decrease in fatigue property. [ABSTRACT FROM AUTHOR]

The effect of loading type on the fatigue lifetime of sintered-silver die attach was investigated. The fatigue lifetime was measured by fatigue testing with micro-load testing equipment. The fatigue tests were conducted under displacement control with (reversed loading (stress ratio ${R}= -1$), pulsating-tensile loading (${R} =0$), and pulsating-compression loading (${R} = -\infty $)) at room temperature. The strain of the fatigue test was estimated by strain-displacement relation obtained from previous tensile test using the strain gauge. Sintered-silver specimens were made from prebaked microscale silver paste and pressurized at 10 MPa for 10 minutes in air atmosphere at 573 K. The fatigue lifetime of reversed-loading case was 1000 cycles, that of pulsating-tensile-loading case was 4000 cycles, and the pulsating-compression-loading case remained unbroken. This suggests that compression load does not contribute to the destruction of the sintered silver. These measured fatigue lifetimes were aligned in a row when these are organized by maximum stress (tensile stress range). For fatigue lifetime evaluation of sintered silver, evaluation focusing on tensile stress seems to be important. [ABSTRACT FROM AUTHOR]

To investigate the performance of asphalt mixture designed by the vertical vibration method, the vertical vibration design method (VTM design method) and Marshall design method were used to design the AC-16 (asphalt concrete with nominal maximum aggregate size = 16 mm) asphalt mixture. The physical properties, mechanical properties, road performance and fatigue property of the asphalt mixture designed by these two methods were examined. The results show that compared with that of the Marshall method, the optimal asphalt content of the asphalt mixture designed by the VTM method is decreased by 9.0%, and the density is increased by 1.8%; the mechanical properties, anti-rut ability and anti-crack ability are increased by at least 30%, 34% and 17%, respectively; and the water stability is also improved slightly. In addition, the fatigue life can be increased by at least 59%. The results also show that the Marshall stability, compression strength, splitting strength, tensile strength and shear strength of field drill cores designed by the VTM method are increased by at least 42%, 32%, 21%, 31% and 33%, respectively, compared with those of the Marshall method. Clearly, the performance of the asphalt mixture designed by the VTM method is better than that of the Marshall method, which could offer a better choice for asphalt mixture design. [ABSTRACT FROM AUTHOR]

To investigate the fatigue resistance, over-load adaptability, and energy dissipation performance of lead-filled steel tube damper (LFSTD), three different LFSTD specimens were designed and tested under fatigue loading conditions, and the remaining LFSTD specimen was designed and tested under conventional cyclic loading. The potential differences of the behavior of the dampers subjected to different loading protocols were revealed. The experimental results indicate that, the fatigue performance characteristics of the LFSTDs under the design displacement loading condition all satisfy the requirements of JGJ 297--2013 'Technical specification for seismic energy dissipation of building' for metallic dampers; under cyclic loading conditions which are 2 times or 1.5 times of design displacement, the LFSTDs still show excellent fatigue performance. The specimens also exhibit good over-load adaptability under an occasionally over-loading condition. The LFSTDs exhibit the same failure mode under either the fatigue loading condition or the conventional cyclic loading condition. The failure mode changes from a shear type to a bending-shear type with increase in the height-to-diameter ratio of the LFSTD. Under different displacement loading conditions, the LFSTDs exhibit good energy dissipation capacity, with symmetrical, full and parallelogram-shaped hysteretic loops. [ABSTRACT FROM AUTHOR]

The fatigue properties and life prediction of 2219 friction stir welded joints are studied based on the microstructure-based modeling. The joint macro-micro model containing the crystal characteristics is established. The stress and strain responses of the grains are obtained through the crystalline plastic theory. The phenomena of stress and strain concentration easily appear at the grain boundaries. The maximum average cumulative shear strain is in the weld nugget zone (WNZ). The maximum shear stress appears in the heat affected zone. The lower initial yield shear stress of crystals in the WNZ makes the slip system activation being liable to happen at the WNZ. It is confirmed that the weak area of the joint is the WNZ based on the analysis of the shear strain and stress distributions and the initial yield shear stresses in the joint. The fatigue life is predicted based on the established joint model. [ABSTRACT FROM AUTHOR]

Mechanical clinching is a connection technology that is widely used in different industrial fields because it has several advantages, including easy preparation, an excellent fatigue property and environmental friendliness. In this study, tensile-shear tests and fatigue tests were conducted to characterize the mechanical properties of clinched joints using aluminium alloys. The experimental results showed that the fracture regions were concentrated in the indentations of the lower sheets. The failed surfaces were examined using a scanning electron microscope and an energy-dispersive X-ray machine to study the fretting fatigue failure mechanisms of the clinched joints. Two types of fretting wear modes were observed: the neck fretting wear mode and indentation-surrounding fretting wear mode. The results also showed that the proportions of these two fretting wear modes could be impacted by the applied load levels. [ABSTRACT FROM AUTHOR]

To study the relationship among the temperature levels to which the high strength concrete is subjected, the time the high strength concrete is heated and the low cyclic compressive fatigue damage of the high strength concrete, fatigue tests were performed on C60 concrete under low cyclic compressive loading after temperatures of 200, 500, 800℃. Tests results show that the color of high strength concrete turns lighter after high temperature, and the structure of specimen is looser. The maximum longitudinal total strain of the high strength concrete after high temperature under low cyclic compressive loading is in accordance with the three-stage development law. Compared with the stress level, the effect of high temperature process on the fatigue strain of high strength concrete is more significant, especially the influence of heating temperature. Estimation formula of fatigue life was proposed based on the second stage of strain development. Fatigue deformation modulus ratio and relative residual strain were defined as damage variables, respectively. And the relationship models between the high temperature process and the fatigue damage were established. According to the damage model established by fatigue deformation modulus ratio, the fatigue life of high strength concrete was predicted. The calculation result has a good agreement with the test result. [ABSTRACT FROM AUTHOR]

The objective was to investigate the influence of grade and surface topography of commercially pure titanium (Cp-Ti) on fatigue properties evaluated via staircase method. Cp-Ti grades 2 and 4 were roughened by shot blasting and acid etching, and compared with machined specimens. Yield force under static loading for Cp-Ti grades 2 and 4 were 672±51 and 1,088±93 N for machined and 724±99 and 1,118±96 N for roughened group. Yield force under cyclic loading for Cp-Ti grades 2 and 4 decreased 27 and 40% compared to static loading. Cp-Ti grade 4 demonstrated significantly greater decrease in yield force after cyclic loading; however surface topography had no effect. [ABSTRACT FROM AUTHOR]

• The combined laser bionic and ultrasonic impact were firstly treated welded joints. • Composite treatment had a compatibility effect and optimized the bionic structure. • Gradient heterogeneous structure was formed by composite treatment. • The fatigue strength of Mg alloy welded joint was increased by composite treatment. The present work investigates the effect of combined laser bionic treatment (LBT) and ultrasonic impact treatment (UIT) on the fatigue properties of AZ31B magnesium alloy TIG welded joints. The fine grains with random orientation were obtained in weld seam after LBT, resulting microhardness increased, and the surface of welded joint formed a "soft-hard" alternating bionic structure. After the composite treatment, the maximum compressive residual stress was induced on the surface of welded joint, which was about −272 ± 30 MPa. In addition, obvious plastic deforming layer and nanocrystalline grains were formed. The grains with preferred orientation were obtained in the plastic deforming layer. The fatigue test showed that the fatigue strength of composite treated welded joint sample increased by 33% and 125% compared with LBT treated welded joint and untreated welded joint samples at 107 cycles, respectively. The composite treatment changed the nucleation position and fracture morphology of the crack, as well as induced a series of strengthening mechanisms. [ABSTRACT FROM AUTHOR]

While Laser Powder Bed Fusion (LPBF) is a popular, rapidly advancing field of research, a comprehensive or deeper understanding of the mechanical, especially fatigue, properties of steels has not yet been fully achieved. In this work, a deeper investigation on the microstructural load capacity, critical defect size distribution and defect tolerance of fatigue performance of the commonly used 316L austenitic steel were performed. The 316L parts were generated via LPBF with three different scan patterns and polar angles. Resulting porosities were measured with Archimedes' method and cross section scanning with optical microscopy. To understand the relation of process parameters, microstructure and mechanical behaviors, the microstructure and mechanical properties were studied. Fatigue damage origins and fracture mechanisms were investigated. Results showed that apart from comparable hardness to the conventional steel, tensile properties (except Young's modulus) are slightly worse than the conventional values, owing to the fact that the presence of pores and inclusions promote earlier plastic deformations and ductile fracture. The fatigue strength is inferior compared to the conventional steel and most samples failed from lack of fusion. The surfaces of lack of fusion areas, triggering fatigue failure, are either smooth or show parallel lines. The different scan strategies lead to no big difference in the microstructures except the size of the largest lack of fusion area. The polar angles determine the orientations of lack of fusion to the loading axis and result in different sizes of fatigue triggering defects and deteriorate the matrix load capacity to different extents. Spherical pores within a certain range have limited impact. Parallel simulations confirm the defect tolerance determined by the morphology and critical size on the fatigue strength. • Lack of fusion size and matrix strength influence the fatigue strength. • The microstructure do not show changes with the scan pattern except the defects. • Polar angle influences the matrix strength and the largest defect size. • Most powder bed fusion generated samples failed from cavity or lamellar structure. • A defect tolerance determined by the morphology and critical size of failure relevant defects is highlighted. [ABSTRACT FROM AUTHOR]

• Fatigue properties of HVAM with different types of fibers were investigated. • The fatigue damage of HVAM mainly occurs at temperatures below 22 °C. • Using high-viscosity asphalt is important for open graded asphalt pavements to meet the anti-fatigue performance. • The fatigue life of polyester fiber reinforced HVAM increases uniformly with the increase of fiber content. • The fatigue life of basalt fiber reinforced HVAM increases significantly when the fiber content exceeds 1%. Open-graded asphalt mixture pavement, with its functional benefits of drainage and noise reduction, holds promising engineering application potential. The high-viscosity asphalt mastic significantly influences the performance of this open-graded asphalt mixture. In this study, the fatigue performance of fiber reinforced high-viscosity asphalt mastic was investigated based on rheology. Shear rheometer was used to perform temperature sweep tests, time sweep tests, and linear amplitude sweep tests on the fiber reinforced high-viscosity asphalt mastic. The influences of filler/binder ratio, filler properties, fiber type, and content on the fatigue performance of the mastic were analyzed. Time sweep test data was used to establish a prediction equation for temperature-stress fatigue life of the mastic. The interconnectivity and differences between various fatigue life indicators were studied based on phenomenology and energy dissipation theory. The fatigue characteristics and damage mechanism of the mastic were investigated using a viscoelastic damage model, and the fatigue lives at different strain levels were observed. The research results indicate that fatigue damage of high-viscosity asphalt mastic mainly occurs at low temperatures. An increase in filler/binder ratio at the same temperature reduces the anti-fatigue performance of the mastic. Compared with dust, mineral powder has a larger specific surface area and better fatigue resistance performance. The established temperature-stress equation can accurately predict the fatigue life of mastic under different temperatures and stresses. The fatigue indicators N p20 and N fm , based on energy dissipation theory, show a favorable linear relation with the fatigue indicator N f50 based on phenomenology, and these three indicators are consistent in evaluating the fatigue performance and life of the mastic. N p20 and N fm are found to be more applicable for evaluating the fatigue performance of fiber reinforced high-viscosity asphalt mastic. The fatigue life of the mastic decreases with increasing strain levels, and high-viscosity asphalt mastic containing basalt fiber shows better adaptability to complex traffic conditions. [ABSTRACT FROM AUTHOR]

In this paper, the surface of 7N01 aluminum alloy profile is sandblasted or electropolished. The influence of different surface conditions on its conditional fatigue strength and fatigue mechanism under the alternating load after prefabricated short crack are studied. Results show that the 7N01 aluminum alloy with sandblasting treatment has formed a work hardened layer and its fatigue strength is increased by 42.9% comparing with the original surface specimens. The fatigue strength of the 7N01 aluminum alloy after electropolishing is almost unchanged compared with the original specimen. The fatigue behavior of the 7N01 aluminum alloy after prefabricated side straight through the notch deviated from the theoretical smooth specimen law and long crack propagation law in which is a ‘shortage effect’. When the notch size is smaller than the transition crack size a _0 , the fatigue limit of the notched specimen is lower than the fatigue limit of the smooth specimen. When the notch size is larger than the transition crack size, the fatigue limit of the long-notched specimen is still lower than that predicted by linear elastic fracture mechanics. Due to the ‘short notch effect’, the effective notch propagation threshold ΔK _eff.th of the long crack is 0.39 Mpa m ^1/2 based on the effective notch propagation size a _0 eff of the alloy.

The fatigue property is significantly affected by the inner inclusions in steel. Due to the inhomogeneity of inclusion distribution in the micro-scale, it is not straightforward to quantify the effect of inclusions on fatigue behavior. Various investigations have been performed to correlate the inclusion characteristics, such as inclusion fraction, size, and composition, with fatigue life. However, these studies are generally based on vast types of steels and even for a similar steel grade, the alloy concept and microstructure information can still be of non-negligible difference. For a quantitative analysis of the fatigue life improvement with respect to the inclusion engineering, a systematic and carefully designed study is still needed to explore the engineering dimensions of inclusions. Therefore, in this study, three types of bearing steels with inclusions of the same types, but different sizes and amounts, were produced with 50 kg hot state experiments. The following forging and heat treatment procedures were kept consistent to ensure that the only controlled variable is inclusion. The fatigue properties were compared and the inclusions that triggered the fatigue cracks were analyzed to deduce the critical sizes of inclusions in terms of fatigue failure. The results show that the critical sizes of different inclusion types vary in bearing steels. The critical size of the spinel is 8.5 μm and the critical size of the calcium aluminate is 13.5 μm under the fatigue stress of 1200 MPa. In addition, with the increase of the cleanliness of bearing steels, the improvement of fatigue properties will reach saturation. Under this condition, further increasing of the cleanliness of the bearing steel will not contribute to the improvement of fatigue property for the investigated alloy and process design.