Search

In this study, the effects of UV radiation on the high temperature fatigue performance of SBS modified asphalt and asphalt mixtures were analyzed, and the effects of outdoor atmospheric UV radiation were simulated by indoor UV accelerated aging test. The results showed that the increase of UV radiation time led to the increase of creep recovery rate of asphalt and the decrease of irrecoverable creep flexibility, i.e., the resistance to permanent high temperature deformation of SBS modified asphalt was improved. The fatigue cracking resistance of asphalt was weakened and accelerated by radiation. UV radiation increased the rutting resistance of asphalt mixtures and weakened the fatigue resistance at high temperatures. At the same time, UV radiation reduced the aromatic and saturated content of SBS modified asphalt, which led to a reduction in the relative aromatic and saturated content of asphalt mixtures. [ABSTRACT FROM AUTHOR]

This paper investigates the tensile and low-cycle fatigue characteristics of S32750 duplex stainless steel subjected to two distinct solid solution treatment temperatures. The microstructures, fracture surfaces, and slip systems of the tested steel were analyzed using optical microscopy (OM), scanning electron microscopy (SEM), and transmission electron microscopy (TEM) techniques. The findings reveal that elevating the solid solution treatment temperature from 1080 °C to 1180 °C results in an increase in the yield strength of the tested steel by approximately 36 MPa and a substantial enhancement in fatigue life by 34%. Microhardness measurements indicate that the degree of hardening in austenite post-fatigue failure significantly surpasses that of ferrite. The variation in solid solution temperature alters the ferrite and austenite content within the matrix, consequently affecting the strain distribution between the two phases. The high-temperature solid solution treatment effectively enhances the two-phase strain-bearing capacity of the tested steel. Following the 1180 °C solid solution treatment, no cloud-like dislocation patterns were observed in the ferrite; instead, they were replaced by a proliferation of thick, interwoven dislocation bundles. In contrast, the dislocations within the austenite predominantly consist of ordered planar slip and twinning. The primary contributor to the extended fatigue life is the increased number of absorbed dislocations within the ferrite grains. [ABSTRACT FROM AUTHOR]

Laser-MIG hybrid welding and MIG welding were carried out on 7B52 aluminum alloy, and the microstructure and mechanical properties of the joints were compared and analyzed. The results show that the average grain sizes of laser-MIG hybrid welding, MIG welding, and the laser weld zone are 18.38 μm, 24.16 μm, and 15.96 μm, respectively. The width of the HAZ of the laser zone is lower than that of the laser-MIG hybrid welding zone and MIG welding zone. The hardness is higher than that of the hybrid welding zone and MIG welding zone. The tensile strength of each laser-MIG hybrid welding joint zone is better than that of the MIG welding zone. The tensile strength of the laser zone is the worst. When stress ratio R = 0.1 and fatigue cycle Nf = 106, the fatigue strength of the laminated zone of the laser-MIG hybrid welding joint is better than that of the MIG welding joint, and the welding defect is the leading cause of fatigue cracks. [ABSTRACT FROM AUTHOR]

The accurate characterization of fatigue life affects the durability and reliability of asphalt pavement for the asphalt mixtures. This paper proposed a new fatigue test method and analysis method which, in addition to increasing the accuracy of fatigue characterization, reduces the time and cost consumed in laboratory tests of asphalt mixtures. According to the loading speed corresponding to different loading frequency and stress levels, the corresponding strength value is selected to determine the stress ratio in the fatigue equation. Therefore, the stress ratio can truly reflect the fatigue loading stress conditions and correspond to the fatigue loading speed one by one, avoiding the unscientific fatigue resistance design problem caused by the traditional S-N fatigue equation stress ratio, which takes a single strength value at a constant loading speed as the standard. Since the stress ratio takes into account the influence of loading speed under different loading frequencies and stress levels, a unified representation model of the fatigue equation of the asphalt mixture under different loading frequencies can be established; that is, the fatigue performance of the asphalt mixture under different loading frequencies can be normalized. The results showed that the loading rate in the strength test differed from the loading rate in the traditional fatigue test, which means that the fatigue curve could not be extended to point (1,1) when the fatigue equation was extended to a fatigue life N f = 1. The fatigue test related to the velocity-dependent stress ratio in multiple experimental works, and data discreteness had a remarkable influence on fatigue characterization. The fatigue curve obtained by the fatigue equation under a constant loading rate was consistent with the fatigue curve under different loading rates. This method can reduce the duration of strength tests and the impact of the strength results of discreteness on fatigue characterization. The fatigue characterization model under constant loading rates considered the viscoelasticity of asphalt mixtures and guaranteed the correspondence of test conditions among stress level t, standard strength St, and fatigue life N f . The stress levels and loading rates of the asphalt mixtures were confirmed to be equivalent. Furthermore, this paper established the relationship between strength and fatigue and obtained the fatigue life curve of the strength values. The fatigue performance of the asphalt mixtures is evaluated comprehensively. [ABSTRACT FROM AUTHOR]

This research produced five hybrid-bonded fiber-reinforced plastic (HB-FRP)-reinforced beam specimens, and different fatigue load amplitudes were used as parameter variables for the fatigue performance tests of the FRP–concrete interface. The results show that FRP sliding with the number of cycles can be roughly divided into fatigue initiation stage, fatigue development stage, and fatigue damage stage, and finally, because the load is too large and friction, pin, and bonding cannot provide a greater inhibition effect, FRP adhesive length is not enough to withstand the stripping load and failure. FRP slip increases with increasing fatigue load amplitude for the same number of fatigue cycles; for the specimens with fatigue damage, the interfacial stiffness of FRP–concrete decreases with the increase in the number of cyclic, and the rate of stiffness damage at the FRP–concrete interface accelerates with increasing fatigue load amplitude. For fatigue load magnitudes higher than 0.6, the slopes of fatigue bond–slip curves decrease with the increase in the number of cycles. When the fatigue load magnitude is lower than 0.4, the slope of the fatigue bond–slip curve increases with the number of cycles and is close to the slope of the monotonically loaded curve. Due to the difference in load class, the bond strength of HB-F-1 continues to decrease with the increase in fatigue times, decreasing by 26% after 100 fatigue cycles and decreasing to 7.33 MPa after 5000 fatigue cycles. The bond strength of the sample HB-F-2 first increased and then decreased with the increase in fatigue times. After 10,000 fatigue cycles, the bond strength decreased by 8%, and at 11,133,300 fatigue breaks, the bond strength of the sample HB-F-3 continued to increase with the increase in fatigue times. At 2 million fatigue load cycles, the bond strength increased to 7 MPa, far from reaching the peak strength. The empirical formulas for the fatigue life curve of HB-FRP-reinforced specimens under single steel fasteners are proposed. [ABSTRACT FROM AUTHOR]

In this paper, (0.2–1 wt%) Yb was added to improve the tensile properties and high-cycle fatigue behavior of the as-cast and as-extruded Mg-10Li-5Zn-0.5Er alloys. It is found that Yb mainly affects the mechanical properties of the alloy by changing the grain size, type and morphology of the second phases. Yb mainly exists in the formation of Mg2Yb and Mg-Zn-Yb phases in the metallographic structure. With the addition of Yb, the grains are refined and these Yb-containing phases replace the large-sized MgLiZn phase to be enriched at the grain boundaries. While the addition of excess Yb reduces the number of small-sized MgLiZn phases in the grain, thus reducing the alloys’ mechanical performance. After extrusion, the small-sized MgLiZn phase is refined and the number increases, which effectively improves the tensile and fatigue strength of the alloy. The fatigue strength is mainly affected by the number and morphology of the second phase, positively correlated with the strength. Balanced in grain size and number and size of second phases, the extruded alloy with 0.2Yb added exhibits excellent mechanical properties with the yield strength, ultimate tensile strength and elongation of 292 MPa, 303 MPa and 11.7%, and an fatigue strength of 130 MPa.

• The effect of Yb on the microstructure and mechanical properties of Mg-Li-Zn alloy is proved. • A Mg-Li alloy with a fatigue strength of 130 MPa is developed. • The small-sized MgLiZn phase in the Mg-Li-Zn alloy has been observed. The transformation law of small-sized MgLiZn phase with the Yb content and hot extrusion treatment and its influence mechanism on the microstructure and mechanical properties have been clarified. In this paper, (0.2–1 wt%) Yb was added to improve the tensile properties and high-cycle fatigue behavior of the as-cast and as-extruded Mg-10Li-5Zn-0.5Er alloys. It is found that Yb mainly affects the mechanical properties of the alloy by changing the grain size, type and morphology of the second phases. Yb mainly exists in the formation of Mg 2 Yb and Mg-Zn-Yb phases in the metallographic structure. With the addition of Yb, the grains are refined and these Yb-containing phases replace the large-sized MgLiZn phase to be enriched at the grain boundaries. While the addition of excess Yb reduces the number of small-sized MgLiZn phases in the grain, thus reducing the alloys' mechanical performance. After extrusion, the small-sized MgLiZn phase is refined and the number increases, which effectively improves the tensile and fatigue strength of the alloy. The fatigue strength is mainly affected by the number and morphology of the second phase, positively correlated with the strength. Balanced in grain size and number and size of second phases, the extruded alloy with 0.2Yb added exhibits excellent mechanical properties with the yield strength, ultimate tensile strength and elongation of 292 MPa, 303 MPa and 11.7%, and an fatigue strength of 130 MPa. [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.)

This paper investigates the tensile and low-cycle fatigue characteristics of S32750 duplex stainless steel subjected to two distinct solid solution treatment temperatures. The microstructures, fracture surfaces, and slip systems of the tested steel were analyzed using optical microscopy (OM), scanning electron microscopy (SEM), and transmission electron microscopy (TEM) techniques. The findings reveal that elevating the solid solution treatment temperature from 1080 °C to 1180 °C results in an increase in the yield strength of the tested steel by approximately 36 MPa and a substantial enhancement in fatigue life by 34%. Microhardness measurements indicate that the degree of hardening in austenite post-fatigue failure significantly surpasses that of ferrite. The variation in solid solution temperature alters the ferrite and austenite content within the matrix, consequently affecting the strain distribution between the two phases. The high-temperature solid solution treatment effectively enhances the two-phase strain-bearing capacity of the tested steel. Following the 1180 °C solid solution treatment, no cloud-like dislocation patterns were observed in the ferrite; instead, they were replaced by a proliferation of thick, interwoven dislocation bundles. In contrast, the dislocations within the austenite predominantly consist of ordered planar slip and twinning. The primary contributor to the extended fatigue life is the increased number of absorbed dislocations within the ferrite grains.

Copyright of Chinese Journal of Applied Mechanics is the property of Chinese Journal of Applied Mechanics 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.)

In this study, 6061-T6 aluminum alloys were plated with electroless Ni–P with different phosphorus content and three-point bending and rotating bending fatigue tests. The effects of hydrogen due to plating on mechanical properties were investigated. It was shown that the ductility decreased immediately after low-phosphorus type and high-phosphorus type Ni–P plating by three-point bending test because a hydrogen was introduced into the alloys. The fatigue strength of the low-phosphorus type Ni–P plated specimen was higher than that of the un-treated specimen, while that of the high-phosphorus type plated specimen was much lower. It is clear that the fatigue strength differs greatly depending on the phosphorus content in the plating film. 6061-T6 aluminum alloy have been reported to exhibit no hydrogen embrittlement in low strain rate tensile tests under wet condition. However, it was found that hydrogen embrittlement occurred when 6061-T6 aluminum alloy was plated with the high-phosphorus type electroless Ni–P and fatigue-tested on rotating bending machine. [ABSTRACT FROM AUTHOR]

The removal of lignin from natural cellulose fibers is a crucial step in preparing high-performance materials, such as compressed high-toughness composites. This process can eliminate non-cellulosic impurities, create abundant compressible pores, and expose a greater number of active functional groups. In this study, biomass waste windmill palm fiber was used as the raw material to prepare holocellulose fibers through various chemical treatments. The structure, chemical composition, Fourier transform infrared spectroscopy analysis, X-ray diffraction analysis, thermal properties, and mechanical properties, particularly fatigue performance, were studied. The sodium chlorite treated fiber had the highest crystallinity index (61.3%) and the most complete appearance structure. The sodium sulfite treated fiber had the highest tensile strength (227.34 ± 52.27) MPa. Hydroxide peroxide treatment removed most of the lignin and hemicellulose, increasing the cellulose content to 68.83% ± 0.65%. However, all the chemical treatments decreased the thermal property of the fibers.

This research produced five hybrid-bonded fiber-reinforced plastic (HB-FRP)-reinforced beam specimens, and different fatigue load amplitudes were used as parameter variables for the fatigue performance tests of the FRP–concrete interface. The results show that FRP sliding with the number of cycles can be roughly divided into fatigue initiation stage, fatigue development stage, and fatigue damage stage, and finally, because the load is too large and friction, pin, and bonding cannot provide a greater inhibition effect, FRP adhesive length is not enough to withstand the stripping load and failure. FRP slip increases with increasing fatigue load amplitude for the same number of fatigue cycles; for the specimens with fatigue damage, the interfacial stiffness of FRP–concrete decreases with the increase in the number of cyclic, and the rate of stiffness damage at the FRP–concrete interface accelerates with increasing fatigue load amplitude. For fatigue load magnitudes higher than 0.6, the slopes of fatigue bond–slip curves decrease with the increase in the number of cycles. When the fatigue load magnitude is lower than 0.4, the slope of the fatigue bond–slip curve increases with the number of cycles and is close to the slope of the monotonically loaded curve. Due to the difference in load class, the bond strength of HB-F-1 continues to decrease with the increase in fatigue times, decreasing by 26% after 100 fatigue cycles and decreasing to 7.33 MPa after 5000 fatigue cycles. The bond strength of the sample HB-F-2 first increased and then decreased with the increase in fatigue times. After 10,000 fatigue cycles, the bond strength decreased by 8%, and at 11,133,300 fatigue breaks, the bond strength of the sample HB-F-3 continued to increase with the increase in fatigue times. At 2 million fatigue load cycles, the bond strength increased to 7 MPa, far from reaching the peak strength. The empirical formulas for the fatigue life curve of HB-FRP-reinforced specimens under single steel fasteners are proposed.

The accurate characterization of fatigue life affects the durability and reliability of asphalt pavement for the asphalt mixtures. This paper proposed a new fatigue test method and analysis method which, in addition to increasing the accuracy of fatigue characterization, reduces the time and cost consumed in laboratory tests of asphalt mixtures. According to the loading speed corresponding to different loading frequency and stress levels, the corresponding strength value is selected to determine the stress ratio in the fatigue equation. Therefore, the stress ratio can truly reflect the fatigue loading stress conditions and correspond to the fatigue loading speed one by one, avoiding the unscientific fatigue resistance design problem caused by the traditional S-N fatigue equation stress ratio, which takes a single strength value at a constant loading speed as the standard. Since the stress ratio takes into account the influence of loading speed under different loading frequencies and stress levels, a unified representation model of the fatigue equation of the asphalt mixture under different loading frequencies can be established; that is, the fatigue performance of the asphalt mixture under different loading frequencies can be normalized. The results showed that the loading rate in the strength test differed from the loading rate in the traditional fatigue test, which means that the fatigue curve could not be extended to point (1,1) when the fatigue equation was extended to a fatigue life Nf = 1. The fatigue test related to the velocity-dependent stress ratio in multiple experimental works, and data discreteness had a remarkable influence on fatigue characterization. The fatigue curve obtained by the fatigue equation under a constant loading rate was consistent with the fatigue curve under different loading rates. This method can reduce the duration of strength tests and the impact of the strength results of discreteness on fatigue characterization. The fatigue characterization model under constant loading rates considered the viscoelasticity of asphalt mixtures and guaranteed the correspondence of test conditions among stress level t, standard strength St, and fatigue life Nf. The stress levels and loading rates of the asphalt mixtures were confirmed to be equivalent. Furthermore, this paper established the relationship between strength and fatigue and obtained the fatigue life curve of the strength values. The fatigue performance of the asphalt mixtures is evaluated comprehensively.

Laser-MIG hybrid welding and MIG welding were carried out on 7B52 aluminum alloy, and the microstructure and mechanical properties of the joints were compared and analyzed. The results show that the average grain sizes of laser-MIG hybrid welding, MIG welding, and the laser weld zone are 18.38 μm, 24.16 μm, and 15.96 μm, respectively. The width of the HAZ of the laser zone is lower than that of the laser-MIG hybrid welding zone and MIG welding zone. The hardness is higher than that of the hybrid welding zone and MIG welding zone. The tensile strength of each laser-MIG hybrid welding joint zone is better than that of the MIG welding zone. The tensile strength of the laser zone is the worst. When stress ratio R = 0.1 and fatigue cycle Nf = 106, the fatigue strength of the laminated zone of the laser-MIG hybrid welding joint is better than that of the MIG welding joint, and the welding defect is the leading cause of fatigue cracks.

The microstructure and performance homogeneity of 80 mm thick ultra-wide 7B50-T7751 plate with different widths and thicknesses were studied by means of mechanical testing machine and scanning electron microscope, and the fatigue properties were compared and discussed with 7050-T7451 plate. The results show that the ultra-wide 7B50-T7751 plate has excellent mechanical properties. In L and LT directions, the tensile yield strength of 1/2 thickness reaches up to 568 MPa and 545 MPa, and the tensile strength reaches up to 612 MPa and 591 MPa, the compressive yield strength reaches up to 575 MPa and 587 MPa, the fracture toughness in L-T direction and T-L direction reaches 30.16 MPa·m1/2 and 26.47 MPa·m1/2, respectively. The ultra-wide thick plate exhibits certain anisotropy at different width positions, the performance homogeneity in LT direction tends to be better than in L direction. Performance at different width positions with 1/4 thickness shows little difference, while the performance at the edge of 1/2 thickness is better than that of the center. No obvious texture exhibits at 1/4 thickness, however, the main textures at the center of 1/2 thickness are S texture and Brass texture, and the main textures at the edge are R texture, S texture and Brass texture. When the stress ratio is 0.06, the T-L anti-fatigue crack growth rate performance of ultra-wide 7B50-T7751 thick plate is better than 7050-T7451 plate with the same thickness. The fatigue limit of LT smooth sample (Kt=1) is about 7.6% inferior than that of 7050-T7451 plate, while the fatigue limit of notch sample (Kt=3) is about 3.7% higher.

Due to their distinct physical, chemical, and mechanical features, high-entropy alloys have significantly broadened the possibilities of designing metal materials, and are anticipated to hold a crucial position in key engineering domains such as aviation and aerospace. The fatigue performance of high-entropy alloys is a crucial aspect in assessing their applicability as a structural material with immense potential. This paper provides an overview of fatigue experiments conducted on high-entropy alloys in the past two decades, focusing on crack initiation behavior, crack propagation modes, and fatigue life prediction models. [ABSTRACT FROM AUTHOR]

The structure and properties of high modulus natural rubber (NR) / cis-1,4-polybutadiene rubber (BR) blends reinforced with carbon black and modified with trans-1,4-poly(butadiene-co-isoprene) rubber (TBIR) and low Mooney viscosity trans-1,4-poly(butadiene-co-isoprene) rubber (LTBIR) were investigated. The results showed that both of the TBIR and LTBIR could significantly improve the compatibility between NR and BR. Compared with NR/BR vulcanizates, the mechanical properties and resilience of high modulus NR/BR vulcanizates modified with TBIR and LTBIR with reducing 4 phr (mass) carbon black were improved, wear volume reduced by 13%, compression heat generation reduced by 10%, rolling resistance reduced by 20%, first-grade flex fatigue life improved by about 1.6 times, and sixth-grade flex fatigue life improved by about 1.1 times.

Copyright of Bulletin of the Chinese Ceramic Society is the property of Bulletin of the Chinese Ceramic Society 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.)

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.)

Impact test is a universal method to characterize the fatigue property of coated tools. For the bilayer TiSiN/TiAlN coated tool, the stress state in the cutting process with different feed rates were explored through cutting experiments. A high-temperature and high-frequency impact test platform was built. Through the impact tests with the introduction of the 'pre-loading depth', the fatigue properties and failure mechanisms of coatings under various test conditions were analyzed. Based on the comparative analysis of the results obtained in cutting experiments and impact tests, the mapping relationship between fatigue properties and cutting performances of the coatings was established, thus providing theory and practice foundation for characterization the cutting performance of coated tools under different cutting parameters by high-temperature and high-frequency impact tests. [ABSTRACT FROM AUTHOR]

The disposal of waste face masks (FM) caused by COVID-19 has become an increasingly severe problem. In order to alleviate this issue, this paper proposes an approach of adding face mask waste as modifiers to asphalt. Extensive performance tests evaluated the feasibility of FM in asphalt binders, including rotational viscosity and rheological behaviors at different temperatures, aging performance, separation tendency, and modification mechanism. Based on this, the road performance of FM-modified asphalt mixtures were also investigated. The results showed that FM increased the rotational viscosity, high-temperature performance, and anticreep performance, whereas it had a negative effect on the stress change sensitivity, low-temperature performance, aging performance, and storage stability of asphalt binder. Based on the linear amplitude sweep test results, the incorporation of FM contributed to the material integrity and load resistance capacity of asphalt binder, whereas it was not conducive to its antideformation performance. According to Fourier transform infrared spectroscopy and fluorescence images, the modification process of FM with a chemical composition of polypropylene was mainly a physical blend, and 5% FM had the best compatibility with asphalt. The addition of FM could improve Marshall stability, rutting resistance, low-temperature cracking resistance, and moisture susceptibility of an AC-13 mixture. The 5% FM-modified asphalt and asphalt mixture met the specific road requirements. The experiment results could provide a new way to deal with waste FM by recycling. [ABSTRACT FROM AUTHOR]

Microwave heating technology is a promising method for asphalt pavement maintenance and de-icing; however, it requires the material to have a good microwave-absorbing ability and can also result in asphalt aging. It is therefore important to develop microwave-sensitive materials used for asphalt pavement maintenance and study the effects of microwave heating on asphalt aging. This study evaluates the electromagnetic characteristics of limestone powder and magnetite powder and explores the influence of microwave heating on the high-temperature rheological and fatigue properties of microwave sensitivity enhanced asphalt mastic with magnetite powder. A vector network analyzer was used to measure the electromagnetic characteristics of limestone powder and magnetite powder. The magnetite filler asphalt mastics were prepared and subjected to microwave heating for 1 h, 2 h, 3 h, and 4 h. Temperature sweep tests, frequency sweep tests, and linear amplitude sweep (LAS) tests were conducted for magnetite filler asphalt mastics before and after microwave heating. LAS experimental results were analyzed based on viscoelastic continuum damage (VECD) theory. The results show that magnetite powders have better electric field energy storage ability, higher dielectric loss and magnetic loss, and better microwave heating efficiency. The complex shear modulus (G*) and rutting factor (G* × (sin δ)−1) rapidly decrease with the increase in temperature, indicating that the mastics' ability to resist deformation decreases sharply. The longer the microwave heating time for magnetite filler asphalt mastics, the faster the high-temperature rheological properties decreased as the temperature rose. The fatigue life of magnetite filler asphalt mastics significantly decreases with the increase in strain and microwave heating time. It is suggested to add anti-aging agents into asphalt materials to reduce the aging effect in the process of microwave heating. This study provides a reference for the application of microwave heating technology in asphalt pavement maintenance. [ABSTRACT FROM AUTHOR]

As one of the widely used materials for hydro turbine runners, 13Cr4Ni martensitic stainless steels (13/4 MSS) manufactured by forging and wire arc additive manufacturing (WAAM), respectively, were selected for high-cycle fatigue tests, and the effects of microstructures and defect characteristics on fatigue mechanism were investigated. The results indicate that compared to the forged 13/4 MSS, the microstructure of the WAAM test piece is very fine, and the martensite units, consequently, are smaller in size. The yield strength and ultimate tensile strength are 685 MPa and 823 MPa for the forged specimen and 850 MPa and 927 MPa for the WAAM specimens, respectively. The fatigue strength of 107 cycles at room temperature is 370 MPa for forged specimens and 468 MPa for WAAM specimens. The predominant defect of the forged 13/4 MSS specimen is inclusion, and the fatigue initiates mainly at the surface and subsurface. While for the WAAM specimen, the most commonly found defects are pores, and the fatigue initiation is internal and at the subsurface. In addition, the fine microstructure, as well as the high strength and hardness, enable the WAAM material to have higher fatigue strength. In order to assess the effect of defects on fatigue performance, the stress intensity factor and El-Haddad model were adopted in the present study. It was found that the forged specimens with fish-eye (FIE) zones and the WAAM specimens with granular bright facet (GBF) zones have longer fatigue life. The fatigue strengths of the forged 13/4 MSS were therefore predicted by defect size. In contrast, the fatigue strengths of the WAAM 13/4 MSS were predicted by both defect and GBF sizes. [ABSTRACT FROM AUTHOR]

Additive manufacturing technologies have several well-known advantages; however, the surface quality of the printed parts is poor, compromising the corrosion and mechanical properties. Thus, surface finishing treatments are necessary. The most post-processing treatments proposed in the literature are mechanical or chemical. The formers are contact techniques and cannot be suitable for complex geometry, while the latter use strong and dangerous reagents. This paper is aimed to investigate the effect of the electropolishing treatment, a contactless technique, using an eco-friendly electrolytic solution in reducing the roughness and improving the fatigue properties of Ti6Al4V specimens produced by electron beam melting technology. Several parameters affecting the effectiveness of the electropolishing treatment have been investigated, as interelectrode distance, stirring rate and duration time. An optimal combination of them allowed a uniform surface treatment and a significant roughness reduction (64% of Sa reduction for cylindrical specimens). Under sinusoidal loading conditions with a maximum stress of 378 MPa and a stress ratio equal to R = 0.1, the mean fatigue life of electropolished dog-bone specimens was 250% longer than that of as-built specimens. [ABSTRACT FROM AUTHOR]

Maraging steel components fabricated by laser powder-bed fusion, which is a technique of additive manufacturing, are expected to be used widely because of their high strength, hardness and toughness. To apply maraging steel manufactured by laser powder-bed fusion in wider industrial fields and prevent the components from fracture, a study was conducted to improve the wear resistance and fatigue properties of the steel by an atmospheric-controlled induction-heating fine particle peening surface modification technique. The technique developed can create hard intermetallic compound layers and introduce peening effects, which are expected to improve the wear resistance and fatigue properties of maraging steel fabricated by laser powder-bed fusion. The prepared specimens were examined using optical microscopy, scanning electron microscopy, energy dispersive X-ray spectroscopy, laser microscopy, X-ray diffraction, micro-Vickers hardness testing, nano-indentation testing, reciprocating ball-on-disk wear tests and axial fatigue tests. It was revealed that atmospheric-controlled induction-heating fine particle peening using mechanically milled particles formed Fe–Al intermetallic compound layers with high hardness, introduced compressive residual stresses and increased the hardness of the maraging steel substrate owing to age hardening. In conclusion, atmospheric-controlled induction-heating fine particle peening can simultaneously improve the wear resistance and fatigue properties of maraging steel fabricated by laser powder-bed fusion within a few minutes. These achievements can expand applications of maraging steel fabricated by laser powder-bed fusion.

Ambiguous fatigue failure mechanism of micro-arc oxidation (MAO) coated samples was an urgent issue to be solved. In this paper, the influence mechanism of coating defects on the fatigue property of the samples with thin MAO coating was studied. Based on the stress analysis of the MAO coated 2024-T3 Al alloy, the effect of the MAO coatings produced using 8%, 10%, 15%, and 20% duty cycles on fatigue behavior was discussed. Fatigue fracture and strain under cyclic stress were measured with SEM and extensometer, respectively. The results showed that the maximum cyclic stress affected the initiation of fatigue cracks. With the increase in the external loading, stress variation of the coatings was the critical issue that caused the changes in the fatigue performance under the high and low cyclic stresses. Furthermore, the fatigue failure mechanism of the samples with the thin MAO coatings was revealed. This study provided a method basis for further exploring the fatigue property of the samples with the thick MAO coatings.

Copyright of Experimental Technology & Management is the property of Experimental Technology & Management 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.)

In this study, 6061--T6 aluminum alloys were plated with electroless Ni--P with different phosphorus content and three--point bending and rotary bending fatigue tests. The effects of hydrogen due to plating on mechanical properties were investigated. It was shown that the ductility decreased immediately after low--phosphorus type and high--phosphorus type Ni--P plating by three--point bending test because a hydrogen was introduced into the alloys. The fatigue strength of the low--phosphorus type Ni--P plated specimen was higher than that of the untreated specimen, while that of the high--phosphorus type plated specimen was much lower. It is clear that the fatigue strength differs greatly depending on the phosphorus content in the plating film. 6061--T6 aluminum alloy have been reported to exhibit no hydrogen embrittlement in low strain rate tensile tests under wet condition. However, it was found that hydrogen embrittlement occurred when 6061--T6 aluminum alloy was plated with the high--phosphorus type electroless Ni--P and fatigue--tested on rotary bending machine. [ABSTRACT FROM AUTHOR]

Lightweight aluminum alloys are widely used in automotive structural parts. Clinching (press-joining) is one of the most promising alternatives to welding for joining aluminum alloys, and as the failure of the joint is mainly caused by fatigue, the fatigue properties of the clinched joints directly affect the reliability and safety of the connected specimens. To gain a deeper understanding of this phenomenon, the static mechanical and fatigue properties of Al7075 aluminum alloy single-lap clinched joints were studied using static strength and tensile-tensile fatigue tests. The F–N curves of the joints were fitted using a straight-line and three-parameter power function method. The fractured samples and wear scars were analyzed by scanning electron microscopy and energy-dispersive spectroscopy. The results showed that the neck of the clinched joint and the upper sheet near the joint experienced the highest degree of fatigue fracture, the fretting wear debris consisted mainly of alumina and metallic aluminum, and the fretting wear was of a mode that differed from the two modes identified in the literature that we have dubbed "upper sheet inter-sheet region fretting wear." [ABSTRACT FROM AUTHOR]

For promoting modifying application of sprayed polyurea (SPUA) in asphalt pavement materials, the effects of sprayed polyurea materials on high-temperature and fatigue performance of asphalt binders were investigated from different aspects. First, the optimal preparation parameters of sprayed-polyurea-modified asphalt binders (SPMAs) were determined by designing an orthogonal test. Then, the high-temperature and fatigue properties of sprayed-polyurea-modified asphalt binders with different contents were characterized by rheological testing methods, including Brookfield rotary viscosity (RV) test, performance grading (PG) test, multiple stress creep recover (MSCR) test, linear amplitude sweep (LAS) test and time sweeping (TS) test. Finally, the thermal properties of the asphalt binders were analyzed by differential scanning calorimetry (DSC) test. The results showed that the optimum preparation parameters were determined by the extreme difference analysis method and analysis of variance (ANOVA) method, and the shearing time was 40 min, the shearing rate was 6000 rpm and the shearing temperature was 150 °C. Sprayed polyurea positively affected high-temperature performance of asphalt binders and could improve fatigue resistance of asphalt binders. Moreover, the Brookfield rotary viscosity test, multiple stress creep recover test and linear amplitude sweep test had high sensitivity to the performance of sprayed-polyurea-modified asphalt binder, which could help to distinguish the effect of sprayed polyurea dosing on performance of asphalt binders accurately. The differential scanning calorimetry test showed that sprayed polyurea was beneficial to high-temperature stability of asphalt binders, which explains the reason why sprayed-polyurea-modified asphalt binders have excellent high-temperature performance from a microscopic perspective. [ABSTRACT FROM AUTHOR]

In this work, porous tantalum scaffolds with structures of cubic, G7 and rhombic dodecahedron with different strut angles were fabricated by electron beam powder bed fusion (EB-PBF). Uniaxial compressive testing and compression–compression fatigue testing were conducted on the EB-PBF built tantalum scaffolds. The role of pore structures on the deformation behavior and fatigue properties of the tantalum scaffolds were analyzed. The effect of buckling component in the rhombic dodecahedron structure on fatigue performance of the porous tantalum scaffolds was investigated. It was demonstrated that the G7 and cubic porous tantalum scaffolds were dominated by buckling deformation under the axial force. Due to the presence of vertical struts, the G7 scaffold showed higher fatigue strength and fatigue ratio than the dodecahedron which deformed mainly via bending, the cubic scaffold showed the highest fatigue ratio. As the strut angel increased from 35.3° to 43°, the fatigue strength and fatigue ratio of the rhombic dodecahedron tantalum scaffolds improved by 59% and 20% at 2 × 106 cycles, respectively. The ratcheting strain and fatigue damage strain during the fatigue test were both decreased with the increase of buckling component, leading to the boosting of compressive fatigue properties of tantalum scaffolds accordingly.

Recently, additive manufacturing for titanium aluminide has received sustained attention. Considering the extensive applications on low pressure turbine blades in aerospace field, dynamic mechanical properties of titanium aluminide, especially the fatigue properties, are of great importance. In present work, fatigue test at ambient temperature was conducted for the first time on twin-wire directed energy deposition-arc (TW-DED-arc) fabricated Ti-48Al-2Cr-2Nb alloy with equiaxed lamellar colonies. More detailed researches on fatigue fracture characteristics and deformation modes are also investigated. The experiment results indicate that TW-DED-arc fabricated Ti-48Al-2Cr-2Nb alloy exhibits flat S–N behavior with a good resistance to fatigue. Fatigue life fluctuates widely at same stress level, but such fluctuations gradually weaken as stress decreases. Furthermore, γ/α 2 interface and lamellar colony boundary as well as special microstructures of as-fabricated Ti-48Al-2Cr-2Nb alloy are weak areas during fatigue process, which easily become crack nucleation sites. As stress level decreases, deformation mode of as-fabricated Ti-48Al-2Cr-2Nb alloy translates from twinning and dislocation slip to predominantly dislocation slip. In general, these findings provide an important reference for engineering applications of titanium aluminide. • Ti-48Al-2Cr-2Nb alloy with equiaxed lamella colonies and small Al fluctuation was successfully fabricated via TW-DED-arc. • Ambient temperature fatigue test was conducted on TW-DED-arc fabricated Ti-48Al-2Cr-2Nb alloy for the first time. • During fatigue process, γ/α 2 interface, lamellar colony boundary and special microstructures are weak areas. • Fatigue deformation mode of TW-DED-arc manufactutred Ti-48Al-2Cr-2Nb alloy consists of mechanical twinning and dislocation slip. [ABSTRACT FROM AUTHOR]

Self-piercing riveting (SPR) is a suitable technology to join various materials and has attracted more attention in the automotive industry. In this work, the effects of forming parameters on the forming qualities and mechanical properties of B1500HS steel/AA5052 aluminum alloy SPR joints were analyzed. The results show that the sheet stack sequence has little influence on the peak tensile load and rigidity of SPR joints. When the steel sheet is placed on the aluminum sheet, the failure displacement, energy absorption, and ductility factor are, respectively, 2.77, 2.13, and 2.28 times larger than those of the joints with the aluminum sheet placed on the steel sheet. The SPR joints with steel sheets placed on aluminum sheets have better mechanical stability. Meanwhile, when the steel sheet is placed on the aluminum sheet, the fatigue life of the joint can be increased by about 98.4%, 88.3%, and 118.1%, respectively, under high, medium, and low fatigue loads. A joint with opposite riveting direction has the optimal fatigue performance and the fatigue life is 1.64 and 2.14 times those of the other two-rivet joints. Generally, the fatigue fractures of aluminum alloy sheets in SPR joints occurred in fatigue tests. The fatigue fracture of a joint with a steel sheet stacked on an aluminum sheet extends uni-directionally to the edge of the sheet from the riveting point, while a symmetric fatigue crack of aluminum occurs for joints with the opposite sequence. The distribution of fatigue cracks is related to fatigue load, and fatigue cracks mainly originate in the fretting wear area of the contact interface between the rivet leg, upper sheet, and lower sheet. [ABSTRACT FROM AUTHOR]

In this paper, the influence of a surface ultrasonic rolling process on the surface integrity of TC4 titanium alloy and its influence on the fatigue properties were studied. By comparing and analyzing the surface roughness, microhardness, residual stress, microstructure, and fatigue fracture, the surface strengthening and modification mechanism of TC4 titanium alloy is discussed. The results show that the surface roughness of titanium alloy is observably decreased after the suitable surface ultrasonic rolling process, and the maximum Ra value can be reduced to 0.052 μm. The axial residual stress on the specimen surface can be increased to −685 MPa. The hardening rate of the surface hardness of the sample was 35%. The residual compressive stress and hardness of the sample surface increased with the increase of static pressure. However, the increase of feed rate and rational speed was less. After surface ultrasonic rolling, the sample surface exhibited obvious grain refinement, the number of high-angle boundaries increased to include the formation of nano-equiaxed grains. The fatigue strength increased by 52% from 280 MPa to 425 MPa. Under 450 MPa, the fatigue life of samples with SUR 2 was the highest, at about 7.7 times that of the original samples. The surface integrity of titanium alloy samples after surface ultrasonic rolling treatment is greatly improved, which is the reason for the significant increase in fatigue life of the samples. [ABSTRACT FROM AUTHOR]

Laser-wire-based directed energy deposition (DED) is a type of additive manufacturing. We investigated the chemical composition and fatigue performance to verify the usefulness of Ti-6Al-4V fabricated by laser-wire-based DED which deposited dot-shaped beads on a base material and conducted in preventing atmospheric intrusion with local shielding only. We compared the fatigue performance to a wrought material equivalent to AMS4967M and evaluated the deposited material in the as-fabricated condition. The chemical composition of the deposited material was within the specifications for the alloy. The fatigue strength at 1 ×107 cycles of the deposited material was more than 100 MPa higher than that of 682MPa of the wrought material. Perhaps the high fatigue strength of the deposited material was caused by the low porosity and the acicular α' martensitic phase. From these results, we showed the usefulness of Ti6-Al-4V deposited by a laser-wire-based DED to which local shielding was applied. [ABSTRACT FROM AUTHOR]

It is necessary to add some fillers into raw rubber to enhance the performance of rubber materials. It is well known that the distribution and dispersion of fillers have a great effect on the mechanical properties of rubber. To understand the relationship between dispersion of fillers and the mechanical properties of rubber, different mixing processes are performed, and then the rubber materials with different dispersion states of fillers are obtained. Moreover, the dispersion grade of fillers, the agglomerate size distribution, the vulcanization property, the tension and fatigue properties of different rubbers are investigated. It is seen that the dispersion grade increases and the Mooney viscosity decreases with increasing internal mixing time from 4 to 16 min. When the internal mixing time is 16 min, the dispersion grade reaches 8. 1. However, the tension property of different rubbers only shows little difference. Astonishingly, the fatigue life is greatly enhanced with increasing internal mixing time. Similar results are found when changing the roll banding time of rubber. It is seen that, with increasing roll banding time, the dispersion of fillers increases first and then decreases, and then the fatigue life greatly increases first and then falls down although the tension property only shows little difference. When the roll banding time is 20 min, the fatigue life reaches 4×104 times, and the fatigue life decreases to 2. 3×104 times when further increasing the roll banding time. This implies that the mixing process can be used to modulate the dispersion state of fillers in rubber, and then changes the fatigue property of rubber. [ABSTRACT FROM AUTHOR]

In this study, with the aim of improving the fatigue characteristics of the A7075 aluminum alloy, A7075-T6511 alloy rod specimens were plated with electroless NiP with different compositions, and the fatigue characteristics were evaluated by a rotary bending fatigue test. The fatigue strength of the specimen plated with low-P type was higher than that of the un-plated specimen. However, the fatigue strength of the specimen plated with high-P type was significantly lower than that of the un-plated specimen, and the fatigue strength of the specimen plated with medium-P type was also lower though the extent was not so significant. It was speculated that these reductions in fatigue strength were due to hydrogen embrittlement by the hydrogen introduced into the specimen during the plating. [ABSTRACT FROM AUTHOR]