Effect of SARA Fractions on Fatigue Properties of Hard Asphalt.

The fatigue performance of hard asphalt is an important factor that affects the service life of asphalt pavement. In order to comprehensively explore the influence of chemical components on the fatigue performance of hard asphalt, and to eliminate the chemical instability between the microstructure of asphalt from different oil sources, seven kinds of hard asphalt were designed and prepared with saturates, aromatics, resins, and asphaltenes (SARA) extracted from the same hard asphalt. Rheological, time sweep and linear amplitude sweep (LAS) tests were carried out to evaluate the fatigue properties. The results show that the complex modulus of asphalt binds increased rapidly with an increase of asphaltene and resins and that the colloidal structure was strengthened, which would increase the fatigue factor. In the time sweep test, the strength of the colloidal structure significantly affected the fatigue life, and the fatigue life was different under different test stresses. In the viscoelastic continuum damage (VECD) model, the cumulative damage was related to the modulus, while with the increase of asphaltene and resins, the fatigue life showed a trend of first increasing and then decreasing. The linear regression analysis showed that the fatigue life of hard asphalt had a good correlation with strain sensitivity. This study investigated the applicability of different fatigue evaluation methods and revealed the influence of four components on the fatigue properties of hard asphalt. The results provide significant insights in the improvement of the fatigue performance of both hard asphalt and corresponding mixtures.

Iron Tailings as Mineral Fillers and Their Effect on the Fatigue Performance of Asphalt Mastic.

Incorporating iron tailings (ITs) into asphalt represents a new method for waste-to-resource conversion. The objective of this study is to evaluate the fatigue performance of ITs as fillers in asphalt mastic and investigate the interaction and interfacial adhesion energy between asphalt and ITs. To achieve that, the particle size distributions of two ITs and limestone filler (LF) were tested through a laser particle size analyzer; the morphology and structure characteristics were obtained by scanning electronic microscopy (SEM), the mineral compositions were conducted through X-ray diffraction (XRD), and the chemical compositions were tested through X-ray Fluorescence Spectrometer (XRF). Furthermore, the fatigue properties of asphalt mastic and the interaction between asphalt binder and mineral fillers (ITs and LFs) were evaluated by Dynamic Shear Rheometer (DSR). The interfacial adhesion energy between ITs and asphalt binder were calculated through molecular dynamics simulation. In the end, the correlation between the test results and the fatigue life is established based on the gray correlation analysis, the environmental and economic benefits of iron tailings asphalt pavement are further evaluated. The results show that the particle size distribution of ITs is concentrated between 30 µm and 150 µm, and the main component is quartz. ITs have rich angularity and a higher interaction ability with asphalt. The adhesion energy of iron tailings filler to asphalt is less than that of limestone. The correlation degree of the interfacial adhesion energy and interaction between asphalt and mineral filler with asphalt mastic fatigue life is close to 0.58. Under the combined action of interaction ability and interfacial adhesion energy, the fatigue life of IT asphalt mastic meets the requirements. ITs as a partial replacement for mineral fillers in asphalt pavement have great environmental and social effectiveness.

Evaluating mechanical and surface properties of zirconia-containing composites: 3D printing, subtractive, and layering techniques.

This study assessed the monotonic and fatigue flexural strength (FS), elastic modulus (E), and surface characteristics of a 3D printed zirconia-containing resin composite compared to subtractive and conventional layering methods. Specimens, including discs (n = 15; Ø = 15 mm × 1.2 mm) and bars (n = 15; 14 × 4 × 1.2 mm), were prepared and categorized into three groups: 3D printing (3D printing - PriZma 3D Bio Crown, Makertech), Subtractive (Lava Ultimate blocks, 3M), and Layering (Filtek Z350 XT, 3M). Monotonic tests were performed on the discs using a piston-on-three-balls setup, while fatigue tests employed similar parameters with a frequency of 10 Hz, initial stress at 20 MPa, and stress increments every 5000 cycles. The E was determined through three-point-bending test using bars. Surface roughness, fractographic, and topographic analyses were conducted. Statistical analyses included One-way ANOVA for monotonic FS and roughness, Kruskal-Wallis for E, and Kaplan-Meier with post-hoc Mantel-Cox and Weibull analysis for fatigue strength. Results revealed higher monotonic strength in the Subtractive group compared to 3D printing (p = 0.02) and Layering (p = 0.04), while 3D Printing and Layering exhibited similarities (p = 0.88). Fatigue data indicated significant differences across all groups (3D Printing < Layering < Subtractive; p = 0.00 and p = 0.04, respectively). Mechanical reliability was comparable across groups. 3D printing and Subtractive demonstrated similar E, both surpassing Layering. Moreover, 3D printing exhibited higher surface roughness than Subtractive and Layering (p < 0.05). Fractographic analysis indicated that fractures initiated at surface defects located in the area subjected to tensile stress concentration. A porous surface was observed in the 3D Printing group and a more compact surface in Subtractive and Layering methods. This study distinguishes the unique properties of 3D printed resin when compared to conventional layering and subtractive methods for resin-based materials. 3D printed shows comparable monotonic strength to layering but lags behind in fatigue strength, with subtractive resin demonstrating superior performance. Both 3D printed and subtractive exhibit similar elastic moduli, surpassing layering. However, 3D printed resin displays higher surface roughness compared to subtractive and layering methods. The study suggests a need for improvement in the mechanical performance of 3D printed material.

On the Difference in Mechanical Behavior of Glass Bead-Filled Polyamide 12 Specimens Produced by Laser Sintering and Injection Molding.

An increasing demand for additively manufactured polymer composites with optimized mechanical properties is manifesting in different industries such as aerospace, biomedical, and automotive. Laser sintering (LS) is an additive manufacturing method that has the potential to produce reinforced polymers, which can meet the stringent requirements of these industries. For the development of a commercially viable LS nylon-based composite material, previous research studies worldwide have focused on adding glass beads to the powder material with the goal to produce fully dense parts with properties more representative of injection molded (IM) thermoplastic composites. This led to the development of a commercially available glass bead-filled polyamide 12 (PA12) powder. Although this powder has been on the market for quite a while, an in-depth comparison of the mechanical behavior of laser sintered versus IM glass bead-filled PA12 is lacking. In this study, laser-sintered glass bead-filled PA12 samples were built in different orientations and compared to IM counterparts. After sample production, the mechanical performance of the produced LS and IM parts was tested and compared to evaluate the quasistatic and dynamic mechanical performance and failure mechanisms at different load levels. In addition, the glass bead-filled PA12 properties were also compared to those of standard (unfilled) LS PA12 to assess whether glass beads actually improve the mechanical performance and fatigue lifetime of the final LS samples, as suggested in literature. Results in this work present and explain the increased stiffness but decreased fatigue life of glass bead-filled polyamide parts made by LS and IM. This research can be regarded as a "benchmark" study, in which samples produced from commercially available, filled and unfilled, PA12 powder grades are compared for both LS and conventional production techniques.

Experimental and Simulation Investigation on Fatigue Performance of H13 Steel Tools in Friction Stir Welding of Aluminum Alloys.

As the central component in friction stir welding, the design and manufacture of welding tools for aluminum alloys have garnered substantial attention. However, the understanding of tool reliability during the welding process, especially in terms of fatigue performance, remains unclear. This paper focuses on the welding of AA2219-T4 as a case study to elucidate the predominant failure mode of the tool during the friction stir welding (FSW) of aluminum alloys. Experimental methods, including FSW welding and fracture morphology analysis of the failed tool, coupled with numerical simulation, confirm that high-cycle mechanical fatigue fracture is the primary mode of the tool failure. Failures predominantly occur at the tool pin's root and the shoulder end face with scroll concave grooves. The experimental and simulation results exhibit a noteworthy agreement, validating the reliability of the simulation model. The FSW Arbitrary Lagrangian-Eulerian (ALE) model developed in this study analyzes stress distribution and variation under the thermo-mechanical coupling effect of the tool. It reveals that stress concentration resulting from structural changes in the tool is the primary driver of fatigue crack initiation. This is attributed to exposure to alternating cyclic stresses such as bending, tension, and torsion at the tool pin's root, manifesting as multiaxial composite mechanical fatigue. Among these stresses, bending alternating cyclic stress exerts the most significant influence. The paper employs the Tool Life module in DEFORM software to predict the fatigue life of the tool. Results indicate that reducing welding speed or increasing rotation speed can enhance the tool's fatigue life to some extent. The methodology proposed in this paper serves as a valuable reference for optimizing FSW structures or processes to enhance the fatigue performance of welding tools.

3D printed, subtractive, and conventional acrylic resins: Evaluation of monotonic versus fatigue behavior and surface characteristics.

This study assessed the mechanical properties and surface characteristics of dental prosthetic acrylic resin fabricated by 3D printing, comparing it with subtractive, pressing, and molding techniques. Bar-shaped specimens (N= 90; 65 × 10 × 3.3 mm; ISO:207951) were prepared and assigned into six groups: PRINT (3D printing vis stereolithography with PriZma 3D Bio Denture, Makertech Labs); SUB (subtractive manufacturing with Vipiblock Trilux, Vipi); PRESS Base (pressing using muffle with Thermo Vipi Wave, Vipi for base); PRESS Tooth (pressing with Onda-cryl, Clássico for tooth); MOLD Base (molding using addition silicone with Vipi Flash, Vipi for base); and MOLD Tooth (molding with Dencor, Clássico for tooth). Monotonic flexural strength (FS) and elastic modulus (E) were measured using a three-point bending approach (n= 5) on a universal testing machine at a crosshead speed of 5 mm/min. Fatigue testing (n= 10) followed similar geometry and settings, with a frequency of 2 Hz, initial stress level at 20 MPa, and stress increments of 5 MPa every 2,500 cycles. Surface roughness (n= 10) was assessed through profilometry, and fractographic and topographic analyses were conducted. Statistical analyses included One-Way ANOVA for monotonic FS, roughness, and E, along with Kaplan-Meier with Mantel-Cox post-hoc and Weibull analysis for fatigue strength. PRINT showed lower monotonic FS than the SUB and PRESS Tooth but comparable fatigue strength to these groups and superior to PRESS Base and MOLD (Base and Tooth) groups. All groups had similar Weibull moduli. Surface roughness of the PRINT group was comparable to most techniques but higher than the PRESS Tooth group. Fractographic analysis revealed fractures originating from surface defects under tensile stress, with SEM showing scratch patterns in all groups except PRINT, which had a more uniform surface. Despite its lower monotonic strength, 3D printed resin demonstrated comparable fatigue strength to subtractive and pressing methods and similar surface roughness to most methods, indicating its potential as a viable option for dental prosthesis.

The effect of RAP content on fatigue damage property of hot reclaimed asphalt mixtures.

The fatigue property of the recycled mixture affects the structural design of recycled pavement. In order to explore the effect of different reclaimed asphalt pavement (RAP) content on the fatigue properties of recycled mixtures, the fatigue properties of recycled mixtures were analyzed through an indoor fatigue test and finite element numerical simulation. Based on the phenomenological method and the dissipated energy theory, the fatigue properties of recycled mixtures with different RAP contents were analyzed and the fatigue damage of the mixtures were also studies under various strain levels. Based on the finite element numerical model of fatigue damage, the stress distribution and internal damage field distribution of trabecular specimens under different temperatures, strain levels and RAP contents were analyzed. The results showed that the anti-fatigue level of the mixture decreased as the RAP content was increased. The relative change rate of dissipated energy for different types of mixtures showed a two-stage change rule with the change of load times, that is, the value is large and decreasing, and the value is small and stable. The correlation between the plateau value (PV) and the fatigue life was established under the double logarithm coordinates, which could better analyze the influence law of the RAP content on the fatigue performance of the recycled mixture. Under different temperatures, strain levels, and RAP contents, the stress at the bottom of trabecular specimen and the overall damage field were mainly generated at the upper part under compressive stress and the bottom under tensile stress, and the damage field distribution area accounted for a small part of the whole specimen. According to the test results and fatigue damage distribution, it is recommended that the content of recycled aggregate in recycled asphalt mixtures be less than 30% to ensure good performance. The research results have important practical significance for the improvement of fatigue performance and engineering application of recycled mixtures.

Investigating the Dynamic Mechanical Properties and Strengthening Mechanisms of Ti-6Al-4V Alloy by Using the Ultrasonic Surface Rolling Process.

The demand for titanium alloy has been increasing in various industries, including aerospace, marine, and biomedical fields, as they fulfilled the need for lightweight, high-strength, and corrosion-resistant material for modern manufacturing. However, titanium alloy has relatively low hardness, poor wear performance, and fatigue properties, which limits its popularization and application. These disadvantages could be efficiently overcome by surface strengthening technology, such as the ultrasonic surface rolling process (USRP). In this study, the true thermo-mechanical deformation behavior of Ti-6Al-4V was obtained by dynamic mechanical experiment using a Hopkinson pressure bar. Moreover, USRP was applied on the Ti-6Al-4V workpiece with different parameters of static forces to investigate the evolution in surface morphology, surface roughness, microstructure, hardness, residual stress, and fatigue performance. The strain rate and temperature during the USRP of Ti-6Al-4V under the corresponding conditions were about 3000 s-1 and 200 °C, respectively, which were derived from the numerical simulation. The correlation between the true thermo-mechanical behavior of Ti-6Al-4V alloy and the USRP parameters of the Ti-6Al-4V workpiece was established, which could provide a theoretical contribution to the optimization of the USRP parameters. After USRP, the cross-sectional hardness distribution of the workpiece was shown to initially rise, followed by a subsequent decrease, ultimately to matrix hardness. The cross-sectional residual compressive stress distribution of the workpiece showed a tendency to initially reduce, then increase, and finally decrease to zero. The fatigue performance of the workpiece was greatly enhanced after USRP due to the effect of grain refinement, work hardening, and beneficial residual compressive stress, thereby inhibiting the propagation of the fatigue crack. However, it could be noted that the excessive static force parameter of USRP could induce the decline in surface finish and compressive residual stress of the workpiece, which eliminated the beneficial effect of the USRP treatment. This indicated that the choice of the optimal USRP parameters was highly crucial. This work would be conducive to achieving high-efficiency and low-damage USRP machining, which could be used to effectively guide the development of high-end equipment manufacturing.

A Design Method on Durable Asphalt Pavement of Flexible Base on Anti-Rutting Performance and Its Application.

To solve the durability of flexible base asphalt pavement, especially its anti-rutting problem, a design method on durable asphalt pavement of flexible base on anti-rutting performance was put forward in the paper, based on many experiments and calculations. Firstly, a method that asphalt could be selected according to penetration and the anti-rutting factor of its base asphalt was found, which solved the problem of the asphalt selection of the flexible base asphalt mixture design. Meanwhile, a method of skeleton-density structure gradation design was proposed based on the fractal void ratio of coarse aggregate, fractal volume of fine aggregate in coarse aggregate, penetration, fractal dimension of gradation particle size, and rutting tests, which effectively solved in advance the rutting and fatigue performance of flexible base asphalt mixtures. Then, on the basis of the fatigue damage, a calculation method of fatigue life was suggested, which solved the problem that the fatigue damage of asphalt mixtures rarely considered the combined effects of creep damage and fatigue damage. In addition, a calculation method of rutting was formulated based on vehicle dynamic load and ANSYS 16.0 software. Lastly, the feasibility of the design method on durable asphalt pavement of flexible base on anti-rutting performance was verified combining with the real engineering of a supporting project and several numerical calculations and tests.

Microstructure, Mechanical Properties and Fatigue Crack Growth Behavior of Gas Tungsten Arc Welding Welded Joint of the Hastelloy N Alloy.

Hastelloy N alloy is an excellent oxidation and corrosion-resistant material, which is selected as the shell material for the main vessel of molten salt reactors (MSRs). In this work, we conducted double-sided gas tungsten arc welding (GTAW) on 4 mm thick Hastelloy N alloy plates to examine the microstructure and mechanical properties of the welded joints. The S-N curve was obtained by fatigue test. The experimental results show that fatigue cracks initiate along the weld toe and propagate inward in a fan-shaped pattern. The hardness is highest in the heat-affected zone (HAZ). The fracture mode observed was trans-granular. The plastic zone in the initial stages of crack propagation remained relatively minimal. However, it gradually expanded during subsequent stages of the process. It is noteworthy that the crack propagation process often involves the development of secondary cracks, accompanied by profound plasticity-induced closure effects. The results of our investigation demonstrate that the welded joint exhibits excellent fatigue performance.

Fatigue Performance Analysis of Welded T-Joints in Orthotropic Steel Bridge Decks with Ultrasonic Impact Treatment.

This study aims to assess the effect of ultrasonic impact treatment (UIT) on the exterior weld seam of S355J2 T-joints used in orthotropic steel bridge decks. The microstructure and mechanical behavior of T-joints after UIT was investigated in this study. Fatigue tests of T-joints before and after UIT were performed. The stress concentration at the interior and exterior weld toe of T-joints was considered using the traction structural stress method. The results showed that hardness increases by 10% due to the localized grain refinement caused by UIT. UIT significantly improves the fatigue life of T-joint specimens by 350% and 150% at stress ratios of 0.1 and 0.3, respectively. As the transition angle between the weld profile and the base metal profile increases, the stress concentration factor decreases.

Review on Fatigue of Additive Manufactured Metallic Alloys: Microstructure, Performance, Enhancement, and Assessment Methods.

Additive manufacturing (AM), which is a process of building objects in a layer-upon-layer fashion from designed models, has received unprecedented attention from research and industry because it offers outstanding merits of flexibility, customization, reduced buy-to-fly ratio, and cost-effectiveness. However, the fatigue performance of safety-critical industrial components fabricated by AM is still far below that obtained from conventional methods. This review discusses the microstructural heterogeneities, randomly dispersed defects, poor surface quality, and complex residual stress generated during the AM process that can negatively impact the fatigue performance of as-printed parts. The difference in microstructural origin of fatigue failure between conventionally manufactured and printed metals is reviewed with particular attention to the effects of the trans-scale microstructures on AM fatigue failure mechanisms. Various methods for mitigating the fatigue issue, including pre-process, inter-process, and post-process treatments, are illustrated. Empirical, semi-empirical, and microstructure-sensitive models are presented to predict fatigue strength and lifetime. Summary and outlooks for future development of the fatigue performance of AM materials are provided.

Optimising Two-Stage Vacuum Heat Treatment for a High-Strength Micro-Alloyed Steel in Railway Spring Clip Application: Impact on Microstructure and Mechanical Performance.

The heat treatment process is a vital step for manufacturing high-speed railway spring fasteners. In this study, orthogonal experiments were carried out to obtain reliable optimised heat treatment parameters through a streamlined number of experiments. Results revealed that a better comprehensive mechanical performance could be obtained under the following combination of heat treatment parameters: quenching temperature of 850 °C, holding time of 35 min, medium of 12% polyalkylene glycol (PAG) aqueous solution, tempering temperature of 460 °C, and holding time of 60 min. As one of the most important testing criteria, fatigue performance would be improved with increasing strength. Additionally, a high ratio of martensite to ferrite is proven to improve the fatigue limit more significantly. After this heat treatment process, the metallographic microstructure and mechanical properties satisfy the technical requirements for the high-speed railway practical operation. These findings provide a valuable reference for the practical forming process of spring fasteners.

A Study on the Fatigue Performance and Corrosion Resistance of 304/45 Bimetallic Composite Bolts.

This paper utilized a hot-rolling process to produce composite rods and subsequently manufactured 304/45 composite bolts through the process of drawing and thread rolling. The study focused on examining the microstructure, fatigue performance, and corrosion resistance of these composite bolts. Additionally, the impacts of quenching and tempering on the fatigue performance of the composite bolts were explored and compared to the performance of 304 stainless steel (SS) bolts and Grade 6.8 35K carbon steel (CS) bolts. The results indicate that the SS cladding of the cold-worked 304/45 composite (304/45-CW) bolts was primarily strengthened by the cold deformation mechanism, which resulted in high microhardness, averaging 474 HV. At a maximum surface bending stress of 300 MPa, the fatigue cycles of the 304/45-CW reached 342,600 cycles at a 63.2% failure probability, which was significantly higher than that of commercial 35K CS bolts. The S-N fatigue curves showed that the fatigue strength of the 304/45-CW bolts was approximately 240 MPa, but the fatigue strength of the quenched and tempered 304/45 composite (304/45-QT) bolts decreased significantly to 85 MPa, due to the loss of the cold deformation strengthening effect. The corrosion resistance of the SS cladding of the 304/45-CW bolts was impressive and remained largely unaffected by carbon element diffusion.

Mechanical Properties and Microstructure of Rice Husk Ash-Rubber-Fiber Concrete under Hygrothermal Environment.

In order to study the mechanical properties of rice husk ash-rubber-fiber concrete (RRFC) under hygrothermal environment, the optimal group was selected by orthogonal test. The mass loss, relative dynamic elastic modulus analysis, strength analysis, degradation degree analysis after cyclic loading and internal microstructure analysis of the optimal group of RRFC samples after dry-wet cycles under different environments and temperatures were compared and analyzed. The results show that the large specific surface area of rice husk ash optimizes the particle size distribution of RRFC specimens, reacts to form C-S-H gel, enhances the compactness of concrete, and forms a dense structure as a whole. The presence of rubber particles and PVA fibers effectively improves the mechanical properties and fatigue resistance of RRFC. The comprehensive mechanical properties of RRFC with rubber particle size of 1-3 mm, PVA fiber content of 1.2 kg·m-3 and rice husk ash content of 15% are the best. The compressive strength of the specimens after dry-wet cycles in different environments generally increased first and then decreased, reaching a peak at the seventh dry-wet cycle, and the compressive strength of the specimens under chloride salt solution decreased more than that under clear water solution. Thes provided new concrete materials for the construction of highways and tunnels in coastal areas. Under the premise of ensuring the strength and durability of concrete, it is of great practical significance to explore new roads for energy conservation and emission reduction.

Fatigue Experiment Study on Internal Force Redistribution in the Negative Moment Zone of Steel-Concrete Continuous Composite Box Beams.

Due to the accumulated fatigue damage in steel-concrete continuous composite box beams, a plastic hinge forms in the negative moment zone, leading to significant internal force redistribution. To investigate the internal force redistribution in the negative moment zone and confirm structural safety under fatigue loading, experimental tests were conducted on nine steel-concrete continuous composite box beams: eight of them under fatigue testing, one of them under static testing. The test results showed that the moment modification coefficient at the middle support increases during the fatigue process. When approaching fatigue failure, an increase of 1.0% in the reinforcement ratio or 0.27% in the stirrup ratio results in a reduction of 13% in the moment modification coefficient. Furthermore, a quadratic function model was proposed to calculate the moment modification coefficient of a steel-concrete continuous composite box beam during the fatigue process, which exhibited good agreement with the experimental results. Finally, we verified the applicability of the plastic hinge rotation theory for steel-concrete continuous composite box beams under fatigue loading.

Fatigue Behaviors of Joints between Steel Girders with Corrugated Webs and Top RC Slabs under Transverse Bending Moments.

Steel-concrete composite box beams are widely used in bridge engineering, which might bear transverse and longitudinal bending moments simultaneously under vehicle loads. To investigate the fatigue performance of joints between the steel girders and the top reinforced concrete (RC) slabs under transverse bending moments, a reduced scale joint between the weathering steel girder with the corrugated steel web (CSW) and the top RC slab was designed and tested under constant amplitude fatigue loads. Test results show that the joint initially cracked in the weld metal connecting the CSW with the bottom girder flange during the fatigue loading process. The initial crack propagated from the longitudinal fold to the adjacent inclined folds after the specimen was subjected to 7.63 × 105 loading cycles and caused the final fatigue failure. Compared with the calculated fatigue lives in the methods recommended by EC3 and AASHTO, the fatigue performance of the details involved in the joint satisfied the demands of fatigue design. Meanwhile, finite element (FE) models of joints with different parameters were established to determine their effect on the stress ranges at the hot spot regions of the joints. Numerical results show that improving the bending radius or the thickness of the CSW helps to reduce the stress ranges in the hot spot regions, which is beneficial to enhance the fatigue resistance of the investigated fatigue details accordingly.

Performance Assessment of Self-Healing Polymer-Modified Bitumens by Evaluating the Suitability of Current Failure Definition, Failure Criterion, and Fatigue-Restoration Criteria.

Fatigue cracking is a common form of flexible pavement distress, which generally starts and spreads through bitumen. To address this issue, self-healing elastomer (SHE) modified bitumens were elaborated to assess whether these novel materials can overcome the neat asphalt (NA) fatigue performance and whether the current failure definition, failure criterion, and fatigue-restoration criteria can fit their performance. All bitumens were subjected to short-term and long-term aging. Linear amplitude sweep (LAS) test, LAS with rest period (LASH), and simplified viscoelastic-continuum-damage (S-VECD) model were utilized to appraise the behavior of the mentioned bitumens. The results showed that maximum stored pseudo-strain energy (PSE) and tau (τ) × N (number of loading cycles) failure definitions exhibited high efficiency to accommodate the fatigue life of NA and SHE-modified bitumens. Both failure criteria identified that SHE-modified bitumen (containing 1% of SHE) showed the highest increment of fatigue performance (67.1%) concerning NA. The failure criterion based on total released PSE, in terms of the area under the released PSE curve, was the only failure concept with high efficiency (R2 up to 0.999) to predict asphalt binder fatigue life. As well, the current framework to evaluate bitumen self-restoration failed to fully accommodate asphalt binder behavior, because bitumen with higher restoration could not exhibit greater fatigue performance. Consequently, a new procedure to assess this property including fatigue behavior was proposed, showing consistent results, and confirming that SHE-modified bitumen (containing 1% of SHE) exhibited the highest increment of fatigue performance (154.02%) after application of the rest period. Hence, the optimum SHE content in NA was 1%. Furthermore, it was found that a greater number of loading cycles to failure (Nf) did not ensure better fatigue performance and stored PSE influenced the bitumen fatigue behavior.

The Effect of Postprocessing on the Fatigue Properties of Ti-5Al-5Mo-5V-1Cr-1Fe Produced Using Electron Beam Melting.

Despite the significant potential advantages of processing Ti-5Al-5Mo-5V-1Cr-1Fe alloy (Ti-55511) using Electron Beam Melting (PBF-EB/M), when compared to conventional manufacturing technologies, the resulting internal defects are an important characteristic of such additive technologies and can highly decrease mechanical properties. One of the most dangerous defects formed during metal additive manufacturing processes are material discontinuities such as a lack of fusion. Defects of this type, due to their "flat" nature, are difficult to characterize. For cycle-loaded specimens, where the loading force acts perpendicular to the lack-of-fusion plane, defects of this type can significantly reduce fatigue properties. This paper presents the results of research aimed at improving the fatigue properties of Ti55511 alloy by reducing the influence of the lack-of-fusion defect on fatigue damage. The static and fatigue properties of specimens in the as-built state, as well as after hot isostatic pressing (HIP) treatment, were analyzed. The effect of HIP on both the reduction of pores and the degree of sphericity when using the X-ray computed tomography (XCT) system was presented. The change in the microstructure after HIP was analyzed in terms of the change in the size of individual phases, as well as the change in the phase ratio. This paper also contains a fractographic analysis of the samples after tensile and fatigue tests.

Solvent-Exchange-Assisted Wet Annealing: A New Strategy for Superstrong, Tough, Stretchable, and Anti-Fatigue Hydrogels.

Hydrogels are widely used in tissue engineering, soft robots, wearable electronics, etc. However, it remains a great challenge to develop hydrogels possessing simultaneously high strength, large stretchability, great fracture energy, and good fatigue threshold to suit different applications. Herein, a novel solvent-exchange-assisted wet-annealing strategy is proposed to prepare high performance poly(vinyl alcohol) hydrogels by extensively tuning the macromolecular chain movement and optimizing the polymer network. The reinforcing and toughening mechanisms are found to be "macromolecule crystallization and entanglement". These hydrogels have large tensile strengths up to 11.19 ± 0.27 MPa and extremely high fracture strains of 1879 ± 10%. In addition, the fracture energy and fatigue threshold can reach as high as 25.39 ± 6.64 kJ m-2 and ≈1233 J m-2 , respectively. These superb mechanical properties compare favorably to those of other tough hydrogels, organogels, and even natural tendons and synthetic rubbers. This work provides a new and effective method to fabricate superstrong, tough, stretchable, and anti-fatigue hydrogels with potential applications in artificial tendons and ligaments.