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.
A novel solvent‐exchange‐assisted wet‐annealing strategy is first proposed to develop superstrong and tough hydrogels with extremely high stretchability and excellent fatigue resistance. The hydrogels have extremely high tensile strength of 11.19 ± 0.27 MPa, a fracture toughness of 82.28 ± 2.89 MJ m−3 with stretchability up to 1879 ± 10%, and a fatigue threshold of ≈1233 J m−2.
To investigate the influence of different modification gradient fields on the fatigue crack initiation mechanisms of the Ti6Al4V alloy, this study employed two surface treatments, polishing (P) and ...polishing combined with ultrasonic rolling process (P+USRP), to generate distinct modification gradient fields for the examination of crack initiation mechanisms, as illustrated in the figure.
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•In our investigation, we employed polishing (P) and polishing combined with ultrasonic rolling process (P + USRP) as surface strengthening treatments for the Ti6Al4V alloy, leading to different modification gradient fields.•The specimens with different modification gradient fields underwent high-cycle fatigue tests, showing different levels of enhancement in the alloy’s fatigue performance.•The differences in modification gradient fields affected the fatigue crack initiation mechanisms of the Ti6Al4V alloy.
In this paper, the high-cycle fatigue (HCF) properties and microcrack initiation mechanism of Ti6Al4V alloy after polishing (P) and after polishing followed by the ultrasonic surface rolling process (P + USRP) treatments are investigated. The results indicate that variations in modified gradient fields would alter the crack initiation location and mode. Specifically, after P treatment, the fatigue crack initiation source occurs approximately 205 μm from the surface, owing to localized strain formation within the internal αp/αp grain boundaries under cyclic loading, thereby promoting rapid cleavage at the (0001) twist interface and evolving into microcracks. This result aligns with the crack initiation mechanism of an untreated specimen. Conversely, fatigue crack initiation after P + USRP treatment occurs approximately 425 μm from the surface, as a result of the deeper modified gradient field, where the crack initiation mechanism results from the competing effects of rapid cleavage at the (0001) twist interface of αp/αp and the accumulation of numerous microvoids. The difference in strain between the α and β phases causes the α/β interface to become a weak region of dislocation accumulation, leading to the formation of microvoids induced by microvoid aggregation. Both P and P + USRP are beneficial for improving the fatigue performance of the alloy.
•Fatigue performance was investigated for various overload levels and steel grades.•The elastic–plastic fracture mechanics approach was used in fatigue calculations.•The effect of welding residual ...stress was considered in fatigue calculations.•RS relaxation was used to support an understanding of the crack growth mechanics.
Individual overloads (OLs) might significantly relax tensile residual stresses (RS) besides generating compressive RS in welded components and, thus, influence the fatigue performance of these components. This study seeks to investigate the effects of steel strength and OL level on the fatigue life performance of welded components. Welding calculations were first performed for different steel grades to predict welding RS (WRS). A series of numerical fatigue calculations were conducted using the elastic–plastic fracture mechanics approach based on FEM to comprehend the fatigue performance under various OL levels. The fatigue calculations were performed in the absence and presence of the WRS effect. The results showed that the higher-level OLs improved the fatigue performance of components made of higher-strength steel when the WRS effect was considered. In contrast, in the absence of the WRS effect, an improvement in fatigue performance was achieved from the higher-level OLs by lower-strength steel. Also, a remarkable RS relaxation with varying degrees was induced from the higher-level OLs for the applied steel grades. This variation in the degree of RS relaxation could be attributed to the difference in WRS distributions over the crack surface. The crack driving force and retardation effect were also used to support the study.
Additive manufacturing (AM) is emerging as an alternative to conventional subtractive manufacturing methods with the goal to deliver unique and complex net or near-net shaped parts. AM components ...should operate under various loading conditions, from static to complex dynamic multiaxial loadings, therefor, fatigue performance is often a key consideration. Intrinsic AM defects such as Lack of Fusion (LOF) defects, porosities, and un-melted particles are important for fatigue as a local phenomenon which usually starts at stress concentrations. Defects can be minimized by process optimization and/or post-processing but may not be fully eliminated. Full-scale testing, which is typically very costly and often necessary to assess reliability for fatigue performance of safety critical components, could be reduced by robust analytical fatigue performance prediction techniques. This work reviews the literature on the influential microstructural attributes on fatigue performance of AM parts with a focus on generated defects. This includes AM defect characterization and statistical analysis methods, as well as effect of process parameters and post-processing on defects, and consequently fatigue performance. The review also includes defect-based, microstructure-sensitive, and multiscale models proposed in the literature for modeling the effect of defects on fatigue performance and provides an outlook for additional research needed.
•The damage of stud has a greater influence on fatigue performances compared to static properties.•Compared with the stud damage, the concrete crack has less influence on the fatigue performance.•The ...existing calculation methods of residual slip are not completely applicable to the test results.
As a key component in composite beams, the studs are prone to fatigue failure under reciprocating load. Fatigue problem is more prominent especially under circumstances of concrete cracking, stud corrosion or with initial damage. Therefore, static and fatigue tests are carried out to study the fatigue properties of push-out specimens with initial defects, including stud damage and concrete cracking. The test results show that the damage of stud has a great influence on fatigue life, while the crack of concrete has a little influence on fatigue life. The damage of stud has a greater influence on fatigue performances compared to static properties. In addition, based on the dissipative energy theory and experimental phenomenon, the roles of stud and concrete in the process of stud fatigue failure and their interaction are summarized. The dissipative energy mainly includes the shear plastic strain energy of the stud, the plastic strain energy of concrete under compression after the stud, and the heat energy generated by the friction between the stud and concrete.
Laser shock peening (LSP) is an advanced surface-strengthening technology that improves the anti-fatigue performance of metallic components. However, there is a significant barrier to the application ...of thin-walled components because the high-energy laser causes deformation and nonuniformity of compressive residual stress, thereby reducing fatigue performance. In this study, an LSP technology based on a low-pulse-energy laser was developed. We applied it to a thin-walled AA7075 aluminium alloy specimen (∼4 mm thickness) and achieved an improvement in the high-cycle fatigue limit of 20.4 and 37.0% for the smooth and pre-cracked fatigue specimens, respectively, in the absence of deformation. It was discovered that the enhanced dynamic nanoscale precipitation and dislocation multiplication effects of the high-pressure shock wave contribute to microstructure stability under cyclic loading, resulting in high compressive residual stress stability. Moreover, the unique heterogeneous grain structure on the surface layer subjected to LSP at low pulse energy effectively restrains crack initiation and propagation. Because these findings apply to a wide range of alloys, the current results create new avenues for improving the fatigue performance of thin-walled components.
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•Laser shock peening at a low pulse energy can improve the fatigue strength of thin-walled parts.•More nanoprecipitations are formed because of the intensified dynamic precipitation effects.•Heterogeneous grain structure are introduced into the materials.•Molecular dynamic simulation is conducted to understand non-uniform grain refinement phenomenon.
This study investigated the synergistic service performances of ultrahigh-performance concrete (UHPC) and normal-strength concrete (NSC). Restrained specimens used in this study were designed to ...assess the non-equivalent deformation of a substrate and UHPC under specific service conditions and shrinkage. Various UHPC repair materials characterized by different shrinkage deformation gradients were developed using expansive agents and lightweight aggregates. The study explored the effects of shrinkage on the synergistic service properties of UHPC-NSC. In addition, the bond fatigue performance of UHPC-NSC was investigated, and a bond fatigue-life equation was formulated. Under static loads and a stress ratio of 0.9, specimens exhibited both substrate and bond failures. By contrast, specimens under stress ratios of 0.8 and 0.7 displayed substrate failure. The synergistic effect of a 10 % dosage of expansive agent and a 15 % dosage of lightweight aggregate resulted in a 67.2 % reduction in UHPC shrinkage after 28 d. Internal stress derived from the non-equivalent deformation of the substrate and UHPC due to shrinkage was quantified. A reduction in UHPC shrinkage led to a 33.0–67.3 % decrease in tensile stress for repair materials. Internal stresses in the UHPC-NSC under alternating environments, including wet–dry, hot–cool, and freeze–thaw cycles, were calculated, where the ratio of internal stress to interfacial strength was defined as the interfacial stress-intensity ratio. This study presents an evaluation method for the synergistic service performance of UHPC-NSC based on an environmental equivalent-force ratio, thereby providing guidance for practical concrete-repair service-life design.
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Steel-concrete composite box girders with corrugated steel webs (CSWs) are broadly used in bridge engineering, in which the joints between top RC slabs and steel girders with CSWs are usually ...subjected to transverse bending moments caused by off-center vehicle loads. Stud connectors arranged in the joints usually bear repeated pull-out forces in this case and are prone to fatigue failure. Therefore, two reduced scale joints between top slabs and weathering steel girders with CSWs were designed and tested, on which variable amplitude fatigue loads were applied to investigate the fatigue performance of studs incorporated in the joints. The two joints presented similar fatigue behavior, i.e., cracks of not more than 0.26 mm in width appeared on the surface of the top slab during the fatigue loading, and the separation of the top RC slabs and the top girder flanges was observed; meanwhile, minute cracks developed along the welds connecting the CSW with the bottom girder flange, and the stiffness of the joints gradually decreased due to the accumulation of fatigue damage. The two joints underwent 2,650,000 and 2,103,600 load cycles respectively before fatigue failure occurred. After partially demolishing the RC slabs, several welded head studs in the joints were observed fractured at the roots and detached from the top girder flange. Whereafter, finite element (FE) models referring to the test joints were developed and analyzed, and the effect of the wave height (WH) of the CSW and the transverse row spacing (TRS) of studs on the distribution of pull-out forces among studs was investigated. It showed that the pull-out force bore by each stud in the joint was distributed unevenly even in the same row. Then, a modification factor α was introduced to revise the pull-out forces of studs calculated in the theoretical method. An equation to determine the factor was fitted, considering the effect of the WH of the CSW and the TRS of studs. Finally, the detail category for studs bearing pull-out forces in the joints was discussed based on the experimental results and the collected test data, and it was preliminarily recommended studs subjected to pull-out forces can be classified into detail category 45 specified by Eurocode 3 in fatigue design.
•Fatigue tests on the joint between the top slab and the steel girder with corrugated steel web (CSW).•Numerical analyses on the stress distribution of group studs in the joints between top slabs and steel girders with CSWs.•Fatigue detail category of studs subjected to pull-out forces caused by transverse bending moments.
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•DED-Arc manufacturing technique was successfully on large-scale structure.•Pressure test up to 111 bar was performer to DED-Arc structure.•Coupons extracted from the structure were ...subjected to quasi-static and fatigue testing.•Fatigue strength assessment considering local quality was introduced.
Wire-arc direct energy deposition was used in this study to manufacture a standing pressure vessel made of stainless steel. Considering the thickness of the additively manufactured sections, the fabricated part was divided into two major components: the shell and the head. The shell with a nominal wall thickness of 5 mm was manufactured using a single-pass technique, while the relatively thicker head, with a maximum thickness of 30 mm, was fabricated using a multi pass approach. The transition from the shell to the 15–30 mm thick head was done by variating wall thickness, enabled by additive manufacturing. After additive manufacturing, the full-scale component was tested up to the maximum internal water pressure of 111 bar (defined per the vessel’s industrial application). Further, to evaluate the mechanical properties of the additively manufactured steel and the effects of pressure loads on it, quasi-static tensile and fatigue tests were conducted on coupons prepared from the material in two conditions: as-built (without any preload) and preloaded (after the pressure test) extracted from various sections. Finally, metallurgical characterization was performed to establish a correlation between the microstructural features and the mechanical performance. The results showed that it is possible to manufacture high-performance and quality pressure vessels using the wire-arc direct energy deposition method.
