In the present work a nickel-base superalloy Inconel 718 manufactured by selective laser melting (SLM) was investigated with focus on microstructure, orientation-dependent mechanical property and ...fatigue performance. Comparative material testing and characterization of the SLM and the forged Inconel 718 revealed significant differences in both microstructures and mechanical properties. The columnar grain structure of SLM alloy leads to the orientation-dependent mechanical properties, which matches the Hall-Petch relation. The inhomogeneous microstructures and slit shaped lack-of-fusion (LoF) defects from the SLM process result in worse fatigue performance and deteriorate the fatigue crack growth behavior.
Due to the poor machinability of SiCf/SiC parts in machining, many problems are caused, such as low machining efficiency, poor machining quality and high processing cost, which seriously limit its ...manufacturing and application. A novel process ultrasonic vibration assisted milling with laser ablation pretreatment (UVAMLAP) was proposed to optimize the fatigue performance and machining efficiency of SiCf/SiC parts. This process was used to fabricate specimens, which were then tested for tensile strength and fatigue performance. The results show that UVAMLAP could enhance surface quality, and increase the tensile strength and residual tensile strength of the sample by 9.4% and 13.5%. This process can avoid damage aggravation in the initial stage of failure, weaken matrix fracture and interface debonding velocity, and reduce fatigue performance degradation caused by machining damage. In addition, comprehensive evaluation based on multi-dimensional indicators such as milling quality, machining efficiency and tool cost for machining strategy was carried out by taking tensile sample machining as an example. The UVAMLAP process can not only improve the machined surface quality, but also reduce the machining time by 31.3% and the tool cost by 75%. Therefore, UVAMLAP provides a feasible process scheme for high-efficiency and low-damage machining of SiCf/SiC parts.
•Lignin increased activation energy, elastic component, rutting resistance of asphalt.•Incorporation of lignin could retard oxidation reactions occurred in the asphalt.•Lignin modified asphalt had ...high percent recovery and low stress sensitivity.•The incorporation of lignin degraded the fatigue life of the asphalt.
The objective of this study was to introduce lignin as a bio-additive to modify the base asphalt and investigate the high-temperature rheological performances of lignin modified asphalts and virgin asphalt. In this study, asphalt PG 58-28 was selected as the virgin asphalt, and four contents, 2%, 4%, 6% and 8%, of the total binder by weight of lignin were incorporated in the base binder. Rotational viscosity (RV), dynamic shear rheometer (DSR), and multiple stress creep recovery (MSCR) tests were conducted to characterize the rheological performances of different types of asphalts. Linear amplitude sweep (LAS) test was employed to evaluate the fatigue performance. The results showed that the incorporation of lignin increased the viscosity of virgin asphalt at different rotational speeds. The activation energy showed an increasing trend as the lignin increased compared with the virgin asphalt. Meanwhile, the lignin incorporated into the asphalt binder increased the elastic components, and improved the resistance of asphalt binder to the permanent deformation regardless of the lignin contents. The addition of lignin in the asphalt binder could retard oxidation reactions that occurred in the asphalt during the rolling thin film oven aging. In addition, the incorporation of lignin may degrade the fatigue life of asphalt. However, when the content of lignin was less than 8%, the reduction was small. This study could provide a prospective foundation for the utilization of lignin extracted from waste biomass as an exceptional and renewable bio-additive in the field of asphalt pavement engineering.
Damaged Reinforced Concrete (RC) beams are commonly strengthened by bonding Carbon Fiber Reinforced Polymer (CFRP) strips to their soffits. However, inaccessible or narrow soffits limit the use of ...bottom-bonded CFRP strips. The Side Bonded (SB) CFRP technique overcomes this, yet studies on SB-CFRP-reinforced beams' fatigue behavior are limited. This paper presents a Finite Element (FE) model for simulating the fatigue behavior of RC beams externally strengthened with SB-CFRP sheets. The model incorporates cyclic-dependent CFRP-concrete interface degradation. Existing experimental results are utilized to validate its accuracy. Computational analyses are undertaken to explore the effects of CFRP dimensions, load and prestress levels, and end-U-shaped wrapping on fatigue performance. A simple model is proposed to predict fatigue life considering load and prestress levels. The FE model effectively predicts fatigue performance. Parametric studies indicate that narrow CFRP strips are unable to prevent concrete failure under high loads. Fatigue failure modes include rebar ruptures and CFRP delamination. Besides, the end-U-shaped wrapping reduces interface damage, extending fatigue life. The study emphasizes the sensitivity of vibration excitation method to CFRP debonding. The proposed equation efficiently predicts the fatigue life of RC beams with externally bonded CFRP strips on their sides.
•Development of a FE model for simulating fatigue in RC beams strengthened with SB-CFRP.•Consideration of cyclic-dependent degradation at the CFRP-concrete interface in the model.•Investigation of parameter effects on fatigue performance through numerical studies.
•Unilateral and bilateral water jet enhanced simulation models were constructed and analyzed.•The effects of bilateral and unilateral water jet strengthening on the fatigue life of Inconel 718 alloy ...were analyzed.•The release and transformation of residual stress during water jet strengthening are analyzed.
This study aims to explore the mechanisms of residual stress formation and the effects on fatigue performance of 12 mm thick Inconel 718 under single-sided one-pass, two-pass, and dual-sided two-pass waterjet peening. Finite element models for waterjet peening and fatigue analysis were established using ABAQUS and Fe-safe, respectively. The study focused on analyzing the residual stresses, surface roughness, and fatigue cycle numbers of Inconel 718 after waterjet peening. The results were validated by conducting waterjet peening experiments and post-peening fatigue tests to ensure their reliability. The research findings indicated that the induced residual compressive stress was most effective with dual-sided two-pass waterjet peening, followed by single-sided two-pass and single-sided one-pass waterjet peening. Among them, after WJP-290 mm/s peening, the maximum residual compressive stresses for dual-sided two-pass, single-sided two-pass, and single-sided one-pass were 718.6, 906.4, and 1042.7 MPa, respectively. The maximum residual compressive stress depth after WJP-230 ∼ 290 mm/s peening was positively correlated with the jet velocity. Surface deterioration occurred after WJP-350 mm/s peening, leading to a significant reduction in the induced residual stress effect. After WJP-230 mm/s peening, the specimen exhibited an overall residual compressive stress of about 507.7 MPa at a depth of approximately 13.1 μm, with a total residual compressive stress depth of about 34.8 μm. Increasing the jet velocity to 290 mm/s shifted the maximum residual compressive stress depth to about 27.2 μm, with a maximum residual compressive stress increase of about 535 MPa, reaching 1042.7 MPa. At the same time, the overall residual compressive stress depth also increased to 39.9 μm. After increasing the jet velocity to 350 mm/s, a maximum residual compressive stress of about 708.7 MPa was induced at a depth of approximately 11.9 μm. The surface roughness, average roughness, and maximum roughness of the specimens were positively correlated with the jet velocity, with the most significant morphological changes occurring at the edges of the waterjet peened area, which coincided with the region prone to fatigue fracture in the cyclic fatigue tests. Increasing the number of jet impacts had a “peak-to-valley” effect on the surface of the peened specimens, making the surface flatter. The specimens peened with dual-sided waterjet showed significantly higher fatigue cycle numbers than those peened with single-sided waterjet. After WJP-230 mm/s peening, the fatigue life at stress levels of 93, 132, and 150 MPa was approximately 2,182,922, 258,000, and 56,575 cycles, respectively, which increased by about 399 %, 274 %, and 218 % compared to single-sided one-pass peening and by about 165 %, 139 %, and 125 % compared to single-sided two-pass peening.
To provide more suggestions for the anti‐fatigue design of cold‐formed steel, a series of high‐cycle fatigue tests are carried out on cold‐rolled steel sheets connected by self‐tapping screws and ...blind rivets in this paper. Subsequently, fatigue failure mode, fatigue strength, and fatigue damage are analyzed in detail. The test results show that all effective data points are below the S‐N curve of screws in the code. Meanwhile, the fatigue limit values of the fitted curves with 95% survival probability fall within the range of 0.3 to 0.67 times the specified value. Besides, the fatigue damage expansion rate of cold‐rolled steel sheets is less than the standard value. Through further discussion, it is noticed that metal grade has little influence on the fatigue performance, while thickness has a significantly positive influence on the shear resistance and fatigue performance. Moreover, the fatigue performance of the two connection types appears to be similar.
Highlights
The base metal has little effect on the fatigue performance of cold‐rolled steel connections.
Thickness raises the shear and fatigue performance of cold‐rolled steel connections.
The fatigue performance of the two types of cold‐rolled steel connections is similar.
In this work, the uniaxial compressive fatigue behaviors of ultra-high performance concrete containing coarse aggregate (UHPC-CA) were investigated, towards a better understanding of the role of CA ...on its fatigue responses. Upon the constant amplitude fatigue tests performed at three stress levels (i.e. S = 0.7, 0.8, and 0.9), the emphases were focused on the effects of CA content (10%, 20%, and 30%) on the failure pattern, deformation characteristics, fatigue life, failure mechanism, and damage evolution. The results showed that compared to the UHPC specimen free of CA, the crack propagation, strain development, and fatigue life of UHPC-CA specimens are largely affected by the CA incorporation, due to the introduction of weak interfacial transition zones and the interference of fiber distribution. As a result, the risk of premature fatigue failure of UHPC-CA will be generally amplified as the CA content increases. Furthermore, inspired by the experimental observation that the fatigue failure strain of UHPC-CA stably approaches the descending branch of the monotonic stress-strain curve, a modified model based on the strain development instead of highly scattered fatigue life was proposed to estimate the nonlinear evolution of the fatigue damage. The good agreements with independent test results demonstrated the applicability of the model, representing a compromise between accuracy and practicability.
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.
•3D printed resin composite showed similar monotonic strength to the layering technique.•3D printed composite had lower monotonic strength compared to the subtractive technique.•3D printed composite exhibited lower fatigue strength than both subtractive and layering techniques.•3D printed composite had a rougher surface than those produced by subtractive and layering techniques.•Mechanical performance of 3D printed materials requires improvement.
Hastelloy X is the trademark for a nickel-based, high-temperature superalloy that is increasingly applied in gas turbine engines because of its exceptional combination of oxidation resistance and ...high-temperature strength. The superalloy suffers from hot cracking susceptibility, however, particularly when processed using additive manufacturing and laser powder bed fusion (LPBF). This paper systematically studies for the first time the effect of post-treatment hot isostatic processing (HIP) on the microstructure and mechanical properties of LPBF-fabricated Hastelloy X, with an emphasis on fatigue performance. The experimental results demonstrate that despite the very small number of remaining gas-filled micropores due to pressure counteraction, the high temperature and high pressure during the HIP process promote recrystallisation and closing of the internal microcracks and gas-free pores. The HIP-processed specimens are shown to be roughly 130 MPa and 60 MPa weaker than the non-processed specimens in yield strength and ultimate tensile strength, respectively. The HIP-processed Hastelloy X exhibits significant improvements in fatigue life, however: the effect of the HIP processing is apparent once the applied stress decreases. This improvement in fatigue performance is attributable to the reduction in stress concentration and residual stress release caused by the HIP process. The paper also studies the hot cracking mechanism and finds that intergranular microcracks generally occur along high angle grain boundaries; the interdendritic liquid pressure drop between dendrite tip and root is found to be a significant factor in the hot crack mechanism. The significance of this research is in developing a comprehensive understanding of HIP processing on the fatigue behaviour of the LPBF-fabricated Hastelloy X. The insights on the cracking mechanism, which presents a significant step towards using additive manufacturing to produce complex crack-free parts from this superalloy.
Polymer composite researchers have extensively explored the influences of fiber orientation, volume fraction, type, length, as well as the impacts of matrix type, matrix/reinforcement interface, ...fibers hybridization, and nanoparticle incorporation on the mechanical behaviors of fiber-reinforced composite materials. The impacts of tailored fiber architectures on the mechanical characteristics of bulk polymeric-based composites, on the other hand, have not been investigated. The purpose of this research is to determine the effect of fiber arrangement on the mechanical characteristics of glass fiber-reinforced polymeric materials (GFRP). Unreinforced (UR) polyester, surface reinforced arranged (SRA) composites and bulk reinforced arranged (BRA) composites were fabricated. Characterizations have been performed using scanning electron microscope rotating bending fatigue machine and a universal testing machine. Results demonstrate that SRA’s lifespan after being exposed to bending fatigue has increased significantly with respect to UR and BRA samples. Average fatigue life for SRA samples is 61 times longer than the life of BRA samples at 56 MPa bending stress. Furthermore, a Weibull distribution function with shape parameter and scale parameter was implemented to analyze the fatigue life dataset statistically. The introduction of SRA novel design has promising results for cost reduction as well as quality improvement.
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