Carbon fiber reinforced polymer (CFRP) is widely used in the lightweight design of high-speed trains due to its high specific strength. In order to further reduce the weight of the high-speed train ...body, it is necessary to study the joining process and fatigue properties of CFRP/aluminum alloys (CFRP/Al) structure. In this work, the CFRP plate and 5083P-O aluminum plate were successfully connected by an induction brazing method. The optimum parameters of induction brazing were determined to be an induction temperature of 290 °C, a normal pressure of 200 kPa, and a holding time of 5 s. After the 5083 plate was pre-anodized, the tensile strength of the CFRP/5083 joint reached a maximum value of 176.5 MPa. The anodization process introduced more surface micro-structures on the 5083 plate, leading to a better wetting behavior between CFRP and oxide film. Meanwhile, a new chemical bond, Al-O-C, was also formed at the interface of the CFRP/5083 joint. The fatigue limit of the CFRP/5083 joint was calculated to be 71.68 MPa through high-cycle fatigue (HCF) testing. The fatigue cracks initiated from the interface of CFRP/oxide film, and then propagated to base metal. Finally, the oxide film was peeled off from the base metal under shear stress, which contributed to the fracture of the CFRP/5083 joint. The bonding strength between CFRP and 5083 aluminum alloy is far from the conventional welded joints. Therefore, feasible approaches should be proposed to obtain a more robust bonding between CFRP and aluminum alloy in the future.
This updated textbook is for people working on fatigue problems of engineering structures and materials associated with design, predictions, load spectra and experimental verifications.
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EMUNI, FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, KILJ, KISLJ, MFDPS, NUK, OBVAL, OILJ, PNG, SAZU, SBCE, SBJE, SBMB, SBNM, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
Ultrasonic fatigue tests were performed on Ti60 titanium alloy up to a very high cycle fatigue (VHCF) regime at various stress ratios to investigate the characteristics. The S-N curves showed ...continuous declining trends with fatigue limits of 400, 144 and 130 MPa at 10
cycles corresponding to stress ratios of R = -1, 0.1 and 0.3, respectively. Fatigue cracks found to be initiated from the subsurface of the specimens in the VHCF regime, especially at high stress ratios. Two modified fatigue life prediction models based on fatigue crack initiation mechanisms for Ti60 titanium alloy in the VHCF regime were developed which showed good agreement with the experimental data.
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•A novel rapid fatigue test method based on stiffness measurements evolution is presented without requiring special testing equipment.•The fatigue damage can be monitored throughout ...the test, defining critical damage as an easy way to determine the fatigue limit.•The method allows to clearly define a fatigue damage threshold and rationalise the temperature regimes of the self-heating method.
The work presented here deals with the implementation of a new methodology that allows fast and reliable determination of the fatigue strength. It is based on monitoring the specimen stiffness changes at different stress levels, as an indicator of the evolution of fatigue damage. This new rapid fatigue test uses techniques available in many laboratories, as the DIC (Digital Image Correlation) technique and common extensometers. Moreover, the obtained data are easier to handle than infrared cameras or acoustic emission systems data, and the experimental procedure to determine the fatigue limit is more evident than in the self-heating method.
Experiments have been conducted in TWIP (Twinning Induced Plasticity) steel, a material used for lightweighting the structural parts of vehicles. With their excellent energy absorption capacity, TWIP steels can satisfy the part requirements in terms of crash performance, while their high tensile strength can deal with the cyclic loads acting on chassis parts. Therefore, many efforts focus on improving the fatigue strength of TWIP steels through pre-straining and/or surface treatments. However, finding the best way to improve the fatigue resistance requires time and resources that often hinder the development of the material. For this reason, a TWIP steel has been selected to check the new rapid fatigue test. The prediction made using the proposed approach is validated by comparison with conventional staircase results and fatigue crack growth standardised tests. The good agreement allows proposing the new method as a fast and efficient way to determine the fatigue resistance in metals.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
As the reliability and lifespan requirements of modern equipment continues to escalate, the problems with very high cycle fatigue (VHCF) has obtained increasingly widespread attention, becoming a hot ...topic in fatigue research. Titanium alloys, which are the most extensively used metal materials in the modern aerospace industry, are particularly prone to VHCF issues. The present study systematically reviewed and summarized the latest (since 2010) developments in VHCF research on titanium alloy, with special focus on the (i) experimental methods, (ii) macroscopic and microscopic characteristics of the fatigue fractures, and (iii) construction of fatigue fracture models. More specifically, the review addresses the technological approaches that were used, mechanisms of fatigue crack initiation, features of the S–N curves and Goodman diagrams, and impact of various factors (such as processing, temperature, and corrosion). In addition, it elucidates the damage mechanisms, evolution, and modeling of VHCF in titanium alloys, thereby improving the understanding of VHCF patterns in titanium alloys and highlighting the current challenges in VHCF research.
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•Fatigue cracks were initiated at the interface between two micro-textured regions.•Crystal plasticity model was used for quantifying the micromechanical response.•Stress concentration and ...dislocation pile-up lead to the fatigue crack initiation.
Micro-textured regions (MTRs) are the presence of large regions of α grains aggregates with strong local texture, which are detrimental to the fatigue performances in titanium alloys. This work proposes an EBSD map-image based crystal plasticity model to study the fatigue crack initiation in MTRs. Crystal plasticity simulations reveal that the crack initiation may be attributed to the significantly high plastic strain accumulated on prismatic a slip systems leading to significantly high dislocation pile-ups, and high stress concentrations on the cluster of hard grains leading to the stress redistribution and cleavage fracture of the specimen.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
•An iron-based shape memory alloy is exploited for fatigue mitigation.•The proposed solution combines the merits of bridging and prestressing mechanisms.•The bonded smart patch is highly effective in ...retarding fatigue crack growth.
An innovative fatigue strengthening solution for metallic structures that takes advantage of the shape memory effect of an iron-based shape memory alloy (Fe-SMA) and the bridging mechanism offered by the bonding technique has been proposed and examined. Fatigue tests on cracked steel plates with bonded carbon fiber-reinforced polymer (CFRP) and nonprestressed and prestressed Fe-SMA strips were conducted. The experimental results demonstrate that the bonded prestressed Fe-SMA strips are much more effective than CFRP strips, extending the fatigue crack growth life by a factor of 3.51. The proposed innovative solution is highly effective in retarding fatigue crack growth in metallic structures.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
The testing and study of emerging materials—such as additively manufactured materials—demands for specimen designs that are cost effective and time saving. The design of a small‐sized bending‐fatigue ...test specimen for an ultrasonic fatigue testing system is reported in this paper. The design is optimized based on the finite element analysis and analytical‐solution results to achieve the proper vibration shape and stress distribution. The proposed design is evaluated in the high‐ and very‐high‐cycle fatigue regimes under 20‐kHz frequency. Both simulation and testing results confirm that the desirable vibration mode occurs and the specimen fails at the designated test (gauge) section, where the maximum stress exists. The stress–life (S–N) curve is obtained for Inconel alloy 718 and indicates an expected trend.
HIGHLIGHTS
A specimen design for the fatigue bending testing of metals via ultrasonic testers is delivered.
The SEM observations of crack initiation/growth indicate failure occurs in the designed gauge section.
The analytical, FEM, and experimental studies indicate the desired bending mode occurs at around 20 kHz.
The maximum stress/strain location from FEM analysis matches with the failure location.
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Combining the weakest-link theory with fatigue crack growth modeling, this study presents a mechanical-probabilistic modeling of specimen size effect for 30NiCrMoV12 steel in a low cycle fatigue ...(LCF) regime. Particularly, the influence of specimen size on fatigue life is quantified by experiments in strain-controlled fatigue and crack propagation. Experimental results from replica tests with three geometrical specimens indicate that nearly all of its fatigue life consists of multiple surface cracking with mutual interactions and coalescences. A probabilistic procedure for multiple surface fracture simulation is then established by incorporating random processes of crack formation, propagation and coalescence between dispersed surface cracks. Moreover, an evaluation of surface damage evolution is elaborated based on statistical physics for different structural sizes/volumes, which showed good agreement between analytical life distributions and test results.
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•A mechanical-probabilistic prediction of size effect for a Q&T rotor steel.•Size effect quantification by effects of statistical defects and crack propagation.•A probabilistic procedure for multiple surface fracture simulation.•Surface damage evolution by mutual crack interactions and coalescences.•Probabilistic modeling of surface cracking describes well the scatter in fatigue life.
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Fretting fatigue is a surface damage phenomenon appearing in mechanical contacts subjected to time variable contact forces. Typical features of fretting fatigue include: wear, oxidation, high stress ...concentration and non-proportional loading. The high stresses near the surface produce a rapid initiation of cracks. Among the different fretting fatigue palliatives, one of the most common is shot peening. This treatment introduces high compressive residual stresses near the surface that retard the initiation of cracks, but it also changes the microstructure and surface roughness. These residual stresses relax with the number of loading cycles. This paper experimentally studies the influence of the residual stresses and the surface condition on fretting fatigue life. To this end, in this work it is analysed the residual stress relaxation produced in fretting fatigue tests due to cycling loading. On the other hand, the effect produced by the characteristic shot peening surface roughness, is analysed by means of a series of tests in which surface's fretting test specimens are polished. In addition, experimental results obtained with fretting fatigue test specimens having a surface roughness resembling that obtained with shot peening, but without residual stress, and tests done with shot peened contact pads, are presented. In all cases, contact surfaces and fretting cracks are analysed in order to understand its fretting fatigue behaviour. Finally, a fatigue life model previously developed by the authors, but including the residual stress relaxation, is applied to the different set of tests obtaining good results. The paper concludes that shot peening greatly increases fatigue life, mainly for high-cycle fatigue. This improvement can be explained mainly through the stress distribution, with little influence of surface roughness.
•The fretting behaviour of shot peened Al 7075-T651 test specimens is experimentally analysed.•The residual stability of the residual stress during fretting tests is analysed, both experimentally and numerically.•A series of tests are carried out in order to study the shot peening induced surface roughness effect on fretting fatigue.•A fatigue life model, incorporating the shot peening residual stresses, is used to predict fretting fatigue life in tests.
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