Bending Fatigue Performance Research Articles

Ultra-high three-point bending fatigue performance of nano-silica-reinforced CFRP

The effect of silica nano-particles on the three-point bending fatigue characteristics of plain weave carbon fiber composites (CFRP) was analyzed in the VHCF regime. The addition of silica had a significant effect on the fatigue life of CFRP, which extended the life by multiples. Rigid nano-particles enhanced the connection strength between polymer and carbon fiber, and had a passivating and even blocking effect on the growth of fatigue cracks. The fatigue damage morphologies of nano-particles modified CFRP were closely related to the stress magnitude. The stiffness degradation changed with the evolution of damage morphologies, showing a staged change characteristics.

Experimental and numerical investigation of the bending fatigue performance of symmetric and asymmetric polymer gears

In this work, the bending fatigue strengths of injection-molded symmetric and asymmetric nylon 66 gears were evaluated experimentally, and the results were substantiated using numerical studies. The symmetric (20°/20°) and asymmetric (34°/20° and 20°/34°) configurations were subjected to bending fatigue tests under a load controlled mode. The bending stresses of the symmetric and asymmetric gears were predicted by quasi-static simulations using a commercial finite element analysis software. The form factor ([Formula: see text]) and the stress correction factor ([Formula: see text]) were computed using an adapted ISO method. The 34°/20° configuration exhibited the lowest bending stress and highest bending fatigue life among the tested configurations. The form factor exerted a decisive influence on the magnitude of the bending stress compared to the stress correction factor. For the considered loading conditions, deflection-induced load sharing occurred in the 20°/20° and 20°/34° configurations but was absent in the 34°/20° configuration. Failure analysis indicated that a high stress concentration caused multiple cracks in the fillets of asymmetric gears.

Effect of weld toe geometry on fatigue life of lap fillet welded ultra-high strength steel joints

The effect of arc weld toe geometry on pulsating bending fatigue performance was studied using as-welded and toe machined welded joints of an ultra-high strength steel with a tensile strength grade of 980 MPa. Weld toe machining significantly improved the fatigue strength of the welded joints even when the radius of the machined toe was 0.5 mm, although this is smaller than the minimum size described in the document, International Institute of Welding (IIW) Recommendations on Post Weld Improvement of Steel and Aluminium Structures, which applies to welded joints of steel with plate thicknesses from 6 mm to 50 mm. The fatigue cracks of the as-welded joints initiated along the bottom of the ripple pattern in the weld metal near the weld toe. A fatigue life prediction based on the fracture mechanics approach for the as-welded and the toe machined joints suggested that consideration of the microscopic geometry of the weld ripple pattern is important for improving the accuracy of fatigue life predictions of as-welded joints.

Experimental and numerical prediction of effect of frequency on bending fatigue performance of polyamide 66/hectorite nanocomposite

ABSTRACTAn increased use of thermoplastics in components and structures that are subjected to cyclic loads necessitates a specific attention to variables that affect the hysteretic heating. Hysteretic heating effect in polyamide 66/hectorite nanocomposite has been investigated under bending strain control mode using a custom-built bending fatigue test setup in a laboratory environment. Dynamic mechanical analysis (DMA) results revealed a considerable rise in loss modulus with a decrease in frequency from 1 to 0.1 Hz irrespective of the temperature of the specimen. Alternatively, a reduction in fatigue test frequency from 2 to 0.5 Hz resulted in a significant decrease in cyclic softening. Fatigue behaviour predicted from DMA results using coupled structural/thermal finite element analysis is fairly in agreement with the experimental one. An accelerated crack initiation at decreased specimen temperature and high cyclic steady state stress reduced the fatigue life at 0.5 Hz compared with 2 Hz.

Effect of hammer peening with tungsten coating on fatigue properties of carbon steel under rotating bending

Abstract In the present study, we investigated the influence of hammer peening (HP) with tungsten carbide surface coating (WCSC) on high cycle bending fatigue performance of the carbon steel (CS) manufactured as specified in Bureau of Indian Standards BIS 2062 steel. Totally there are twenty-four numbers of specimens cast and tested to investigate fatigue performance. Constantly high cycle bending fatigue load (HBFL) were applied for all specimen, different range of bending stress applied to the specimen and the stress ratio maintained as R = 1. Investigation results show there is up to 40 percent of the fatigue life improvement possible by the surface treatments to the CS material. From the research to date the corrosion and pitting corrosion can be treated by modifying the surface layer of the metal by treating different peening methods and coating.

A novel bending fatigue test device based on self-excited vibration principle and its application to superelastic Nitinol microwire study

Most Nitinol-alloy-based biomedical devices are usually manufactured from straight drawn microwires or microbeams. Fatigue due to cyclic bending is interpreted as the primary failure mechanism in these devices. However, the bending fatigue performance of a Nitinol microwire is rarely studied because of the lack of test devices. Therefore, we firstly establish a bending fatigue test device based on the self-excited vibration principle. Then, we further improve and experimentally verify the device in three aspects to enlarge the strain amplitude: electrode distance optimization, electrode placement angle optimization and local stiffness enhancement. Based on these improvements, the strain amplitude is increased to 6%, successfully meeting the requirements of Nitinol microwire bending fatigue tests. Using the improved test device, a group of superelastic Nitinol (55.8% Ni-44.2% Ti) microwires with a diameter of 50.8 μm are tested. The test results show that the fatigue strain limit for the chosen life (1 × 106 cycles) is around 1.9%, and the inflexion appears at a strain amplitude of 2.3%. SEM observation shows the typical features of low-cycle and high-cycle fatigue on the fracture surfaces.

The effects of ultrasonic nanocrystal surface modification on the fatigue performance of 3D-printed Ti64

3D-printed metals have great potential for application in the biomedical and the aerospace industries. Unfortunately, they suffer from poor surface finish, high porosity, and high tensile residual stresses, leading to inferior mechanical properties as compared with traditional cast or wrought metals. In this study, we introduce an innovative method, ultrasonic nanocrystal surface modification (UNSM), for the processing of a 3D-printed Ti-6Al-4V alloy. The surface finish, microstructure, residual stresses and mechanical properties of the samples before and after UNSM treatment were characterized and compared. It was found that the UNSM treatment resulted in much better surface finish, lower subsurface porosity, and a high magnitude of compressive residual stresses, leading to significant improvement in rotation bending fatigue performance.

On estimating axial high cycle fatigue behavior by rotating beam fatigue testing: Application to A356 aluminum alloy castings

Three methods available in the literature to estimate the axial S-N curve from the rotating bending fatigue performance were summarized. Axial and rotating bending fatigue tests were conducted at various alternating stresses on specimens excised from A356 aluminum alloy castings in the high cycle fatigue range. These data were used to assess the effectiveness of the models. Among the three models, the one developed by Manson and Muralidharan did not provide good estimates of the axial fatigue performance from rotating bending data. The geometric correction factor proposed by Philipp yielded the best fit, however, did not alter the Basquin exponent whereas the one proposed by Halford and Manson provided a poor estimate. Only the model proposed by Esin provided accurate estimates of fatigue performance as well as the Basquin exponent.

Effect of laser shock peening on bending fatigue performance of AISI 9310 steel spur gear

The effect of laser shock peening (LSP) on bending fatigue performance of AISI 9310 steel spur gear has been investigated in this study. To help to explain bending fatigue test results, residual stress distribution induced by LSP is studied by means of finite element modelling, results of which are verified by X-ray diffraction analysis. It is found that a compressive layer of desirable depth can be induced on the gear root fillet after LSP, and both magnitude and depth of compressive stress increase with laser energy. The bending fatigue test is conducted using the single-tooth bending method to compare fatigue performance of laser peened teeth and non-peened teeth, which is followed by relevant statistical analysis. S-N curves acquired from the fatigue test reveal that bending fatigue lives of gear teeth has been significantly improved after LSP in comparison with those non-peened teeth, and the bending fatigue limit is enhanced correspondingly. It is noticeable that higher laser energy does not necessarily lead to much better fatigue performance of test gears.

Bending Fatigue Performance of Pre-Stressed Concrete Beams Containing Mineral Admixtures

Existing scientific research and engineering practice have shown that the proper use of mineral admixtures can improve both the mechanical behavior and the durability property of concrete structures, but due to lack of necessary fatigue test basis, the use of mineral admixtures is strictly limited in railway bridges in China. Pre-stressed concrete T-beams with different dosage of mineral admixtures were prepared and then were subjected to fatigue test and failure test. It is found that these beams have good stiffness and ductility, which means excellent fatigue resistance within a certain dose range. By a suitable mix design, concrete with mineral admixtures can be applied to railway bridge construction.

Bi-directional and uni-directional bending fatigue performance of unreinforced and carbon fiber reinforced polyamide 66 spur gears

Gears are generally subjected to uni-directional cyclic loads, however, in applications like actuators of satellite launchers, gears experience bi-directional cyclic loads due to its rotation in both clockwise and counter clockwise directions. In the present study, bidirectional and uni-directional bending fatigue performance of injection molded unreinforced and carbon fiber reinforced polyamide 66 gears were evaluated using a test rig developed in-house. During testing, torque applied and the angular displacement of the gears were continuously recorded. The net surface temperature measured by an infrared camera was higher for the gears subjected to bi-directional loading as compared to uni-directional loading. Reinforced gears exhibited about 84% lower temperature than that of unreinforced gears, due to lesser material hysteresis and better thermal conductivity. Fatigue failure of unreinforced gears exhibited almost straight root cracks and confirmed ductile failure. Fatigue failure of reinforced gears exhibited tortuous crack path due to the existence of reinforced fibers. For both the type of loads, carbon fiber reinforced gears exhibited superior bending performance than unreinforced gears (2-51 times) due to its improved mechanical and thermal properties. Significant fatigue life reduction (83-99%) of the tested gears, were observed when subjected to bi-directional loading when compared to that of uni-directional loading.

Mechanical Properties of Thin-Film Parylene–Metal–Parylene Devices

Structures and testing methods for measuring the adhesion strength, minimum bending diameter, and bending fatigue performance of thin film polymer electronic architectures were developed and applied to Parylene-metal-Parylene systems with and without the moisture barrier Al2O3 (deposited using atomic layer deposition (ALD)). Parylene-metal-Parylene interfaces had the strongest average peel test strength and Parylene-Parylene interfaces had the weakest peel. Layers of ALD Al2O3 deposited within the device increased the average peel strength for Parylene-Parylene interfaces when combined with silane A-174, but did not increase the Parylene-metal-Parylene interface. Metal traces in the middle of 24 µm thick Parylene-metal-Parylene devices had a minimum bending diameter of ~130 µm before breaking and being measured as an open circuit. The addition of one layer of Al2O3 above the traces allowed them to be completely creased when bent away from the Al2O3 layer without producing an open circuit, but increased the minimum bending diameter to ~450 µm when bent away from the Al2O3. Although fatigue testing produced cracks in all devcies after 100k bends, the insulation of the Parylene-metal-Parylene devices without Al2O3 performed well with electrochemical impedance spectroscopy (EIS) showing only small decreases in impedance magnitude and small increases of impedance phase at low frequencies. However, devices with Al2O3 failed during EIS due to Al2O3 being deteriorated by water.

Experimental Investigations of the Bending Fatigue Performance of TRC-Strengthened RC Beams in Conventional and Aggressive Chlorate Environments

AbstractTo study the fatigue performance of a reinforced-concrete (RC) beam strengthened with textile-reinforced concrete (TRC), a four-point bending fatigue test was conducted, in which the strengthening forms, reinforcement ratio, textile ratio, static load damage, and sustained load corrosion were considered. The results of this test show that TRC can modify the fatigue failure mode and significantly improve the fatigue life of RC beams. The strengthened beams exhibited better performance than the unstrengthened beams with regard to controlling cracks. TRC can increase the number of cracks and decrease the crack width in RC beams, and the strengthened beams exhibit an increase in midspan deflection that rapidly progresses, while the unstrengthened beams do not exhibit this progression. In terms of improving the fatigue life of beams, the single-sided strengthening form is shown to perform better than the three-sided form, and a beam with a high reinforcement ratio is superior to that with a low ratio. ...

Rotating bending fatigue behaviour of a Ni3Al-based single crystal alloy IC6SX at 760°C

The high cycle fatigue behaviour at 760°C of a Ni3Al-based single crystal alloy IC6SX has been studied in the present investigation. The specimens for the fatigue tests were prepared by screw selection crystal method in a directional solidification furnace. The rotating bending fatigue tests of the specimens was carried out at the temperature of 760°C in air, the stress ratio of R (σmax/σmin) was − 1, and the rotating speed of the fatigue tests was 6500 r min− 1 (108 Hz). The stress–fatigue life cycle (S − Nf) curve was obtained based on the fatigue tests, and the fracture surfaces were examined using scanning electron microscopy (SEM). The results showed that the fatigue cracks initiated from the surface defects of the specimens and the cracks propagated along the (111) crystal plane. The fatigue fracture was composed of three different characteristic regions corresponding to the three fatigue stages, including fatigue crack initiation stage, steady-state propagation stage and the fast propagation stage. The research results also showed that the rotating bending fatigue performance of alloy IC6SX is superior to that of the second-generation single crystal nickel-based superalloys containing 3 wt-% Re.

The bending fatigue performance of cement-stabilized aggregate reinforced with polypropylene filament fiber

Cement-stabilized aggregate reinforced with polypropylene filament fiber (CAPFF) is a new material for road base course of semi-rigid pavements whose bending fatigue performance has been rarely studied. The paper studied the bending fatigue performances of CAPFF (including two types of CAPFF, i.e., cement-stabilized macadam and gravel respectively reinforced with polypropylene filament fiber) with low mixing content, and then established their bending fatigue equations. Results show that, when under the same stress level, the fatigue life of CAPFF is improved by 1.0–4.2 times comparing with that of ordinary cement-stabilized aggregate. Meanwhile, the analysis of the fatigue equations indicates that, when using fibers, the bending fatigue strength of mixtures is appreciably improved, respectively about 30% in case of CMPFF and about 20% for CGPFF. When the stress level is under 0.75, the enhancement of fiber to cement-stabilized macadam is better than to cement-stabilized gravel; when the stress level is higher than 0.75, a reverse conclusion can be obtained. Ultimately, by the results from microtopography analysis by scanning electron microscope (SEM), the enhancement of the polypropylene filament fiber to the bending fatigue resistance of the cement-stabilized aggregates is analyzed.

Low-cost and flexible ultra-thin silicon solar cell implemented with energy-down-shift via Cd0.5Zn0.5S/ZnS core/shell quantum dots

Flexible ultra-thin silicon solar cells with power-conversion-efficiency of 12.4 % implemented with an energy-down-shift layer show stable, flexible and twistable characteristics.

Mechanical and fatigue characteristics of Ti-6Al-4V extra low interstitial and solution-treated and annealed alloys after ultrasonic nanocrystal surface modification treatment.

This study investigates the influence of ultrasonic nanocrystal surface modification (UNSM), a novel surface treatment technology, on the mechanical characteristics and rotary bending fatigue performance of solution-treated and annealed (STA) Ti-6Al-4V and Ti-6AI-4V extra low interstitial (ELI) alloys. Various techniques have been developed to use surface modification in order to improve fatigue performance of machine parts. The UNSM treatment emerges due to its ability to induce a distinctive combination of modifications in the top surface and the subsurface of the material. The mechanical properties are acquired and compared for UNSM-treated and untreated specimens. Fatigue data is acquired and compared for UNSM-treated and untreated specimens of Ti-6Al-4V ELI alloy by subjecting specimens to rotary-bending fatigue tests. Fracture analysis of failed specimens is performed. The improvement in the fatigue performance is observed for UNSM treated specimens. This improvement is attributed mainly to the UNSM-induced combination of following modifications: compressive residual stress, micro-hardness, and nanograin in the subsurface of the material.

Preliminary bending fatigue performance evaluation of asymmetric composite gears

In this work, symmetric gears 20°/20° and asymmetric gears 20°/34° were injection molded using unreinforced and 20% glass fiber reinforced polypropylene materials. To evaluate the bending fatigue performance of symmetric and asymmetric gears, a test rig was specially designed and developed and integrated with the servo hydraulic fatigue test facility. Gear teeth were subjected to constant, completely reversed deflection and the load required to maintain constant gear tooth deflection was continuously measured.Addition of glass fibers improved the bending load carrying capacity of both symmetric and asymmetric gears. Test gears exhibited superior performance at higher loading frequencies due to the strain rate sensitiveness of polymer based materials. The effective cantilever length of the gear tooth contributed to the improvement of the load carrying capacity of 34°/20° asymmetric gears over 20°/34° asymmetric gears as well as symmetric gears. The load carrying capacity of 20°/34° asymmetric gears were found to be superior to that of 20°/20° symmetric gears due to the increased gear tooth width at the root region.

Numerical analyses of bending fatigue of four-step three-dimensional rectangular-braided composite materials from unit cell approach

This paper reports the numerical analyses of three-point bending fatigue behavior of four-step three-dimensional braided composite with three types of representative unit cell (RUC) model. The three types of unit cell models are the unit cell model for the interior, surface, and corner regions of the three-dimensional braided composite. A user-defined material subroutine was developed to characterize the stiffness matrix and fatigue damage evolution of the unit cells and furthermore the braided composite. The fatigue bending behaviors were calculated from the unit cell model with finite element method. It is found that the stress concentration and large deflection located at the middle of the braided composite specimen and both the ends of the bottom areas. As the increase of the stress level, the braided composite is subjected to larger deformation and faster damage accumulation, resulting in a fast fatigue failure. The RUC model could be extended to predict and design the bending fatigue performance of other three-dimensional braided composite structures.

Fatigue Performance and Multiscale Mechanisms of Concrete Toughened by Polymers and Waste Rubber

For improving bending toughness and fatigue performance of brittle cement-based composites, two types of water-soluble polymers (such as dispersible latex powder and polyvinyl alcohol powder) and waste tire-rubber powders are added to concrete as admixtures. Multiscale toughening mechanisms of these additions in concretes were comprehensively investigated. Four-point bending fatigue performance of four series concretes is conducted under a stress level of 0.70. The results show that the effects of dispersible latex powder on bending toughness and fatigue life of concrete are better than those of polyvinyl alcohol powder. Furthermore, the bending fatigue lives of concrete simultaneously containing polymers and waste rubber powders are larger than those of concrete with only one type of admixtures. The multiscale physics-chemical mechanisms show that high bonding effect and high elastic modulus of polymer films as well as good elastic property and crack-resistance of waste tire-rubber powders are beneficial for improving bending toughness and fatigue life of cementitious composites.