Papers by Keyword: Fatigue

Abstract: Abstract. In this paper, the fatigue life of the 45 # steel specimens is tested. Two groups of fatigue damage specimens are prepared for the experimental study. Their fatigue cycles respectively reached 80% and 90% of the fatigue life tested. The repairing experiments to the two groups’ specimens by the high voltage pulse discharge are finished. After these repairing experiments, the residual fatigue lives of the two group specimens repaired are tested. The results show that the residual fatigue lives of the specimens are improved greatly. The total fatigue lives of the specimens have been increased at least 160% of the fatigue life tested.

Abstract: Through stress-controlled fatigue testing under different stress amplitudes, effects of stress amplitude on the fatigue life and crack propagation mechanism of the extruded Mg-3Al-2Sc alloy were investigated. The results show that, within the stress range of 13.5~82.5 MPa and stress ratio of 0.2, the fatigue life of the alloy decreases and growth rate of fatigue crack increases with increasing stress amplitude. Cleavage fracture mode dominates the crack initiation area and stable crack propagation area. For the final rapid fracture area, the fatigue fracture is combined mode of semi-cleavage and cleavage as well as intercrystalline fracture.

Abstract: This paper investigates the effect of various cycle counting correction factors in spectral fatigue damage calculations. Spectral fatigue calculations are based on complex stress transfer functions established through direct wave load analysis combined with stress response analysis. Cycle counting correction factors are introduced in the computation process to cater swell’s effect and to reduce the conservatism in the results due to narrow band approximation for a wide band random process. In this study, fatigue life of a ship structural detail is predicted by spectral method utilizing ANSYS software along with 3D liner sea-keeping code AQWA. Cumulative fatigue damage is calculated by a MATLAB program based on direct calculation procedure of spectral fatigue using cycle counting correction factors proposed by Wirsching, Rice and Dirlik. The results show an overall decrease in the computed fatigue damage and a corresponding increase in the expected fatigue life of the structure.

Abstract: The fatigue life prognosis of concrete is becoming more important with the development for demanding higher quality and safety in industrial. However, effective methods for this prognosis are still in need now, due to the feature of concrete. This paper proposes the extended grey Markov model (i.e. EGMM) for fatigue life prognosis of concrete. Firstly, the GM (1, 1, λ1, λ2) (i.e. EGM) is proposed by integrating the particle swarm optimization algorithm (PSOA) with GM (1, 1) (i.e. GM). Then the Markov model is integrated with EGM and a novel prognosis method of the extended grey Markov model is proposed. The EGMM is used to combine the health states and transition probability. And a real case study is used to demonstrate the implementation and potential applications of the proposed fatigue life prognosis approach on concrete.

Abstract: Fatigue stiffness degradation behaviour of woven composite π joint subjected to tensile-tensile cycle loading is studied. Because of the complex structural configuration of woven composite π joints and a variety of failure modes, there exhibited four stiffness degradation modes in fatigue test. For example, stable slight reduction mode, abruptly decreasing mode, step decreasing mode and constant stiffness mode. Each stiffness degradation mode has a corresponding failure mode in fatigue test.

Abstract: Energy efficiency is a key issue worldwide, and not confined solely to the realm of engineers. Past failures of mechanical power system components must be examined carefully in order to minimise future occurrences and increase energy efficiencies. Improved design procedures have been highly sought by engineers and researchers over the past few decades. The latest verified method with strong application potential within the power industry is that of the Theory of Critical Distances (TCD). TCD is not one method, but a group of methods that have a common feature; the use of a characteristic material length parameter, the critical distance L, for calculating the influence of notch-like stress raisers under static and fatigue loading. A case study from a hydro power plant turbine shaft was chosen to illustrate the development of this methodology. The paper illustrates the application of TCD to the fatigue life assessment of a turbine shaft with stress concentrations due to pitting corrosion.

Abstract: This research focuses on mechanical performances of UHTCC-FGC beams under monotonic and fatigue loading. Three UHTCC-FGC beams are tested, including two monotonic beams and one fatigue beam. The stress level of fatigue beam is set as 0.85. The constant ratio of minimum stress to maximum stress is set to 0.2 to avoid any impact and slip between the loading machine and the specimens during testing. The specimen is subjected to sinusoidal cyclic loading at 1 frequency. During the experiments, the fatigue life, deformability and loading capacity of UHTCC-FGC beams are measured and recorded. Meanwhile，the development of cracks and the failure pattern of UHTCC-FGC beams during the test are observed at the same time.

Abstract: The aim of this study is to investigate the cyclic behavior and the fatigue life of an industrial α/β brass through mechanical tests and microstructural observations. The main obtained results are about the cyclic behavior of the alloy and the characterisation of fatigue life in connection with the evolution of the microstructure. Cyclic tensile test shows a great and rapid evolution of the isotropic hardenig during cycling.

Abstract: The post mechanical behavior of Ti/APC-2 hybrid nanocomposite laminates after low velocity impact was investigated. The three layered Ti/APC-2/Ti cross-ply nanocomposite laminates were fabricated according to the modified the diaphragm curing process. Each sample, L×W×t=240mm×25mm×1.55mm, was first subjected to free drop of a rigid steel sphere (diameter=12.7mm) of 1m and 2m high. Then, the samples were due to static tensile tests at room temperature to measure their residual ultimate strength and longitudinal stiffness as the base-line data for constant stress amplitude tension-tension cyclic tests. The corresponding S-N curve, fatigue strength and life were obtained. Also, the failuremechanisms were observed.The mechanical properties do not reduce significantly due to low-velocity impact. Similarly, the fatigue resistance of impacted samples does not lose much. The enhancement by nanoparticles and superior bonding capability of matrix PEEK with Ti sheets take the responsibility of improvement of mechanical responses.

Abstract: Abstract. Structural adhesively bonded and spot welded structures in a car body will experience cyclic loading resulting in degradation, especially in energy absorption performance of welded terms. This paper is focused on the degradation of adhesively bonded and weld-bonded box beams versus equivalent spot welded samples. In the first part of this paper, results from the experimental testing of box beams with different joint methods under cyclic torque are presented. The torsional stiffness of box beams is shown to degrade and box beams with different joint methods show different performance. In the second part, 3-point bending crash test results show the different performance of energy absorption with different joint methods. Bonded and weld-bonded box beams with toughened structural adhesive maintain energy absorption performance compared to the original level, while spot welded profiles show a significant decrease.