Papers by Keyword: Stress Amplitude

Abstract: The article is devoted to studying of stress and displacement amplitude distribution in ultrasonic concentrators of different forms. The modelling of different forms of ultrasonic concentrators was considered in detail that allowed to choose an optimal form of concentrator providing maximum amplitude of vibrational speed and uniform stress amplitude distribution across the concentrator section. The modelling was carried out for purpose of the subsequent application of ultrasonic treatment to nanostructured materials. Numerical calculation in the environment of MatLab is carried out and diagrams of dependences of stress and displacement amplitude distribution of conic, exponential, ampoule and two-ampoule forms of concentrators are constructed. Visual distribution models of stresses on the section of concentrators and elastic displacements of material in samples of these forms are constructed, resonance frequencies of longitudinal fluctuations of ultrasonic half-wave concentrators are found in the program Abaqus complex.

Abstract: Experiments on U75V rail steel were carried out to investigate the cyclic feature, ratcheting behavior and low-cycle fatigue under both strain- and stress-controlled loadings at room temperature. It was found that U75V rail steel shows strain amplitude dependent cyclic softening feature, i.e., the responded stress amplitude under strain-controlled decreases with the increasing number of cycles and reaches a stable value after about 20th cycle. Ratcheting strain increases with an increasing stress amplitude and mean stress, except for stress ratio, and the ratcheting strain in failure also increases with an increasing stress amplitude, mean stress and stress ratio. The low-cycle fatigue lives under cyclic straining decrease linearly with an increasing strain amplitude, the fatigue lives under cyclic stressing decrease with an increasing mean stress except for zero mean stress, and decrease with an increasing stress amplitude. Ratcheting behavior with a high mean stress reduces fatigue life of rail steel by comparing fatigue lives under stress cycling with those under strain cycling. Research findings are helpful to evaluate fatigue life of U75V rail steel in the railways with passenger and freight traffic.

Abstract: Ratcheting is the progressive directional accumulation of deformation due to asymmetric loading in structures. Coffin-Manson plots derived from ratcheting experiments conducted at temperatures over the range, 823-923 K showed anomalous behavior at 873 K and 923 K in the form of dual slope and positive slope respectively, which was attributed to a change in the deformation mechanism during ratcheting in the above temperature domain. This was also reflected in the transition in the fracture mode from fatigue to creep at 873 and 923 K.

Abstract: As a new material type, elastic concrete has been used in pavement and bridge deck paving due to its superior properties to ordinary concrete. Nowadays, fatigue behavior of steel-concrete composite beams has become the focus in engineering design. This paper summarized the research status, methods, influence factors on fatigue behavior of elastic concrete and steel-concrete composite beams and compared various fatigue specifications among different countries. The result shows that elastic concrete has longer fatigue life than ordinary concrete, so we can solve fatigue problems by using elastic concrete instead of ordinary concrete in composite beams. Finally the author puts forward suggestions for further advanced study in this area.

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: Effects of stiffness, carrying efficiency and fatigue of the end anchor cable on the mechanical behavior of long span cable-stayed bridge, were discussed respectively. Firstly, the concept of the effective stiffness and the stress ratio were introduced to discuss the effects of the dead load stress level and the stress ratio on the effective stiffness of the end anchor cable. Secondly, the effect of the cable material on the vertical carrying efficiency of the structure was analyzed. Finally, the main influential factors on the fatigue performance of the end anchor cable were analyzed in detail. It is shown that improving the dead load stress level and keeping the low stress ratio would increase the effective stiffness of the end anchor cable. The section of the end anchor cable effects on stiffness of the structure under high stress level. It can be drawn that as a novel material, The CFRP end anchor cable will increase the load carrying level of the long span cable-stayed bridges. It can also be concluded that the length of side span and main span, the height of pylon, the area of the cable section and the live load collection degree are all the main effective factors to the stress amplitude of the end anchor cable. It is suggested that in the practical design of large span cable-stayed bridge, all the effective factors together with the global state of the structure should be taken into account comprehensively.

Abstract: The behaviour of composite cellular floor beams is becoming important as such members are increasingly used in multistory buildings. But, in the design of some special cellular beam with sharp corner web holes such as eye-shaped openings, the issue of low cycle fatigue failure becomes increasingly critical. In this paper, three-dimensional nonlinear finite element models of composite cellular floor beams with eye-shaped openings have been developed, taking into consideration the influence of the changes in degree of shear connections. The assessment based on stress amplitude for risk of fatigue failure under low cycle service load is presented as design guides in this paper. It is concluded that the risk grows along with the increase of composite actions in beams.

Abstract: Studies about the effect of stress characteristics on multi-axial high-cycle fatigue of metals are still insufficient. Up to now, little work about the effect of different ratio of stress amplitude has been done on multi-axial fatigue under the same equivalent stress. In this paper, the effect of ratio of stress amplitude, under the same Von-Mises equivalent stress is studied from theory and experiment. The results show that the main factor of multi-axial high-cycle fatigue failure is the maximum principal stress. For proportional loading, fatigue life raises when ratio of stress amplitude increase. The variety of fatigue life is not obvious when is larger than a certain value and its value closes to that of pure torsion. For non-proportional loading, when ratio of stress amplitude increases, fatigue life raise at first, then has an inflection point. The value of at the inflection point changes with phase difference and its value is 0.5 while phase angle is 90º. Fatigue life of uniaxial tension was lower than that of pure torsion.

Abstract: In this technical manuscript the cyclic stress amplitude controlled fatigue properties and fracture behavior of an emerging titanium alloy (referred to by its designation as ATI 425TM by the manufacturer) is presented and discussed. The alloy was provided as rod stock in the fully annealed condition. Test specimens of the as-received alloy were cyclically deformed under total stress amplitude control at two different stress ratios (R = 0.1 and R = 0.3) with the purpose of establishing the conjoint and mutually interactive influences of magnitude of cyclic stress, load ratio and intrinsic microstructural effects on cyclic fatigue life, final fracture behavior and viable mechanisms governing failure at the microscopic level. The high cycle fatigue resistance of this titanium alloy is described in terms of maximum stress, load ratio, and maximum elastic strain. The final fracture behavior of the alloy under cyclic loading conditions is discussed in light of the mutually interactive influences of intrinsic microstructural features, magnitude of cyclic stress, load ratio and resultant fatigue life.

Abstract: In this research paper, the cyclic stress amplitude controlled fatigue response and fracture behavior of an Al-Cu (Aluminum Association designation 2219) is presented and discussed. The alloy was provided as a thin sheet in the T62 temper in the fully anodized condition. A small quantity of the as-provided sheet was taken and the surface carefully prepared to remove the thin layer of anodized coating. Test specimens of the alloy, prepared from the two sheets (anodized and non-anodized), were cyclically deformed under stress amplitude control at two different load ratios with the primary objective of establishing the conjoint influence of magnitude of cyclic stress, load ratio and intrinsic microstructural effects on cyclic fatigue life and final fracture characteristics. The high cycle fatigue resistance of the alloy is described in terms of maximum stress, load ratio, and microstructural influences on strength. The final fracture behavior of the alloy sheet is discussed in light of the concurrent and mutually interactive influences of intrinsic microstructural effects, deformation characteristics of the alloy microstructure, magnitude of cyclic stress, and resultant fatigue life.