Papers by Keyword: Stress Ratio

Abstract: Taking the mode I crack of finite width plate as the research object, the nodal displacement extrapolation method of type I stress intensity factor is discussed, and the stress intensity factor expressed by nodal displacement is obtained. Taking A7N01 aluminum alloy as the research object, the finite element software ABAQUS was used to numerical simulation and analysis. The effect of stress ratio on stress intensity factor K _I was discussed. The results showed that in the same crack size ratio a/W, the stress intensity factor increases with the increase of the stress ratio; at the same stress ratio R, the stress intensity factor increases with increasing crack size ratio. At the same time, change law of the stress intensity factor increase: under the condition of different stress ratio, when a/W≤0.6, the increase of stress intensity factor is almost consistent; when a/W>0.6, the increase of stress intensity factor will increase obviously.

Abstract: The fatigue crack growth threshold ΔK_th is an important characteristic of crack growth assessment for the integrity of structural components. However, the accurate threshold ΔK_th values for austenitic stainless steels in air environment are lacking in many fitness-for-service (FFS) codes, although fatigue crack growth tests have been performed and many test data had been published. This paper focuses on fatigue crack growth threshold ΔK_th values for austentic stainless steel in air environment. The paper introduces the current ΔK_th values provided by four major FFS codes and summarizes the available test data based on the literature survey. The paper then discusses the applicability of the existing ΔK_th for stainless steels and proposes a new relation as a function of the stress ratio (the R ratio) for use by FFS codes.

Abstract: In this paper, effect of stress ratio was investigated on macro and micro of fatigue crack growth rates (FCGRs) of Al-alloy 2024 T351. Microscopic fatigue crack growth rate present a change of slope with respect to the macroscopic fatigue crack growth rate. In addition, an increasing in stress ratio increases the fatigue life. Fractographic examination showed the presence of striations in Paris domain and secondary cracks at grain boundaries.

Abstract: The high cycle fatigue tests for smooth specimens of TC25 titanium alloy under different stress ratios are carried out on a MTS 809 Material Test Machine at a given maximum stress level of 917MPa at ambient temperature, the high cycle fatigue lifetimes for such alloy are measured, and the effects of stress amplitude and mean stress on high cycle fatigue life are analyzed. The initial resistance is measured at the two ends of smooth specimen of TC25 titanium alloy, every a certain cycles, the fatigue test is interrupted, and the current resistance values at various fatigue cycles are measured. The ratio of resistance change is adopted to characterize the fatigue damage evolution in TC25 titanium alloy, and a modified Chaboche damage model is applied to derive the fatigue damage evolution equation. The results show that the theoretical calculated values agree well with the test data, which indicates that the modified Chaboche damage model can precisely describe the accumulated damage in TC25 titanium alloy at high cycle fatigue under unaxial loading. Finally, the high cycle fatigue lifetimes for TC25 titanium alloy specimens at different strain hardening rates are tested at a given stress ratio of 0.1, the effect of strain hardening on fatigue life is investigated based on a microstructure analysis on TC25 titanium alloy, and an expression between fatigue life and strain hardening rate is derived

Abstract: The change law for fatigue properties of polyester fiber asphalt concrete was acquired under different asphalt content by three point bending tests. The results indicate that fatigue life of polyester fiber asphalt concrete increases firstly and then declines with asphalt content increasing, which shows an optimum asphalt content,4.8%. The optimal asphalt content of polyester fiber asphalt concrete is bigger than that of common asphalt concrete. The way to improve fatigue performance of asphalt pavement is found through studying on polyester fiber asphalt concrete. All will provide a theoretical basis for structural design of asphalt pavement.

Abstract: In this research work, the effect of cooling rate on fatigue behaviour of eutectic A413 Al-Si cast alloy is investigated. Castings produced by two different cooling rates, water-cooled and air-cooled are studied. The structural morphology of alloy castings was characterized using Inverted Trinocular Metallurgical Optical Microscopy. A Comprehensive tension–tension fatigue test was carried out with a stress ratio of R=0.5, and a sinusoidal waveform under three different mean stress conditions (25%, 50% & 75% of UTS) at room temperature (32°C). The microstructural evaluations show that the eutectic script size is smaller for water-cooled casting than the air-cooled casting. It is also observed that the fatigue life of the water-cooled cast alloy is greater than that of cast alloy produced with conventional air-cooled method.

Abstract: The crack propagation behavior in a 2024 T351 Aluminum Alloy under constant amplitude loading has been studied. This study is analyzed in term of crack opening load measurements using a compliance technique. The results obtained under constant amplitude fatigue tests show that different crack propagation stages can be identified. Significant effects due to load ratio changes have been quantified.

Abstract: Nowadays composite material especially Glass fibre reinforced epoxy (GRE) composites is one of the most widely used composite materials in such areas, especially in the marine, building and oil industry due to their lightweight, high strength and chemical/corrosion resistant properties. The aim of this paper is to provide an improved understanding of the performance of glass fibre reinforced epoxy (GRE) pipe under combined pressure and axial loads. The performances of GRE composite pipes is investigated through finite element modelling of ultimate elastic wall stress test under multi-axial loading ranging from pure axial to pure hoop loadings. ANSYS software will be used for finite element modelling of GRE pipes. A stress-strain response was obtained for each winding angle and the results for modelling then compared with those experimental computed through laminate theory. It is also concluded that the experimental results stress, which represent the onset of non-linearity were very much dependent on the transverse and shear stress response, and these values were found to be consistent with the predicted values from the commonly used Tsai-Wu failure criterion.

Abstract: In this paper, permeability of concrete after loading at various stress levels, including recycled aggregate concrete (RAC) and natural aggregate concrete (NAC) (at W/B ratio of 0.586 and 0.250), is measured by means of surface infiltration experiment and chloride penetrating test to study the effect of loading size on permeability of recycled aggregate concrete. The results show that there exists a critical stress ratio value of around 0.65 to 0.75 for NAC at W/B ratio of 0.586, and among the four types of RAC, the critical stress ratio exists only in 60R50, while the water permeability coefficient increases linearly with the stress ratio for the other 3 types of RAC. The charge passed of RAC increases with the W/B ratio, and the more the recycled aggregates mixed, the higher the charge passed. As the stress ratio increases, the charge passed increases slightly in samples at W/B ratio of 0.25, while the charge passed of samples at W/B ratio of 0.586, whether NAC or RAC, increases almost linearly.

Abstract: The short fatigue crack growth tests for circular notched compact tension specimens of GH4133B superalloy used in turbine disk of aero-engine are carried out at ambient temperature and atmospheric pressure. The stress intensity factor ranges and the fatigue crack growth rates at various stress ratios are measured, and the corresponding effective stress intensity factor ranges considering the crack closure effect are calculated. It is shown that the effective stress intensity factor range ΔK_eff, can be applied to describe the deceleration and acceleration of crack growth rate during the short crack propagation. The fatigue fracture surface morphologies in the short crack growth region are investigated using a scanning electron microscopy. It is found that there is a cleavage step between two adjacent radial striations, a series of early fatigue striations exist on the cleavage step, and some secondary cracks perpendicular to the direction of main crack propagation emerge on the fracture surface, the superalloy exhibits a mixed fracture mode in the short crack growth region, which reveals the microscopic mechanism of short crack propagation that the fatigue crack growth rate is primarily higher, and then gradually decreases with the propagation of short crack.