Papers by Keyword: Fatigue Property

Abstract: The surface morphologies of micro-arc oxidation coatings and chemical oxidation coating formed on AZ91D alloy were observed by scanning electron microscopy. The fatigue properties of both specimens with micro-arc oxidation coatings and chemical oxidation coating after the pre-corroded treatments in neutral salt spray test were investigated comparatively. The result shows that pre-corrosion treatment decreases the fatigue life, but the pre-corroded fatigue life of specimens with chemical oxidation is lower than that with micro-arc oxidation. The thickness of micro-arc oxidation coatings has no obvious influence on the pre-corroded fatigue life of AZ91D alloy.

Abstract: The population and size of porosities in three kinds of cast aluminum alloys, i.e. A713, A356T6-1 and A356T6-2, were statistically measured using a commercial software Spirit, and several distribution functions were tried to fit the cumulative pore size distribution data. It was found that a general extreme value (GEV) distribution function was the most appropriate function to quantify the cumulative pore size distribution in these cast aluminum alloys. The stress-number of cycles to failure (S-N) curves of these alloys were characterized by four point bend fatigue testing on MTS810 materials testing system, with the parameter f=20Hz, R=0.1, and in ambient air. The fatigue strength of A713, A356T6-1 and A356T6-2 aluminum alloy was measured to be 94.5 MPa, 150.6MPa and 117.3MPa respectively. The fatigue properties of these alloys could not be evaluated just by population and size distribution of the pores, the microstructure state, shape and position of pores, and other weakest links that may initiate a fatigue crack should be taken into account synthetically.

Abstract: Groundbreaking work and past standard of surface integrity regarding description, measurement and evaluation of machined components are retrospected. Typical surface integrity characteristics such as surface topography, macro and microstructure, microhardness and residual stress distribution are preferentially adopted for quantitatively describing and systematically evaluating of surface integrity. Corresponding processing conditions and fatigue performance along with surface integrity characteristics are also detailedly classified and digitally defined through meaningful data sets. A framework of surface integrity model for machined components is subsequently proposed and preliminarily established by understanding the nature of surface integrity and its relation with processing parameters and fatigue properties. This pilot study offers a conceptual model as well as some feasible operational approaches for control of surface integrity in cutting technology and consequent improvement of the fatigue life for machined components.

Abstract: Semi-automatic and automatic pulsed gas metal arc welding (GMAW) of aluminium alloy 5083 with ER5356 filler wire causes considerable softening in the weld. The tensile strength of dressed automatic welds approaches that of the base metal, but the stress concentration caused by the weld toe in undressed semi-automatic welds reduced the tensile strength significantly. Fully automatic welds displayed improved fatigue properties compared to semi-automatic welds.

Abstract: This paper presents a research on the effects of ultrasonic frequencies of 19.9 kHz, 23.6 kHz and 29.3 kHz on both of cyclic amplitude and fatigue life of Al2O3-ZrO2 nano-composite ceramics. According to the high-cyclic-life tests at low load level, some prohibition influence on the process of crack initiation and propagation under ultrasonic vibration is revealed as frequencies are raised from 19.9 kHz to 29.3 kHz. During the low load level tests, the toughness increment induced by the transcrystalline fracture is found in the scanning electronic micrographs of the fractures, which shows the existence of the inhibition effect on the crack initiation and propagation. At the same time, the fracture XRD indicates that t-m phase transition of ZrO2 under 29.3 kHz is higher than that under 19.9 kHz, which means that both the required cyclic amplitude and the fatigue life can be improved if the ultrasonic frequency is increased to 23.6 kHz. All the test results show that high frequencies exhibit stronger toughening improvements than the lower ones do. This paper is a pre-research for the ultrasonic ceramic grinding and the conclusions obtained are meaningful for the study of the crack propagation mechanism during the grinding.

Abstract: Ultrafine-grained steels with a grain size of about one micron offer the prospect of high strength coupled with high toughness among conventional steel compositions and are attracting the attention of researchers worldwide. Application of these ultrafine-grained steels to potential engineering structures demands extensive study of their mechanical properties. While there are many studies on the development of ultrafine-grained microstructures through various deformation processing techniques on a spectrum of compositions, fewer studies were reported on the more important aspect of evaluating their mechanical properties. This is to verify the basic assumption that the microstructural refinement at bulk level indeed improves the mechanical properties offering the prospect of a realistic replacement of the existing conventional steels in the near future. As we move towards the ultimate goal of applying these advanced high strength materials, this review article attempts to present a comprehensive picture on the mechanical properties of ultrafine-grained steels with varying carbon contents fabricated by large strain warm deformation. Finally, it is believed that time is ripe for exploring the possible applications of these materials for structural applications.

Abstract: High Speed Machining (HSM) has been proved to be useful in the machining of many materials. This research is concerned with the performance of HSM in the milling of Ti-6.5Al-2Zr-1Mo-1V (TA15) titanium alloy. The tool life and wear mechanism of the milling tool under different cutting speed were investigated, and the influences of cutting speed on the surface integrity and fatigue property of the machined part were studied. According to the experimental results, acceptable tool life can be obtained in a speed range up to 200m/min. The results also show that increasing cutting speed can help to improve the surface integrity and fatigue property of the machined part.

Abstract: The effects of aging on the fatigue property of polymer modified asphalt mixtures are investigated in this paper. Two kinds of aging procedures are adopted for the aging of specimens prepared with polymer modified asphalt mixtures. One is the short-time aging which means that the hot asphalt mixtures was heated in the oven for 4 hours at 135°C before compacted; The other called natural aging, with the original specimen exposed in the sunlight and subjected to the rain and temperature change for 3, 6 and 9 months. Four-Point Bending Test was conducted to evaluate fatigue properties of aged asphalt mixtures at 15°C compared with the original specimens. Test results indicate that the fatigue line of aged specimens have the same tendency as the original asphalt mixtures. However, the life of aged specimen is decreased significantly when compared with the original ones, especially of the natural aged specimens.

Abstract: Surface integrity has a great effect on the fatigue property of titanium alloy. The surface integrity and fatigue property of a high speed milled Ti-6.5Al-2Zr-1Mo-1V (TA15) titanium alloy were investigated in this research. The main objective of this paper is to study the influence of milling speed on the surface integraty and fatigue property of the machined part. The surface roughness, work hardening, metallurgical structure and residual stress of the machined surface were studied in a cutting speed range of from 50m/min to 300m/min. To verify the relationship between cutting speed and the surface integrity of machined surface, the fatigue property of titanium alloy specimens milled at four different cutting speeds ranging from 50 to 200m/min were compared at two stress levels. This research shows that the cutting speed has little effect on the work hardening, metallurgical structure and residual stress, but the surface roughness decreases with the increasing cutting speed. Therefore, increasing milling speed has a positive effect on the surface integrity and fatigue property of the machined surface.

Abstract: Aluminum alloys are increasingly used in automotive and aeronautic applications to produce high performance, lightweight parts. Among the reasons for this, is the emergence of high integrity processes (HIP), which widens the field of application for cast aluminum alloys. In fact, metallurgical quality and consistency that characterize components produced by HIP are necessary for critical safety components. In addition to attaining maximum strength, critical safety components need to be ductile and resistant to cyclic loading. According to the North American Die Casting Association, rheocasting is a high integrity process capable of producing parts with fewer defects than conventional casting process. Rheocast components are known to have better mechanical properties than permanent mold castings. Moreover, they can be heat-treated which is impractical in the case of classical die cast components. However, the fatigue behavior of rheocast aluminum alloys has been investigated since about 2000 and few results have been published on this subject. This paper reviews the studies of fatigue behavior of aluminum semi-solid cast components. Published experimental results on high cycle fatigue resistance (S-N diagrams), long crack propagation, crack closure effects and short crack particularities are presented.