Papers by Keyword: Corrosion Pit

Abstract: Polycrystalline cubic boron nitride (PcBN) was a high temperature and high pressure composite material with high hardness. With its high wear resistance and good chemical stability, it conforms to the basic characteristics of modern advanced cutting technology of "high efficiency, high precision, high efficiency and green". Currently, it was widely used in the field of ferrous metal cutting tools. Electrical discharge grinding was one of the most effective methods for machining polycrystalline cubic boron nitride cutters. It was especially suitable for machining complex shapes and thin edge cutters. Single pulse electrical discharge grinding is the basis of continuous EDG machining and an effective method to study micro-scale electrical discharge grinding. In this study, the morphology of single pulse discharge corrosion pits and the relationship between discharge parameters and material removal rate, such as the deep-diameter ratio of the corrosion pits, the pulse width and the deep-diameter relationship of the corrosion pits, were studied with the polycrystalline cubic boron nitride composite sheet of 2 micron particle size as the test material and the independently developed single pulse discharge power supply as the device. The experimental results show that the radius and heat affected area of the discharge corrosion pit increase rapidly, then slowly, and finally gradually with the extension of pulse duration. The corrosion depth generally varies gently in the range of 0.2 ~ 0.5 micron, and the pulse duration has no obvious effect on the depth of the discharge corrosion pit. With the extension of pulse duration, the ratio of radius to depth of the corrosion pit changed in the range of 13 ~ 20, and the ratio basically declined.

Abstract: Tensile residual stress can cause a reduction in the fatigue strength of steel not only in air but also in corrosive environments. In air, for example, the effect of residual stress on fatigue strength can be estimated by using relations between fatigue strength and mean stress such as the modified Goodman diagram. However, it is not clear whether a sort of fatigue strength estimation can be applicable to corrosion fatigue properties. This paper presents an experimental method to evaluate the effect of welding residual stress on corrosion fatigue properties quantitatively, where corrosion fatigue tests were conducted in synthetic seawater by using characteristic fatigue specimens that have two parts, a tensile residual stress part and the other supporting part. Bead-on-plate welding was performed for applying welding residual stress in the tensile residual stress part. Residual stress relaxation was measured using the X-ray diffraction method in the midst of fatigue testing. Effects of tensile residual stress on corrosion pit growth and S-N curves were discussed.

Abstract: Corrosion of steel bars has become the primary cause for the concrete durability problem. Stress concentration due to uneven corrosion affect the mechanical properties of reinforced bar. This paper take HRB400 rebar for example to analyze the effect. FEM is conducted to analyze the effect of corrosion pit position on yield strength and ultimate strength. The result shows that corrosion pit in transverse rib has a different effect on yield strength and ultimate strength, while corrosion pit in longitudinal rib and reinforced column make yield strength and ultimate strength of reinforced bar decrease in varying degrees.

Abstract: In this paper the emphasis is focused upon nitriding effect on corrosion fatigue strength of Cr-Mo low alloy steel in 1% HCl aqueous solution.Corrosion fatigue strength enhancement of Cr-Mo low alloy steel by nitriding is discussed on the basis of the corrosion fatigue testing results on gas and ion nitrided Cr-Mo low alloy steel plate specimen with 3.5mm thickness in 1%HCl aqueous solution. It can be concluded that residual compressive stress distributed on the nitrided specimen surface caused improvement of corrosion fatigue strength of Cr-Mo low alloy steel.

Abstract: Corrosion damage (pit) is a stress raiser that can have deleterious effects on the fatigue life of airframe structural components. A better understanding and method for modeling the corrosion pit to fatigue crack transition would advance the fidelity of aircraft structural integrity estimates and fleet management decision making. Here, the focus is on developing a standardized fatigue test method for investigating the transition of a corrosion pit to fatigue crack in aluminum alloy AA 7075-T651 specimens. The standardized test method requires the development and validation of two sub-protocols (1) a pitting protocol to create a corrosion pit less than 200 μm diameter at the intersection of the central hole bore and planar surface of sheet and (2) a spot welding protocol for attaching the direct current potential drop (dcPD) probes on either side of the corrosion pit for fatigue crack growth measurement. A dcPD fatigue test method coupled with a unique 10-4-6 marker load sequence is used to measure the fatigue crack growth. The crack shape evolution and crack growth life are predicted using AFGROW.

Abstract: Ultrasonic Corrosion Fatigue Tests were Conducted for SUS329J3L in Air and 3%NaCl Aqueous Solution. Reduction of Giga-Cycle Corrosion Fatigue Strength was 12.5%. Corrosion Pit was Observed on Corrosion Fatigue Crack Initiation Area. Striation was Predominantly Observed on Crack Propagation Area both in Air and 3% Nacl Aqueous Solution. it can be Concluded that the Reduction of Corrosion Fatigue Strength of SUS329J3L is due to the Corrosion Pit Formation at Corrosion Fatigue Crack Initiation Area.

Abstract: This document describe accelerated corrosion test and fatigue test for the LD2 aluminum alloy test specimen, the research object is a LD2 aluminum alloy test-piece which has crack in the corrosion pit, the crack initiation life in the area of Corrosion pit has been defined, the influence of the Corrosion on the crack initiation life in corrosion pit area has been researched. Finally, the simulation of crack propagation for the LD2 aluminum alloy test-piece has been made. By comparing, the result of simulation is more conservative than the actual test value.

Abstract: Based on measurement data and the specific morphology of corrosion pit, three-dimensional finite element model of the corrosion damage specimen is established. Then the local stress condition of corrosion pits is given making use of finite element method, the results of stress concentration due to corrosion pits are also obtained, we can compare the stress concentration arised from the corrosion pit on aluminum alloy specimens in different corrosion time. Results show that the corrosion pits produce stress concentration and become the source of fatigue crack initiation and propagation. With the increasing of corrosion time, the pits get deeper and deeper, and the stress concentration gets more serious near the pits.

Abstract: Measurement of shape and dimension of pits and cracks formed in corrosion fatigue tests of a high-strength aluminium alloy, 7075-T651 were conducted by computed-tomography using ultra bright synchrotron radiation X-ray. Complex corrosion process could be observed and detail shapes of corrosion pits could be identified. Sometimes, corrosion pit and corroded area were formed under passive film, and those were not observed from the surface.

Abstract: The relation between corrosion depth and width with corrosion time is according with the power function. The corrosion pits can be seen as ellipse balls through the examination of QUESTAR three-dimensional optics microscope. Corrosion can decrease the fatigue life of materials and is the main reason of fatigue crack form and grow; through AFGROW analyze we can see that the AFGROW software can simulate crack growth life well and the error is low, the crack growth life and critical crack length are conservative than experiment values.