Papers by Keyword: Compressive Stress

Abstract: Self-lubricating spherical plain bearings are widely used in industry due to their high load capacity, excellent self-lubrication performance and superior impact resistance. The composite made of PTFE/Nomex fabrics and phenolic resin is selected as self-lubricating liners because of the great tribological properties. In this study, the effect of stress during press-fitting process on the tribological behavior of the composite liners in bearings was investigated. Five levels of stresses within a range of 0MPa~680MPa were firstly applied by upsetting process, and then ball-on-disk friction tests were conducted to evaluate the tribological properties. The variation of measured friction coefficient over testing time under different stresses was measured, and the microscopic surface morphology before and after friction tests was observed. Results show that the stress generated during the press-fitting process increases the friction coefficient, while decreases the fluctuation of friction coefficient. In addition, the fluctuation amplitude of the friction coefficients introduced by stress reaches 5.6%.

Abstract: This paper presents an experimental study to investigate the effects of compressive stress during the CO₂ attack on wellbore cement under carbon capture and storage (CCS) conditions. Oil well cement samples were designed to be exposed to humid supercritical CO₂ gas and CO₂-saturated brine and simultaneously subjected to external compressive stresses with load levels of 0, 25%, 50%, and 75% of the ultimate compressive strength. Morphology changes were determined using phenolphthalein dye testing and scanning electron microscopy. Mineral changes were detected by X-ray diffraction. Relative compressive strength and gas permeability of exposed cement were analyzed. It is shown that the 25% stress level has little effect on degradation of cement while the applied compression load up to 50% increased the compactness of cement and finally slowed down the degradation rate. In contrast, a much higher compressive stress level up to 75% facilitated the generation and propagation of micro-cracks. The stress induced micro-crack finally caused a surge in CO₂-rich fluids and then significantly accelerated the degradation rate of oil well cement. Findings from this study expanded the understanding of the integrity of oil well cement for CCS wells.

Abstract: The oxidation behavior of Fe-20Ni alloy under compressive stress in air was studied at 800, 900 °C. The results examined by using scanning electron microscope (SEM) and X-ray diffraction (XRD) indicates that the oxide scales were consisted of an external scale and a subscale which has an intragranular scale (above 5 h at 800 °C and 900 °C) and an intergranular scale. Compared with the unstressed specimen, the growth kinetics of external scale was accelerated by an applied compressive stress. Besides, the compressive stress induced an increase in the growths of intragranular scale and intergranular scale formed on the specimens oxidized at 900 °C. However, the effect of compressive stress on the growth of intergranular scale and intragranular scale was not obvious in the case of 800°C. In addition, cracks developed in the subscale for the specimens oxidized under 2.5 MPa compressive stress when the oxidation time exceeded 20 h.

Abstract: The High Welding Residual Stress is the Main Factors Affecting the Service Life of Welded Structures. Post Weld Cool Treatment (PWCT) is a Novel Method by Introducing Reverse Process Welding Temperature Field to Eliminate the Residual Stress and to Obtain Compressive Stress Layer. the Major Factors Affecting the Effects of Post Weld Cool Treatment (PWCT) is Preheating Temperature, Cooling Time and Cooling Range. in this Paper, a Model to Calculate the Residual Stress was Built Using Finite Element Code ABAQUS, and Different PWCT Processes were Applied on 304L Stainless Steel Specimens. at the same Time, Impact Indentation Method (IIM) was Used to Measure the Residual Stress on the Specimens. the Results Show that the Longitudinal Stress and the Transverse Stress were Reduced Obviously and Compressive Stress was Generated after PWCT in both of the Simulation and the Experiment. the Proposal Preheating Temperature was 400°C and the Cooling Range was 2 Times of Weld Width. Besides, the Cooling Time had Little Effect on the Residual Stress.

Abstract: Magnesium has made an attention as implant material. Because it is decomposed and absorbed in the body, and its mechanical strength is stronger than that of polymers. It is, however, reported that the corrosion rate increases under the compressive elastic stress. In the other hand, it decreases in the specimen whose surface is applied to compressive residual stress by laser shot peening. This implies that compressive plastic deformation reduces the corrosion rate. In the present paper, the corrosion rate of magnesium that was plastically deformed by uniform high compressive stress was researched. As the result, the corrosion rate decreased as the compressive stress increased.

Abstract: This study investigates the durability of partially-damaged concrete with the addition of Silica Fume and Ground Granulated Blast Furnace Slag. Portland cement was replaced by 10% SF and 60% of GGBFS as a replacement of Portland cement. Thirty-six concrete cylinders (100 x 200 mm) were subjected to three compressive loading levels (50%, 75%, and 90% of its ultimate strength capacity). After 28 days of curing, the concrete specimens were experimentally tested for electrical resistivity, rapid chloride penetration (RCPT) and chloride migration coefficient (D_nssm) according to NT-BUILD 494. The experimental results showed that the GGBFS improves significantly the durability of concrete with the highest electrical resistivity and lowest chloride permeability compared to control and SF concrete and both SF and GGBFS had significant effect the concrete durability properties even when the concrete was subjected to compressive damage up to 90% of the compressive strength. A correlation between D_nssm and RCPT in partially damaged concrete was observed and an empirical linear relationship was developed to estimate D_nssm.

Abstract: Shot peening operation is used to improve the mechanical properties of the materials. In this study new rotary peening machine is fabricated. The Hardness and Compressive stress were investigated with help of Vickers Hardness and UTM respectively. The peening parameters such as number of balls (75,100,125), diameter of ball (8,10,12mm), speed (200,300,400rpm) is considered and experimental setup is formulated by L9 orthogonal array. The above parameters are optimized by Taguchi method and MINITAB software. The microstructures of the sample are viewed with help of SEM images.

Abstract: A lanthanum doped lead zirconate titanate (PLZT) ceramic specimen was prepared by the conventional solid state reaction method. The crystal phase and morphology of the PLZT specimen were characterized by XRD and SEM techniques, with the hysteresis loop by RT6000HVS system. The compressive stress was applied to the PLZT specimen through the microtest mechanical loading device. In-situ Raman spectra focused on a fixed grain under various compressive stresses were recorded for different polarization directions of the scattered light. The effects of stresses on the Raman spectra and the intensity ratio between the E+B1 and E(2TO) modes are discussed.

Abstract: Micro electroforming technology is widely used in fabrication of multilayer or moveable metal micro devices. The fabrication of these devices is usually suffered from high internal stress in micro-electroformed layers which seriously restricts the application and development of micro electroforming technology. Therefore, to control the internal stress is very important for improving the quality and performance of micro-electroformed layer. However, published studies on internal stress in the electroforming layer were mostly based on additive-free solution. According to additive solution, the effect of ultrasonic and current density on compressive stress occurring in the electroforming layer is investigated in this paper. The results indicate that the compressive stress keeps increasing with current density within range from 0.2 to 2 A/dm². Meanwhile, the compressive stress in ultrasonic solution decreases by 73.4 MPa averagely comparing to that in ultrasonic-free solution, and the compressive stress also keeps decreasing with the ultrasonic power which gets the lowest value at 200W. Moreover, the mechanisms of additive-induced compressive stress and ultrasonic relieving compressive stress are discussed. This research work will complement the ultrasonic-stress reduction theory and may contribute to the development of micro electroforming technology.

Abstract: A nanoindentation technique with a spherical indenter of tip radius 10 μm is applied to the evaluation of stress-strain curve at a local area of a pure iron under the uniaxial compressive stress exerted through the iron, and the influence of the compressive stress on the estimated stress-strain curve has been examined. A continuous multiple loading method is employed to determine the stress-strain curve. In the method, a set of 21 times of loading/unloading sequences with increasing terminal load are made and load-displacement curves with the different terminal loads from 0.1 mN to 100 mN are then continuously obtained and converted to a stress-strain curve. To examine the stress dependence of the stress-strain curve, the estimation by the nanoindentetion is performed under different uniaxial compressive stresses up to 250 MPa. It has been found that the stress-strain curve determined by the nanoindentation shifts upward as the compressive stress increases and the quantity of the shift is almost equal to the uniaxial stress acting on the iron specimen. It is also noted that the yield stress (0.2 % proof stress) estimated from the stress-strain curve increases almost proportionally to the uniaxial stress and the increase ratio tends to decrease as the stress reaches around 200 MPa.