Abstract: Shot peening process is a cold performed function to enhance the mechanical properties which is widely used in many industries. This process introduces compressive residual stress which was proven to increase the fatigue life, geometry stability and corrosion resistance. However, the benefit of the residual stress is still unstable due to the relaxation during the operation. This paper will study on the trend of the relaxation of residual stress against cyclic loading as well as the change in the hardness. The material used in this study is carbon steel ASTM A516/ SA 516 Grade 70. Shot peening process with steel shots was applied to the samples to introduce compressive residual stress in the samples. Cyclic load was applied to samples after shot peening process with low load of 52Mpa (20% of Yield Strength) and high load of 208Mpa (80% of Yield Strength). The measurement of residual stress using X-Ray diffraction and hardness test was done on the samples to study the trend of the relaxation of residual stress and the change in hardness values. The result shows that more relaxation of residual stress occurs if the applied cyclic load is higher. The change of hardness trend is found non-sequenced in this study due to random coverage of shot peening.
Abstract: TC4 titanium alloy plate was processed under multiple laser shocks and bending deformation was studied. A method was proposed to determine the curvature radius of bending deformation of metal plate under multiple laser shocks based on the theoretical model of curvature radius of bending deformation and the eigenstrain field was calculated by a modified finite element analysis method. Effect of shock wave peak pressure and the number of impacts on the curvature radius was studied. Results show that bending deformation increases rapidly at the beginning and then it stops growing. Bending deformation increases rapidly with the increase of the number of impacts and it cannot increase after three impacts.
Abstract: The straightness is an important indicator in measuring the quality of shaft parts. Laser peening straightening (LPS) is a new mechanical method to straight the shaft through inducing residual compressive stress into the shaft surface. Compared with the traditional method, the process of laser peening correction is high efficiency and can be controlled precisely. In the present work, the mechanism of laser peening straightening for shaft straightness is revealed and a three-dimensional finite model is developed to investigate the effects of laser parameters for shaft straightness correction. The results show that the peak pressure and pulse duration should be more than 4 GPa and 8 ns when laser peening straightening is used to correct the shaft straightness. The straightening amount increases with laser power density, laser pulse duration, multiple laser peening. The maximum correction amount for shaft straightness with LPS is no more than 0.01mm.
Abstract: This research proposed a method to improve bending strength of RCS used in hollow core production by finding the optimal levels of factors in the mixing process. Process factors under study were temperature of sand, time to release phenolic resin, time to release hexamine solution, time to start air blowing, air blowing time duration, and time to release calcium stearate. Experiments with Central Composite Face-centered (CCF) design were performed to save the number of experimental runs. Then, backward elimination regression analysis was performed to find out the relationship equation of bending strength and significant process factors. Next, the optimization technique was applied to determine the optimal setting of those significant process factors. The comfirmatory result showed that bending strength was significantly improved.
Abstract: This research proposed a method to find out the relationship between bending strength of resin coated sand and the proportion of different types of sand and resin. It was figured out that Central Composite Design (CCD) was suitable to be used to save the number of experimental runs. Then, backward elimination regression analysis was used to determine the relationship equation of bending strength and proportion of different types of sand and resin. Next, optimization technique was applied to determine the optimal new setting, which provided any targeted level of bending strength with the minimal total cost of sand and resin. The results showed that the experimental results obtained from the CCD experiments provided the regression model, which had less than 6% error from the actual bending strength value. With this proposed method the total cost of sand and resin was reduced by 28.6% on average and it also provided the bending strength on any required target level.
Abstract: During the test of DC(direct current) abrasive magnetic fluid technology,many bubbles and noises were generated near the graphite electrode , and the yellow green liquid was produced, which affected the further test.Through the study of graphite electrode, it was found that NaCl solution magnetic fluid produced hydrogen and chlorine gas after electrolysis. At the same time, chlorine gas dissolved in water to form yellow green liquid.The magnetic field of neodymium boron permanent magnet was equivalent to a mechanical stirring, which inhibited the production of chlorine gas.According to the difference of impressed current system, the abrasive magnetic fluid jet technology was divided into DC and AC(alternating current) .There was no electrode in AC abrasive magnetic fluid jet technology, so no gas or noise would be produced.The rotating magic ring permanent magnet produced alternating magnetic field, acting on the abrasive magnetic fluid to form an induced current.Under the action of the magnetic field, the electromagnetic force was applied to move along the circumferential direction to promote the motion of the abrasive magnetic fluid.
Abstract: Sugarcane bagasse is among the abundantly available waste in agriculture industry. The proportion of siliceous ashes after the incineration process is one of the attractive features in sugarcane bagasse. However, its low bulk density would result in an additional issue for further use as cement replacement material, since higher replacement volume will bring more hydrophilic particles of sugarcane bagasse ash into the mixture. Therefore this research aims to extract the reactive silica from sugarcane bagasse ash and increase its bulk density by converting it into soluble form. The process was divided into three stages, which were pre-treatment and incineration of sugarcane bagasse, conversion into soluble form, and production of mortar specimen. Soluble silica from sugarcane bagasse ash was used to partially replace cement content in mortar, hence its effect on the hydration process can be evaluated. Compression test and scanning electron microscope analysis were performed to observe its effect on the strength and microstructural development of mortar framework. The results show that the inclusion of soluble silica would enhance the early hydration rate and improve the consolidation of cement matrix via additional calcium silicate hydrate formation, which would increase the capability of internal mortar framework to distribute loads and achieve higher strength.
Abstract: Disparity of anion and cation in geopolymer framework may result in the formation of efflorescence on the surface of hardened geopolymer specimen. The existence of efflorescence would be intensified with the use of dipotassium hydrogen phosphate (K2HPO4) as a chemical retarder for geopolymer mixture. In this study, paper mill sludge ash (PMSA) was used as a Ca-rich aluminosilicate source to reduce the development of efflorescence crystals. PMSA was utilized to partially replace fly ash at 5% and 10% (by weight of fly ash). Meanwhile, K2HPO4 was used as the external agent with various proportions, which were 0.1%, 0.3%, and 0.5% (by weight of fly ash). The external agent in this study was purposed to extend the setting time and enhance the mechanical properties of geopolymer. Fly ash and PMSA (if any) were activated by reacting them with 6M sodium hydroxide and sodium silicate solution. Freshly cast specimens were cured for 24 hours in electronic oven with the temperature setting of 30°C and 90°C. They were demoulded after 24 h and kept at room temperature (28±2 °C) until the testing day. Evaluation on the setting time characteristic of fresh geopolymer mortar was conducted with Vicat test while degree of reaction was performed on the hardened specimens to measure the reaction of fly ash during geopolymerization. Based on the experimental result, the inclusion of 5% PMSA shows the greatest effect in reducing the development of efflorescence crystal and increase the degree of reaction of geopolymer system. It is presumed that PMSA has altered the geopolymerization process by activating calcium oxide precursors to form three tetrahedral structures in the framework.
Abstract: The environmental footprint of the construction industry in general must be reduced. The process of manufacturing cement involves the release of appreciable amounts of CO2 into the atmosphere. This paper summarizes the findings of an experimental study aiming at assessing the splitting tensile strength of self-consolidating concrete (SCC) in which 90% of the cement was replaced with various amounts of the industrial by-products including silica fume, fly ash, and ground granulated blast furnace slag (GGBS). Due to the high replacement ratio of cement with recycled industrial by-products, the produced SCC is referred in this study as green concrete. The compressive strength ranged between 30 MPa and 50 MPa and was produced with water/cementitious material ratios of 0.33 and 0.36. The splitting tensile strength was determined and a correlation was developed using regression analysis between the splitting tensile strength and compressive strength.
Abstract: Supplementary cementitious materials such as fly ash, silica fume and ground granulated blast furnace slag (GGBS) have been used widely to partially replace cement in producing self-consolidating concrete (SCC). The production of cement is associated with emission of significant amounts of CO2 and increases the human footprint on the environment. Fly ash, silica fume, and GGBS are recycled industrial by-products that also impart favorable fresh and hardened properties on concrete. This study aims to assess the effect of the amounts of fly ash and silica fume on strength and chloride penetration resistance of concrete. Rapid Chloride Penetration Test (RCPT) was used to assess the ability of SCC to resist ingress of chlorides into concrete. SCC mixes with different dosages of fly ash and silica fume were developed and tested at different curing ages. Test results showed that replacing 20% of cement with fly ash produced the highest compressive strength of 67.96 MPa among all fly ash-cement binary mixes. Results also showed that replacing15% of cement with silica fume produced the highest compressive strength of 95.3 MPa among fly ash-cement binary mixes. Using fly ash and silica fume consistently increased the concrete resistance to chloride penetration at the early ages. Silica fume at all dosages results in low or very low levels of chloride penetration at all curing ages of concrete.