Abstract: The size and distribution of nanoscale precipitate particles in Ti-Mo ferrite matrix microalloyed steel under three different final rapid cooling temperatures were studied by scanning electron microscopy(SEM), transmission electron microscope(TEM) and microhardness test. The results show that the interphase precipitation could be weakened by the excessive final rapid cooling temperature. A higher supersaturated solid solubility and high-density dislocation in ferrite matrix can be obtained under a relatively lower final rapid cooling temperature, which makes it easier to precipitate in ferrite. The related thermodynamic analysis indicated that the precipitation behavior was influenced by the final rapid cooling temperature during austenite/ferrite region. It is not conducive to get a large amount of small size precipitates in Ti-Mo ferrite matrix microalloyed steel when the final rapid cooling temperature is too high or low.
Abstract: The aim of this study is to develop a predicted model of the machining parameters with relation to material removal rate (MRR) and surface roughness (SR) of electrical discharge machining (EDM) in gas. The experimental tasks were implemented by a specific design of experimental method named central composite design (CCD) method. The mathematical prediction models between operating parameters and machining characteristics based on artificial neural network (ANN) were established. The back propagation neural network (BPNN) was employed to construct the architecture of the input layer, the hidden layer and the output layer to build the ANN model. Moreover, the weight and the bias values were examined by the steepest descent method (SDM) with the training data. Thus, the suitable ANN models were established with the acquired weight and bias values. The essential parameters of the EDM in gas such as peak current (Ip), pulse duration (tp), gas pressure (GP), servo reference voltage (Sv) were chosen to investigate the effects on MRR and SR. The developed ANN model with 4 input variables on the input layer, one hidden layer with 5 neurons, and 2 response variables on the output layer was obtained by the training with 30 experimental data. Moreover, as the prediction values obtained from the ANN compared with the 5 testing data, the error falls in the rage of 5% indicating the developed ANN is appropriate and predictable. Moreover, the developed ANN model can be used to predict the machining characteristics such as MRR and SR for the EDM in gas with various parameter settings.
Abstract: In the present study, a novel method for mechanically interlocking the dissimilar alloys of A6061-T6 aluminum alloy and SS400 structural steel using friction-stir forming (FSF) is suggested. In this study, the aluminum alloy is placed on top of a steel sheet containing a screwed hole. The present study suggests that friction-stir spot forming (FSSF) can be used to form a mechanical interlock between the aluminum alloy and steel sheet. FSSF is conducted on top of the aluminum alloy, which produces sufficient heat to plasticize the aluminum alloy. This results in a flow of aluminum into the screw hole in the steel, due to the plastic deformation, thereby mechanically interlocking the aluminum with the steel. Moreover, with the proposed method, the authors present a new concept of an easily separable joining of dissimilar alloys. The mechanical properties of the developed interlock are investigated through tensile and hardness tests and microstructural observation.
Abstract: There have been two cathodic protection methods to inhibit corrosion of the structural steel piles which are being immerged under seawater, or to control corrosion of a hull part of the ship exposed to sea water. One of them is a sacrificial anode cathodic protection method that the steel pile can be protected with galvanic current by potential difference between sacrificial anode and corrosive structural steel. And, the sacrificial anode cathodic protection method have generally merits compared to impressed current method because it can be easily applied to everywhere which is not connected with electricity. However, when the steel piles are being submerged in low conductivity solution mixed with fresh water and sea water, the structural steel piles mentioned above have not been protected occasionally perfectively due to decreasing of galvanic current of zinc anode caused by deposited with oxide film on the surface of anode. In this study, four types of zinc anodes samples which are included with three types of additives such as NaCl, KCl, and ZnCl2 were prepared, and galvanic currents, the polarization characteristics of these anodes was investigated using electrochemical methods such as polarization curves, impedance, cyclic voltammogtam and galvanic current in order to evaluate the effect of additive affecting to quality of zinc anode. The sample added with NaCl indicated the highest value of galvanic current density compared to other samples in the case of lower and higher conductivity solutions such as 0.32 and 2.97mS respectively, and the sample added with KCl revealed the smallest galvanic current density in middle value of conductivities such as 1.53 and 2.27 mS. Moreover, Zn sample no added with additive exhibited the smallest value of galvanic current density in the lowest conductivities such as 0.32 and 0.98 mS. Therefore, it is considered that the galvanic current of the sacrificial anode can be increased by adding of additive when the anode is submerged in low conductivity solution mixed with fresh water and sea water.
Abstract: Recently, many types of constructional steels have been often exposed to severely corrosive environments due to acid rain with increasing environmental contamination. To control corrosion problems, a painting protection method has been widely applied to numerous constructional steels on land as well as offshore. Therefore, development of anti-corrosive paint with good quality of corrosion resistance is very important from an economical perspective. In this study, four types of anti-corrosive paint were coated to test specimens, and then, were immersed in various salt solutions (0.1, 3 and 9% NaCl solution) for 11 days. Corrosion resistance of these samples by effect of osmotic pressure with various salt concentration was investigated with electrochemical methods such as measurement of corrosion potential, impedance and corrosion current density. Corrosion current density of these samples submerged in 0.1% NaCl solution exhibited highest value than those immersed in 3% and 9% NaCl solutions because water, dissolved oxygen and chloride ion etc. is easily to invade towards inner side of coating film due to increasing osmotic pressure compared to 3% and 9% NaCl solutions. However, corrosion current densities of all samples in the case of submerged in 9% NaCl solution exhibited higher values compared to 3% NaCl solution.Thus, a large amount of chloride ion dissolved in 9% NaCl solution plays a more critical role in corrosion behavior of coated steel rather than osmotic pressure. Consequently, the corrosion mechanism between coated steel and bare steel plates is different from each other because of presence of osmotic pressure between salt solution and coating film of coated steel plate. As a result, corrosion resistance of tcoated steel plate may be depend on the osmotic pressure as well as salt concentration
Abstract: Phenyl silicone resin reinforced addition type liquid phenyl silicone rubber was prepared by vulcanization of vinyl end-capped polymethylphenylsiloxane (PVPS), phenyl MT resins and hydrogen end-capped polydiphenylsiloxane (PHPS) under Pt catalysis at 150°C for 4h. The effects of the proportion and the vinyl content of phenyl MT resins on the mechanical properties of cured products were investigated. The thermal stability was explored by thermogravimetric analysis. The changes of mechanical properties were also studied before and after irradiation. Phenyl silicone rubber with good performance was obtained when the phenyl MT resin content was 50~60 wt% and the vinyl content was at 5.5~6.6 wt%. The onset temperature of thermal degradation and the center temperature of thermal degradation were 443.7°C and 502°C, respectively. When the radiation dose increased from 0 to 300 KGy, the tensile strength decreased from 4.1MPa to 2.3MPa and the tearing strength decreased from 8.9MPa to 5.1MPa. When the radiation dose continues to increased from 300 to 900 KGy, the tensile strength increased from 2.3MPa to 6.4MPa and the tearing strength increased from 5.1MPa to 6.5MPa. During the process of radiation, the elongation at break had been kept down from 96% to 52%, and the hardness increased from 80A to 90A.
Abstract: The kinetics of the thermal degradation and thermal stability of thermal conductive silicone rubber filled with Al2O3 and ZnO were investigated by thermogravimetric analysis in a flowing nitrogen atmosphere at a heating rate of 10°C/min. The rate parameters were evaluated by the method of Freeman–Carroll. The results show that the thermal degradation of silicone rubber begins at about 350°C and ends at about 600°C. The thermal degradation is multistage, in which zero-order reactions are principal. The kinetics of the thermal degradation of thermal conductive silicone rubber has relevance to its loading of thermal conductive filler. The activation energies are temperature-sensitive and their sensitivity to temperature becomes weak as temperature increases.
Abstract: The article presents the data of an experimental study on how heat treatment influences the physical and mechanical properties of cured samples of sandwich structures. The sandwich structures were made using VaRTM method. Heat treatment at 80 °С and 60 °С leads to increase in the tensile strength. Three-point bend tests were conducted. The results characterize the relationship between the durability and the temperature and exposure time of the sandwich structures. The results correlate with the data of structural studies of fracture cross-sections and research on the extent of swelling of the cured binder. The SEM micrographs of the microstrustructures of fiberglass reinforced plastic samples show that during heat treatment there is a structural refinement of the polymer matrix. As a result of heat treatment at 80 °С for 4 hours, the extent of swelling decreased by 14%. The heat treatment of sandwich structures at a temperature of 80 °С for 4 hours is optimal and leads to increase in the tensile strength by 30.7%.
Abstract: This study aims to investigate numerically the damage area of a sandwich composite structure. In this work, the optimal sandwich core modeling method was proposed. This study applied two modeling methods to compare their analysis results for the structural analysis of the sandwich composite structure. Firstly, the modeling of sandwich core structure was performed with laminate modeling method. Secondly, the modeling of core structure was performed with core solid modeling method. The laminate modeling method was compared with the core solid modeling method. For the modeling, a carbon/epoxy composite structure was applied to the face sheet. And a nomex honeycomb core was applied to the core. Finally, comparing the result of modeling as actual shape with the one of virtually applying the thickness and modeling, it was examined that the former had three times more stress than the latter.