Applied Mechanics and Materials Vols. 190-191

Abstract: In this study, three dimensional structures are fabricated by a self-developed three dimensional printing machine with eight different particle size distribution scrubbed silica sand. In order to evaluate particle size distribution effect on the properties of sand mold, the physical and mechanism properties of printed specimens, including weight, gas evolution, air permeability, tensile strength and compressive strength, were measured. The mechanism of effect was analyzed and studied. The results show that the printed specimens from the 80-140 mesh sand powder have the best comprehensive properties. Both wider and narrower particle size distribution adversely affects the properties of printed specimens.

Abstract: A laminate of silver/atomic layer deposition TiN/Si was prepared to research the thermal reliability. The atomic layer TiN was subjected into different kinds of plasma to modify its surface chemistry. The surface tension of the TiN/Si surface was found to be reduced by O2 plasma bombardment. The reaction mechanism of the continuum of silver film was also explored in this paper.

Abstract: Electroless silver film was deposited on the Ti/Si substrate which was suffered from plasma bombardment to modify its surface chemistry. The surface tension of the Ti/Si surface was found to be reduced after plasma bombardment. After thermal annealing, the silver film was smoothened and showed a fine microstructure. However, the recrystal at high temperature annealing facilitated an increase of sheet resistance instaneously.

Abstract: Hot compression tests of 7075 aluminum alloy were carried out on the Gleeble-1500 thermal simulation machine at strain rates of 0.01 s-1 ,0.1s-1, 1s-1 and at temperatures of 320°C,400°C,480°C. The compression direction are aligned at 0°and 45°to the axis direction of the bar. Microstructure was studied using Optical Microscopy. The results show that the true stress of both specimen increases with the decrease of temperature and the increase of strain rates. The true stresses rose rapidly to peak value and then held constant or decreased with the increase of the true strains at different deformation conditions. The yield strength and stable flow stress of the specimens in 0° to the axis direction is higher than that of 45° specimen, which could be attributed to the elongated grain structures of the bar and the texture of the extruded bar.

Abstract: Based on the laboratory testing of mercury injection with natural cores of low permeability, such analyses were made as the changing law of capillary pressure curves, the distribution features of different size pores and the correlation of pore structures to inside fluid distribution. The fractal method was also used to analyze the two-section line fitting effect of the fractal dimensions and their relationship with the pore distribution laws. The results show that the low permeability reservoir has complicated pore system with high scale of fractal pores, of which the log-log correlation of SHg～Pc can be fitted well with two-section lines, and the two-sections fractal dimensions calculated have greater difference than that of medium & high permeability reservoirs. The study indicates advantages of the fractal method to describe the heterogeneous pore distribution of the low permeability sandstones.

Abstract: The fracture behavior of a brittle thin film on an elastic substrate under residual stress and uniaxial tensile loading is investigated. It is assumed that the residual stress in the thin film is not large enough to cause the thin film to fracture. Using a mechanical model presented in this work, the analytical solutions for the distribution laws of the tensile stress developed in the thin film, the shear stress developed along the interface and the relationship between the crack density of the thin film and the applied strain of the substrate can be obtained. The results presented in this work can provide a new analytic solution to the interfacial shear stress for characterizing the interfacial shear strength of the thin film/substrate system when the uniaxial tensile test is adopted to evaluate the mechanical properties of the thin film/substrate system.

Abstract: A room-temperature ionic liquid, 1-n-butyl-3-methylimidazolium tetrafluoroborate([bmim]BF4), was synthesized with two-step method and its structure was characterized by IR, H-NMR. Putting p-benzenediol and AgNO3 ethanol solution into [bmim] BF4, ultra-fine silver powder were prepared successfully in this paper. The effects of the temperature and material mol ratio of AgNO3 and p-benzenediol on the shape of products were studied. The products were characterized by XRD, SEM, IR and TEM. The results showed that the particle size of silver was much smaller and in the range of nanometers, and had narrowly, uniform distribution, which indicates that the synthesis method using ionic liquid, is the better “green” and “environment friendly” method to prepare ultra-fine silver powder.

Abstract: Temperature field on the road inside the tunnel has a significant difference with normal road surface temperature field, according to the actual situation of the temperature inside the tunnel, calculate the slab length of the cement concrete pavement, obtained the conclusion that cement concrete road slab can be longer inside the tunnel, the conclusion has practical significance for the construction of cement concrete pavement inside the tunnel.

Abstract: Uniaxial tensile tests of extruded 7075 aluminum alloy bar were carried out on the universal test machine at strain rate of 0.001 s-1. The tensile direction are aligned at 0°, 45°and 90°to the axis direction of the bar. Microstructure and texture was characterized using Optical Microscopy and x ray diffraction analysis. The results show that the yield stress for 0° orientation specimen, which was solution treated, is the highest, while that of 45° orientation is the lowest. The yield stresses are anisotropic for solution treated 7075 extruded bar, which could be attributed to the elongated grain structures and the texture of the bar. The yield stress anisotropic behavior diminished after peak aged.

Abstract: Mud loss while drilling fractured formations is a major problem for drilling operating. It is a key to successful temporary sealing technology that lost circulation materials (LCM) can quickly form the plugging zone in the fractures. The permeability of plugged zone influences its bearing strength, as drilling fluid can penetrate and break it, causing it destabilizing and then failure of lost circulation controlling. With the soap film flowmeter, designing different LCM under variable confining pressures, considering the matching relationship of grain diameters and fracture width is (0.5～1):1, analyzing the permeability of plugging zones with different materials. The results indicated that permeability of plugging zone with peanut grains is lower than that of calcium carbonate, but its bearing strength is not as good as that of calcium carbonate, while using merely single LCM. Comparing other materials, the ideal plugging zone is formed with the mixture of peanut grains and calcium carbonate, which has the lowest permeability as well as the bearing strength. The mixture of matching calcium carbonate and smaller peanut grains, comparing to the width of fracture could stands 5 MPa of pressure difference at normal temperature, and 3.9 MPa at 80°C temperature in laboratory. To some extent, it can meet the needs of temporary sealing technology and successfully deal with lost circulation, which demands plugged tightly and bilateral pressurization.