Advanced Materials Research Vols. 97-101

Abstract: This present work investigate the hydrogen content in Al-12Si alloy at different holding temperatures of 993K, 1023K, and 1053K and under different ambient relative humidity 30%RH, 50%RH, 80%RH. The relationship of the hydrogen content with atmosphere relative humidity and the reaction time was investigated. A HYSCAN II analyzer was used to evaluate the hydrogen content in aluminum melts. The experimental results show that the hydrogen content increased with the holding temperature and the relative humidity. At the temperature 1053K, the hydrogen content has an inverse change. The hydrogen content is more depend on the liquid structure than physical mass transfer and chemical reaction because of the sudden change in liquid microstructure. A group of kinetic regression equations of the hydrogen absorption in Al-12Si melts was obtained.

Abstract: Al-10Sn matrix composites reinforced by TiB2 particles were fabricated by Mixed Salt Reaction in situ synthesis process. The oil lubricated sliding wear tests of composites and matrix alloy were conducted on a small thrust ring versus disc wear testing machine at room temperature under different applied loads and the wear surfaces were observed using SEM. The results indicate that the coefficient of friction, friction temperature, and wear weight loss increase with the increase of applied loads, but compared with matrix alloy, the composites exhibit better anti-friction property and higher wear resistance. The analysis of wear surface suggests that light ploughing is predominant for composites and matrix alloy at low loads, and ploughing is still predominant for composites at high loads, but adhesion and delamination are predominant for matrix alloy at high loads

Abstract: This study performed the finite element analysis of the cycle of stress intensity factors at the surface initiated rolling contact fatigue crack tip under Hertzian contact stress including an accurate model of friction between the faces of the crack and the effect of fluid inside the crack. A two-dimensional model of a rolling contact fatigue crack has been developed with FRANC-2D software. The model includes the effect of Coulomb friction between the faces of the crack. The fluid in the crack was assumed not only to lubricate the crack faces and reduce the crack face friction coefficient but also to generate a pressure.

Abstract: In order to determine the ductile to brittle transition behavior of nuclear primary pipe material (Z3CN20.09M) during the thermal aging procedure, instrumented impact tests at different temperatures were performed on Z3CN20.09M aged at 400°C for up to 3000 hours. The load-deflection curves from the instrumented impact tests described both the loading and the fracture stages, from which the dynamic strengths and energy were calculated. The results indicated that the thermal aging decreases the impact energy and shifts the ductile-to-brittle transition curves to higher temperatures.

Abstract: Two groups of magnesium alloys with various Al and Zn components are studied in this paper. One group of alloys are constant Al content of about 6% and various Zn content from 0 to 3%, another group are constant Zn content of about 0.4% and various Al content from 0 to 6%. The microstructures and mechanical properties of these alloys are investigated in as-cast and homogenized at 380°C for 15h. The results show that the tensile strength increases but yield strength decreases after homogenizing treatment. It can also be found that the morphology of second phrase and the size of grain exert the more effect on the mechanical properties than Zn content does. The alloys with uniform, fine and non-dendrite microstructure exhibit both high strength and elongation regardless of Zn content. On the other hand, the tensile strength and yield strength elevate significantly as Al content increases, and the elongation has a peak value in Al content of about 1.90%. The results show that the as-cast magnesium alloys with Al content of 5.6~6.0% and Zn content of 0.6~1.0% exhibit the best comprehensive mechanical properties.

Abstract: The hot plasticity of Mnl8Crl8 high nitrogen austenitic stainless steel is studied using the thermal simulated test in this paper. In addition, microstructural evolution and precipitate morphology are investigated through optical microscope(OM), scan electron microscope(SEM), X-ray diffraction(XRD) and Electron probe micro-analyzer(EPMA). The results show that the area reduction of Mnl8Crl8 steel varies in a “V” shape in the elevated temperature region. It means that plasticity of Mnl8Crl8 steel is relatively low when the deformation temperature is in 1000~1100°C, whereas an excellent plasticity can be obtained in 850~950°C and 1150~1200°C. The peak value of area reduction appears at 1050°C. The analysis of SEM on fracture morphology indicates that the inter-granular fracture and dimple fracture occur at 1050°C and 1150°C respectively. The results of OM exhibit that the dendrite precipitation occurs while the precipitate in grain boundary solutions as the temperature increasing and the grain coarsens immensely beyond 1000°C. However, dendrite precipitate solutions into the austenite matrix at further elevated temperatures. It causes the plasticity substantial improvement in 1150~1200°C. Moreover, the observed precipitation of the steel is confirmed to be Cr23C6 by XRD and EPMA.

Abstract: The epoxy asphalt concrete is extensively used as paving material for long-span steel bridges in China. But mode I crack, which is most prominent cracking pattern for the pavement, often appears on the pavement surface. Therefore, the stress intensity factor K and J-integral were adopted to analyze fracture properties of single-edge notched three-point bending beams. The influence of temperature on the two parameters was studied. The analyses indicate epoxy asphalt concrete exhibits ductile fracture property at 5~25°C and brittle fracture property at -15~5°C. It is also found that fracture property of epoxy asphalt concrete is better than other kinds of bituminous concrete. Finally, a double-parameter K~J fracture criterion is founded for the epoxy asphalt concrete and provides basis for anti-cracking design and repair of cracks of the pavement.

Abstract: One of the greatest drawbacks to predicting the behaviour of bonded joints has been the lack of reliable data on the mechanical properties of adhesives. In this study, methods for determining mechanical properties of structural adhesive were discussed. The Young’s modulus, Poisson’s ratio and tensile strength of the adhesive were tested by dogbone specimens (bulk form) and butt joint specimens (in situ form). The shear modulus and shear strength were test by V-notched specimens (bulk form) and thick adherend lap-shear (TALS) joint specimens (in situ form). The test results show that the elastic modulus provided by the manufacturer is too low, the dogbone specimen is better than the butt joint specimen to test the tensile strength and elastic modulus and the TALS joint specimen is better than the V-notched specimen to test the shear strength.

Abstract: Statistical analysis was carried on weld defects of low carbon bainite ADB610 steel using shielded metal arc welding (SMAW) and mixed active-gas arc welding (MAG). By Pareto diagram analysis, although the ratio of porosity air hole using SMAW is slightly higher than the one using MAG, there is no qualitative difference in ADB610 steel weld defect types between two welding methods. And the crack occurs seldom, which indicates ADB610 steel has lower crack-sensitivity using SMAW and MAG. By histogram analysis and rank test, it can be concluded that there is distinctive difference in defect size between SMAW and MAG, and the average size using SMAW is bigger than the one using MAG. So if possible, MAG is recommended for low carbon bainite ADB610 steel.

Abstract: SiC particle reinforced aluminum metal matrix composites (SiCp/Al) were prepared by powder metallurgy method, and the volume fraction was 5% with size of 3.5 micron and 10 micron. Uniaxial tensile experiments were carried out and the fracture modes were observed. The results demonstrated that the SiC particles in matrix might improve the strength and elastic modulus of the material, but the plastic deformation ability of the material decreased obviously. Based on SEM observation on the microstructure, the boundary cell model (boundary cell finite element method, BCFEM) was established to consider the particle debonded from its surroungding matrix. The particle debonding described by nucleation and growth of voids in matrix，which was investigated using GTN(Gurson-Tvergaard-Needleman) model. The BCFEM model was valid to describe the damage behavior due to the accurate characterization for microstructure of the model.