Influence of random shrinkage porosity on equivalent elastic modulus of casting： A statistical and numerical approach

Shrinkage porosity is a type of random distribution defects and exists in most large castings. Different from the periodic symmetry defects or certain distribution defects, shrinkage porosity presents a random "cloud-like" configuration, which brings difficulties in quantifying the effective performance of defected casting. In this paper, the influences of random shrinkage porosity on the equivalent elastic modulus of QT400-18 casting were studied by a numerical statistics approach. An improved random algorithm was applied into the lattice model to simulate the "cloud-like" morphology of shrinkage porosity. Then, a large number of numerical samples containing random levels of shrinkage were generated by the proposed algorithm. The stress concentration factor and equivalent elastic modulus of these numerical samples were calculated. Based on a statistical approach, the effects of shrinkage porosity's distribution characteristics, such as area fraction, shape, and relative location on the casting's equivalent mechanical properties were discussed respectively. It is shown that the approach with randomly distributed defects has better predictive capabilities than traditional methods. The following conclusions can be drawn from the statistical simulations:(1) the effective modulus decreases remarkably if the shrinkage porosity percent is greater than 1.5%;(2) the average Stress Concentration Factor(SCF) produced by shrinkage porosity is about 2.0;(3) the defect's length across the loading direction plays a more important role in the effective modulus than the length along the loading direction;(4) the surface defect perpendicular to loading direction reduces the mean modulus about 1.5% more than a defect of other position.

Comparative study of static and dynamic parameters of rock for the Xishan Rock Cliff Statue

Ultrasonic wave testing was applied to investigate the quality and weathering status of rock specimens obtained in two borings situated in the Xishan Buddha rock slope in Taiyuan, China. This paper pays special attention to the distribution of bulk density, dynamic parameters and static parameters of rock specimens as well as the relationship between static and dynamic parameters. The results illustrate that the distribution of both parameters is identical along the depth of two drilled holes in the rock slope. When the hole depth increases, the density of rock mass, saturated compression strength and static elastic modulus, dynamic elastic modulus and wave velocity also show increase tendency. The weathering degree in the rock mass ranging from the surface of cliff to the depth of 2.5 m is the highest while the rock mass is unsalted and more rigid when the depth is larger than 3.0 m. The relationship between dynamic elastic modulus, sonic wave velocity and horizontal depth indicates that dynamic elastic modulus is more sensitive than sonic wave velocity. Conversely, by comparing quantity relationship between static elastic modulus and sonic wave velocity, it is found that the composition of rock has a great influence on the relationship between static and dynamic parameters, that is, inequality of rock composition will lead to dispersion and abnormality of the distribution of static and dynamic parameters.