MATCH provides an overview of segmentation methodologies for IAs and highlights the variability of surface reconstruction. Further, the study emphasizes the need for careful processing of initial segmentation results for a realistic assessment of clinically relevant morphological parameters.

A method is presented to use a dimensionless form of the well-known Niyama criterion to directly predict the amount of shrinkage porosity that forms during solidification of metal alloy castings. The main advancement offered by this method is that it avoids the need to know the threshold Niyama value below which shrinkage porosity forms; such threshold values are generally unknown and alloy dependent. The dimensionless criterion accounts for both the local thermal conditions (as in the original Niyama criterion) and the properties and solidification characteristics of the alloy. Once a dimensionless Niyama criterion value is obtained from casting simulation results, the corresponding shrinkage pore volume fraction can be determined knowing only the solid fraction-temperature curve and the total solidification shrinkage of the alloy. Curves providing the shrinkage pore volume percentage as a function of the dimensionless Niyama criterion are given for WCB steel, aluminum alloy A356, and magnesium alloy AZ91D. The present method is used in a general-purpose casting simulation software package to predict shrinkage porosity in three-dimensional (3-D) castings. Comparisons between simulated and experimental shrinkage porosity results for a WCB steel plate casting demonstrate that this method can reasonably predict shrinkage. Additional simulations for magnesium alloy AZ91D illustrate that this method is applicable to a wide variety of alloys and casting conditions.

A volume-averaged model for finite-rate diffusion of hydrogen in the melt is developed to predict pore formation during the solidification of aluminum alloys. The calculation of the micro-/macro-scale gas species transport in the melt is coupled with a model for the feeding flow and pressure field. The rate of pore growth is shown to be proportional to the local level of gas supersaturation in the melt, as well as various microstructural parameters. Parametric studies of one-dimensional solidification under an imposed temperature gradient and cooling rate illustrate that the model captures important phenomena observed in porosity formation in aluminum alloys. The transition from gas to shrinkage dominated porosity and the effects of different solubilities of hydrogen in the eutectic solid, capillary pressures at pore nucleation, and pore number densities are investigated in detail. Comparisons between predicted porosity percentages and previous experimental measurements show good correspondence, although some uncertainties remain regarding the extent of impingement of solid on the pores.

A methodology is developed to relate measured shrinkage porosity levels in steel castings to predictions from casting simulations, in order to determine feeding distances. Low-alloy steel casting trials were conducted to acquire a statistically meaningful set of experimental data for top-risered cast steel sections having various ASTM shrinkage X-ray levels. Simulations of the casting trials were then performed, using casting data recorded at the foundries during the trials. The actual casting soundness resulting from these trials, measured in terms of the ASTM shrinkage X-ray level, is quantitatively compared to the soundness predicted by simulations, measured in terms of a local thermal parameter known as the Niyama criterion. A relationship is shown to exist between the X-ray level and both the minimum Niyama criterion value as well as the area (in the plane of the X-ray) with Niyama values below a threshold value. Once the correlations developed in Part I of this article were established, an extensive set of additional casting simulations was performed to determine the feeding distances for castings with a wide variety of casting parameters. These data were then used to develop a new set of feeding-distance rules, which are given in Part II of this article.

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