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tion calculations were compared with experimental results.


Tests Results and Discussions Resin-bonded silica sand is more


Fig. 2 This graph shows a typical bilinear force vs. deflection curve of a three-point bending sample.


ties and a material model for casting process simulation.


Process Simulation and Casting Experiment Validation


To validate the material data of


resin-bonded silica sand in casting simulation, sand cup molds with three different types of geometries, named as intact cup mold, flat-notch cup mold and V-notch cup mold, were designed for process simulation and experimental validation. Trough the only change of geometry, the main idea is to create different stress conditions for each cup mold dur- ing heating and cooling of a cast- ing process. Figure 1 is a schematic cross-section of an intact sand cup. It has a uniform thickness of 0.22 in. (5.7 mm), depth of 2.76 in. (70 mm), top inner diameter of 1.5 in. (38 mm) and a 1.5-degree draft for easy release from the stainless-steel mold after the sand is cured. Te minimum wall thickness is the only difference among the three cup molds: 0.09 in (2.4 mm) for the flat-notch mold and 0.05 in (1.2 mm) for the V-notch mold, while the original intact mold has a uniform wall thickness of 0.22 in (5.7 mm). Additionally, both the flat notch and V notch shapes are acting as stress risers with different levels, and such


changes will cause stress variations in the casting process. All cup-shaped sand molds were made in a stainless- steel mold first by compacting using a CT-200 compaction table, followed by curing at 482F (250C) for 45 minutes in a forced air convection oven. Default properties of aluminum


alloy A356 in the simulation software were used in the simulation. Minimum mesh size was 0.04 in (1 mm) for intact cup mold, 0.035 in (0.9 mm) for flat-notch cup mold and 0.023 in (0.7 mm) for V-notch cup mold. Simula-


like a brittle material. Fracture stress of a brittle material varies in a much wider range as compared to that of ductile one. Terefore, 36 three-point bending samples were tested so that the results would be more representa- tive and reliable. In addition to this, seven uniaxial tensile tests were com- pleted as a supplement for mechanical properties. Te reason more bending tests were planned than tensile is because normally a tension test is not preferred for brittle materials. Te stress concentration near the jaws of the testing machine causes failure at the jaws, rather than in the gage section. Tus, more specimens were loaded in bending than in tension. For the bending samples, the


bonded sand behaved in a predomi- nantly elastic manner and fractured in a brittle mode as expected. However, about one-third of the specimens exhibited a linear hardening behavior right before failure occurred. A repre- sentative curve of force vs. deflection for this bilinear behavior is shown in Figure 2. Te red line was fit to both the elastic portion and linear harden- ing stage. Te presence of inelastic behavior of resin-bonded silica sand is rarely reported. While the elastic part is expected to be the same under dif-


Fig. 3 The Gaussian probability distribution function was applied to fracture stress. July 2017 MODERN CASTING | 31


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