Hertzian contact response of ceramic matrix interpenetrating phase materials with dual infiltration
Antonio, Marina Pilar V
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Objectives: This study investigated the damage accumulation and strength degradation properties of interpenetrating phase structures in response to Hertzian contacts. The structures examined included glass-infiltrated alumina, resin-infiltrated alumina and combined glass/resin infiltration tested on both glass- and resin-infiltrated surfaces. Methods: Vita In-Ceram alumina blocks were sectioned into 25 mm x 4 mm x 3 mm bars. The bars were divided into 4 groups, (1) fully glass infused, (2) fully resin infused, (3) dual infused, tested at the glass-infiltrated surface, and (4) dual infused, tested at the resin-infiltrated surface. Glass infusion was performed according to the manufacturer’s recommendations. In the dual-infusion groups, glass was infiltrated to a depth of 1.5 mm and the remainder was infused with a heat-polymerizing resin. Resin infiltration was accomplished by using vacuum pressure. The infused plates were polished to 1 [mu]m diamond grit. Specimens used for strength degradation tests were indented at the center of the polished surface at loads ranging from 200-2200 N, by using a 3.18 mm-radius tungsten carbide indenter. The specimens were later broken by using the 4-point bending test. Beam theory and equivalent width technique were applied for calculations of strength. For the damage accumulation tests, 2 bars were polished on complementing surfaces and joined with cyanoacrylate. The test surface was then polished and a load was applied at the bond interface. Measurements for the load (P), indenter radius (r), and contact radius (alpha) were used to calculate stress and strain. Contact radius was measured by using a videomicrometer at 5x magnification. The bonded specimens were separated and the resulting indentation and crack field was examined with an optical microscope. Results: Stress-strain curves of specimens tested on the glass-infiltrated surface had an initial linear behavior before deviating from the straight line. Two damage modes were identified for these specimens: cone cracking (brittle damage), and quasiplasticity (yield damage). Stress-strain curves of specimens tested on the resin-infiltrated surface had an immediate non-linear curve. Only yield damage could be observed through the techniques used in this study. Specimens indented on the glass-infiltrated surfaces prior to being subjected to a 4-point bending test showed no statistically significant difference within the 2 groups (p =.840 for fully glass-infiltrated group and p =.070 for the dual-infiltrated group). Specimens indented on the resin-infiltrated surface prior to being subjected to a 4-point bending test showed a statistically significant difference within both groups (p =.001 for the fully resin-infiltrated group and p [less than] .0001 for the dual-infiltrated group). As the indenter radius was decreased, stress and strain within the same group increased. Conclusion: The interpenetrating material on the testing surface dictated the behavior of the entire specimen in bars with a thickness of 3 mm and a 1 :1 ratio of infiltration depth. Specimens indented on the glass-infiltrated surfaces had an ability to accumulate damage without a signicant degradation in strength. Stress-strain curves showed that specimens indented on the resin-infiltrated surfaces had the ability to accumulate damage, but flexural tests indicated that there was a significant degradation in strength as damage accumulated. The amount of stress and strain that could be produced by an indenter was inversely proportional to its radius. Indenter radius had a greater influence on stress and strain than indentation load.
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