Determining the role of fractal geometry and fracture energy in brittle bilayer materials

Many applications in the ceramic field require bilayer design to be successful. One example is the application of bilayers in dentistry for all ceramic crowns and bridges. Although fracture in bilayers has been studied, research has not explored if the fracture surface changes as a crack travels from one material to another in a bilayer and if a change in the fracture surface reflects changes in the mechanical properties of the bilayer. The work of fracture, fractal dimension, fracture strength, and apparent fracture toughness were determined for two sets of bilayer bars composed of e.max CeramRTM veneer bonded to e.max PressRTM core The work of fracture was determined from the actual fracture surface area, using atomic force microscopy, to determine if the work of fracture can be used to estimate the minimum fracture energy of the materials. The location of crack initiation was examine to see if the work of fracture is the same in both sets of bilayers and if the fracture process results in the veneer and core having the same fractal dimension.;It was confirmed that the location of crack initiation did change the work of fracture of the bilayers but did not change the fractal dimension of the two materials in the bilayer. The work of fracture was used to estimate the minimum fracture energy of the ceramic monoliths and bilayers. Using the actual fracture surface to determine the work of fracture resulted in a decrease in the work of fracture but did not estimate the theoretical minimum fracture energy of the dental materials. The work of fracture for the bilayer was dependent on the material that the crack initiated in, further indicating that the selection of the materials used in these bilayers is important in designing these bilayer structures. The fractal dimensions of the veneer and core in the bilayers were similar to that of the monolithic specimens. This implies that the fracture process does not change the fractal dimension of these materials and that the fractal dimension is an intrinsic property of these ceramics.