Fracture in Bioceramics

V. Apablaza, E. Hamm, F. melo

The characterization of elastic properties of natural bioceramics such as eggshells or "picoroco" shells, by using mechanical tests and acoustical methods, is one of the new activities of the group. Specifically, we have developed a simple fracture machine to carry out experiments on fracture of egg shells. This allows us to observe in situ the fracture propagation in a full egg shell under polar compression. In addition, a second fracture miniature machine designed in conjunction with an optical microscope, allows us to apply flexural stress on a rectangular sample cut from the egg shell or a variety of spines. A short article containing our results on egg shells fracture will be ready in a few months.
In March 2003, Dr. Eugenio Hamm has joined the group. In the framework of the Project "Stress distribution and basic mechanisms of fracture in natural bioceramic materials" we designed a mechanical testing machine for small samples. We can study bending and fracture phenomena by performing three- and four-point mechanical tests on thin or thick samples of nacre or any biological rigid material, subjected to an external force. This force is applied with the free end of a cantilever that is attached to a rigid moving body. By measuring the deflection of the cantilever relative to the displacement of the rigid body towards the specimen, we are able to measure the imposed displacement and force. We also developed a method for the preparation of small sized samples of nacre. In addition, most of the equipment required to perform deformation field measurements using speckle methods is now available in the laboratory.