Fellow 1993-94

Huseyin Sehitoglu

Mechanical Science and Engineering

Fatigue of Brittle Materials

Professor Sehitoglu is moving in a new direction in the study of the mechanical response of brittle ceramic materials. Through experiments and collaborative efforts, he aims to improve the toughness and fatigue resistance of brittle ceramic materials with full cognizance of their underlying microstructure. These materials possess superior high temperature properties compared to metallic materials, yet their widespread utilization is hampered by their lack of ductility and toughness. Working under the general heading of mechanics of materials, the professor is seeking to integrate the disciplinary fields of mechanics and materials science by developing a better understanding of the hierarchy of size scales that govern the material behavior.

Specifically, the research will focus on brittle ceramics and methods to enhance their extrinsic properties via the introduction of ductile phases and enhance their extrinsic properties via the introduction of ductile phases and layers. Although significant strides have been made in modeling, further new ideas will depend on novel experiments and observations which have not been undertaken in this field. For example, by forming these materials in layered shapes, it may be possible to enhance threshold stress intensity levels in fatigue loading and, moreover, increase the fracture toughness. These improvements will allow wider use of these materials at temperatures where their low ductility has prohibited their use. The work will guide processing routes for these materials to attain better properties and help evaluate theoretical models which characterize the interaction of ductile and brittle layers.

Professor Sehitoglu has previously investigated fatigue resistance in metallic materials and established external parameters that accelerate this failure mode. Specifically, he made notable contributions to understanding fatigue crack closure phenomenon, which is now a widely used concept in predicting crack growth in metallic materials. The proposed research will extend these ideas to ceramic materials in the presence of surrounding ductile layers. New mechanisms are operative in these materials. This new work will shed further light on how to design materials and structures employing brittle materials.