LAUSR

This editorial is part of the series ‘‘1000 at 1000’’ highlighting the most highly cited publications in the Journal of Materials Science as part of the journal’s celebration of 1000 issues. In this issue: ‘‘Evaluation of KIc of brittle solids by the indentation method with low crack-to-indent ratios,’’ K. Niihara, R. Morena, D.P.H. Hasselman, [1] from the Virginia Polytechnic Institute and State University, Blacksburg, Virginia, USA. In the 1980s, a technological drive to develop advanced structural ceramics was extremely active. The activity was based on the intrinsic advantages offered by ceramic materials, such as chemical and thermal stability, surface wear resistance, and bulk stiffness, along with dielectric and optical properties not found in metals. Structural (i.e., load bearing) components based on ceramic materials such as Al2O3, ZrO2, SiO2, SiC, and Si3N4 were developed and attention was naturally focused on optimizing the mechanical performance of such components, primarily by increasing ceramic strength. The strength of most ceramic materials at room temperature is controlled by brittle fracture: the ceramic sustains an applied stress elastically until a critical flaw becomes unstable at the maximum sustainable stress—the strength—and a crack propagates through the material leading to near instantaneous component failure. Many development efforts were therefore directed towards controlling processing of structural ceramics to minimize flaw size, thereby enhancing strength. The major effort in structural ceramic development, however, was directed towards optimizing processing to generate ceramic microstructures with increased resistance to crack propagation—increased toughness—thereby increasing strength. Hence, there was a need for methods to evaluate ceramic toughness and the development of such a method, using a commonly observed range of indentation crack lengths, was the focus of a much cited Letter by Niihara, Morena, and Hasselman [1]. Measurement of ceramic toughness using conventional methods can be an exacting task. Large centimeter-scale specimens must be machined to prescribed geometries, such as the double cantilever beam, into which carefully-formed, long, straight cracks must be introduced. The specimens are then