Abstract
This thesis describes a study of indentation fracture transitions in poly (methylmethacrylate) (PMMA). The objective of this study was to deteimine the ductile-to-brittle transition temperature (DBTT) and to investigate its correlation with indenter radius. For this purpose PMMA has been indented by ball indenters of radii ranging from 0. 5 mm to 8 mm over a temperature range of -80 C to 60 C with various testing speeds. It has been shown that at least two types of cracking can be formed, radial cracking and ring cracking. A fracture transition in a given test is defined as that temperature at which one of these crack types is observed to form. The DBTT obtained by observing both types of cracking are governed by a size effect related to the indenter radius in a form predicted by the Puttick theory of fracture transitions. In connection with the main investigation, subsidiary studies have been made of (a) the ball indentation hardness and (b) the extent of crazing around indentations as functions of temperature.