INTRODUCTION

Engineering materials play a vital role in this modern age of science and technology. Various kinds of materials are used in industry to meet the requirements of human beings. The selection of a specific material for a particular use is a very complex process. However, one can simplify the choice if the details about use parameters, manufacturing processes, functional requirements, and cost considerations are known. While selecting materials for engineering purposes, properties such as impact strength, tensile strength, and hardness indicate the suitability for selection but the design engineer will have to make sure that the radiography and other properties of the material are as per the specifications.

In recent years, polymeric materials or plastics have gained considerable popularity as engineering materials. Though inferior to most metallic materials in strength and temperature resistance, these are being used not only in corrosive environment but also in places where minimum wear is required, e.g., small gear wheels, originally produced from hardened steels, are now manufactured from nylon or teflon. These materials perform satisfactorily, are quiet, and do not require lubrication