Mechanical Properties: Tensile Strength

1. Synopsis

The aim of this experiment is to be familiarised with the method of tensile testing of materials, and also to understand the behaviour of four different thermoplastic materials through a tensile test. The procedure includes the usage of the LLOYD tensile testing machine to test for the tensile strengths of the different plastic materials as they snap after being stretched. This result will be recorded by the computer which will give specific results for the different materials. The results of tensile tests are used in the selection of materials for engineering applications. GPPS was found to have the highest tensile strength and tensile modulus. PP has the highest yield strength and GPPS is the only material without yield strength as it is brittle and hence does not exhibit yielding.

2. Introduction

In this experiment, the four different plastic materials investigated are General Purpose Polystyrene (GPPS), High Impact Polystyrene (HIPS), High Density Polyethylene (HDPE) and Polypropylene (PP). By performing the tensile test, the following properties will be determined: tensile strength, tensile modulus and yield strength.

A tensile test, also known as tension test, is probably the most fundamental type of mechanical test you can perform on materials to quantitatively measure some of the key mechanical properties of materials. Tensile tests are easy to carry out, inexpensive, and fully standardised. By pulling on something, you will be able to determine how the material will react to forces being applied in tension. As the material is being pulled, you will find its strength along with how much it will elongate. A ductile material exhibits ductile failure (i.e. yields before failure and experiences plastic deformation), while a brittle plastic exhibits brittle failure (i.e. experiences very little or no yielding). An example of a ductile material is paper clips and an example of a brittle material is windshield.