The Tensile Behaviour of Common Engineering Polymers

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The Tensile Behaviour of Common Engineering Polymers

Abstract

The mechanical properties of polymers vary significantly from polymer to polymer as a result of atomic structures and bond strength. The tensile properties of representative samples from the common polymer were tested and evaluated in this experiment. This laboratory experiment is also designed to demonstrate the procedure used for obtaining mechanical properties as modulus of elasticity, yield strength, ultimate tensile strength (UTS), uniform elongation, elongation and reduction in area at rupture. This report is based on the fact of understanding how tensile properties are controlled by the nature of the polymers chain and how tensile properties of polymers vary with testing speed.

Introduction

The tensile strength of a material quantifies how much stress the material will endure before failing. This is very important in applications that rely upon a polymer's physical strength or durability. For example, a rubber band with a higher tensile strength will hold a greater weight before snapping. The tensile test consists on the application of a tensile stress on a chosen specimen attached to a device that calculates the force applied on it and the elongation. Polymers or plastic as they are commonly known, consist of long molecular chains of carbon compounds. This type of long chain structure of the plastics or polymers give it special properties that may not be exist in metals. It’s very easy to change the shape of polymers because they are light and corrosion resistant. Additionally in the pure state all polymers are colourless and easy to produce any coloured products by the addition of dyes and pigments. Polymer`s physical, mechanical and electrical properties depends on its structure, temperature and bonds between the monomers. In general, tensile strength increases with polymer chain length and cross linking of polymer chains. For example, as chain length is increased, melting and boiling temperatures increase quickly. Impact resistance also tends to increase with chain length, as does the viscosity, or resistance to flow, of the polymer in its melt state. Chain length is related to melt viscosity roughly as 1:103.2, so that a tenfold increase in polymer chain length results in a viscosity increase of over 1000 times. Increasing chain length furthermore tends to decrease chain mobility, increase strength and toughness, and increase the glass transition temperature (Tg). This is a result of the increase in chain interactions such as Van der Waals attractions and entanglements that come with increased chain length. These interactions tend to fix the individual chains more strongly in position and resist deformations and matrix breakup, both at higher stresses and higher temperature. Materials and Method

Tensile test in board sense is the measurement of the ability of the material to withstand forces that tend to pull it apart and to what extent the material stretches before breaking. As the material is, being pulled you will find its strength along with how much it will elongate. Materials, which exhibit the largest strengths during tensile testing, have the lowest impact values. Tensile modulus is an indication of the relative stiffness of the material, and can be determined from the stress strain diagram. Many plastic are very sensitive to the rate of straining and environmental conditions. Therefore the data obtained from this method cannot be considered valid for applications involving load time scales or environmental widely different from this method. The tensile property data helps in preferential selection of a particular type of plastic from a large group of plastic material and such data are of limited use in actual design of the part. This is because the test does not take in to account the time dependent behaviour of plastic material. As the pull of the material is continued until it breaks, a complete tensile profile is obtained. A...
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