Students should work in groups of 5 to complete this assessment item. The aim is to investigate the tensile properties of the various classes of materials
and relate these properties to real-world applications, i.e., a bicycle frame.
Project 2 Tensile Test of Materials Laboratory Manual Prepared for 1502ENG Engineering Materials Outline Students should work in groups of 5 to complete this assessment item. The aim is to investigate the tensile properties of the various classes of materials, and relate these properties to real-world applications, i.e., a bicycle frame. 1502ENG Engineering Materials Griffith College i CONTENTS 1 Mechanical Properties of Materials 1 1.1 Aim ............................................................................................................................................1 1.2 Introduction ...............................................................................................................................1 1.3 Scenario .....................................................................................................................................3 1.4 Equipment .................................................................................................................................3 1.5 Testing Procedure ......................................................................................................................3 1.6 Results .......................................................................................................................................5 References 10 1502ENG Engineering Materials Griffith College 1 m2 1 MECHANICAL PROPERTIES OF MATERIALS 1.1 AIM The of this part is to characterise various specimens by means of the tensile test. 1.2 INTRODUCTION There are various tests to characterise the properties of a material and they are classified in two main cat- egories: destructive and non-destructive tests. The latter are mainly utilized to check for defects whereas the former are used to obtain the material strength and stiffness. Amongst the destructive material tests, the uniaxial tensile test is the most important of them all (see Fig. 1). Figure 1: Schematic depiction of a sample under tensile loading, (a) before deformation, and (b) after deformation. Adapted from (Öchsner 2016, p. 3, Fig. 1.2) A tensile test is conducted by means of a specialised machine, called the tensile testing machine. In such machines, a controlled loading of the sample is possible. The deformation of the sample is its response to the applied load. During the test, the values of the force and deformation are continuously recorded. Engineering stress (σ ) can be calculated using the recorded forces: F σ = , (1) A0 where F is the instantaneous load applied perpendicular to the specimen cross section in units of newtons (N), A0 is the original cross-sectional area before any load is applied (m2). The units of engineering stress is pascal (Pa) which is equivalent to newton per square meter ( N ). Engineering strain (ε) is the change in the dimension per unit length. Engineering strain can be calculated by knowing the deformation at every instance: l − l0 l0 ∆l = , (2) l0 ⑧ Write down the hypothesis of this experiment using the mentioned aim. What was the research question? 1502ENG Engineering Materials Griffith College 2 where l0 is the original length, i.e., the gauge length, before any loading, l is the the instantaneous length, l − l0 is the deformation elongation or change in length at some instant, as referenced to the original length. The percentage of strain is the engineering strain times 100. During the test, the applied force and the displacement, which is the response of the sample to the applied load, is constantly measured. The tensile testing machine to be used is depicted in Fig. 2. (a) General view (b) Components of the testing equipment Figure 2: Tensile testing apparatus. A tensile sample, or sometimes called a coupon, has a plain geometry (see Fig. 3). It consist of clamping areas at the two ends of the sample and a prismatic section in the middle. The prismatic section is the area of interest which incorporates the gauge length. This is the same area in which failure will happen. The two ends serve the sole purpose of fixating the sample in the apparatus with a better grip. Nevertheless, other geometries are also possible for the sample. Figure 3: Flat tensile sample and fixation equipment. 1502ENG Engineering Materials Griffith College 3 1.3 SCENARIO In this activity, your group should conduct some tensile tests and provide the answer for the following scenario: 1.4 EQUIPMENT The following equipment will be provided: 1.5 TESTING PROCEDURE You must work in a group of 5 people and obtain the force-deformation data for each sample. Before starting the test, you should record the required specimen information, e.g., sample number, material type, cross-sectional area, length, and other required measurements. Additionally, it is required to mark the gauge length, i.e., 25 cm, on each specimen. The very first step is to install and clamp the specimen. Tip Do not trust the provided measurements, check everything! ➠ Watch the How to use a digital calliper video. Tip You need to get the detailed description of the equipment. Refer to Special Issue: Academic Writing. Equipment • a digital calliper, • an extensometer, • a data acquisition unit, • the WP300 Universal Material Tester (20 kN), and • 8 tensile samples: – Tempered steel (3 samples), – Annealed steel (1 sample), – Copper (1 sample), – PMMA (Acrylic) (1 sample), – PVC (1 sample), and – Plywood (1 sample). Note The answer to the question must be incorporated in the discussion and be reflected in the conclusion part of the report. Therefore, it is an individual component of the report. Scenario The Scrap Metal Co. You are employed as the designer engineer in Byke Corp. which is a manufacturer of bicycle frames. There are a few options available for the frames and you need to compare them in terms of their mechanical properties. The material options are two types of steel, copper, two polymers, and a composite. Discuss the mechanical properties of the available materials and choose a suitable material based on the results of the tensile test. http://youtu.be/zBvJDlljvLA 1502ENG Engineering Materials Griffith College 4 Figure 4: Mounted tensile sample with attached extensometer The force is measured by the load cell, located at the lower part of the machine whereas the defor- mation of the gauge length is measured by an extensometer (see Fig. 2a). Namely, the deformation is measured along a specific length in