EXPERIMENT 1 - TENSILE TEST

Transcription

1 EXPERIMENT 1 - TENSILE TEST LECTURER : MOHAMMAD SHAHRIL SALIM PLV : MAIZATUL NURUL BARIAH AHMAD ROBIYANTI ADOLLAH TECHNICIAN : MOHAMMAD ABID BIN ABDUL RAHMAN Student s Particulars: Name : Matric. No: Date : REPORT : Group :

2 1.0 OBJECTIVES 1.1 To understand the concept of mechanical properties of strength of materials 1.2 To construct the stress-strain diagram based on Universal Testing Machine data 1.3 To understand the concept of engineering stress-strain 1.4 To understand the concept of and true stress and strain 1.5 To understand how to determine: a) Young s Modulus/Elastic Modulus b) Yield strength c) Proportional limit d) Ultimate stress e) Fracture stress f) Percent reduction of area g) Percent elongation h) Modulus of Resilience 2.0 INTRODUCTION The basic understanding of stress-strain behavior of materials is most importance to the material and design engineers. The tensile test is one of a common mechanical test that gives stress strain behavior on chart/ plot. This test allows us to determine several important mechanical properties such as yield strength, ultimate tensile strength, etc. The tensile test is carried out on Universal Testing Machine (UTM). Fig. 1 Structure Diagram of Testing Machine 2

3 Fig. 2 Tensile Test Fig. 3 Standard Specimen Fig 4. Stress-Strain Curve 3

4 In a tensile test specimen is deformed by a gradually increasing tensile load applied along its vertical axis. The specimen will elongate at a constant rate. For a better understanding of the stress-strain curve, it is necessary to define a few basic terms that are associated with the stress-strain plot. Stress: the force applied to produce deformation in a unit area of a test specimen. The value which is obtained by dividing tensile load applied to the test piece at any moment by area of original cross section within the reference lines. Stress = Load Area P δ = (kgm -2 ) A Strain: the measurement of the deformation length that has occurred in specimen or simply stated as changed in length per unit of the original length. Strain = Final length original length Original length L ε = L o Elongation: the increase in the length of a test specimen produced by a tensile load. L Percent elongation: % Elongation = 100%, where L o : initial length L o Yield stress/ yield strength: the stress at the first point on the stress-strain curve at which an increase in strain occurs without the increase in stress. Break stress/ break strength: The stress at the break point of the specimen. Proportional limit: the stress at the point where the straight line portion of the stress-strain curves ends or the relation between stress-strain begins to deviate from linearity. 4

5 Modulus of elastic/ Young s modulus: the ratio of stress corresponding strain within the proportional limit. In case where the tensile stress-strain curve has no linear portion, it is defined as the inclination of tangent to the curve at the starting point of deformation. Modulus is a measurement of material s stiffness. Ultimate strength: the maximum/ highest stress a material will withstand when subjected to an applied load. Percent reduction of area: a measurement of the fracture ductility Ao A f % Reduction of Area = 100%, where A o : initial cross sectional area A o A f : final cross sectional area 5.1. EQUIPMENTS & MATERIALS: 3.1 Equipments 1) Universal Testing Machine 2) Gripper 3) Personal Computer Fig 5. Universal Testing machine (UTM) 5

6 3.2 Material 1) Specimens-Round Bar(Mild steel & Aluminum) 5.2. EXPERIMENTAL PROCEDURE 4.1. Run the machine and make sure take a warm-up time before of appox.15 minutes after turning ON the power Measure the width and thickness of specimen and place the specimen on the supports 4.3. Start the test until a specified displacement is achieved Obtain the data from data acquisition software and save the data in ASCII file. 5. EXPERIMENTAL ANALYSIS 5.1. Make a table giving the specimen, the original dimensions and the final dimensions. This will be Table Construct a stress-strain curve from the load-elongation curve i. Make a table for load-elongation curve data, stress and strain. Insert the data in Table 2. ii. Construct the load-elongation curves by utilizing spreadsheet software and name it as Fig. 1. The load is on the y-axis and elongation is on the x-axis. The unit of load and elongation are kn and mm,respectively. iii. Compute the strain and stress (engineering values) up to 2 %, and draw the graph name as Fig 2(a). iv. Compute the strain and stress (engineering values) up to failure and draw the graph name as Fig 2(b) Using the Fig. 2(a), where the strain goes to 2 percent, make the following calculations (and on the graphs, show how you made those calculations) i. The elastic modulus. ii. The 0.2% offset yield strength if you have the graph that does not have a well-defined yield point. 6

7 5.4. Determine the mechanical properties for the specimen. Insert data and calculation in the table and name it as Table DATA & RESULT: 6.1 TABLE 1 : Specimen dimension 6.2 TABLE 2 : Load-elongation curve data, stress and strain data (Show the calculation for stress and strain for 1 sample for each materials used) 6.3 Fig. 1 : Force vs. Elongation curve 6.4 Fig. 2 (a): Stress vs. Strain up to 2% 6.5 Fig. 2 (b): Stress vs. Strain up to failure 6.6 TABLE 3: Mechanical properties (Shown the calculation or remarks it on the graph) 7.0 QUESTIONS: 7.1 Define ductile material? Give three (3) example ductile materials. 7.2 Give three reasons why Tensile Tests was performed? 7.3 What do you understand about elastic behavior in stress-strain diagrams? 8.0 DISCUSSION (Include a discussion on the result noting trends in measured data, and comparing measurements with theoretical predictions when possible. Include the physical interpretation of the results and graphs, the reasons on deviations of your findings from expected results, your recommendations on further experimentation for verifying your results, and your findings.) 9.0 CONCLUSION (Based on data and discussion, make your overall conclusion by referring to experiment objective) REFERENCES 7