Tensile Test Eng Ahmed AlAfeefy Eng Ibrahim Aljaish
Tensile Test Eng. Ahmed Al-Afeefy Eng. Ibrahim Aljaish 1
Introduction The stress and elastic strain are directly proportional and related by the Modulus of Elasticity (or Young's Modulus). The stress necessary to produce permanent deformation is the yield strength of the material. The yield strength is conventionally defined as the stress necessary to produce a plastic strain of 0. 2%. Exp. 5: Tensile Test strain is the elongation per unit length ε = ΔL / L. 3/8/2021 Stress is the force per unit area σ = F/A 2
Introduction The deformation is elastic if it is completely recovered immediately after the load is removed. Exp. 5: Tensile Test Fracture Strength is the stress at fracture point. 3/8/2021 Ultimate Tensile strength is the maximum stress that can be sustained by structure during the test in tension and necking begins after it. Purely elastic deformation is associated with the stretching of primary bonds in materials. 3
In ductile materials, the strain to fracture is relatively large compared with brittle materials. Plastic deformation of ductile materials can require progressively higher stresses because dislocations multiply in the process and their motion becomes more difficult due to the increased degree of interaction among them. This process is called work-hardening. Exp. 5: Tensile Test If permanent deformation occurs, it is called plastic. The plastic deformation corresponds to a stress level necessary to initiate the motion of dislocations (a type of defect) in crystalline materials. 3/8/2021 Introduction 4
Øthe engineering stress-strain curve does not give a true indication of the deformation characteristics of a metal because it is based entirely on the original dimensions of the specimen, and these dimensions change continuously during the test. Exp. 2: Tensile Test ØEngineering stress is the force per unit original cross-sectional area of the specimen σ = F/Ao. Engineering strain is the elongation per unit original length of the specimen ΔL/Lo. The true stress and strain are determined from the instantaneous dimensions during the test. 3/8/2021 introduction 5
ØIn ductile materials, the strain to fracture is relatively large compared with brittle materials. ØPlastic deformation of ductile materials can require progressively higher stresses because dislocations multiply in the process and their motion becomes more difficult due to the increased degree of interaction among them. This process is called work-hardening. Exp. 2: Tensile Test ØSome materials exhibit a sharp yield point, whereas others show a slow change in slope at the end of the elastic range. In the latter, the yield strength is conventionally defined as the stress necessary to produce a plastic strain of 0. 2% (elongation). 3/8/2021 introduction 6
Exp. 5: Tensile Test 3/8/2021 Stress- Strain Diagram = 0. 002 7
Objective Exp. 5: Tensile Test § Characterize the physical properties of various metals from their stress-strain curves. 3/8/2021 § Understand the basic process of deformation due to tensile loading. 8
Equipment • Dial Gauge (elongation) • Digital Load Meter (force) Exp. 5: Tensile Test • Hand-Operated Pump 3/8/2021 • Universal Testing Machine. 9
Mount the specimen on the universal testing machine Start applying loads gradually using the hand operated pump Take readings of the force applied from the digital load meter Take readings of length using the digital caliper. Calculate the stress and strain values. Plot the stress strain curve and point out the yield stress, the maximum tensile stress, the modulus of elasticity. 7. Remove the specimen for study of fractured area. Fit the two pieces together and measure the final length and the diameter in the "neck" using a vernier. 8. Calculate values for percentage reduction in area and elongation. Exp. 2: Tensile Test 1. 2. 3. 4. 5. 6. 3/8/2021 Procedures 10
Exp. 2: Tensile Test 3/8/2021 ﺗﻌﺪﻳﻞ ﻣﻬﻢ • 11
Results Force KN Stress (MPa) Exp. 5: Tensile Test Strain 3/8/2021 The diameter of the specimen = 8 mm, A= pi (d^2/4) L=68 mm, specimen material is malleable iron Stress = F/A MPa 12
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