AERO214 Axial Loading

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Texas A&M University *

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214

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Mechanical Engineering

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Dec 6, 2023

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docx

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8

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Tension Test INTRODUCTION Tensile testing is performed on materials to ascertain important mechanical properties like Young’s modulus, tensile strength, yield strength, ductility and fracture strength. The fundamental purpose of a tensile test is to determine the deformation response of a given material under a specified load. This information is critical in the design of load carrying structural members. Tensile tests are performed with specimens of various geometries. Often, a specimen with a circular or flat rectangular cross section is used. In this laboratory experiment, we will be using a flat rectangular configuration. OBJECTIVES • To understand how a tensile test is performed and how to obtain the relevant material properties • To determine the following properties for given metallic specimens (Aluminum 6061, 316 Stainless Steel, and 1018 Carbon Steel) using a uniaxial tensile test: Young’s modulus, E Yield strength, σ Tensile strength, Strain to failure Lab-Specific Information Each lab group will conduct the experimental portion for the entirety of the lab, examining the response of each of the three samples to tensile loading. Each group will be responsible for writing a lab report due two weeks after the date the lab was conducted. Axial Loading: This lab examines the elastic and plastic deformation of an axially-loaded material to failure. Three separate materials are examined in this work. Each lab group is responsible for developing stress-strain curves to obtain a deeper understanding of constitutive relationships, strain hardening, strength, and failure. THEORY Inputs: F Measured Outputs: ∆ L Calculated Outputs: ε , E Known Parameters: A, L, For a rod with gage length L with both ends fully constrained (no translational or rotational movement allowed), the applied force can be converted to stress by dividing the applied load by the cross-sectional area: L
σ = F A The axial strain ε can be obtained – correlating the change in length of the sample ( ∆ L ) to the original gage length. ε = ∆ L L The sample geometry shown in the shape is referred to as a dog bone sample. We use the gage length (measured from the beginning of curvature of the sample) rather than the total length in calculating the strain. This is because the deformation scales inversely with cross-sectional area: The two “heads” of the sample experience much less strain than the gage length, and the strain in the heads is considered to be negligible. A COUPLE OF KEY TERMS The modulus of elasticity : also known as the young’s modulus – can be obtained for an elastic response of the material. E = σ ε Elastic modulus does not use data from the plastic regime or failure regime of the stress-strain curve. Gage Length: constant-radius section of experimental sample. Necking: visible reduction in cross-sectional area in a sample at the point where failure is imminent. Strain to failure: The maximum strain that the sample can take right before rupture. Yield stress: The minimum stress required for the solid to undergo plastic deformation. Energy to failure: The energy per unit volume of the material required to break the sample. It is equal to the area under the stress-strain curve.
TEST PROCEDURE This lab examines three separate materials: Aluminum 2024 Aluminum 6061 ASTM-A36 Carbon Steel For each material, begin by obtain the gage length and cross-sectional dimensions of each sample. Each sample will be loaded to fracture in the INSTRON tensile testing apparatus, seen below: Figure 1: Instron Test Apparatus The test methods for each of the tests below have already been programmed into the INSTRON Bluehill software package. These methods will automatically output the force and deformation data to an excel sheet, with a separate sheet for each run, which you can email to yourself for data analysis. Aluminum 6061 and 316 Stainless Samples ONLY: Loading to Fracture 1. Position your sample in the test apparatus, zeroing the force and deformation gages or readings 2. Log in to the computer with your TAMU ID and password, then access the data folder on the desktop window. Each run will store data to this folder. Open the Instron software package on the desktop window. Upon opening, enter the userID and password provided by the TA.
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