Tensile Test. with those in reference books.

Transcription

1 San Francisco State University School of Engineering ENGR 200, Materials of Engineering Tensile Test I. OBJECTIVESS The purpose of this experiment is to familiarize the student with performing tension tests and obtaining the strength and ductility values from the test results of several metals. The tensile properties of thesee metals will be contrasted and the properties will be compared with those in reference books. II. INTRODUCTION The tensile test is the primary test used in determining the mechanical properties of materials. From this test, it is possible to determine the yield strength, tensile strength, modulus of elasticity, and ductility of a given material. This type of data is essential forr mechanical and structural designs and is usually compiled in materials handbooks for commercially available materials. III. EXPERIMENTAL Materials and Apparatus Instron Tensilee Test System (Series 3369, Figure 1) Four tension test specimenss aluminum (2024-T4), copper (C11000), brass (C36000), and steel (1010 cold-rolled) (seee Figure 2) Rockwell Hardness Tester Vernier caliper Figure 1. Instron Tensile Test Machine, Series Figure 2. Tensilee test specimens.

2 Experimental Procedure 1) Material to be supplied: aluminum (2024-T4), copper (C11000), brass (C36000), and steel (1010 cold-rolled) 2) Prior to testing, measure and label the specimens dimensions, and record them in your data sheet. You may also digitally photograph the specimen. 3) Test procedure: Turn on the machine and let it warm up for 15 minutes before performing any test. a) Specimen preparation Mark a 2 (50.8mm) gage length within the center portion of the specimen using a marker pen. (see Figure 2 for the location of gage length) b) Attach specimen to grip assembly Mount the specimen to the upper grip assembly and allow it to hang freely. This is to minimize side loading or bending moment created in the specimen. Make sure the faces of the grip cover the entire area to be gripped, otherwise your specimen may slip or even break inside the gripped area ("jaw break"). Tighten the clamp. Repeat the same procedure for the lower grip assembly, and tighten the lower clamp c) Set up test program Check to ensure these parameters are entered accurately in the right fields: - Gage length - Sample thickness (Note: thickness of steel is different from the rest) - Ambient temperature d) Testing Zero out all the load and strain values on the specimen as shown on the screen Begin the test the cross-head will begin to move at a pre-determined speed When the pre-set strain value is reached and the cross-head stops moving, remove the extensometer. Continue the test until the sample begins to neck and finally ruptures (breaks). Note the specimen temperature at which this occurs. Carefully remove the fractured samples. 4) Use the Vernier caliper to measure the following dimensions of the fractured sample:

3 - Gage length (Note: put the fractured sample back together and measured the distance between your original markings) - Width (of fractured surface) - Thickness (of fractured surface) 5) Sketch and label the fractured specimens top view and side view. Pay particular attention to the fractured region. In addition, you may digitally photograph the fractured specimens. Include these sketches (and photos) in your Appendices section. 6) Sketch the fractured surface (oblique view). In addition, you may digitally photograph the fractured surfaces. Include these sketches (and photos) in your Appendices section. 7) Computer-generated data for all four test specimens will be available in Excel format and distributed to the class after the lab session. These data will be used to - construct the stress-strain graphs - compute the modulus of elasticity - locate the yield strength - locate the tensile strength - locate the fracture load - compute ductility of the specimen Note: If you are not familiar with data manipulation and graphing using Microsoft Excel, please inform your lab instructor ASAP.

4 IV. DELIVERABLES FROM YOU 1. Each Group presents a FORMAL REPORT on this experiment Please include the following two sections in your memo: i) Introduction (½ page): Discuss What is a tensile test, its purpose and significance, the materials tested, what material properties can we obtain from this test, why are these properties important, what equations do we use (list all that you use) -- Use these questions as a guideline to write your Introduction. ii) Results and Discussion (1½ pages): Discuss results and observations based on the tables, figures, and sketches/photos you prepared. Please provide insights, don t just regurgitate numbers. E.g. don t just write Based on Figure 1 and 2, the Young s moduli of steel and copper are 100GPa and 50GPa, respectively, instead, write Based on Figure 1 and 2, the Young s modulii of steel and copper are 100GPa and 50GPa, respectively. Therefore, steel is twice stiffer than copper and under similar tensile loads, copper will elongate twice as much as steel. 2. Please include and discuss the followings in your report: a) From specimen dimension measurements construct Table 1, for initial and final areas and change in the gage length for the four specimens. b) From Table 1, calculate the ductility from the initial and final dimensions of the specimen, i.e. based on (i) percent elongation and (ii) percent reduction in area. Present the results in Table 2. c) Using computer data, plot stress versus strain diagrams for the four materials. Label these graphs as, e.g., Figure 1, Figure 2, Figure 3, and Figure 4. d) Using computer data, construct Table 3, comparison of Young s moduli values for the four materials and those obtained from textbook (Appendix B). e) From computer data construct Table 4, comparison of yield and ultimate tensile strength values for the four materials and those obtained from textbook (Appendix B).

5 San Francisco State University School of Engineering ENGR 200, Materials of Engineering Date Sheet for Tensile Test Name: Group Members: Date: 1. Sketches of specimens: Please sketch, label, and dimension the specimens clearly on the following pages. (Note: thickness of steel specimen is different from the other 3 specimens.) These sketches will be included in your Appendix section. a) Specimens after test top view & side view b) Specimens fractured surfaces oblique view of both surfaces 2. Data Collection: Material Initial Thickness Initial Width Initial Area [mm 2 ] Initial Gage Length Final Thickness Final Width Final Area [mm 2 ] Final Gage Length

6 Steel Specimen (Top View & Side View) 1 (a) Specimen Top and Side Views (After Test) (Please dimension and label sketches) Top: Side: Brass Specimen (Top View & Side View) Top: Side: Aluminum Specimen (Top View & Side View) Top: Side: Copper Specimen (Top View & Side View) Top: Side:

7 1(b) Specimens Fractured Surfaces (Oblique Views of Both Surfaces) (Please dimension and label sketches) Steel Specimen (Oblique View) Brass Specimen (Oblique View) Aluminum Specimen (Oblique View) Copper Specimen (Oblique View)

8 Filename: 200-Lab4-Tensile Test Directory: C:\Documents and Settings\Mutlu Ozer\Desktop Template: C:\Documents and Settings\Mutlu Ozer\Application Data\Microsoft\Templates\Normal.dotm Title: San Francisco State University Subject: Author: KSTEH Keywords: Comments: Creation Date: 1/24/2012 1:18:00 PM Change Number: 2 Last Saved On: 1/24/2012 1:18:00 PM Last Saved By: Mutlu Ozer Total Editing Time: 0 Minutes Last Printed On: 1/24/2012 1:18:00 PM As of Last Complete Printing Number of Pages: 7 Number of Words: 1,043 (approx.) Number of Characters: 5,949 (approx.)