AERO 213 Mechanical Properties Tensile Testing Experiment [PDF]

properties. ▫ To determine the following properties for three given metallic specimens (Aluminum. 2024, Aluminum 6061,

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AERO 213 Mechanical Properties Tensile Testing Experiment

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 cross section is used. However, flat rectangular specimens are fairly common. In this laboratory experiment, we will be using a circular configuration.

OBJECTIVES 

To understand how a tensile test is performed and how to obtain the relevant material properties



To determine the following properties for three given metallic specimens (Aluminum 2024, Aluminum 6061, and A36 Carbon Steel) using a uniaxial tensile test: Young’s modulus, E Yield strength, σy Tensile strength, TS Toughness Ductility, %EL



To ascertain the effect of strain hardening on the yield strength.

THEORY A discussion on mechanical properties using tensile testing is provided in Chapter 7 of the Callister text. The geometry of the specimens used in this laboratory experiment is shown in Figure 1 below.

Figure 1. Schematic of a tensile specimen.

The section under test is the called the “gage length”, with original length l0, and diameter d. The applied stress can be calculated using equation 1 below:

σ=

F A

(1)

Where F is the force measured on the force display of the machine and A is the cross-sectional area of the specimen. The corresponding strain ε is given below:

ε=

∆l0 l0

(2)

Where ∆lo is the change in the gage length. The Young’s modulus is given by Hooke’s law (ratio of stress to strain in the linear elastic region of the loading curve): E=

σ ε

(3)

MATERIALS Today, you will be testing three test specimens of different materials: 1. Aluminum 6061 2. Aluminum 2024 3. ASTM-A36 Carbon Steel The schematic of the tensile testing equipment is shown in the figure below (observe carefully and understand the functions of the different parts):

2

Figure 2. Schematic of the tensile testing equipment. TEST PROCEDURE The general test procedure is as follows: 1) Identify the metal specimens assigned to your team. You will have two different metals and a total of three specimens. 2) Measure the dimensions necessary for analysis (l0 and d) on all your specimens. Refer to Figure 1. 3) Position your first specimen in the grips. 4) Make sure the force display and the dial gage are on zero positions. 5) Make sure that the “Max Force Pointer” – the red colored pointer in the force display– is on the zero position. 6) Apply loads very slowly by turning the handwheel in small increments and measure the corresponding deformation on the dial gage. 7) Calculate the stress corresponding to the load and the strain corresponding to the deformation and plot stress (y-axis) vs. strain (x-axis). You will conduct a total of four experiments (1 test each with each aluminum specimen and 2 tests with the steel specimen). The specific test procedures for the experiments are given below: Experiment #1 (Aluminum 6061) and #2 (Aluminum 2024): Loading until fracture. 1. Make sure all pointers are on zero. 2. Proceed in increments of 0.02 mm (2 divisions on the dial gage) for the first 30 readings. THEN, proceed in increments of 1 mm till the specimens fracture. 3. Write down the load and the corresponding deformation for each increment. 4. Stop when the specimen fractures. The specimen will fracture loudly in two parts. 3

5. Observe the fracture surface and comment on it in the report. 6. Put the fractured pieces together and measure the final gage length; you will require this for calculating ductility. Experiment #3: Strain hardening of steel specimen. 1. Make sure all pointers are on zero. 2. Proceed in increments of 0.02 mm (2 divisions on the dial gage) for the first 30 readings. THEN, proceed in increments of 1 mm TILL you reach 13 kN on the force indicator. 3. STOP at 13 kN load. 4. Now, slowly release the load by the same increments by turning the handwheel counter-clockwise. 5. Again, write down the load and the corresponding deformation as the load is released. 6. Make a note of what the deformation is when the load falls back to zero. 7. Without removing the specimen from the grips, proceed to Experiment #4 below. Experiment #4: Continuation of Experiment #4 - Loading until fracture. 1. Make sure all pointers are on zero. 2. Proceed in increments of 0.02 mm (2 divisions on the dial gage) for the first 30 readings. THEN, proceed in increments of 1 mm till the specimen fractures. 3. Write down the load and the corresponding deformation for each increment. 4. Stop when the steel specimen fractures. The specimen will fracture loudly in two parts. 5. Put the fractured pieces together and measure the final gage length; you will require this for calculating ductility. REPORTING REQUIREMENTS 1. Plot load vs. deflection for each material and each of the experiments. 2. For each material, determine the modulus of elasticity using Equation 3. Use only the linear portion of the stress-strain diagrams obtained from your experiments. 3. Estimate the scatter in your data—standard deviation. Also, if you fit a line to the data with Excel or other software, what are the R2 value and the equation for the line? What does the R2 value tell us? 4. Compare the calculated values of modulus of elasticity values with those reported in the literature (Appendix in Callister for example) 5. Using data from Experiment #1 and #2, calculate and report yield strength, tensile strength, fracture stress, ductility and toughness. Specify clearly what methods you are using to estimate these values. Compare them to published data whenever possible. 6. Compare the yield strength of steel as obtained from Experiment #3 and #4. Comment on the difference. 7. Prepare results as a technical report (Format: see Handout; Maximum Length 5 pages plus tables and graphs). Be sure to address all reporting requirements. Final results MUST be shown using the “Results Table” included in the next page. 8. Include all raw data in an appendix. Include all calculations in an appendix as well. Note: Those who miss the lab or do not contribute to the lab report will not get credit.

4

Results Table Aluminum 6061 Young’s Modulus Yield Strength

Aluminum 2024

ASTM- A36 Steel

Compare for Experiment #3 and #4

Tensile Strength Fracture Stress Ductility Toughness

5

AERO 213-500 Technical Laboratory Report Format The following sections must be included in each Technical Laboratory Report. 1.

TITLE PAGE This is the cover page and should present the report in a professional manner. The following should be included: a. Title of Report b. Authors (Team #, Team Leader(s) for this report, other Team Members) c. Date

2.

TABLE OF CONTENTS This page should include all sections of the report, figures, tables, and appendices and their corresponding page numbers.

3.

ABSTRACT This is a brief summary (6-10 sentences) of what was done, what was found, and why it is important.

4.

INTRODUCTION This section provides motivation and a general summary of the experiment. definitions, theory, and background literature are included in this section.

Any

5.

EXPERIMENTAL PROCEDURE This section describes step-by-step the procedures used to conduct the experiment(s). If an ASTM standard test method was used, only the standard test number needs to be cited along with any deviations from this standard method.

6.

RESULTS This section includes summary data in tables and figures used in the analysis (next section) and text to describe these tables and figures. Each table and figure must have a number and be cited in the text. This section does not include raw data.

7.

DISCUSSION In this section, results presented in the previous section are analyzed and discussed in response to the reporting requirements. Additional figures may also be added. Any problems encountered in the experiment should also be highlighted as well as the effects of these problems on the results and analysis and methods by which to avoid these problems in the future.

8.

CONCLUSIONS AND RECOMMENDATIONS This section contains summary conclusions based on the analysis, positive aspects of the experiment in terms of learning, and recommendations for improving and/or expanding the experiment.

9.

APPENDICES This section (if necessary) contains specific calculations and raw data. 6

Mechanical Properties: Brinell Hardness Test

OBJECTIVES -To determine the hardness for different materials using a Brinell Hardness Tester -To understand the relationship between a material’s hardness, indentation size, and the Brinell number (no units) associated with the material.

THEORY Hardness is a measure of the resistance of a metal to plastic deformation. The hardness of the metal is measured by forcing an indenter into its surface. The indenter material which is usually a ball or cone, is made of a material much harder, usually diamond or carbon steel, than the material being tested. For most standard hardness tests, a known load is applied slowly by pressing the indenter orthogonally into the metal surface being tested. After the indentation has been made, the indenter is withdrawn from the surface. An empirical hardness number is then determined, which is based on the cross-sectional area and depth of the impression. The hardness of a metal depends on the ease with which it plastically deforms. Thus a relationship between hardness and strength for a particular metal can be determined empirically. The hardness test is much simpler than the tensile test and can be nondestructive (i.e., the small indentation, shown in figure 1 and 2, of the indenter may not be detrimental to the use of an object). For these reasons, the hardness test is used extensively in industry for quality control. “Materials Science and Engineering: An Integrated Approach” by Callister; Chapter 7, Section 16 (Page 213) has more information regarding material hardness.

Fig. 1

Fig. 2

The Brinell hardness test method consists of indenting the test material with a 10 mm diameter hardened steel or carbide ball subjected to a defined load (for this experiment 10,000 N). The full load is normally applied for at least 10 to 15 seconds in the case of steel and for at

least 30 seconds in the case of other metals. The diameter of the indentation left in the test material is then measured (either with a caliper or with a low powered microscope). The Brinell harness number is calculated by dividing the load applied by the surface area of the indentation using the following formula: 0.102 F Brinell Hardness (HB) = A where, F = Applied test force in Newton and, A = Surface area of the impression given by:



A  0.5 *  * D * D  D 2  d 2



where, D = diameter of the hardened steel ball = 10 mm and, d = diameter of the impression produced by the hardened steel ball on the sample. d is measured as shown in Fig. 3

d1

d2

d = (d1 + d2) / 2 Fig. 3 : Measuring diameter of the impression

TEST PROCEDURE 1. Insert the test sample between the test ball and the pressure plate (See Fig. 4)

Test ball Pressure plate

Fig. 4. Sample positioning 2. Carefully lower the test ball onto the sample by rotating the hand wheel. 3. Smoothly apply the test force of 10,000 N (corresponding to 10 kN on the force display). DO NOT apply the force too quickly. From 0 to 10kN, it should take at least 20 seconds. 4. Hold the test force for at least 30 seconds and then release the load (by turning the hand wheel in the opposite direction). 5. Remove the sample and carefully measure the diameter of the impression. 6. Repeat the test 5 times for EACH sample. 7. Calculate the hardness for EACH indentation (since you are running the test 5 times for each specimen, 5 Brinell hardness numbers for each of the 4 tests (for each specimen) should be reported.) 8. For each sample, compare the values for Brinell hardness you obtained with values reported in literature. 9. Examine each tested specimen’s indentation under a microscope/magnifying glass to create a subjective opinion of the material’s hardness. 10. Report your data in the following tabular format for EACH sample: Test

Impression diameter d1 d2 d(average)

Brinell Hardness (HB)

Remarks

1 2 3 4 5 Average Brinell hardness Brinell Hardness reported in literature

Errors and discrepancies can arise during the experiment from many sources, the most likely being from human error. For example, if the cam handle is turned to quickly or not in a smooth constant motion, the resulting hardness could be inaccurate. If the hardness test is performed too close (within 3 indentation diameters) to a previous indentation, the results

may differ. Also a specimen may not be entirely homogeneous and may sometimes have different hardness in different areas due to deformations or corrosion.

REPORTING REQUIREMENTS 1. Report the measured average indentation and corresponding standard deviation for each metal. 2. Compare the Brinell hardness number that you obtained with hardness numbers reported for the materials in literature. 3. What is the relationship of the Brinell number to the size of the indentation and the hardness of the material? (i.e., If metal A has a higher Brinell number than metal B, then what can be assumed about the indentation size and hardness of metal A with respect to metal B assuming they are on the same scale.) 4. What is the relationship of the Brinell number to the following (directly proportional or inversely proportional) and explain your reasoning. a. Material’s tensile strength? b. Material’s modulus of elasticity? c. Material’s ductility? 5. Determine the metals’ tensile strength based on the Brinell hardness numbers measured.

Technical Laboratory Report Format The following sections must be included in the Technical Laboratory Report. (Report limit is 5 pages not including Appendices or Title Page) 1.

TITLE PAGE This is the cover page and should present the report in a professional manner. The following should be included: a. Title of Report b. Authors (Team #, Team Leader(s) for this report, other Team Members) c. Date

2.

TABLE OF CONTENTS This page should include all sections of the report, figures, tables, and appendices and their corresponding page numbers.

3.

ABSTRACT This is a brief summary (6-10 sentences) of what was done, what was found, and why it is important.

4.

INTRODUCTION This section provides motivation and a general summary of the experiment. Any definitions, theory, and background literature are included in this section.

5.

EXPERIMENTAL PROCEDURE This section describes step-by-step the procedures used to conduct the experiment(s). If an ASTM standard test method was used, only the standard test number needs to be cited along with any deviations from this standard method.

6.

RESULTS This section includes summary data in tables and figures used in the analysis (next section) and text to describe these tables and figures. Each table and figure must have a number and be cited in the text. This section does not include raw data.

7.

DISCUSSION In this section, results presented in the previous section are analyzed and discussed in response to the reporting requirements. Additional figures may also be added. Any problems encountered in the experiment should also be highlighted as well as the effects of these problems on the results and analysis and methods by which to avoid these problems in the future.

8.

CONCLUSIONS AND RECOMMENDATIONS This section contains summary conclusions based on the analysis, positive aspects of the experiment in terms of learning, and recommendations for improving and/or expanding the experiment.

9.

APPENDICES. This section (if necessary) contains specific calculations and raw data.

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