Measuring Mechanical Properties of Materials: A Tensile Test Study, Exercises of Mechanics

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Tensile Test Experiment

ME 3228: Materials and Mechanics Lab

Section: 519

Tyler Myers

Due: March 6

th

Turn in to: Cargi M, Bakirci

Summary

For the Tensile Test Experiment, data was collected from using an MTS machine

and lab computer. The data collected was the position and load of what was going on

to a sample material. The materials used were two different types of aluminum and

steel. The simple tensile test was performed on each of the four samples. With the

data found in the experiment, calculations of stress and strain were done, finding the

different material properties of the four samples. With the stress and strain values,

graphs were created to illustrate the experiment, and with those graphs some of the

material properties were directly found. The material properties consisted of

elasticity, yield and ultimate strengths, resilience, toughness, percentage of

elongation, and percentage of reduction in area of the samples. As for most of the

material properties, having to have been calculated, charts were drawn up for the

comparison of the experimental data to the real world reference data provided by any

common engineering book. Details of the experiment and its results will be provided

later in the report, along with all the tables and graphs generated from the

experiment’s data.

• List of Figures ________________________________________________________
• List of Tables ________________________________________________________
• List of Equations ________________________________________________________
• Summary ________________________________________________________
• Introduction ________________________________________________________
• Theory ________________________________________________________
• Test Description ________________________________________________________
• Results ________________________________________________________
• Discussion ________________________________________________________
• Conclusion ________________________________________________________
• References ________________________________________________________
• Appendix ________________________________________________________
• Figure 1: Tensile Test in Action List of Figures
• Figure 2: The MTS Machine
• Figure 3: Four Different Sample Materials
• Figure 4: The Stress-Strain Graph of ASIS
• Figure 5: The Stress-Strain Graph of AISI
• Figure 6: The Stress-Strain Graph of Al
• Figure 7: The Stress-Strain Graph of Al
• Figure 8: The .2% Offset Graph of AISI
• Figure 9: The .2% Offset Graph of AISI
• Figure 10: The .2% Offset Graph of Al
• Figure 11: The .2% Offset Graph of Al
• Figure 12: The Young’s Modulus Graph of AISI
• Figure 13: The Young’s Modulus Graph of AISI
• Figure 14: The Young’s Modulus Graph of AL
• Figure 15: The Young’s Modulus Graph of Al
• Figure 16: The Elasticity Comparison Chart
• Figure 17: The Yield Strength Comparison Chart
• Figure 18: The Ultimate Strength Comparison Chart
• Figure 19: The Comparison between Ductile and Brittle Fractures

List of Tables

Table 1: Initial and Final Measurements of the Sampled Material 11

Table 2: Experimental Mechanical Properties of Four Samples 23

Table 3: The Comparison Table between the Experimental and Referenced Data 23

Introduction

This experiment consisted of measuring the mechanical properties of two

different types of materials using a tensile testing machine. The purpose of this

experiment is to recreate a real world application of what these materials might be

subjected to when the materials are put to work. These experiments are done often

to construct a set of data for all engineers to be able to have quick access to correct

information and material specifications and properties. So with this type of

experiment, the elastic modulus, the ultimate strength, and the yield strength can be

calculated and compared to old references from previous experiments to see how the

material properties have changed, if any. The two materials being tested in this

experiment will be steel and aluminum. Those two types of materials have also been

split into two sub-types: Steel: 1018 and 1045, Al: 7075 and 6061.

Theory

The idea of this tensile test experiment is to calculate the specific material

properties from each material tested and see how they compare to a standard

reference of the same material’s properties already provided in the real world. Below

is a snap shot of an actual tensile test being taken on a sample material.

Figure 1: Tensile Test in Action

The specific properties the experiment will provide will be elasticity, yield and

ultimate strengths, resilience, toughness, percentage of elongation, and percentage

of reduction in area of the samples. Finding these will have to come from finding the

tensile stress of the experiment being performed. The tensile stress, σ, is calculated

through this equation:

𝐴𝑜^ (Equ. 1)

Where F is the load being applied and A 0 is the original cross-sectional area at the gage

section of the sample. Then the strain, ε, is also needed for calculations purposes to

measure what is being done to the sample in terms of it being stretched out. The

engineering strain is calculated by:

𝑙 0 (Equ. 2)

Here, l is the new gage length and l 0 is the original gage length. With the calculations

of both the stress and strain of the sample, a Stress vs. Strain graph can then be created

to see how the sample acts while the tensile test is being performed. After setting up

a proper stress-strain graph, the calculation of the modulus of elasticity, E, can be

found using the simple slope definition:

∆𝜀 (Equ. 3)

With the elasticity, obtaining the yield strength is done by performing a .2% offset on

the stress-strain graph, and figuring out where the two lines intersect. The Ultimate

tensile strength, σu, is found by:

𝜎𝑢 = 𝐹𝑚/𝐴 0 (Equ. 4)

With Fm being the maximum load applied to the sample. Resilience, or the energy

absorbed by the sample when it is being deformed elastically, is found by using:

2 𝜎𝑦^ ∗ 𝜀𝑦^ (Equ. 5)

Figure 2: The MTS Machine

The samples being tested in this experiment are AISI 1018, AISI 1045, Aluminum 6061-

T6, Aluminum 7075-T24.

Figure 3: Four Different Sample Materials

During the Tensile Test experiment, the four samples were measured for their original

gage length and diameters. Each sample was then put in and clamped down by the

upper and lower hydraulic grips. Then using the lab computer, the MTS machine was

activated, calibrated, and began pulling the sample down with the lower grip while the

upper grip remained stationary. During this, the computer stores the data of the

position of the grips, and the load that is being applied to the sample at the current

time. The sample was then pulled until fracture. Once fracture was reached, the

machine was deactivated. The sample was then measured once more for its final gage

length and diameters.

Results

The first thing in this experiment was to document the initial gage length and

diameters of the sample, immediately following fracture of the sample, the final gage

length and diameters were taken.

Table 1: Initial and Final Measurements of the Sampled Material

Sample

Gage Diameter Gage Length Cross-Sectional

(cm) (cm) Area (cm)

Initial Final Initial Final Initial Final

After the experiment, calculations to find the stress and strain were done on each

sample. With those stress and strain values, a Stress-Strain graph was created per

sample. Shown next are the four samples Stress-Strain graphs.

Figure 6: The Stress-Strain Graph of Al 6061

Figure 7: The Stress-Strain Graph of Al 7075

Stress (MPa)

Strain

Stress vs Strain Graph, 6061

Exp. Data

Stress (MPa)

Strain

Stress vs Strain Graph, 7075

Exp. Data

With the Stress-Strain graphs generated per sample, a .2% Offset graph was created to

find the values of the yield strength of the samples.

Figure 8: The .2% Offset Graph of AISI 1018

Figure 9: The .2% Offset Graph of AISI 1045

Stress (MPa)

Stain

.2% Offset Graph, 1018

Exp. Data .2% offest

Stress (MPa)

Strain

.2 % Offset Graph, 1045

Exp. Data .2% Offset

To do so, a simple calculation of Young’s Modulus had to be done in order to find, E,

the elasticity of the sample to create the .2% Offset Graph. The Young’s Modulus was

calculated by finding the slope of the original data of stress and strain using up to the

first one hundred to two hundred megapascals of stress for ease of finding the

equation of the line. The following four graphs illustrate the linear relationship of the

Young’s Modulus for the samples.

Figure 12: The Young’s Modulus Graph of AISI 1018

Stress (MPa)

Strain

Young's Modulus Graph, 1018

Exp. Data Linear (Exp. Data)

Figure 13: The Young’s Modulus Graph of AISI 1045

Figure 14: The Young’s Modulus Graph of AL 6061

Stress (MPa)

Strain

Young's Modulus Graph, 1045

Exp. Data Linear (Exp. Data)

Stress (MPa)

Strain

Young's Modulus Graph, 6061

Exp. Data Linear (Exp. Data)

Figure 16: The Elasticity Comparison Chart

Next is the comparison of the Yield strengths for the four samples.

Figure 17: The Yield Strength Comparison Chart

Elasticity (GPa)

Exp. Ref.

Yield Strength (MPa)

Exp. Ref.

Lastly, illustrated below is the comparison of the Ultimate Strengths of the four

samples.

Figure 18: The Ultimate Strength Comparison Chart

Discussion

There appears to be a clear difference between the two steel and the two

aluminum materials upon completion of the results for the experiment. When talking

about the two steel materials, AISI 1045 shows a clear difference in its ability to hold a

greater force when compared to the AISI 1018. Its ultimate strength is greater, but its

yield strength is lower. AISI 1045 also has a greater elasticity, meaning it is less brittle.

When comparing the two aluminum materials, the Al 7075’s yield and ultimate

strengths are higher than the Al 6061. But the elasticity of the Al 6061 is greater than

the Al 7075 as far as the experimental data, but in a perfect analysis, the Al 7075 should

have a greater elasticity, meaning that the Al 6061 is less ductile than the Al 7075.

Looking at the aluminum and steel materials together, even from the tensile test

experimental data, the steel’s properties of elasticity, yield and ultimate strengths are

far beyond those of the aluminums. Which makes sense knowing that the steel should

be far more brittle and the aluminum more ductile. With being more brittle, the steel

Ultimate Strength (Mpa)

Exp. Ref.