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Spring 2016

ENGR 2411 Mechanics of Materials Lab

Section No. 001

Lab No. 3

Lab Title: Tensile Test of Metal Specimen

Submitted to:

Dr. Zahid Hossain

And

Mr. AM Feroze Rashid

College of Engineering

Submitted By:

Name: Kudakwashe Makuvire

Student ID: 50378716

03/07/2016

Title	Pg. No.
List of Tables	3
List of Figures	4
Abstract	5
Introduction	5
Background and Methodology	5
Results and Discussions	7
Conclusions and Recommendations	9
References Cited	9
Appendix A Raw Data	10

List of Tables

Table No. and Title	Pg. No
Table 1. Tensile Test Results for lab section one	8
Table 2. Published Value of Specimen Strength Properties	8

List of Figures

Figure No. and Title	Pg. No
Figure 1: T&O Testing Machine	6
Figure 2. Stress Strain Diagram for Group 2	8

ABSTRACT

For this lab we studied the engineering properties, mainly the tensile strength of an unknown material; which we were given by the instructor. Our task was to use the values we got from the T&O machine to determine what our specimen was. The ultimate strength was 98.4 ksi, and the yield strength was 78 ksi. The specimen we had was found to be Steel C1018 CF.

Keywords: Stress, Strain, Tensile strength, Yield strength, modulus of elasticity

INTRODUCTION

One of the key properties in assessing which material to use when is its ductility or brittleness. As defined on the website metals.about.com, Ductility is “a measure of how much strain a material can take before rupturing” in other words how much a material can be drawn out or stretched before it breaks or ruptures. A brittle material is one that has really low ductility. It has a very high yielding point, i.e. it is very strong; but it will not elongate very much if at all. Instead it will simply fracture and break.

To find out what our given specimen was, we put it under tensile stress using the Tinius and Olsen machine, and measured the values of strain at a given stress until the material yielded. These values were compared to those supplied in the American Society for Testing Materials document, which is included in the original handout; in appendix B.

BACKGROUND AND METHODOLOGY

The equipment used in the experiment was the Tinius and Olsen Testing Machine. It provided a tensile force on each of three specimens that caused failure. Shown below in Figure 1 is a picture of the machine. The top part of the machine held our specimen in place, and the middle section exerted a force downward until the true breaking strength was reached.

Figure 1: T&O Testing Machine

Definitions

To understand the experiment we needed to define a number of key terms.

Definitions:

· Stress – total applied force divided by total cross-sectional area of a given specimen

· Strain – elongation or compression of a given segment per unit of length

· Gage Length – the initial length of part of a specimen

· Ductile Materials – any material that can be subjected to large strains before it fractures

· Brittle Materials – a material that shows little or no yielding before failure

· Yield Strength – the highest stress a material can withstand without permanent deformation

· Ultimate Strength – the maximum stress that a specimen can withstand, which causes failure; maximum axial load divided by the cross-sectional area

· Breaking Strength – the theoretical tension at which a line will part, when a load is applied

· True Breaking Strength – the actual tension at which a line will part, when a load is applied

· Strain Hardening – upon the ending of a materials yield, once a further load is applied the curve rises but becomes flatter as it reaches the maximum stress; the curve created is the strain hardening

· Yield Strength at 0.2% Offset – the point reached on the curve of a stress-strain diagram, where a parallel line 0.2% (usually 0.1 to 0.2 strain) off from the initial linear stress-strain line

· Percent Elongation – the fracture strain of a specimen: final length minus initial length, divided by original length, then expressed as a percent by multiplying by 100

· Modulus of Elasticity – the slope of the beginning linear portion of a stress-strain diagram; permanent deformation will not occur if loading stays within the linear constraints

· Modulus of Resilience – the area under the linear portion of the stress-strain curve, found through integration

· Modulus of Toughness – the ability of a material to absorb amounts of energy, which is the entire area under the stress-strain curve

· Percent Reduction in Area – the original cross-sectional area of a specimen minus the final cross-sectional area, divided by the original cross-sectional area and all multiplied by 100; the change in cross-sectional area of a specimen

· Stress Concentration – a certain location in a specimen that causes stress to multiply, or concentrate; a fillet has a high stress concentration for example

Equations

After the data was collected from the experiment we had to derive a few equations which would help us understand the data and compare it to the accepted values for the Morehouse Ring.

· Percent Elongation ………..………………….…..... (1)

Modulus of Elasticity ………………………………….…... (2)

· Percent Area Reduction A% = | (A-Ao)/Ao |* 100 ……….………...…... (3)

The following steps were followed to obtain the values we were given by our instructor:

Initial set up of machine was the same as Lab 2.

1) We turned the machine on and made sure load and unload knobs were at zero.

2) We turned pump on.

3) We zeroed the loads and position.

4) The specimen was placed into the loading cell.

5) The mode was turned to ‘Auto’.

6) Load was applied using computer program connected with T&O machine.

7) Stress and strain data was saved in the program.

RESULTS AND DISCUSSIONS

The experiment done measured the tensile strength of three unknown materials. We were tasked with finding out what our material was. Once the breaking point was reached, final length and diameter of the specimens were recorded. Percent elongation was then found using equation (1) as well as percent area of reduction using equation (3). The modulus of elasticity was found using equation (2) as well as using the linear range of the graph to find the gradient, which was the Modulus of elasticity. Table 1 shows a comparison of our collected data to that of the other groups. All sample calculations done were from group 2.

Table 1. : Tensile Test Results for lab section one

Test material
Group/ Specimen	Ultimate Strength (ksi)	Yield Strength (ksi)	Modulus of Elasticity	Percent Elongation (%)	Percent Reduction of Area (%)
1	97.44	92	3959	8.3	33.6
2	98.40	78	4196	4.5	9.0
3	61.10	50	2798	8.8	38.6

We compared our specimen (group 2) to the Published Value of Specimen Strength Properties, shown below in table 2, to determine what our specimen was. The closest specimen correlating to our values were that of Steel C1018 CF.

Table 2: Published Value of Specimen Strength Properties

Specimen Type	Tensile Strength (psi)	Yield Strength (psi)	Percentage of Elongation
Copper Alloy 110	48,000	40,000	20
Aluminum 2011 T3	55,000	43,000	15
Cast Iron Gray -20	20,000 - 25,000	N/A	N/A
Steel C1018 CF	82,000	70,000	20
Brass Free Cutting -360	58,000	42,000	20

Figure 2 shows the stress-strain diagram for our specimen, for this were able to determine all our values we put into table 1.

Figure 2. Stress Strain Diagram for Group 2

Form Figure 2 it can be suggested that our specimen was fairly ductile because of the amount of strain hardening and necking that took place.

CONCLUSIONS AND RECOMMENDATIONS

From the comparison between our collected data and the Published Value of Specimen Strength Properties, our experiment was a success in helping us identify our specimen. As shown by figure 2, our specimen showed us the typical characteristics of a ductile material.

Reference

Ductility. (n.d.). Retrieved March 14, 2016, from http://metals.about.com/od/metallurgy/g/Ductility.htm

APPENDIX A RAW DATA and ORIGINAL HANDOUT

APPENDIX B DETAIL CALCULATIONS

Stress-Strain Diagram

Strain (in/in)

Stress (ksi)

E = ε σ

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TABLE OF CONTENTS

List of Tables

List of Figures