failure mechanics final report group 11

© Dept. of Mechanical Engineering Technology, All rights reserved.

Mechanical Engineering Technology

Fatigue Characteristic Analysis of 1018 Cold Rolled Steel Involving Pre and Post Annealed States

Name of Principal Author: Ryan Schwartz Names of Contributors: Austin Allessio Kathy Feinberg Stephanie Ulman Tyler Peterson

Instructor Signature: __________________________ Date: ____________

0610-403 Failure Mechanics Project

Technical Report #: _20121-403-01.11__

Date of Submission:

November 9, 2012

Abstract:

This project determined the fatigue characteristics of AISI 1018 Cold Rolled Steel with a 95% confidence level. The published value was placed in an SN diagram with appropriate correction factors for the samples. Fatigue, hardness, and tensile tests were run on the samples, resulting in a remarkably higher vale for ultimate tensile strength than what is published for AISI 1018 CRS. After annealing the samples, the fatigue, tensile and hardness tests were repeated, finding that the annealed parts showed an ultimate tensile strength within 4.95% of published values.

0610-403 Failure Mechanics Project 20121-403-01.11

Professor Leonard Mechanical Engineering Technology 11/12/2012

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Table of Contents

EXECUTIVE SUMMARY ......................................................................................................................................... 3

OBJECTIVE ................................................................................................................................................................ 4

DISCUSSION ............................................................................................................................................................... 4

CONCLUSION ............................................................................................................................................................ 9

APPENDIX A ............................................................................................................................................................. 10

1 PRE-ANNEAL FATIGUE TESTING .......................................................................................................................... 10 2 PRE-ANNEAL HARDNESS TESTING ...................................................................................................................... 13 3 PRE-ANNEAL TENSILE TESTING .......................................................................................................................... 16 4 SPARK TESTING .................................................................................................................................................... 20 5 COMBUSTION TESTING ........................................................................................................................................ 25 6 PRE-ANNEAL METALLOGRAPHY TESTING ........................................................................................................... 28 7 POST--ANNEAL FATIGUE TESTING ...................................................................................................................... 34 8 POST--ANNEAL HARDNESS TESTING ................................................................................................................... 37 9 POST--ANNEAL TENSILE TESTING ....................................................................................................................... 40 10 POST--ANNEAL METALLOGRAPHY TESTING ....................................................................................................... 43

APPENDIX B ............................................................................................................................................................. 49

1 VOC/CTQ ......................................................................................................................................................... 49 2 PROJECT CHARTER ............................................................................................................................................ 50 3 Gantt Chart ......................................................................................................................................................... 52 4 SIPOC ................................................................................................................................................................ 53 5 Fatigue Test Flow Chart ..................................................................................................................................... 54 6 Ishikawa Cause & Effect Diagram ..................................................................................................................... 55 7 Pareto Diagram .................................................................................................................................................. 56

8 Boxplot of Pre-annealed Fatigue, Hardness, Tensile, & Published Data ........................................................... 56 9 ANOVA of Pre-annealed Fatigue, Hardness, Tensile, & Published Data .......................................................... 57 10 T-test Pre-Annealed vs. Post-Annealed Tensile ................................................................................................. 57 11 Boxplot of Post-annealed Fatigue, Hardness, Tensile, & Published Data .......................................................... 58 12 ANOVA of Post-annealed Fatigue, Hardness, Tensile, & Published Data ........................................................ 58 13 PDCA ................................................................................................................................................................. 59 14 Cost Analysis ..................................................................................................................................................... 60

BIBLIOGRAPHY ...................................................................................................................................................... 61

ACKNOWLEDGEMENTS ...................................................................................................................................... 61



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Executive Summary

The objective was to determine the fatigue characteristics of 1018 Cold Rolled Steel. The DMAIC process for Lean Six Sigma was used to determine the Ultimate Tensile Strength of the material within a 95% confidence interval. The samples underwent fatigue, hardness, tensile, metallography and combustion tests to gain multiple bases of confirmation for this data. The fatigue data for pre-annealed samples returned a mean value of Sut=113.2 kpsi with a standard deviation of 8.7 kpsi, resulting in a variance of 77.4% from published values. The hypothesis formed as a result of this data is as follows: The cold working process has produced a higher Ultimate Tensile Strength than that of accepted published values.

In the interest of affirming the hypothesis, metallography testing was performed on the pre-anneal specimens in order to investigate the material’s grain structure, as well as IMR and spark testing to ascertain the material’s carbon content. Though the carbon content of the material proved to be within acceptable ranges of 0.18% ±0.03%, the grain structure was found to be aligned along the long axis of the part, confirming the proposed hypothesis. In order to prove this hypothesis an annealing process was performed to return the material’s grain structure to a normalized state, wherein the original testing was repeated.

Post anneal values for the tensile tests show a mean value of Sut=60.64 kpsi with a standard deviation of ±0.92 kpsi, a 4.95% difference from the accepted published value of Sut=63.8 kpsi. The fatigue tests however yielded an Sut value of Sut=79.0 kpsi, showing that the fatigue test did not provide conclusive results. It is clear that the annealing process has returned the samples’ UTS to within acceptable ranges of published values ± 5.0%.

10

100

1.0E+00 1.0E+01 1.0E+02 1.0E+03 1.0E+04 1.0E+05 1.0E+06 1.0E+07 1.0E+08

Stre

ngt

h (

kpsi

)

Cycles N

Stress-Life Diagram of AISI 1018 CRS Adjusted Theoretical

Group 11 Pre Anneal

Class Data postAnnealed

SUT=63.8

SUT=124.2

SUT=79.0

SM=111.8

SM=71.1

SM=57.4

SE=31.6

SE=23.5

SE=20.3

LCF HCF



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Objective of This Document

The objective was to determine the fatigue characteristics of 1018 Cold Rolled Steel. The DMAIC process for Lean Six Sigma was used to determine the Ultimate Tensile Strength of the material within a 95% confidence interval by week 10.

Discussion

After obtaining the Voice of the Customer (VOC), the team was assembled and parts were obtained from the supplier, the machine shop manager. The parts were marked for identification then measured individually. An SN diagram was created using published values. The Sut was used to estimate the uncorrected graph. Average correction factors were used to estimate a corrected SN diagram. Correction factors were calculated for each part’s individual measurements when calculating the stresses within the materials. Fatigue testing was performed on the samples of AISI 1018 cold rolled steel to determine the materials fatigue characteristics. The samples were tested in a fatigue testing machine which put them in fully reversed bending. The data from the samples was used to calculate a best fit line and create a SN curve. The test data was compared to published data for the same material and a difference between the values as shown on the SN graph on page 3. At this point the project goal switched to finding the source of the difference between the two values for the ultimate tensile strength between the published data and the test data.

The most likely causes for the unexpected data was brainstormed by the team and displayed on a cause & effect diagram using the Ishikawa format displayed in Appendix B6. These potential causes for variation were then weighted by the team and displayed in the Pareto Chart displayed below. From the Pareto Chart the team hypothesized that the machine was causing the data variation and both hardness and tensile testing were performed to prove this theory.

Pareto Chart



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The ultimate tensile strength test results of the hardness and tensile tests were compared to the fatigue test and published data in the boxplot from Appendix B8, also seen below.

The results from this chart show the maximum difference between hardness, tensile, and fatigue data to be 19 ksi. This is data doesn’t show statistical significance that the tests yielded the same results as illustrated by the ANOVA below but it does confirm that all three tests vary from published values by a minimum of 30 ksi. This concludes the previous hypothesis that the fatigue testing machine was the cause of the data variance to be false.



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Since the material was identified as the second highest possible source of data variance it was investigated first. The carbon content of steel can vary from .1% to over 1.2% and the strength of the steel will increase in accordance with the increased carbon content. The samples could have had an increased ultimate tensile strength because the material actually had higher carbon content then stated. The 1018 cold rolled steel should have had .18% carbon with a tolerance of +/- .03%. A new hypothesis was formed that the carbon content of the material was the cause of the higher ultimate tensile strength. To prove this hypothesis the team decided to test carbon content of the material with a spark test and a combustion test.

The spark test results displayed in Appendix A4 determined that the material was a low-carbon steel, the expected result for 1018 steel. Another team had a combustion test performed on one part and resulted in a carbon content of 0.15%, within tolerance for 1018 steel. The team brainstormed new causes for variation of the mechanical properties of the material. After investigating other possibilities of changes in the material process which could increase the strength of the material the team decided that the cold rolling process which the material went through could be a possible cause for this variance. Cold rolling or cold forming of round parts like the samples involves the material being pulled through a die which decreases its diameter. The more the diameter is deceased the more the material strength can be increased. The graph below illustrates this behavior. The drawing process elongates the normally isotropic grain structure of the metal. The elongated grains have more surface area and are all oriented in the same direction. The increase in surface area allows for more bonds to be formed between the grains which makes the material stronger in the direction of the grain orientation. In the cold forming process of round stock the grain structure would be aligned with the material’s long axis. The increase in this direction would increase the ultimate tensile strength in the direction which the material was loaded. A new hypothesis was formed that the material underwent strengthening through the cold-working process. To prove this hypothesis the team performed metallography testing displayed in Appendix A6 to view the grain structure in line with and perpendicular to the axis.



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The grain structure was found to be both elongated and oriented along the material’s long axis. The results of this test proved the team’s hypothesis. The team discussed and decided to fully anneal the parts to reform the grain structure without the grain elongation and lower the ultimate tensile strength. The final hypothesis of the team was that the material would show the expected properties after fully annealing the parts.

The team obtained 3 more parts from the supplier, physically marked them, annealed them fully in a nitrogen atmosphere at 5psi and was set to cool in the nitrogen for 8 hours. The parts then underwent the same processes for fatigue, hardness, tensile, and metallography testing. The T-test displayed below was performed to statistically confirm the difference between the pre-annealed and post-annealed tensile tests.

Two-sample T for Pre Tensile Sut vs Post Tensile Sut

N Mean StDev SE Mean

Pre Tensile Sut 65 94.43 2.31 0.29

Post Tensile Sut 28 60.641 0.939 0.18

Difference = mu (Pre Tensile Sut) - mu (Post Tensile Sut)

Estimate for difference: 33.791

95% CI for difference: (33.122, 34.460)

T-Test of difference = 0 (vs not =): T-Value = 100.34 P-Value = 0.000 DF = 90

The post-annealed metallography displayed in Appendix A10 confirms that there has been a change made by the annealing process. The Boxplot displayed below and in Appendix B11 visually confirms that ultimate strength estimated from the post-annealed fatigue, hardness, and tensile tests were closer to published values than pre-annealed tests.



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One-way ANOVA: Post Fatigue Sut, Post Tensile Sut, Post Hardness Sut, Published Source DF SS MS F P

Factor 3 2170.27 723.42 188.18 0.000

Error 50 192.22 3.84

Total 53 2362.49

S = 1.961 R-Sq = 91.86% R-Sq(adj) = 91.38%

Individual 95% CIs For Mean Based on

Pooled StDev

Level N Mean StDev --------+---------+---------+---------+-

Post Fatigue Sut 4 70.383 5.433 (--*---)

Post Tensile Sut 28 60.641 0.939 (*)

Post Hardness Sut 19 49.842 2.106 (*-)

Published 3 63.800 0.000 (--*---)

--------+---------+---------+---------+-

54.0 60.0 66.0 72.0

Pooled StDev = 1.961

The ANOVA displayed above measures the statistical similarity between the tests. The results of this analysis indicate that there is not enough statistical evidence to say that the annealing process yielded the same ultimate tensile strength as published values. While statistical significance cannot be proven from the results of the annealed testing practical significance can. The most accurate test results, the tensile test, were within 4.95%, an acceptable value for use in engineering calculations.



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Conclusion

The fatigue test showed the ultimate tensile strength of the specimens to be higher than the ultimate tensile strength of the published valves by 77.4%. Therefore tensile and hardness tests were performed in order to conclude whether the fatigue testing machine was properly. The results from the tensile, hardness and, fatigue tests were higher than the published values by at least 47.9%, warranting further investigation. Combustion analysis was conducted in order to determine the material’s carbon content, supported by a spark test; the combustion analysis returned a content of 0.15%, a value within acceptable industry standards.

The Metallography was done to find the grain structure of the material. The test samples’ grain structure was found to be in an elongated form aligned along the long axis. After an annealing process, the samples were tested again using fatigue, hardness, tensile, and metallography tests. The metallography yielded a grain structure that was not aligned as previously indicated. Being the most accurate, the tensile results of Sut= 60.64 kpsi were chosen as the basis for comparison against the published value of Sut=63.8 kpsi, yielding a difference of 4.95%, falling within the allowable range for use in engineering practices.



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Appendix A

1.

Fatigue Testing – Pre-Anneal

Lab Info: Materials Testing Lab: GOL (70) – 1190

Testing Machine Used: Gunt Hamburg WP 140 Fatigue Testing Machine

Data Collection Date: 10/1/12 – 10/30/12

Principal Contributors: Austin Allessio, Kathy Feinberg, Tyler Peterson, Ryan Schwartz, Stephanie Ulman.

Objective:

The objective of this lab is to determine the number of cycles a fatigue sample can withstand

when subjected to fully reversed bending before failure when a specified stress is induced in a

sample. The stress induced in the part and the number of cycles a part undergoes is plotted on a log-

log graph. The points plotted on the graph are used to create a best-fit line to predict the relationship

between the stress induced in a part and the number of cycles it will undergo before failure.

Procedure:

1. Ensure the emergency stop is engaged

2. Turn off the machine power

3. Ensure there is a 1/8” minimum gap between hand nut and rig

4. Loosen 4 quarter-turn screws

5. Remove the protective cage

6. Remove the collar nut and extract the collet from the spindle

7. Place the large end of a fatigue sample into the collet and slide the collar nut over the small

diameter of the sample

8. Ensure the flat face of the bearing is facing away from the motor

9. Slide the small diameter of the sample into the bearing

10. Place the collet into the spindle and loosely screw the collar nut onto the spindle

11. Leave approx. 1/8” (measured with a 1/8” scale) of the small diameter of the shaft protruding

from the flat side of the bearing

12. Tighten the collar nut onto the spindle using the wrenches

13. Replace the cage and fasten the quarter-turn screws until they click

14. Disengage the emergency stop and turn on the machine power

15. Zero both cycle count displays by pressing the “RST” buttons

16. Press the start button and immediately begin loading the rig by turning the hand nut CW

17. Slow turning speed when load is within 10N of the desired load

18. Wait for the sample to break

19. Ensure the machine power is off and the emergency stop is engaged

20. Remove quarter-turn screws and cage



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21. Remove the long piece of the fatigue sample from the bearing

22. Unload the rig by turning the hand nut CCW until there is a 1/8” minimum gap between the

hand nut and the rig

23. Remove the collar nut from the spindle using the wrenches

24. Spin the spindle while gently tapping the fatigue sample stub with a brass mallet until the

sample and collet are released

25. Remove the sample from the collet

26. Label broken parts of fatigue sample

27. Replace the collet and collar nut on the spindle loosely fastening the collar nut

28. Replace the cage Data/Results:



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Discussion:

The fatigue was test performed to estimate the ultimate tensile strength of the material. To

calculate the ultimate tensile strength of the material from the fatigue test the data is plotted on a log-

log graph of Stress vs. Number of cycles. A best fit line was then created from 106 to 103, the value at

103 cycles, Sm, is then divided by 0.9 to yield an Ultimate Tensile Strength. This uses the assumption

that the fatigue strength of a material at 103 cycles is 90% of its ultimate tensile strength. The best fit-

line was calculated to be y = 187.26x-0.169 yielding an Sut of 78.7 ksi.

Conclusion:

The best fit-line was calculated to be y = 187.26x-0.169 yielding an Sut of 78.7 ksi.

The fatigue test yielded an Sut of 78.7 ksi.



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2.

Hardness Testing of Fatigue Parts

Lab Info: Materials Testing Lab - 1190

Testing Machine Used: Instron Wilson-Rockwell Series 2000 Hardness Testing Machine

Data Collection Date: October 11th, 2012

Principal Contributors: Austin Allessio, Ryan Schwartz, Kathy Feinberg, Tyler Peterson, Stephanie Ulman.

Executive Summary:

The hardness information of the test pieces was determined in order to get a rough estimate

of the material’s ultimate tensile strength, through use of tables/conversion factors. The test

pieces are speculated to be AISI 1018 Cold Rolled Steel, resulting in the use of the Rockwell B

hardness scale. The samples were found to have an average hardness of 95.2 B, yielding an

ultimate tensile strength of 105.5 ±2.0 kpsi1.

Objective:

The objective of this lab was to determine the sample pieces hardness. This information is an

indicator of what exactly the material is, and a rough estimator of the ultimate tensile strength. This

information will be used in comparison to the UTS discovered from the fatigue tests to determine if

the hypothesis or an improper material is correct.

Procedure:

1. Gather specimens, and power up test machine.

2. Select appropriate scale, the Rockwell B scale was used.

3. Apply proper corrections due to a round test piece.

4. Test 5 separate spots per specimen.

5. Record data.

6. Compile data in a visual aid, a box plot was well suited.

7. Convert the range and mean hardness to an UTS.



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Data/Results:

Rockwell B Hardness Data

Part Number Test 1 Test 2 Test 3 Test 4 Test 5 Average

Part 1 95.0 95.4 94.6 95.4 94.5 95.0

Part 2 95.7 96.4 95.5 94.8 95.5 95.6

Part 3 94.5 94.2 94.5 94.2 95.3 94.5

Part 4 94.8 95.1 94.9 94.9 95.6 95.1

Part 5 95.7 95.6 95.3 95.8 96.0 95.7

Part 6 94.6 96.0 95.2 95.1 94.5 95.1

Part 7 95.5 96.0 96.7 94.0 95.4 95.5

Part 8 95.1 95.2 95.6 96.1 95.1 95.4

Overall Average 95.2

97.0

96.5

96.0

95.5

95.0

94.5

94.0

Ro

ckw

ell

B H

ard

ne

ss

Boxplot of Hardness Testing

Discussion:

The hardness values collected a very low variability, indicating that specific test pieces are not contaminated. This also gives a very good idea of what value to select as the resultant Ultimate Tensile Strength. The UTS indicated by the hardness testing does not align with what was indicated by previous fatigue testing, garnering a need for further testing i.e. tensile test.



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Conclusion:

The hardness data gathered clearly shows an ultimate tensile strength above the published

vales of 1019 Cold Rolled Steel. These results however are not as accurate as other tests, such as a

tensile test. The variance in data, ranging from a Hardness of 94.0 to 96.7 HRB (102.5 to 106.5 kpsi

UTS) is also compounded by the fact that a conversion factor is used from Rockwell to UTS. Not all

sources agree on what exactly this factor is, resulting in some values higher and some lower than

what was chosen to represent the data with.

This variance however, does not condemn the data, which clearly shows that the UTS of the

fatigue tested parts are above standard published values. Many possible factors were discussed,

though the likely cause chosen is a direct result of the cold forming process. This hypothesis will be

confirmed upon the completion of a more accurate Tensile Test, and a Metallography inspection to

determine how the grain structure is oriented.



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3.

Tensile Testing of Fatigue Parts – Pre-Anneal


Testing Machine Used: MTS Universal Test Machine, Tensile Test



Objective:

The objective of this lab was to determine the sample pieces’ Ultimate Tensile Strength with

a more accurate method than a hardness or fatigue test. This data aggregated was used in conjunction

with fatigue and hardness test data in order to form a hypothesis as to why the results of these tests

yielded a value for Ultimate Tensile Strength much higher than anticipated with published values.

Procedure:

1. Gather specimens, and power up test machine and

attached computer.

2. Adjust machine clamp heads to fit specimen and ensure alignment.

3. Enter appropriate test data i.e. specimen diameter etc.

4. Place specimen in top jaw.

5. Toggle program to lower testing head, securing bottom jaw on sample once

complete.

6. Attach extensometer to specimen.

7. Start test.

8. Once prompted to or after the part breaks, remove the extensometer.

9. Remove specimen.

10. Repeat as necessary with more sample pieces.

11. Convert test data to Microsoft Word document, and save results.



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Data/Results



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Discussion:

The hardness test garnered a great set of data points. With a mean Ultimate Tensile Strength (Peak Load) of 94.85 kpsi and a standard deviation of only 0.62 kpsi, the results have proven to be highly accurate. This is a very reassuring fact, as this UTS value lines up nicely with the hardness test data, 94.84 kpsi compared to the mean of 95.2 kpsi yielded from the hardness tests. These data points allow for 3 possible hypothesis for data variance, Machine, Material and, Process. Further tests are necessary to affirm these hypotheses as viable or not.



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Conclusion:

The tensile test was very conclusive in the proof of a higher Ultimate Tensile Strength than published values for AISI 1018 Cold Rolled Steel. This data lines up very nicely with the hardness test’s results for UTS, resulting in a hypothesis needing to be formed for the discrepancies with the fatigue test. The most likely culprits of these are Material: Carbon content not to spec, and Process: Cold working changed the material properties in some way.



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4.

Spark Test of Fatigue Parts


Testing Machine Used: Rotary Grinding Wheel



Executive Summary:

It is known that the carbon content of steel affects its strength. A spark test was deemed

necessary in order to test for this. This test gives a decent indicator of carbon content, as well as

other alloying elements. It was found that the specimens were in the mild steel range, with

carbon content around 0.15% and 0.25%. Given this data, it was decided that the material’s

carbon content was most likely in the range it should be (0.15%-0.20%), indicating that further

investigation to a more accurate test was unnecessary.

Objective:

The objective of this lab was to roughly determine the sample’s carbon content. A higher

carbon content would produce a material with a higher Ultimate Tensile Strength. Being able to place

the approximate content will allow an educated insight to if the material supplied is to spec. This

gives a good indication of whether or not further investigation is necessary.



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Procedure:

1. Gather specimens, testing machine, and camera.

2. Touch specimen to grinding wheel so that the spray of sparks is visible.

3. Capture images and compare to published data.

Data/Results:

Many charts for carbon/alloying materials content can be found. The chart below was chosen as a basis for comparison.

Image Courtesy of MechLook (mechlook.com)

The highlighted column shows 1020 Machine Steel, exhibiting extremely similar behavior to the samples tested (pictured below).



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Image 1



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Image 2



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Discussion:

The testing proved slightly difficult, as only a rotary grinding wheel was available. The specimens however produced some very telling results. The sparks captured followed along with an appropriate carbon content, and were of an appropriate color, size, and amount.

Conclusion:

The specimens tested produced long tails, with a few intermittent bursts. Predominantly

colored orange, with white bursts is indicative of steel with carbon content on the lower range

(0.15%-0.25%). The bursts themselves contained very few mini-bursts and few legs as well. This

is further proof that the material’s carbon content is not higher than 0.50%, as well as ruling out

any other alloying elements out of the ordinary.

The spark test gives reasonable doubt to conclude that that material’s carbon content is not a concerning factor in the discrepancies between the tested Ultimate Tensile Strength and published values.



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5.

Combustion Testing

Lab Info: IMR Report Number 201210359



Executive Summary:

It is known that the carbon content of steel affects its strength. Since the samples material

composition was in question, specifically the percentage of the materials carbon content, a

sample was sent to an independent material testing laboratory for carbon analysis test. The

results from this test concluded that the carbon content by weight was .15 %, indicating that it is

in the published range of a mild steel, whose carbon content typically is between 0.15% and

0.25%.

Objective:

The objective of this lab report was to determine the carbon content of a fatigue sample.



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Data/Results:



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Discussion:

The test results provided concrete evidence that the material is indeed 1018 steel and that the high ultimate strength values were not due to the materials carbon content. Other factors must now be investigated to see the root cause.

Conclusion:

The IMR report provided conclusive results to conclude that the carbon content is not the cause of variability in data for the Ultimate Tensile Strength results.



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6.

Metallography Pre-Anneal

Lab Info:

Testing Machine Used:

Data Collection Date: October 26th 2012

Principal Contributors: Tyler Peterson, Ryan Schwartz, Kathleen Feinberg, Austin Allessio, Stephanie Ulman

Executive Summary:

Fatigue testing samples of 1020 cold rolled steel produced higher than expected ultimate

strength values. It is believed that these values are increased because the raw stock of the test parts is

cold drawn when it is manufactured. The cold drawing aligns the metals grain structure and elongates

it along the parts axis. This alignment and elongation of the grain structure increases the materials

strength above the published data for fully annealed 1020 steel. To prove this theory the samples

were polished and etched so that their grain structure could be examined under a microscope. The

grain structure was verified to be both aligned and elongated along the parts axis proving the theory

correct. TO fully validate the theory further a duplicate part from the same stock should be fully annealed and run through the same test to see if its grain structure no longer shows alignment.

Objective:

Metallography is being performed on the samples to see if the grain structure shows signs of

elongation. Elongation of the grain structure would increase the strength of the material in the

direction which the grain structure is directed. Showing that elongation exists would support the theory that the material was cold worked which would increase its strength along its axis.



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Procedure:

1. First the round Samples must have a flat milled into them, it is better to mill the surface then

grind it to avoid heating the material which could change the grain structure

a. The flat should be at least .250 inches wide

2. The flat surface needs to be polished starting at a course grit like 200 grit

a. Sand the surface until the whole surface is uniform and has no deep sanding lines

3. Repeat step 2 progressing to finer grit sand paper ex. 320, 400, 600

4. Use commercial metal polish to bring the surface to a mirror finish

a. If at any point there are scratches that can’t be removed with the current grit in use it may be necessary to drop back to a more coarse grit to remove the scratches.

5. Now the surface must be cleaned with isopropyl, cover the surface with a thin layer and let it

evaporate

6. Next apply a thin layer of Nitol HNO3 to the surface and let it sit for 15 seconds

a. This will etch the grain boundaries making them visible under a microscope.

7. After the 15 seconds quickly remove all the Nitol by covering the surface with more isopropyl, wait until it evaporates again

8. Now the part may be inspected under the microscope, place it on the base of the microscope and secure it with the spring foot

9. Turn the microscope lamp on and select the magnification level (80X is a good start)

10. Focus the microscope and observe the grain structure

11. Take pictures to document the grain structure

a. It may be ideal to change the microscope focus and light level to get an ideal picture



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Data/Results:

Material grain structure (80X magnification)

Part is aligned with its axis left to right (side view of part)



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Part is aligned with its axis into or out of the page (end view of part)



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Discussion:

The fatigue test parts were polished and etched so view their grain structure. It was believed that the grain structure may be altered from a uniform grain structure due to the manufacturing of the raw stock by cold drawing. Cold drawing is done for round parts by pulling material through a die which tappers down in size. The part goes in one diameter and is pulled through to the other side where it now has a decreased diameter. This process tends to align the grain structure of the material towards the outside of the stock, or in cases where the stock is a small diameter it may be affected through its entire cross section. Depending on the ratio of diameter change the part sees, it could have its ultimate tensile strength increased by up to 20%, as shown by the graph below.

Percent Reduction Graph

The grain structure images above are taken from two different sides of the part. The top picture is a view of the long side of the part along its axis. This picture shows a common grain direction, where the grains are going left to right in the same direction as the part axis. These grains are a shaped like a cigar or elongated oval. This elongated grain has more surface area



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then a uniform grain which would have a more spherical shape. This increased surface area allows the grain to have more bonds to other grains. Increasing the number of bonds allows the bond between each individual grain to increase, therefore increasing the material strength along the direction the grain is pointing. This common grain direction along the part axis is due to the cold drawing process of the raw stock.

The bottom picture of the end of the part only solidifies the conclusion. The bottom picture shows that the cross section of the part has a random grain structure showing no alignment direction. This is expected since there should be no alignment across the part in this direction and further proves the theory that the grain direction is aligned to the part axis and that axis only.

Conclusion:

The fatigue test parts have been polished and etched to observe their grain structure. It was found that the grain structure shows alignment along the parts axis. This grain alignment along with the elongation of the grains has increased the ultimate tensile strength of the parts. This grain structure change is due to the cold drawn manufacturing process which the raw stock has been through. Further testing should be done to anneal another sample of the same stock and see if the grain structure changes along with the expected drop in ultimate tensile strength.

Citations:

Percent Reduction Graph, http://pmpaspeakingofprecision.files.wordpress.com/2010/06/cold-

work-graph.jpg Graph and data: AISI Cold Finished Steel Bar Handbook, 1968.

http://pmpaspeakingofprecision.files.wordpress.com/2010/06/cold-work-graph.jpg




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7.

Fatigue Testing – Post-Anneal

Lab Info: Materials Testing Lab: GOL (70) – 1190

Testing Machine Used: Gunt Hamburg WP 140 Fatigue Testing Machine

Data Collection Date: 10/1/12 – 10/30/12

Principal Contributors: Austin Allessio, Kathy Feinberg, Tyler Peterson, Ryan Schwartz, Stephanie Ulman.

Objective:

The objective of this lab is to determine the number cycles a fatigue sample can withstand

when subjected to fully reversed bending before failure when a specified stress is induced in a

sample. The stress induced in the part and the number of cycles a part undergoes is plotted on a log-

log graph. The points plotted on the graph are used to create a best-fit line to predict the relationship

between the stress induced in a part and the number of cycles it will undergo before failure.

Procedure:

1. Ensure the emergency stop is engaged

2. Turn off the machine power

3. Ensure there is a 1/8” minimum gap between hand nut and rig

4. Loosen 4 quarter-turn screws

5. Remove the protective cage

6. Remove the collar nut and extract the collet from the spindle

7. Ensure any scale, from the anneal process, is removed from the surface, utilizing a hand file.

8. Place the large end of a fatigue sample into the collet and slide the collar nut over the small

diameter of the sample

9. Ensure the flat face of the bearing is facing away from the motor

10. Slide the small diameter of the sample into the bearing

11. Place the collet into the spindle and loosely screw the collar nut onto the spindle

12. Leave approx. 1/8” (measured with a 1/8” scale) of the small diameter of the shaft protruding

from the flat side of the bearing

13. Tighten the collar nut onto the spindle using the wrenches

14. Replace the cage and fasten the quarter-turn screws until they click

15. Disengage the emergency stop and turn on the machine power

16. Zero both cycle count displays by pressing the “RST” buttons

17. Press the start button and immediately begin loading the rig by turning the hand nut CW

18. Slow turning speed when load is within 10N of the desired load

19. Wait for the sample to break

20. Ensure the machine power is off and the emergency stop is engaged

21. Remove quarter-turn screws and cage

22. Remove the long piece of the fatigue sample from the bearing



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23. Unload the rig by turning the hand nut CCW until there is a 1/8” minimum gap between the

hand nut and the rig

24. Remove the collar nut from the spindle using the wrenches

25. Spin the spindle while gently tapping the fatigue sample stub with a brass mallet until the

sample and collet are released

26. Remove the sample from the collet

27. Label broken parts of fatigue sample

28. Replace the collet and collar nut on the spindle loosely fastening the collar nut

29. Replace the cage Data/Results:



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Discussion:

The fatigue was test performed to estimate the ultimate tensile strength of the material. To

calculate the ultimate tensile strength of the material from the fatigue test the data is plotted on a log-

log graph of Stress vs. Number of cycles. A best fit line was then created from 106 to 103, the value at

103 cycles, Sm, is then divided by 0.9 to yield an Ultimate Tensile Strength. This uses the assumption

that the fatigue strength of a material at 103 cycles is 90% of its ultimate tensile strength. The best fit-

line was calculated to be y = 187.26x-0.169 yielding a Sut of 79.0 ksi.

Conclusion:

The best fit-line was calculated to be y = 291.02x-0.204

yielding a Sut of 79.0 ksi.

The fatigue test yielded a Sut of 79.0 ksi. Citation: Data points were collected from Groups 1, 2, 3, 6, 8, and 10.



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8.

Hardness Testing of Fatigue Parts - Post Anneal


Testing Machine Used: Instron Wilson-Rockwell Series 2000 Hardness Testing Machine

Data Collection Date: October 27, 2012


Executive Summary:

The hardness information of three test pieces was required to determine if the annealing

process had an effect and what these effects were on the material’s properties. The initial ten pre-

annealed samples had higher hardness values than what would be expected for AISI 1018 Cold

Rolled Steel, the material under scrutiny. The cold drawing process is thought to have had an

effect on the hardness and strength on these pieces, a hypothesis that previous testing has shown

to be viable. The annealing process was done in order to relax the specimens and release built in

strains 1.

With the utilization of the Rockwell B scale, the samples were found to have an average

hardness of 57.9 B post anneal. Most industrial charts that convert the Rockwell Hardness B

value to the materials ultimate tensile stress do not go as low as this. As a result, a formula 2 was

utilized to convert the Rockwell B Hardness value to an Ultimate Tensile Strength value. For a

mean Rockwell Hardness B value of 57.93 +/-2.7, it was calculated to have an estimated tensile

strength of 58.3 kpsi.

1. Machine Design An Integrated Approach 4ed/ Robert L Norton. Paragraph 4, Page 53.

2. <http://www.ehow.com/how_8759475_convert-rockwell-hardness-tensile-

strength.html>.

Objective:

The objective of this lab was to determine the post-anneal sample pieces’ hardness. This

information will be used to compare the previous non annealed samples to the post annealed samples.

The annealing process was speculated to have lowered the hardness values, which also would

correlate with a lower ultimate tensile strength of the material .This test, in addition to others, should

help in determining if the hypothesis that cold drawing process changes the material’s properties,

specifically Ultimate Tensile Strength.



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Procedure:

1. Gather specimens, and power up test machine.

2. Select appropriate scale, the Rockwell B scale was used.

3. Apply proper corrections due to a round test piece.

4. Test 10 separate spots per specimen, avoiding scale on the material surface.

5. Record data.

6. Compile data in a visual aid, a box plot was well suited.

7. Convert the range and mean hardness to an UTS.

Data/Results:

Part Number Test 1 Test 2 Test 3 Test 4 Test 5 Test 6 Test 7 Test 8 Test 9 Test 10

Part 11 54.7 55.8 59.2 55.9 55.5 54.5 56.1 60.6 60.5 60.9

Part 12 62.7 57.9 59.2 56.2 57.7 56.5 60.7 56.5 53.6 53.2

Part 13 62 62.5 60 58.1 59.9 56.1 62.4 54.7 58 56.2

57.93Overall Average

Rockwell B Hardness Data



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Conversion Formula Used to Convert of Rockwell Hardness B to an approximate

Tensile Strength

TS (kpsi) =c3*RH^3+c2*RH^2+c1*RH+c0

Where RH = Rockwell Hardness B value, the mean value of 57.93 was used.

Given:

c3 = .0006

c2 = - 0.1216

c1= 9.3502

c0= - 191.89

Discussion:

The grain structures of the pre-anneal samples were found to be elongated in one direction, a

result of the cold drawn process, which changes the material’s properties. To reverse the effects, it

was determined that annealing three new samples was necessary to prove the hypothesis. The thirty

readings were then averaged, with a mean value of 57.93 +/-2.7 Rockwell B Hardness. Utilizing the

conversion formula previously mentioned, the tensile strength of the post annealed samples is

approximately 58.34 kpsi.

Conclusion:

The hardness data gathered does indeed have a much lower value than the non-annealed

specimens. In fact it is closer to published values, validating the hypothesis that the cold forming

process had affected the material properties, specifically Ultimate Tensile Strength, was correct.

Additional Tensile Testing, along with Metallographic inspection will also be performed on these

specimens, aiding in the confirmation of this hypothesis.



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9.

Tensile Testing of Fatigue Parts – Post Anneal


Testing Machine Used: MTS Universal Test Machine, Tensile Test



Objective:

The objective of this lab was to prove that the hypothesis of annealing in order to return to

published values is true. The tensile test is most accurate at determining the Ultimate Tensile

Strength of the samples, and so was chosen as a go-to test for proving the effectiveness of this

annealing.

Procedure:

1. Gather specimens, and power up test machine and attached computer.

2. Adjust machine clamp heads to fit specimen and ensure alignment.

3. Enter appropriate test data i.e. specimen diameter etc.

4. Place specimen in top jaw.

5. Toggle program to lower testing head, securing bottom jaw on sample once

complete.

6. Attach extensometer to specimen.

7. Start test.

8. Once prompted to or after the part breaks, remove the extensometer.

9. Remove specimen.

10. Repeat as necessary with more sample pieces.

11. Convert test data to Microsoft Word document, and save results.



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Data/Results

Specimen # Specimen

Comment

Diameter

in

Peak Load

lbf

Peak Stress

psi

Modulus

psi

Stress At

Offset Yield

psi

Break Stress

psi

1 Sample 13 0.312 4664 61009.3 4.993e+007 3.852e+004 4.297e+004

2 Sample 11 0.311 4651 61230.5 3.789e+007 3.857e+004 4.376e+004

3 Sample 12 0.311 4627 60911.2 3.043e+007 3.668e+004 4.244e+004

Mean 0.311 4648 61050.4 3.942e+007 3.792e+004 4.306e+004

Std. Dev. 0.001 19 163.5 9.839e+006 1.079e+003 6.634e+002

Specimen # Strain At

Break

%

Total

Energy

Absorbed

ft*lbf/in^2

1 33.335 2340

2 34.379 2473

3 31.731 2151

Mean 33.148 2321

Std. Dev. 1.334 162



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Discussion:

The annealed parts showed a great drop in the Ultimate Tensile Strength from the previous pre-annealed tests. This is a great indicator that the hypothesis of material deformation having an effect on the test sample’s properties. The Tensile test returned a mean value of 61.05 kpsi with a standard deviation of 0.16 kpsi, giving an extremely accurate result that is only 4.3% difference from published values. This, alongside with the post anneal hardness data is an extremely good indicator that the cold working process to form the stock from which the samples were made had a drastic effect on the material’s physical properties.

Conclusion:

The tensile test proved that the annealing process had an effect at reducing the sample’s Ultimate Tensile Strength to near published values. This is proof that the hypothesis of the cold drawing process raising the material’s Ultimate Tensile Strength is very likely to be true. The tensile test returned UTS values within 4.3% of the published values, 61.05 kpsi for the test and 63.8 kpsi for published values.



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10.

Post-Anneal Metallography

Lab Info:

Testing Machine Used:

Data Collection Date: November 1st, 2012

Principal Contributors: Tyler Peterson, Ryan Schwartz, Kathleen Feinberg, Austin Allessio, Stephanie Ulman

Executive Summary:

Fatigue testing samples of 1020 cold rolled steel produced higher than expected ultimate

strength values. It is believed that these values are increased because the raw stock of the test parts is

cold drawn when it is manufactured. The cold drawing aligns the metals grain structure and elongates

it along the parts axis. This alignment and elongation of the grain structure increases the materials

strength above the published data for fully annealed 1020 steel. This was proven through earlier

testing which observed the grain being elongated and aligned with the part axis. To fully validate the

theory r a duplicate part from the same stock was fully annealed and run through the same etch and

observed. This fully annealed sample showed no sign of having elongated or aligned grain structure.

This proves that the change in grains structure was modified by manufacturing the stock. The new

grain structure has no bias and therefore the material would have the same strength in all directions.

Objective:

To prove that the 1020 cold rolled steels grain structure was changed through the

manufacturing of the stock a copy of the part made from the same stock was fully annealed. This full

anneal should let the grain structure relax and become isotropic so that the material has the same

properties in every direction. This annealed material will be polished and etched so that its grain structure can be observed and verified to be random without elongation or orientation.



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Procedure:

1. First the round Samples must have a flat milled into them, it is better to mill the surface then

grind it to avoid heating the material which could change the grain structure

a. The flat should be at least .250 inches wide

2. The flat surface needs to be polished starting at a course grit like 200 grit

a. Sand the surface until the whole surface is uniform and has no deep sanding lines

3. Repeat step 2 progressing to finer grit sand paper ex. 320, 400, 600

4. Use commercial metal polish to bring the surface to a mirror finish

a. If at any point there are scratches that can’t be removed with the current grit in use it may be necessary to drop back to a more coarse grit to remove the scratches.

5. Now the surface must be cleaned with isopropyl, cover the surface with a thin layer and let it

evaporate

6. Next apply a thin layer of Nitol HNO3 to the surface and let it sit for 15 seconds

a. This will etch the grain boundaries making them visible under a microscope.

7. After the 15 seconds quickly remove all the Nitol by covering the surface with more isopropyl, wait until it evaporates again

8. Now the part may be inspected under the microscope, place it on the base of the microscope and secure it with the spring foot

9. Turn the microscope lamp on and select the magnification level (80X is a good start)

10. Focus the microscope and observe the grain structure

11. Take pictures to document the grain structure

a. It may be ideal to change the microscope focus and light level to get an ideal picture



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Data/Results:


Part is aligned with its axis left to right (side view of part)



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Part is aligned with its axis into or out of the page (end view of part)



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Discussion:

The annealed fatigue test parts were polished and etched so view their grain structure. It was believed that the grain structure may be altered from a uniform grain structure due to the manufacturing of the raw stock by cold drawing. Cold drawing is done for round parts by pulling material through a die which tappers down in size. The part goes in one diameter and is pulled through to the other side where it now has a decreased diameter. This process tends to align the grain structure of the material towards the outside of the stock, or in cases where the stock is a small diameter it may be affected through its entire cross section. Depending on the ratio of diameter change the part sees, it could have its ultimate tensile strength increased by up to 20%, as shown by the graph below.

Percent Reduction Graph

The grain structure images above are taken from two different sides of the part. The top picture is a view of the long side of the part along its axis. This picture shows no common grain direction. These grains are not elongated. The random grain shape and direction would give the part similar strength in all directions. This annealed part proves that the grain direction and shape was caused by the stock being manufactured by cold drawing.



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Conclusion:

The fatigue test parts have been polished and etched to observe their grain structure. It was found that the grain structure shows no alignment along the parts axis. The random shape of the grain and the it’s orientation proves that the grain structure was altered by the cold drawing of the stock which would have increased its strength along the parts axis.

Citations:

Percent Reduction Graph, http://pmpaspeakingofprecision.files.wordpress.com/2010/06/cold-

work-graph.jpg Graph and data: AISI Cold Finished Steel Bar Handbook, 1968.





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Appendix B

1.



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2.



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3.



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4.



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5.



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6.



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7.

8.



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9.

One-way ANOVA: Pre Fatigue Sut, Pre Tensile Sut, Pre Hardness Sut, Published Source DF SS MS F P

Factor 3 9930.5 3310.2 164.24 0.000 Error 146 2942.5 20.2

Total 149 12872.9

S = 4.489 R-Sq = 77.14% R-Sq(adj) = 76.67%


Pooled StDev

Level N Mean StDev -+---------+---------+---------+--------

Pre Fatigue Sut 11 113.19 8.71 (*-)

Pre Tensile Sut 65 94.43 2.31 (*)

Pre Hardness Sut 71 105.43 5.13 *)

Published 3 63.80 0.00 (---*--)

-+---------+---------+---------+--------

60 75 90 105

Pooled StDev = 4.49

10.

Two-Sample T-Test and CI: Pre Tensile Sut, Post Tensile Sut Two-sample T for Pre Tensile Sut vs Post Tensile Sut

N Mean StDev SE Mean

Pre Tensile Sut 65 94.43 2.31 0.29

Post Tensile Sut 28 60.641 0.939 0.18

Difference = mu (Pre Tensile Sut) - mu (Post Tensile Sut)

Estimate for difference: 33.791

95% CI for difference: (33.122, 34.460)

T-Test of difference = 0 (vs not =): T-Value = 100.34 P-Value = 0.000 DF = 90



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11.

12.

One-way ANOVA: Post Fatigue Sut, Post Tensile Sut, Post Hardness Sut, Published Source DF SS MS F P

Factor 3 2170.27 723.42 188.18 0.000

Error 50 192.22 3.84

Total 53 2362.49

S = 1.961 R-Sq = 91.86% R-Sq(adj) = 91.38%


Pooled StDev

Level N Mean StDev --------+---------+---------+---------+-

Post Fatigue Sut 4 70.383 5.433 (--*---)

Post Tensile Sut 28 60.641 0.939 (*)

Post Hardness Sut 19 49.842 2.106 (*-)

Published 3 63.800 0.000 (--*---)

--------+---------+---------+---------+-

54.0 60.0 66.0 72.0

Pooled StDev = 1.961



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13.



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Cost Analysis of Fatigue Testing of AISI 1018 CRS

Cost Analysis of Fatique Characteristic Testing of AISI 1018 CRS

Test to Perform Rate ($) Burden Rate Cost/Hour Cost of Test Hours

Fatigue Test 25/hour 3x 75 2,475.00$ 33

Tensile Test 150 /test 4x 600 1,200.00$ 2

Hardness Test 100/test 3x 300 1,200.00$ 4

Metallography 100/test 3x 300 600.00$ 2

IMR 60/test 1x 200 60.00$ 1

Spark 12 /hour 3x 36 36.00$ 1

Profilometer 12 /hour 3x 36 36.00$ 1

Any Heat Treatment 100/part 6x 600 1,800.00$ 3

47

7,407.00$ Total Cost of Testing

Total # hours

Graphical Analysis-Pie Chart

70%

4%

9%

4%

2% 2%

2% 7%

Cost Analysis of AISI 1018 CRS Fatigue Characteristic Testing

Fatigue Test

Tensile Test

Hardness Test

Metallography

IMR

Spark

Profilometer

Any Heat Treatment



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Bibliography

"Rockwell Hardness (HRC, HRB) to Brinell Hardness (HB or BHN) Conversion." Rockwell Hardness (HRC, HRB) to Brinell Hardness (HB or BHN) Conversion. N.p., n.d. Web. 1 Nov. 2012. <http://www.iron-foundry.com/hardness-hrc-hrb-hb.html>.

Su = 63800 psi "AISI 1018 Steel, Cold Drawn." AISI 1018 Steel, Cold Drawn. N.p., n.d. Web. 12 Sept. 2012. <http://www.matweb.com/search

Su = 63800 psi AISI 1018 Cold Rolled Steel http://www.eaglesteel.com/download/techdocs/Carbon_Steel_Grades.pdf

Su = 63800 psi AISI 1018 Cold Rolled Steel http://www.onlinemetals.com/alloycat.cfm?alloy=1018

Acknowledgements

Mike Caldwell

William Leonard

Leslie Gregg

Mike Rodriguez

Steve Parish

Steve Kosicol

Alex Pera

Tom Mordovancey

Groups 1 - 10 of the 20121-403 Class

http://www.matweb.com/tools/unitconverter.aspx?fromID=123&fromValue=63800


http://www.eaglesteel.com/download/techdocs/Carbon_Steel_Grades.pdf


http://www.onlinemetals.com/alloycat.cfm?alloy=1018

failure mechanics final report group 11

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