Mechanical Testing: Impact and Hardness Testing ME-3701-02 3rd March 2009 Ke Chen Abstract This experiment, as may be derived from the title, involves testing multiple metallic specimens to determine their toughness, strength and hardness. The three tests used to determine these characteristics are called the Charpy Impact test, tensile strength test and Rockwell Hardness test. As stated by www. key-to-steel. com {1}, “Charpy impact test method for metallic materials is specified by European EN 10045 standard.
This specification defines terms, dimension and tolerances of test pieces, type of the notch (U or V), test force, verification of impact testing machines etc. The test consists of breaking by one blow from a swinging pendulum, under conditions defined by standard, a test piece notched in the middle and supported at each end. The energy absorbed is determined in joules. This absorbed energy is a measure of the impact strength of the material. ” Furthermore, www. flti. com {2} states the following as the proper procedure for conducting the Rockwell Hardness test: “A standard specimen is placed on the surface of the Rockwell Hardness tester.
A minor load is applied and the gauge is set to zero. The major load is applied by tripping a lever. After 15 seconds the major load is removed. The specimen is allowed to recover for 15 seconds and then the hardness is read off the dial with the minor load still applied. ” The standard specimen for the Rockwell Harness test is 1/4” thick. Finally, www. instron. us {3} shows us that “A tensile test, also known as tension test, is probably the most fundamental type of mechanical test you can perform on material. Tensile tests are simple, relatively inexpensive, and fully standardized.
By pulling on something, you will very quickly determine how the material will react to forces being applied in tension. As the material is being pulled, you will find its strength along with how much it will elongate. ” Once the three tests were performed, Chavenet’s criterion was applied to process the collected data. Figure (1) Figure (2) Figure (3) Table of Contents 1. Title Page 2. Abstract 3. Table of Contents 4. List of Nomenclature 5. List of Figures and Tables 6. Experimental Apparatus and Procedure 7. Experimental Results 8. Discussion 9. Conclusions 10. References 11. Appendix List of Nomenclature
Hardness- a measure of a material’s resistance to localized plastic deformation. Toughness-a measure of the amount of energy a material can absorb before fracturing. Minor Load-initial load applied to a specimen in the Rockwell test to eliminate backlash in the load train and cause the indenter to break through slight surface roughness to improve accuracy. Major Load-secondary load applied a specimen that is applied at a prescribed, controlled rate. Impact test-a method to discover a specimen’s toughness. Chavenet’s Criterion-A method to process the data following Gaussian distribution.
Tensile-the ability of a metal to be stretched out and the limit thereof. Tensile Test-a test to determine the reaction of a material to an applied force. List of Figures and Tables Figure (1)-photo demonstration of Charpy impact test Figure (2)-photo demonstration of Rockwell hardness test Figure(3)-photo of a tensile strength testing machine Experimental Apparatus and Procedure Hardness Test-for the hardness test, specimens will be subjected to the Rockwell Harness test. The procedure is as follows: A standard specimen is placed on the surface of the Rockwell Hardness tester.
A minor load is applied and the gauge is set to zero. The major load is applied by tripping a lever. After 15 seconds the major load is removed. The specimen is allowed to recover for 15 seconds and then the hardness is read off the dial with the minor load still applied. {1} Standard specimen size is . 25” thick. The hardness is read directly from the dial with either the R, L, M, E or K scales. The higher the number in each scale, the harder the material. R and M scales are commonly used with plastics. {1} The Rockwell Hardness Tester is implemented in this experiment.
Impact Test-for the impact test, specimens will be subjected to the Charpy Impact Test to test their toughness. This is the procedure: Charpy impact test method for metallic materials is specified by European EN 10045 standard. This specification defines terms, dimension and tolerances of test pieces, type of the notch (U or V), test force, verification of impact testing machines etc. The test consists of breaking by one blow from a swinging pendulum, under conditions defined by standard, a test piece notched in the middle and supported at each end.
The energy absorbed is determined in joules. This absorbed energy is a measure of the impact strength of the material. {2} The Charpy Impact testing machine is used to determine the material’s toughness in this experiment. Strength/Tensile Test-for the strength test, specimens will be subjected to tests performed by the tensile strength test. The procedure is specified in ASTM E-8 and is performed as follows: “Tensile test is carried out by gripping the end E, E of the specimen in a tensile testing machine and applying and increasing pull on to the specimen till it fractures.
During, the test, the tensile load as well as the elongation of a previously marked gauge length in the specimen is measured with the help of load dial of the machine and extensometer respectively. These readings help plotting stress strain curve. After fracture, the two pieces of the broken specimen are placed as if fixed together and the distance Lf between two gauge marks and the area Af at the place of fracture are noted. ”{4} Experimental Results From the Hardness Testing- From the hardness tests we did we found the following raw data. Steel| | Aluminum| | Copper| Steel (cold)| HRC| | HRB| | HRB| HRC|
Diamond tip 50kg| Steel ball 100kg| Steel ball 100kg| Diamond tip 50 kg| 20. 3| 23| 74. 6| 83. 9| 68. 4| 17. 5| 22. 2| 22. 7| 82. 2| 83. 8| 68. 2| 17. 9| 21. 6| 23. 4| 82. 6| 83. 5| 67| 15. 3| 22. 3| 23| 81. 5| 82. 1| 65. 3| 17. 3| 22. 4| 23. 2| 84| 82. 9| 66. 5| 17. 6| 22. 7| 22. 8| 84| 80. 2| | | 22. 4| 22. 7| 82. 5| 82. 1| | | 22. 4| 22. 8| 81. 8| 82. 8| | | 23. 2| 21. 9| 80. 5| 82. 3| | | 22. 9| 22. 7| 83. 7| 81. 2| | | The copper sample used in the test was a solid rod so an end correction must be added to the raw data to scale it correctly. Using the in class chart the copper data needs to have 2. 3 units added to each data point.
A new representation of the data after the copper is scaled and everything is put into numerical order would look like the chart below. Steel| | Aluminum| | Copper| Steel (cold)| HRC| | HRB| | HRB| HRC| Diamond tip 50kg| Steel ball 100kg| steel ball 100kg| Diamond tip 50 kg| 20. 3| 22. 7| 74. 6| 82. 5| 67. 6| 15. 3| 21. 6| 22. 7| 80. 2| 82. 6| 68. 8| 17. 3| 21. 9| 22. 8| 80. 5| 82. 8| 69. 3| 17. 5| 22. 2| 22. 8| 81. 2| 82. 9| 70. 5| 17. 6| 22. 3| 22. 9| 81. 5| 83. 5| 70. 7| 17. 9| 22. 4| 23| 81. 8| 83. 7| | | 22. 4| 23| 82. 1| 83. 8| | | 22. 4| 23. 2| 82. 1| 83. 9| | | 22. 7| 23. 2| 82. 2| 84| | | 22. 7| 23. 4| 82. 3| 84| | |
Now that the data is sorted and scaled Chavenet’s Criterion can be applied. Means Steel mean| 22. 53| Aluminum mean| 82. 11| Copper mean| 69. 38| Steel(cold) mean| 17. 12| Standard Deviation Steel SD| 0. 686025932| Aluminum SD| 2. 091813618| Copper SD| 1. 275539102| Steel(cold) SD| 1. 04019229| Mean minus each value Steel| | Aluminum| | Copper| | Steel (cold)| HRC| | HRB| | HRB| | HRC| | Diamond tip 50kg| mean-value| Steel ball 100kg| mean-value| steel ball 100kg| mean-value| Diamond tip 50 kg| mean-value| 20. 3| 1. 79| 74. 6| 6. 25| 67. 6| 1. 78| 15. 3| 1. 82| 21. 6| 0. 49| 80. 2| 0. 65| 68. 8| 0. 58| 17. 3| 0. 18| 21. 9| 0. 9| 80. 5| 0. 35| 69. 3| 0. 08| 17. 5| 0. 38| 22. 2| 0. 11| 81. 2| 0. 35| 70. 5| 1. 12| 17. 6| 0. 48| 22. 3| 0. 21| 81. 5| 0. 65| 70. 7| 1. 32| 17. 9| 0. 78| 22. 4| 0. 31| 81. 8| 0. 95| | | | | 22. 4| 0. 31| 82. 1| 1. 25| | | | | 22. 4| 0. 31| 82. 1| 1. 25| | | | | 22. 7| 0. 61| 82. 2| 1. 35| | | | | 22. 7| 0. 61| 82. 3| 1. 45| | | | | 22. 7| 0. 61| 82. 5| 1. 65| | | | | 22. 7| 0. 61| 82. 6| 1. 75| | | | | 22. 8| 0. 71| 82. 8| 1. 95| | | | | 22. 8| 0. 71| 82. 9| 2. 05| | | | | 22. 9| 0. 81| 83. 5| 2. 65| | | | | 23| 0. 91| 83. 7| 2. 85| | | | | 23| 0. 91| 83. 8| 2. 95| | | | | 23. 2| 1. 11| 83. 9| 3. 05| | | | | 23. 2| 1. 1| 84| 3. 15| | | | | 23. 4| 1. 31| 84| 3. 15| | | | | (Mean)-(Value)/(Standard Deviation) Steel| | | Aluminum| | | HRC| | | HRB| | | Diamond tip 50kg| mean-value| (mean-value)/STDIV| Steel ball 100kg| mean-value| (mean-value)/STDIV| 20. 3| 1. 79| 2. 609230554| 74. 6| 6. 25| 2. 987837351| 21. 6| 0. 49| 0. 714258643| 80. 2| 0. 65| 0. 310735084| 21. 9| 0. 19| 0. 276957433| 80. 5| 0. 35| 0. 167318892| 22. 2| 0. 11| 0. 160343777| 81. 2| 0. 35| 0. 167318892| 22. 3| 0. 21| 0. 306110847| 81. 5| 0. 65| 0. 310735084| 22. 4| 0. 31| 0. 451877917| 81. 8| 0. 95| 0. 454151277| 22. 4| 0. 31| 0. 451877917| 82. 1| 1. 25| 0. 59756747| 22. 4| 0. 1| 0. 451877917| 82. 1| 1. 25| 0. 59756747| 22. 7| 0. 61| 0. 889179127| 82. 2| 1. 35| 0. 645372868| 22. 7| 0. 61| 0. 889179127| 82. 3| 1. 45| 0. 693178265| 22. 7| 0. 61| 0. 889179127| 82. 5| 1. 65| 0. 788789061| 22. 7| 0. 61| 0. 889179127| 82. 6| 1. 75| 0. 836594458| 22. 8| 0. 71| 1. 034946197| 82. 8| 1. 95| 0. 932205253| 22. 8| 0. 71| 1. 034946197| 82. 9| 2. 05| 0. 980010651| 22. 9| 0. 81| 1. 180713267| 83. 5| 2. 65| 1. 266843037| 23| 0. 91| 1. 326480337| 83. 7| 2. 85| 1. 362453832| 23| 0. 91| 1. 326480337| 83. 8| 2. 95| 1. 41025923| 23. 2| 1. 11| 1. 618014478| 83. 9| 3. 05| 1. 458064627| 23. 2| 1. 11| 1. 618014478| 84| 3. 5| 1. 505870025| 23. 4| 1. 31| 1. 909548618| 84| 3. 15| 1. 505870025| Copper| | | Steel (cold)| | HRB| | | HRC| | | steel ball 100kg| mean-value| (mean-value)/STDIV| Diamond tip 50 kg| mean-value| (mean-value)/STDIV| 67. 6| 1. 78| 1. 395488495| 15. 3| 1. 82| 1. 749676983| 68. 8| 0. 58| 0. 454709734| 17. 3| 0. 18| 0. 173044976| 69. 3| 0. 08| 0. 062718584| 17. 5| 0. 38| 0. 365317172| 70. 5| 1. 12| 0. 878060177| 17. 6| 0. 48| 0. 46145327| 70. 7| 1. 32| 1. 034856637| 17. 9| 0. 78| 0. 749861564| Now that everything is calculated the outlining data can be eliminated and used. The correct, final data appears in the following chart.
Steel| | Aluminum| | Copper| Steel (cold)| HRC| | HRB| | HRB| HRC| Diamond tip 50kg| Steel ball 100kg| steel ball 100kg| Diamond tip 50 kg| 21. 6| 22. 7| 80. 2| 82. 6| 67. 6| 15. 3| 21. 9| 22. 8| 80. 5| 82. 8| 68. 8| 17. 3| 22. 2| 22. 8| 81. 2| 82. 9| 69. 3| 17. 5| 22. 3| 22. 9| 81. 5| 83. 5| 70. 5| 17. 6| 22. 4| 23| 81. 8| 83. 7| 70. 7| 17. 9| 22. 4| 23| 82. 1| 83. 8| | | 22. 4| 23. 2| 82. 1| 83. 9| | | 22. 7| 23. 2| 82. 2| 84| | | 22. 7| 23. 4| 82. 3| 84| | | 22. 7| | 82. 5| | | | Specific Aluminums Charts- Aluminum| Mean Dev| Mean Dev / Std Dev| Accept? | 79. 6| 2. 68| 2. 146731477| Y| 80. 2| 2. 08| 1. 666119952| Y| 0. 5| 1. 78| 1. 42581419| Y| 81. 2| 1. 08| 0. 865100744| Y| 81. 5| 0. 78| 0. 624794982| Y| 81. 8| 0. 48| 0. 38448922| Y| 82. 1| 0. 18| 0. 144183457| Y| 82. 1| 0. 18| 0. 144183457| Y| 82. 2| 0. 08| 0. 064081537| Y| 82. 2| 0. 08| 0. 064081537| Y| 82. 3| 0. 02| 0. 016020384| Y| 82. 5| 0. 22| 0. 176224226| Y| 82. 6| 0. 32| 0. 256326147| Y| 82. 8| 0. 52| 0. 416529988| Y| 82. 9| 0. 62| 0. 496631909| Y| 83. 5| 1. 22| 0. 977243434| Y| 83. 7| 1. 42| 1. 137447275| Y| 83. 9| 1. 62| 1. 297651117| Y| 84| 1. 72| 1. 377753038| Y| 84| 1. 72| 1. 377753038| Y| Rank| Sorted | % Below| Median Rank| 1| 79. 6| 5| -1. 959963985| 2| 80. | 10| -1. 439531471| 3| 80. 5| 15| -1. 15034938| 4| 81. 2| 20| -0. 934589291| 5| 81. 5| 25| -0. 755415026| 6| 81. 8| 30| -0. 597760126| 7| 82. 1| 35| -0. 45376219| 8| 82. 1| 40| -0. 318639364| 9| 82. 2| 45| -0. 189118426| 10| 82. 2| 50| -0. 062706778| 11| 82. 3| 55| 0. 062706778| 12| 82. 5| 60| 0. 189118426| 13| 82. 6| 65| 0. 318639364| 14| 82. 8| 70| 0. 45376219| 15| 82. 9| 75| 0. 597760126| 16| 83. 5| 80| 0. 755415026| 17| 83. 7| 85| 0. 934589291| 18| 83. 9| 90| 1. 15034938| 19| 84| 95| 1. 439531471| 20| 84| 100| 1. 959963985| Specific Steel Charts- Now A Normal Probably graph can be composed. For steel- For Aluminum
Charpy Test Steel| 34J| Steel(cold)| 57J| Aluminum| 45J| Aluminum(cold)| 44J| zero pt| 20J| From the Tensile Strength tests- Steel rod- Stress vs. Strain Modulus of Elasticity-207. 5179 GPa Aluminum Rod- Stress vs Strain Modulus of Elasticity- 717. 73866 GPa Discussion Hardness Test- In the hardness test we found the hardness of the different materials based on two different scales. The HRB and HRC scale was used with the HRB being the scale used for softer materials and the HRC scale used for steel. To put some of the numbers into perspective, the number 82 on the HRB scale relates to number 1 on the HRC scale.
So HRC is 81 units lower than the HRB scale. This is why at first glance aluminum looks harder than steel but it really is not since on the B-scale, steel would be in the range of 95 or so. Also what makes a difference is the weight used on the B-scale test and the C-scale test. Obviously, if a lighter weight is used then the indenter will not go as deep in the material. The tip used in the testing procedure also affects the data. A diamond tip was used on the steel, where a steel ball was used on the aluminum. These factors seem to at a quick glance make aluminum look harder than steel, but it is not.
Our data also compares cold steel to room temp steel. It can be told than even against common since that the room temperature steel is harder. The colder steel is more brittle and the indenter had an easier time leaving a mark in it compared to the room temp steel. Common since would say that the atoms of the cold steel are closer packed and that it would provide more resistance towards the indenter but it is shown here that that is not the case. Charpy Test- In the Charpy test the cold steel was the weakest where the cold aluminum really wasn’t far from the room temperature aluminum.
This shows how much temperature affects steel compared to aluminum. The Charpy test is designed to test temperature-dependent brittle ductile transitions. It is clear to see that with the low energy absorption of the cold steel that room temperature steel is much stronger. Also, based on the test temperatures, aluminum isn’t affected. But we all know that when extreme heat will soften aluminum making it break easier in the Charpy test. Tensile Test- Based on the collected data from the tensile strength test, the aluminum is much more malleable than the steel and allowed for a much greater modulus of elasticity.
This is to be assumed since aluminum is normally softer than steel. Aluminum could not with stand the pressures that steel with stood before it separated, but it did stretch and move much more. Depending on the application that the materials were to be used, each has a benefit. Conclusions During the hardness, or denting, test the steel proved to be much stronger and denser than the aluminum. Although two different scales were used, the steel was much harder and this can be figured by looking at the type of scale used and indenter. The c-scale was used for steel because of its hardness.
The b-scale would be on its outer edge of accuracy if it would include the steel at all. Also, against the steel, we used a diamond tip denter. This is because of the diamonds strength, and that the steel ball would not provide the point needed to dent the steel. The aluminum on the other hand easily dented with the steel ball even though more force was used. The Charpy test proved that steel is very susceptible to temperature changes and that aluminum isn’t. The room temperature steel proved to use the highest amount of energy to break it, but at the same time the cold steel used the least amount of energy to break.
Aluminum seemed to not be affected by the temperature change at all. The tensile test was the last test done and concluded that aluminum is much more malleable than steel. The change in length in the aluminum was much more than the steel, yet the steel took much more pressure to actually break. This is all to be expected though based on our knowledge of the materials. References {1}Charpy Impact Test for Metallic Materials. Key to Steel: The World’s Most Comprehensive Steel Database. http://steel. keytometals. com/Articles/Art94. htm {2} Rockwell Hardness: ASTM D785, ISO 2039.
Intertek Plastics Technology Laboratories. 1996-2009. http://www. ptli. com/testlopedia/tests/Rockwell-d785. asp {3}Tensile Strength Testing: What is a Tension Test? Instron: Materials Testing Solutions. Instron Worldwide Headquarters, 825 University Ave, Norwood, MA 02062-2643, USA. http://www. instron. us/wa/applications/test_types/tension/default. aspx {4}Tensile Test, Butt Joint, Metal Tensile Test, Tensile Testing Machine. Welding Tecnology Machines. http://www. welding-technology-machines. info/inspection-and-testing-of-welds/tensile-test. htm. Appendix
