1 Engineering Materials Lab Report Impact Toughness of Metallic Materials Name – Gunathilaka R.A.C.K. ID – EN18405514 Group – 8(D) Date – 6th September 2018 Date of Submission – 19th September 20182 Continuous Assessment Cover Sheet Faculty of Engineering Module Details Module Code MT1010 Module Title Engineering Materials Program: SLIIT UGC Course: BSc Stream: Mechanical Assessment details Title Impact Toughness of Metallic Materials Group assignment NO If yes, Group No. Lecturer/ Instructor Wickramarachchi S.
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C.K. OFFICE USE ONLY3 Receiving Officer (seal, signature, date) Specific comments about the work (including overall comments and guidelines for improvement) Tutor: Signature: Date: Marks: All marks are subject to external moderation and approval of board of examinations 1) Title Impact Toughness of Metallic Materials 2) Objectives ? Study the principles and theories of brittle fracture in mild steels ? Discover the impact toughness of materials with different heat and strengthening treatments ? Analyze obtained experimental data for the selection of engineering materials 3) Introduction Impact toughness is known as the strength of a material. Impact toughness is absorbed energy of a material after an impact. Energy is measured by Joule. There are two methods of impact tests. I.
Charpy Test4 II. Izod Test Difference between the Charpy and Izod is the position of keeping the specimen on anvil. This experiment was done through the method of Charpy.
A pendulum machine was used for this experiment. Specimens should be prepared earlier with notching and keeping under different temperatures. Mechanical properties such as ductility, brittle qualities of a metal specimen can be examined by results of this impact test. Area under a stress – strain curve of any metal is given the absorbed energy of an impact testing. This value is directly given by analog indicator of the pendulum machine without any calculations. 4) Theory Law of conservation of mechanical energy – Difference between initial potential energy and final potential energy is equal to the absorbed energy of the metal specimen. Toughness Reading = mg(h-h/)5 5) Materials and apparatus ? A Pendulum Testing Machine ? 3 cuboid shaped mild steel specimens (55mm x 10mm x 10mm) ? A digital thermometer ? A lab refrigerator6 ? A lab oven ? Forceps ? A Notching Device (Notch Maker)7 6) Procedure ? Firstly, 3 mild steel specimens were chosen which contained 55mm x 10mm x 10mm dimensions.
? Secondly, 3 mild steel specimens were machined to cut the V-type notch by using a notching device. ? After that, one specimen was kept on the refrigerator; another specimen was kept in an oven. Remained specimen was kept in the room temperature. ? Next, the scale of the Pendulum Testing Machine was adjusted to the zero point. ? Then, the specimen which in the room temperature was taken and mounted on the anvil of Pendulum Testing Machine.
? After that, the pendulum was raised and locked up to the ‘preparation’ position. ? Next the pendulum was released and the specimen was broken after the impact. ? The toughness reading was taken by the indicator of the Pendulum Testing Machine. ? Two broken pieces of specimen were picked up and the temperature of the room was measured by a digital thermometer. ? After that, reading of the toughness was noted in a data sheet. ? Next the specimen which in the refrigerator was taken out by using forceps and the temperature value inside the refrigerator was read and noted.
? Then the specimen was fitted on the anvil and again the impact test was done to read the toughness of cold specimen. ? After noting the value of toughness on the data sheet, the hot specimen was taken out from the oven with reading the value of the inside temperature of the oven at that time. Forceps was used in this step. ? Again the impact test was done and toughness value was noted in the data sheet. ? Finally, all the data were analyzed to discover the interconnection between temperature of the specimen and toughness values.8 7) Observations9 8) Calculations No calculations were needed because all values of toughness were directly given by the dial gauge of Pendulum Machine.
9) Results Sample No Sample Details Notch Type Temperature Broken or Unbroken Toughness Reading Percent Ductility 1 Mild Steel V notch 23 0C Broken 30 J 5-10 2 Mild Steel V notch -37 0C Broken 10 J 0-5 3 Mild Steel V notch 153 0C Broken 54 J 40-45 10) Discussion 10.1 Differences of fracture type of different specimen According to the stress – strain curve of any metal, there are probably two regions which are known as elastic regions and plastic regions. Fracture point is situated in the plastic region. Area under the curve is given the toughness of the metal.
In this process a hammer is impacted with the metal specimen and the absorbed energy is indicated by the dial gauge. At the beginning hammer was fitted at a high position and suddenly it was impacted with the metal specimen. Initial potential energy was transferred to the kinetic energy. After the impact value of toughness was taken.
In this experiment, friction between the pendulum and the machine was neglected. Interconnection between toughness and the temperature is shown by this graph. This curve is clearly given by low strength metals such as structured as Body Centered Cubic due to their alloy composition. According to the graph above, specimen is behaved as a brittle metal at lower temperatures. The toughness of the metal specimen is increased exponentially at the beginning, but after that it is behaved as ductile metal. Toughness is increased with a rate of decreasing. Brittle metals10 are contained the lowest values for toughness.
Otherwise, ductile metals are contained the highest values for toughness. Fractures can be occurred as brittle and ductile. Brittle materials such as glass are being fractured immediately without reach the plastic deformations. However, ductile materials are reached the both elastic and plastic deformations. In this experiment V notched specimen was used to get readings for impact toughness. Specimens can be notched as V shape, square shape or circular shape.
Entire experiment was based only on V shaped notch. Readings of the pendulum machines are given the absorbed energy by the specimen to get fractured. After the impact of the specimen it must be separated into two parts. Under this condition V shaped notch is recommended to do this experiment. Shearing waves after the impact on different notched specimens are differently behaved. In square shaped notch it is contained only 2 sharp edges. Due to this, square notched specimen can be separated into 3 parts. Circular notched specimen can be separated into many parts due it’s uncountable sharp edges.
This is the reason for use a v notched specimen to do this experiment. 10.1.1 Under the room temperature The first specimen of this experiment was kept under the room temperature. That temperature was 23 0C. Specimen was broken after the impact. Reading was 30J.
Looking at the side appearance of the broken pieces, some silver lines were originated along the edges of side view. These silver lines are explained that the specimen was stretched at a normal length before the fracture. 10.1.2 Under the cold condition Second specimen was taken out from the lab refrigerator. Inside temperature was -37 0C. As a result of impact testing the specimen was broken. Reading was 10J.
Appearances of broken faces were quite different from previous ones. Silver lines were not clearly appeared on that. Then it is easy to understand that the specimen under the cold condition was broken being stretched minimally.11 10.1.3 Under the hot condition Last specimen was taken out from the lab oven with a temperature of 153 0C.
Specimen was broken after the impact testing. Reading was 54J. Bright silver lines were clearly appeared on the broken faces. Maximum stretch was taken from this specimen. 10.
1.4 Summary Under the low temperature, toughness of the mild steel is very low. Under the room temperature, toughness is at a normal value. Under a high temperature, toughness of mild steel is high. Considering above results, it is clear to recognize that there is a close connection between toughness of the metal and the temperature of it. When the temperature is at a minimum level, toughness of that metal is at a low value. Percent ductility is also at a low range.
Specimen is not stretched along due to this condition. When the temperature is equal to the room temperature, toughness of the metal is at a normal value. Percent ductility is stood at an average range. Specimen is stretched more than previous condition.
Silver lines which are surrounded on the broken face showed the visual of the ductility which was activated on the mild steel specimen. When the temperature is at a high temperature, toughness of the metal is increased at a high value. Percent ductility is gone to at high range.
Due to the high ductility at that temperature, specimen is stretched longer than previous two conditions.12 10.2 Importance of the impact test ? Impact tests are very important when using materials for a manufacturing ships or any other craft to certify the ability and affordability. For instance, materials which were selected to manufacture Titanic was considered only for the normal temperature, but at the cold condition, ship was biased to break and damage highly because of these facts of ductility and fracture.
? Forging is defined as a manufacturing method of pressing, pounding metal into strong parts. Forging is done under a high temperature. Metals are heated at to that temperature.
Impact test are done to relieve the malleability of a material in forging industry. ? Rubber is used to manufacture belts, coatings, seals etc. In rubber industry, impact tests are done to certify the ability of shock absorbing.13 ? In plastic industry, impact tests are done to verify and analyze the breaking strength of a product. Specially in automobile industry, impact tests are done to control the quality of plastics which are used in their products. Furthermore, impact tests are tested to the polymers to determine the resistance against to the fracture.14 11) Conclusion Impact test is an important test in metallography. Specially in manufacturing field, impact tests are done to certify the quality of the manufacturing product.
Ductility and the brittleness are affected by the temperature of the metal specimen. Above results are witnessed this statement. 12) References ? Charpy impact test and its application Available from: https://www.testing-instruments.com/blog/charpy-impact-test-and-its-applications/ Accessed on 17th September 2018 ? Impact test on metals Available from: https://www.slideshare.net/engomar84/impact-test-on-metals-75746485 Accessed on 17th September 2018 ? Charpy impact test of cold formed and hot rolled steels under diverse temperature conditions Available from: https://www.jove.com/science-education/10385/charpy-impact-test-cold-formed-hot-rolled-steels-under-diverse Accessed on 18th September 2018