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Effect of temperature on fracture energy

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Effect of temperature on fracture energy

The purpose of the experiment was to become familiar with one type of impact test and the energy absorption ability of three separate materials: aluminum alloy (2024-T4), A36 steel, and alloy steel (4140).  Each material was tested at a wide range of temperatures using a standard Charpy impact machine. Changes in temperature allow the tester to easily see the changes in strength and toughness.  Generally speaking, lower temperatures will cause lower levels of ductility and toughness. Introduction/ Expermental setup:                              The main goal of this lab is to determine and evaluate effect of temperature on fracture energy of different metals. The experimental method began by first preparing the following liquid baths to the desired temperature.  The various liquids required are liquid nitrogen, dry ice with a small amount of acetone, dry with a large amount of acetone, regular ice in salt water, ice water, tap water, warm water, and boiling water.  The tester also needs to obtain 8 specimens of the 3 various metals to be tested in the dimensions of 2.16 inches x 0.375 inches x 0.375 inches with a 45 degree 0.01 inch radius notch in the middle of one long side of the specimen.                  To perform the experiment, one must first soak each specimen in the appropriate bath for approximately 10 minutes, at which point a thermocouple must be used to measure the exact temperature of the bath.  Specimens are then removed from the bath and, within 10 seconds of removal, are placed with the notch forward in the Charpy impact test machine, at which point the energy required to fracture the specimen will be recorded.  Prior to testing of each specimen, it is important to ensure the pointer on the Charpy tester is zeroed and is not moved during the test.  Also ensure that the brake of the Charpy machine is not on prior to the test being performed.  The temperature of the baths and the impact energy are recorded.  The results for each material are plotted on a graph of fracture energy vs. temperature.  The graphs are then used to make observations about the experiment.

Discussion

a)         The A36 steel snapped cleanly when tested in the range of temperatures between -300 and -100 degrees.  After this point the steel began to exhibit