The objective of this experiment is to determine the ductile-brittle transition temperature, Tdt, for the low carbon steel and to give you an appreciation for the large decrease in toughness that occur in certain materials when the temperature is reduced. You will; therefore determine the impact energy for the type of specimen provided, at different temperature. The following temperature baths should be prepared:
Hot water both (about 100 °C)
melting ice (0 °C)
liquid nitrogen (-195.8 °C)
Place two specimens in each bath and allow it to come to the temperature of the bath before testing.
BE VERY CAREFUL WITH THE LIQUID NITROGEN. CONTACT WITH LIQUID NITROGEN OR WITH OBJECTS AT LIQUID NITROGEN TEMPERATURE WILL FREEZE YOUR SKIN INSTANTANEOUSLY AND CAUSE BLISTERS WHICH HEAL VERY SLOWLY.
Move the pendulum of the impact tester to its highest position and ascertain that it is surely locked in this position. Set the plastic pointer to 15 joules (straight down). Now release the pendulum by turning the black knob clockwise.
BE SURE THAT NOTHING, INCLUDING YOUR ARMS AND HANDS, ARE IN THE PATH OF THE PENDULUM. IT CAN EASILY BREAK YOUR ARM!
Stop the pendulum with beak by pushing the red knob up. The pointer on the dial should read zero, because the pendulum will not have lost any of its energy. If it does not read zero contact the TA.
We are now ready to do the actual experiment. The specimens should be transfered from the bath to the anvil as fast as possible, otherwise the temperature of the specimen will change too much (for the low temperatures the specimens will warm up somewhat anyway). Use tongs to transfer the specimen and let the tongs' temperature equilibrate in the bath before removing the specimen. The specimen should be placed on the anvil with its notch on the side opposite where the hammer will hit, and the notch should be in the middle between the supports. Release the pendulum as soon as possible. Read the amount of energy lost in the fracturing process and inspect and describe the fracture surface. The surface should change from dull for ductile fracture, to shiny for brittle fracture. Explain this behavior in your report.
For your report you should plot the impact energy as a function of temperature and draw a smooth curve through your data points. Look at note at bottom of lab for the data. (warning:there may be substantial scatter in your data and you should see a TA if you are not sure how to draw the best curve through your data points). From this curve you should determine Tdt. Several different definitions are used for the transition temperature. We define it as the temperature for which the impact energy is halfway between the impact energy for the highest temperature and the impact energy for the lowest temperature. This definition is usually expressed as the temperature corresponding to the average energy of the upper and lower shelf values.
Dear All ,
What is DBTT(Ductile to brittle transition temperature)?
How we can find DBTT?
Is there any relationship between DBTT and Drop weight tear test?Regards,Limesh--
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