BE 1310
Creep in Metals Laboratory Report
Creep in metals is evaluated by the change in length versus time. For the creep to take place its important to consider the magnitude of the stress as well as the temperature. When evaluating the creep curve, the initial strain has significant effects on the length, which is followed by decrease in the strain rate as the primary creep takes place. The derivative of the primary creep is noted as the steady-state creep rate. After the steady-state creep rate a rapid change in the data will be observed as the strain causes fracture. This time dependent deformation must be considered during engineering design for safety and longevity.
Materials and Methods
A Sm 106 Mk II creep testing machine was used along with a stop watch and lead specimens in the lab experiment. The creep machine consists of a lever, steel pins that hold the specimen, bearing block, weight hanger, and a dial test indicator. Three lead specimens were pulled to failure with loads of 0.6kg, 0.7kg, and 0.8kg weights. The cross sections (length, width, thickness) of the lead specimens were measured using a micrometer. With this information, we were able to find the stress. The lead specimen was fitted in to the lever arm using the steel pins. Weight of 0.6kg was loaded onto the weight hanger and the hanger was gently released. We recorded the extension readings from the dial test indicator every 15 seconds for the primary stage of creep and every minute when the extension rate slowed down. During the tertiary stage, readings were recorded every 15 seconds until fracture occurred. This process was repeated 2 more times with a new lead specimen each time and weights of 0.7kg and 0.8kg, respectively.
