Chapter 6 - Lecture 11_1

# Chapter 6 - Lecture 11_1 - t t Strain Rate vs Temperature...

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Chapter 6 Mechanical Behavior Issues to address… Hardness Creep Steady-state creep rate

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Hardness Figure 6-28
Table 6.9 Common Types of Hardness-Test Geometries

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Hardness vs Strength Figure 6-29
Vickers Hardness Testing

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The simple expressions for Rockwell hardness numbers involve indentation, t, expressed in millimeters. A given steel with a BHN of 235 is also measured by Rockwell hardness tester. Using a 1/16 –in.- diameter steel sphere and a load of 100kg, the indentation t is found to be 0.062 mm. What is the Rockwell hardness number? Example
Stress-Strain at Room Temperature Figure 6-30 ε σ E =

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Creep Test Figure 6-31
Stress-Strain at “High” Temperature - Creep Figure 6-32 Creep occurs if T is > 1/3 to ½ times the melting point on an absolute temp scale (e.g., A36 steel, T melting ~ 1500 o C (1773K)). T Operating ~591 - 886K (318 - 613 o C)

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Figure 6-33 Dislocation Climb
Figure 6-34 time-to-creep rupture time-to-creep rupture

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Unformatted text preview: t t Strain Rate vs Temperature Figure 6-35 RT Q Ce /-= ε . T R Q C 1 ln ln ×-= In a laboratory creep experiment at 1000C. A steady-state creep rate of 5×10-1 % per hour is obtained in a metal alloy. The creep mechanism for this alloy is known to be dislocation climb with an activation energy of 200 kJ/mol. Predict the creep rate at a service temperature of 600 C Example The relaxation time for a rubber band at 25C is 60 days. (a)If it is stressed to 2MPa initially, how many days will be required before the stress relaxes to 1 MPa (b) If the activation energy for the relaxation process is 30 kJ/mol, what is the relaxation time at 35C? Example The stress on a rubber disk is seen to relax from 0.75 to 0.5 MPa in 100 days. (a)What is the relaxation time for this material? (b) What will be the stress on the disk after 200 days? Practice...
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