Material since

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Honor pledge: I _______________________________ acknowledge that I have neither received nor given any unauthorized help/aid during this assignment.

Part 1 Key Engineering Terms: fill in the blanks – 10 points

1. Ductile fracture: a mode of fracture characterized by ______________________________ crack propagation.

2. Brittle fracture: a mode of fracture characterized by ________________________________ crack propagation.

3. Transgranular fracture: crack propagates _______________________________ the grains.

4. Intergranular fracture: crack propagates ______________________________________ the grain boundaries.

5. Fatigue life: _______________________________________ of stress or strain of a specific character that a sample sustains before failure.

6. Creep: _______________________________________ deformation of materials when subjected to ___________________________________________ load or stress.

7. Creep rate: ____________________________________________ of creep-time curve at a given time.

8. Ductile to brittle transition: observed _____________________________________ and _________________________________________ a material when temperature is low.

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Part 2 Learning concepts/reflections/problems – 40 points

1. A specimen of a 1095 steel alloy with a plane strain fracture toughness of 65 ksi) is exposed to a stress of 120,000 psi. Will this specimen experience fracture if the largest surface crack is 0.015 in. long? Why or why not? Assume that the parameter Y has a

value of 1.0. 10 points

2. Determine the critical crack length for an inside crack in a thick 2024-T6 alloy plate that has fracture toughness KIC = 23.5 MPaand is under stress of 300 MPa. Assume Y =

1.0. 10 points

3. Describe the four major factors that affect fatigue strength of a material in at least 3-4 sentences each.

4. (a) Describe the three stages of ductile fracture of a metal.

(b) Describe the three stages of brittle fracture of a metal. 10 points

Part 3 Materials design – 10 points

1. What factors would you consider in selecting materials for coins? Suggest materials for this applications. 5 points

2. Give 2 examples of cyclic stress that can result in fatigue failure. 5 points

Bonus questions: -10 points

1. Define fracture toughness of a materials. Write the expression for fracture toughness of a material and explain meaning of each term. 5 points

2. Identify basic structural changes that occur in a ductile material in fatigue process in one sentence each. 5 points

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