Biomaterials Lecture 3

Question 1

• What is the difference between static and Dynamic loading?

Answer 1

• Static loading is involved in a single event while dynamic loading is more “real world” cyclic events

Question 2

• What is time dependent stress-strain behavior (viscoelastic)?

Answer 2

• If a stress is applied in a short amount of time it is more likely to experience plastic deformation compared to a longer time where it may experience elastic deformation

Question 3

• What is Stress relaxation?

Answer 3

• ie Carpet depressed after something left on top of it for a long time
• Fixed strain, stress decreases with time

Question 4

• What is Creep?

Answer 4

• Rubber band stretch over time will stay stretched

* Fixed stress, strain changes with time

Question 5

• What is fatigue?

Answer 5

• Breaking or fracturing of material caused by repeated cycling to stress below the elastic limit
• Cycling process accumulates plastic deformations

Question 6

• What is the fatigue curve (S/N) curve?

Answer 6

• Stress vs. number of cycles

* Represents the number of cycles required for a material to fatigue

Question 7

• What is the endurance limit?

Answer 7

• Apparent limit below which the material can be cycled indefinitely without failure

Question 8

• Which testing is more important cyclic or static? Why is one used more often?

Answer 8

• Cyclic gives a more realistic understanding but more expensive

Question 9

• What are stress concentrators?

Answer 9

• Notches corners scratches etc that focus stresses and produce cracks that contribute to failure