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T-Mobile 1:02 PM https://mail.google.com/mail/mu.... 26 Google+Gmail CalendarWeb more Inbox o How do the crack length (a) and the crack tip radius of curvature (rho) affect the stress concentration factor (K)? o How is sigmac (the critical stress for crack propagation) related to gammas (specific surface energy) and to the fracture toughness (Kc, or more often Kic) o What are the units on Kic? o What is the Ductile-to-Brittle transition in BCC metals, and how do we measure the temperature at which this happens? In fatigue, what are mean stress, stress range, and R-ratio? And how do these affect the fatigue life (i.e., the number of cycles to failure) of a material? For an S-N curve, what do “S\" and \"N” represent? o What is a fatigue limit? And do all materials exhibit one? o What are the differences between fatigue striations and Beachmarks (also called clamshell marks)? What kind of microscope might we use to observe each one?

Solution

6) In a S-N curve S represent stress and N represent number of cycles

7)The highest stress that a material can withstand for an infinite number of cycles without breaking the material is called fatigue limit or endurance limit. each material has it\'s own separate endurance value

8)Fatigue striations are microscopic features on a fatigue fracture surface that identify one propagation cycle of a fatigue crack. They are not always present and can only be seen under a scanning electron microscope. Beach marks (also sometimes clamshell marks) are macroscopic fatigue features marking an interruption of some sort in the fatigue cracking progress. Both features are used to identify fatigue fractures. Fatigue striations can also be used to estimate number of cycles, etc.

5)Stress produced due to fluctuating loads causes most of the mechanical fatigue failures. mean stress is the average of maximum and minimun stress in the flucatuating load and stress range is the range of lower value of stress and upper value of stress. The normal fatigue life of a specimen is 10^6 cycles

4)The ductile-brittle transition is exhibited in bcc metals, such as low carbon steel, which become brittle at low temperature or at very high strain rates.In metals, plastic deformation at room temperature occurs by dislocation motion. The stress required to move a dislocation depends on the atomic bonding, crystal structure, and obstacles such as solute atoms, grain boundaries, precipitate particles and other dislocations. If the stress required to move the dislocation is too high, the metal will fail instead by the propagation of cracks and the failure will be brittle.

3)units of Fracture toughness in SI system Pa?m or mega pascal under root meter