Homework Assignment

1
Homework Assignment

• Appendix 1Prob. 34. (Hint First calculate the
  critical crack size at the working pressure of
  5.1 MPa using sPr/t. Then calculate the initial
  crack size ao which would grow to this critical
  size after 3000 cycles. Finally, calculate the
  pressure which would cause fast fracture with a
  pre-existing crack of size ao.)
• Appendix 1Prob. 36. (Hint Note that the rate
  of of polymer injection (e.g. mass/time) is
  proportional to e(-Q/RT).)
• Give the approximate temperature at which creep
  deformation becomes an important consideration
  for each of the following metals Al, Cu, Sn, Fe,
  Ni, W.

2
Homework Assignment--II

• For a cylindrical low carbon-nickel alloy
  specimen (see Chapt. 19 Example Problem for data)
  originally 10 mm in dia. x 500 mm long, what
  tensile load is needed to produce a total
  elongation of 3.2 mm after 10,000 hrs at 427oC?
  Assume that the sum of the instantaneous and
  primary creep elongations is 0.8 mm.

3
Homework Assignment--III

• It is known that the steady-state creep creep
  rate for nickel at 1000oC is 10-4/s at a stress
  of 15 MPa, and 10-6/s at a stress of 4.5 MPa. If
  the activation energy for creep in this material
  is 272,000 J/mole, compute the steady-state creep
  rate at a temperature of 850oC and a stress of 25
  MPa.