S.S. Brenner, (Jour.Appl.Phys., 27 1484 [1956]), has reported that iron whisker single crystals may have a tensile strength of 13,130 MPa. Assume that the iron whiskers have a <100> orientation; that is, a <100> direction of the crystal lies along its central axis.

Question

(a) Compute the magnitude of the shear stress on the most highly stressed {110}<111> slip systems when the ultimate tensile strength is attained. How many of these slip systems are there?
(b) The shear modulus, µ, along a <100> direction of a {110} plane is 59,810 MPa. Compute the ratio of ?tmax/u.
(c) According to theoretical calculations, the maximum shear strength of a crystal should be ofthe order of 10u ? to 30u? . How does the value obtained in (b) of this problem compare to the theoretical predictions?
(d) Now assume that one of the slip planes is ideally oriented, so as to have both ? and ? in the resolved shear stress equation equal to 45 degrees, and compute ?tmax/u
(e) On the basis of these calculations, what can one conclude about the occurrence of slip in the iron whiskers? Does this signify anything about the perfection of the crystal structure in the iron crystal whiskers?

Answer 1