《材料科学与工程基础》英文影印版习题及思考(16)

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subject to detection.

9.25 For thermoplastic polymers, cite five factors that favor brittle fracture.

9.26 Tabulated below are data that were gathered from a series of Charpy impact tests

on a ductile cast iron:

(a) Plot the data as impact energy versus temperature.

(b) Determine a ductile-to-brittle transition temperature as that temperature corresponding to the average of the maximum and minimum impact energies. (c) Determine a ductile-to-brittle transition temperature as that temperature at which the impact energy is 80 J.

9.27 Tabulated as follows are data that were

gathered from a series of Charpy impact

tests on a tempered 4140 steel alloy:

(a) Plot the data as impact energy

versus

temperature.

(b) Determine a ductile-to-brittle transition

temperature as that temperature

corresponding to the average of the

maximum and minimum impact energies.

(c) Determine a ductile-to-brittle transition

temperature as that temperature at which the

impact energy is 70 J.

9.28 Briefly explain why BCC and HCP metal alloys may experience a

ductile-to-brittle transition with decreasing temperature, whereas FCC alloys do not experience such a transition.

9.32 A12.5mm(0.50 in.) diameter cylindrical rod fabricated from a 2014-T6 alloy

(Figure 9.46) is subjected to a repeated tension-compression load cycling along its axis. Compute the maximum and minimum loads that will be applied to yield a fatigue life of 1.0×107 cycles. Assume that the stress plotted on the vertical axis is stress amplitude, and data were taken for a mean stress of 50 MPa(7250

psi).