Problem Set 5
EMA 4714 - Materials Selection and Failure Analysis
Due Wednesday, February 28, 2001 - 11:45 am
Dieter Exercise 8.8
In an aerospace application, total cost of a component can be expressed by:
Ct = Cf + CmW + PW
where: Cf = cost of fabrication
Cm = material coast, $/lb
W = weight of component, lb
P = penalty factor by which performance is jeopardized, $/lb
[a] Discuss the various strategies available to minimize Ct.
[b] Determine whether material B can be economically substituted for material A if [1] there is no
weight penalty factor and [2] the weight penallty is $100 per lb.
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[a] [i] Lower Cf by changing to a lower cost process [or a place where processing costs are lower]
or increase production rate [reducing cost per component].
[ii] Lower material cost [Cm].
[iii] Lower component weight [W] by redesign - involves analysis of function and property
relationship.
[iv] Lower W by selection of alternate [higher strength] material which is likely to be more
expensive. If CB > CA, but WB < WA, selection of material B will be justified when the total
costs of using B are less than those for using A:
CBWB < CAWA
CB < CA[WA/WB]
CB < CA/[1-f]
where f = [WA - WB]/WA
[b] assuming Cf(A) = Cf(B), when weight is penalized [P factor introduced], use of B is justified if:
CBWB + PWB < CAWA + PWA
CB < CA/[1-f] + Pf/[1-f]
f = [90 - 2]/90 = 0.978
2100B901A
W, lbCm, $/lbmaterial
