13. The maximum stress found on an S-N curve is: a. tensile b. yield c. modulus

Question

13. The maximum stress found on an S-N curve is:

a. tensile

b. yield

c. modulus

d. mean

14. Use the rule of mixtures to find the maximum modulus possible for a material that has 30 vol% glass fibers with a modulus of 89 GPa dispersed in an epoxy resin with a modulus of 3.5 GPa.

a. 63.4 GPa

b. 29.2 GPa

c. 4.9 GPa

d. 44.6 GPa

15. A hypothetical metal has the BCC crystal structure, a density of 7.24 g/cm3, and an atomic weight of 48.9 g/mol. The atomic radius of this metal is:

a. 0.122 nm

b. 1.22 nm

c. 0.0997 nm

d. 0.154 nm

Explanation / Answer

13) b) yield (yield stress limit the maximum stress that can cause damage]

b)Elastic modulus of composites=Ec=VmEm+VpEp c=composite,m=matrix=resin,p=particulate=glass fibre(rule of mixtures)

Ec=(3.5 GPa)*0.70+(89GPa)*0.30=29.15 GPa (b option)

c)mass of two atoms in bcc cell=48.9 g/mol/6.022*10^23=8.12*10^-23 g

volume of unit cell=mass/density=8.12*10^-24 g/7.24 g/cm3=1.12*10^-23 cm3

determine edge length=cube root of volume=(11.2*10^-24 cm3)^1/3=3.3*10^-8 cm3

atomic radius=r=sqrt [3d^2/16]=sqrt[3*(3.3*10^-8)^2/16]=1.42*10^-8 cm=142 pm=0.142 nm

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