Answer:
Explanation:
The missing diagram is attached in the image below which shows the deformation map of the Tungsten.
Given that:
Stress level [tex]\sigma = 160 MPa[/tex]
T = 0.5 Tm
[tex]\implies \dfrac{T}{Tm} = 0.5[/tex]
G = 160 GPa
[tex]\implies \dfrac{\sigma}{G} = 10^{-3}[/tex]
a)
The regulating creep mechanism is dislocation driven, as we can see from the deformation mechanism.
The engineer's recommendation would not be approved because increasing grain size results in a decrease in the grain-boundary count, preferring dislocation motion. The existence of grain borders is a hindrance to dislocation motion, as the dislocation principle explicitly states. To stop the motion, we'll need a substance with finer grains, which would result in more grain borders, or a material with higher pressure. In the case of Nabarro creep, which is diffusion-driven, an engineer's recommendation would be useful.
b)
If stress level reduced to [tex]\sigma = 1.6 MPa[/tex]
[tex]\implies \dfrac{\sigma }{G} = 10^{-5}[/tex]
Cable creep is now the controlling creep mode, which entails tension-driven atom diffusion along grain borders to elongate grain along the stress axis, a process known as grain-boundary diffusion. Cable creep is more common in fine-grained materials. As a result, the engineer's advice would succeed in this case. The affinity for cable creep is reduced when the grain size is increased.
c)
From the map of creep mechanism for [tex]\dfrac{\sigma}{G} = 10^{-3} \ and \ \dfrac{T}{Tm} = 0.5[/tex]
We read strain rate [tex](e) = 10^{-6}/sec[/tex]
Therefore,
[tex]Strain (E) = e * \Delta t[/tex]
[tex]= 10^{-6} \times 10000 \times 3600[/tex]
= 36
Therefore, [tex]\Delta L = E \times Li[/tex]
= [tex]36 * 10 cm[/tex]
= 360 cm
Thus, the increase in length = 360 cm
