How is the yield point or yield strength defined?
the stress (or strain) at which a material begins to deform plastically
How does a material deform before reaching its yield point?
elastically
In which configeration can a yield point be determined?
tension, compression, torsion, flexure
Describe the three ways to identify the yield point in stress-strain diagramms.
Name the two points
How is the hydrostatic pressure calculated?
How is the hydrostatic component applied to a stress tensor?
How does geometric instability look on a stress strain curve?
How is the true strain in a stress strain curve calculated?
What is the difference between true stress and engineering stress?
What is the instability condition for geometric instability in a true stress engineering strain curve?
from
What is the instability condition for geometric instability in a true stress true strain curve?
What are the two main mechanisms for polymer yielding?
shear yielding
crazing
How is shearing characterized in Polymers?
Formation of shear bands at 45°
no volume variations
What is meant by crazing in the context of polymer yielding
Microcavitation in volume increasing stresses (eg. elongation) which are connect by poymeric fibres.
Development perpendicular to applied stress.
Which parameters effect the yield strength of polymers?
crystallinity degree
molecular orientation
average molar weight
enviromental conditions
temperature
strain rate
How can the yield strength dependancy of polymers on the temperature be described?
Eyring equation:
How do polymers strain harden?
By the orientation of the inner polymeric chains
How can the relation between grain size and yield strength be described?
Hall Petch relationship:
How is the Temperature dependency of the yield strength described in metals?
Arrhenius equation
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