Photo-elasticity Tutorial sheet Flashcards
Define “Collimated light beam”
A light beam (or rays of light) that has been made accurately parallel
Define “monochromatic light beam”
A light beam containing only one colour/wavelength
Define “dark field polariscope”
A polariscope that has its polariser and its analyser perpendicular to each other
How do you count the fringes from an object in a dark field polariscope
Count fringes in integers, start from 0 (e.g. 0,1,2,3 etc..) - start from a point of no strain
Count the dark fringes
Define “light field polariscope”
A ploariscope that has its polariser and its analyser in the same orientation as each other
How do you count the fringes from an object in a light field polariscope
Count fringes in half integers, start from 0.5 (e.g. 0.5,1.5,2.5 etc..) - count the dark fringes
Define polariscope
A polariscope is a device through which we can observe the effects of birefringence/temporary birefringence
What are the three crack modes
Mode I - Opening
Mode II - In plane shear
Mode III - Out of plane shear
How would you prepare a component for reflection photoelasticity? (5 Points)
Clean component - Use a solvent to remove grease
Cast epoxy sheet in a flat mold - remove once polymerised into its rubbery state
Form epoxy to the shape of component surface - wait for the polymerisation to be completed
Remove epoxy mold from component as a rigid shell - Measure the shell thickness
Attach shell to component with an adhesive containing a reflective agent - e.g. chrome disks) -
(Shell should not bridge any crack/reinforce any component)
If a component had a constant load applied to it over a long period of time, how would its photoelastic stress response change? (2 points)
- Time edge effects may appear initially but they would fade as the disk reaches equilibrium with the atmosphere
- Component will exhibit creep causing strain levels to increase - this will cause fringe orders to increase
