New Lecture 12 Strain Gauge second half

Question 1

Why are residual stresses present in unloaded components? (3) Give specific examples of processes (5)

Answer 1

Fabrication processes (casting, rolling, welding, stamping, forging), assemble, plastic loading

Question 2

Matrix solidification and variation in laminate thermal expansion cause residual stresses in fibre reinforced composites. Why might these be intentional? (2)
Why are they undesirable?

Answer 2

Shot-peening, Tempering glass

They are difficult to measure and add stresses due to applied loads

Question 3

When could you use hole drilling methods? (monitoring change in stress when hole is drilled) (2)

Give examples (4)

Answer 3

When semi-destructive testing is applicable (hole is relatively insignificant and easily repaired)

When structure is large / flat

Fillets, welds, castings, rolled shapes

Question 4

Difference between stresses before and after drilling can be calculated using what variables?

Answer 4

Question 5

LIMITING ASSUMPTIONS:
Stresses do not vary with _____, therefore not applicable to __ geometeries
The plate is very _____ with respect to the ____
The hole is drilled __________ though the plate
The residual stresses _____ _________ly

Answer 5

Stresses do not vary with depth, therefore not applicable to 3D geometeries
The plate is very large with respect to the hole
The hole is drilled completely though the plate
The residual stresses relax elastically

Question 6

Basic Method for Biaxial residual stresses?

Answer 6

Place strain gauge rosette halfway centre and corner of plate. (Guage B between A and C)
Use readings and mohrs circle/equations to find principal stresses

Question 7

Why are Strain gauges the most widely used of the methods covered so far?

Answer 7

SIMPLE
ACCURATE
COST EFFECTIVE

Question 8

Summarise Advantages of Strain gauge method

Measures ______ component
Determines principal strains and their __________
___________ stable w.r.t. temperature and ____
Gauges exhibit ______ response over large strain _____
Many ____________

Answer 8

Measures actual component
Determines principal strains and their directions
Calibration stable w.r.t. temperature and time
Gauges exhibit linear response over large strain range
Many Applications

Question 9

Summarise Disadavantages

Only measures at _____
not ____-_____
_____ ______ must be selected carefully
strain ________ effects
De_______ can cause spurious results
Some SGs can be susceptible to ___________ changes

Answer 9

Only measures at point
not full-field
Gauge length must be selected carefully
strain gradient effects
Debonding can cause spurious results
Some SGs can be susceptible to temperature changes