chapter 6 - materials Flashcards

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1
Q

tensile force

A

produces an extension

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2
Q

compressive force

A

reduces the length of an object

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3
Q

hookes law

A

force is proportional to extension so long as elastic limit isn’t exceeded
F = kx
- its device specific - changes for every spring

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4
Q

spring constant k

A

k = F/x
gradient of an F x graph
stiffer spring = greater k

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5
Q

elastic deformation

A

before elastic limit - object will return to original shape when load is removed

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6
Q

plastic deformation

A

after elastic limit
permenant change in shape that remains when load is removed

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7
Q

area under force extension graph

A

work done in stretching the object

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8
Q

elastic material

A

will return to origional shape

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9
Q

tensile stress

A

force applied per unit cross sectional area
F/A (Pa)

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10
Q

tensile strain

A

fractional change in length of object
x/L

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11
Q

Youngs modulus

A

stress/ strain = FL/Ax
(Pa)
stiffness - higher YM means it is more stiff
gradient of stress strain graph

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12
Q

ductile material

A

can be drawn into wire or hammered into thin sheets
- behave elastically until elastic limit after it stretches more and has plastic behaviour
- a straight graph that then curves

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13
Q

brittle material

A

snaps easily
- stretches slightly then fractures
- elastic behaviour up until point of fracture
- behaves same both ways (unloading and loading)
- straight graph

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14
Q

limit of proportionality of a material

A

point at which a material stops obeying hooks law

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15
Q

ultimate tensile strength of materials

A

maximum stress a material withstands before breaking
- end of a stress strain graphs

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16
Q

measure to what dp

A

the dp you can measure to
- has to be the same for even your average
- can’t have a value more accurate than your measuring devices

17
Q

breaking strength of a material

A

stress at the point of fracture

18
Q

what is a strong material

A

one with a high ultimate tensile strength

19
Q

when does Young modulus apply to a material

A

when stress is proportional to strain OR when its obeying hooks law

20
Q

how do you find young modulus from a stress-strain graph

A

gradient of the initial straight line region

21
Q

polymeric materiaal

A

material made from long chain molecules
behaviour depends on temp as well as molecular structure

22
Q

elastic limit

A

beyond which the material becomes permanently deformed
- won’t return to normal when load removed

23
Q

young modulus experiment

A
  • measure diameter
  • calculate CSA
  • find original length
  • increase load
  • record mass, and find extension
  • plot graph (stress/strain)
  • calculate gradient = YM
24
Q

elastic behaviour

A

returns to original length when load is removed
- all materials show it till the elastic limit

25
Q

plastic behaviour

A

shown when materials are loaded above the beyond the elastic limit - permanently deformed

26
Q

elastic potential energy

A
  • energy stored when a solid is stretched/compressed
  • if strained elastically energy can be recovered - if plastically some work done has gone into moving atoms so is lost
  • area under F x graph before elastic limit
  • E = 1/2Fx = 1/2kx^2
27
Q
A
28
Q
A