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FOSC301 > Rheology > Flashcards

Rheology Flashcards

1
Q

define texture

A

response of tactile senses to physical stimuli that result from contact between some part of the body and the food

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2
Q

what is the tactile sense?

A

touch

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3
Q

what is kinesthesics

A

sense of movement and position

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4
Q

senses used to evaluate the texture

A

touch
kinethesis
sight
sound

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5
Q

define rheology

A

science of dealing with deformation and flow of materials
-properties that govern a material stress/strain relationship

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6
Q

difference between rheology and texture

A

Texture is subjective
rheo is measurable, well-defined geometry and sample shape, instrument independent (mechanical properties)

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7
Q

why is rheo important

A

Design, operation, and optimization of processes (pumping, mixing, spraying, emulsifying, filling)
behaviour of packaging material under load
consumer perception of consistency or texture of foods (flow, gel strength, crunchiness, tenderness)

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8
Q

Rheology in food context

A

designing machines
determining ingredient functionality
quality control
shelf life testing
investigation of sensory attributes

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9
Q

what is a food rheological affected by

A

temperature
material history
composition
microstructure

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10
Q

sources of force

A

processing plant: pump, agitator, milling
storage: weight of product stacked above gravity
applied by the consumer: breaking, chewing
lab instruments: viscometers, TPA

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11
Q

types of rheological tests

A

compression
tension
shearing

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12
Q

what is compression

A

applied stress is directed towards the material

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13
Q

describe tension

A

applied stress is directed away from the material

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14
Q

describe shear

A

applied stress is tangential
-cutting/sliding

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15
Q

stress equation

A

force/area

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16
Q

strain equation

A

change in dimension/ original dimension

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17
Q

when will deformation occur

A

when the stress applied is higehr than the force keeping it intact

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18
Q

what happens to the volume during compression

A

nothing, it stays the same for solid material

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19
Q

why doesn’t the volume change

A

the height decreases but diameter increases

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20
Q

what is barrelling

A

when a sample being compressed begins to bulge into a barrel-shape

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21
Q

how can barreling be avoided?

A

applying oil

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22
Q

Why is barreling unwanted

A

the area is used to calculate the force, barreling changes the area

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23
Q

3 sections of a deformation curve

A

linear elastic
elastic buckling
densification

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24
Q

what is Ff

A

force at fracture

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25
what is Ff important for
understanding how a material behaves -important to consider when stacking/transporting
26
describe the shape of a deformation curve
lightning bolt
27
Another name for the slope of the line on the deformation curve
modulus of elasticity
28
describe the shape of the first linear elastic part of the curve
linear
29
where is the limit of elasticity
the end of the linear elastic section
30
what is the limit of elasticity?
the point at which if stress is removed then no permanent deformation will occur
31
what is the fracture point of a material dependent on
composition physical and chemical interactions taking place within the material
32
what happens in the elastic buckling phase of the curve
deformation is occuring
33
what happens during densification
the material becomes condensed
34
greek symbol for stress
tau
35
greek symbol for strain
gamma
36
equation to work out stress from strain
tau = E(gamma) * gamma
37
what is the effect of force on a solid
deform elastically unless too high in which case it breaks
38
key parameters for solid deformation
amount of deformation for given applied force maximum force while still being elastic maximum force that will cause breakage
39
effect force has on liquid
deform irreversibly
40
key parameter for force on a liquid
relationship between the rate of deformation and applied force
41
example of semi-solid material
cheese
42
a semi-solid material will have both liquid and solid properties depending on...
the magnitude of force applied time-frame observation
43
what is time-frame observation
observing what is happenign at single time points (snapshots)
44
Type of stress used to test in material science
tension
45
type of stress used to test in food science
compression
46
what two things can happen after yeild point is reached
brittle materials fracture plastic materials begin to flow
47
what kind of stress yeild do strong materials have
high
48
what is the modulus of elasticity a measure of
stiffness
49
define hardness
resistance to indentation
50
how is hardness measured
size of indentation left by a fixed load force required for a fixed depth of indentation
51
what levels are hardness measurements performed at
well above stress of a material
52
define brittleness/toughness
measure of the fracture behaviour
53
how can toughness be estimated
integrating the area under the stress/strain curve
54
what happens when force is applied to brittle material
a crack propagates easily once formed and little energy input to generate a fracture
55
relationship increased temp has with hardness stiffness brittleness
they all decrease
56
geometry of emprical tests
flat plates probes cutting wire or blades 3 point bending jig extrusion jig
57
terms used to define texture
adhesiveness bounce chewiness cohesiveness gumminess roughness viscosity
58
define adhesiveness
force required to remove a material that adheres to a specific surface
59
define bounce
resilience rate at which a sample returns to the original shape after partial compression
60
define chewinesss
number of chews needed to masticate the sample to consistency suitable for swallowing
61
define cohesiveness
degree to which the sample deforms before rupturing when biting with molars
62
define gumminess
energy required to disintegrate a semi-solid food to a state ready for swallowing
63
define roughness
degree of abrasiveness of a product surface perceived by the tongue
64
define viscosity
force required to draw a liquid from a spoon over the tongue
65
symbol used to describe a viscous body
dashpot
66
symbol used to describe a elastic body
spring
67
three ways to characterise the viscoelasticity of a food material
dashpot, spring, sliding frictional
68
what is the deborah number
dimensionless number used to charaterise the fluidity of material under specific flow conditions
69
De value for fluids
<<1
70
De values for solids
>>1
71
what is the viscosity of newtonian fluids dependant on
temperature
72
what makes a fluid non-newtonian
doesnt have a linear stress/strain relationship
73
how are shear stress and shear rate linked
by viscosity
74
what is viscosity
a materials resistance to flow
75
shape of relationship newt fluids have with shear rate and shear stress
linear
76
types of fluids
bingham plastic herschal-buckley psuedoplastic newtonian dilatant
77
what is yield stress
a material required stress to generate a response
78
examples of fluids that require yeild stress
bingham plastic herschel buckley
79
example of shear thinning fluids
hershel buckley pseudoplastic
80
example of shear thickening fluids
dilatant
81
what is shear thickening
fluid thickens upon shearing
82
what is shear thinning
fluid thins upon shearing
83
examples of bingham plastic fluids
mayo playdough dessert sauces
84
example of dilatant fluids
paint, corn starch dispersion
85
example of pseudo plastic
most hydrocolloids
86
what is important when enrobbing chocolate
yield stress
87
What component of chocolate decreases yield stress
increasing fat
88
what can low yeild stress lead to in chocolate
thin layer, mishapen product, tails, poor decoration
89
what can high yeild stress lead to in chocolate
thick layer, incomplete coverage, prominent decoration, poor handling
90
other food example of plastic like materials
butter and marg, mayo, tomato paste
91
what is responsible for yeild stress in -butter -mayo -tomaot paste
fat oil phase emulsion (oil in gel structure) fibre/pulp
92
describe the flow profile of a dilatant fluid
viscosity increases with yeild stress
93
describe the flow profile of a Bingham plastic and pseudoplastic with yield stress
viscosity decreases
94
what is thixotropy
decrease in viscosity with shearing
95
what is rheopexy
increase in viscosity with shearing
96
example of rheopexy
whipping cream
97
what are the simplest viscometer based on
capillary or falling ball -time for the liquid level or ball to fall
98
What do the rotational viscometer measure
torque required to turn a rotor iin submerged liquid
99
what viscometers are favoured in theoretical studies and why
cylinder, cone and plate geometries -they have a well-defined shear rate
100
how is viscoelastic behaviour normally evaluated
oscillatory rheometer
101
what does oscillatory rheometry provide
information about microstructure small scale deformation measure strain from specific stress separate elastic and viscous components of moduli
102
What does oscillatory rheometry involve
small amplitudes of oscillation are applied while measuring the stress and strain waves + the phase angle (delta)
103
what is G'
storage modulus -measure of the solid behaviour of the material
104
what is G''
loss modulus -measure of the liquid behaviour
105
the ratio between these is often _____
reported/quoted
106
what is the weisenburg effect
creation of a different shape around a tube when placed in a viscoelastic fluid
107
what is self-siphoning
the ability of a viscoelastic fluid to siphon itself out of a tube
108
what is jet swell
The ability of a viscoelastic fluid to remember the shape of a tube after exiting
109
3 levels of structure that affect rheology
molecular microscopic macroscopic
110
what is meant by molecular structure
denaturation of proteins cross-linking between polymers
111
How does microscopic structure affect rheology
-Fat crystals in networks spread- only part of the structure returns when disrupted, hence work softening behavior -a network of aggregated particles - time constant associated with particles re-aggregating
112
how does the macroscopic structure affect rheology
air cells in bread cracks and slits
113

FOSC301 (17 decks)

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