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Questions and Answers
What character does recoverable strain primarily indicate in viscoelastic materials?
Which polysaccharide gel is known for showing almost complete recovery after stress is removed?
In the context of viscoelastic materials, what does irrecoverable strain represent?
Which material shows minimal recovery when the stress is removed due to its liquid-like response?
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What characteristic do 'weak gel' networks like Xanthan exhibit during stress application?
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What does the yield stress represent in Bingham Plastic fluids?
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In the Herschel-Bulkeley model, which equation represents the relationship between shear stress and shear rate?
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Which statement best describes Casson fluids?
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How is the Casson viscosity index determined from a plot of g1/2 vs t1/2?
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Which of the following behaviors is characteristic of viscoelastic materials?
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What is a primary purpose of creep testing in viscoelastic materials?
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In creep testing, what happens after the stress is removed from a viscoelastic material?
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What phenomenon describes how a solid-like sample's strain increases with time under a fixed stress in creep testing?
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Which of the following statements about the recovery phase in creep testing is true?
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What key factor is often altered in developing reduced fat chocolate in relation to creep testing?
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In which format are creep and stress relaxation tests most commonly performed?
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What does stress relaxation testing primarily measure?
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Which of the following behaviors characterizes viscoelastic materials when subjected to creep testing?
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Study Notes
Creep-Recovery Testing
- Creep-recovery testing is used to determine the viscoelastic properties of materials.
- A fixed stress is applied to a material and the strain is recorded over time.
- This is called creep or retardation.
- The stress is then removed and the strain is recorded again over time, referred to as recovery or relaxation.
Creep-Recovery Curves for Polysaccharides
- Carrageenan gels show almost complete recovery when the stress is removed, indicating a strong elastic component.
- Guar Gum solutions demonstrate a predominantly liquid-like response with little to no recovery, indicating a viscous nature.
- Xanthan solutions, categorized as “weak gels”, show notable elastic recovery despite substantial flow during the creep period, indicating a balance between elastic and viscous behavior.
Creep-Recovery Curves for Acid ‘Milk’ Gels
- Acidified cow’s, soy, and quinoa milk all exhibit viscoelastic properties.
- Cow’s milk demonstrates the highest gel strength.
- The compliance of all milks changes significantly with increasing stress.
Creep Testing of Ideal Materials
- Ideal Solid Materials: The strain increases instantaneously upon stress application and completely recovers upon stress removal.
- Ideal Liquid Materials: Strain increases linearly with time under constant stress.
- Viscoelastic Materials: The strain increases gradually under constant stress and partially recovers upon stress removal.
Viscoelastic Rheological Behaviour
- Bingham Plastic Materials: Exhibit Newtonian flow above a certain yield stress.
- Herschel-Bulkeley Model describes the relationship between shear stress, yield stress, consistency index, shear rate index, and plastic viscosity for Bingham plastic materials.
- Casson Model is another equation that can be used to determine the yield stress and plastic viscosity of Bingham plastic materials.
Yield Stress – Importance in Chocolate
- Enrobing: Chocolate's yield stress determines its ability to evenly coat surfaces.
- Reducing Fat Content: Emulsifiers are used to mimic the flow properties of full-fat chocolate in reduced-fat chocolate, helping maintain appropriate viscosity.
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Description
This quiz explores creep-recovery testing, a method used to evaluate the viscoelastic properties of materials such as gels and fluids. It covers the behavior of various polysaccharides and acid milk gels under stress conditions and the implications of their recovery traits. Test your understanding of these crucial material properties and their applications.
