1.5 solids under stress Flashcards
(33 cards)
What does Hooke’s Law state?
For an elastic spring, the extension is directly proportional to the force applied to its end.
How is strain (ε) defined?
Strain is defined as extension divided by original length: ε = Δl/l.
What are tensile properties?
Stress and strain are both tensile properties used when a material is in tension.
How is stress (σ) defined?
Stress is defined as force divided by cross-sectional area: σ = F/A.
What is Young Modulus (E)?
The Young modulus is the ratio of stress to strain when the sample is obeying Hooke’s law: E = σ/ε.
What does the area under a force-extension graph represent?
The area under the force-extension graph is equal to the work done in extending the material.
What is elastic extension?
The wire returns to its original shape when the load/force is removed.
What is plastic extension?
From point X to point Y, the material extends plastically and does not return to its original shape.
What is the elastic potential energy equation?
The work done in extending the material elastically is equal to W = 1/2 kx^2.
What is the elastic region?
The region where Hooke’s law applies and the material can return to its original shape.
What are crystalline solids?
Materials with atoms arranged in an ordered structure making a crystal lattice.
What are amorphous solids?
Solids that do not have a long-range ordered structure.
What are polymeric solids?
Solids made from long chains of molecules, which can exhibit elastic behavior.
What is permanent deformation?
When the material extends beyond the elastic region, it undergoes permanent deformation.
What does the work done equal in a force-extension graph?
The work done is equal to the area under the force-extension graph.
What is bond breaking?
Additional work done beyond the elastic region is used to break bonds in the material.
What does ductile mean?
Can be drawn out into a wire.
What does tough mean?
Absorb a lot of energy before breaking.
What does amorphous refer to?
Materials where the atoms or molecules are arranged in a non-ordered structure.
What does polymeric refer to?
Materials that contain long chain polymer molecules.
What are cross-links?
Where chains are tied together to make polymer chains stiffer.
What are dislocations?
Small gaps in the ordered structure of crystalline materials that allow planes of atoms to slip more easily.
What are foreign atoms?
Atoms introduced to fill gaps in dislocations to prevent them from moving.
What are grain boundaries?
Creating more of these means fewer dislocations per grain, making it harder for dislocations to move.
