5 Written questions
5 Matching questions
- A value of 0.3 for Poisson's ratio is typical. Thus, the shear modulus is usually about ___% of the elastic modulus.
- Shear stress
- When a metal had been stressed beyond its proportional limit, the hardness and strength of the metal ________ at the area of deformation.
- Give 4 reasons why shear stress often is not the cause of fractures in oral environment.
- Flexural stress (Bending stress)
- a a. increases
although ductility of the metal ↓↓
- b Force per unit area of a material subjected to flexural loading.
- c Ratio of force to the original cross-sectional area parallel to the direction of the force applied to a test specimen.
- d 1. most restorations have rough, <b>curved</b> surfaces
2. tensile strength is <b>below</b> shear strength value
3. force must be applied exactly adjacent to the
- e 38%
5 Multiple choice questions
Change in length per unit initial length.
Units are in %
- 1. the <i>percent elongation</i> <b>after</b> fracture.
2. the <i>reduction in area </i>of the tensile test specimen
3. the max # of bends performed in a cold bend test.
- Relative ability of a material to deform physically under a <b>tensile</b> stress before it fractures
- Ultimate strength
Area or point of significantly higher stress associated with a structural discontinuity such as a crack or pore or a marked change in dimension of a structure.
5 True/False questions
Percent elongation → Maximum amount of plastic strain a tensile test specimen can sustain before it fractures (See Ductility).
Proportional limit →
line below which the material will NEVER fail under an
infinite amount of cycles: IDEAL!!!!
Materials with a high elastic modulus have:
a. high strength values.
b. low strength values. → ????
What does the straight line in the strain-stress curve represent? → flaws on the surface are associated with higher stresses than are flaws of the same size in interior regions. Thus surface finishing of brittle materials such as ceramics, amalgams, and composites is extremely important in areas subjected to tensile stress.
the restorative material should exhibit a moderately ____ elastic modulus and relatively ____ resilience, thereby limiting the elastic strain that is produced. → ↑ elastic modulus