5 Written Questions
5 Matching Questions
- fatigue failure
- As the interatomic spacing increases, the internal energy increases. As long as the stress is <b>not greater than the proportional limit</b>, this <u>energy</u> is known as__________.
- Yield strength
- A _______ stress is caused by a load that tends to stretch or elongate a body.
- a b. tensile
Repeated stresses resulting in fractures. the fracture due to fatigue occurs at stress levels well below tensile strength.
- c resilience
the term resilience is associated with 'springiness'
Change in length per unit initial length.
Units are in %
• The <b>stress</b> at which a test specimen exhibits a specific amount of plastic strain (0.2%)
• The YS at 0.2% strain offset from the origin is 1536 MPa in this case.
5 Multiple Choice Questions
- Ultimate strength
- Stress and/or strain
- Ability of a material to absorb elastic energy and to deform plastically before fracturing; measured as the total area under a plot of tensile stress vs. tensile strain.
- 1. <b>strain rate</b>
2. the shape of the test speciment
3. the surface finish (control flaws)
4. the environment in which material is tested
- Relative stiffness of a material; ratio of elastic stress to elastic strain
5 True/False Questions
Materials with a high elastic modulus have:
a. high strength values.
b. low strength values. →
dentin → 50 MPa
enamel → 10 MPa
Two important aspects of microscopic flaws in brittle materials: → 1. tensile stress
2. shear stress
3. compressive stress
Units of Modulus of elasticity →
Maximum stress at which stress is proportional to strain and above which plastic deformation occurs.
in this case: PL= 1020 MPa
Tensile strength for:
a. Dental porcelain
c. Resin-based composite
e. Alumnia ceramic → a. Dental porcelain → 50-100 MPa
b. Amalgam → 27-55 MPa
c. Resin-based composite → 30-90 MPa
d. Poly → 60 MPa
e. Alumnia ceramic → 120 MPa
Stress concentration → Maximum amount of plastic strain a tensile test specimen can sustain before it fractures (See Ductility).