1. Tests For Materials

2. Mechanical testing of materials
Monocyclic strength tests
Cyclic strength tests
Monocyclic fracture toughness tests
Cyclic fracture toughness tests

3. Test for small, brittle specimens
microhardness
transverse strength
biaxial flexure strength
diametral tensile strength

4. Hardness:
Tests which measure a material’s resistance to penetration by an indentor.

5. Knoop microhardness test:
The Knoop test is frequently used in dental biomaterials research. A tiny diamond indentor is impressed in the material at a specified load and loading rate. The length of the indentation is measured.
NOTE: the shorter the indentation, the harder the material.

6. Knoop microhardness test:
eyepiece
a system of weights,
levers, and a dashpot
produce a repeatable
loading rate
objective
indentor
Moveable stage (the spec-imen is moved under the indentor and then moved under the microscope’s objective.

7. Knoop microhardness test:
The specimen is under the
indentor, which is pressed
in its surface.
The specimen is moved
under the objective and
the length of the Knoop
indentation is measured.

8. Knoop microhardness test:

9. Microhardness shows change in properties with position
in a specimen. Unfortunately, hardness is not easily correlated to strength or elastic modulus. Such correlations are the subject of a great deal of current research.

10. Test for small, brittle specimens
microhardness
transverse strength
biaxial flexure strength
diametral tensile strength

11. 300 200 100 0.2 0.4 0.6 strain (%) X Ultimate strength yield strength
point
200
100
0.2
0.4
0.6
strain (%)

12. Tests of fracture resistance:
ultimate strength tests
slow strain rate (if viscoelasticity is important)
high strain rate (if not interested in viscoelasticity

13. Transverse Tensile Strength:b d
Transverse strength
= 3 F L / ( 2 b d2 ) F
compressive
stresses
tensile
stresses
Fracture occurs on tensile
side; tensile stresses open
cracks making many materials
weaker in tension.

14. Test for small, brittle specimens
microhardness
transverse strength
biaxial flexure strength
diametral tensile strength

15. Biaxial Strength Test:
Advantages:
A major advantage of this
test is that the load is
applied well away from
the edges of the specimen.
This, minimizes the effects of stress concentrations at
the edges.
For materials that are condensable into molds biaxial test specimens are simple to make.

16. Test for small, brittle specimens
microhardness
transverse strength
biaxial flexure strength
diametral tensile strength

17. Diametral tensile test:
A tensile test for brittle materials in which a compressive load is placed parallel to the diameter of a cylindrical specimen.
Note: To be valid, the material to be tested must be very brittle. Diametral fracture will not occur if there is plastic flow.

18. Mechanical testing of materials
Monocyclic strength tests
Cyclic strength tests
Monocyclic fracture toughness tests
Cyclic fracture toughness tests

19. F

20. F

21. F

23. Fatigue Tests
A test in which a material is repeatedly subjected to stresses below it yield strength. The fatigue life is the number of load applications required to produce failure at a given stress.

24. stress 103 104 105 cycles the materials fails at lower
and lower stresses as the
number of cycles increases.
103
104
105
cycles

25. Tests of crack resistance:
impact tests (toughness tests)
un-notched
notched
fracture toughness tests
single-edge-notch bending (SENB)
compact tensile (CT)

26. Impact test

27. Tests of crack resistance:
impact tests (toughness tests)
un-notched
notched
fracture toughness tests
single-edge-notch bending (SENB)
compact tensile (CT)

28. Fracture toughness – compact tensile specimen:

29. The End