three point flexural test について

and the flexural stress-strain response of the material. The main advantage of a three point flexural test is the ease of the specimen preparation and testing. However, this method has also some disadvantages: the results of the testing method are sensitive to specimen and loading geometry and strain rate.
== Testing method ==
The test method for conducting the test usually involves a specified test fixture on a universal testing machine. Details of the test preparation, conditioning, and conduct affect the test results. The sample is placed on two supporting pins a set distance apart and a third loading pin is lowered from above at a constant rate until sample failure.
Calculation of the flexural stress

\sigma_f

\sigma_f = \frac

for a rectangular cross section
:

\sigma_f = \frac

for a circular cross section
Calculation of the flexural strain

\epsilon_f

\epsilon_f = \frac

Calculation of flexural modulus

E_f

E_f = \frac

in these formulas the following parameters are used:
*

\sigma_f

= Stress in outer fibers at midpoint, (MPa)
*

\epsilon_f

= Strain in the outer surface, (mm/mm)
*

E_f

= flexural Modulus of elasticity,(MPa)
*

F

= load at a given point on the load deflection curve, (N)
*

L

= Support span, (mm)
*

b

= Width of test beam, (mm)
*

d

= Depth of tested beam, (mm)
*

D

= maximum deflection of the center of the beam, (mm)
*

m

= The gradient (i.e., slope) of the initial straight-line portion of the load deflection
curve,(P/D), (N/mm)
*

R

= The radius of the beam, (mm)

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