1. ST
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BEN TES
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By:- Krishna Kr. Hansdah
2. FLEXURAL TEST
In engineering mechanics, flexure or bending characterizes
the behavior of a slender structural element subjected to an
external load applied perpendicularly to a longitudinal axis
of the element.
Typical Materials used for Flexural Test
1.Polymers
2.Wood And Composites
3.Brittle Materials
4. WHY PERFORM A FLEXURE TEST?
A flexure test produces tensile stress in the convex side of the specimen
and compression stress in the concave side. This creates an area of shear
stress along the midline. To ensure the primary failure comes from tensile
or compression stress the shear stress must be minimized. This is done
by controlling the span to depth ratio; the length of the outer span divided
by the height (depth) of the specimen.
For most materials S/d=16 is acceptable.
Some materials require S/d=32 to 64 to
keep the shear stress low enough.
5. The Flexural test measures the force required to bend a
beam under 3-point loading conditions.
The data is often used to select materials for parts that will
support loads without flexing.
Flexural modulus is used as an indication of a material’s
stiffness when flexed.
6. 3-POINT BEND TEST
In this test a specimen with rectangular or flat cross-section is placed on two
parallel supporting pins. The loading force is applied in the middle by means
loading pin.
The supporting and loading pins are mounted in a way, allowing their free
rotation about:
-axis parallel to the pin axis;
-axis parallel to the specimen axis.
7. It provides values for the modulus of elasticity in bending , flexural stress ,
flexural strain and the flexural stress-strain response of the material.
Advantage -ease of the specimen preparation and testing.
Disadvantage -the results of the testing method are sensitive to specimen
and loading geometry and strain rate.
Flexural strength or modulus of rupture -The stress required to fracture a
specimen in a bend test.
Flexural modulus - The modulus of elasticity calculated from the results of a
bend test, giving the slope of the stress-deflection curve.
8.
9. TESTING METHOD
For a rectangular cross section,
Calculation of the flexural stress ,
Calculation of the flexural strain ,
Calculation of flexural modulus ,
10. where,
= Stress in outer fibers at midpoint, (MPa)
= Strain in the outer surface, (mm/mm)
= flexural Modulus of elasticity,(MPa)
P= 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)
