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Flexure Test

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The flexure test method measures behavior of materials subjected to simple beam loading. It is also called atransverse beam test with some materials.Maximum fiber stressand maximum strain are calculated forincrements of load. Results are plotted in astress-strain diagram. Flexural strength is defined as the maximumstress in the outermost fiber. This is calculated at the surface of the specimen on the convex or tension side.Flexural modulus is calculated from the slope of the stress vs. deflection curve. If the curve has no linear regiona secantline is fitted to the curve to determine slope.

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Flexure !verview"onfigurations

Standards

Why Perform a Flexure Test?

Flex testing produces tensile stress in the convex side of the specimen and compression stress in the concaveside. This creates an area of shear stress along the midline. To ensure the primar# failure comes from tensile orcompression stress the shear stress must be minimi$ed. This is done b# controlling the span to depth ratio% thelength of the outer span divided b# the height &depth' of the specimen. For most materials S(d)*+ is acceptable.Some materials re,uire S(d) to +/ to 0eep the shear stress low enough.

Types of Flex Tests

Flex testing is often done on relativel# flexible materials such as pol#merswood and composites. There are two test t#pes% -point flex and /-point flex. In a -point test the area ofuniform stress is ,uite small and concentrated under the center loading point. In a /-point test the area ofuniform stress exists between the inner span loading points &t#picall# half the outer span length'.

Typical Materials

Polymers

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The -point test is the most common for pol#mers. Specimen deflection is usuall# measured b# the crossheadposition. Test results include flexural strength and flexural modulus.

Wood and Composites

The /-point test is common for wood and composites. The /-point test re,uires a deflectometer to accuratel#measure specimen deflection at the center of the support span. Test results include flexural strength and flexural

modulus.

Brittle Materials

1hen a -point flex test is done on a brittle material li0e ceramic or concrete it is often called modulus of rupture&M!R'.This test provides flex strengthdata onl# not stiffness&modulus'. The /-point test can also be used onbrittle materials. 2lignment of the support and loading anvils is critical with brittle materials. The test fixture forthese materials usuall# has self-aligning anvils.

Flexure - Test Standards

STM

D790-02Standard Test Methods for Flexural 3roperties of 4nreinforced and Reinforced 3lastics and

5lectrical Insulating Materials

D6272-02Standard Test Method for Flexural 3roperties of 4nreinforced and Reinforced 3lastics and

5lectrical Insulating Materials b# Four-3oint 6ending

C393-00Standard Test Method for Flexural 3roperties of Sandwich "onstructions

C78-02Standard Test Method for Flexural Strength of "oncrete &4sing Simple 6eam with Third-3oint

7oading'

C293-02Standard Test Method for Flexural Strength of "oncrete &4sing Simple 6eam 1ith "enter-

3oint 7oading'

C1161-02bStandard Test Method for Flexural Strength of 2dvanced "eramics at 2mbient Temperature

D143-94(2000)e1Standard Test Methods for Small "lear Specimens of Timber

D6109-97e1Standard Test Methods for Flexural 3roperties of 4nreinforced and Reinforced 3lastic

7umber

D198-99Standard Test Methods of Static Tests of 7umber in Structural Si$es

C1341-00Standard Test Method for Flexural 3roperties of "ontinuous Fiber-Reinforced 2dvanced

"eramic "omposites

D5572-95(1999)Standard Specification for 2dhesives 4sed for Finger 8oints in 9onstructural 7umber

3roducts

!S"

178:20013lastics - :etermination of Flexural 3roperties

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