FLEXURAL STRENGTH AND MODULUS
Flexural strength is the measure of the stiffness of a material, that is to say how well it resists bending.
Testing Strength and Modulus
A simple beam of material is supported either end and a load applied at the mid-point. The load is pushed onto the specimen at a constant rate of 2mm per minute.
Measurements are taken using at least five values of load and deflection. From these results a deflection curve is plotted from which the flexural modulus is calculated. As with tensile modulus this is a ratio of stress to strain. Values are reported in MPa (psi).
The only difference between ASTM D790 and ISO 178 is the size of the test bar – 125mm x 12.5mm x 3mm and 80mm x 10mm x 4mm respectively. Therefore, the values reported in ASTM and ISO seldom differ significantly.
Typical results for a selection of materials as follows:
|Material||Flex Strength||Flex Modulus|
|30% Glass Filled Acetal||150||7.5|
There are various measures which are defined as follows:
|Flexural Modulus||The ratio of stress to strain|
|Flexural Stress at Yield||The stress corresponding to test specimen yield|
|Flexural Stress at Break||The stress corresponding to test specimen failure|
|Flexural Strength||The maximum stress sustained by a specimen during testing|