Above or below what Youngs and Rigidity modulus is a material considered flexible?
so what engineering term would I use to measure stiffness?
- CurlyLv 61 decade agoFavorite Answer
Flexible isnt used much in the engineering vernacular.
Rigidity modulus was not used in my classes, but shear modulus was.
Rigid is and it means a relatively high modulus.
Ductile means that it can be deformed greatly without failure. Copper is ductile.
Toughness is related to the area under the deformation-load curve.
The Dictionary of Architecture and Construction, edited by Cyril M. Harris, published by The McGraw-Hill Companies, Inc.defines flexibility of a material as:
The property of a material that allows it to bend without damage (and without losing its strength) and then to return to its original shape.
So the ideal material for this is going to have a high yield strength, and a low modulus.
A handbook of encapsulants gives the following:
Flexural Strength and Flexural Modulus, ASTM D790. Flexural strength is a three-point bending
test run on molded test bars typically 1/8 by 1/2 by 5 inches. Flexural modulus is an indication of the elasticity
of the material being tested. The higher the modulus, the less compliant is the material. The flexural
strength test is often run at 215 to 260°C to simulate conditions in solder reflow. Flexural strength
and modulus are important factors in controlling stress-related cracking and delamination. Many
stress models have been published, with most including thermal expansion and flexural modulus as
the main factors. A useful model for comparing stress of different encapsulants on a silicon die is
S= stress index
Ea = expansion of the mold compound
Esi = expansion of the silicon chip
M = flexural modulus of the mold compound
Ideally, an encapsulant should have high flexural strength with low flexural modulus. High flexural strength is needed to withstand the mechanical stress of bending under pressure. Low modulus adds flexibility, allowing an encapsulant to yield without breaking.
Bottom line: these terms are only meaningful in the context of a family of materials. Every problem has different materials requirements, and these terms are valid in all of those subsets.
There is no globally universal definition of flexibility, but there are many local definitions that are valid and useful.
- Back WLv 61 decade ago
When a material is subjected to stress and it has the ability to return to its original shape... its flexible.