what is th edifference between stiffness and strength?

Question

here have a question ask me about resistance to elastice bending. is this a property about stiffness or strength? so i am confused with stiffness and strength.

Answer 1

Stiffness is a material's resistance to deformation, while strength is its ability to endure stress without fracturing. Deformation includes bending and elongation; a material with greater stiffness (quantified by such properties as Young's modulus and shear modulus) will deform less under a given load than a material with lower stiffness. So your question about resistance to elastic bending refers to stiffness. On the other hand, strength refers to the load at which the material will yield (deform plastically, i.e., permanently, instead of the elastic deformation that goes away when the load is removed)or break. There is not necessarily a correlation between stiffness and strength.

Answer 2

Stiffness is the resistance of an elastic body to deflection or deformation by an applied force. It is an extensive material property.

[edit] Definition
The stiffness k of a body that deflects a distance δ under an applied force P is


In the International System of Units, stiffness is typically measured in newtons per metre.

As both the applied force and deflection are vectors (respectively P and δ), in general their relationship is characterised by a stiffness matrix, k where:

P = k δ.
The deflection can, in general, refer to a point distinct from that where the force is applied and a complicated structure will not deflect purely in the same direction as an applied force. The stiffness matrix enables such systems to be characterised in straightforward terms.

The inverse of stiffness is compliance, typically measured in units of metres per newton.


[edit] Rotational stiffness
A body may also have a rotational stiffness, where the stiffness k for a rotation θ under an applied moment M is


In the S.I. system, rotational stiffness is typically measured in newton-metres per radian.

Further measures of stiffness are derived on a similar basis, including:

shear stiffness - ratio of applied shear force to shear deformation
torsional stiffness - ratio of applied torsion moment to angle of twist

[edit] Relationship to elasticity
In general, elastic modulus is not the same as stiffness. Elastic modulus is a property of the constituent material; stiffness is a property of a solid body. That is, the modulus is a property of the material; stiffness, on the other hand, is a property of the solid body dependent on the material and the shape and boundary conditions. For example, for an element in tension or compression, the axial stiffness is


where A is the cross-sectional area, E is the Young's modulus, and L is the length of the element. See also, stress stiffening.

For the special case of unconstrained uniaxial tension or compression, Young's modulus of elasticity can be thought of as a measure of the stiffness of a material.


[edit] Use in engineering
The stiffness of a structure is of principal importance in many engineering applications, so modulus of elasticity is often one of the primary properties considered when selecting a material. A high modulus of elasticity is sought when deflections are undesirable, while a low modulus of elasticity is required when flexibilty is needed
Strength may refer to:

Physical ability:

Physical strength, as in people or animals
Superhuman strength, as in fictional characters
a character attribute (role-playing games)
Conflict between persons or groups:

Virtue and moral uprightness
Fortitude in the face of moral or social pressure
Persuasiveness of an argument.
Military strength
Politics :

Party strengths. See political party
Physics:

Strength of materials
Compressive strength
Tensile strength
Shear strength
Strength (explosive)
Field strength
Signal strength
Musical works:

Strength (band), a band from Portland, Oregon
Strength (album), an album by Enuff Z'nuff
Strength, an album by Asiatic Warriors
"Strength", a song by the Gear Daddies from their 1988 album Let's Go Scare Al
"Strength", a song by Screaming Jets from their 1997 album World Gone Crazy
Strength may also refer to:

Strength (Tarot card), numbered either XI or VIII

Answer 3

Stifnes is resistance to bending. Stength may be one of several characteristics such as resistance to stretch or compressive failure.