Stiffness

flexibilityrigidityrigidtorsional rigiditycompliancestiffflexiblecompliantstiffertorsional stiffness
Stiffness is the extent to which an object resists deformation in response to an applied force.wikipedia
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Hooke's law

spring constantforce constantelasticity tensor
A description including all possible stretch and shear parameters is given by the elasticity tensor.
That is: F_s=kx, where k is a constant factor characteristic of the spring: its stiffness, and x is small compared to the total possible deformation of the spring.

Young's modulus

Young’s modulusmodulustensile modulus
For the special case of unconstrained uniaxial tension or compression, Young's modulus can be thought of as a measure of the stiffness of a structure.
Young's modulus, or the Young modulus, is a mechanical property that measures the stiffness of a solid material.

Euler–Bernoulli beam theory

Euler–Bernoulli beam equationbeam theoryEuler-Bernoulli beam equation
For example, a point on a horizontal beam can undergo both a vertical displacement and a rotation relative to its undeformed axis.
:The quantity A_{xx} is the extensional stiffness,B_{xx} is the coupled extensional-bending stiffness, and D_{xx} is the bending stiffness.

Durotaxis

durotactic
In biology, the stiffness of the extracellular matrix is important for guiding the migration of cells in a phenomenon called durotaxis.
With information from the previous observations, Lo and colleagues formulated the hypothesis that individual cells can detect substrate stiffness by a process of active tactile exploration in which cells exert contractile forces and measure the resulting deformation in the substrate.

Torsion constant

torsional
The torsion constant, together with material properties and length, describes a bar's torsional stiffness.

Elastic modulus

modulus of elasticityelastic modulimodulus
The elastic modulus of a material is not the same as the stiffness of a component made from that material.

Extracellular matrix

ECMmatrixextracellular matrices
In biology, the stiffness of the extracellular matrix is important for guiding the migration of cells in a phenomenon called durotaxis.
The ECM can exist in varying degrees of stiffness and elasticity, from soft brain tissues to hard bone tissues.

Deformation (mechanics)

straindeformationshear strain
Stiffness is the extent to which an object resists deformation in response to an applied force.

Force

forcesattractiveelastic force
Stiffness is the extent to which an object resists deformation in response to an applied force.

Degrees of freedom (mechanics)

degrees of freedomdegree of freedompitch
For an elastic body with a single degree of freedom (DOF) (for example, stretching or compression of a rod), the stiffness is defined as

International System of Units

SISI unitsSI unit
In the International System of Units, stiffness is typically measured in newtons per meter.

Newton (unit)

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

Pound (force)

lbflb f pound-force
In Imperial units, stiffness is typically measured in pounds(lbs) per inch. In the SAE system, rotational stiffness is typically measured in inch-pounds per degree.

Deflection (engineering)

deflectiondeflectionsdeflect
Generally speaking, deflections (or motions) of an infinitesimal element (which is viewed as a point) in an elastic body can occur along multiple DOF (maximum of six DOF at a point).

Displacement (vector)

displacementdisplacement vectordisplacements
For example, a point on a horizontal beam can undergo both a vertical displacement and a rotation relative to its undeformed axis.

Matrix (mathematics)

matrixmatricesmatrix theory
When there are M degrees of freedom a M x M matrix must be used to describe the stiffness at the point.

Multiplicative inverse

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

Rheology

rheologicalrheologistrheological properties
In rheology, it may be defined as the ratio of strain to stress, and so take the units of reciprocal stress, e.g.

Newton metre

N·mNmnewton-metre
In the SI system, rotational stiffness is typically measured in newton-metres per radian.

Radian

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

Degree (angle)

°degreesdegree
In the SAE system, rotational stiffness is typically measured in inch-pounds per degree.