188 Measurement Technique
imc CANSAS Users Manual - Doc. Version 1.9 - 05.12.2014© 2014 imc Meßsysteme GmbH
5.1.2.1.11 Scaling for the strain analysis
It is possible to choose whether to determine the strain or the mechanical stress suffered by the part. In
the range of elastic deformation, the axial stress (force / cross section) is proportional to the strain. The
proportionality factor is the modulus of elasticity.
Mechanical stress = modulus of elasticity * strain (Hooke’s law)
K-factor
The K-factor is the ratio by which the mechanical quantity (elongation) is transformed to the electrical
quantity (change in resistance). The typical range is between 1,9 and 4,7. The exact value can be found in
the spec sheet for the WSG used. If the value entered for this parameter is outside of this range, a
warning message will appear but the imc CANSAS module can still be configured.
Poisson's ratio
If a body suffers compression or tension and is able to be freely deformed, then not only its length but
also its thickness changes. This phenomenon is known as transversal contraction. It can be shown that for
each kind of material, the relative change in length is proportional to the relative change in thickness D.
The transversal elongation coefficient (Poisson’s ratio) is the material-dependent proportionality factor.
The material constant is in the range 0,2 to 0,5.
In bridge circuits where the WSGs are positioned transversally to the main direction of strain, this
constant must be supplied by the user. The ratios for various materials are accessible in the list box.
These values are only for orientation and may need to be adjusted.
Elastic modulus
The elastic modulus E, is a material parameter characterizing how a body is deformed under the action of
pressure or tension in the direction of the force. The unit for E is N/mm². This value must be entered for
the mechanical stress to be determined The e-moduli for various materials are accessible in the list box.
These values are only for orientation and may need to be adjusted.
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