4.6.2.2.10 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)
Gauge factor (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 module can still be configured.
Transverse strain coeff.
(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 available 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 available in the list box.
These values are only for orientation and may need to be adjusted.
Unit:
When the strain is determined, the readings appear with the unit µm/m.
For the mechanical stress one can toggle between GPa and N/ mm
2
.
1 GPa = 10
3
N/ mm
2
Note that the elastic modulus is always in GPa.
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