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Substituting Gx = 50.2 N/mm 2 , G2 = -22 N/mm 2 and G3 = 0 in Equation 4.5 gives
The equivalent stress Cv y according to Equation 4.7 for the conical failure criterion, is
obtained from
withm= 1.4 for POM.
The yield point of POM is around 58 N/mm 2 . Thus, the assumed joint strength is too
high. In the case of deformation of the part by shear, the shear stress is given by [I]
T = 0.5 O (4.10)
4.3 Time-Dependent Deformational Behavior
4.3.1 Short-Term Stress-Strain Behavior
As mentioned in Section 1.4, polymers are viscoelastic materials and their deformational
behavior is nonlinear. A typical stress-strain curve of POM under short-term loading is
shown in Figure 4.2. Curves of this type can be expressed by a fifth degree polynomial of
the form [4]
(4.11)
where PK0 ... PK5 are polynomial coefficients dependent on the resin at a given temperature.
Stress 6 N/mm 2
Figure 4.2 Stress-strain diagram for POM
Strain £
%