Product Guide for Design Engineers - Quadrant

Effective Selection & Design Techniques
The modulus of elasticity of most plastics is temperature dependent [decreases with increasing temperature]
and in order to allow calculation of deformation under short term loads at various temperatures, we have
included in this brochure several graphs showing stiffness versus temperature of our materials [see pages
36 and 55].
When a plastics part is subjected to a constant static load, it deforms quickly to a strain roughly predicted by
its short-term modulus of elasticity [Hooke‘s law] and then continues to deform at a slower rate indefi nitely,
or if the load is high enough until rupture occurs. This phenomenon, which also occurs in structural metals at
very high temperatures, is called creep.
Fig. 2: Tensile Creep Behaviour of Ertacetal ® C at 23 °C [*]
5
4
1 - 6 : different stress levels
6
5
10 MPa
15 MPa
20 MPa
25 MPa
30 MPa
35 MPa
Strain [%]
3
2
4
3
[*]: based on raw
material supplier data
2
1
1
0
0.1
1 10 100
1000 10000 100000
Loading time [h]
Fig. 3:
Isometric Stress-Time Curve for a
Deformation of 2%
Fig. 4:
Isochronous Stress-Strain Curve
40
60
Stress [MPa]
30
20
10
2% strain
Stress [MPa]
50
40
30
20
10
10 h loading time
0
0.1
1 10 100 1000 10000 100000
0
0
1 2 3 4 5 6 7 8 9 10 11 12 13
Loading time [h]
Strain [%]
8