Strength reductions
If there is a risk of stress cracks or similar reductions in strength, the following guidelines for determining the permissible elongation (εzul) for tank materials (plastics) should be observed:
Reference value ranges of critical strains from tests in an air environment
The following range specifications of the critical elongation (εkrit) result from material-structural influences and from the physical measuring principle of the test methods. They should be used by the user for design calculations in terms of the usual safety assessment for different requirements and risks.
Critical strains are not polymer-specific material parameters:
|
Polymers |
Operating temperature |
εkrit [%] |
Examples |
|
Amorphous thermoplastics (except PS) |
less than Tg |
0.6 to 0.9 |
PC, ABS, SAN, PVC-U, PMMA, SB, PSU, PESU, (PC+ABS), (PPE+SB) |
|
Polystyrene |
less than Tg |
0.2 to 0.3 |
PS |
|
Semi-crystalline thermoplastics |
less than Tg |
0.4 to 0.8 |
PA6 (d), PA66 (d), PA610 (t), PEEK |
|
more than Tg |
1.5 to 2.5 |
PA6 (nh), PA66 (nh), PA610 (nh), PP, PE-HD, POM |
|
|
Glass fiber reinforced thermoplastics (over 15% GF) |
less than Tg |
0.2 to 0.3 |
all thermoplastics |
|
more than Tg |
0.3 to 0.5 |
||
|
Glass mat-reinforced thermosets (over 10% GM) |
─ |
0.3 to 0.5 |
UP, EP |
|
Thermoset press and injection molding materials |
─ |
(0.2 to 0.3) • εB |
All types according to DIN EN ISO 14526 to 14530 (PMC) and according to DIN EN 14598 (BMC, SMC) |
|
|||