.Size effect
The size effect can be switched on for the LESA method in the Calculation Methods menu. The only implemented solution there is the one defined in FemFat. The size effect should take the effect found by the larger volumes of materials, where increased tendency to initiate the crack was observed. The FemFat method is based on data given in [FKM03], where proposals on the technology influence factor are summed.
Note: The description of method found in [FKM03] differs from that one reported in [ECS4.4]. The core of the method in [FKM03] is nevertheless a bit unclear, therefore the [ECS4.4] method is the only one implemented.
The solution is described in [FKM03], here only its transcription is done. If no other influence is active, the technology factor FZ modifies the actual fatigue limit:
.
The size effect is calculated as a minimum relative value:
* grey cast iron: 
* all other materials: 
.
The FZ,S is a tabular value related to the material sort and can be found in the table below. The symbol FZ,eff is the value computed for the effective diameter found in the examined point.
|
Material group |
deff,S [mm] |
ad [-] |
FZ,S [-] |
|
structural steel |
40 |
0.15 |
0.9162 |
|
hardened and tempered steel (hardened and tempered state) |
16 |
0.3 |
0.9241 |
|
hardened and tempered steel (hardened and tempered state - 30 CrNiMo 8, 36 CrNiMo 16) |
40 |
0.3 |
0.8324 |
|
hardened and tempered steel (normally annealed state) |
16 |
0.1 |
0.9747 |
|
hardened steel (blank-hardened state) |
11 |
0.5 |
0.9360 |
|
nitration steel (hardened and tempered state) |
100 |
0.2 |
0.8271 |
|
cast steel |
100 |
0.15 |
0.8703 |
|
air-hardened and tempered cast steel |
300 |
0.15 |
0.8153 |
|
liquid-hardened and tempered cast steel |
100 |
0.15 |
|
© PragTic, 2007
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