Uniaxial analysis
In: Local elastic-plastic strain methods
The methods grouped in this section are:
All of them are based on a reduction of the complex load state to a scalar equivalent value (see also the section uniaxial analysis). The most of the methods here are obtained from the paper by Nihei et al. [NHB86]. The resulting equivalent load history is decomposed by a common rain-flow decomposition to individual cycles and these are input into damage parameters of appropriate methods. A use of Newton-Raphson iterative formula allows derivation of the resulting number of cycles. Palmgren-Miner cumulative law is applied for summation of fatigue damages of individual load cycles.
The methods are suitable for a damage calculation in the region of finite life with number of cycles approx. < 1e5-1e6. The induced plastic deformation has to be covered in the load inputs. These thus can be:
- elastic stresses - the conversion method by Glinka or Neuber has to be used;
- elastic-plastic stresses - the preparation of the transient analysis removes the dependency on any of those two methods above.
Note: Although the methods themselves are based on Basquin and Manson-Coffin (BMC) curves and are thus strain-based, the current version of PragTic calls for the input of stresses. The methods implemented in PragTic were converted for the stress input via the Ramberg-Osgood curve once and I have not finished until now the direct solution utilizing strains.
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© PragTic, 2007
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