Varmuuskerroin jännitysväsymisen kontinuumimallissa

Tiivistelmä Artikkelissa tarkastellaan äärettömään elinikään liittyvää varmuuskertoimen laskentaa kontinuumimekaniikkaan perustuvassa jännitysväsymismallissa. Jännityshistoria voi olla joko deterministinen tai stokastinen. Varmuuskertoimen laskenta redusoituu kestävyysfunktion maksimiarvon etsimiseen. Stokastisen jännityshistorian tapauksessa myös kestävyysfunktion arvot muodostavat stokastisen prosessin, jonka maksimiarvon todennäköisyysjakauma voidaan muodostaa. Menetelmää havainnollistetaan sekä yksinkertaisella yksidimensioisella että moniakselisella teollisella esimerkkilaskennalla

Stochastic continuum approach to high-cycle fatigue:modelling stress history as a stochastic process

Abstract In this article, the continuum-based high-cycle fatigue analysis method, introduced by Ottosen, Stenström and Ristinmaa in 2008, is extended to cases where the stress history is a stochastic process. The basic three-parameter Ornstein–Uhlenbeck process is chosen for stress description. As a practical example, the theory is applied in both finite and infinite life cases. A definition for the safety factor is introduced, which is reduced to a minimization problem of the value for the endurance surface. In the stochastic case, the values of the endurance surface form a stochastic process and the cumulative distribution function can be constructed for its maximum values

A continuum based macroscopic unified low-and high cycle fatigue model

Abstract In this work, an extension of a previously developed continuum based high-cycle fatigue model is enhanced to also capture the low-cycle fatigue regime, where significant plastic deformation of the bulk material takes place. Coupling of the LCFand HCF-models is due to the damage evolution equation. The high-cycle part of the model is based on the concepts of a moving endurance surface in the stress space with an associated evolving isotropic damage variable. Damage evolution in the low-cycle part is determined via plastic deformations and endurance function. For the plastic behaviour a non-linear isotropic and kinematic hardening J2-plasticity model is adopted. Within this unified approach, there is no need for heuristic cycle-counting approaches since the model is formulated by means of evolution equations, i.e. incremental relations, and not changes per cycle. Moreover, the model is inherently multiaxial and treats the uniaxial and multiaxial stress histories in the same manner. Calibration of the model parameters is discussed and results from some test cases are shown