Experimental study on ratcheting-fatigue interaction of 20 carbon steel in uniaxial cyclic loading

2012

This study intends to compare ratcheting response of 42CrMo, 1020, SA333 and SS304 steel alloys over uniaxial stress cycles evaluated by a parametric ratcheting model and Bower's hardening rule. The parametric ratcheting equation was formulated to describe triphasic stages of ratcheting deformation over stress cycles. Mechanistic parameters of mean stress, stress amplitude, material properties and cyclic softening/hardening response of materials were employed to calibrate parametric equation. Based on the framework of cyclic plasticity theory, the modified Armstrong–Frederick nonlinear hardening rule of Bower was employed to assess ratcheting response of steel alloys under uniaxial stress cycles. Bower's model was chosen mainly due to simplicity of the model and its lower number of constants required to predict ratcheting strain over stress cycles as compared with other hardening rules. Ratcheting strain values predicted by Bower's model showed good agreements over stage I of stress cycles as compared with experimental values of ratcheting strain. Beyond of stage I stress cycles, Bower ratcheting strain rate stayed constant resulting in an arrest in ratcheting process. The predicted ratcheting strains based on the parametric equation were found in good agreements over three stages of ratcheting as compared with those of experimentally obtained.

Section: P R E D I C T E D V E R S U S E X P E R I M E N T a L R A T supporting

confidence: 79%

Section: Materials and Testing Conditionsmentioning

confidence: 99%

Ratcheting assessment of steel alloys under uniaxial loading: a parametric model versus hardening rule of Bower

Ahmadzadeh

2012

“…Research on material ratcheting in literature highly focuses on various aspects of metallic/nonmetallic, ductile/brittle, plastic/viscoplastic, and softening/hardening responses. Ratcheting of metallic materials mainly included (i) ferrous alloys, carbon steels, [36][37][38][39][40][41][42] 42CrMo, 304, and SA333 steel alloys [43][44][45][46][47] and (ii) nonferrous alloys, copper alloys, 19,48 aluminium, 49 titanium, 50 and Inconel 51 alloys. Ferrous and nonferrous metallic alloys were categorized as softened and hardened materials over stress cycles.…”

Section: Ratcheting and Various Materialsmentioning

confidence: 99%

Ratcheting in pressurized pipes and equipment: A review on affecting parameters, modelling, safety codes, and challenges

Nayebi

2018

The current study has attempted to comprehensively review ratcheting response of materials involving various influential parameters such as loading spectra, thermal cycles, stress levels, stress raisers, strain rate, and visco‐plasticity and material types with a focus on pressurized pipes and equipment. The mechanism of deformation, types, and the rate of progress over stages of ratcheting were discussed. Safety design codes and procedures were highlighted for reliable design of pressurized pipes against progressive ratcheting and to safeguard the system against catastrophic failure at which both mechanical and thermal ratcheting were integrated. Boundaries and demarcation of ratcheting‐shakedown zones developed based on Bree's diagram were employed to assess plastic deformation accumulation over stress cycles. Shakedown and ratcheting boundaries were discussed through methods developed on the basis of Melan's theorem over last few decades. Ratcheting response of materials was reviewed through descriptions of parametric models and kinematic hardening rules involving various variables and parameters. Interaction of ratcheting with creep and low‐cycle fatigue has promoted progressive damage in materials. Pressurized pipes subjected to thermal cycles and external bending cycles were evaluated by numerical solutions along with kinematic hardening rules to assess ratcheting over stress cycles.

“…To evaluate the ratcheting strain response of materials over stress cycles, four different materials of 42CrMo, 20CS, SA333 steels and OFHC copper were cyclically loaded under stress‐control at various mean and amplitude stresses 2,17,21,22,25,26 Table 1 presents properties of these materials.…”

Section: Materials and Experimentationmentioning

confidence: 99%

“…Cyclic stress–strain diagram of 42CrMo shows a softening response for strain values exceeding 2%. Geometry and dimensions of tested samples have been reported in references 2,17,21,22,25,26 …”

Section: Materials and Experimentationmentioning

confidence: 99%

Triphasic ratcheting strain prediction of materials over stress cycles

Ahmadzadeh

2012

A B S T R A C T This study intends to formulate ratcheting strain evolution in steel alloys of 42CrMo, 20CS, SA333 Gr. 6 C-Mn and OFHC copper over uniaxial stress cycles. Stages of ratcheting deformation were related to stress cycles, lifespan, mechanical properties and amplitude and mean stress components by means of linear and nonlinear functions. Terms of mechanical properties in the ratcheting formulation enabled to characterize ratcheting response of various materials over life cycles. These terms were further employed to interpret the influence of softening/hardening response of materials on ratcheting deformation. Ratcheting data for 42CrMo, 20CS, SA333 steels and OFHC copper reported in the literature were employed to evaluate the proposed ratcheting formulation. The predicted ratcheting strain values based on the proposed equation were found in good agreements as compared with the experimental data.