• Title/Summary/Keyword: ratcheting

Search Result 48, Processing Time 0.041 seconds

Influence of stress level on uniaxial ratcheting effect and ratcheting strain rate in austenitic stainless steel Z2CND18.12N

  • Chen, Xiaohui;Chen, Xu;Chen, Haofeng
    • Steel and Composite Structures
    • /
    • v.27 no.1
    • /
    • pp.89-94
    • /
    • 2018
  • Uniaxial ratcheting behavior of Z2CND18.12N austenitic stainless steel used nuclear power plant piping material was studied. The results indicated that ratcheting strain increased with increasing of stress amplitude under the same mean stress and different stress amplitude, ratcheting strain increased with increasing of mean stress under the same stress amplitude and different mean stress. Based on least square method, a suitable method to arrest ratcheting by loading the materials was proposed, namely determined method of zero ratcheting strain rate. Zero ratcheting strain rate occur under specified mean stress and stress amplitudes. Moreover, three dimensional ratcheting boundary surface graph was established with stress amplitude, mean stress and ratcheting strain rate. This represents a graphical surface zone to study the ratcheting strain rates for various mean stress and stress amplitude combinations. The graph showed the ratcheting behavior under various combinations of mean and amplitude stresses. The graph was also expressed with the help of experimental results of certain sets of mean and stress amplitude conditions. Further, experimentation cost and time can be saved.

Bending ratcheting behavior of pressurized straight Z2CND18.12N stainless steel pipe

  • Wang, Lei;Chen, Gang;Zhu, Jianbei;Sun, Xiuhu;Mei, Yunhui;Ling, Xiang;Chen, Xu
    • Structural Engineering and Mechanics
    • /
    • v.52 no.6
    • /
    • pp.1135-1156
    • /
    • 2014
  • The ratcheting effect greatly challenges the design of piping components. With the assistance of the quasi-three point bending apparatus, ratcheting and the ratcheting boundary of pressurized straight Z2CND18.12N stainless steel pipe under bending loading and vertical displacement control were studied experimentally. The characteristics of progressive inelastic deformation in axial and hoop directions of the Z2CND18.12N stainless steel pipes were investigated. The experiment results show that the ratcheting strain occurs mainly in the hoop direction while there is less ratcheting strain in the axial direction. The characteristics of the bending ratcheting behavior of the pressure pipes were derived and compared under load control and displacement control, respectively. The results show that the cyclic bending loading and the internal pressure affect the ratcheting behavior of the pressurized straight pipe significantly under load control. In the meantime, the ratcheting characteristics are also highly associated with the cyclic displacement and the internal pressure under displacement control. All these factors affect not only the saturation of the ratcheting strain but the ratcheting strain rate. A series of multi-step bending ratcheting experiments were conducted under both control modes. It was found that the hardening effect of Z2CND18.12N stainless steel pipe under previous cyclic loadings no matter with high or low displacement amplitudes is significant, and the prior loading histories greatly retard the ratcheting strain and its rate under subsequent loadings. Finally, the ratcheting boundaries of the pressurized straight Z2CND18.12N stainless steel pipe were determined and compared based on KTA/ASME, RCC-MR and the experimental results.

Effects of temperature on the ratcheting behavior of pressurized 90° elbow pipe under force controlled cyclic loading

  • Chen, Xiaohui;Wang, Xingang;Chen, Xu
    • Smart Structures and Systems
    • /
    • v.19 no.5
    • /
    • pp.473-485
    • /
    • 2017
  • Ratcheting behavior of $90^{\circ}$ elbow piping subject to internal pressure 20 MPa and reversed bending 20 kN was investigated using experimental method. The maximum ratcheting strain was found in the circumferential direction of intrados. Ratcheting strain at flanks was also very large. Moreover, the effect of temperature on ratcheting strain of $90^{\circ}$ elbow piping was studied through finite element analysis, and the results were compared with room condition ($25^{\circ}$). The results revealed that ratcheting strain of $90^{\circ}$ elbow piping increased with increasing temperature. Ratcheting boundary of $90^{\circ}$ elbow piping was determined by Chaboche model combined with C-TDF method. The results revealed that there was no relationship between the dimensionless form of ratcheting boundary and temperature.

Ratcheting behavior of pressurized Z2CND18.12N stainless steel pipe under different control modes

  • Chen, Xiaohui;Chen, Xu;Chen, Gang;Li, Duomin
    • Steel and Composite Structures
    • /
    • v.18 no.1
    • /
    • pp.29-50
    • /
    • 2015
  • With a quasi-three point bending apparatus, ratcheting deformation is studied experimentally on a pressurized austenitic stainless steel Z2CND18.12N pipe under bending load and vertical displacement control, respectively. The characteristic of ratcheting behavior of straight pipe under both control methods is achieved and compared. The cyclic bending loading and internal pressure influence ratcheting behavior of pressurized straight pipe significantly under loading control and the ratcheting characteristics are also highly associated with the cyclic displacement and internal pressure under displacement control. They all affect not only the saturation of the ratcheting strain but the ratcheting strain rate. In addition, ratcheting simulation is performed by elastic-plastic finite element analysis with ANSYS in which the bilinear model, Chaboche model, Ohno-Wang model and modified Ohno-Wang model are applied. By comparison with the experimental data, it is found that the CJK model gives reasonable simulation. Ratcheting boundaries under two control modes are almost same.

Low cycle fatigue and ratcheting failure behavior of AH32 steel under uniaxial cyclic loading

  • Dong, Qin;Yang, Ping;Xu, Geng
    • International Journal of Naval Architecture and Ocean Engineering
    • /
    • v.11 no.2
    • /
    • pp.671-678
    • /
    • 2019
  • In this paper, the low cycle fatigue failure and ratcheting behavior, as well as their interaction of AH32 steel were experimentally investigated under uniaxial cyclic loading. The effects of mean stress, stress amplitude and stress ratio on the low cycle fatigue life and ratcheting strain were discussed. It was found that the ratcheting strain increased while the fatigue life decreased with the increase of mean stress and stress amplitude, and the increasing stress ratio would result in smaller ratcheting and larger fatigue life. Two kinds of failure modes, i.e. low cycle fatigue failure due to crack propagates and ratcheting failure due to large plastic strain will take place respectively. Based on the experimental results, considered the effect of ratcheting on fatigue life, a model with the maximum stress and ratcheting strain rate was proposed. Comparison with the experimental result showed that the new model provided a good prediction for AH32 steel.

Multiaxial ratcheting behavior of Inconel 718 at elevated temperature (Inconel 718 의 고온 다축피로하중 하에서의 라체팅 거동)

  • Kim, Hyo-Shin;Kim, Kwang-Soo
    • Proceedings of the KSME Conference
    • /
    • 2008.11a
    • /
    • pp.344-349
    • /
    • 2008
  • Ratcheting behavior of IN 718 was investigated at $649^{\circ}C$ under various proportional and non-proportional loading conditions with stress control. The material response was initially elastic but substantial plastic strain was developed as the material softened cyclically. Ratcheting strain was measured to near fatigue life, and is found to have three stages of development - primary, secondary (steady-state) and tertiary. The secondary stage dominates for most cases. Under the same equivalent stress amplitude and mean stress, it was revealed that circular path loading gives higher ratcheting rates and shorter lives than linear paths and that the more ratcheting occurs when the cyclic load is in the same direction as the mean stress. The ratcheting strain at failure depends not only on its rate but also on fatigue life itself, and it is not a primary life-determining factor.

  • PDF

Effect of local wall thinning on ratcheting behavior of pressurized 90° elbow pipe under reversed bending using finite element analysis

  • Chen, Xiaohui;Chen, Xu
    • Steel and Composite Structures
    • /
    • v.20 no.4
    • /
    • pp.931-950
    • /
    • 2016
  • Ratcheting deformation of pressurized Z2CND18.12N stainless steel $90^{\circ}$ elbow pipe with local wall thinning subjected to constant internal pressure and reversed bending was studied using finite element analysis. Chen-Jiao-Kim (CJK) kinematic hardening model, which was used to simulate ratcheting behavior of pressurized $90^{\circ}$ elbow pipe with local wall thinning at extrados, flanks and intrados, was implemented into finite element software ANSYS. The local wall thinning was located at extrados, flanks and intrados of $90^{\circ}$ elbow pipe, whose geometry was rectangular cross-section. The effect of depth, axial length and circumferential angle of local wall thinning at extrados, flanks and intrados on the ratcheting behaviors of $90^{\circ}$ elbow pipe were studied in this paper. Three-dimensional elastic-plastic analysis with Chen-Jiao-Kim (CJK) kinematic hardening model was carried out to evaluate structural ratcheting behaviors. The results indicated that ratcheting strain was generated mainly along the hoop direction, while axial ratcheting strain was relatively small.

Ratcheting analysis of joined conical cylindrical shells

  • Singh, Jaskaran;Patel, B.P.
    • Structural Engineering and Mechanics
    • /
    • v.55 no.5
    • /
    • pp.913-929
    • /
    • 2015
  • The ratcheting and strain cyclic behaviour of joined conical-cylindrical shells under uniaxial strain controlled, uniaxial and multiaxial stress controlled cyclic loading are investigated in the paper. The elasto-plastic deformation of the structure is simulated using Chaboche non-linear kinematic hardening model in finite element package ANSYS 13.0. The stress-strain response near the joint of conical and cylindrical shell portions is discussed in detail. The effects of strain amplitude, mean stress, stress amplitude and temperature on ratcheting are investigated. Under strain symmetric cycling, the stress amplitude increases with the increase in imposed strain amplitude. Under imposed uniaxial/multiaxial stress cycling, ratcheting strain increases with the increasing mean/amplitude values of stress and temperature. The abrupt change in geometry at the joint results in local plastic deformation inducing large strain variations in the vicinity of the joint. The forcing frequency corresponding to peak axial ratcheting strain amplitude is significantly smaller than the frequency of first linear elastic axial vibration mode. The strains predicted from quasi static analysis are significantly smaller as compared to the peak strains from dynamic analysis.

Fatigue Life Prediction and Ratcheting behavior of the Elbrodur-NIB under Fatigue loading with mean stress (평균응력을 포함한 피로하중 하에서 Elbrodur-NIB의 피로수명예측 및 Ratcheting 거동)

  • Lim, Chang-Bum
    • Journal of the Korean Society for Aeronautical & Space Sciences
    • /
    • v.39 no.7
    • /
    • pp.612-617
    • /
    • 2011
  • An experimental study was carried out for the Elbrodur-NIB(copper alloy) at room temperature under stress-controlled uniaxial fatigue loading with and without mean stress. As a result, the effects of stress amplitude, mean stress and stress rate on ratcheting behavior were investigated. The ratcheting strain increased with increasing stress amplitude for a given mean stress, and with mean stress for a given stress amplitude. But, the ratcheting strain decreased as the stress rate increased. The three mean stress models were investigated and the mean stress models of Smith-Watson-Topper and Walker yielded good correlation of fatigue lives in the life range of $10^2-10^5$cycles.

An Analytic Study on the Contact Stress and Thermal Stress of Rails (레일의 라체팅에 미치는 접촉응력 및 열응력에 대한 해석적 연구)

  • Goo, Byeong-Choon;You, Won-Hee
    • Proceedings of the KSR Conference
    • /
    • 2007.05a
    • /
    • pp.767-774
    • /
    • 2007
  • Even though a constant repeated load is applied, plastic deformation may cumulate. This kind of behavior is called ratcheting. Ratcheting may lead to cracks and finally to failure of the rail. Usually ratcheting occurs on high rails in curves. Ratcheting is influenced by residual stresses, wheel-rail contact stresses, thermal stresses due to wheel/rail rolling contact, shear strength of the rail, strain hardening behavior, etc. In this study, contact stresses and thermal stresses are examined. It is found their value is considerable compared to the maximum contact pressure.

  • PDF