scholarly journals An investigation of the nonlinear creep damage accumulation of different materials: Application of a novel damage model

2021 ◽  
Author(s):  
Xu Zhao ◽  
Xuming Niu ◽  
Yingdong Song ◽  
Zhigang Sun
Keyword(s):  
Damage Accumulation ◽  
Failure Modes ◽  
Damage Model ◽  
Evolutionary Process ◽  
Creep Damage ◽  
Experimental Result ◽  
Nonlinear Creep ◽  
The Novel ◽  
Proposed Model ◽  
Damage Accumulation Model

Variable creep load is one of the most important failure modes for hot-component of aero-engine. To accurately predict creep damage and remaining life, a novel nonlinear creep damage accumulation model is proposed based on the Wilshire function and isodamage line, which takes the influence of load history into account and uses ultimate tension strength to compensate the temperature effect. Experimental result of tests on four kinds of material were utilized to verify the accuracy of the proposed model and to compare it with existing models. It was determined that the novel model was better at predicting damage accumulation than all others model. Furthermore, the proposed model elucidates the evolutionary process of creep damage, and four cases of damage evolution process are discussed.

An improved nonlinear damage model of rocks considering initial damage and damage evolution

2020 ◽  
Vol 29 (7) ◽  
pp. 1117-1137 ◽  
Author(s):  
Wenlin Feng ◽  
Chunsheng Qiao ◽  
Shuangjian Niu ◽  
Zhao Yang ◽  
Tan Wang
Keyword(s):  
Damage Evolution ◽  
Least Squares Method ◽  
Damage Model ◽  
Creep Damage ◽  
Secondary Creep ◽  
Nonlinear Creep ◽  
Creep Failure ◽  
Initial Damage ◽  
Nonlinear Damage Model ◽  
Creep Damage Model

The experimental results show that the creep properties of the rocks are affected by the initial damage, and the damage evolution also has a significant impact on the time-dependent properties of the rocks during the creep. However, the effects of the initial damage and the damage evolution are seldom considered in the current study of the rocks' creep models. In this paper, a new nonlinear creep damage model is proposed based on the multistage creep test results of the sandstones with different damage degrees. The new nonlinear creep damage model is improved based on the Nishihara model. The influences of the initial damage and the damage evolution on the components in the Nishihara model are considered. The creep damage model can not only describe the changes in three creep stages, namely, the primary creep, the secondary creep, and the tertiary creep, but also reflect the influence of the initial damage and the damage evolution on creep failure. The nonlinear least squares method is used to determine the parameters in the nonlinear creep damage model. The consistency between the experimental data and the predicted results indicates the applicability of the nonlinear damage model to accurately predict the creep deformation of the rocks with initial damage.

A nonlinear creep damage model for salt rock

2018 ◽  
Vol 28 (5) ◽  
pp. 758-771 ◽  
Author(s):  
Fei Wu ◽  
Jie Chen ◽  
Quanle Zou
Keyword(s):  
Test Data ◽  
Damage Model ◽  
Creep Damage ◽  
Nonlinear Creep ◽  
Salt Rock ◽  
Creep Tests ◽  
Nonlinear Constitutive Equation ◽  
Damage Constitutive Model ◽  
Creep Damage Model ◽  
Actual Stress

In the creep tests, stress is no longer a constant and increases gradually under the influence of damage occurring during accelerating creep, which is a slow-loading process rather than a conventional creep. With the accumulation of the damage over time, the actual stress increases greatly. The increased actual stress not only generates loading strain but also causes the steady creep rate to rise. This coupling possibly explains why salt rock presents nonlinear accelerating characteristics at the accelerating creep stage. In this work, the constraint of the present creep concept was overcome by assuming that the acceleration creep phase is a coupling process of loading and creeping. Furthermore, we demonstrate that the total strain in this phase is equal to the sum of loading strain and creeping strain. A new nonlinear constitutive equation for creep was then derived, and the mechanisms underlying the nonlinear accelerating characteristics emerging at the stage of accelerating creep are further explained. A step-loading experiment on salt rock was performed for a period of six months. The characteristics of accelerating creep appeared in the last step of loading. This new nonlinear creep damage constitutive model was used to fit and analyze the test data. Obtained results show that this model fits well to these test data and also favorably represents the nonlinear characteristics of accelerating creep, thus supporting the model’s validity.

Fatigue–oxidation–creep damage model under axial-torsional thermo-mechanical loading

2019 ◽  
Vol 29 (5) ◽  
pp. 810-830 ◽  
Author(s):  
Dao-Hang Li ◽  
De-Guang Shang ◽  
Jin Cui ◽  
Luo-Jin Li ◽  
Ling-Wan Wang ◽  
...  
Keyword(s):  
Damage Model ◽  
Creep Damage ◽  
Fatigue Loading ◽  
Damage Mechanism ◽  
Critical Crack ◽  
Critical Crack Length ◽  
Mechanical Fatigue ◽  
Proposed Model ◽  
Oxidation Damage ◽  
Creep Damage Model

A fatigue–oxidation–creep damage model that can take into account the effect of multiaxial cyclic feature on the damage mechanism is proposed under axial-torsional thermo-mechanical fatigue loading. In the proposed model, the effects of non-proportional additional hardening on fatigue, oxidation, and creep damages are considered, and the variation of oxidation damage under different high temperature loading conditions is also described. Moreover, the intergranular creep damage needs to be equivalent to the transgranular damage before accumulating with the fatigue and oxidation damages. The fatigue, oxidation, and creep damages can be expressed as the fractions of fatigue life, critical crack length, and creep rupture time, respectively, which allows the linear accumulation of different types of damages on the basis of life fraction rule. In addition, the proposed model is validated by various fatigue experimental results, including uniaxial thermo-mechanical fatigue, axial-torsional thermo-mechanical fatigue, and isothermal axial-torsional fatigue under proportional and non-proportional loadings. The results showed that the errors are within a factor of 2.

scholarly journals A Modified Nonlinear Damage Accumulation Model for Fatigue Life Prediction Considering Load Interaction Effects

2014 ◽  
Vol 2014 ◽  
pp. 1-7 ◽  
Author(s):  
Huiying Gao ◽  
Hong-Zhong Huang ◽  
Shun-Peng Zhu ◽  
Yan-Feng Li ◽  
Rong Yuan
Keyword(s):  
Experimental Data ◽  
Fatigue Life ◽  
Life Prediction ◽  
Damage Accumulation ◽  
Interaction Effects ◽  
Fatigue Life Prediction ◽  
Accumulation Model ◽  
Proposed Model ◽  
Fatigue Damage Accumulation ◽  
Damage Accumulation Model

Many structures are subjected to variable amplitude loading in engineering practice. The foundation of fatigue life prediction under variable amplitude loading is how to deal with the fatigue damage accumulation. A nonlinear fatigue damage accumulation model to consider the effects of load sequences was proposed in earlier literature, but the model cannot consider the load interaction effects, and sometimes it makes a major error. A modified nonlinear damage accumulation model is proposed in this paper to account for the load interaction effects. Experimental data of two metallic materials are used to validate the proposed model. The agreement between the model prediction and experimental data is observed, and the predictions by proposed model are more possibly in accordance with experimental data than that by primary model and Miner’s rule. Comparison between the predicted cumulative damage by the proposed model and an existing model shows that the proposed model predictions can meet the accuracy requirement of the engineering project and it can be used to predict the fatigue life of welded aluminum alloy joint of Electric Multiple Units (EMU); meanwhile, the accuracy of approximation can be obtained from the proposed model though more simple computing process and less material parameters calling for extensive testing than the existing model.

scholarly journals Features and Constitutive Model of Gypsum’s Uniaxial Creep Damage considering Acidization

Geofluids ◽  
2020 ◽  
Vol 2020 ◽  
pp. 1-16
Author(s):  
Wei Chen ◽  
Wen Wan ◽  
Senlin Xie ◽  
Wenlong Kuang ◽  
Wenqing Peng ◽  
...  
Keyword(s):  
Hydrochloric Acid ◽  
Constitutive Model ◽  
Stress Level ◽  
Failure Modes ◽  
Failure Time ◽  
Acid Corrosion ◽  
Creep Damage ◽  
Nonlinear Creep ◽  
Creep Tests ◽  
Acidic Groundwater

Acidic fluids cause rock erosion and further endanger the safety of rock engineering, especially the corrosion of pillars by acidic or weakly acidic groundwater. In this paper, the rock samples in the gypsum mining area were taken as the research object. Uniaxial compression creep tests were carried out under neutral water, pH=6 and pH=5 hydrochloric acid solutions, respectively. Meanwhile, the specimens before and after saturation were observed by an electron microscope scanner. The results show that (1) the gypsum specimens with pH=5 hydrochloric acid were damaged at the first stress level, while that with pH=6 and pH=7 were destroyed at the second stress level. The failure modes of the three groups were basically the same, with cleavage and end damage of different degrees. The difference is that the failure time of the former is earlier than that of the latter, which indicates that the stronger acidity causes greater corrosion on the creep of the samples. (2) From the perspective of microstructure, the samples saturated in the neutral aqueous solution and dry state are compact and complete in structure, and the whole is relatively homogeneous. However, after saturating in the acid solution, the samples significantly increased dense pores with large size and loose structure. Due to the rapid increase, the surfaces of the samples are almost like “holes”. (3) A new nonlinear creep constitutive model was established by connecting Burgers model with nonlinear viscoplastic body (NVPB) model in series, which can well describe the creep characteristics of gypsum rocks under acid corrosion.

An elasto-plastic damage accumulation model for fatigue life predication of ductile metals at the yield stress

2021 ◽  
pp. 105678952110454
Author(s):  
Jindong Huo ◽  
Xiaochuan You ◽  
Jianan Hu ◽  
Zhuo Zhuang
Keyword(s):  
Fatigue Life ◽  
Yield Stress ◽  
Fatigue Test ◽  
Fatigue Damage ◽  
Damage Accumulation ◽  
Cycle Fatigue ◽  
Ductile Metals ◽  
Plastic Damage ◽  
Proposed Model ◽  
Damage Accumulation Model

From the analysis of massive fatigue test data, we find a mismatch between the fatigue life predictions done by stress-life method (SN) and those by strain-life method (εN) around the yield stress of ductile metals. Since the SN and εN methods are widely used in engineering applications, this work aims to explain such mismatch and thereby to address the fatigue life prediction at material’s yield stress, at which the material’s elastic damage and plastic damage are comparable. Based on a normalized damage concept, we propose an elasto-plastic damage accumulation model, a data-driven approach, to evaluate the fatigue damage at the yield stress. By differentiating the damage caused by the elastic from the plastic, the damage of each loading cycle is formulated as a function of both stress and strain amplitudes to accurately capture the material’s response state. With introducing the strain-energy-density based weighting factor, the proposed model can accord well with the classical methods from low-cycle fatigue to high-cycle fatigue. When it comes to the yield stress, the fatigue life estimated by the proposed model compares favorably with the fatigue test data. Therefore, beyond clarifying the mismatch between the classical approaches, the proposed model is expected to improve the accuracy in fatigue damage evaluation of ductile metals at the yield stress.

Creep Fatigue Behavior and Life Prediction Including the Load History Effect Under High Temperature

2009 ◽  
Author(s):  
Jie Dong ◽  
Xuedong Chen ◽  
Zhichao Fan ◽  
Huifeng Jiang ◽  
Heng Jiang
Keyword(s):  
High Temperature ◽  
Failure Modes ◽  
Fatigue Behavior ◽  
Damage Model ◽  
Material Behavior ◽  
Cyclic Behavior ◽  
Nonlinear Creep ◽  
Load History ◽  
Creep Fatigue ◽  
History Effect

Creep fatigue interaction is one of the main failure modes for high temperature pressurized equipment. In practice, the amplitude of load on structure often changes which results in the load history effect on cyclic behavior and life of material. Therefore, 316L stainless steel 1-step and 2-step creep fatigue test under high temperature was conducted, the influence of two kinds of load history on material behavior was analyzed. The results showed the first step load with different amplitude and life fraction would lead to different hardness or softness of material and affect the cyclic behavior under the second step load. There is also much difference of material behavior at the time of load change for high-low and low-high load case. A uniform nonlinear creep fatigue damage model based on “disorder” and a modified failure rule coupled with the load history effect were presented in the paper. The creep fatigue life under 2-step load at high temperature was evaluated by the damage model and the modified rule. The predicted results were in good agreement with the experimental data.

scholarly journals A Nonlinear Creep Damage Model of Layered Rock under Unloading Condition

2018 ◽  
Vol 2018 ◽  
pp. 1-8 ◽  
Author(s):  
Ruihong Wang ◽  
Yuzhou Jiang ◽  
Chao Yang ◽  
Fei Huang ◽  
Yuxuan Wang
Keyword(s):  
Rock Specimen ◽  
Damage Model ◽  
Creep Damage ◽  
Nonlinear Creep ◽  
Term Strength ◽  
Layered Rock ◽  
Rock Creep ◽  
Creep Time ◽  
Creep Damage Model

Triaxial unloading creep tests of layered rock specimen of Jinping II hydropower station were carried out using the rock creep testing machine; thus the creep deformation curves under different confining pressures were acquired. The test results showed that, in addition to the obvious unloading creep characteristics of rock specimen, the nonlinear accelerating creep deformation emerged under the last stage confining stress condition, and the whole creep curves presented the typical rock creep three stages. On the other hand, the Burgers creep model constitutive equations under the three-dimensional stress state were also deduced. Based on the creep test data, through identifying the creep parameters using the optimized algorithm, the corresponding parameters of triaxial creep constitutive model were obtained. By comparative analysis of creep parameters, it can be concluded that creep parameters nonlinearly degraded with the decrease of confining pressure gradually. Moreover, when the load is below the long-term strength of rock, the creep parameters are only related to the unloading ratio, while in the case that the load is larger than the long-term strength of rock, the unloading creep parameters are related to both unloading ratio and creep time. According to the creep parameters under the first-stage stress level, and through introducing unloading ratio damage factor to describe the degrading rule of creep parameters on other stress levels, the method of uniformity determining the creep parameters was proposed. It was assumed that the damage degree in rock interior was relative to both unloading ratio and creep time; a nonlinear creep damage model of rock under unloading was proposed, which could better reflect the nonlinear characteristics of rock creep. The results showed that rock nonlinear creep damage model achieved perfectly consistent results with the creep test.

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