Search

To describe the uniaxial mechanical behavior of 316LN stainless steel more accurately, a polycrystalline cyclic plasticity constitutive model is constructed based on the Ahmadzadeh-Varvani (A-V) kinematic hardening rule in the framework of the rate‑dependent crystal plasticity theory. The constitutive model is implemented to the finite element software ABAQUS through the UMAT, and a two‑dimensional polycrystalline finite element model is established through Voronoi diagrams. And then the deformation behavior of 316LN stainless steel is simulated under different loading rates, strain cycles and asymmetric stress cycles, respectively. The simulated results compared with the experimental data show that under the uniaxial tensile condition, the stress errors of both fluctuate around±0. 9%, and the maximum stress error is only 1. 9%; under the strain cycle condition, the maximum stress error between the two appears in the 5th cycle, with 11. 4% and 12. 2% errors in the tensile and compression phases, respectively, and 7. 4% and 7. 9% errors in the tensile and compression phases, respectively, after cycle stabilization. Under the asymmetric stress cycle condition, the errors of both mainly appear in the hysteresis loop width, the simulated hysteresis loop width is narrower, but the error of the hysteresis loop evolution trend is smaller. [ABSTRACT FROM AUTHOR]

A strain isolation pad is a critical connection mechanism that enables deformation coordination between the rigid thermal insulation tile and the primary structure in the thermal protection system of a reusable hypersonic vehicle. An experimental investigation has been conducted to determine the static, loading–unloading, and high-cycle fatigue (HCF) responses of the SIP with 0.2 mm adhesive under through-thickness tension at room temperature. The contributions of the rigid thermal insulation tile and metallic substructure have not been considered so far. The results indicate that the tensile behavior of the SIP joint is highly nonlinear. The static and fatigue tensile failures both initiate from the corner close to the adhesive/SIP interface due to the stress concentration and the edge effect. The uniform breakage of the aramid fiber can be seen on the cross-section. A novel method is proposed to quantify the residual strain due to the short-time ratcheting effect of the SIP joint in the initial loading–unloading tensile response. As the number of fatigue cycles increases, the thickness of the SIP joint continues to increase until failure. An explicit expression associated with the growth of SIP joint thickness, fatigue cycle number, and peak cyclic stress is established. The turning point of the thickness growth rate with the fatigue cycle number is proposed as a new fatigue failure index for the SIP joint under tensile fatigue, and a fatigue life prediction model is developed. [ABSTRACT FROM AUTHOR]

A strain isolation pad is a critical connection mechanism that enables deformation coordination between the rigid thermal insulation tile and the primary structure in the thermal protection system of a reusable hypersonic vehicle. An experimental investigation has been conducted to determine the static, loading–unloading, and high-cycle fatigue (HCF) responses of the SIP with 0.2 mm adhesive under through-thickness tension at room temperature. The contributions of the rigid thermal insulation tile and metallic substructure have not been considered so far. The results indicate that the tensile behavior of the SIP joint is highly nonlinear. The static and fatigue tensile failures both initiate from the corner close to the adhesive/SIP interface due to the stress concentration and the edge effect. The uniform breakage of the aramid fiber can be seen on the cross-section. A novel method is proposed to quantify the residual strain due to the short-time ratcheting effect of the SIP joint in the initial loading–unloading tensile response. As the number of fatigue cycles increases, the thickness of the SIP joint continues to increase until failure. An explicit expression associated with the growth of SIP joint thickness, fatigue cycle number, and peak cyclic stress is established. The turning point of the thickness growth rate with the fatigue cycle number is proposed as a new fatigue failure index for the SIP joint under tensile fatigue, and a fatigue life prediction model is developed.

Monotonic and pulsating cyclic compression tests were performed systematically based on high density polyethylene (HDPE). The compressive creep behaviors were further implemented to compare with the ratcheting deformation under the same peak stress level. Monotonic compression experiments reveal that HDPE shows obvious four-stage characteristics which are sensitive to temperature, but independent of the stress rate when the temperature is greater than 80 °C. Interestingly, the strain range during the stage III always starts at 7.4% and ends at 62.6% under various temperatures and stress rates. Moreover, the compressive ratcheting behavior of HDPE significantly depends on temperature T, peak stress σp, stress rate σ˙, stress amplitude Δσ and stress ratio R, especially when T ≥ 80 °C, σp ≥15 MPa, σ˙ ≤0.1 MPa/s and R ≥ 0.8. Additionally, decreasing the stress rate or increasing the temperature will decrease the compressive modulus of HDPE. An approximate linear relationship between the creep strain rate and the ratcheting strain rate under different temperatures and stress ratios was observed. The compressive deformation characteristics of HDPE were compared with that of some other gasket materials, a universal phenomenon is found that the compressive ratcheting evolution with time can be characterized by creep approximately under the same loading peak stress, stress rate and temperature for various gasket materials when the stress ratio is greater than zero, which indicates that the ratcheting deformation for gaskets under cyclic loads may be estimated by the corresponding static creep strain in practical engineering.

In order to better describe the uniaxial ratcheting behavior of Z2CDN18.12N austenitic stainless steel, the Abdel-Karim-Ohno model was improved under the framework of the unified viscoplastic cyclic constitutive theory. By introducing a plastic strain memory surface into the isotropic hardening rule, the model parameters were determined. Further, the Abdel-Karim-Ohno model and the improved Abdel-Karim-Ohno model were used to predict the uniaxial ratcheting effect behavior of Z2CDN18.12N austenitic stainless steel at the room temperature. The influences of mean stress, stress amplitude, stress rate and loading history on the uniaxial ratcheting strain of Z2CDN18.12N austenitic stainless steel were studied by the two models, respectively. The uniaxial ratcheting strain level increased with the increasing mean stress and stress amplitude, decreased with the increasing stress rate, being more sensitive to the lower stress rate, and the loading history had great influence on the ratcheting behavior. Comparison of the prediction results of the two models with the experimental data proved the effectiveness of the improved model. [ABSTRACT FROM AUTHOR]

Copyright of Railway Standard Design is the property of Railway Standard Design Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

The modeling of cyclic behavior in rock remains a challenge due to complex deformation characteristics. This paper studied the mechanical behaviors of granite samples under uniaxial cyclic loading and unloading through cyclic compression tests and acoustic emission (AE) monitoring. Then, a comprehensive body that consisted of an elastic element, plastic element, and friction element was proposed to describe the stress–strain relationship with respect to cyclic behavior, in which the friction element was connected in parallel with the serial combination of the elastic element and plastic element. Finally, the parameters of the proposed model were calibrated based on the mechanism analysis and backpropagation (BP) neural network. Results show that the behavior during unloading is primarily elastic and is accompanied by the obstruction of friction. During reloading, the behavior changes from elastic to elastic–plastic before and after the Kaiser point. The tangential modulus of the elastic element is dynamic in a linear positive correlation with elastic strain and a linear negative correlation with plastic strain; specifically, the elastic strain controls the variation process of the elastic modulus while the plastic strain determines the lower limit. The constitutive law of the plastic element is expressed by a logistic function, which means that the plastic strain increases in a trend of acceleration–deceleration. The friction element plays a major role in processing the massing effect, and the plastic element is prompted before the historical maximum stress, which reflects the ratcheting effect and Felicity effect. The reliability of the proposed constitutive model is confirmed by the comparison of the simulated stress–strain curves with the experimental curves. [ABSTRACT FROM AUTHOR]

Taut moorings have become a prospective solution for keeping associated stations of floating production systems stationary. For most taut mooring lines, the uplift angle at the padeye of the anchor can reach up to 40°. To withstand this vertical load, embedded anchors are widely employed with the padeye some distance below the mud-line, causing part of the bottom chain to be embedded in the soil. This configuration gives rise to chain–soil interaction problems. The complex chain–soil interaction impedes reliable estimation of the mooring line response. In the present study, an experimental investigation of a taut mooring line in silica sand has been conducted, with the chain–soil interaction taken into consideration, to have a better understanding of the mooring dynamics. Two configurations were employed for the case study and the sensitivity study on the fairlead motion amplitude and period. The mechanism of the chain–soil interaction is reflected by the line tension, as measured by load cells and video capture by underwater cameras. A ratcheting effect is observed, which is the irreversible mobilisation of the mooring line and tension reduction during cyclic excitations. This is caused by the plastic and elastic nature of the soil. Sensitivity results indicate that the maximum load increased with the excitation amplitude but was insensitive to the excitation period. [ABSTRACT FROM AUTHOR]

Taking advantage of the EUM-25 K20 tension-torsion fatigue testing machine by CARE,the cryogenic uniaxial ratcheting tests were carried out for the S30408 specimens with and without weld,and with 0%,8%,and 12% pre-strains at110 K. It is shown that ratcheting behavior of specimens with and without weld is closely related to mean stress,amplitude stress and loading history. Because of the softening effect of a small amount of ferrite in weld metal,the initial ratcheting strain of weld specimen and ratcheting strain of weld specimen under small cyclic stress is larger than that of base metal. However,with the increase of plastic deformation,the higher content of alloying elements in weld metal has a more obvious strengthening effect,which makes the subsequent ratcheting strain of weld specimens with a certain number of cycles smaller than that of base metal under larger cyclic stress. The ratcheting strain of specimens with and without weld decreases with the increase of the pre-strain at cryogenic temperature. The accumulation of ratcheting strain can be completely restrained by pre-strain at a small cyclic stress level. S30408 is rate-dependent material at 110 K,and ratcheting strain decreases with the increase of loading rate.

Background: Ratcheting is an important mechanical behavior of metals and alloys, which is caused by the repeated accumulations of tensile and compressive strain in circle load. However, the current characterization methods of ratcheting effect are mostly based on standardized testing and uniform data, and more comprehensive field measurement data cannot be used. Objective: This paper focuses on how to make full use of field measurement data to characterize ratcheting effect and identify the corresponding kinematic constitutive. Methods: A nonlinear virtual field method that can invert the parameters of Chaboche constitutive from strain field data is proposed. And a return mapping strategy driven by iteration of internal variables is used to reconstruct the stress field, which ensures the convergence speed and global convergence in the black box search of the nonlinear virtual field method. Results: By using the finite-element model to generate the strain field data, the numerical experiment shows that the ratchet path identified by the nonlinear virtual field algorithm is basically consistent with the prior ratchet path generated by the finite-element simulation. The adaptability of the algorithm to data density and noise amplitude was also verified: under lower data noise interference, more strain field training data makes the inversion results more accurate; but in the case of high sound amplitude, it is necessary to reduce the data size to obtain accurate fitting results of the ratchet path. Conclusions: By training the measured field data from 3D-digital image correlation, it is shown that the algorithm can also run effectively under the complex working conditions of non-uniform deformation. [ABSTRACT FROM AUTHOR]

An aluminium/steel CMT-welded joint is mainly composed of fusion zone (FZ), interfacial intermetallic compound (IMC) zone, and heat-affected zone (HAZ). IMC and FZ are the weakest link in the welded joint. The fatigue fracture indicates that the lattice distortion caused by the lattice mismatch of Fe2Al5 and Fe is more likely to engender dislocation slipping and cracks easily nucleate during the fatigue testing. The hysteresis loop is shifted to the right, which indicating that the specimen experiences a ratcheting effect. In the high-stress condition, the cyclic hardening induced by the ratcheting strain is much stronger than that in the lower stress condition, which improves the fatigue life of the materials. [ABSTRACT FROM AUTHOR]

In this paper, a study was conducted on the ratcheting-fatigue tests of internal pressurized elbow in the primary circuit of nuclear power plant under force and displacement cycling, and the ratcheting effects at the critical locations of the elbow were evaluated. Based on thermodynamics and continuous damage mechanics theory, the damage evolution rule of the material was derived according to the derivative relationship between damage dissipation potential and damage related variable. A cyclic plastic constitutive model with damage was established by combining the damage evolution rule with Chen-Jiao-Kim (CJK) kinematic hardening rule. The subroutine of this constitutive model was embedded in ANSYS finite element software to numerically evaluate the evolution law of the whole-life ratcheting of the elbow. The results indicate that this damage-coupled kinematic hardening model can describe the whole-life ratcheting behavior of the elbow, and the numerical calculation results and experimental data are basically identical. • Ratcheting-fatigue behavior of internal pressurized elbow is studied. • A new damage evolution rule is derived and coupled with kinematic hardening rule. • The model describes the whole-life ratcheting behavior of the elbow well. [ABSTRACT FROM AUTHOR]

Soil-abutment or soil-pile interactions under cyclic static loads have been widely studied in integral abutment jointless bridges (IAJBs). However, the IAJB has the combinational interaction of soil-abutment and soil-pile, and the soil-abutment-pile interaction is lack of comprehensively study. Therefore, a reciprocating low-cycle pseudo-static test was carried out under an cyclic horizontal displacement load (DL) to gain insight into the mechanical behavior of the soil-abutment-pile system. Test results indicate that the earth pressure of backfill behind abutment has the ratcheting effect, which induced a large earth pressure. The soil-abutment-pile system has a favorable energy dissipation capacity and seismic behavior with relatively large equivalent viscous damping. The accumulative horizontal deformation in pile will be occurred by the effect of abutment and unbalance soil pressure of backfill. The test shows that the maximum horizontal deformation of pile occurs in the pile depth of 1.0b~3.0b of pile body rather than at the pile head due to the accumulative deformation of pile, which is significantly different from those of previous test results of soil-pile interaction. The time-history curve for abutment is relatively symmetrical and its accumulative deformation is small. However, the time-history curve of pile is asymmetrical and its accumulative deformation is dramatically large. The traditional theory of deformation applies only to the calculation of noncumulative deformation of pile, and the influence of accumulative deformation should be considered in practical engineering. A significant difference of inclinations in the positive and negative directions increases when the displacement load is relatively large. The rotation of abutment when bridge expands is larger than that when bridge contracts due to earth pressure of backfill. [ABSTRACT FROM AUTHOR]

Asymmetric ratcheting effect occurs when an unfavorable (favorable) budget variance causes in increase (decrease) in next period’s budget. The current study aims to investigate the existence of this effect on budgeted earning in Tehran stock exchange. We assume that the forecasted earning, which the firms listed in TSE are obligated to disclose, is the reflection of internal budget of the firm and the determined performance. By this disclosure, firms give their controlling instrument to capital market. Statistical sample includes 325 firms listed on TSE during 1386 to 1392. The results reveal that deviation from budgeted earning has a significant effect on the next period’s budget and unfavorable deviation effect is more than the favorable one.

This paper modifies the Gurson-Tvergaard-Needleman (GTN) model, originally limited to depicting the microvoids evolution under monotonic loading, into a constitutive model capable of reflecting the effect of alternating loads, and compiles a VUMAT user subroutine in the Abaqus/Explicit to calculate the microvoids evolution and mechanical behavior of materials under specified stress triaxiality. Before the calculation, the parameters of the modified GTN model were calibrated by the finite-element cell model. The results show that the modified GTN model can rationally describe the mechanical behavior of materials with microvoid evolution under uniaxial and multiaxial cyclic load, and that the void evolution law under cyclic load is closely related to the stress state. The research findings shed new light on damage theories. [ABSTRACT FROM AUTHOR]

In this paper, deformation behaviors and microstructure evolution of a hot-rolled AZ31B magnesium alloy under cyclic loadings are investigated. The relationship between plastic deformation and microstructure evolution and the crack formation mechanisms are discussed. Under a high cyclic stress (90–140 MPa), steady ratcheting effect occurred in the material and the development of ratcheting strain went through three stages: 1) Stage I - initial rapid increase stage; 2) Stage II - steady stage; and 3) Stage III - final abrupt increase stage. Under a low cyclic stress (≤ 90 MPa), inconspicuous ratcheting effect was found in the material, indicating a light damage in the material. When the cyclic stress is below 30 MPa, no ratcheting effect is found and only elastic deformation occurs in the material. The formation of cracks in Stages I & II is mainly due to the activation of the basal slip system. The mean geometrically necessary dislocations (GND) are calculated to analyze the relationship between the basal slip and the ratcheting effect during the cyclic loading. Finally, a new approach is proposed to estimate the AZ31B magnesium alloy’s cyclic strength (at 10 7 cycles) according to the cyclic stress at which steady ratcheting effect starts to occur in the material. [ABSTRACT FROM AUTHOR]

Ratcheting effect refers to the cyclic accumulation of plastic strain under alternating load, is one of the reasons leading to the failure of mechanical structures. The concept of structural ratchet was first put forward in 1996, in which the ratcheting effect of pressurized piping belongs to a kind of structural ratchet. In this paper, the related research on ratcheting effect of pressurized piping structure in recent years is reviewed, including the experimental research and finite element analysis of typical pipeline structures such as straight pipe and elbow pipe, as well as some special structure pipelines. On this basis, some cyclic methods and non-cyclic methods are used to determine the ratcheting boundary of the structure and guide the safety design of the pipeline structure. The continuous development of finite element technology provides a reliable research method for the follow-up study of ratcheting effect of structures under complex conditions. Determining the parameters of the constitutive model from the structural level also provides a new idea for the follow-up study of structural ratchet. The rise of some frontier science and technology can also be used as a new method for research in this field. • Recent progress on ratcheting effect of pressurized piping is reviewed from 2010. • Experimental study of ratcheting effect of pressurized piping is introduced. • Finite element analysis of ratcheting effect of pressurized piping is introduced. • Methods of determining the ratchet boundary of pressurized piping are summarized. [ABSTRACT FROM AUTHOR]

Soil-abutment or soil-pile interactions under cyclic static loads have been widely studied in integral abutment jointless bridges (IAJBs). However, the IAJB has the combinational interaction of soil-abutment and soil-pile, and the soil-abutment-pile interaction is lack of comprehensively study. Therefore, a reciprocating low-cycle pseudo-static test was carried out under an cyclic horizontal displacement load (DL) to gain insight into the mechanical behavior of the soil-abutment-pile system. Test results indicate that the earth pressure of backfill behind abutment has the ratcheting effect, which induced a large earth pressure. The soil-abutment-pile system has a favorable energy dissipation capacity and seismic behavior with relatively large equivalent viscous damping. The accumulative horizontal deformation in pile will be occurred by the effect of abutment and unbalance soil pressure of backfill. The test shows that the maximum horizontal deformation of pile occurs in the pile depth of 1.0b~3.0b of pile body rather than at the pile head due to the accumulative deformation of pile, which is significantly different from those of previous test results of soil-pile interaction. The time-history curve for abutment is relatively symmetrical and its accumulative deformation is small. However, the time-history curve of pile is asymmetrical and its accumulative deformation is dramatically large. The traditional theory of deformation applies only to the calculation of noncumulative deformation of pile, and the influence of accumulative deformation should be considered in practical engineering. A significant difference of inclinations in the positive and negative directions increases when the displacement load is relatively large. The rotation of abutment when bridge expands is larger than that when bridge contracts due to earth pressure of backfill.

The ratcheting fatigue behavior of Z2CN18.10 austenitic stainless steel elbow under internal pressure and cyclic loading was studied. The evolution of axial and hoop ratcheting strains at four different positions, respectively at intrados (0°), 45°, crown (90°) and extrados (180°) on the outer surface of the elbow was discussed. It is shown that the hoop ratcheting strain of the elbow is always greater than the axial ratcheting strain. Under cyclic test with force control, the order of ultimate hoop ratcheting strain is intrados (0°)>crown (90°)> 45°> extrados (180°). Under cyclic test with displacement control, the order of ultimate hoop ratcheting strain is 45°> intrados (0°)> crown (90°)> extrados (180°). Under cyclic tests with both force and displacement control, the crown (90°) of the elbow leaked first, which is the critical point to evaluate ratcheting fatigue life. Afterward, the ratcheting fatigue life is predicted based on ASME code, and it is found that the prediction results tend to be non-conservative. Then, a modified Manson-Coffin equation considering ratcheting strain is proposed to predict fatigue life of elbow well. • Ratcheting fatigue behavior of Z2CN18.10 stainless steel elbow is studied. • Crown (90°) of elbow is the critical position to evaluate ratcheting fatigue life. • ASME code tends to be non-conservative in predicting ratcheting fatigue life. • A modified Manson-Coffin equation can predict ratcheting fatigue life well. [ABSTRACT FROM AUTHOR]

Ratcheting deformation is studied on straight pipe made of Z2CND18.12 N stainless steel with local wall thinning subjected to constant internal pressure and reversed bending using finite element analysis. The local wall thinning is located at the center of straight pipe, whose geometry is rectangular cross-section. The effect of depth, axial length and circumferential length on the ratcheting behavior of straight pipe is studied in this paper. Three-dimensional elastic-plastic analyses with ANSYS employed Chen–Jiao–Kim (CJK) kinematic hardening model is carried out to evaluate structural ratcheting behaviors. Results indicate that ratcheting strain is along the center of straight pipe extending to the two ends. The ratcheting strain occurs mainly at hoop direction. Axial ratcheting strain is relatively small. The effects of the depth, axial length and circumferential length of local wall thinning on the ratcheting response are discussed by CJK model. [ABSTRACT FROM AUTHOR]

Ratcheting deformation is studied on straight pipe made of Z2CND18.12N stainless steel with local wall thinning subjected to constant internal pressure and reversed bending using finite element analysis. The local wall thinning is located at the centre of straight pipe, whose geometry is rectangular cross-section. The effect of depth, axial length and circumferential length on the ratcheting behavior of straight pipe is studied in this paper. Three-dimensional elastic-plastic analyses with ANSYS in which Chen–Jiao–Kim (CJK) kinematic hardening model is carried out to evaluate structural ratcheting behaviors. Results indicate that ratcheting strain is along the centre of straight pipe extending to the two ends. The ratcheting strain occurs mainly at hoop direction. Axial ratcheting strain is relatively small. The effects of the depth, axial length and circumferential length of local wall thinning on the ratcheting response are discussed by CJK model. [ABSTRACT FROM AUTHOR]

• The whole process of ratcheting effect is simulated. • The proposed anisotropic damage evolution law coupled with the constitutive model can well simulate the evolution of the ratcheting effect. • Different damage evolution trends are well identified by damage index ζ. Stress-controlled low cycle fatigue tests with different mean stress of a second-generation nickel-based single crystal superalloy DD6 with [0 0 1] orientation is investigated in the current study. The observation of fracture surface and microstructure show that although the phase structure does not change for different conditions, the damage failure mode changes for different mean stress. It is found that ratcheting strain exhibits a significant dependency on mean stress and microstructure damage. Ratcheting strain cannot be simulated only considering the evolution of back stress. To simulate the whole process evolution of ratcheting strain, crystal plasticity constitutive model coupled with a new anisotropic damage is developed. The simulated results showed that the anisotropic damage model could accurately predict the ratcheting strain for different mean stress. Different damage evolution modes are well identified by a damage index in the proposed model. [ABSTRACT FROM AUTHOR]

The paper tries to explain the biological evolutionary mechanism based on Parrondo's games. The multi-agent Parrondo's games proposed include game A and game B. Game A, a zero-sum game, reflects the interactive relationship of competition or cooperation between individuals. A two-dimensional lattice network is used to represents the spatial carrier of interactive relationship. Game B, a negative-sum game, reflects the environmental effect on survival evolution of individuals. Three patterns which are based on individual survival states, on historical experience and on neighbors' environment are adopted to represent the mechanisms. The simulation results show that: (1) A zero-sum game (game A) and a losing game (game B) combined could produce a winning result. Improvement of the average fitness of the population represents the essence that Parrondo's paradox is counterintuitive. The special structure of game B reflects the ratcheting effect that natural environment has on biological evolution where both competition and cooperation are successful evolution directions. (2) The ratcheting effect of the environment-based pattern is the strongest. In the course of biological evolution, neighbors' environment usually uses an efficient mechanism to guide the evolution. Just because of the neighbors' environment-based guidance, a coevolution model is formed where individuals compose the population which composes the community and the community composes the ecosystem which composes the biosphere. (3) Competition can raise the average fitness of the population. Therefore, competition may be an adaptive behavior on the population level. (4) Research to-date has shown that the necessary condition of producing cooperation is that the cost is less than profit. While the results in this paper show that a zero-sum game can also give rise to cooperation, which can bring about positive gain for the whole population. [ABSTRACT FROM AUTHOR]

Abstract: 16MnR steel is widely used in pressure vessel in China and its ratcheting and fatigue behavior have attracted numerous interest during the past years. In this study, a series of experiments were performed on the uniaxial ratcheting deformation of 16MnR steel. The effects of stress amplitude and mean stress on the ratcheting strain were discussed under uniaxial asymmetrical stress cycling. It shows that ratcheting strain and ratcheting strain rate increase with mean stress and stress amplitude increased under the same stress amplitude and mean stress. At the same time, the increasing ratcheting strain causes fatigue damage, which reduces fatigue life of the material. With the mean stress increased, the fatigue life decreases correspondingly. The fatigue lives obtained from the fully reversed uniaxial loading are also compared with the ratcheting-fatigue experiment results. Finally, the modified model based on Ohno–Wang model by Chen and Jiao is used to predict ratcheting strain. The modified model predicts the uniaxial ratcheting strain of 16MnR steel till 400 cycles very well. [Copyright &y& Elsevier]

This paper describes a general method for deriving the plastic corrections and the consistent tangent modulus for a wide range of arbitrary non-linear hardening models within the framework of standard small strains elastoplasticity. The features of the proposed formulation are: (i) the local solution is obtained through an iterative procedure. The plastic corrections are given in closed forms exhibiting one scalar function denoted by Galg and three fourth-order tensors Dalg, Galg, Lalg, which are shown to be the algorithmic discrete counterparts of usual theoretical continuum quantities, (ii) the consistent tangent modulus has a symmetrical expression involving the same quantities. Finite element computations are performed using a particular non-linear kinematic hardening model and allow to exhibit the ratcheting phenomenon usually observed on mechanical components subjected to cyclic loadings. [Copyright &y& Elsevier]

The thermomechanical fatigue (TMF) of single-crystal air-cooled turbine blades is critical for accurately evaluating the lifetimes of advanced aero-engines. The present work focuses on the mechanical behavior and damage mechanism of a single-crystal Ni-based superalloy (DD6) under stress-controlled TMF loading, and in-phase (IP) and out-of-phase (OP) mode of TMF were conducted and compared with low cycle fatigue (LCF) loading. A ratcheting effect is observed during the deformation of DD6 under TMF loading, and the direction and size of the ratcheting strain are considerably influenced by the phase angle and mechanical load. The ratcheting strain increases with mechanical load and dwell time at high temperature, consequently shortening the lifetime of the material. The key factors affecting the TMF damage of DD6 are identified through a SEM analysis, which shows that the damage under IP TMF loading mainly comes from creep and fatigue, whereas that under OP TMF loading is dominated by oxidation and fatigue. Based on the critical plane approach, a fatigue life prediction model is proposed considering the ratcheting effect to predict the fatigue life of DD6 under TMF loading. The good agreement between the proposed model and experimental data indicates that the model has the potential to predict the fatigue life of DD6 under TMF loading. • The phase angle and mechanical load influence the direction and size of the ratcheting strain for DD6 under TMF loading. • The ratcheting strain increases with mechanical load and dwell time at high temperature, shortening lifetime of materials. • The damage under IP TMF mainly due to creep and fatigue, whereas under OP TMF is dominated by oxidation and fatigue. • Propose a fatigue life model considering the ratcheting effect to predict the fatigue life of DD6 under TMF loading. [ABSTRACT FROM AUTHOR]

The concept of "cyclic ultimate strength" of ship hull structures is proposed. In navigating in waves a ship is subjected to alternate bending moments in hogging and sagging conditions. The present study aims to demonstrate that the ship hull girder can experience a weaker ultimate strength under cyclic loading than under monotonically increasing bending moment as assumed in the conventional analysis. Nonlinear finite element method is employed, using the explicit LS-DYNA solver, to analyse the ultimate strength of a container ship hull structure subjected to monotonic and cyclic bending moments. The numerical analyses under cyclic loading consider the ratcheting effect and the Bauschinger effect in steel. The ship hull girder can break due to the plastic strain accumulation and alternating plasticity collapse when the cyclic external load is greater than the elastic limit but lower than the monotonic ultimate limit. The collapse modes of the hull girder under monotonic and cyclic loadings are compared to reveal their different failure principles. • The concept of "cyclic ultimate strength" of ship hull structures is proposed. • It is demonstrated that the ship hull girder can experience a weaker ultimate strength under cyclic loading. • The numerical analyses under cyclic loading consider the ratcheting effect and the Bauschinger effect in steel. • The ship hull girder breaks due to the plastic strain accumulation and alternating plasticity collapse. [ABSTRACT FROM AUTHOR]

• Ratcheting effect is studied on lateral nozzle of cylinder with local wall thinning. • Lateral nozzle of cylinder with different defect is under different bending. • Ratcheting boundary of lateral nozzle of cylinder with defect is determined by LMM. Ratcheting effect of pressurized lateral nozzle of cylinder with local wall thinning is studied using Chaboche model in ANSYS. Firstly, the influence of internal pressure, bending loading, loading path, loading history and the different defect sizes on ratcheting effect of pressurized oblique nozzle with local wall thinning is studied in this study. The results indicate that ratcheting strain increased with the increasing of internal pressure and bending moment and is affected by the different loading paths and loading history. Secondly, the effect of different defect sizes such as defect depth, depth length and defect hoop angle on ratcheting behavior of pressurized oblique nozzle with local wall thinning is studied. The results investigated that ratcheting strain of the lateral nozzle of cylinder with local inside wall thinning under cyclic bending increased with the increasing of defect depth, had no relationship with the increasing of defect length and ratcheting strain of the lateral nozzle of cylinder with local wall thinning under cyclic bending increased with the increasing of defect circumferential angle. Finally, the ratcheting boundary of pressurized lateral nozzle of cylinder with different defect size is determined by linear matching method. The results show that the increase of the defect depth could induce a remarkable increase of the reverse plasticity and the ratchet limits of the component, the defect length has a slight effect on the reverse plasticity and ratchet limits of the component and the increase of the defect circumferential angle could induce a remarkable increase of the reverse plasticity and the ratchet limits of the component. [ABSTRACT FROM AUTHOR]

In this contribution, the ratcheting behavior and local field distribution of unidirectional metal matrix composites are investigated under cyclic loading. To that end, we extended the finite-volume direct averaging micromechanics (FVDAM) theory by incorporating the rule of nonlinear kinematic hardening. The proposed method enables efficient and accurate simulation of the ratcheting behavior of unidirectional composites. The local satisfaction of equilibrium equations of the FVDAM theory facilitates quick and rapid convergence during the plastic iterations. To verify the proposed theory, a finite-element (FE) based unit cell model is constructed with the same mesh discretization. The remarkable correlation of the transverse response and local field distribution generated by the FVDAM and FE techniques demonstrates the effectiveness and accuracy of the proposed models. The stress discontinuities along the fiber/matrix interface that are generic to the finite-element theory are absent in the FVDAM prediction. The effects of thermal residual stresses induced during the consolidation process, as well as fiber orientations, are revealed. The generated results indicate that the FVDAM is well suited for simulating the elastic-plastic ratcheting behavior of metal matrix composites, which will provide the conventional finite-element based technique with an attractive alternative. [ABSTRACT FROM AUTHOR]

The ground motion characteristics are essential for understanding the structural seismic response. In this paper, the time-frequency analytical method is used to analyze the time-frequency energy distribution of ground motion, and its effect on the dynamic response of nonlinear structure is studied and discussed. The time-frequency energy distribution of ground motion is obtained by the matching pursuit decomposition algorithm, which not only effectively reflects the energy distribution of different frequency components in time, but also reflects the main frequency components existing near the peak ground acceleration occurrence time. A series of artificial ground motions with the same peak ground acceleration, Fourier amplitude spectrum, and duration are generated and chosen as the earthquake input of the structural response. By analyzing the response of the elasto-perfectly-plastic structure excited by artificial seismic waves, it can be found that the time-frequency energy distribution has a great influence on the structural ductility. Especially if there are even multiple frequency components in the same ground motion phrase, the plastic deformation of the elasto-perfectly-plastic structure will continuously accumulate in a certain direction, resulting in a large nonlinear displacement. This paper reveals that the time-frequency energy distribution of a strong ground motion has a vital influence on the structural response. [ABSTRACT FROM AUTHOR]