Journal of the Mechanics and Physics of Solids, 2021
The cyclic plasticity behaviour and failure mechanism of the cathode material in lithium-ion batt... more The cyclic plasticity behaviour and failure mechanism of the cathode material in lithium-ion batteries urgently need to be understood due to the cyclic lithium-ion diffusion-induced stress during charging-discharging process. Many researches have focused on the shakedown and ratcheting responses of lithium-ion battery anode. However, the systematic investigation on the plasticity behaviour of lithium-ion battery cathode is still lacking. In this paper, the cyclic plasticity behaviour of LiNixMnyCozO2 electrode subjected to cyclic lithiation/delithiation under a constant mechanical load is investigated comprehensively. The shakedown, ratcheting and fatigue analyses of active layer are conducted using direct numerical techniques based on the Linear Matching Method framework, while coin cell electrochemical experiments are performed simultaneously to support the analysis. The effect of thickness of coating on the shakedown and ratcheting response is investigated, and the thickness is confirmed 2 as a crucial parameter that can influence the battery performance. The strain-fatigue life curve is also obtained to effectively predict the life of active coating. Moreover, the numerical results reveal the existence of low cycle fatigue at the centre, and ratcheting mechanism on the edge of the cathode, which is consistent well with the experimental result.
LiNixMnyCozO2 (NMC) is among the most promising cathode materials for commercial Li-ion batteries... more LiNixMnyCozO2 (NMC) is among the most promising cathode materials for commercial Li-ion batteries due to its high electrochemical performance. However, NMC composite cathode is still plagued with limited cyclic performance, which is influenced by its structural stability during the cycling process. The cathode, which comprises of the active material, polymeric binder, and porous conductive matrix, often exhibits large structural variation during the electrochemical cycling process. This inevitably increases the challenge of measuring the mechanical properties of the material. Even though single crystal NMC possesses better stability as compared to the polycrystalline NMC, the electrochemical performance degradation of single crystal NMC cathode remains relatively unexplored. Different sample preparation methods are compared systematically in accordance to the previous report, and a new method of sample preparation is proposed. Nano-indentation instrument is used to measure the elast...
International Journal of Pressure Vessels and Piping, 2021
For industrial components such as pressure vessels and piping systems, it is important to determi... more For industrial components such as pressure vessels and piping systems, it is important to determine the shakedown domains of structures under complex variable thermo-mechanical loads to avoid low cycle fatigue due to alternating plasticity or incremental plastic collapse caused by ratcheting. In this paper, the interaction among three common types of stresses are considered based on a plane model, namely, mechanical membrane stress, thermal membrane stress and thermal bending stress. Strict shakedown analysis is performed based on the Linear Matching Method under multiple variable mechanical and thermal loads. Three-dimensional shakedown domains for three types of modified Bree problems involving thermal membrane stress and generalized loading conditions are given for the first time, and the three-dimensional shakedown boundaries are expressed as two-dimensional parametric equations by introducing a new parameter called "secondary membrane bending ratio" R. By comparing the 3S criterion plane with the newly obtained 3D shakedown boundaries ， the conservatism and non-conservatism of the 3S criterion are discussed under different loading paths. As an extension of the 3S criterion, a new and economical criterion on elastic shakedown assessment is proposed for generalized thermomechanical loading. The proposed shakedown boundary parametric equations and shakedown checking method can provide guidance for engineering design and safety assessment.
International Journal of Pressure Vessels and Piping, 2021
Creep-cyclic plasticity and creep-fatigue damage interaction of a welded flange are studied consi... more Creep-cyclic plasticity and creep-fatigue damage interaction of a welded flange are studied considering both the thermo-mechanical load and the welding residual stress (WRS). The presence of WRS was found to have a minimal effect on the shakedown and ratcheting interaction curve, though the stress distribution changes considerably in the presence of WRS. The effect of WRS is predominant for the initial cycles after which it relaxes so that at steady state the creep-cyclic plasticity response is similar with and without WRS. Depending on the magnitude and sign of the WRS at different locations in the weldment, it has both detrimental and beneficial effect on the creep-fatigue life. Investigations are carried out using the Linear Matching Method (LMM), which is further modified to assess the creepfatigue damage considering both transient cycles and the WRS. Results show that the presence of weldment induces tensile and compressive stress/strain at the vicinity of the weldment, which substantially influences the creep and fatigue damage. The presence of WRS further complicates this. For all the combinations of damage calculations undertaken, with and without the consideration of WRS or mean strain, the order of elements with maximum damage differed.
The mechanical failure of battery electrode, caused by the cyclic diffusion-induced stress, is ge... more The mechanical failure of battery electrode, caused by the cyclic diffusion-induced stress, is generally thought to be a direct reason leading to the loss of capacity and deterioration of performance for Liion battery. In the present work, the cyclic plasticity behaviour of primary electrode particle under electrochemical-mechanical condition is evaluated by using the Linear Matching Method (LMM). The coupled diffusion-stress analysis of electrode particle during lithiation-delithiation process is performed with the developed finite element subroutines as the groundwork for the subsequent cyclic plasticity assessment. The shakedown boundaries are established for electrode particle considering the variation of particle diameter by means of the LMM. ABAQUS full cyclic incremental analysis is employed to verify the applicability and accuracy of the obtained boundary. Two types of failure mechanisms known as low-cycle fatigue and ratcheting are investigated for particle subjected to loading history out of shakedown boundary. Steady state cycle analysis is conducted to study the generation of plastic strain range of particle under certain electrochemical-mechanical condition and the corresponding low-cycle fatigue damage is assessed. Different forms of ratcheting boundaries for electrode particle with various dimensions are created and the influences of cyclic current density and mechanical load on cyclic plasticity limits are clarified. The established critical failure diagrams will offer the instructional information regarding the design of electrode material in microscale within designated electrochemical condition.
Evaluation of creep rupture limit and prediction of creep rupture life are two significant issues... more Evaluation of creep rupture limit and prediction of creep rupture life are two significant issues for high-temperature devices under the action of cyclic thermo-mechanical loadings. In this paper, the shakedown solution procedure proposed recently by the authors, so-called stress compensation method (SCM), is extended for creep rupture assessment via an extended shakedown theory including creep. Two distinct numerical schemes based on the SCM framework are presented, where Scheme 1 is utilised for evaluation of creep rupture limit and Scheme 2 is utilised for prediction of creep rupture life. Instead of using the detailed creep constitutive equations, the present methods just need to know several material parameters including the creep rupture data. A holed plate is provided as a typical example to validate the reliability of two numerical schemes. Detailed cycle-by-cycle analyses are carried out to illustrate the good accuracy of these calculated creep rupture limits and reveal the failure mechanisms of the structure under different combinations of loads. A numerical study on a pipe junction is also conducted to show the engineering application of the methods. As a result, the two numerical schemes are proved to be effective and reliable for solving practical industrial problems.
This paper presents a novel direct method for the structural shakedown analysis considering limit... more This paper presents a novel direct method for the structural shakedown analysis considering limited kinematic hardening and non-isothermal effect. The Melan's static shakedown theorem is extended to consider limited kinematic hardening material and implemented into the Linear Matching Method (LMM) shakedown module. Instead of using a specific kinematic hardening rule and an explicit back stress field, the general nonlinear hardening laws are considered by using a two-surface hardening model. A two-stage procedure is developed in the extended LMM algorithm, which can generate the limited hardening shakedown envelope and the unlimited hardening curve efficiently and accurately. Also, the material non-isothermal effect is considered during the computation process of the shakedown limit by proposing a temperature-dependent hardening factor, in place of a constant and fictitious one. To validate the extended LMM method, a numerical test on a thin cylinder pipe with temperature-independent material properties is performed, and the results match well with ones from literature. Then, a numerical study on a typical aero-engine turbine disk is conducted to investigate the influence of temperature-dependent material properties and operating conditions. Several shakedown curves considering kinematic hardening effect are derived and adequately discussed. As a result, the extended LMM shakedown module is proven to be a robust, efficient and versatile tool for practical industrial problems.
In this paper a state-of-the-art numerical method is discussed for the evaluation of the shakedow... more In this paper a state-of-the-art numerical method is discussed for the evaluation of the shakedown and ratchet limits for an elastic-perfectly plastic body subjected to cyclic thermal and mechanical load history. The limit load or collapse load, i.e. the load carrying capacity, is also determined as a special case of shakedown analysis. These design limits in plasticity have been solved by characterizing the steady cyclic state using a general cyclic minimum theorem. For a prescribed class of kinematically admissible inelastic strain rate histories, the minimum of the functional for these design limits are found by a programming method, the Linear Matching Method (LMM), which converges to the least upper bound. By ensuring that both equilibrium and compatibility are satisfied at each stage, a direct algorithm has also been derived to determine the lower bound of shakedown and ratchet limit using the best residual stress calculated during the LMM procedure. Three practical examples of the LMM are provided to confirm the efficiency and effectiveness of the method: the behaviour of a complex 3D tubeplate in a typical AGR superheater header, the behaviour of a fiber reinforced metal matrix composite under loading and thermal cycling conditions, and effects of drilling holes on the ratchet limit and crack tip plastic strain range for a centre cracked plate subjected to constant tensile loading and cyclic bending moment.
Design and Analysis Methods and Fitness for Service Evaluations for Pressure Vessels and Components, 2003
Methods for the Evaluation of Creep Relaxation and the Amplitude of Reverse Plastic Strain for Bo... more Methods for the Evaluation of Creep Relaxation and the Amplitude of Reverse Plastic Strain for Bodies Subjected to Cyclic Loading. [ASME Conference Proceedings 2003, 155 (2003)]. Haofeng Chen, Alan RS Ponter. Abstract. ...
International Journal of Pressure Vessels and Piping, 2005
In an accompanying paper [Int J Pres Ves Pip, 2004], a 3D tubeplate in a typical AGR superheater ... more In an accompanying paper [Int J Pres Ves Pip, 2004], a 3D tubeplate in a typical AGR superheater header was analysed for the shakedown limit, reverse plasticity and ratchet limit based on the application of the linear matching method (LMM). Both the perfectly plastic model and the cyclic hardening model were adopted for the evaluation of the plastic strain range. In the present paper, based on the creep-reverse plasticity model, the accumulated creep strain during a creep dwell at the steady cyclic state is assessed by the LMM. The accumulated creep strains, the creep flow stresses as well as the elastic follow-up factors with differing dwell times are evaluated in detail. The total inelastic strain over the cycle at the steady cyclic state is calculated. By comparing these results with ABAQUS step-by-step inelastic analyses, the applicability of the methods is demonstrated.
International Journal of Pressure Vessels and Piping, 2004
A series of numerical procedures have been presented recently for the integrity assessment of str... more A series of numerical procedures have been presented recently for the integrity assessment of structures based upon the Linear Matching Method. A typical example of a holed plate has been used to verify these procedures for the evaluation of plastic and creep behaviours of components. In this paper, a more complex 2D tubeplate at the outlet from a typical AGR heat exchanger is analysed for the shakedown limit, reverse plasticity, ratchet limit and creep relaxation based on the application of the Linear Matching Method for a thorough case study. Both a constant material yield stress and a temperature-dependent yield stress are adopted for the evaluation of the ratchet limit. For the evaluation of accumulated creep strains, flow stresses and elastic follow-up factors with differing dwell times at the steady cyclic state, a monotonic creep computation is performed, where the start-of-dwell stress is the rapid cycle creep solution at the beginning of the dwell period. An estimation of the tubeplate lifetime is then obtained by the evaluation of fatigue and creep endurances.
International Journal for Numerical and Analytical Methods in Geomechanics, 2006
We investigate the performance of a sequential programming method, based on the linear matching m... more We investigate the performance of a sequential programming method, based on the linear matching method, for the direct evaluation of limit loads and shakedown limits for elastic-perfectly plastic bodies subjected to complex histories of loading. This end is achieved by solving a sequence of linear problems defined with spatially varying moduli, which relates properties of the yield condition to those of the linear problems. The method provides a sequence of upper bounds that monotonically reduces and converges to the least upper bound associated with the chosen class of displacement fields, provided a sufficient condition is satisfied. We applied this method to a class of isotropic yield condition that depends not only on the von Mises effective stress but also on the hydrostatic pressure. This is followed by a set of examples of finite element solutions including the problem of a circular Hertzian contact region that repeatedly traverses the surface of an elastic-perfectly plastic half-space. Numerical examples demonstrate that the convergence is still obtained when the sufficient condition as given by Ponter et al. (Eur. J. Mech. 2000; 19:401-421) is violated, i.e. the condition is sufficient but not a necessary condition for convergence.
International Journal of Solids and Structures, 2006
There is a range of problems where repeated rolling or sliding contact occurs. For such problems ... more There is a range of problems where repeated rolling or sliding contact occurs. For such problems shakedown and limit analyses provides significant advantages over other forms of analysis when a global understanding of deformation behaviour is required. In this paper, a recently developed numerical method. Ponter and Engelhardt (2000) and Chen and Ponter (2001), for 3-D shakedown analyses is used to solve the rolling and sliding point contact problem previously considered by Ponter, Hearle and Johnson (1985) for a moving Herzian contact, with friction, over a half space. The method is an upper bound programming method, the Linear Matching Method, which provides a sequence of reducing upper bounds that converges to the least upper bound associated with a finite element mesh and may be implemented within a standard commercial finite element code. The solutions given in Ponter, Hearle and Johnson (1985) for circular contacts are reproduced and extended to the case when the frictional contact stresses are at an angle to the direction of travel. Solutions for the case where the contact region is elliptic are also given.
During the crack propagation process, the crack-branching behavior makes fracture more unpredicta... more During the crack propagation process, the crack-branching behavior makes fracture more unpredictable. However, compared with the crack-branching behavior that occurs in brittle materials or ductile materials under dynamic loading, the branching behavior has been rarely reported in welded joints under quasi-static loading. Understanding the branching criterion or the mechanism governing the bifurcation of a crack in welded joints is still a challenge. In this work, three kinds of crack-branching models that reflect simplified welded joints were designed, and the aim of the present paper is to find and capture the crack-branching behavior in welded joints and to shed light on its branching mechanism. The results show that as long as there is another large enough propagation trend that is different from the original crack propagation direction, then crack-branching behavior occurs. A high strength mismatch that is induced by both the mechanical properties and dimensions of different re...
Back-to-back pipe bends are widely adopted applications in many industries including nuclear sect... more Back-to-back pipe bends are widely adopted applications in many industries including nuclear sectors. Evaluation of their load bearing capability under complex cyclic loading is very important. Recently, a couple of research reported shakedown boundary of a 90° back-to-back pipe bends by adopting a conservative approach but no comprehensive post yield structural behaviors have been dealt with. In this research the concerning pipe bends subjected to cyclic opening in-plane (IP)/out-of-plane (OP) bending and steady internal pressures are analyzed to construct shakedown and ratchet limit boundary by means of the Linear Matching Method. Analyzed results present that the concerning pipe bends under out-of-plane bending has higher resistance to cyclic bending than under in-plane bending. In additions, the out-of-plane bending causes very small alternating plasticity areas, unlike the in-plane bending. Full cyclic incremental analyses known as step-by-step analysis are performed to verify ...
Different strength mismatched laboratory specimens that contain the compact tension (CT), single ... more Different strength mismatched laboratory specimens that contain the compact tension (CT), single edge-notched tensile (SENT), and central-cracked tension (CCT) specimens with various specimen geometries, loading configurations, and initial cracks were selected to investigate the effect range of the material constraint systematically. The results showed that the effect range of material constraint exists in all the strength mismatched specimens and structures. The numerical value of the effect range is influenced by the geometry constraint. The high geometry constraint reduces the effect range of material constraint. When a material is located outside the effect range of material constraint, the fracture resistance curves and crack propagation paths of the specimens and structures are no longer influenced by the mechanical properties of the material. In addition, an interaction exists between the geometry constraint and material constraint. The high geometry constraint strengthens th...
Fatigue & Fracture of Engineering Materials & Structures, 2017
In this paper, the extended Direct Steady Cyclic Analysis method (eDSCA) within the Linear Matchi... more In this paper, the extended Direct Steady Cyclic Analysis method (eDSCA) within the Linear Matching Method Framework (LMMF) is combined with the Stress Modified Ductility Exhaustion method and the modified Cavity Growth Factor (CGF) for the first time. This new procedure is used to systematically investigate the effect of several load parameters including load level, load type and creep dwell duration on the creep-fatigue crack initiation process in a notched specimen. The results obtained are verified through a direct comparison with experimental results available in the literature demonstrating great accuracy in predicting the crack initiation life and the driving mechanisms. Furthermore, this extensive numerical study highlighted the possible detrimental effect of the creepratchetting mechanism on the crack growth process. This work has a significant impact on structural integrity assessments of complex industrial components and for the better understanding of creepfatigue lab scale tests.
As the energy demand increases the power industry has to enhance both efficiency and environmenta... more As the energy demand increases the power industry has to enhance both efficiency and environmental sustainability of power plants by increasing the operating temperature. The accurate creep fatigue life assessment is important for the safe operation and design of current and future power plant stations. This paper proposes a practical creep fatigue life assessment case of study by the Linear Matching Method (LMM) framework. The LMM for extended Direct Steady Cycle Analysis (eDSCA) has been adopted to calculate the creep fatigue responses due to the cyclic loading under high temperature conditions. A pipe intersection with dissimilar material joint, subjected to high cycling temperature and constant pressure steam, is used as an example. The closed end condition is considered at both ends of main and branch pipes. The impact of the material mismatch, transitional thermal load, and creep dwell on the failure mechanism and location within the intersection is investigated. All the resul...
To meet the growing energy demands, the power sector continuously strives at enhancing the effici... more To meet the growing energy demands, the power sector continuously strives at enhancing the efficiency of its power plants by increasing the operating temperature. Under cyclic loading conditions, this leads to creep-cyclic plasticity driven damage mechanisms such as cyclically enhanced creep, creep enhanced plasticity and creep ratcheting. A detailed understanding of creep and related damages is therefore essential for predicting any potential failure mechanisms and ensuring confidence in the safe-working of the components. This becomes particularly difficult and challenging in the presence of welds due to two main reason; a) presence of different material zones, namely parent metal, weld metal and heat affected zone; b) introduction of residual stress during welding. An extended Direct Steady Cycle Analysis within the Linear Matching Method (LMM) framework has been previously developed to consider the full interaction between creep and cyclic plasticity. This paper presents the bas...
International Journal of Pressure Vessels and Piping, 2018
Ratcheting and low cycle fatigue are failure mechanisms observed in components subjected to cycli... more Ratcheting and low cycle fatigue are failure mechanisms observed in components subjected to cyclic temperature and mechanical loads. Ratcheting is a global failure mechanism which leads to an incremental plastic collapse of the component whereas low cycle fatigue is a localized mechanism which leads to crack initiation. It is exacerbated by grooves, notches and changes in the geometry of the component. To estimate the remaining life of the component and predict its failure mechanism, it is important to understand how it responds to various combinations of cyclic loads. This paper includes investigation of the ratchet limit and the plastic strain range, which is associated with the low cycle fatigue, of a circumferential butt-welded pipe by using the ratchet analysis method which includes Direct Steady Cycle Analysis (DSCA) within the Linear Matching Method Framework (LMMF). The pipe is subjected to a constant internal pressure and a cyclic thermal load. The investigation is carried out by varying 1) material properties of the weld metal (WM); 2) ratio of inner radius to wall thickness; 3) weld geometry. Within the specified ranges, yield stress and the ratio of inner radius to wall thickness affect the ratchet limit curve. The cyclic thermal load plays a crucial role compared to the internal pressure in influencing the ratchet limit curve. It is observed that the pipe experiences thermal ratcheting in the absence of pressure load at lower yield stress values of the WM. The results obtained are combined to create a limit load envelope, which can be used for the design of welded pipes within the specified ranges.
Journal of the Mechanics and Physics of Solids, 2021
The cyclic plasticity behaviour and failure mechanism of the cathode material in lithium-ion batt... more The cyclic plasticity behaviour and failure mechanism of the cathode material in lithium-ion batteries urgently need to be understood due to the cyclic lithium-ion diffusion-induced stress during charging-discharging process. Many researches have focused on the shakedown and ratcheting responses of lithium-ion battery anode. However, the systematic investigation on the plasticity behaviour of lithium-ion battery cathode is still lacking. In this paper, the cyclic plasticity behaviour of LiNixMnyCozO2 electrode subjected to cyclic lithiation/delithiation under a constant mechanical load is investigated comprehensively. The shakedown, ratcheting and fatigue analyses of active layer are conducted using direct numerical techniques based on the Linear Matching Method framework, while coin cell electrochemical experiments are performed simultaneously to support the analysis. The effect of thickness of coating on the shakedown and ratcheting response is investigated, and the thickness is confirmed 2 as a crucial parameter that can influence the battery performance. The strain-fatigue life curve is also obtained to effectively predict the life of active coating. Moreover, the numerical results reveal the existence of low cycle fatigue at the centre, and ratcheting mechanism on the edge of the cathode, which is consistent well with the experimental result.
LiNixMnyCozO2 (NMC) is among the most promising cathode materials for commercial Li-ion batteries... more LiNixMnyCozO2 (NMC) is among the most promising cathode materials for commercial Li-ion batteries due to its high electrochemical performance. However, NMC composite cathode is still plagued with limited cyclic performance, which is influenced by its structural stability during the cycling process. The cathode, which comprises of the active material, polymeric binder, and porous conductive matrix, often exhibits large structural variation during the electrochemical cycling process. This inevitably increases the challenge of measuring the mechanical properties of the material. Even though single crystal NMC possesses better stability as compared to the polycrystalline NMC, the electrochemical performance degradation of single crystal NMC cathode remains relatively unexplored. Different sample preparation methods are compared systematically in accordance to the previous report, and a new method of sample preparation is proposed. Nano-indentation instrument is used to measure the elast...
International Journal of Pressure Vessels and Piping, 2021
For industrial components such as pressure vessels and piping systems, it is important to determi... more For industrial components such as pressure vessels and piping systems, it is important to determine the shakedown domains of structures under complex variable thermo-mechanical loads to avoid low cycle fatigue due to alternating plasticity or incremental plastic collapse caused by ratcheting. In this paper, the interaction among three common types of stresses are considered based on a plane model, namely, mechanical membrane stress, thermal membrane stress and thermal bending stress. Strict shakedown analysis is performed based on the Linear Matching Method under multiple variable mechanical and thermal loads. Three-dimensional shakedown domains for three types of modified Bree problems involving thermal membrane stress and generalized loading conditions are given for the first time, and the three-dimensional shakedown boundaries are expressed as two-dimensional parametric equations by introducing a new parameter called "secondary membrane bending ratio" R. By comparing the 3S criterion plane with the newly obtained 3D shakedown boundaries ， the conservatism and non-conservatism of the 3S criterion are discussed under different loading paths. As an extension of the 3S criterion, a new and economical criterion on elastic shakedown assessment is proposed for generalized thermomechanical loading. The proposed shakedown boundary parametric equations and shakedown checking method can provide guidance for engineering design and safety assessment.
International Journal of Pressure Vessels and Piping, 2021
Creep-cyclic plasticity and creep-fatigue damage interaction of a welded flange are studied consi... more Creep-cyclic plasticity and creep-fatigue damage interaction of a welded flange are studied considering both the thermo-mechanical load and the welding residual stress (WRS). The presence of WRS was found to have a minimal effect on the shakedown and ratcheting interaction curve, though the stress distribution changes considerably in the presence of WRS. The effect of WRS is predominant for the initial cycles after which it relaxes so that at steady state the creep-cyclic plasticity response is similar with and without WRS. Depending on the magnitude and sign of the WRS at different locations in the weldment, it has both detrimental and beneficial effect on the creep-fatigue life. Investigations are carried out using the Linear Matching Method (LMM), which is further modified to assess the creepfatigue damage considering both transient cycles and the WRS. Results show that the presence of weldment induces tensile and compressive stress/strain at the vicinity of the weldment, which substantially influences the creep and fatigue damage. The presence of WRS further complicates this. For all the combinations of damage calculations undertaken, with and without the consideration of WRS or mean strain, the order of elements with maximum damage differed.
The mechanical failure of battery electrode, caused by the cyclic diffusion-induced stress, is ge... more The mechanical failure of battery electrode, caused by the cyclic diffusion-induced stress, is generally thought to be a direct reason leading to the loss of capacity and deterioration of performance for Liion battery. In the present work, the cyclic plasticity behaviour of primary electrode particle under electrochemical-mechanical condition is evaluated by using the Linear Matching Method (LMM). The coupled diffusion-stress analysis of electrode particle during lithiation-delithiation process is performed with the developed finite element subroutines as the groundwork for the subsequent cyclic plasticity assessment. The shakedown boundaries are established for electrode particle considering the variation of particle diameter by means of the LMM. ABAQUS full cyclic incremental analysis is employed to verify the applicability and accuracy of the obtained boundary. Two types of failure mechanisms known as low-cycle fatigue and ratcheting are investigated for particle subjected to loading history out of shakedown boundary. Steady state cycle analysis is conducted to study the generation of plastic strain range of particle under certain electrochemical-mechanical condition and the corresponding low-cycle fatigue damage is assessed. Different forms of ratcheting boundaries for electrode particle with various dimensions are created and the influences of cyclic current density and mechanical load on cyclic plasticity limits are clarified. The established critical failure diagrams will offer the instructional information regarding the design of electrode material in microscale within designated electrochemical condition.
Evaluation of creep rupture limit and prediction of creep rupture life are two significant issues... more Evaluation of creep rupture limit and prediction of creep rupture life are two significant issues for high-temperature devices under the action of cyclic thermo-mechanical loadings. In this paper, the shakedown solution procedure proposed recently by the authors, so-called stress compensation method (SCM), is extended for creep rupture assessment via an extended shakedown theory including creep. Two distinct numerical schemes based on the SCM framework are presented, where Scheme 1 is utilised for evaluation of creep rupture limit and Scheme 2 is utilised for prediction of creep rupture life. Instead of using the detailed creep constitutive equations, the present methods just need to know several material parameters including the creep rupture data. A holed plate is provided as a typical example to validate the reliability of two numerical schemes. Detailed cycle-by-cycle analyses are carried out to illustrate the good accuracy of these calculated creep rupture limits and reveal the failure mechanisms of the structure under different combinations of loads. A numerical study on a pipe junction is also conducted to show the engineering application of the methods. As a result, the two numerical schemes are proved to be effective and reliable for solving practical industrial problems.
This paper presents a novel direct method for the structural shakedown analysis considering limit... more This paper presents a novel direct method for the structural shakedown analysis considering limited kinematic hardening and non-isothermal effect. The Melan's static shakedown theorem is extended to consider limited kinematic hardening material and implemented into the Linear Matching Method (LMM) shakedown module. Instead of using a specific kinematic hardening rule and an explicit back stress field, the general nonlinear hardening laws are considered by using a two-surface hardening model. A two-stage procedure is developed in the extended LMM algorithm, which can generate the limited hardening shakedown envelope and the unlimited hardening curve efficiently and accurately. Also, the material non-isothermal effect is considered during the computation process of the shakedown limit by proposing a temperature-dependent hardening factor, in place of a constant and fictitious one. To validate the extended LMM method, a numerical test on a thin cylinder pipe with temperature-independent material properties is performed, and the results match well with ones from literature. Then, a numerical study on a typical aero-engine turbine disk is conducted to investigate the influence of temperature-dependent material properties and operating conditions. Several shakedown curves considering kinematic hardening effect are derived and adequately discussed. As a result, the extended LMM shakedown module is proven to be a robust, efficient and versatile tool for practical industrial problems.
In this paper a state-of-the-art numerical method is discussed for the evaluation of the shakedow... more In this paper a state-of-the-art numerical method is discussed for the evaluation of the shakedown and ratchet limits for an elastic-perfectly plastic body subjected to cyclic thermal and mechanical load history. The limit load or collapse load, i.e. the load carrying capacity, is also determined as a special case of shakedown analysis. These design limits in plasticity have been solved by characterizing the steady cyclic state using a general cyclic minimum theorem. For a prescribed class of kinematically admissible inelastic strain rate histories, the minimum of the functional for these design limits are found by a programming method, the Linear Matching Method (LMM), which converges to the least upper bound. By ensuring that both equilibrium and compatibility are satisfied at each stage, a direct algorithm has also been derived to determine the lower bound of shakedown and ratchet limit using the best residual stress calculated during the LMM procedure. Three practical examples of the LMM are provided to confirm the efficiency and effectiveness of the method: the behaviour of a complex 3D tubeplate in a typical AGR superheater header, the behaviour of a fiber reinforced metal matrix composite under loading and thermal cycling conditions, and effects of drilling holes on the ratchet limit and crack tip plastic strain range for a centre cracked plate subjected to constant tensile loading and cyclic bending moment.
Design and Analysis Methods and Fitness for Service Evaluations for Pressure Vessels and Components, 2003
Methods for the Evaluation of Creep Relaxation and the Amplitude of Reverse Plastic Strain for Bo... more Methods for the Evaluation of Creep Relaxation and the Amplitude of Reverse Plastic Strain for Bodies Subjected to Cyclic Loading. [ASME Conference Proceedings 2003, 155 (2003)]. Haofeng Chen, Alan RS Ponter. Abstract. ...
International Journal of Pressure Vessels and Piping, 2005
In an accompanying paper [Int J Pres Ves Pip, 2004], a 3D tubeplate in a typical AGR superheater ... more In an accompanying paper [Int J Pres Ves Pip, 2004], a 3D tubeplate in a typical AGR superheater header was analysed for the shakedown limit, reverse plasticity and ratchet limit based on the application of the linear matching method (LMM). Both the perfectly plastic model and the cyclic hardening model were adopted for the evaluation of the plastic strain range. In the present paper, based on the creep-reverse plasticity model, the accumulated creep strain during a creep dwell at the steady cyclic state is assessed by the LMM. The accumulated creep strains, the creep flow stresses as well as the elastic follow-up factors with differing dwell times are evaluated in detail. The total inelastic strain over the cycle at the steady cyclic state is calculated. By comparing these results with ABAQUS step-by-step inelastic analyses, the applicability of the methods is demonstrated.
International Journal of Pressure Vessels and Piping, 2004
A series of numerical procedures have been presented recently for the integrity assessment of str... more A series of numerical procedures have been presented recently for the integrity assessment of structures based upon the Linear Matching Method. A typical example of a holed plate has been used to verify these procedures for the evaluation of plastic and creep behaviours of components. In this paper, a more complex 2D tubeplate at the outlet from a typical AGR heat exchanger is analysed for the shakedown limit, reverse plasticity, ratchet limit and creep relaxation based on the application of the Linear Matching Method for a thorough case study. Both a constant material yield stress and a temperature-dependent yield stress are adopted for the evaluation of the ratchet limit. For the evaluation of accumulated creep strains, flow stresses and elastic follow-up factors with differing dwell times at the steady cyclic state, a monotonic creep computation is performed, where the start-of-dwell stress is the rapid cycle creep solution at the beginning of the dwell period. An estimation of the tubeplate lifetime is then obtained by the evaluation of fatigue and creep endurances.
International Journal for Numerical and Analytical Methods in Geomechanics, 2006
We investigate the performance of a sequential programming method, based on the linear matching m... more We investigate the performance of a sequential programming method, based on the linear matching method, for the direct evaluation of limit loads and shakedown limits for elastic-perfectly plastic bodies subjected to complex histories of loading. This end is achieved by solving a sequence of linear problems defined with spatially varying moduli, which relates properties of the yield condition to those of the linear problems. The method provides a sequence of upper bounds that monotonically reduces and converges to the least upper bound associated with the chosen class of displacement fields, provided a sufficient condition is satisfied. We applied this method to a class of isotropic yield condition that depends not only on the von Mises effective stress but also on the hydrostatic pressure. This is followed by a set of examples of finite element solutions including the problem of a circular Hertzian contact region that repeatedly traverses the surface of an elastic-perfectly plastic half-space. Numerical examples demonstrate that the convergence is still obtained when the sufficient condition as given by Ponter et al. (Eur. J. Mech. 2000; 19:401-421) is violated, i.e. the condition is sufficient but not a necessary condition for convergence.
International Journal of Solids and Structures, 2006
There is a range of problems where repeated rolling or sliding contact occurs. For such problems ... more There is a range of problems where repeated rolling or sliding contact occurs. For such problems shakedown and limit analyses provides significant advantages over other forms of analysis when a global understanding of deformation behaviour is required. In this paper, a recently developed numerical method. Ponter and Engelhardt (2000) and Chen and Ponter (2001), for 3-D shakedown analyses is used to solve the rolling and sliding point contact problem previously considered by Ponter, Hearle and Johnson (1985) for a moving Herzian contact, with friction, over a half space. The method is an upper bound programming method, the Linear Matching Method, which provides a sequence of reducing upper bounds that converges to the least upper bound associated with a finite element mesh and may be implemented within a standard commercial finite element code. The solutions given in Ponter, Hearle and Johnson (1985) for circular contacts are reproduced and extended to the case when the frictional contact stresses are at an angle to the direction of travel. Solutions for the case where the contact region is elliptic are also given.
During the crack propagation process, the crack-branching behavior makes fracture more unpredicta... more During the crack propagation process, the crack-branching behavior makes fracture more unpredictable. However, compared with the crack-branching behavior that occurs in brittle materials or ductile materials under dynamic loading, the branching behavior has been rarely reported in welded joints under quasi-static loading. Understanding the branching criterion or the mechanism governing the bifurcation of a crack in welded joints is still a challenge. In this work, three kinds of crack-branching models that reflect simplified welded joints were designed, and the aim of the present paper is to find and capture the crack-branching behavior in welded joints and to shed light on its branching mechanism. The results show that as long as there is another large enough propagation trend that is different from the original crack propagation direction, then crack-branching behavior occurs. A high strength mismatch that is induced by both the mechanical properties and dimensions of different re...
Back-to-back pipe bends are widely adopted applications in many industries including nuclear sect... more Back-to-back pipe bends are widely adopted applications in many industries including nuclear sectors. Evaluation of their load bearing capability under complex cyclic loading is very important. Recently, a couple of research reported shakedown boundary of a 90° back-to-back pipe bends by adopting a conservative approach but no comprehensive post yield structural behaviors have been dealt with. In this research the concerning pipe bends subjected to cyclic opening in-plane (IP)/out-of-plane (OP) bending and steady internal pressures are analyzed to construct shakedown and ratchet limit boundary by means of the Linear Matching Method. Analyzed results present that the concerning pipe bends under out-of-plane bending has higher resistance to cyclic bending than under in-plane bending. In additions, the out-of-plane bending causes very small alternating plasticity areas, unlike the in-plane bending. Full cyclic incremental analyses known as step-by-step analysis are performed to verify ...
Different strength mismatched laboratory specimens that contain the compact tension (CT), single ... more Different strength mismatched laboratory specimens that contain the compact tension (CT), single edge-notched tensile (SENT), and central-cracked tension (CCT) specimens with various specimen geometries, loading configurations, and initial cracks were selected to investigate the effect range of the material constraint systematically. The results showed that the effect range of material constraint exists in all the strength mismatched specimens and structures. The numerical value of the effect range is influenced by the geometry constraint. The high geometry constraint reduces the effect range of material constraint. When a material is located outside the effect range of material constraint, the fracture resistance curves and crack propagation paths of the specimens and structures are no longer influenced by the mechanical properties of the material. In addition, an interaction exists between the geometry constraint and material constraint. The high geometry constraint strengthens th...
Fatigue & Fracture of Engineering Materials & Structures, 2017
In this paper, the extended Direct Steady Cyclic Analysis method (eDSCA) within the Linear Matchi... more In this paper, the extended Direct Steady Cyclic Analysis method (eDSCA) within the Linear Matching Method Framework (LMMF) is combined with the Stress Modified Ductility Exhaustion method and the modified Cavity Growth Factor (CGF) for the first time. This new procedure is used to systematically investigate the effect of several load parameters including load level, load type and creep dwell duration on the creep-fatigue crack initiation process in a notched specimen. The results obtained are verified through a direct comparison with experimental results available in the literature demonstrating great accuracy in predicting the crack initiation life and the driving mechanisms. Furthermore, this extensive numerical study highlighted the possible detrimental effect of the creepratchetting mechanism on the crack growth process. This work has a significant impact on structural integrity assessments of complex industrial components and for the better understanding of creepfatigue lab scale tests.
As the energy demand increases the power industry has to enhance both efficiency and environmenta... more As the energy demand increases the power industry has to enhance both efficiency and environmental sustainability of power plants by increasing the operating temperature. The accurate creep fatigue life assessment is important for the safe operation and design of current and future power plant stations. This paper proposes a practical creep fatigue life assessment case of study by the Linear Matching Method (LMM) framework. The LMM for extended Direct Steady Cycle Analysis (eDSCA) has been adopted to calculate the creep fatigue responses due to the cyclic loading under high temperature conditions. A pipe intersection with dissimilar material joint, subjected to high cycling temperature and constant pressure steam, is used as an example. The closed end condition is considered at both ends of main and branch pipes. The impact of the material mismatch, transitional thermal load, and creep dwell on the failure mechanism and location within the intersection is investigated. All the resul...
To meet the growing energy demands, the power sector continuously strives at enhancing the effici... more To meet the growing energy demands, the power sector continuously strives at enhancing the efficiency of its power plants by increasing the operating temperature. Under cyclic loading conditions, this leads to creep-cyclic plasticity driven damage mechanisms such as cyclically enhanced creep, creep enhanced plasticity and creep ratcheting. A detailed understanding of creep and related damages is therefore essential for predicting any potential failure mechanisms and ensuring confidence in the safe-working of the components. This becomes particularly difficult and challenging in the presence of welds due to two main reason; a) presence of different material zones, namely parent metal, weld metal and heat affected zone; b) introduction of residual stress during welding. An extended Direct Steady Cycle Analysis within the Linear Matching Method (LMM) framework has been previously developed to consider the full interaction between creep and cyclic plasticity. This paper presents the bas...
International Journal of Pressure Vessels and Piping, 2018
Ratcheting and low cycle fatigue are failure mechanisms observed in components subjected to cycli... more Ratcheting and low cycle fatigue are failure mechanisms observed in components subjected to cyclic temperature and mechanical loads. Ratcheting is a global failure mechanism which leads to an incremental plastic collapse of the component whereas low cycle fatigue is a localized mechanism which leads to crack initiation. It is exacerbated by grooves, notches and changes in the geometry of the component. To estimate the remaining life of the component and predict its failure mechanism, it is important to understand how it responds to various combinations of cyclic loads. This paper includes investigation of the ratchet limit and the plastic strain range, which is associated with the low cycle fatigue, of a circumferential butt-welded pipe by using the ratchet analysis method which includes Direct Steady Cycle Analysis (DSCA) within the Linear Matching Method Framework (LMMF). The pipe is subjected to a constant internal pressure and a cyclic thermal load. The investigation is carried out by varying 1) material properties of the weld metal (WM); 2) ratio of inner radius to wall thickness; 3) weld geometry. Within the specified ranges, yield stress and the ratio of inner radius to wall thickness affect the ratchet limit curve. The cyclic thermal load plays a crucial role compared to the internal pressure in influencing the ratchet limit curve. It is observed that the pipe experiences thermal ratcheting in the absence of pressure load at lower yield stress values of the WM. The results obtained are combined to create a limit load envelope, which can be used for the design of welded pipes within the specified ranges.
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Papers by Haofeng Chen