Fatigue design of structures under thermomechanical loadings

This paper presents a global approach to the design of structures that experience thermomechanical fatigue loading, which has been applied successfully in the case of cast‐‐iron exhaust manifolds. After a presentation of the design context in the automotive industry, the important hypotheses and choices of this approach, based on a thermal 3D computation, an elastoviscoplastic constitutive law and the dissipated energy per cycle as a damage indicator associated with a failure criterion, are first pointed out. Two particular aspects are described in more detail: the viscoplastic constitutive models, which permit a finite element analysis of complex structures and the fatigue criterion based on the dissipated energy per cycle. The FEM results associated with this damage indicator permit the construction of a design curve independent of temperature; an agreement is observed between the predicted durability and the results of isothermal as well as non isothermal tests on specimens and thermomechanical fatigue tests on real components on an engine bench. These results show that thermomechanical fatigue design of complex structures can be performed in an industrial context.     

An energetic approach in thermomechanical fatigue for silicon molybdenum cast iron

Abstract

The purpose of this paper is to define a low cycle fatigue criterion in order to predict the failure of engineering structures. The major problem in defining a predictive fatigue criterion is that it should be applicable for structures submitted to complex multiaxial thermo-mechanical loadings but should be identifiable from simple experiments on specimens. After a short critical review of the principal criteria used in low cycle fatigue it will be shown that the dissipated energy per cycle permits a correlation of isothermal and anisothermal results obtained on silicon molybdenum cast iron in the case of specimens and also on structures.     

Mortar fatigue model for meso-mechanistic mixture design of ravelling resistant porous asphalt concrete

This paper presents the development of a practical mortar fatigue model on the basis of the dissipated energy concept. A specially designed test setup was developed for characterization of mortar fatigue at meso-scale by means of dynamic shear rheometer. Test results showed that mortar fatigue models based on the dissipated energy concept can be developed for the purpose of life predictions under complicated loading conditions. The dissipated energy per cycle in the initial phase of fatigue tests is a practical indicator for fatigue life determination purposes than the total energy dissipated during a fatigue test. Since a mortar fatigue model based on the initial dissipated energy per cycle was adopted, effects of random stress and strain signals on mortar fatigue can be taken into account.     

Energy dissipation under thermomechanical fatigue loading

The paper presents a numerical approach to compute the total amount of dissipated energy under arbitrary rate independent uniaxial thermomechanical fatigue (TMF) loading. Such an approach is based on the stress controlled Prandtl type operator enabling continuous energy dissipation calculation. It focuses on non-isothermal stress–strain conditions of a spring–slider segment, and relates slider movements to irreversible energy dissipation. The correct amount of dissipated energy is computed at any moment (online), without the need of ‘waiting’ the cycle to finish. The operator approach guaranties monotonically increasing progress of energy dissipation, which is within the framework of thermodynamics. It is also shown that the operator approach results in the same dissipated energy after closed isothermal cycle as the traditional integration approach.     

高温合金材料时间相关热机械疲劳寿命预测技术

本文在变温非线性运动强化规律所描述的高温合金材料热机械疲劳应力－应变循环特性的基础上,重点讨论了应变控制的时间相关热机械疲劳寿命预测技术。对于温度循环的影响,采用由应变能密度表示的损伤参数,并且引入了温度损伤系数。对于循环时间的影响,引入了蠕变─疲劳相互作用的损伤机制,采用韧性耗散损伤模型。在确定模型的一些参数时,采用等温力学试验和疲劳试验的数据,把等温疲劳研究成果推广到变温疲劳分析领域。     

Crack initiation under thermal fatigue: An overview of CEA experience: Part II (of II): Application of various criteria to biaxial thermal fatigue tests and a first proposal to improve the estimation of the thermal fatigue damage

A Part I accompanying paper clearly showed that for a given level of strain range (Δ?), the number of cycles required to achieve crack initiation is significantly lower in biaxial thermal fatigue than in uniaxial isothermal fatigue.Such discrepancy does not come from a thermal effect, as it is emphasized by a comparison between the uniaxial data, coming either from thermomechanical fatigue tests, or from isothermal low cycle fatigue tests. A detrimental effect of multiaxial loading on fatigue life is noticed in many cases as reported in the literature.In this frame, the goal of this paper is to propose criteria in order to take into account the reduction of fatigue life resulting from the multiaxiality. Among all the examined multiaxial criteria, a criterion based on strain proposed by Zamrik, and a new criterion based on energy proposed by “Ecole Polytechnique” give the best estimations. Furthermore, application of the Zamrik’s criterion using the RCC–MR method is very promising for the design engineer. Indeed, these two criteria exhibit a notable potential, since they are well adapted to all the available thermal fatigue experimental data, despite significant differences between approaches and processes developed by both accessible facilities.However, such investigation must be continued with achievement of additional thermal fatigue tests (for higher number of cycles…), and isothermal biaxial fatigue tests.     

Thermomechanical design in the automotive industry

In this paper thermomechanical fatigue assessment in the automotive industry is discussed. The design strategy is based upon a consistent approach of the thermomechanical loading, the mechanical constitutive law of the material, the damage parameters and the fatigue strength criteria. The good understanding of these different steps allows one to perform predictive calculations of automotive parts subjected to thermomechanical loading. The main hypotheses and modelling choices are presented and results are illustrated by a series of computations on real 3D structures. Cracked area and lifetime prediction are described in the case of aluminium alloy cylinder heads subjected to transient thermal loadings.     

A unified approach for high and low cycle fatigue based on shakedown concepts

ABSTRACT The purpose of this paper is to present a unified analysis to both high and low cycle fatigue based on shakedown theories and dissipated energy. The discussion starts with a presentation of the fatigue phenomena at different scales (microscopic, mesoscopic and macroscopic) and of the main shakedown theorems. A review of the Dang Van high cycle fatigue criterion shows that this criterion is essentially based on the hypothesis of elastic shakedown and can therefore be expressed as a bounded cumulated dissipated energy. In the low cycle fatigue regime, recent results by Skelton and Charkaluk et al. show that we can speak of a plastic shakedown at both mesoscopic and macroscopic scale and of a cumulated energy bounded by the failure energy. The ideas are also justified by infrared thermography tests permitting a direct determination of the fatigue limit.     

Stepped‐isothermal fatigue analysis of engine piston

Stepped‐isothermal fatigue failure is the main failure mechanism of modern engine pistons under bench reliability test condition. This paper presents a methodology for stepped‐isothermal fatigue analysis of engine pistons, which consists of a fatigue criterion, evaluation of temperature and stress distribution by finite element analysis and the final life prediction. The major character of the methodology is the fatigue definition of engine pistons with respect to engine load change cycle and a damage‐based fatigue criterion accounting for the nonlinear creep–fatigue damage. Taking as an example, the fatigue life of an engine piston was predicted by the proposed analysis procedures. The analysis results showed that the most critical area was located in the throat edge. Moreover, the proposed methodology can give a relatively accurate and reasonable life prediction for an engine piston under the loading condition of bench reliability test, with a benefit of decreasing the needed component's reliability tests and design time.     

Synergistic Effects of Temperature,Oxidation and Multicracking Modes on Damage Evolution and Life Prediction of 2D Woven Ceramic-Matrix Composites under Tension-Tension Fatigue Loading

In this paper, the synergistic effects of temperature, oxidation and multicracking modes on damage evolution and life prediction in 2D woven ceramic-matrix composites (CMCs) have been investigated. The damage parameter of fatigue hysteresis dissipated energy and the interface shear stress were used to monitor the damage evolution inside of CMCs. Under cyclic fatigue loading, the fibers broken fraction was determined by combining the interface/fiber oxidation model, interface wear model and fibers statistical failure model at elevated temperature, based on the assumption that the fiber strength is subjected to two-parameter Weibull distribution and the load carried by broken and intact fibers satisfy the Global Load Sharing (GLS) criterion. When the broken fibers fraction approaches to the critical value, the composite fatigue fractures. The evolution of fatigue hysteresis dissipated energy, the interface shear stress and broken fibers fraction versus cycle number, and the fatigue life S–N curves of SiC/SiC at 1000, 1200 and 1300 °C in air and steam condition have been predicted. The synergistic effects of temperature, oxidation, fatigue peak stress, and multicracking modes on the evolution of interface shear stress and fatigue hysteresis dissipated energy versus cycle numbers curves have been analyzed.     

A continuum damage model applied to high-temperature fatigue lifetime prediction of a martensitic tool steel

High‐temperature operational conditions of hot work tool steels induce several thermomechanical loads. Depending on the processes, (i.e. forging, die casting or extrusion), stress, strain, strain rate and temperature levels applied on the material are nevertheless very different. Thus, lifetime prediction models need to be able to take into account a broad range of working conditions. In this paper, a non‐isothermal continuum damage model is identified for a widely used hot work tool steel AISI H11 (X38CrMoV5) with a nominal hardness of 47 HRc. This investigation is based on an extensive high‐temperature, low‐cycle fatigue database performed under strain rate controlled conditions with and without dwell times in the temperature range 300–600°C . As analysis of experimental results does not reveal significant time‐dependent damage mechanisms, only a fatigue damage component was activated in the model formulation. After normalization, all fatigue results are defined on a master Woehler curve defined by a nonlinear damage model, which allows the parameter identification. Last, a validation stage of the model is performed from thermomechanical fatigue tests.     

Mechanical properties of concrete to cyclic uniaxial tensile loading using variable waveforms

The mechanical properties of concrete under cyclic tensile loading using square waveform, sine waveform and ramp waveform are studied. The experiments are performed on a closed-loop electro-hydraulic servo-controlled material testing system (MTS). The axial strain, dissipated energy per loading cycle, the damage evolution law and deformation modulus are mainly studied. The results show that the three-stage evolution law of axial strain and damage variable of concrete under ramp waveform and sine waveform are more obvious than those under the square waveform. The dissipated energy changes at different stages of fatigue life. At the beginning and end of the fatigue life, the rate of dissipated energy is higher than that at the medium stage of the fatigue time, which is attributed to the formation of cracks. The evolution of deformation modulus of concrete subjected to cyclic tensile loading using three loading waveforms also shows three stages: fast increase in the damage—increase at a slow constant rate—and accelerated increase in damage until failure.     

Relationship Between Hysteresis Dissipated Energy and Temperature Rising in Fiber-Reinforced Ceramic-Matrix Composites Under Cyclic Loading

In this paper, the relationship between hysteresis dissipated energy and temperature rising of the external surface in fiber-reinforced ceramic-matrix composites (CMCs) during the application of cyclic loading has been analyzed. The temperature rise, which is caused by frictional slip of fibers within the composite, is related to the hysteresis dissipated energy. Based on the fatigue hysteresis theories considering fibers failure, the hysteresis dissipated energy and a hysteresis dissipated energy-based damage parameter changing with the increase of cycle number have been investigated. The relationship between the hysteresis dissipated energy, a hysteresis dissipated energy-based damage parameter and a temperature rise-based damage parameter have been established. The experimental temperature rise-based damage parameter of unidirectional, cross-ply and 2D woven CMCs corresponding to different fatigue peak stresses and cycle numbers have been predicted. It was found that the temperature rise-based parameter can be used to monitor the fatigue damage evolution and predict the fatigue life of fiber-reinforced CMCs.     

Creep–fatigue interaction in two gas turbine Ni based superalloys subjected to service-like conditions

Abstract

Creep–fatigue interaction has been studied in single crystal and equiaxed Ni based superalloys, adopted for critical gas turbine component applications. Cyclic hold tests have been performed to understand the influence of creep damage and deformation on fatigue endurance, considering also the effect of the position of the hold time in the low cycle fatigue cycle. Service-like thermomechanical fatigue (TMF) benchmark tests have been carried out, involving TMF cycles based on the loading conditions at component critical locations determined by finite element (FE) simulation. Damage calculations have been performed on all the conducted tests for both materials, comparing results obtained by different methodologies (e.g. time fraction, ductility exhaustion, strain energy density). The results have been compared with actual in-service damage revealed by microstructural examination.     

基于迟滞耗散能的纤维增强陶瓷基复合材料疲劳寿命预测方法

纤维增强陶瓷基复合材料(CMCs)在疲劳载荷作用下,纤维相对基体在界面脱粘区往复滑移导致其出现疲劳迟滞现象,迟滞回线包围的面积,即迟滞耗散能,可用于监测纤维增强CMCs疲劳损伤演化过程。提出了一种基于迟滞耗散能的纤维增强CMCs疲劳寿命预测方法及考虑纤维失效的迟滞回线模型,建立了迟滞耗散能、基于迟滞耗散能的损伤参数、应力-应变迟滞回线与疲劳损伤机制(多基体开裂、纤维/基体界面脱粘、界面磨损与纤维失效)之间的关系。分析了疲劳峰值应力、疲劳应力比与纤维体积分数对纤维增强CMCs疲劳寿命S-N曲线、迟滞耗散能和基于迟滞耗散能的损伤参数随循环次数变化的影响。疲劳寿命随疲劳峰值应力增加而减小,随纤维体积含量增加而增加;迟滞耗散能随疲劳峰值应力增加而增加,随应力比和纤维体积分数增加而减小;基于迟滞耗散能的损伤参数随纤维体积分数增加而减小。      

A simple energy‐based model for nonproportional low‐cycle multiaxial fatigue life prediction under constant‐amplitude loading

From the literature concerning the traditional nonproportional (NP) multiaxial cyclic fatigue prediction, special attentions are usually paid to multiaxial constitutive relations to quantify fatigue damage accumulation. As a result, estimation of NP hardening effect decided by the entire history path is always proposed, which is a challenging and complex task. To simplify the procedure of multiaxial fatigue life prediction of engineering components, in this paper, a novel effective energy parameter based on simple material properties is proposed. The parameter combines uniaxial cyclic plastic work and NP hardening effects. The fatigue life has been assessed based on traditional multiaxial fatigue criterion and the proposed parameter, which has been validated by experimental results of 316 L stainless steel under different low‐cycle loading paths.     

On the use of infrared thermography for the analysis of fatigue damage processes in welded joints

The paper presents an experimental approach for the analysis of localized fatigue damage processes during fatigue testing of welded steel structures by thermographic investigations of thermomechanical coupling phenomena. Special data processing of the recorded infrared sequences is proposed to separate linear and nonlinear damage-indicating effects. The method has been successfully applied to analyze the damage progress during fatigue testing of welded components. On the tested components localized damage processes could be observed as early as 10–30% of the total fatigue lifetime. The results confirm the high potential of the methodology for the determination of fatigue damage initiation. The technique provides a powerful experimental tool to investigate localized inhomogeneous damage and to analyze complex fatigue processes.     

Application of the dissipated energy criterion to predict fatigue crack growth of Type 304 stainless steel following a tensile overload

This paper presents the results of numerical simulations of fatigue crack growth performed using three-dimensional elastic–plastic finite element analysis. A simple node release scheme is used to simulate crack advancement. The crack front is assumed to be straight. Crack growth following a tensile overload is simulated. The total energy dissipated per cycle is calculated directly from the finite element analysis and used to predict fatigue crack growth. For comparison, fatigue crack growth rate experiments were performed on Type 304 stainless steel C(T) specimens to determine the effect of a single tensile overload. The dissipated energy per cycle is found to correlate well with the measured fatigue crack growth rate following an overload.     

Strain-life approach in thermo-mechanical fatigue evaluation of complex structures

This paper is a contribution to strain‐life approach evaluation of thermo‐mechanically loaded structures. It takes into consideration the uncoupling of stress and damage evaluation and has the option of importing non‐linear or linear stress results from finite element analysis (FEA). The multiaxiality is considered with the signed von Mises method. In the developed Damage Calculation Program (DCP) local temperature‐stress‐strain behaviour is modelled with an operator of the Prandtl type and damage is estimated by use of the strain‐life approach and Skelton's energy criterion. Material data were obtained from standard isothermal strain‐controlled low cycle fatigue (LCF) tests, with linear parameter interpolation or piecewise cubic Hermite interpolation being used to estimate values at unmeasured temperature points. The model is shown with examples of constant temperature loading and random force‐temperature history. Additional research was done regarding the temperature dependency of the K_p used in the Neuber approximate formula for stress‐strain estimation from linear FEA results. The proposed model enables computationally fast thermo‐mechanical fatigue (TMF) damage estimations for random load and temperature histories.