Thermomechanical Fatigue Behavior Research Articles

The Effect of Phase Angle on the Thermo-Mechanical Fatigue Life of a Titanium Metal Matrix Composite.

The thermo-mechanical fatigue (TMF) behaviour of a Ti-6Al-4V matrix composite reinforced with SCS-6 silicon carbide fibres (140 μm longitudinal fibres, laid up hexagonally) has been investigated. In-phase and out-of-phase TMF cycles were utilized, cycling between 80–300 °C, with varying maximum stress. The microstructure and fracture surfaces were studied using electron backscatter diffraction (EBSD), energy-dispersive X-ray spectroscopy (EDS), scanning electron microscopy (SEM), profilometry, and optical microscopy. The results have shown the damaging effect of out-of-phase cycling with crack initiation occurring earlier than in in-phase tests and crack propagation rates being accelerated in out-of-phase cycles. Fatigue crack initiation has been shown to be sensitive to crystallographic texture in the cladding material and thermo-mechanical fatigue test results can be considered according to a previously proposed conceptual framework for the interpretation of metal matrix composite fatigue.

Modeling of the Thermomechanical Fatigue Behavior of Fiber-Reinforced Ceramic-Matrix Composites Subjected to Different Phase Angles

AbstractUnder thermomechanical fatigue (TMF) loading, the thermal cyclic temperature may change with decreasing or increasing applied stress upon unloading or reloading. The damage inside of fiber-...

Thermo-mechanical fatigue behavior of nickel-based 23Cr-45Ni-7W alloy for boiler pipes and tubes

This study focuses on thermo-mechanical fatigue (TMF) behaviors of nickel-based 23Cr-45Ni-7W alloy for pipes and tubes in high-efficiency power boilers. TMF tests (maximum temperature = 700 °C; minimum temperature = 100 °C) were conducted under in-phase (IP) and out-of-phase (OP) conditions. The lives under the IP condition is 0.30–0.44 times of that under the OP condition when same total strain range, Δεt, is applied. The TMF properties obtained via the tests are compared with the results of isothermal fatigue (ITF) tests conducted at 700 °C and bithermal fatigue (BTF) tests with maximum and minimum temperatures of 700 °C and 100 °C, respectively. The fracture morphology for each type of TMF, ITF, and BTF is similar under the test conditions of this study. Intergranular cracking is predominant under application of cyclic tensile creep strain during the fatigue tests, and transgranular cracking is predominant under application of cyclic compressive creep strain during the fatigue tests. The inelastic strain range–fatigue life (Δεin–Nf) relation in the TMF test and the inelastic strain range components–life (Δεij–Nij) relation determined using the strain range partitioning method show a good agreement within a factor of 1.5 scatter band. These results indicate the possibility of predicting the TMF life of the 23Cr-45Ni-7W alloy using the results of the ITF test by considering the amount and direction (tension or compression) of creep strain applied to the alloy.

Thermo-mechanical fatigue damage behavior for Ni-based superalloy under axial-torsional loading

The axial-torsional thermo-mechanical fatigue behavior for Ni-based superalloy GH4169 was investigated experimentally in the temperature interval from 360 °C to 650 °C. The experimental results showed that, in the same von Mises equivalent mechanical strain amplitude condition, the fatigue life can be seriously decreased when the axial mechanical strain and the temperature are in-phase, and the non-proportional loading of mechanical strains can result in the fatigue life to further decrease. The analysis results showed that the fatigue lives depend on the summation of fatigue, creep and oxidation damages. The interaction between dislocations and precipitations can induce the additional hardening under mechanical non-proportional loading, which can obviously increase the fatigue damage. The tensile mean stress and the non-proportional additional hardening can further increase the oxidation damage existed in all loading conditions, which result in the increase of inelastic strain at high temperature. Creep damage behavior on grain boundaries can be shown in the case of the high tensile stress and the high temperature acting simultaneously, and increased with shear stress at the same time. In addition, the tensile stress has an obvious effect on the nucleation of creep cavities contrasted to the shear stress at high temperature, and more creep damage can be caused by the non-proportional additional hardening.

Comparisons of the Thermomechanical Fatigue Behavior of C/SIC and SIC/SIC Ceramic-Matrix Composites Subjected to Different Phase Angle

ABSTRACTIn this paper, the comparisons of thermomechanical fatigue behavior of C/SiC and SiC/SiC fiber-reinforced ceramic-matrix composites (CMCs) subjected to different phase angles of θ = 0, π/3, π/2 and π have been investigated. The relationships between the fatigue damage mechanisms, phase angle, fatigue hysteresis dissipated energy, fatigue hysteresis modulus and fatigue peak strain, fiber/matrix interface debonding and sliding have been established. The differences between C/SiC and SiC/SiC composites under thermomechanical fatigue loading with different phase angles have been analyzed. The damage accumulation of 2.5D C/SiC and 2D SiC/SiC composites under thermomechanical fatigue loading have been predicted. With increasing of the phase angle, the fatigue hysteresis dissipated energy, fatigue peak strain and interface debonded length decrease for the SiC/SiC composite; however, for the C/SiC composite, the fatigue hysteresis dissipated energy, fatigue peak strain and the interface debonded length increase at the same cycle number.

Thermomechanical fatigue behaviour of ferritic stainless steel grades for high temperatures applications

Nowadays high temperatures resistant materials are needed to resist to high temperature applications (up to 1000°C), such as automotive exhaust gas manifolds. Some developed stainless steel grades, including ferritic grades or austenitic refractory grades, can be used in this temperature range and both in continuous or cyclic thermal conditions. In order to predict the thermomechanical fatigue damage of stainless steel parts submitted to cyclic thermal loading and constrained bonding conditions, the elastoviscoplastic model by Chaboche is determined for a wide range of temperatures, of strain amplitudes and strain rate levels thanks to isothermal traction-compression tests. The validation procedure is performed afterward by comparison with stabilized behavior under non isothermal conditions on a dedicated thermal fatigue test performed on V-shape specimens. Results of simulation show very good fitting with the experimental curves which would lead to a more accurate fatigue life prediction. A damage model was derived from Taira’s thermal low-cycle fatigue model to include dwell-time period at high temperature and creep-oxidation effect. In this paper the example of K44X, a dedicated grade for high temperatures applications, is presented.

Thermo-mechanical fatigue behavior and life prediction of the Al-Si piston alloy

The thermo-mechanical fatigue (TMF) behaviors and corresponding damage mechanisms of Al-Si piston alloy were investigated in the temperature ranges of 120–350°C and 120–425°C in this study. For TMF cyclic stress response behavior, the rapid cyclic softening occurs in the initial stage and then the cyclic stress maintains stable at lower strain amplitudes; but the cyclic stress displays gradual decrease up to the final failure at higher strain amplitudes. For TMF damage behavior, the cracks mainly initiate from the broken primary silicon in the temperature of 120–350°C range, and commonly nucleate from the boundary between primary Si and matrix in the temperature of 120–425°C range. For both cases, creep may have obvious influence and result in the formation of many micro-voids, but the oxidation may only have a little effect. A new energy-based model for low-cycle fatigue (LCF) and TMF life prediction was proposed based on the hysteresis energy with strain rate modification, considering both fatigue and creep damages. The predicted results agree well with the experimental ones for the Al-Si piston alloy.

Electromigration and Thermomechanical Fatigue Behavior of Sn0.3Ag0.7Cu Solder Joints

The anisotropy of Sn crystal structures greatly affects the electromigration (EM) and thermomechanical fatigue (TMF) of solder joints. The size of solder joint shrinkage in electronic systems further makes EM and TMF an inseparably coupled issue. To obtain a better understanding of failure under combined moderately high (2000 A/cm2) current density and 10–150°C/1 h thermal cycling, analysis of separate, sequential, and concurrent EM and thermal cycling (TC) was imposed on single shear lap joints, and the microstructure and crystal orientations were incrementally characterized using electron backscatter diffraction (EBSD) mapping. First, it was determined that EM did not significantly change the crystal orientation, but the formation of Cu6Sn5 depended on the crystal orientation, and this degraded subsequent TMF behavior. Secondly, TC causes changes in crystal orientation. Concurrent EM and TC led to significant changes in crystal orientation by discontinuous recrystallization, which is facilitated by Cu6Sn5 particle formation. The newly formed Cu6Sn5 often showed its c-axis close to the direction of electron flow.

Isothermal and thermo-mechanical fatigue behavior of 16Mo3 steel coated with high-velocity oxy-fuel sprayed nickel-base alloy under uniaxial as well as biaxial-planar loading

Abstract

Crystal viscoplasticity model for the creep-fatigue interactions in single-crystal Ni-base superalloy CMSX-8

A crystal viscoplasticity (CVP) model for the creep-fatigue interactions of nickel-base superalloy CMSX-8 is proposed. At the microstructure scale of relevance, the superalloys are a composite material comprised of a γ phase and a γ′ strengthening phase with unique deformation mechanisms that are highly dependent on temperature. Considering the differences in the deformation of the individual material phases is paramount to predicting the deformation behavior of superalloys at a wide range of temperatures. In this work, we account for the relevant deformation mechanisms that take place in both material phases by utilizing two additive strain rates to model the deformation on each material phase. The model is capable of representing the creep-fatigue interactions in single-crystal superalloys for realistic 3-dimensional components in an Abaqus User Material Subroutine (UMAT). Using a set of material parameters calibrated to superalloy CMSX-8, the model predicts creep-fatigue, fatigue and thermomechanical fatigue behavior of this single-crystal superalloy. Finally, a sensitivity study of the material parameters is done to explore the effect on the deformation due to changes in the material parameters relevant to the microstructure.

Thermomechanical fatigue behavior of annealed Cu-Cr-Zr-Ti alloy in argon atmosphere

Strain controlled thermomechanical fatigue (TMF) behavior of Cu-Cr-Zr-Ti alloy was studied in the temperature range of 375–525°C in high purity argon atmosphere under both in-phase (IP) and out-of-phase (OP) loading. In the case of OP TMF tests, the material exhibited continuous hardening without any saturation of stress. On the other hand, it showed cyclic hardening for the first few cycles followed by saturation of stress in IP TMF tests. The material exhibited superior lives under OP TMF loading compared to that under IP TMF loading especially at lower strain amplitudes. This may be attributed to the fact that the material experienced peak tensile stress at lower temperatures in OP TMF tests, where the resistance to crack initiation is expected to be higher. Microstructural observations and fractographic studies indicated mixed mode of fracture involving Intergranular facets and transgranular cracking in both IP and OP TMF tests.

Identification, size classification and evolution of Laves phase precipitates in high chromium, fully ferritic steels

To fulfil the new challenges of the German “Energiewende” more efficient, sustainable, flexible and cost-effective energy technologies are strongly needed. For a reduction of consumed primary resources higher efficiency steam cycles with increased operating parameters, pressure and temperature, are mandatory. Therefore advanced materials are needed. The present study focuses on a new concept of high chromium, fully ferritic steels. These steels, originally designed for solid oxide fuel cell applications, provide favourable steam oxidation resistance, creep and thermomechanical fatigue behaviour in comparison to conventional ferritic-martensitic steels. The strength of this type of steel is achieved by a combination of solid-solution hardening and precipitation strengthening by intermetallic Laves phase particles. The effect of alloy composition on particle composition was measured by energy dispersive X-ray spectroscopy and partly verified by thermodynamic modelling results. Generally the Laves phase particles demonstrated high thermodynamic stability during long-term annealing up to 40,000h at 600°C. Variations in chemical alloy composition influence Laves phase particle formation and consequently lead to significant changes in creep behaviour. For this reason particle size distribution evolution was analysed in detail and associated with the creep performance of several trial alloys.

In‐phase and out‐of‐phase thermomechanical fatigue behavior of 4Cr5MoSiV1 hot work die steel cycling from 400 °C to 700 °C

AbstractThe hysteresis loops, stress and strain behavior, lifetime behavior and fracture characteristic of 4Cr5MoSiV1 hot work die steel at a wide range of mechanical strain amplitudes (from 0.5% to 1.3%) during the in‐phase (IP) and out‐of‐phase (OP) thermomechanical fatigue (TMF) tests cycling from 400 °C to 700 °C under full reverse strain‐controlled condition were investigated. Stress‐mechanical strain hysteresis loops of 4Cr5MoSiV1 steel are asymmetric, and stress reduction appears at high‐temperature half cycles owing to a decrease in strength with increasing temperature. 4Cr5MoSiV1 steel always exhibits continuous cyclic softening for both types of TMF tests, and the cyclic softening rate is larger in OP loading condition. OP TMF life of 4Cr5MoSiV1 steel is approximately 60% of IP TMF life at the same mechanical strain amplitude and maximum temperature. Lifetime determined and predicted in both types of TMF tests is adequately described by the Ostergren model. Fracture surfaces under IP TMF loading display the striation and tear ridge, showing quasi‐cleavage characteristics, and the cracks are less but longer. However, fracture surfaces under OP TMF loading mainly display the striation and dimple characteristics, and the cracks are more and shorter.

Microstructure of intermetallic particle strengthened high-chromium fully ferritic steels

An improvement of power plant efficiency necessitates an increase of the process parameters and thus enables a reduction of consumed primary resources. Furthermore more efficient, sustainable, flexible and cost-effective energy technologies are strongly needed. For this reason the current research concentrates on a new concept of high-chromium fully ferritic stainless steels which are strengthened by a combination of solid-solution and intermetallic Laves phase particles. Such steels exhibit favourable creep, thermomechanical fatigue and steam oxidation behaviour up to 650°C. Based on detailed analysis by high-resolution scanning and transmission electron microscopy the particle size evolution and compositions were studied. Variations in chemical compositions were analysed experimentally and compared with thermodynamic equilibrium composition modelling results.This paper is part of a thematic issue on the 9th International Charles Parsons Turbine and Generator Conference. All papers have been revised and extended before publication in Materials Science and Technology.

Thermomechanical fatigue behavior of nitrogen enhanced 316LN stainless steel: Effect of cyclic strain

Thermomechanical fatigue (TMF) behavior of nitrogen enhanced 316LN stainless steel (with 0.14wt.% N) is investigated under in-phase (IP) and out-of-phase (OP) conditions at cyclic strain amplitudes of ±0.25 to ±0.8% and with a temperature interval of 623–873K. The study elucidates the differences in cyclic stress-strain response, TMF lives and fracture behavior of the material under IP and OP-TMF in the light of dynamic strain aging, thermal recovery and creep. The manifestations of these factors/phenomena are found to vary along stress-strain hysteresis loops, thereby leading to differences in cyclic strain hardening exponent (n′) and coefficient (K′) between the tensile and compressive branches of hysteresis loops. Irrespective of the imposed cyclic strain, transgranular fatigue failure is observed under OP-cycling in contrast to mixed-mode fracture under IP-cycling. The IP-cycling led to considerably lower cyclic life (i.e. 34–49%) compared to those under OP-TMF, with the life reduction being more significant (∼48.5%) at intermediate mechanical strain amplitudes of ±0.4 and ±0.6%. A comparison of the fatigue design curves under TMF with the corresponding isothermal fatigue curves (as per the RCC-MR design code) revealed a lack of conservatism in the latter.

Modeling of cyclic thermo-elastic-plastic behaviour of P91 steel

Thermomechanical low cycle fatigue behaviour of P91 steel used in power industry applications has been extensively investigated. The constitutive model of Armstrong-Frederick, extended with temperature rate effects, has been applied to describe the behaviour of the thermo-elastic-plastic material. The proposed model has been successfully implemented in simulation of low cycle fatigue of the examined steel in two different temperatures.

Recent Developments in 3D Multiphysics Modelling of Whole Fuel Cell Systems for Assisting Commercialisation and Improved Reliability

3D multiphysics modelling of fuel cell components and fuel cell systems has been a core research field since many years. Current focus has been to support the commercialisation of the technology. Especially, gaining detailed information about the durability and life duration of the utilised fuel cell systems is of paramount importance. As a fuel cell system consists of many components like the fuel cell stack, reformer, afterburner, heat exchanger etc., it is important to account for the coupled processes, occurring within each component and their interaction with the neighbour components. To interpret the long-term reliability of the system, the thermomechanical fatigue behaviour of the critical system regions have been investigated in detail to predict and understand the durability under cyclic load. The life expectation of a system has been predicted using a 3D full scale system level multiphysics model based on coupled CFD-FEM.

An assessment of thermo-mechanically induced fatigue damage of a steam turbine shaft

The increasing demands on the flexibility of steam turbines due to the use of renewable energy sources substantially alters the fatigue strength requirements of components of these facilities. The work summarized hereafter was initiated by the effort to develop the methodology of prediction of thermo-mechanical fatigue of steam turbine rotors. A significant effort was put into local thermo-mechanical stress-strain response modelling in the shaft material. An FE model of the structure assuming 2D axisymmetry idealisation was developed and verified. In-house codes based on a variety of approaches to assess critical location and fatigue damage, including the Manson-McKnight and the Nagode methods, were created. The experimental programme aimed to investigate the material fatigue behaviour under the thermo-mechanical conditions was initiated in order to provide data for calibrating and verifying the fatigue prediction procedures. A preliminary study on thermo-mechanical fatigue behaviour was conducted and the results are summarized in the paper.

An investigation on crack growth rate of fatigue and induction heating thermo-mechanical fatigue (TMF) in Hastelloy X superalloy via LEFM, EPFM and integration models

In this research, fatigue and induction heating thermo-mechanical fatigue (TMF) were performed on Hastelloy X superalloy in the small and large scale yielding in plane stresses mode. The crack growth rates were measured and formulated by fracture mechanics parameters. Furthermore, the fatigue life was predicted by employing resistance curves technique. The TMF behavior of this superalloy was investigated. The results demonstrated that in-phase loading TMF conditions lead to short fatigue life (more crack growth rate) at high strain amplitudes and temperatures up to 600°C. For higher temperatures, the predominant damage was due to creep. A model based on damage contributions due to pure fatigue and cyclic creep has been presented for predicting TMF crack growth rates. Fracture mechanic method was used to suggest a model for fatigue part of TMF crack growth rate, while the temperature effects during TMF crack growth rate was considered to be due to cyclic creep. In addition the TMF crack healing or crack closure occur during application of induced eddy currents were investigated explicitly, as environmental effects of induction heating. The results show the higher current density in the crack tip area produced more heat and resulted in a significant rise in temperature. So it was concluded that the compressive thermal stress due to change of thermal expansion causes crack healing.

Cyclic thermo-mechanical stress, strain and continuum damage behaviors in light alloys during fatigue lifetime considering heat treatment effect

In this article, thermo-mechanical fatigue behaviors in light alloys have been investigated to find the effect of heat treatments. For this objective, thermo-mechanical fatigue tests were performed on the A356.0 aluminum alloy and the AZE911 magnesium alloy, with and without typical T6 heat treatments. Obtained results demonstrated no significant difference in thermo-mechanical fatigue lifetime of the A356.0 alloy between non-heat-treated and heat-treated test specimens at 250°C of the maximum temperature, which was attributed to the over-ageing phenomenon. As a consequence, this low effect showed that the heat treatment could be eliminated for cylinder heads. However, the thermo-mechanical fatigue lifetime of the AZE911 alloy was significantly affected by the heat treatment. The explanation for the mentioned behavior could be found in the material micro-structure, which was affected by dissolving the brittle intermetallic phase in the matrix of the AZE911 alloy. However, the magnesium alloy still requires more improvements in the fatigue lifetime for a possible substitution in cylinder heads. Continuum damage behaviors showed that higher damage values occurred in the aluminum alloy, in comparison to the magnesium alloy, both for heat-treated and non-heat-treated specimens.