Thermal Fatigue Conditions Research Articles

Conventional shot peening treatment effects on thermal fatigue crack growth and failure mechanisms of a solid solution alloy

This study presents the effects of conventional shot peening as a surface post-treatment method on the fatigue crack growth behavior and failure mechanism of a solid solution alloy used in the flat seal component under thermal fatigue conditions. The study employs a combination of experimental tests and finite element simulations to evaluate the effect of shot peening on thermal fatigue crack growth behavior. The corrected J-integral and Paris model are used to calculate the stress intensity factor and predict the thermal fatigue crack growth behavior, respectively. Additionally, the ZENCRACK method is employed to predict thermal fatigue life. The results indicate that shot peening induces compressive residual stress, leading to a decreased distribution of thermal stress, particularly along the crack propagation path. The simulated fatigue life curve obtained by ZENCRACK demonstrated a good agreement between the simulated and experimental crack growth results. The incorporation of shot peening caused a significant reduction in the rate of thermal fatigue crack growth, and the simulated stress intensity factor analysis revealed an increase during the heating stage. Consequently, the thermal fatigue crack propagated during the heating-up process. SEM evaluation reveals that the shot peening post-treatment impacts both thermal fatigue crack initiation and propagation. Furthermore, the failure mode of shot-peened specimens involves inter- and trans-granular cracking, while non-shot-peened specimens exhibit trans-granular cracking.

Thermal fatigue failure enhancement for FGM coolant pipes subject to high-temperature and hydrostatic lateral pressure

This paper intends to enhance the corrosion resistance of coolant pipes in thermal fatigue conditions and lateral hydrostatic pressure in critical engineering environments. This research applies to circular coolant pipes under hydrostatic pressure of the LBE (lead-bismuth eutectic) boundary in nuclear power plants. The resistance against corrosion caused by liquid LBE is mainly formed by Fe12Cr2Si solid solutions coatings on the pipe. The silicon concentration in Fe12Cr2Si can interact with LBE as an effective oxidized compound such as SiO2 and Fe2SiO4 when the silicon concentration is above 1.25 wt%. The oxide film formed on the coating can resist the LBE corroding in the Fe12Cr2Si structure. The primary material for constructing a coolant pipe is T91 ferritic-martensitic alloys, and the surface anti-corrosion coating is Fe12Cr2Si solid solution. With a high-strength structure, FGC (functionally graded composite material) ensures that the pipe resists the corrosion from Liquid LBE. This study evaluates the thermal fatigue failure of coolant pipes and the silicon concentration when the pipe model is under thermal shock testing by a CO2 laser. The research result indicates that the FGM (functionally graded material) structure performs better in effectively raising the margin of safety and reserving the silicon concentration on the inner surface higher than 1.25 wt% as compared to the FGC structure.

Temperature dependence of the tensile and thermal fatigue cracking properties of laser-deposited cobalt-based coatings for brake disc application

A new cobalt-based coating, CoNiTi, was developed for brake disc applications. The effect of temperature on the tensile and thermal fatigue cracking properties of CoNiTi was evaluated between room temperature (RT) and 700 °C, and compared with those of the commercial CoCrMoW and Stellite 6 coatings. The strength of all coatings decreased with increasing test temperature, and the elongation to fracture of Stellite 6 increased with increasing test temperature. However, CoNiTi and CoCrMoW presented deterioration in elongation to fracture at 400–500 °C. In addition, the crack propagation rate of CoCrMoW and CoNiTi also presented a trend of accelerated increase under RT ∼700 °C thermal fatigue condition. By combining the finite element simulation of thermal fatigue and in-situ tensile test, the grain boundary weakness at middle temperature was revealed to clarify the reason for the deterioration of plasticity and crack growth resistance in CoCrMoW and CoNiTi. The microstructure evolution of γ-Co → ε-Co martensitic transformation during tests depended on the temperature and chemical composition associated with stacking fault energy (SFE). Increasing temperature and nickel content could improve SFE, stabilize γ-Co, and make dislocation glide in cross-slip mode, on the contrary, γ-Co tended to undergo martensitic transformation, and the dislocation was in planar-slip mode, when SFE was low.

Failure mode and effects analysis of forging die design: An integrated approach

The factors such as cyclic mechanical loads, thermal fatigue and friction condition has serious consequences on the service life of the dies as well as effects the production cost. Reduction in service life or early die failure may also occur due to improper die-design, forming defects and process parameters. Out of these, die design plays major role in failure of dies. So, there is a need to analyse reasonable design criteria and their effects. While designing of forging dies, there are several important design criteria which must be considered like material selection, selection of parting line, allowances and tolerances, draft, fillet and corner radii, design of flash and gutter, preform design, and finisher design. To improve the die life, it is required to investigate and prioritize the effect of design criteria on failure of dies, which can be done by assessing the total impact of each criterion. In this paper, a new method is proposed to prioritize the design criteria based on severity, occurrence, detection, and impact of failure. The proposed method involves using a new parameter Impact factor(I) in conjugation with traditional FMEA analysis. By considering the impact factor in the traditional FMEA it is observed that there is an improvement in ranking result. It is also observed that the ranking obtained using proposed method is well in line with the previous research.

A method for predicting the delamination life of thermal barrier coatings under thermal gradient mechanical fatigue condition considering degradation characteristics

To establish a method for predicting the delamination life under thermal gradient mechanical fatigue (TGMF) conditions considering thermally grown oxides and sintering behavior, degradation tests were conducted on a thermal barrier coating (TBC) under various degradation conditions. Accordingly, damage factors were defined, and a life prediction method was developed by applying them to the constant term of the strain–life diagram. For validation, a TGMF test was performed on a specimen in which the same TBC was applied to a different type of substrate (CM247LC). The actual and predicted lives were similar, thus confirming the validity of the prediction method.

Matrix Channel Width Evolution of Single Crystal Superalloy Under Creep and Thermal Mechanical Fatigue

In this study, experiment and probabilistic modeling of matrix channel (MC) width evolution for single crystal (SC) superalloy is conducted under creep and thermal mechanical fatigue (TMF) conditions. Firstly, fractured and interrupted tests are carried out on SC superalloy, and an image processing program is developed to identify and measure the MC width. Test results show that the rafting rate is greater as the stress, temperature levels or phase difference is larger. Besides, the MC width obeys lognormal distribution, and the standard deviation of MC width follows linear relationship with mean value. In modeling part, a static model is established to predict the mean value evolution of MC width under creep condition. To be generalized to TMF condition, the model is modified to consider non-quasi-static effect. Further, probabilistic model is derived to predict the probability density distribution of MC width. The predictions are in good agreement with the experimental results.

WITHDRAWN: Comparison of magnesia ramming mass and zirconia for refractory wall of induction furnace

Abstract Furnaces are most commonly used for melting of ferrous metals and its alloy materials. Induction furnaces use electrical power so that they are more advantageous as no fuel is required. It is a very critical problem to find life span of induction melting furnace wall under thermal fatigue conditions. The life cycle of induction furnace refractory wall is a variable as minor variation is always present due to effect of skill of workers and many other factors. The heating cooling cycle of induction furnace wall will result in increasing and decreasing thermal stresses. The thermal fatigue behaviour of induction furnace wall is compared in this paper for magnesia ramming mass and zirconia. We have used two different methods including experimental investigation and numerical analysis.

Method for Predicting Thermal Fatigue Life of Thermal Barrier Coatings Using TGO Interface Stress

Thermal barrier coatings (TBCs) applied to high-temperature components of gas turbines consist of a ceramic top coat, a metallic bond coat, and thermally grown oxide (TGO) generated between the top coat and bond coat. Because TBCs are subjected to repeated thermal stress at the coating interface under thermal fatigue conditions and eventually breakage, it is crucial to evaluate the thermal fatigue durability of TBCs according to the stress. In this study, coin-type TBC specimens were prepared by depositing commercial coating powders on Ni-based super alloys via the air plasma spray method, and the thermal fatigue life of the TBCs was experimentally evaluated. According to the test results and references, a finite-element analysis was conducted. The maximum stress of the TGO interface was evaluated according to the thickness and equivalent elastic modulus, and simulating the microstructure including the pores of the top coat. Using these relationships, a thermal fatigue life prediction equation considering the coating thickness (t), equivalent elastic modulus (E), and operating temperature (T) was derived, and subsequently verified.

Parametric analysis of delamination in GFRP composite profiles by performing rotary ultrasonic drilling approach: Experimental and statistical study

Application of glass fiber reinforced polymers (GFRP) has been appreciably increased in recent decades because of their admirable properties. Thus, various investigations are focused in machinability of GFRPs. Delamination is one of the major damages in drilling of GFRPs. Rotary ultrasonic drilling (RUD) is a state-of-the-art drilling operation that has been noticeably considered in composites machining industry. In this paper, delamination of GFRPs in RUD process is examined. To reach the goal, appropriate ultrasonic system was established and using a HSS tool, the experiments were carried out. Then, the influence of multi-walled carbon nanotube (MWCNT) addition, thermal fatigue and drilling parameters on delamination were investigated. Additionally, statistical analysis was performed. The results showed that the delamination quality can be well optimized by increase of the cutting velocity. It was also established that thermal fatigue condition results in delamination deterioration. In contrary, addition of nanoparticles enhances the delamination state.

Environmental, mechanical and materialistic effects on delamination damage of glass fiber composites: Analysis and optimization

Machining process of glass fiber composites usually induces delamination damage. The presence of delamination may cause changes in the mechanical characteristics of the composite structures. In this research, a comprehensive experimental study is performed to analyze the influence of different parameters such as thermal fatigue, lay-up arrangement, resin type, feed rate and cutting velocity on the delamination of glass fiber composites under different drilling processes. Besides, influence of ultrasonic vibration exerting on the tool as a new and high-tech process is investigated. To follow this aim, different composite specimens with various resin types and lay-up arrangements are fabricated and a thermal fatigue condition is provided. Additionally, the Taguchi method is employed to obtain the optimized damage reduction condition in terms of mentioned parameters. The results indicated that thermal fatigue and unsymmetrical lay-up arrangement result in more delamination damage. It was also established that the influence of mentioned parameters is more considerable in higher cutting velocities. Moreover, ultrasonic vibration application is suggested to have the least delamination damage.

Application of slitting method to characterize the effects of thermal fatigue, lay-up arrangement and MWCNTs on the residual stresses of laminated composites

Residual stresses in engineering components can have a profound effect on service performance, particularly fatigue life. In this research, the effects of consequential parameters on the thermal residual stresses of glass fiber reinforced polymer (GFRP) composite structures such as thermal cycle fatigue, lay-up configuration and addition of multi-walled carbon nanotubes are characterized experimentally. The slitting method is performed to measure the non-uniform residual stresses over the thickness. Additionally, an extended finite element modeling is carried out to simulate the slitting process. Experimental results indicated that residual stress quality of the composite profiles can be considerably affected by thermal fatigue condition. It was observed that thermal residual stresses decrease with increment of the number of thermal cycles. It was also revealed that symmetric lay-up arrangements show less residual stresses than the unsymmetrical ones.

High temperature wear resistance and thermal fatigue behavior of Stellite-6/WC coatings produced by laser cladding with Co-coated WC powder

The Stellite-6/WC composite coatings were produced on AISI H13 hot work tool steel by laser cladding with mixture of Co-coated WC (WC-12Co) particles and Stellite-6 powder. The phase composition, microstructural characterization, high temperature wear resistance and thermal fatigue behavior of Stellite-6/WC coatings were investigated and compared with the properties of the coatings produced from mixture of WC particles and Stellite-6 powder. The results showed that using the WC-12Co particles alleviated the decomposition of WC and resulted in the weaker intensity of W2C, CoCx and Co6W6C peaks in the X-Ray Diffraction (XRD) patterns. Compared with using the WC particles directly as the coating material, using the WC-12Co particles could further improve the wear resistance of coatings according to the relative lower width and depth of wear scars at the same WC content. In addition, fewer fatigue cracks were observed on the surface of coatings made by adding WC-12Co particles under the same thermal fatigue conditions, which indicates that using WC-12Co is beneficial to extend the life of Stellite-6/WC coatings.

Parametric investigation of machining parameters in determining the machinability of Inconel 718 using taguchi technique and grey relational analysis

High performance super alloys are most in demand for mission critical components to perform in aggressive working conditions. These alloys withstand high thermal fatigue conditions and provide better stability to machine components in aerospace, marine, energy production, biomechanical, automotive industries. Inconel 718 is one such alloy extensively used in this loading conditions due to high thermal corrosion, chemical stability, mechanical friction and high strength. Cutting tools such as tungsten carbide are being used to machine such hard to cut materials. This paper discusses the cutting parameters needed for the machining of Inconel 718 to produce low tool wear and minimum surface roughness.

Failure analysis of thermally cycled columnar thermal barrier coatings produced by high-velocity-air fuel and axial-suspension-plasma spraying: A design perspective

Axial-suspension-plasma spraying (ASPS) is a fairly recent thermal spray technology which enables production of ceramic top coats in TBCs, incorporating simultaneously the properties of both the conventional-plasma sprayed (highly insulating porous structures) and electron-beam-physical-vapor-deposited (strain-tolerant columnar structures) top coats. TBCs are required to insulate the hot components in a gas turbine engine against high temperature and harsh operating conditions. Periodic heating and cooling of turbine engines during operation can create severe thermal cyclic fatigue conditions which can degrade the performance of these coatings eventually leading to the failure. An in-depth experimental investigation was performed to understand the failure behavior of columnar TBCs subjected to thermal cyclic fatigue (TCF) test at 1100ᵒC. The study revealed that the TCF performance was influenced to an extent, by the top coat microstructure, but was primarily affected by the severity of thermally grown oxide (TGO) growth at the bond coat-top coat interface. Mixed failure modes comprising crack propagation through the bond coat-TGO interface, through TGO and within the top coat were identified. Based on the analysis of the experimental results and thorough discussion a novel design of microstructure for the high TCF performance columnar TBC is proposed.

Experimental and numerical investigation on thermal fatigue behaviour of 9Cr 1Mo steel tubes

Abstract Boiler tubing is subjected to alternate cycles of heating and cooling during operation initiating alternate thermal expansion and contraction. Alternate cycles of differential expansion and contraction causes thermal fatigue of the component. Thermal fatigue causes tube failures, significantly reducing the working life of the tubular components. Boilers have matured into super critical design using T91 grade materials thereby increasing the operating efficiency. The studies involving thermal fatigue of tubes of T91 grades for boiler components in operating conditions are thus an important area. A simple experimental set up has been developed to simulate thermal fatigue conditions in the internal diameter (ID) side of the tube. The work involves both experimental and numerical investigations of the thermal fatigue behaviour by creating a simulated environment and a Finite Element Model (FEM). FEM analyses are carried out based on the decoupled thermal and inelastic stress analyses to compute the total plastic strain range experienced by the boiler tubes. The cyclic spray cooling causes thermal fatigue cracks in the T91 tube. The number of cycles to crack initiation has been obtained from the experimentation and number cycles to failure has been calculated using modified Coffin-Manson relation. The study thus presents a reliable fatigue failure analysis of 9Cr 1Mo steel tubes used in boiler industry.

The study on delamination life of TBC through burner-rig test

Since gas turbines operate under extremely high temperatures, the hot-section parts of gas turbines should be protected from severe environmental conditions. Thermal Barrier Coating (TBC) is a protection technique that lowers the surface temperature of the hot-section parts. To design reliable gas turbines, the delamination life of TBC should be accurately evaluated. This study evaluated the delamination life of TBC by conducting a burner-rig test simulation of thermal fatigue conditions using a hot flame. Two types of TBCs were considered: one with vertical cracks and the other without vertical cracks. To evaluate the effects of pre-isothermal deterioration on thermal fatigue life under flame conditions, burner-rig tests were performed using isothermally deteriorated specimens. The burner-rig tests were conducted until the coating layer was completely delaminated. Using the tests results, predictive equations for delamination life and delaminated TBC area were derived and analyzed.

Stress Life Analysis of Induction Furnace Wall for Magnesia Ramming Mass

Furnaces are most commonly used for melting of materials. Induction furnaces are more beneficial as no fuel is required. It is a problem to find life cycle of Induction Melting Furnace Wall under load variation. The induction melting furnace wall is made of magnesia ramming mass which is one kind of refractory material. The failure occurs due to cyclic thermal stresses due to heating and cooling cycles. Temperature distribution and thermal stress distribution fields of the induction melting furnace refractory wall were calculated by using explicit finite difference analysis based on the physical description of its failure under low cycle thermal fatigue conditions. The life span of the refractory wall is required to be found out by means of critical thermal stresses created inside the refractory wall of induction melting furnace wall from modified S - log N Curve.

Analysis of Mechanical Behaviour of Heat Affected Zone on Ferritic Side of Bimetallic Welds under Thermal Fatigue Conditions

In this paper the effect of thermal fatigue on mechanical behaviour of the heat affected zone on ferritic side of bimetallic weld was investigated. The bimetallic weld coupons between ferritic steel SA516 Grade 70 and stainless steel 304L were fabricated using TIG (Tungsten Inert Gas) welding process. In this investigation, an experimental test rig was developed and used to simulate the thermal fatigue conditions at laboratory scale. The thermal fatigue factors selected were heating time, notch radius and number of cycles.

Life prediction of thermal barrier coating considering degradation and thermal fatigue

A thermal barrier coating (TBC) is used to protect gas turbine components from extreme environments. Typically, the TBC system consists of two parts: a ceramic top coat and metallic bond coat. Thus, the TBC system is exposed to thermal fatigue owing to the mismatch between the thermal expansions of the ceramic top coat and metallic bond coat. The durability of the TBC decreases with repeated thermal fatigue and degradation under high-temperature conditions, which can eventually result in failure. Therefore, the life of the TBC should be predicted while considering degradation and thermal fatigue. In this study, TBC specimens were produced under different degradation and thermal fatigue conditions, and the bond test was performed on these specimens. Based on the bond test results, the life of the TBC was predicted according to degradation and thermal fatigue.

Evaluation of thermal gradient mechanical fatigue characteristics of thermal barrier coating, considering the effects of thermally grown oxide

Gas turbines of aircraft and power generation plants operate at a high turbine inlet temperature (TIT) or combustion temperature higher than 1,000°C to obtain high thermal efficiency. The parts directly in contact with the high temperature flame are made of a nickel-base superalloy, which has strong heat resistance. In addition, the thermal barrier coating (TBC) technique is applied to increase the heat resistance. The TBC prevents direct heat transfer from the high temperature flame to the metallic substrate. Thus, the TBC technique reduces the substrate surface temperature by approximately 100~170°C. The delamination caused by the growth of thermally grown oxide (TGO) decreases the life of the TBC system. In addition, gas turbine blades experience centrifugal forces owing to high speeds of approximately 3600 rpm and they experience low cycle fatigue because of frequent startup and shutdown. Therefore, the integrity of the TBC system should be evaluated under the thermal gradient mechanical fatigue condition. In this study, finite element analysis (FEA) was performed for the TBC model considering TGO, and the effect of TGO on TBC systems was evaluated under the thermal gradient mechanical fatigue condition.