Thermal Failure Research Articles

Comparison and Selection of Data Processing Methods for the Application of Cr3+ Photoluminescence Piezospectroscopy to Thermal Barrier Coatings

Thermal barrier coatings (TBCs) are an indispensable part of the blades used in aeroengines. Under a high-temperature service environment, the thermal oxidation stress at the interface is the main cause of thermal barrier failure. Cr3+ photoluminescence piezospectroscopy has been successfully used to analyze the thermal oxidation stress of TBCs, but systematic and quantitative analysis results for use in data processing are still lacking, especially with respect to the identification of peak positions. The processing methods used to fit spectral data were studied in this work to accurately characterize TBC thermal oxidation stress using Cr3+ photoluminescence spectroscopy. Both physical and numerical experiments were carried out, where Cr3+ photoluminescence spectra were detected from alumina ceramic samples under step-by-step uniaxial loading, and the simulated spectra were numerically deduced from the measured spectral data. Then, the peak shifts were obtained by fitting all spectral data by using Lorentzian, Gaussian and Psd-Voigt functions. By comparing the fitting results and then discussing the generation mechanism, the Lorentzian function—not the Psd-Voigt function that is most widely utilized—was regarded as the most applicable method for the application of Cr3+ photoluminescence piezospectroscopy to TBCs because of its sufficient sensitivity, stability and confidence for quantitative stress analysis.

Sensitivity to Input Parameters of Failure Detection Methods for Out-of-Plane Loaded Glass Panels in Fire

In recent years, glass has been a largely used material for load-bearing or non-structural components in buildings and constructions. For this reason, dedicated calculation methods and approaches are required for the major loading and boundary conditions that are of technical interest for safe design purposes. Among others, the resistance and mechanical performance of glass elements under fire exposure still represents an open challenge. This paper elaborates on the failure detection methods for out-of-plane loaded glass panels that are subjected to fire loading and simultaneous mechanical loads. As known, the conventional method for thermal failure detection is based on the maximum temperature gradient in glass, and its comparison with a set of allowable standardized values. However, especially for ordinary glass components in buildings that are required to sustain combined mechanical loads, the overall structural performance is even more complex to predict. This design issue is given to a combination of pure mechanical aspects (i.e., sustained loads and corresponding stress–strain analysis) and thermo-physical phenomena, that depend on the progressive modification of material properties while increasing temperatures. This research study, accordingly, investigates the sensitivity of input parameters on the failure time of a given glass element under fire and sustained mechanical loads. A major advantage is taken from finite element (FE) numerical analyses and standardized failure detection methods of literature, that are selected for comparative purposes. Further, the paper also introduces the “stress approach” that can be used to quantify (in place of the conventional thermal gradient) the actual effects of assigned thermal exposure and mechanical loads.

Design and development of microcontroller-based temperature monitoring and control system for power plant generators

The protection of turbine generator systems is an important factor that must be considered in power plant for efficient production of electricity. This project deals with temperature level monitoring of the power generator and it will be compared with the predetermined standard value through an LM35 sensor. Once it exceeds the predetermined value then the cooling fan will automatically turn on which will be useful to prevent the generator from internal winding thermal failure. The protection system consists of 16x2 LCD display, LM35 temperature sensor, a coolant fan and a microcontroller [ATMEGA328P]. The internal winding temperature of generator is increased as the turbine is rotated at its axis which may lead to major damages in the axial position and shafts of the power generator. To overcome this, an LM35 sensor is connected and linked with the microcontroller which monitors the temperature and once it exceeds the standard temperature the coolant fan automatically is turned on by the microcontroller and the heat of the steam will be countered by the cooling air produced by the coolant fan. The fan runs continuously until the temperature is sensed to have dropped below the standard temperature. At the same instances, the LCD display outputs readable current temperature parameters for the operator. The protection of power generator system is a vital component in power plant for efficient production of electricity.

Thermal shock life and failure behaviors of La2Zr2O7/YSZ, La2Ce2O7/YSZ and Gd2Zr2O7/YSZ DCL TBCs by EB-PVD

Double layer ceramic (DCL) thermal barrier coatings (TBCs) have attracted extensive attention due to their high thermal stability under high temperature. The thermal shock life and failure behaviors of DCL TBCs still remain a challenge. This work focuses on crystal structure, thermal expansion coefficients, thermal conductivity, microstructure and failure behaviors of the La2Zr2O7/YSZ (LZ/YSZ), La2Ce2O7/YSZ (LC/YSZ) and Gd2Zr2O7/YSZ (GZ/YSZ) DCL TBCs. The advanced ceramic material exhibits low thermal diffusivity and thermal conductivity. Furthermore, the advanced DCL TBCs exhibit good thermal shock life at 1100 °C due to the feathery microstructure with inter-columnar gaps and inter-columnar pores. After thermal shock test, the broken regions occur on the cracks area within ceramic coatings, TGO and interface leading to the TBCs instabilities. The TBCs interface instabilities play a key role on the failure behaviors of DCL TBCs.

Optimization of Tunnel Field-Effect Transistor-Based ESD Protection Network

The tunnel field-effect transistor (TFET) is a potential candidate for replacing the reverse diode and providing a secondary path in a whole-chip electrostatic discharge (ESD) protection network. In this paper, the ESD characteristics of a traditional point TFET, a line TFET and a Ge-source TFET are investigated using technology computer-aided design (TCAD) simulations, and an improved TFET-based whole-chip ESD protection scheme is proposed. It is found that the Ge-source TFET has a lower trigger voltage and higher failure current compared to the traditional point and line TFETs. However, the Ge-source TFET-based secondary path in the whole-chip ESD protection network is more vulnerable compared to the primary path due to the low thermal instability. Simulation results show that choosing the proper germanium mole fraction in the source region can balance the discharge ability and thermal failure risk, consequently enhancing the whole-chip ESD robustness.

Thermal shock resistance and failure analysis of La2(Zr0.75Ce0.25)2O7-based TBCs produced by atmospheric plasma spraying

High-temperature thermal barrier coatings (TBCs) have important application prospects in the high-performance gas turbine. It is of great significance to study the thermal shock behaviors in improving the reliability and durability of TBCs. In this study, three groups of high-temperature La2(Zr0.75Ce0.25)2O7 (LCZ)-based coatings (LCZ, LCZ/8YSZ and LCZ/CYSZ) were designed and produced by atmospheric plasma spraying. Two cooling ways, water cooling and air cooling, were employed to conduct the thermal shock tests, which facilitates a comprehensive understanding of the thermal shock resistance and the failure mechanisms of LCZ-based TBCs in cyclic thermal shocks. The thermal shock resistance of these coatings was evaluated by thermal cycling lifetime and the failure mechanisms were analyzed in the framework of crack initiation and propagation. Based on the present results, LCZ/8YSZ coating remains intact after 100 air-cooled thermal shock cycles, indicative of remarkable thermal shock resistance. The initiation and propagation of transverse cracks at the interface between the ceramic layer and bond coat result in interface debonding, which is the only failure mechanism of these coatings in air-cooled thermal shock. Except for the interface debonding, in water-cooled thermal shock, the spalling of top coat is another failure mechanism due to the intersection of vertical cracks and interlayer microcracks. The main reasons for the growth of these cracks were also discussed and analyzed in detail.

Towards Fire Forensic Characteristics of Failed Cylindrical Format Lithium–Ion Cells and Batteries

Fire forensic investigators are challenged to determine in what scenarios can lithium ion batteries initiate a fire, and what post-fire signatures exist to determine if the battery was more likely the cause of the fire or a victim of the fire. Towards this goal, this study experimentally characterizes the ignition characteristics of cylindrical format 18650 cells and the post-failure properties of the cells. First, failure tests of individual 18650 cell were used to quantify the temperature of vented gases and heat fluxes from these gases to cold objects for battery thermal failure at various states-of-charge (SOC) in either inert or normal oxygen environments. Experiments were then conducted with 18650 cells failed on composite cushion materials to evaluate how failures from different SOC cells ignite common fabric materials. Finally, laptop tests were conducted to investigate the effect of a common appliance package on the propagation of individual cell thermal runaway within the power bank of a common laptop configuration. The experimental results show that in the event of a thermal runaway, batteries can either explode or release a jet flame. The ignition behavior of fabric materials varies with varying SOCs with more vigorous ignition occurring at larger SOC. It was observed that the final mass of failed batteries is lower for higher SOC cells. Finally, propagation of thermal runaway inside a laptop power bank can be facilitated by having the failure take place at the center location of the power bank and can be hindered if the SOC is sufficiently low.

Enabling thermal-neutral electrolysis for CO2-to-fuel conversions with a hybrid deep learning strategy

High-temperature co-electrolysis of CO2/H2O through the solid oxide electrolysis cells (SOECs) is a promising method to generate renewable fuels and chemical feedstocks. Applying this technology in flexible scenario, especially when combined with variable renewable powers, requires an efficient optimisation strategy to ensure its safety and cost-effective in the long-term operation. To this purpose, we present a hybrid simulation method for the accurate and fast optimisation of the co-electrolysis process in the SOECs. This method builds multi-physics models based on experimental data and extends the database to develop the deep neural network and genetic algorithm. In the case study, thermal-neutral condition (TNC) is set as the optimisation target in various operating conditions, where the SOEC generates no waste heat and needs no auxiliary heating equipment. Small peak-temperature-gradient (PTG) inside the SOEC is found at the TNC, which is vital to prevent thermal failure in the operation. For the cell operating with 1023 K and 1123 K of inlet gas temperatures, the smallest PTGs reach 0.09 and 0.31 K mm−1 at 1.13 and 1.19 V, respectively. Finally, a 4-D map is presented to show the interactions among the applied voltage, required power density, inlet gas composition, and temperature under the TNC. The proposed method can be flexibly modified based on different optimisation targets for various applications in the energy sector.

Effects of Elevated Temperatures on the Microstructural, Physico-Mechanical and Elastic Properties of Barakar Sandstone: A Study from One of the World’s Largest Underground Coalmine Fire Region, Jharia, India

Experimental investigations of the effects of elevated temperature on microstructural, mineralogical, physico-mechanical and elastic properties of rocks were carried out to understand the effect of underground coal fire along with thermal damage and failure initiation in Barakar sandstone from the Jharia coalfield, India. Discolouration analysis, petrographic studies, scanning electron microscopy, thermogravimetry, differential thermal analysis and electron probe micro analysis were carried out to understand the microstructural and mineralogical changes in thermally treated samples. The experimental results suggest that the changes in investigated properties follow three characteristic thermal zones: zone I (25–300 °C), zone II (300–500 °C) and zone III (500–800 °C). Among all, zone II is a prominent transition region where a rapid increase in crack density, porosity and thermal damage is observed along with a sharp reduction in seismic wave velocities, uniaxial compressive strength, tensile strength and elastic parameters. Development of thermal stress-induced intergranular and intragranular micro-cracks, evaporation of organic matters, and dehydration and thermal decomposition of minerals are the most conspicuous reasons for the observed changes in this zone. Zone III is characterized by phase transformation of quartz, recrystallization and partial melting of cement and phyllosilicates that filled some of the existing micro-cracks, resulting in a local change of porosity, strength and elastic properties. Developments of different failure modes are observed in different temperature ranges such as simple shear along a single plane in zone I, progressive growth of Y-shaped (double plane) shearing in the zones II and III (400–700 °C) and axial splitting at 800 °C. The results from this study provide comprehensive elaboration of thermal effects on sandstones at a particular temperature range.

Design of Drain-Extended MOS Devices Using RESURF Techniques for High Switching Performance and Avalanche Reliability

The drift region of conventional drain extended NMOS (DeNMOSC) is engineered to reduce gate charge for high performance and to enhance avalanche ruggedness for reliability in switching applications. Reduced-surface-field (RESURF) techniques, including surface implant (P-Top), split-gate (SG), and shallow trench isolation (STI), with an optimum doping implant of the drift region, are presented to improve the on-state safe operating area (SOA) and hot carrier stress (HCS) reliability of DeNMOS after the gate charge reduction. It is shown that under unclamped inductive switching (UIS) conditions, the avalanche ruggedness of optimized devices is improved, whereas DeNMOSC shows high susceptibility towards thermal runaway and device failure due to electrothermal effects. Switching performance shows a reduction of up to 46% in total gate charge (Qg) and more than 65% in gate-to-drain coupling charge (Qgd). Moreover, the highest improvement achieved in switching delay is 34%. The high-frequency figure of merits such as FoM1 (RON ×Qgd) and FoM2 (RON ×Qg) show significant improvement of up to 65% and 35%, respectively. The tradeoff in the DC figure of merits FoM3 (VBD/RON) and Baliga-FoM (VBD 2/RON) are also analyzed. Comparative analysis of optimized DeNMOS structures indicates that split gate DeNMOS without STI shows a minimum degradation of DC performance and the most significant improvement in high-frequency performance and switching reliability.

Microstructure Evolution, Thermal Properties Improvement and Failure Mechanism of Thermal Barrier Coatings After Shot Peening

Microstructure Evolution, Thermal Properties Improvement and Failure Mechanism of Thermal Barrier Coatings After Shot Peening

Study on thermal, mechanical, microstructural properties and failure analyses of lanthanum zirconate based thermal barrier coatings: A review

This research study summarizes the recent information about the characteristics of multi layer and composite lanthanum zirconate based thermal barrier coatings (TBCs) that provide high-temperature thermal protection for the jet engines parts. Thus the outcome of lightweight gas turbine components able to work at 3000° F nearly 1650 °C needs to be built. Such difficulties can be solved using coatings with optimized microstructure and chemical composition. Recently, Lanthanum zirconate (La2Zr2O7-LZ) based pyrochlore oxides (Ra2Zr2O7, Re = rare earth) are now developing TBC material, owing to their fewer thermal conductivity with enhanced stability at elevated operating temperatures. Even though LZ cannot be directly replaced for standard YSZ because of its mismatch between the grew of thermal oxide (TGO) film. When LZ compared to Zirconia partially stabilized with yttria (YSZ), LZ possesses a poor thermal conductivity, lesser coefficient of thermal expansion, lower sintering ability, and lack of toughness than YSZ. Hence LZ comes to be combined with standard TBC YSZ in order to integrate advantages in multilayer architecture. In this study describes the thermal, mechanical and physical properties and failure analysis of Multilayer LZ/YSZ were described. It also reviews the characterization of coatings according to different criteria and conditions. At last, suggestions for investigation on layered LZ based TBCs applications for next-generation was indicated.

An investigation of thermal related failure in the extruder barrel cooling system and the recommendation

Repeated failure of barrel cooling system resulting in leakage of water during operation after serving about a year was reported from our customer. Barrel cooling system is crucial to maintain the extruders at a specific temperature typically in the range of 250–400 °C for the processing of polymers. Hence failure in the cooling system affects the quality of the processing material. Comprehensive failure analysis involving detailed macro examination, metallography examination and casual analysis of the failed part reveals the influence of the thermal cyclicity from the process on the failure. Appropriate selection of material to enhance the elevated temperature properties of the barrel and further actions in direction to increase the welding strength eliminated the barrel cooling system failure at the customer site.

Mathematical Models for Assessing the Thermal Engineering Reliability of Boiler Units of Power Complexes

The analysis is carried out and the definitions of the concept of thermal engineering reliability, the determining parameter and the determining function of boiler units, are given. A classification has been developed for the determining parameters of steam and hot water boilers by level in the chain of cause-and-effect relationships in the event of a thermal failure. It is proposed to divide the determining parameters and functions of boilers according to their spatial localization into integral and local. A lot of models for defining functions with different mathematical properties (for example, the presence or absence of discontinuities of the second kind) are considered. The defining functions (reliability criteria) currently used in boiler construction have been identified. The analysis of the safety factors for overturning and stagnation in direct-flow and drum boiler units is carried out. The incorrectness of the currently used dependence is shown. A formula has been proposed for these coefficients using internal useful heads, which is especially relevant for boilers with natural circulation at ultrahigh pressure.

Implementation of a cooling system to develop experimental fatigue tests below zero grades Celsius

Temperature is one of the matter properties with the greatest influence on the materials behavior existing in nature and those man designed. This physical magnitude allows to demonstrate and define behaviors and materials characteristics in the industry in general. Its influence is present in all the places where the materials fulfill functions, however, in some applications its influence is very little, which allows to disregard its effects. In the steels case (one of the most used materials at the industrial level today), the temperature variation produces dilation or contraction, depending on the temperature magnitude and its variation that affects them. Temperature increases generate an expansion phenomenon in the materials, which under load will reach a point where they present thermal fatigue failure. The opposite is that of temperature drops, where the phenomenon that occurs is contraction, often leading to the loss of adjustments and interference that compromise the equipment functionality and integrity. The fatigue failure mentioned is presented as a result of the stresses and deformations present in both cases. It is desired to condition a rotational flex fatigue test equipment with a cooling system to bring the sample material to temperatures below zero degrees Celsius, in order to check how low temperatures, affect the resistance of steel to fatigue. For this, a cooling system was designed and the fatigue equipment was adapted to reduce heat transfer. After carrying out this implementation and determining that the sizes of the devices were suitable for the proposed purposes, the initial temperature tests were carried out and, once this part was achieved, three repetitions of a rotary fatigue test were performed that demonstrated that the equipment can operate normally.

Numerical analysis and thermal fatigue life prediction of solder layer in a SiC-IGBT power module

Limited by the mechanical properties of materials, silicon (Si) carbide insulated gate bipolar transistor (IGBT) can no longer meet the requirements of high power and high frequency electronic devices. Silicon carbide (SiC) IGBT, represented by SiC MOSFET, combines the excellent performance of SiC materials and IGBT devices, and becomes an ideal device for high-frequency and high-temperature electronic devices. Even so, the thermal fatigue failure of SiC IGBT, which directly determines its application and promotion, is a problem worthy of attention. In this study, the thermal fatigue behavior of SiC-IGBT under cyclic temperature cycles was investigated by finite element method. The finite element thermomechanical model was established, and stress-strain distribution and creep characteristics of the SnAgCu solder layer were obtained. The thermal fatigue life of the solder was predicted by the creep, shear strain and energy model respectively, and the failure position and factor of failure were discussed.

LaGdZrO/YSZ thermal barrier coatings by EB-PVD: Microstructure, thermal properties and failure mechanism

Advanced thermal barrier coatings (TBCs) have got an increasing number of attention in advanced aero-engine. The thermal cycling life and failure behavior still remain a big challenge under high temperature. This work focuses on the microstructure, element diffusion, and cracks evolution of the LaGdZrO/YSZ (LGZ/YSZ) double ceramic layers (DCL) TBCs. Characterizations mainly include X-ray diffraction (XRD), scanning electron microscope (SEM), energy dispersive spectroscopy (EDS), transmission electron microscopy (TEM) and electron probe micro-analyzer (EPMA). The LGZ/YSZ DCL TBCs exhibit good thermal shock life and thermal cycling life. Element diffusion is investigated in detail, which is relevant with crack formation and propagation. After thermal cycling test, the failure regions mainly occur on the cracks regions and the interface regions. The interface instability plays a critical role on the failure behavior of LGZ/YSZ DCL TBCs.

Y–Er–ZrO2 thermal barrier coatings by EB-PVD: Thermal conductivity, thermal shock life and failure mechanism

Rare earth stabilized ZrO2 thermal barrier coatings (TBCs) have attracted much attention due to their low thermal conductivity and high thermal stability under high temperature. The investigation of thermal shock life and failure mechanism of rare earth stabilized ZrO2 TBCs still remain a challenge. This work focuses on structure, thermal conductivity, thermal shock life and failure mechanism of the rare earth stabilized ZrO2 advanced TBCs. The advanced ceramic material exhibits low thermal diffusivity and thermal conductivity. Furthermore, the advanced TBCs also exhibit good thermal shock life at 1100 °C. After thermal shock test, the broken regions occur on the crack area within ceramic coating, TGO and interface. The TBCs interface instabilities play a key role on the failure mechanism of rare earth stabilized ZrO2 TBCs.

Prediction of thermally induced failure for electronic equipment based on an artificial olfactory system

The failure of electronic equipment causes serious consequences and even catastrophic fires. Abnormal thermal signals are one of the main characteristics of the failure of electronic equipment. Thus, a new method for recognizing and predicting the thermally induced failure states of electronic equipment was proposed, based on an artificial olfactory system (AOS). The AOS recognizes the state of the volatile components released during the early stages of thermally induced failure and uses it to predict the state of health of the electronic equipment. Some typical electronic devices, such as microcomputer units, electronic rectifiers, transformers, and battery modules, were tested with the AOS to recognize the failures indicated by abnormal thermal accumulation. Compared with infrared thermal imagers and gas analyzers, the PEN3 electronic nose was utilized to monitor the status of the devices under different thermal failure scenarios. It was found that infrared thermal imaging was only able to monitor the local surface temperature, and the air temperature in the device chamber changed slowly with the surface temperature of the electronic modules. However, the AOS was able to detect the abnormal change in the whole chamber. Linear discriminant analysis (LDA) and principal component analysis (PCA) were then adopted to investigate the features of thermally induced failure for different thermal states. The results showed that the models obtained both from LDA and PCA were able to distinguish the different states of the electronic devices. Furthermore, a support vector machine model was built, based on the AOS data, to recognize and predict the thermally induced failure processes. All the failure states of the electronic devices caused by thermal simulations were recognized successfully and the prediction accuracy was above 95%. Hence, the experimental results of this research proved that using the AOS, it is feasible to predict the thermally induced failure states of electronic equipment, and the failure of electronic devices can be forecast in advance, before the obvious temperature rise and smoke release. Moreover, the method proposed in this research can also be applied to the prediction of, and warning about, electrical fires, indoor fires, and other thermally induced accidents.

Thermal Damage Process and Failure Mechanism of Epoxy/SF6 Composite Insulation Subjected to Arc Ablation

In this work, the effects of arc ablation on the surface of epoxy (EP) in EP/SF <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">6</sub> composite insulation are analyzed. Based on the results, the characteristics of streamers on the surface of EP is captured by a photomultiplier array and the failure mechanism of the EP is studied. The results show that the arc heat flow applied to the EP/SF <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">6</sub> interface can lead to the decomposition of EP molecular chains and degradation of the SF <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">6</sub> . The pyrolysis products re-couple to generate complex carbides and pyrolysis gases, resulting in severe irregular carbonization on the EP surface and the increase in surface conductivity. When an external electric field is applied, a large quantity of photons will accumulate in the carbonization region on the EP surface and this gives rise to the surface streamer and thereby greatly decreases the surface electrical strength of EP/SF <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">6</sub> composite insulation.