Thermal Failure Research Articles

Low cycle fatigue behavior and life prediction of a directionally solidified alloy

Low cycle fatigue behavior and life prediction of a directionally solidified alloy

Thermal runaway and induced electrical failure of epoxy resin in high‐frequency transformers: Insulation design reference

AbstractSolid‐state transformers (SSTs) have applications in medium‐voltage (MV) DC grids and compact power systems. High‐frequency transformer (HFT) is the core component of SSTs. High levels of high frequency high dv/dt voltage stresses challenged the integrity of the galvanic insulation of HFTs. However, dielectric thermal runaway and resultant electrical failure mechanisms in epoxy resin (EP) cast insulation remain unclear. Dielectric heating of EP across varying voltages, frequencies, rising edges, duty cycles and DC biases were measured and corroborated by simulation. The thermal runaway threshold mainly depends on the tangency point of the loss generation and heat dissipation curves below the glass transition temperature. Observations reveal that thermal runaway does not directly cause breakdown; instead, thermal decomposition above 200°C triggers discharge and eventual failure. Simulations demonstrate that temperature rise mainly depends on the average field within the electrode region and inter‐segment and inter‐layer distances within the HFT winding definitively impact insulation thermal runaway. By applying different criteria for MV and high‐voltage (HV) transformers, the reference electric fields for insulation design with unfilled and filled EP were obtained. For instance, limiting dielectric heating below 5 K at 50 kHz necessitates an RMS average field less than 0.44 V/mm, which is much lower than dry‐type transformer conventions. The authors prove the necessity of re‐evaluating the permissible field strength in HFT insulation design.

Investigation of experimental and numerical analysis of thermal load of WEDM on all metals through process parameters on wire electrode temperature

The thermal load on wire electrode in a wire electrical discharge machining (WEDM) is the most important factor in predicting wire electrode breakage. Thermal failure of wire electrode may be expected when the maximum temperature of the wire crosses a critical value. The maximum temperature of wire electrode is a function of process parameters of the machine and hence the failure depends upon what settings we choose to run WEDM process. In this investigation, simulation is done using finite-difference thermal model for continuous pulse without clustering of the spark. The model is used for determining distribution of the temperature throughout the length of wire electrode and analyzed the significance of various factors on wire breakage. The outcome of the present simulation model is validated by comparing it with the works of other researchers followed by its validation through experiments. A parametric study is also done to determine the effect of input process parameters and their interaction on the temperature of the wire. For finding the interaction effect, analysis of variance analysis is carried out followed by developing an empirical model. The predictive performance of our simulation model and developed regression models is assessed by comparing them with experimental value. The regression model is found to be closer, with an average percentage deviation of −2.55% on the experimental dataset, compared to 2.64% for the simulation model. During the validation test, the minimum and maximum deviations are 0.08% and 0.20% for simulation versus regression model predictions, −3.31% and −1.65% for experimental versus predicted results, and 1.82% and 3.40% for simulation versus experimental results, respectively. It is observed through this study that temperature of wire electrode mainly depends on the intensity of sparks per unit area which is a function of the input parameters of the WEDM.

On the Thermal Shock Resistance and Failure Mechanism of the Pt-Modified Aluminide Bond Coating

The failure mechanism of the Pt-modified aluminide (Pt-Al) bond coating (β-(Ni, Pt)Al coating) in a simulated service environment has seldom been investigated. Based on a self-developed thermal barrier coating service environment simulator, a thermal shock experiment of single-phase Pt-Al bond coating on DD419 substrate at a temperature of 1170 °C was conducted combined with a real-time monitoring infrared thermal imager. The lifespan and failure mechanism of the coating are analyzed in detail. The results reveal that specimens of the Pt-Al bond coating, subjected to three repeated tests, exhibit failure after 650, 528, and 793 thermal shock cycles at 1170 °C, respectively. After failure, the contents of Pt and Al elements in the peeled region are lower than those in the unpeeled area, and a diffusion zone emerges in the bond coating. The failure mechanism of the Pt-Al bond coating during the thermal shock test can be attributed to three main aspects: (1) the diffusion and consumption of the Pt element reduced the oxidation resistance of the Pt-Al bond coating; (2) the diffusion and depletion of elemental Al causes a phase change in the coating, leading to the failure of the coating; (3) thermal stresses are generated in the Pt-Al bonded coating during the thermal shock test, which ultimately leads to wrinkling.

Application of the thermal death time model in predicting thermal damage accumulation in plants.

The thermal death time (TDT) model suggests that the duration an organism can tolerate thermal stress decreases exponentially as the intensity of the temperature becomes more extreme. This model has been used to predict damage accumulation in ectothermic animals and plants under fluctuating thermal conditions. However, the critical assumption of the TDT model, which is additive damage accumulation, remains unverified for plants. We assessed thermal damage in Thymus vulgaris under different heat and cold treatments and used TDT models to predict time to thermal failure of PSII. Additionally, thermal tolerance estimates from previous studies were used to create TDT models to assess the applicability of this framework in plants. We show that thermal damage is additive between 44 to 47 °C and -6.5 to -8 °C and that the TDT model can predict damage accumulation at both temperature extremes. Data from previous studies indicate a broad applicability of this approach across plant species and traits. The TDT framework reveals a thermal tolerance landscape describing the relationship between exposure duration, stress intensity and percentwise damage accumulation. The extreme thermal sensitivity of plants emphasizes that even 1°C increase in future extreme temperatures could impact their mortality and distribution.

Fatigue Failure in Polymeric Materials: Insights from Experimental Testing

The investigation of fatigue failure in polymeric materials subjected to cyclic loading holds significant importance across diverse engineering applications. Numerous variables influence material behavior, encompassing material-related factors such as composition, molecular weight, orientation, and additives, as well as external factors like applied stress magnitude (stress amplitude, dynamic stress frequency and mean stress), and operating temperature. This paper presents an experimental exploration into the impact of loading parameters—mean stress, stress amplitude, and dynamic stress frequency—on the failure modes of two thermoplastic materials: high-density polyethylene (HDPE) and polyvinyl chloride (PVC). The study begins with an assessment of the mechanical and physical properties of the materials, followed by the design and manufacturing of a specialized uniaxial fatigue test rig. Tensile–tensile fatigue tests incorporating positive mean stress are conducted, evaluating the influence of altering stress amplitude and frequency on fatigue life and failure mode. The outcomes reveal that HDPE primarily experiences thermal and creep failure modes, with a lack of observed fatigue failure. Conversely, PVC specimens manifest three distinct failure modes: ductile, creep, and fatigue, with the type of failure contingent upon loading parameters. These findings offer significant insights into the various fatigue failure modes and contribute to an enhanced comprehension of the intricate interplay between loading dynamics and failure modes in polymeric materials.

Composite structure failure analysis post Lithium-Ion battery fire

The use of composite materials has expanded significantly in a variety of sectors. In road transport,lithium-ion batteries (LIB) are the most commonly used.It is standard practice for batteriesto be housed within a metal enclosure, whichprotects and enables extinguishment in the event ofThermal Runaway (TR). Composite materials have been shown to contribute to lightweighting in many vehicle structures and their use inbattery enclosures has been growing in recent years - with the aim of reducing the weight of the battery assembly and positively impacting vehicle range.This work develops Finite Element (FE) models to assess thermal and mechanical damage and failure mechanisms during a TR event considering a section of a composite battery enclosure. Experimental data for a cylindrical 18650 lithium-ion battery fire is studied and used to define representative thermal loading. This validated loading profile is applied to a composite specimen and material temperature data is used to appraise damage. Finally, the predicted damage isused to predict and quantify the residual failure mechanism and strength of the specimen post battery fire. Results have shown the presence of damage from a single cell runaway can potentially reduce the strength of the specimen by 20% while multi-cell runaway can potentially reduce the strength by 56%. The predictive simulation capability herein could be used as a design tool for battery fire protection of composite enclosures, potentially reducing the need for corrective action, minimising the number of physical tests to support design and certification, as well as aiding in the interpretation of physical test results.

A comprehensive investigation on both the combustion characteristic and electrochemical performance of lithium battery with flame retardant tris (2-chloropropyl) phosphate

Thermal failures of lithium batteries have become more and more critical for the further development of energy storage technologies. Adding flame retardant additives has been proven promising to improve safety. However, the electrochemical performance usually degrades with additives. It is important to balance flame retardancy and electrochemical performance. In this study, both the combustion characteristics and electrochemical performance of Tris (2-ChloroPropyl) Phosphate (TCPP) are investigated to seek its potential for application in practical batteries. A novel experimental setup as well as key parameters are proposed to quantificationally characterize the flame retardancy of TCPP. The experimental results indicate that only 5 wt% of TCPP additives can lengthen both the jet delay times and auto-ignition delay times of the electrolyte jets by 50.6 % and 38.1 %, indicating the excellent flame-retardant efficiency of TCPP. The lithium salt in the electrolytes also presents significant flame retardancy on the combustion of electrolyte jets, particularly lengthening the auto-ignition delay times by as high as 74.8 %. Tests on the electrochemical performance reveal that 5 wt% of TCPP additives have negligible impacts on the discharge capacity. The overall deterioration of the discharge retention ratio is less than 6.0 % during long-term and various C-rates cycling tests.

Stiffness design, failure modes, and lightweight design of truss-lattice with filler sandwich plate under thermal loading

A homogeneous stiffness equation of a lattice with a filler has been obtained by the conservation of strain energy. Using this equation, the relationships between the physical and geometric factors of the truss, filler, and homogeneous stiffness were derived, and stiffness design criteria were obtained. The relationships between different thermal failure modes of the truss-lattice with the filler sandwich plate and its physical and geometric parameters were discussed, including their effects on global plate buckling, local plate buckling, truss buckling, and yielding. Strength improvement measures have been obtained. Failure maps with three geometric ratios and different physical ratios were obtained by failure mode analysis. Finally, a lightweight design method that achieves the strength and stiffness requirements was obtained based on four independent variables.

Thermal full-field prediction of an air-cooled data center using a novel multi-scale approach based on POD and CFD coupling

A full-knowledge of the temperature distribution in a data center is crucial for the design and operation to avoid thermal failure. However, it is a great challenge to conduct full-field simulations using the computational fluid dynamics/heat transfer (CFD/HT) method due to the unacceptable computational cost caused by the multi-scale structure of data centers. In this paper, a novel multi-scale model based on POD and CFD coupling is proposed to predict the thermal and fluid characteristics in data centers from room scale to chip scale. The temperature and flow fields in an air-cooled data center are predicted and analyzed under the scales of room, server, IGBT and chip. Based on the CFD results of Room-Server level, 16 sets of design cases’ temperature fields for Server-IGBT level are compared using the POD and CFD methods, which shows that the maximum average absolute deviation and average relative deviation are 0.004 °C and 0.59%, respectively. Subsequently, three sets of off-design cases for Server-IGBT level and IGBT-Chip level are predicted using the aforementioned methods, yielding the maximum relative deviation 7.21% and 0.98%, respectively. The salient outcome is the remarkable 175-fold reduction in CPU processing time achieved with the POD model compared to traditional CFD simulations.

Thermal fatigue analysis and structural optimization of sliding composite leaf spring

The thermal failure mechanism of sliding composite leaf springs (SCLSs) is examined in this research. Bench fatigue testing is used in the experimental investigation of the thermal failure temperature and mode. The findings demonstrate that after 20 min, when the temperature reaches the glass transition temperature, cracks start to form around the bolt hole of the composite body. The findings from bench experiments indicate that thermal fatigue failure of SCLS can be divided into three main forms: delamination failure of the resin-rich layer, the resin-fiber interface, and fibre pull-out failure. The utilization of finite element simulation has demonstrated that when subjected to thermal load, the leaf spring’s internal defects can lead to localized stress concentration. The structure of the spring end is optimized using the insulating panel scheme and the metal joint scheme. The thermal fatigue issue with SCLS is best addressed by the heat dissipation approach, according to bench tests.

Influence of the Arrangement of the Cells/Modules of a Traction Battery on the Spread of Fire in Case of Thermal Runaway

When designing the battery of an electric vehicle, different parameters must be considered to obtain the safest arrangement of the battery/modules/cells from the mechanical and thermal points of view. In this study, the thermal runaway propagation mechanism of lithium-ion cells is analyzed as a function of their arrangement within a battery pack in case of a fire propagation of a battery pack in which a thermal runaway has occurred. The objective is to identify which cell/module arrangement is most critical within the battery pack, using microscopic analysis of the structure and chemical composition of the most damaged cells, both horizontally and vertically, of a battery belonging to a burnt vehicle. And their final condition was compared with the condition of new cells of the same type. In this way, the structure and chemical composition of the cathode, anode, and separator after thermal runaway were compared. This research was carried out to obtain information to understand the mechanical properties of lithium-ion cells and their behavior after thermal runaway heating leading to the propagation of a fire. Through the analysis carried out, it is concluded that cells placed in a vertical arrangement have worse behavior than cells in a horizontal arrangement. Regarding the safety of the battery, the results of this study will allow us to determine which arrangement and structure of the cells in the battery pack is safer against thermal runaway due to thermal failure.

Electrothermal Coupling Modeling and Electrothermal Dynamic Characteristics of Nickel-Cadmium Battery

Although Nickel-Cadmium batteries are widely used, there is a general problem of thermal failure and even thermal safety, and a lack of thermal characteristics and temperature rise law research. Accordingly, a typical Nickel-Cadmium battery’s equivalent circuit model, thermal model, and electrothermal coupling model were established in this article. The model’s open-circuit voltage, resistance, and capacitance, as well as its entropy heat coefficient, thermal conductivity and heat transfer coefficient were measured, and finally, according to these parameters, the verification analysis of the electrothermal coupling model was carried out in Simulink under the HPPC working condition and constant current working condition. The results show that the simulation results are basically consistent with the experimental data, the absolute value of voltage error is less than 0.02V under HPPC condition, the maximum voltage error is only 0.7% under constant current condition, and the temperature maximum error is only 3%. Consequently, the constructed electrothermal coupling model can well reflect the electrothermal characteristics of the battery, which provides data support and reference for solving the thermal failure problem.

Evaluation of Fire Spread and Suppression Techniques in Micro-Mobility Battery Packs

Lithium-ion battery packs used in micro-mobility devices, such as e-bikes and e-scooters can lead to substantial safety hazards should a single cell go into thermal runaway. In this paper we explore the extent and severity of e-mobility battery fires resulting from a single cell thermal runaway failure and evaluate various suppression techniques a user may attempt to implement if they experience a battery fire at home. We tested a household water hose as well as different fire blankets deployed both before the forced thermal runaway event and after initiation. The water hose was unable to supply a sufficient amount of water to extinguish the thermal event, however, the average pack temperature was decreased and the cell-to-cell propagation rate was slowed. Neither fire blanket tested was able to contain the flames or debris ejected from the battery packs and both acted to hold in the heat from the event, increasing the temperature, rather than allowing it to dissipate. In addition, we also demonstrated how various design approaches, such as added thermal insulation between cells, can help prevent cell-to-cell propagation and reduce the severity of a battery pack failure.

Numerical study and multi-optimization of heat transfer performance in counter flow minichannel heat sink with slots on ribs using NSGA-Ⅱ

High temperature and nonuniformity temperature cause thermal failure and thermal deformation for high-heat flux electronic devices. To address this issue, a counter flow minichannel heat sink with slots on ribs is designed. A 3D conjugated heat transfer model based on computational fluid dynamics (CFD) was developed to investigate effect of slots number (i) and growth rate of slot width (j) on average Nusselt number (Nu), local temperature distribution and temperature standard deviation (σ). The results show that design parameters i and j significantly influence heat transfer capability and temperature uniformity. However, there is no clear pattern between design parameters (i and j) and heat transfer performance (Nu and σ) to guide design. Furthermore, a non-dominated sequencing genetic algorithm (NSGA-Ⅱ) multi-objective optimization coupled Artificial Neural Network (ANN) is conducted with the consideration of maximum Nusselt number Nu and minimum temperature standard deviation (σ) as objectives. Technique for Order Preference by Similarity to Ideal Solution (TOPSIS) method is employed to determine the best solution from the Pareto front, i.e., multi-objective optimization solutions set. The optimized solution obtains 2.1 times increase in average Nusselt number and 0.36 times decrease in temperature standard deviation compared with conventional counter flow minichannel heat sink. This work serves as a guideline for designing minichannel heat sinks for thermal management of electronic components.

Influence of hot corrosion on thermal fatigue behavior of Ni-based single crystal superalloy: Invisible and accelerated crack

As an important failure model for single crystal materials in service, with the increasing complexity of working environments, the thermal corrosion fatigue failure needs to be studied urgently. In this study, the thermal corrosion fatigue crack initiation and propagation behaviors of an Ni-based single crystal superalloy in both air and hot corrosion environments at 25–900 °C were studied by using a designed precise thermal fatigue test device. The microstructure characteristics and crack composition were analyzed by SEM, TEM and EDS, and the internal stress and recrystallization during thermal fatigue were characterized by EBSD. Moreover, the detailed and comprehensive crack morphology was characterized with different surface treatments. The results showed that the crack morphology was invisible in the hot corrosion environment, which is worthy of being highlighted. The initiation and propagation of thermal fatigue cracks were also accelerated in the hot corrosion environment, which contributed to the sufficient thermal stress, the accelerated material degradation of the inner/outer layers in the crack region, and the rapid forward diffusion of O2 in the inner crack layer. Finally, the influence mechanism of hot corrosion on the thermal fatigue behavior of the Ni-based single crystal superalloy is proposed.

Finite Element Analysis on Thermoelastic Instability of Multidisc Clutches Involving Deformation Modes of Multilayer Material Friction Disc

Abstract A two-dimensional finite element model was developed to investigate thermoelastic instability in multilayered friction discs with finite thickness, considering the deformation modes of the steel core. The model was used to simulate four unstable modes that can occur during the engagement process, and the Fourier reduction was applied to calculate the change in critical speed under these modes. Additionally, the influence of thermal physical parameters, including the elastic modulus, thermal expansion coefficient, Poisson’s ratio, and thermal conductivity of the friction pair, on thermoelastic instability was examined. The findings indicate that the critical speed of the friction pair is lower under the symmetric (friction disc)–antisymmetric (steel disc) mode compared to the other three modes. Consequently, the symmetric–antisymmetric mode is the first to be excited and serves as the dominant mode during thermoelastic instability. Moreover, there exists a specific wave number at which the system exhibits the lowest critical speed and poorest stability. Enhancing the thermal conductivity of the friction disc and steel disc, as well as reducing the thermal expansion coefficient of the steel disc and the elastic modulus and Poisson’s ratio of both discs, can improve the thermoelastic stability of the friction pair. Notably, the thermal expansion coefficient of the friction disc has minimal impact on thermoelastic instability. These results provide a theoretical foundation for exploring the relationship between the thermal failure of friction pairs and rotational speed, as well as optimizing overall performance design.

Microstructure evolution and tribo-oxidation induced by friction and wear of cast iron brake discs

Braking discs play an important role for the safety of vehicles whereas severe frictional contacts in repeated braking operations result in thermal and tribological failures. This paper reports comprehensive surface and subsurface analyses of a used grey cast iron braking disc to investigate its failure mechanisms as well as related microstructure evolution. Thermal cracking, spalling wear and tribo-oxidation have been found to contribute to the wear failure. The flake-type graphite of the grey cast iron triggered propagation and internal oxidation of the metallic matrix. In a depth of 3 mm beneath the rubbing surface, extensive microstructure evolution occurred by severe plastic deformation of the ferritic matrix, nodularisation and partial dissolution of the lamellar carbides, and internal oxidation. The microstructure evolution resulted in decreased surface hardness to HV0.3 247 as compared to HV0.3 284 of the bulk cast iron.

Thermal failure optimization of foil thrust bearings

The problems of wear and failure seriously endangers the operational quality and life of foil bearings. This work establishes a thermo-elastic-hydrodynamic foil thrust bearing model to investigate thermal failure performance and compare it with an elastic-hydrodynamic model. The study analysis the thermo-elastic mechanism and thermal seizure behavior of three different bump foil models. Alterations in foil parameters and structure to optimize the risk of bearing thermal failure. Findings indicate that the bump foil design has a significant impact on the risk of thermal failure, and the bump foil's fixed position determines the characteristic of the thermal seizure risk. The integrated bump foil design exhibits superior load performance and risk resistance compared to the separated type. The inner radius of the bump foil is greater than 13.5 mm and the thickness is less than 125 μm, which helps reduce the risk of thermal failure. Consequently, the proposed optimization is beneficial for the design and operation of foil bearings resist thermal failure.

A novel microchannel heat sink with staggered inlet and outlet to improve base surface temperature uniformity

Non-uniform temperature distribution can lead to performance degradation and thermal failure of electronic devices. So as to improve the base surface temperature uniformity, we proposed a novel microchannel heat sink with staggered inlet and outlet. This arrangement divides a complete flow channel into three regions, and the flow direction in each channel can be changed to form different flow modes. The effects of flow mode, the inlet and outlet spacing, Reynolds number and channel length on the temperature uniform performance of base heating surface are investigated numerically. It is found that the microchannel heat sink with staggered inlet and outlet has more uniform fluid distribution and can ensure the same highest temperature in each region to improve the base surface temperature uniformity. The optimal spacing between middle inlet and outlet decreases as Reynolds number decreases for optimal flow mode, and the improving effect of temperature uniformity becomes worse with increasing channel length. Within the calculation parameter range, compared with the straight microchannel unit, the base temperature difference and the pumping power of staggered microchannel unit with countercurrent flow in each region are reduced by 77.6% to 81.3% and 56.1% to 68.8%, respectively.