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Energy storage capacitors for advanced pulse power systems and high-power electric devices is a kind of important electronic components, the demand continues to grow, specifications are constantly being upgraded, and performance boundaries are continuously being pushed. Multilayer ceramic capacitors (MLCCs) for energy storage applications have received increasing attention due to the advantages of ultralow equivalent series inductance, equivalent series resistance, good frequency characteristics, strong voltage overload ability, and stable operability at high temperatures. However, the relatively low energy storage density significantly limits its broader applications. Here, 0.4Ba 0.55 Sr 0.45 TiO 3 -0.4Bi 0.5 Na 0.5 TiO 3 -0.2SrZrO 3 (0.4BST-0.4BNT-0.2SZ) relaxor ferroelectric MLCCs are prepared at different heating rates. Excellent recoverable energy storage density of 10.3 J cm−3 and high energy efficiency of 93 % are achieved in fast-fired MLCCs under the electric field of 106.3 V μm−1. The impedance spectroscopy and thermally stimulated depolarization current technologies are employed to investigate the conductance mechanism of MLCCs, and the results can explain the effect of heating rate on the performance of MLCCs. In addition, the charge-discharge performances of fast-fired MLCCs are also thoroughly investigated, exhibiting great thermal and fatigue stability. [ABSTRACT FROM AUTHOR]

Aging of binders is a complex phenomenon which reduces the longevity of flexible pavements. Aging involves change in physical, chemical, and morphological properties of binder which makes the binder brittle and highly susceptible to fatigue and thermal cracking. Antiaging additives enhance the service life of flexible pavements by reducing the impact of aging on the performance of binders. An iterative approach is essential to identify the optimal dosage of antiaging additive necessary to counteract the aging effects on binder. The present study aims to evaluate the mixing conditions for uniform dispersion of carbon black and hydrated lime within the binder matrix and thereby evaluate the impact of incorporating these antiaging additives on the conventional properties of binder. For this purpose, varying proportions of carbon black and hydrated lime are added to VG 30 binder and is subjected to softening point, ductility, and penetration tests. The optimal dosage of carbon black and hydrated lime is found to be 6 and 12% respectively based on their significant effects on the conventional properties of the binder. An optimal mixing duration of 60 and 75 min ensures uniform dispersion of carbon black and hydrated lime within the binder matrix at a mixing temperature of 120 °C and a speed of 1000 rpm thereby producing a homogenous binder mastic. Incorporation of antiaging additives up to the optimal dosage enhances the softening point whereas decreases the penetration and ductility of binder. The increase in softening point of binder with incorporation of carbon black and hydrated lime signifies enhanced resistance to rutting and permanent deformation of binder, whereas the reduction in ductility and penetration of binder with incorporation of carbon black and hydrated lime signifies the reduced susceptibility of binder to environmental factors such as temperature fluctuations, UV radiation, and oxidation. The surface texture of the additive influences the ability of binder adsorption, which subsequently affects the rheological properties of binder mastics. Significant improvement in conventional properties of binder with incorporation of carbon black and hydrated lime paves a viable and cost-effective solution for engineering application as it has a subsequent effect on the rheological properties of binder. [ABSTRACT FROM AUTHOR]

Aging of asphalt binder is one of the major causes of pavement distresses such as fatigue and thermal cracking. Many laboratory aging methods, namely rotational thin film oven (RTFO) with pressure aging vessel (PAV), loose mix aging and compacted mix aging, are widely practiced to test the durability of polymer-modified binder (PMB). In this investigation, binder aging (RTFO + PAV) with three PAV durations (i.e., normal 20 h (1C-PAV), extended 40 h (2C-PAV) and 60 h (3C-PAV)), extracted binder from long-term-aged (LTA) loose mix (LMAB; 85 °C, 8 days) and LTA compacted mix (CMAB; 85 °C, 5 days) were studied. Chemical analysis of LTA binders was conducted using Fourier transform infrared spectroscopy (FTIR) test, and rheological response was evaluated using dynamic viscosity, high-temperature performance grade, Superpave rutting factor and multiple stress creep and recovery (MSCR) tests. Fatigue performance of the aged binders was evaluated using linear amplitude sweep (LAS) test and binder yield energy test (BYET). FTIR results suggested that the stiffness of PAV-aged binders is predominantly due to the development of carbonyl compounds during aging, whereas the stiffening effect of mix aging is a combination of formation of carbonyl and sulfoxide compounds and polymer degradation. Findings of this investigation suggest that the present MSCR testing procedure is unable to detect polymer degradation in LTA PMB and BYET-elastic recovery parameter is a better tool. According to LAS and BYET results, 20 h of PAV aging may overestimate fatigue performance of SBS–PMB; therefore, aging of asphalt mix may be a more practical approach. [ABSTRACT FROM AUTHOR]

Fluorescence intensity ratio (FIR) thermometry has been regarded as new optical thermometry because of its faster response, higher sensitivity, and accuracy. However, improving the sensitivity is still a challenge. Here, Ba2LuNbO6:Er3+,Yb3+ up‐conversion specimens were synthesized, characterized, and designed for dual‐mode thermometry based on FIR. The 2H11/2/4S3/2 thermally coupled energy levels (TCELs) and 2H11/2/4F9/2 non‐TCELs (NTCELs) of Er3+ were selected as two FIR modes for optical thermometry. The energy gap of 2H11/2/4S3/2 TCELs of Er3+ in Ba2LuNbO6:Er3+,Yb3+ phosphors was confirmed as 977 cm−1. Therefore, the maximal relative sensitivity (Sr) of FIR based on TCELs is 1.53% K−1 @ 303 K. For FIR based on NTCELs, a higher maximal Sr value of 1.81% K−1 @ 303 K is obtained, which surpasses other Er3+‐doped up‐conversion specimens. In addition, the phosphors exhibit excellent thermal fatigue resistance and temperature resolution. Results suggest that Ba2LuNbO6:Er3+,Yb3+ specimens might be applied in the temperature sensing field. [ABSTRACT FROM AUTHOR]

ANSYS finite element analysis software is used to calculate the fatigue life of a certain turbine blade during the thermal shock process in this paper. The various state parameters of the turbine blades during the thermal shock process are calculated and analyzed. The changes in temperature, stress, and strain of the turbine blade at various locations during the thermal shock process are obtained. The stress and strain results obtained from various monitoring points are used to calculate the fatigue life using the local stress–strain method. A thermal shock test bench is established to conduct thermal shock fatigue tests on the blades. The full life formula is used to calculate the blade's crack propagation life. The stress and strain changes at various points near the leading edge of the blade during the thermal shock process are similar to the trend of gas temperature changes. The point of maximum stress and strain appears at the leading edge of the blade. The location of fatigue failure first appears near the leading edge of the blade, with fatigue damage traces also found at the trailing edge of the blade. Using the full life formula, the estimated crack propagation life of the blade is approximately 3500–4500 cycles. The total life is estimated to be approximately 6500–7500 cycles. The fatigue life calculation method based on transitional state parameters can significantly reduce the number of thermal shock experiments and calculate the fatigue life at each stage of the turbine blade. [ABSTRACT FROM AUTHOR]

Exhaust manifolds in diesel engines undergo continuous thermal cycle loading of varying thermal cycles with different mean, amplitude, and rate of temperature change created by application duty cycles. This makes analysis and testing of the exhaust manifold to meet the thermal mechanical fatigue life expectation of different applications challenging. In this paper, a simulation-based product development approach, which uses application duty cycles, simulation models of different capabilities, including three-dimensional Finite element simulation model, one-dimensional (1D) physis-based damage model to develop an abusive thermal cycle engine test for validating exhaust manifold, is presented. [ABSTRACT FROM AUTHOR]

The wear and degradation of tools applied in the high-pressure die casting of Al alloys induce significant financial losses. The formation of failures on the surface of mold parts caused by erosion, thermal fatigue, corrosion, and soldering negatively affects the surface quality of castings. In this study, the lifetime of inserts protected by physical-vapor-deposited coatings (TiN, TiAlN, and CrAlSiN) is examined under real manufacturing conditions while considering requirements for the castings' surface quality (maximum average roughness Ra) defined by the customer. The goal was to identify the most suitable solution for HPDC in the foundry organization. After the deposition of PVD coatings on the inserts, the hardness (HRC) values increased from two to five depending on the coating used, and also the surface roughness was higher in the case of all inserts (Ra values increased from 0.24 to 0.36 µm). The lifetime of all PVD-coated inserts was higher compared to the uncoated insert. The highest lifetime was achieved by the application of a TiN coating, when 15,000 shots were achieved until the inserts' wear negatively affected (increased) the surface roughness of castings, considering the customer requirements for the maximum Ra value. SEM analysis was used to identify examples of wear and degradation on the surface of the TiN coated insert. [ABSTRACT FROM AUTHOR]

Spacecraft observations revealed that rocks on carbonaceous asteroids, which constitute the most numerous class by composition, can develop millimeter-to-meter-scale fractures due to thermal stresses. However, signatures of this process on the second-most populous group of asteroids, the S-complex, have been poorly constrained. Here, we report observations of boulders' fractures on Dimorphos, which is the moonlet of the S-complex asteroid (65803) Didymos, the target of NASA's Double Asteroid Redirection Test (DART) planetary defense mission. We show that the size-frequency distribution and orientation of the mapped fractures are consistent with formation through thermal fatigue. The fractures' preferential orientation supports that these have originated in situ on Dimorphos boulders and not on Didymos boulders later transferred to Dimorphos. Based on our model of the fracture propagation, we propose that thermal fatigue on rocks exposed on the surface of S-type asteroids can form shallow, horizontally propagating fractures in much shorter timescales (100 kyr) than in the direction normal to the boulder surface (order of Myrs). The presence of boulder fields affected by thermal fracturing on near-Earth asteroid surfaces may contribute to an enhancement in the ejected mass and momentum from kinetic impactors when deflecting asteroids. Here, authors study boulders' fractures on S-type asteroid, Dimorphos, and show that their size-frequency distribution and orientation are consistent with formation through thermal fatigue. Such fractures seem to propagate horizontally much faster (~kyr) than normal to the boulder's surface (~Myr). [ABSTRACT FROM AUTHOR]

Fatigue crack growth (FCG) studies have been conducted on compact tension specimens of alloy 617M for as-received and aged for 1000, 5000 and 10,000 h at 710°C. Effects of thermal ageing on FCG behaviour of alloy 617M forged has been characterised at 27°C, 650°C, 710°C and 750°C. Results reveal that threshold stress intensity factor $(\Delta {K_{th}}$(ΔKth) decreases as temperature increases upto 710°C and then increases at 750°C for all the ageing conditions except for 1000 h aged. The $\Delta {K_{th}}$ΔKth value also decreases with an increase in ageing time till 5000 h, but at 10,000 h a reverse trend is observed. The influence of thermal ageing and temperature reflects major deviations for Paris constant (C) and exponent (m). Additionally, thermal ageing and temperature influences on FCG, the effects of dynamic strain ageing, Cr-rich carbides and γ’-phase precipitations have been discussed and corroborated with fractographic and microstructural changes. [ABSTRACT FROM AUTHOR]

As an important part of die steels, hot-work die steels are mainly used to manufacture molds made of solid metal or high-temperature liquid metal from heating to recrystallization temperature. In view of the requirements for mechanical properties and service life for hot-work die steel, it is conducive to improve the thermal fatigue resistance, wear resistance, and oxidation resistance of hot work die steel. In this review, the main failure modes of hot-work die steel were analyzed. Four traditional methods of strengthening and toughening die steel were summarized, including optimizing alloying elements, electroslag remelting, increasing the forging ratio, and heat treatment process enhancement. A new nano-strengthening method was introduced that aimed to refine the microstructure of hot-work abrasive steel and improve its service performance by adding nanoparticles into molten steel to achieve uniform dispersion. This review provides an overview to improve the service performance and service life of hot work die steel. [ABSTRACT FROM AUTHOR]

This paper reports the damage mechanism of 30Cr1Mo1V rotor steel during thermal fatigue at 540°C. Detailed information on macro‐failure characteristics and micro‐failure mechanisms was revealed here. The results showed that both intragranular micro‐defects and intergranular micro‐crackings were formed during the fatigue process. The formation of intragranular micro‐defects was related to the dislocation tangle inside the ferrite sub‐grains, while the formation of intergranular micro‐cracking could be related to the weakening of atomic cohesion at the matrix/cementite interface. Eventually, the transgranular crackings occurred in the 30Cr1Mo1V steel. The morphology of these crackings presented an edge‐shaped discontinuity, which may propagate perpendicularly to the loading direction and cause the material to fracture. [ABSTRACT FROM AUTHOR]

High-Density Polyethylene (HDPE) like other thermoplastics has low mechanical properties which limits its range of applications, especially under the influence of dynamic loads and high temperatures. Therefore, as one of the highly attractive approaches for improving mechanical properties, nanomaterials have been used as reinforcement materials in polymer matrix composite. The present study focuses on the role of nanomaterials on the mechanical properties and fatigue resistance of high-density polyethylene reinforced with (1, 2, and 3%) nano alumina oxide at a range of testing temperatures between 20 and 60ºC. The results manifested that the addition of nano alumina oxide improves the strength of base polyethylene and increases the fatigue resistance by (63.7%, 146.5%, and 228.4%), (69.25, 163.5 and 202.8) and (94%, 214.8% and 290.3) at (20. 40 and 60°C), respectively in cooperation with the pure high-density polyethylene. In addition, as the applied testing temperature increases, the fatigue resistance in all test specimens decreases. It was found that the highest fatigue resistance occurred at (HDPE+3%Al2O3) composite due to the good distribution of nano Al2O3 within the HDPE base which led to a better crack propagation prevention than other composites. [ABSTRACT FROM AUTHOR]

Purpose: This study aims to investigate the thermal fracture mechanism of moisture-preconditioned SAC305 ball grid array (BGA) solder joints subjected to multiple reflow and thermal cycling. Design/methodology/approach: The BGA package samples are subjected to JEDEC Level 1 accelerated moisture treatment (85 °C/85%RH/168 h) with five times reflow at 270 °C. This is followed by multiple thermal cycling from 0 °C to 100 °C for 40 min per cycle, per IPC-7351B standards. For fracture investigation, the cross-sections of the samples are examined and analysed using the dye-and-pry technique and backscattered scanning electron microscopy. The packages' microstructures are characterized using an energy-dispersive X-ray spectroscopy approach. Also, the package assembly is investigated using the Darveaux numerical simulation method. Findings: The study found that critical strain density is exhibited at the component pad/solder interface of the solder joint located at the most distant point from the axes of symmetry of the package assembly. The fracture mechanism is a crack fracture formed at the solder's exterior edges and grows across the joint's transverse section. It was established that Au content in the formed intermetallic compound greatly impacts fracture growth in the solder joint interface, with a composition above 5 Wt.% Au regarded as an unsafe level for reliability. The elongation of the crack is aided by the brittle nature of the Au-Sn interface through which the crack propagates. It is inferred that refining the solder matrix elemental compound can strengthen and improve the reliability of solder joints. Practical implications: Inspection lead time and additional manufacturing expenses spent on investigating reliability issues in BGA solder joints can be reduced using the study's findings on understanding the solder joint fracture mechanism. Originality/value: Limited studies exist on the thermal fracture mechanism of moisture-preconditioned BGA solder joints exposed to both multiple reflow and thermal cycling. This study applied both numerical and experimental techniques to examine the reliability issue. [ABSTRACT FROM AUTHOR]

This research aims to investigate the influence of pre-isothermal aging on the mechanical behaviour of 98.5Sn–1.0Ag-0.5Cu (SAC105) and 96.5Sn–3.0Ag–0.5Cu (SAC305) interconnects using non-linear finite-element simulations. To accomplish this, reliable literature sources are used to gather the material properties (both elastic and inelastic) of the aged SAC solders, which are then appropriately incorporated into the simulation process. Various aging durations, ranging from 1 to 6 months, are analysed. The results of the numerical computations demonstrate that the mechanical response of pre-aged SAC solders, subjected to thermal cycling, is significantly influenced by the ageing process. Specifically, the non-aged SAC305 configuration exhibits lower inelastic deformations and strain energies compared to the SAC105 system, indicating potentially better thermal fatigue performance. However, SAC105 solders generally exhibit greater resistance to aging, leading to lower levels of inelastic strains and strain energies, particularly for shorter aging durations. In general, it is expected that pre-aged SAC105 solders will demonstrate improved thermal fatigue performance compared to aged SAC305 interconnects. [ABSTRACT FROM AUTHOR]

The article discusses the phenomena and destructive mechanisms occurring on the surface of 1.2344 steel dies used during the hot forging of disc-type forgings. Preliminary research has shown that gas nitriding alone, used so far, is insufficient due to the occurrence of destructive mechanisms other than abrasive wear, such as thermal and thermomechanical fatigue, which cause the average durability of such tools to be approximately 5000 forgings. Analyses were also carried out to assess the load on forging tools using numerical modeling (Forge 3.0NxT), which confirmed the occurrence of large and cyclically changing thermal and mechanical loads during the forging process. Therefore, in order to increase operational durability, it was decided to use two types of hybrid layers, differing in the PVD coating used: TiCrAlN and CrN, and then subjected to gas nitriding (GN). The obtained results showed that, depending on the area of the tool and the current working conditions, the applied PVD coatings protect the surface layer of the tool against the dominant destructive mechanisms. In both cases, the strength increased to the level of 7000 forgings, the tools could continue to work, and globally, slightly better results were obtained for the GN+TiCrAlN layer. The CrN-type layer protects the tool more against thermal fatigue, while the TiCrAlN layer is more resistant to abrasive wear. In areas where the hybrid layer was worn, a decrease in hardness was observed from 1300 HV to 600–700 HV, and in places of intense material flow (front—point 2 and tool bridge—point 9) the hardness dropped to below 400 HV, which may indicate local tempering of the material. Moreover, the research has shown that each process and tool should be analyzed individually, and the areas in the tool where particular destructive mechanisms dominate should be identified, so as to further protect the forging tool by using appropriate protective coatings in these areas. [ABSTRACT FROM AUTHOR]

Ni-base superalloys operate in harsh service conditions where cyclic heating and cooling introduce deformation fields that need to be investigated in detail. We used the high-angular-resolution electron backscatter diffraction method to study the evolution of internal stress fields and dislocation density distributions in carbides, dendrites, and notch tips. The results indicate that the stress concentrations decay exponentially away from the notch, and this pattern of distribution was modified by the growth of cracks and the emission of dislocations from the crack tip. Crack initiation follows crystallographic traces and is weakly correlated with carbides and dendrites. Thermal cycles introduce local plasticity around carbides, the dendrite boundary, and cracks. The dislocations lead to higher local stored energy than the critical value that is often cited to induce recrystallization. No large-scale onset of recrystallization was detected, possibly due to the mild temperature (800 °C); however, numerous recrystallized grains were detected in carbides after 50 and 80 cycles. The results call for a detailed investigation of the microstructure-related, thermally assisted recrystallization phenomenon and may assist in the microstructure control and cooling channel design of turbine blades. [ABSTRACT FROM AUTHOR]

Fe-25Mn-9Al-8Ni-1C-xTi (x = 0, 0.1, 0.2, 0.3, 0.4 wt.%) alloy was prepared by vacuum arc melting method, and the corresponding microstructure, tensile properties and thermal fatigue properties were studied. The results show that the Fe-25Mn-9Al-8Ni-1C-xTi alloy mainly consists of austenitic phase, ferrite phase and TiC phase. Ti element addition can significantly increase both the plasticity and tensile strength of the alloy. In particular, when Ti addition is 0.2%, the product of strength and ductility reached a maximum value of 25.09 GPa %. Compared with the alloy without Ti addition, its tensile strength and elongation increase 9.3% and 959%, respectively. Furthermore, Ti element can also improve the alloy thermal fatigue performance. The thermal fatigue performance of Fe-25Mn-9Al-8Ni-1C-0.2Ti is excellent with the crack length 1985 μm, which is reduced by 53.8% compared with Fe-25Mn-9Al-8Ni-1C alloy. Further research found that the formation of thermal fatigue cracks is mainly due to the difference in thermal expansion coefficient and thermal conductivity between austenite matrix, ferrite and TiC phase. It is easy to form oxidation corrosion micropores at the interface of these phases, which eventually become the source of fatigue. Meanwhile, the crack propagation modes of the series alloys are intergranular propagation, transgranular propagation and mixed propagation. [ABSTRACT FROM AUTHOR]

Apart from low-temperature cracking, asphalt pavement may also suffer from thermal fatigue cracking. To clarify the impact of cold waves on the thermal fatigue performance of asphalt mixtures, the typical atmospheric temperature characteristics of different regions in China from 2012 to 2019 were analyzed, and the frequency of cold waves in these regions was determined. The viscoelastic parameters of an asphalt mixture are determined through an indirect tensile relaxation test. The thermal stress of the asphalt mixture is simulated and analyzed by using the finite element method. The effect of cold waves on the thermal fatigue life of the asphalt mixture was evaluated. The results show that the frequency of cold waves is different from region to region in China, and the cold waves mainly occurred from October of one year to February of the next year. Northeast China has the most frequency and the largest temperature drop amplitude, followed by North China. The maximum thermal stress increases with the decrease in temperature drop and initial temperature and is unrelated to the duration of cold waves. The thermal stress calculated based on the atmospheric thermal boundary is higher than the value using the road surface temperature. The thermal fatigue lives of asphalt mixtures in North China and Northeast China are very short, while the thermal fatigue life of the mixture in Central China is the longest. To meet the requirement of thermal fatigue damage caused by cold waves during the designed service stage, the recommended threshold for thermal stress is 0.39–0.77 MPa. [ABSTRACT FROM AUTHOR]

Thermal striping is a phenomenon characterized by oscillatory mixing of non-isothermal streams, which is commonly seen in industrial processes such as nuclear coolant piping, petrochemical plants and liquefied natural gas transportation. The oscillatory mixing of hot and cold fluid can produce thermal field fluctuations and pose a potential risk of high-cycle thermal fatigue failures. Predicting and evaluating spatiotemporal fluctuations in thermal striping often requires high resolution and massive computational power. Although there have been extensive studies using machine learning algorithms on surrogate modeling, research focused on spatiotemporal fluctuation predictions is very limited. Due to the high dimensionality, it often requires complex algorithms with a large amount of high-fidelity training data, which limits the adoption of such methods for industrial applications. In this research, a two-level machine learning framework based on turbulence coherent structures is proposed and its application to a practical problem is demonstrated. The two-level design leverages vortex identification and local bias correction techniques, efficiently reducing the number of full-order simulations required for training. In the first level, well-organized coherent structures are extracted by performing Proper Orthogonal Decomposition on local parameters and then a tree-based machine-learning model is used to down-select the reference structures for the field reconstruction. In the second level, a parameterized convolution neural network is trained to predict the bias introduced by reference structures approximation. The demonstration of the methodology shows that the method can accurately capture the fluctuation frequencies and amplitudes of the spatiotemporal fields in a highly variational setting. Based on the vortex identification method, the methodology is expected to be applicable to general phenomenon driven by large coherent structures. [ABSTRACT FROM AUTHOR]

This paper constituted an extension of two previous studies concerning the mathematical development of the grain boundary grooving in polycrystalline thin films in the cases of evaporation/condensation and diffusion taken separately. The thermal grooving processes are deeply controlled by the various mass transfer mechanisms of evaporation–condensation, surface diffusion, lattice diffusion, and grain boundary diffusion. This study proposed a new original analytical solution to the mathematical problem governing the grain groove profile in the case of simultaneous effects of evaporation–condensation and diffusion in polycrystalline thin films by resolving the corresponding fourth-order partial differential equation ∂ y ∂ t = C ∂ 2 y ∂ x 2 − B ∂ 4 y ∂ x 4 obtained from the approximation ∂ y ∂ x 2 ≪ 1 . The comparison of the new solution to that of diffusion alone proved an important effect of the coupling of evaporation and diffusion on the geometric characteristics of the groove profile. A second analytical solution based on the series development was also proposed. It was proved that changes in the boundary conditions of the grain grooving profile largely affected the different geometric characteristics of the groove profile. [ABSTRACT FROM AUTHOR]

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Copyright of Experimental Technology & Management is the property of Experimental Technology & Management Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Mechanical failure and chemical degradation of device heterointerfaces can strongly influence the long-term stability of perovskite solar cells (PSCs) under thermal cycling and damp heat conditions. We report chirality-mediated interfaces based on R-/S-methylbenzyl-ammonium between the perovskite absorber and electron-transport layer to create an elastic yet strong heterointerface with increased mechanical reliability. This interface harnesses enantiomer-controlled entropy to enhance tolerance to thermal cycling-induced fatigue and material degradation, and a heterochiral arrangement of organic cations leads to closer packing of benzene rings, which enhances chemical stability and charge transfer. The encapsulated PSCs showed retentions of 92% of power-conversion efficiency under a thermal cycling test (−40°C to 85°C; 200 cycles over 1200 hours) and 92% under a damp heat test (85% relative humidity; 85°C; 600 hours). [ABSTRACT FROM AUTHOR]

In electronic packaging products in the service process, the solder joints experience thermal fatigue due to temperature cycles, which have a significant influence on the performance of electronic products and the reliability of solder joints. In this paper, the thermal fatigue failure mechanism of solder joints in microelectronic packages, the microstructure changes of the thermal fatigue process, the influence factors on the joint fatigue life, and the simulation analysis and forecasting of thermal fatigue life are reviewed. The results show that the solder joints are heterogeneously coarsened, and this leads to fatigue cracks occurring under the elevated high-temperature phase of alternating temperature cycles. However, the thickness of the solder and the hold time in the high-temperature phase do not significantly influence the thermal fatigue. The coarsened region and the IMC layer thicken with the number of cycles, and the cracks initiate and propagate along the interface between the intermetallic compound (IMC) layer and coarsened region, eventually leading to solder joint failure. For lead-containing and lead-free solders, the lead-containing solder shows a faster fatigue crack growth rate and propagates by transgranular mode. Temperature and frequency affect the thermal fatigue life of solder joints to different degrees, and the fatigue lifetime of solder joints can be predicted through a variety of methods and simulated crack trajectories, but also through the use of a unified constitutive model and finite element analysis for prediction. [ABSTRACT FROM AUTHOR]

Restoration of the concrete and glass windows of St. Mauritius Church in accordance with the preservation requirements The development of repair systems for use on heritage‐listed concrete structures represents a major challenge in terms of materials and aesthetics. The reinforced concrete structures of the St. Mauritius Church in Wiesbaden, in particular the artistically designed concrete and glass window bands, are severely corroded and need to be repaired. Based on historical data collections and visual inspections of the degree of damage to these window bands, a restoration approach was developed to extend the service life of the glass surrounds under current conditions of use. Taking into account the material compatibility, dedicated fiber‐reinforced concretes were developed for the repair. Care was taken to ensure that the materials used were matched to each other in order to achieve an optimized packing density. In this way, a similar structural density was achieved for the repair concrete as for high‐strength or ultra‐high performance concretes. The physical and mechanical properties were adapted to the old concrete; especially compressive strength, flexural strength and adhesive tensile strength as well as the modulus of elasticity, shrinkage, thermal fatigue resistance and water absorption. It was experimentally proven that fiber reinforcement significantly improves the adhesive tensile strength of the repair concrete and increases its durability. [ABSTRACT FROM AUTHOR]

This article investigates the failure mode and mechanism of copper pillar solder joints in temperature cycling experiments, focusing on a Cu/nano Ag/Cu solder joint structure. The hot pressing bonding condition at 300 °C with insulation for 10 s is chosen for the experiments. Based on the life test results, the thermal cycling fatigue life of the nanosilver solder joint is determined to be 2050 cycles. To gain further insights, finite element software ANSYS is employed to simulate nanosilver solder joints in flip chips, revealing the stress–strain distribution within the solder joints. The simulation utilizes the Anand viscoplastic constitutive model for the solder joint, providing a reasonable representation of the stress–strain behavior under thermal cycling load. Notably, the simulation highlights that the maximum stress and strain occur in the contact area between the solder joint and the copper column. To enhance accuracy, the calculation equation is refined using relevant experience, resulting in a prediction of the thermal fatigue life of nanosilver solder joints. This prediction aligns closely with the experimental results. The research outcomes not only contribute valuable insights into the behavior of nanosilver solder but also serve as a reference for its application in electronic packaging. [ABSTRACT FROM AUTHOR]

The increase in payload capacity of trucks has heightened the demand for cost-effective yet high performance brake discs. In this work, the thermal fatigue and wear of compacted graphite iron brake discs were investigated, aiming to provide an experimental foundation for achieving a balance between their thermal and mechanical properties. Compacted graphite iron brake discs with different tensile strengths, macrohardnesses, specific heat capacities and thermal diffusion coefficients were produced by changing the proportion and strength of ferrite. The peak temperature, pressure load and friction coefficient of compacted graphite iron brake discs were analyzed through inertia friction tests. The morphology of thermal cracks and 3D profiles of the worn surfaces were also discussed. It is found that the thermal fatigue of compacted graphite iron discs is determined by their thermal properties. A compacted graphite iron with the highest specific heat capacity and thermal diffusion coefficient exhibits optimal thermal fatigue resistance. Oxidization of the matrix at low temperatures significantly weakens the function of alloy strengthening in hindering the propagation of thermal cracks. Despite the reduced hardness, increasing the ferrite proportion can mitigate wear loss resulting from low disc temperatures and the absence of abrasive wear. [ABSTRACT FROM AUTHOR]

As the prime candidate for plasma-facing materials (PFM), the response of tungsten (W) to thermal shock loads is an important research topic for future fusion devices. Under heat loads, the surface of tungsten plasma-facing materials (W-PFM) can experience thermal damage, including brittle cracking and fatigue cracks. Therefore, exploring solutions for thermal damage of W-PFM remains one of the current research focuses. We propose a novel approach to mitigate thermal radiation damage in PFM, namely, the stacked structure W-PFM. The surface thermal stress distribution of the stacked structure W-PFM under heat loads was simulated and analyzed by the finite element method. As the foil thickness decreases, both the peak thermal stresses in the normal direction (ND) and rolling direction (RD) decrease. When the thickness decreases to a certain value, the peak thermal stress in the RD decreases to about 1384 MPa and no longer decreases; while the peak thermal stress in the ND approaches 0 MPa and can be neglected. In the range of approximately 5–100 mm, the accumulated equivalent plastic strain decreases sharply as the thickness decreases; in other thickness ranges, it decreases slowly. Thermal fatigue experiments were conducted on the stacked structure W composed of W foils with different thicknesses and bulk W using an electron beam facility. The samples were applied with a power density of 30 MW/m2 for 10,000 and 20,000 pulses. The cracks on the surface of the stacked structure W extended along the ND direction, while on the surface of bulk W, besides the main crack in the ND direction, a crack network also formed. The experimental results were consistent with finite element simulations. When the pulse number was 10,000, as the thickness of the W foil decreased, the number and width of the cracks on the surface of the stacked structure W decreased. Only four small cracks were present on the surface of stacked structure W (0.05 mm). When the pulse number increased to 20,000, the plastic deformation and number of cracks on the surface of all samples increased. However, the stacked structure W (0.05 mm) only added one small crack and had the smallest surface roughness (Ra = 1.536 μm). Quantitative analysis of the fatigue cracks showed that the stacked structure W-PFM (0.05 mm) exhibited superior thermal fatigue performance. [ABSTRACT FROM AUTHOR]

Failure of pipe network components in so-called mixing zones due to high-cycle thermal fatigue (HCTF) can occur within nuclear power plants where fluids of different thermal and hydraulic properties interact. Given that the consequences of such failures are potentially deadly, a method to monitor HCTF non-invasively in real-time is expected to be of great use. This method may be realised by a technique to determine the inaccessible temperature distribution of a component since thermal gradients drive HCTF. Previous work showed that a physics-based method called the inverse thermal modelling (ITM) method can obtain the temperature distribution from external temperature and ultrasonic time of flight (TOF) measurements. This study investigated whether the long-short-term memory (LSTM) machine learning architecture could be a faster alternative to the ITM method for data inversion. On experimental data, a 25-member ensemble of LSTM networks achieved an ensemble median root mean square error (RMSE) of 1.04°C and an ensemble median mean error of 0.194°C (both relative to a resistance temperature device measurement). These values are similar to the ITM method which achieved a RMSE of 1.04°C and a mean error of 0.196°C. The single LSTM network and the ITM method achieved a computation-to-real-world time ratio of 0.008% and 14%, respectively demonstrating that both methods can invert data in real-time. Simulation studies revealed that LSTM performance is sensitive to small differences between the training and real-world parameters leading to unacceptable errors. However, these errors can be detected via an ensemble of independent networks and, corrected by simply adding a correction factor to the TOF prior to being input into the networks. The results show that LSTM has the potential to be an alternative to the ITM method; however, the authors favour ITM for temperature distribution monitoring given its interpretability. [ABSTRACT FROM AUTHOR]

This work represents a preliminary study of atmospheric plasma-sprayed (APS) Yttria-Stabilized Zirconia (YSZ)-based thermal barrier coatings (TBCs) deposited on forged and additive manufactured (AM) HAYNES®282® (H282) superalloy substrates. The effect of different feedstock morphologies and spray gun designs with radial and axial injection on APS-deposited YSZ layer characteristics such as microstructure, porosity content, roughness, etc., has been investigated. The performance of TBCs in terms of thermal cycling fatigue (TCF) lifetime and erosion behaviour were also comprehensively investigated. In view of the high surface roughness of as-built AM surfaces compared to forged substrates, two different types of NiCoCrAlY bond coats were examined: one involved high-velocity air fuel (HVAF) spraying of a finer powder, and the other involved APS deposition of a coarser feedstock. Despite the process and feedstock differences, the above two routes yielded comparable bond coat surface roughness on both types of substrates. Variation in porosity level in the APS topcoat was observed when deposited using different YSZ feedstock powders employing axial or radial injection. However, the resultant TBCs on AM-derived substrates were observed to possess similar microstructures and functional properties as TBCs deposited on reference (forged) substrates for any given YSZ deposition process and feedstock. [ABSTRACT FROM AUTHOR]

In this study, in situ investigation of the coupling damage mechanisms of SnAgCu/Cu solder joints under thermal cycling and current was carried out to compare the thermal fatigue under the same temperature range, and to analyze the influence of temperature. It was found that the current increased the temperature of the solder joint, making it obviously higher than the ambient temperature. On the other hand, there was little difference between the thermal–electrical coupling damage and thermal fatigue before a significant increase in solder temperature; the interfacial plastic deformation was only slightly more serious, and the electromigration was not significant. With an increasing number of thermal cycles, the damage, resistance, and temperature of the solder joint increased, and the plastic deformation resistance of the solder decreased, leading to further damage and temperature increase, exhibiting an accelerating damage process. After the temperature reached a certain degree, the solder softened significantly, and its deformation behavior was similar to that of high-viscosity fluids, resulting in surface unevenness with significant height differences. As the temperature of the solder joint increased, the electromigration of Cu in the solder gradually increased, and the migration rate was dominated by the solder grain orientation. With higher peak temperature of the ambient thermal cycle, the thermal cycling–electric current coupling damage rate increased substantially. [ABSTRACT FROM AUTHOR]

Thermal stress fatigue failure caused by mismatch in the coefficients of thermal expansion (CTE) between the metal layer and ceramic sheet during a high and low temperature cycle is considered as the big issue of high-power ceramic substrates. The aim of this study is to explore the thermal fatigue mechanism of nano Cu/Ti–Si 3 N 4 ceramic substrates after thermal fatigue test. Thermal fatigue test has been performed by thermal cycles experiment from −30 °C to 150 °C. After thermal cycles, the microstructure of the interface is observed by SEM and TEM. The results show after 400 thermal cycles, the nano-Cu metal layer oxidizes severely. Various oxides are found in the corrosion zone, such as CuO, CuAlO 2 and CuAl 2 O 4. Higher dislocation density and nanoscale-twins are observed in Cu or Cu 2 O, which indicate that Cu and Cu 2 O alleviates thermal stress. As the number of thermal cycles increases, CuO CuAlO 2 , CuAl 2 O 4 as a corrosion layer in the corrosion zone were formed. The corrosion layer is difficult to alleviate interfacial thermal stress, and easy to form cracks in the joint zone. [ABSTRACT FROM AUTHOR]

The emergence of new semiconductor devices puts forward higher requirements for packaging technology. Sintered silver technology has gradually developed into critical packaging technology in silicon carbide power module packaging due to its good heat dissipation performance and reliability. However, high sintering drive requirements, low sintering densification, and high thermal–mechanical stresses limit the application of sintered silver technology for large-area bonding. In this study, the high-pressure-assisted (≥10 MPa) large-area sintered-silver interconnection process between a substrate and baseplate was discussed. C-scan acoustic microscopy, warpage testing, and microanalysis were used to analyze the effects of drying methods, sintering pressure, and holding time on the sintered joints, and thermal fatigue reliability tests were conducted on large-area sintered silver joints. The results demonstrated that the quality of large-area sintered joints obtained via open-face convective drying is higher than that via close-face convective drying. Combining the performance of sintered joints and productivity, the recommended process condition is determined as follows: open-face convective drying, sintering temperature of 250 °C, sintering pressure of 15 MPa, and holding time of 5 min. Large-area sintered joints have outstanding reliability, with slight delamination of the sintered layer at the corners and no cracking after 1000 cycles of temperature cycling. [ABSTRACT FROM AUTHOR]

Second-stage gas turbine nozzles are an important part of the gas turbine due to their performance in hot temperature conditions. In this investigation, service-induced failure analysis and microstructural variations of different sides of a second-stage nozzle in a 100 MW gas turbine made of FSX-414 cobalt-based alloy were comprehensively studied to determine the conditions and mechanisms of the failure process. The primary carbides M3C2 and M7C3 types were converted to secondary carbides M23C6 type by phase transformation process and formed a continuous layer in the grain boundaries owing to high-temperature operation conditions. A network of cracks was created in the grain boundaries, leading to a fracture in the vane of the nozzle. The continuity and density of the produced carbides decreased ductility and toughness of the nozzle. The results demonstrated that hot oxidation and sulfidation occurred in the leading-edge zone. The aggregation and asymmetry of the combustion line and, consequently, the increasing temperature were the reasons for the damage. Some macrocracks were observed by visual inspection on the surface of the nozzle owing to exposure to high temperatures and placement in the path of the hot gas with high pressure. Based on the results, the continuous and coarse brittle M23C6 carbides on the grain boundaries were the major cause of the failure due to the crack growth caused by stress corrosion. These carbides provided appropriate paths for the growth of the crack through grain boundaries, leading to failure after the operational out-of-service condition of a second-stage gas turbine nozzle. Operational in over-hot conditions and an inappropriate filtration system were the main reasons for the operational-induced thermal fatigue failure process of the second-stage gas turbine nozzles. Based on the results, oxidation and microstructural variations were the main causes of the failure process of the second-stage gas turbine nozzles. [ABSTRACT FROM AUTHOR]

Purpose: This study aims to investigate the reliability issues of microvoid cracks in solder joint packages exposed to thermal cycling fatigue. Design/methodology/approach: The specimens are subjected to JEDEC preconditioning level 1 (85 °C/85%RH/168 h) with five times reflow at 270°C. This is followed by thermal cycling from 0°C to 100°C, per IPC-7351B standards. The specimens' cross-sections are inspected for crack growth and propagation under backscattered scanning electronic microscopy. The decoupled thermomechanical simulation technique is applied to investigate the thermal fatigue behavior. The impacts of crack length on the stress and fatigue behavior of the package are investigated. Findings: Cracks are initiated from the ball grid array corner of the solder joint, propagating through the transverse section of the solder ball. The crack growth increases continuously up to 0.25-mm crack length, then slows down afterward. The J-integral and stress intensity factor (SIF) values at the crack tip decrease with increased crack length. Before 0.15-mm crack length, J-integral and SIF reduce slightly with crack length and are comparatively higher, resulting in a rapid increase in crack mouth opening displacement (CMOD). Beyond 0.25-mm crack length, the values significantly decline, that there is not much possibility of crack growth, resulting in a negligible change in CMOD value. This explains the crack growth arrest obtained after 0.25-mm crack length. Practical implications: This work's contribution is expected to reduce the additional manufacturing cost and lead time incurred in investigating reliability issues in solder joints. Originality/value: The work investigates crack propagation mechanisms of microvoid cracks in solder joints exposed to moisture and thermal fatigue, which is still limited in the literature. The parametric variation of the crack length on stress and fatigue characteristics of solder joints, which has never been conducted, is also studied. [ABSTRACT FROM AUTHOR]

Based on the theory of reliability enhancement testing technology, this study used a variety of testing combinations and finite element simulations to analyze the stress–strain properties of 3D packaging storage modules and then evaluated its operating and destruction limits during temperature cycling tests (−65 °C~+150 °C) for the purpose of identifying the weak points and failure mechanisms affecting its reliability. As a result of temperature cycling ultimate stress, 3D packaging storage devices can suffer from thermal fatigue failure in the case of abrupt temperature changes. The cracks caused by the accumulation of plastic and creep strains can be considered the main factors. Crack formation is accelerated by the CTE difference between the epoxy resin and solder joints. Moreover, the finite element simulation results were essentially the same as the testing results, with a deviation occurring within 10%. [ABSTRACT FROM AUTHOR]

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SpaceX's Starship is a fully reusable spacecraft that aims to revolutionize space travel by reducing launch costs and enabling deep space missions. However, the reusability of the Starship introduces challenges, particularly in mitigating engine failure risks. The Raptor engines, which power the Starship, must withstand multiple flights and endure wear, tear, and exposure to extreme conditions. To address these risks, SpaceX employs advanced failure analysis techniques such as non-destructive testing, telemetry and data analysis, and material characterization and testing. By learning from past failures and continuously innovating, SpaceX aims to minimize the risk of engine failures and pave the way for a sustainable and cost-effective spacefaring future. The editorial calls for continued research and development, collaboration, and investment in advanced infrastructure to advance failure analysis methodologies and ensure the success of the Starship. [Extracted from the article]

An Aquila optimizer-back propagation (AO-BP) neural network was used to establish an approximate model of the relationship between the design variables and the optimization objective to improve elevator block brake capabilities and achieve a lightweight brake design. Subsequently, the constraint conditions and objective functions were determined. Moreover, the multi-objective genetic algorithm optimized the structural block brake design. Finally, the effectiveness of the optimization results was verified using simulation experiments. The results demonstrate that the maximum temperature of the optimized brake wheel during emergency braking was 222.09°C, which is 36.71°C lower than that of 258.8°C before optimization, with a change rate of 14.2%. The maximum equivalent stress after optimization was 246.89 MPa, 28.87 MPa lower than that of 275.66 MPa before optimization, with a change rate of 10.5%. In addition, the brake wheel mass was reduced from 58.85 kg to 52.40 kg, and the thermal fatigue life at the maximum equivalent stress increased from 64 times before optimization to 94 times after optimization. [ABSTRACT FROM AUTHOR]

To assess the combined effects of thermal aging and cyclic fatigue on the constitutive and failure behavior of crosslinked polymers, a novel physics-informed data-driven constitutive model is proposed. While extensive research has been conducted on the individual degradation modes, the simultaneous impact of these two aging mechanisms has not been explored in depth. Our objective is to simulate the mechanical properties degradation resulting from simultaneous exposure to these two aging processes. To accurately capture the complex interactions between the two aging processes, we developed a physics-informed machine-learning approach that uses the respective aging mechanisms to model the effects of each aging condition separately. We then couple the kinetic equations representing the damage associated with each aging condition using the conditional neural network. By doing so, our model can account for the mechanical and environmental damage synergy on the constitutive response of the polymer macromolecular network. The model is built based on the assumption of complete independence of mechanical and environmental effects, building upon our recent models of thermal-oxidative aging and hydrolytic aging. The model is validated using a wide range of experimental data based on sequential aging. The suggested model showed a satisfactory correlation with the experimental results, demonstrating its potential for predicting the long-term durability and reliability of materials subjected to thermal aging and cyclic fatigue. Overall, our approach provides a valuable tool for designing and optimizing materials that are subjected to complex aging conditions. [ABSTRACT FROM AUTHOR]

Hybrid plasma spraying combines plasma spraying of dry coarse powders and liquids (suspensions or solutions) potentially providing high deposition rates and coatings with novel microstructures and amended functionality. Such composites may be potentially interesting also for the thermal barrier coatings (TBCs). In this study, the first experimental TBCs with hybrid ceramic top-coats were deposited by hybrid water-/argon-stabilized plasma (WSP-H) technology. Coarse dry YSZ (yttria-stabilized zirconia: ZrO2-Y2O3) powder was selected to form the top-coat matrix. Suspensions of YSZ, Al2O3 (alumina), YAG (yttrium aluminum garnet: Y3Al5O12), or GZO (gadolinium zirconate: Gd2Zr2O7) were the source of the additional miniature phase. Uniform functionalized coatings with TBC-relevant thickness and microstructure were successfully deposited. Hybrid and reference coatings deposited also with WSP-H torch and with YSZ feedstocks showed comparable thermal diffusivity regardless of the spraying conditions but the addition of Al2O3 and YAG increased it by ~ 65%, whereas GZO decreased it by ~ 20%. Thermal cycling resistance of the coatings was evaluated by thermal cycling fatigue (TCF) test. Hybrid coating with the addition of YSZ miniature phase endured on average 640 TCF cycles, which was 250-300 cycles less than the reference YSZ coatings deposited without liquid feedstocks but still comparable to the currently used YSZ-based industrial TBCs. Coatings with dissimilar chemistry of additional miniature splats showed inferior mean TCF lifetimes: GZO 438 cycles, Al2O3 272 cycles, and YAG 173 cycles, opening space for further coating optimization. All hybrid coatings failed above the bond-coat/top-coat interface. Comparison of coatings before and after the thermal exposure by scanning electron microscopy (SEM) and x-ray diffraction (XRD) revealed possible changes within the coating microstructure, namely sintering (typical for top-coat consisting only of YSZ), conversion of metastable and amorphous phase (top-coats with the addition of Al2O3 and YAG) or interaction between the matrix and secondary phase (top-coat with the addition of GZO). [ABSTRACT FROM AUTHOR]

This perspective outlines the research directions of ferroelastic rare‐earth (RE) tantalates (RETaO4), which have been studied as multifunctional thermal/environmental barrier coatings (T/EBCs) with working temperatures above 1600°C. Ferroelastic RETaO4 ceramics exhibit several distinct features, including the reversible second‐order ferroelastic phase transition, high toughness, low thermal conductivity, low oxygen ion conductivity, and adjustable thermal expansion coefficients. This perspective provides a concise summary of the research progress on tantalate coatings synthesized via air plasma spraying and electron beam physical vapor deposition. The service performance of tantalate coatings is typically evaluated through thermal fatigue and shock measurements. Uncovering the failure mechanisms and understanding influencing factors are key aspects for future studies. In this regard, establishing the synthesis‐structure‐property relationship of RETaO4 coatings is essential. This brief perspective can serve as a guide for future work on RETaO4 coatings and further advancements in their applications across various fields, including aviation engines and gas turbines. [ABSTRACT FROM AUTHOR]

Infrared thermography has been under review in the last 30 years due to its versatility and potential in the detection of the thermal signature associated with intrinsic energy phenomena due to dissipative processes, specifically those relying on mechanical fatigue. Nowadays, it is a well‐established technique that can support mechanical and structural engineers to implement a damage‐tolerant design, assess the residual life, and finally characterize the fatigue behavior of materials. The aim of this work is to review all thermography‐based approaches and procedures for fatigue limit estimation by rapid tests, drawing considerations on the applicability of thermal methods in fatigue assessment of mechanical components, proposing the capabilities of different thermal indices in fatigue assessment, and discussing the pros and cons of each method as well as the open points. On one hand, this review intends to sum up what has already been done in the field; on the other hand, it provides a guideline to direct new researches toward issues that should be resolved or understood. [ABSTRACT FROM AUTHOR]

Thermomechanical processes caused by short-and long-term temperature fluctuations are a prevalent weathering mechanism on exposed rock walls. While many authors have explored the potential for thermomechanical weathering in alpine and polar regions, few have examined the effects of seasonality on weathering in temperate climates. This is pertinent as seasonal climatic conditions may influence both short-term temperature oscillations which produce incipient fractures and diurnal-to annual-scale cycles which propagate pre-existing fractures via thermal fatigue. In this study, three rock outcrops located along the Niagara Escarpment in Hamilton, Canada were monitored to examine changes in the thermal regime at the rock surface and within pre-existing fractures over a 1-year period. Temperature was sampled in 1-min intervals, providing data at a fine temporal resolution. Our unique dataset demonstrates that the rock surface and fracture experience minute-scale temperature oscillations which magnify over time. Longer-term temperature cycles during theyearare superimposed upon minute-and diurnal-scale fluctuations which likely augment weathering potential. This produces considerable thermal stress over the year which we estimate to be on the order of 18 GPa at the rock surface and 8 GPa in fractures. We also observed diurnal reversals of the temperature gradient between the rock surface and fracture which may further amplify crack propagation. Seasonality and site-specific characteristics interact to modify different components of the rockwall thermal regime. Vegetation shading has seasonal and diurnal-scale impacts on the temperature gradient between the surface and fracture, and the amplitude of daily warming and cooling cycles. Aspect has a stronger influence on minute-scale temperature oscillations. Estimates of diurnal thermal stress indicate that the thermomechanical weathering potential is seasonally variable, but highest in the spring. Our findings demonstrate that in a temperate climate, rockwall thermal regimes experience variability across the gradient of temporal scale with strong seasonal effects. [ABSTRACT FROM AUTHOR]

Conventional lubricants are widely used for die release as well as for cooling assistance on the die surface. However, lubrication is difficult at high temperatures. Oxidation and scaling occur on the work pieces that lead to poor surface finish and a possible warping of the material during cooling. The aim of this research is to develop self-lubricating CrAlAgN nanocomposite coatings for metal forming dies and evaluate their thermal fatigue resistance and wear behavior at elevated temperatures. The CrAlAgN coatings with different Ag contents have been deposited by plasma-enhanced magnetron sputtering. The structure and properties of the coatings were systematically studied to determine the optimal Ag content for achieving a combination of good adhesion, thermal fatigue resistance, and surface lubricity at elevated temperatures. The thermal fatigue resistance of the coatings was evaluated using thermal cyclic testing by cycling the coatings from room temperature to 800 °C up to 1200 cycles. The high temperature wear behavior of the coatings was evaluated using a tribometer up to 900 °C. Good thermal fatigue resistance and low coefficient of friction (COF) were observed in the CrAlAgN coatings with an Ag content in the range of 5–10 at. % at 800 °C. The CrAlAgN coating with 10 at. % Ag exhibited the lowest average COF of 0.05 at 800 °C. The COF of thick CrAlAgN coatings (8 at. % Ag) decreased from 0.5 to 0.2 from 500 to 900 °C, accompanied by an increase in the wear rate under more aggressive wear test conditions. The lubricity of the CrAlAgN coatings at high temperatures was attributed to the lubrication effects from the mixed oxides and encapsulated Ag diffused toward the surface. To further evaluate the coating performance, a hydraulic hot forging punch was coated with a thick CrAlAgN (8 at. % Ag) coating and evaluated in the industrial forging process. The preliminary in-plant trials demonstrated that the coating significantly reduced the dimensional distortion and wear for the forging punch. [ABSTRACT FROM AUTHOR]

Railroad vehicles require the use of disc brakes for safety purposes, however, the brakes are susceptible to thermal stress, which ultimately shortens their lifespan. Hence, to accurately predict the life of railway disc brakes in thermal load simulations, the availability of a model that considers spatial and temporal variations of temperature and thermal stress is essential. A non-axisymmetric moving heat source model was successfully developed to address spatial temperature variations (Deressa and Ambie in Urban Rail Transit 8(3–4):198–216, 2022. 10.1007/s40864-022-00176-9), and this study aims to extend this model to predict thermal stress and fatigue life, and assess its effectiveness. The analysis includes braking time thermal analysis, cooling time thermal analysis, and structural analysis. Spatially varying temperature is incorporated into the structural analysis to calculate thermal stress and strain. A fracture mechanics-based fatigue life estimation method is applied to critical areas of the friction surface. The model is implemented on two braking conditions (service and emergency) and two disc geometries (actual and modified). The model successfully resolves spatial heat considerations by estimating maximum stress variations of up to 46 MPa along the disc circumference. Stress differences of 3 MPa and 6 MPa are observed between the leading and trailing edges of the pad trace during late and mid-braking times, respectively. Fatigue life results identify critical positions and directions for fatigue life initiation. Additionally, these results are in accord with previous observations available in the literature. The proposed model can be easily implemented in various sliding friction applications such as drum brakes, engine pistons/cylinders, and camshafts. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Leaf spring is often used in commercial vehicles' suspension systems to ensure ride comfort and support dynamic wheel loads. This paper studies the thermal failure mechanism of sliding composite leaf springs. The thermal failure temperature and thermal failure mode were investigated by the bench test. The results show that when the temperature exceeds the glass transition temperature (Tg point 115 °C) for 30mins, cracks will appear around the bolt hole of the composite body. The damaged area expanded with the continuous increase in temperature. When the gap (between the fiber and the resin) grows to a stable stage, the failure temperature of the composite body becomes stable. The crack propagates first longitudinally first and then transverse. When the transverse crack is transformed into a sharp fracture, the spring may fail with decreased stiffness. This study can better understand the performance of composite leaf springs working at high temperatures and provide an effective reference for the study of the spring's service condition. [ABSTRACT FROM AUTHOR]

In this study, a magneto‐thermo‐structural coupling finite element method was proposed to calculate the electromagnetic field, temperature field, stress field, and strain field of an aluminum alloy piston during thermal shock process. The computed temperature results at the measurement points of T3 and T4 agree well with the measured data. The concept of tensile strain energy density was proposed as a thermal fatigue damage parameter, and the thermal fatigue life of the piston was predicted on the basis of the calculated results by magneto‐thermo‐structural coupling analysis and tensile strain energy density‐life equation; the discrepancy between the predicted life and the experimental one is 16%. The thermal fatigue failure mechanism of the piston was also clarified. High cyclic stresses occur on the edge of Si due to the difference in thermal expansion coefficient of Al and Si; micro cracks first originate on the edge of Si, then grow through combining other micro cracks, and eventually form macro cracks. Highlights: A magneto‐thermo‐structural coupling finite element method was developed.A novel thermal fatigue life prediction method was proposed.The thermal fatigue failure mechanism of the piston was clarified. [ABSTRACT FROM AUTHOR]