Transient Thermal Stress Research Articles

Mechanism of Crack Initiation and Propagation of Re-Entrant Auxetic Honeycombs Under Thermal Shock

Abstract Thermal shock multiple cracking behaviors of re-entrant auxetic honeycombs with a negative Poisson’s ratio are investigated, and the crack initiation and propagation behavior are discussed. An effective macro continuum model is developed to detect the effects of cracking density and microstructures of auxetic honeycombs on the thermal stress and intensity. The microscale tensile stresses in the struts ahead of the crack as functions of the corresponding thermal stress intensity factor (SIF) at the macroscale are evaluated by employing a macro–micro model. Then, a lower-bound method is proposed to assess the critical thermal load of auxetic honeycombs by combining the macro-micro model and the macro continuum model. A significant increase in both transient thermal stress and intensity as the growing cell-wall angle is demonstrated. Results for the maximum thermal SIF as well as the maximum tensile stress in the middle of cracks are calculated as functions of crack density and length. With the identical SIF, the microscale tensile stresses ahead of the crack in honeycombs with smaller cell-wall angles are greater than that in mediums with larger angles due to the more significant crack tip opening displacement. Critical thermal load prediction reveals that the honeycombs with smaller cell-wall angles generally possess more excellent thermal shock resistance. Also, the varying failure modes of different auxetic honeycomb strips under specific thermal load are predicted. The corresponding mechanisms of crack initiation and propagation are revealed.

Immunogenicity and Protective Efficacy of a Highly Thermotolerant, Trimeric SARS-CoV-2 Receptor Binding Domain Derivative.

The receptor binding domain (RBD) of SARS-CoV-2 is the primary target of neutralizing antibodies. We designed a trimeric, highly thermotolerant glycan engineered RBD by fusion to a heterologous, poorly immunogenic disulfide linked trimerization domain derived from cartilage matrix protein. The protein expressed at a yield of ∼80–100 mg/L in transiently transfected Expi293 cells, as well as CHO and HEK293 stable cell lines and formed homogeneous disulfide-linked trimers. When lyophilized, these possessed remarkable functional stability to transient thermal stress of up to 100 °C and were stable to long-term storage of over 4 weeks at 37 °C unlike an alternative RBD-trimer with a different trimerization domain. Two intramuscular immunizations with a human-compatible SWE adjuvanted formulation elicited antibodies with pseudoviral neutralizing titers in guinea pigs and mice that were 25–250 fold higher than corresponding values in human convalescent sera. Against the beta (B.1.351) variant of concern (VOC), pseudoviral neutralization titers for RBD trimer were ∼3-fold lower than against wildtype B.1 virus. RBD was also displayed on a designed ferritin-like Msdps2 nanoparticle. This showed decreased yield and immunogenicity relative to trimeric RBD. Replicative virus neutralization assays using mouse sera demonstrated that antibodies induced by the trimers neutralized all four VOC to date, namely B.1.1.7, B.1.351, P.1, and B.1.617.2 without significant differences. Trimeric RBD immunized hamsters were protected from viral challenge. The excellent immunogenicity, thermotolerance, and high yield of these immunogens suggest that they are a promising modality to combat COVID-19, including all SARS-CoV-2 VOC to date.

Gut Microbiota of Drosophila subobscura Contributes to Its Heat Tolerance and Is Sensitive to Transient Thermal Stress.

The gut microbiota can contribute to host physiology leading to an increase of resistance to abiotic stress conditions. For instance, temperature has profound effects on ectotherms, and the role of the gut microbiota on the thermal tolerance of ectotherms is a matter of recent research. However, most of these studies have been focused on single static temperatures instead of evaluating thermal tolerance in a wide range of stressful temperatures. Additionally, there is evidence supporting that the gut microbiota is sensitive to environmental temperature, which induces changes in its composition and diversity. These studies have evaluated the effects of thermal acclimation (>2 weeks) on the gut microbiota, but we know little about the impact of transient thermal stress on the composition and diversity of the gut microbiota. Thus, we investigated the role of the gut microbiota on the heat tolerance of Drosophila subobscura by measuring the heat tolerance of conventional and axenic flies exposed to different heat stressful temperatures (35, 36, 37, and 38°C) and estimating the heat tolerance landscape for both microbiota treatments. Conventional flies exposed to mild heat conditions exhibited higher thermal tolerance than axenic flies, whereas at higher stressful temperatures there were no differences between axenic and conventional flies. We also assessed the impact of transient heat stress on the taxonomical abundance, diversity, and community structure of the gut microbiota, comparing non-stressed flies (exposed to 21°C) and heat-stressed flies (exposed to 34°C) from both sexes. Bacterial diversity indices, bacterial abundances, and community structure changed between non-stressed and heat-stressed flies, and this response was sex-dependent. In general, our findings provide evidence that the gut microbiota influences heat tolerance and that heat stress modifies the gut microbiota at the taxonomical and structural levels. These results demonstrate that the gut microbiota contributes to heat tolerance and is also highly sensitive to transient heat stress, which could have important consequences on host fitness, population risk extinction, and the vulnerability of ectotherms to current and future climatic conditions.

Transient Thermal and Mechanical Stress Analysis of 2D-Functionally Graded Finite Cylinder: A Truly Meshless Formulation

Transient Thermal and Mechanical Stress Analysis of 2D-Functionally Graded Finite Cylinder: A Truly Meshless Formulation

Evaluation of the Performance of Published Point Defect Parameter Sets in Cone and Body Phase of a 300 mm Czochralski Silicon Crystal

Prediction and adjustment of point defect (vacancies and self-interstitials) distribution in silicon crystals is of utmost importance for microelectronic applications. The simulation of growth processes is widely applied for process development and quite a few different sets of point defect parameters have been proposed. In this paper the transient temperature, thermal stress and point defect distributions are simulated for 300 mm Czochralski growth of the whole crystal including cone and cylindrical growth phases. Simulations with 12 different published point defect parameter sets are compared to the experimentally measured interstitial–vacancy boundary. The results are evaluated for standard and adjusted parameter sets and generally the best agreement in the whole crystal is found for models considering the effect of thermal stress on the equilibrium point defect concentration.

Fast Calculation of Transient Thermal Stress in Surge Lines with Thermal Stratification Region

Nuclear power plants applying for license renewal are required to undertake a fatigue assessment of various components, which demands the fast calculation of transient thermal stress of the fatigue-sensitive components such as surge lines. In this study, the strategy of Green’s function database construction for the thermal stratification region was investigated, and the thermal stress calculation was shown to be more accurate by dividing the flow cases and thermal zones. Furthermore, a method to determine the fluid temperature for the thermal zones of the thermal stratification region was studied. In addition to the temperature of the hot leg fluid and the outlet fluid from the pressurizer, seven thermocouples installed on the outside wall in the thermal stratification region were used to determine the fluid temperature of thermal zones with stratification, and the calculation result of the fluid temperature was verified with the temperature Green’s functions.

Transient thermal stress analysis for a short thick hollow FGM cylinder with nonlinear temperature-dependent material properties

In this study, nonlinear transient thermo-elastic analysis for a thick hollow 1D-FGM (functionally graded material) axisymmetric cylinder with finite length is investigated using higher-order graded finite element method. The material property gradations are along the radial direction and the power-law volume fraction and simple rule of mixture scheme are utilized to perform the effective material properties. As the cylinder exposed to high temperature, the temperature dependency of material properties is considered. So it led to nonlinear thermal conduction equation and in spite of the material distribution along one-direction by changing the temperature, the material properties are varied along two-direction with time. The nonlinear heat equation leads to 2D-temperature distribution for an axisymmetric cylinder. Also the thermal stress field would be different from an infinite cylinder which has been studied before. The temperatures, displacements and stresses for different values of volume fraction exponents along radial direction are investigated. It is revealed that the stresses and temperature in FGM cylinder are lower than the ceramic rich one. In other words, functionally graded cylinder wall gives better results in both stress and temperature cases than non-FGM cylinder.

Numerical investigation of thermo-mechanical properties for disc brake using light commercial vehicle

A brake is a device using which frictional resistance is applied for stopping a moving vehicle. In disc brakes, the component on which the pads are squeezed when the brake pedal is applied. Disc brakes are subjected to both mechanical and thermal stresses. The cyclic thermal stress is more significant than mechanical stress. In this study, three-disc brakes with different profiles are selected to investigate the thermo-mechanical behavior analytically and numerically. This analysis develops a three-dimensional (3D) thermo-structural coupling model, implements transient thermal Analysis and transient structural Analysis of disc brake profiles with a frictional heat. The thermo-structural problem is solved by the finite element method to get the transient temperature and thermal stress fields of the disc brake under emergency braking. Comparison between the three profiles has been made using different parameters, including the maximum temperature on the surface, equivalent thermal stress (Von-Mises), and thermal deformation. The result has shown that the having grooved profile on its surface exhibited 34Mpa of equivalent stress, whereas the solid type and the drilled type have shown 80Mpa and 57Mpa. It also shows that the grooved type brake is efficient by far more magnitude than the other two profiles. In general, the thermal stress developed and thermal deformation on the would significantly decrease when it has a profile that allows for better heat dissipation to the surrounding.

Dimensional analysis and inertial effects in transient thermal stress analysis

Thermoelasticity or thermally-induced stress is an important scientific problem across many industries. These problems become even more challenging as devices become smaller and smaller, and are required to withstand large temperature gradients in small volumes. Non-dimensionalization or dimensional analysis for the transient form of Navier’s equation of elasticity coupled with the constitutive relationship that relates stress to strain and temperature reveals a dimensionless parameter for the characteristic ratio of inertial forces to thermoelastic forces. This ratio, referred to as the thermal inertial mass effect (T.I.M.E.) ratio, quantifies the relative importance of these two forces in a medium. As this ratio increases, the relative importance of inertial forces increases, and the medium’s resistance to movement increases. Transient numerical modelling for a simplified model problem demonstrates the effects of varying this characteristic ratio on the thermoelastic stress and deformation in a medium.

Transcriptomic and life history responses of the mayfly Neocloeon triangulifer to chronic diel thermal challenge

To better understand the effects of transient thermal stress in an aquatic insect, we first identified static temperatures associated with fitness deficits, and then reared larvae from egg hatch to adulthood under diurnally variable regimens including daily forays into deleterious temperatures. We sampled mature larvae at the coolest and warmest portions of their respective regimens for RNA-seq analysis. Few transcripts (28) were differentially expressed when larvae oscillated between favorable temperatures, while 614 transcripts were differentially expressed when experiencing daily transient thermal stress. Transcripts associated with N-glycan processing were downregulated while those associated with lipid catabolism and chitin turnover were significantly upregulated in heat stressed larvae. An across-regimen comparison of differentially expressed transcripts among organisms sampled at comparable temperatures demonstrated that the effects of daily thermal stress persisted even when larvae were sampled at a more optimal temperature (806 differentially expressed transcripts). The chronically stressed population had reduced expression of transcripts related to ATP synthesis, mitochondrial electron chain functions, gluconeogenesis and glycolytic processes while transcripts associated with cell adhesion, synaptic vesicle transport, regulation of membrane potential and lipid biosynthesis increased. Comparisons of constant vs. variable temperatures revealed that the negative consequences of time spent at stressful temperatures were not offset by more time spent at optimal temperatures.

Current Scientific Evidence of Clinical Performance of Veneered Zirconia Crowns and Fixed Dental Prostheses

This paper aims to summarize recent scientific evidence regarding the clinical performance of veneered zirconia prostheses. In addition, the residual thermal stress studies were critically analyzed and associated with the veneering ceramic chipping issue. Despite extensive materials and technique developments, the chipping of the veneering layer in zirconia-based crowns is still not fully solved. Randomized clinical trials (RCTs) published within the last 5 years showed that the extension of chipping fracture is more significant for zirconia-based compared to the metal-based prostheses. Residual and transient thermal stresses might be associated with the chipping fracture in veneered zirconia crowns. In vitro and in silico studies should evaluate anatomically correct crown specimens to obtain relevant evidence regarding thermal treatments and fracture resistance of porcelain-veneered zirconia. Clinical studies should provide a more in-depth investigation of the chipping failure mechanisms to help further material development and technical protocols to solve this clinical complication.

Characterization of Absorption Losses and Transient Thermo-Optic Effects in a High-Power Laser System

(1) Background: The modeling, characterization, and mitigation of transient lasers, thermal stress, and thermo-optic effects (TOEs) occurring inside high energy lasers have become hot research topics in laser physics over the past few decades. The physical sources of TOEs are the un-avoidable residual absorption and scattering in the volume and on the surface of passive and active laser elements. Therefore, it is necessary to characterize and mitigate these effects in real laser systems under high-power operations. (2) Methods: The laboratory setup comprised a 10-kW continuous wave laser source with a changeable beam diameter, and dynamic registration of the transient temperature profiles was applied using an infrared camera. Modeling using COMSOL Multiphysics enabled matching of the surface and volume absorption coefficients to the experimental data of the temperature profiles. The beam quality was estimated from the known optical path differences (OPDs) occurring within the examined sample. (3) Results: The absorption loss coefficients of dielectric coatings were determined for the evaluation of several coating technologies. Additionally, OPDs for typical transmissive and reflective elements were determined. (4) Conclusions: The idea of dynamic self-compensation of transient TOEs using a tailored design of the considered transmissive and reflecting elements is proposed.

Transient temperature and stress fields on bonding small glass pieces to solder glass by laser welding: Numerical modelling and experimental validation

Laser welding of transparent materials, including glasses, established in the recent years. This study reports the results of the theoretical with experimental validation to transient temperature and stress fields on bonding small glass pieces to solder glass by laser welding. A 3D finite element model of bonding small glass pieces to solder glass by laser welding is developed and validated with experimental micro-structural analysis. An influence of laser average power and welding speed on the temperature field and stress field during welding is studied. A range of average laser power and welding speed, with a standard of the appropriate temperatures and ultimate stresses of sealing during laser welding, are determined. The results show that in the range of laser average power of 45~75 W and welding speed of 1–2 mm/s, the heat source central temperature increases with an increase of laser average power or the decrease of welding speed, and the corresponding maximum temperature exceeds 650 °C. The maximum transient thermal stress is calculated to be 152 MPa, it appeared at the boundary of the upper glass interface. The boundary stress at the front end of the heat source and the transient thermal stress at the inflection point are larger than the transient thermal stress at the middle point. The experimental and theoretical results show that the melting layer has excellent morphology and mechanical properties at the average laser power of 65 W and welding speed of 90 mm/min, which is applicable for the bonding of small glass pieces to solder glass by laser welding.

Calibrated Low-Order Transient Thermal and Flow Models for Robust Test Facility Design

This paper describes an upgrade to high temperature operation of the Engine Component AeroThermal (ECAT) facility, an established engine-parts facility at the University of Oxford. The facility is used for high-TRL research and development, new technology demonstration, and for component validation (typically large civil-engine HP NGVs). In current operation the facility allows Reynolds number, Mach number, and coolant-to-mainstream pressure ratio to be matched to engine conditions. Rich-burn or lean-burn temperature, swirl and turbulence profiles can also be simulated. The upgrade will increase the maximum inlet temperature to 600 K, allowing coolant-to-mainstream temperature ratio to be matched to engine conditions. This will allow direct validation of temperature ratio scaling methods in addition to providing a test bed in which all important non-dimensional parameters for aero-thermal behaviour are exactly matched. To accurately predict the operating conditions of the upgraded facility, a low order transient thermal model was developed in which the air delivery system and working section are modelled as a series of distributed thermal masses. Nusselt number correlations were used to calculate convective heat transfer to and from the fluid in the pipes and working section. The correlation was tuned and validated with experimental results taken from tests conducted in the existing facility. This modelling exercise informed a number of high-level facility design decisions, and provides an accurate estimate of the running conditions of the upgraded facility. We present detailed results from the low-order modelling, and discuss the key design decisions. We also present a discussion of challenges in the mechanical design of the working section, which is complicated by transient thermal stress induced in the working section components during facility start-up. The high-temperature core is unusually high-TRL for a research organisation, and we hope both the development and methodology will be of interest to engine designers and the research community.

Role of thermal gradients on the depolarization and conductivity in quenched Na1/2Bi1/2TiO3-BaTiO3

Quenching has been demonstrated to increase the thermal stability of the piezoelectric properties of relaxor (1−x)Na1/2Bi1/2TiO3-xBaTiO3 (NBTxBT) by 40 °C. This work establishes a correlation between the quenching temperature and salient electrical (conductivity, piezoelectric and dielectric) properties of two NBTxBT variants. The impact of quenching on the mechanical properties is quantified in terms of changes in Young's modulus. The perspective for application is interrogated using a variation in the sample thickness and separating the sample interior from the sample surface. An in situ measurement of surface temperature during the quenching treatment is applied to validate the simulation for thickness-dependent thermal transport in the material and ensuing transient thermal stresses. The calculated stress intensity factor is then compared with the fracture toughness of the material. This study asserts that air quenching can be conducted without mechanical degradation. Thus, it can be an important alternative to existing industrial strategies to enhance the thermal stability of the piezoelectric properties of relaxor NBTxBT.

Transient thermal stress analysis of functionally graded annular fin with free base

The present study aims to provide a deeper understanding for the transient thermal stress distributions of an annular fin made of FGM. The material properties of annular fin are assumed to be graded along the fin radius as a power-law function while the Poisson’s ratio is taken to be constant for simplicity. The energy balance equation is solved on Laplace domain by using exponential like solution introduced by Keller and Keller and Gauss quadrature method. The transformation to time domain achieved by using Durbin fast Fourier transformation method. The temperature distribution and thermal stresses are presented in graphical form for FG annular fin that is pure ceramic in the base and pure metal on the tip.

A stress function based model for transient thermal stresses of composite laminates in various time-variant thermal environments

We present a study of transient thermal stresses of composite laminate in this work by means of stress function based approach considering various time-variant thermal environments. Two-dimensional temperature distribution is considered for both linear and quadratic temperature distributions. For each type of distribution, we consider three different cases to examine the effect off thermal transfer point on the distribution of thermal stresses. The proposed methodology uses the principle of complementary virtual work to develop the governing equations and consider the thermomechanical coupling in its constitutive equation. The Lekhnitskii stress functions are adopted as stress fields and the mode shape functions of clamped beam are adopted as stress trial functions. By means of the Rayleigh–Ritz method, we obtain a standard eigenvalue problem and further solve the eigen problem to obtain the solutions. We find that different temperature distributions affect the inhomogeneous equations, but they don't affect the homogeneous equations in the present model. The results will demonstrate the distributions of transient thermal stresses in angle-ply and cross-ply laminates under linear and quadratic temperature distributions. The present methodology is computationally efficient and accurate in calculating the transient thermal stresses, and it can be used in thermal stress analysis of laminated structures.

Analysis of residual stress in welding parts of cryogenic materials for LNG storage tank

Research in LNG fueled ships are actively underway in the world. Accordingly, various materials were widely used as materials for storage tanks for ultra-low temperatures, and high manganese steel for ultra-low temperature was recently developed. In this paper, the transient thermal and residual stress analysis of the welding of 9% nickel steel and high manganese steel are presented. 9% nickel steel tended to have higher transverse direction stress and longitudinal direction stress than high manganese steel.

Fracture behavior of tungsten-based composites exposed to steady-state/transient hydrogen plasma

The fracture behavior of plasma-facing components (PFCs) under extreme plasma-material interaction conditions is of great concern to ITER and future fusion reactors. This was explored in the current study by exposing pure tungsten (W), W-1%TiC and W-2%Y2O3 composites to a combined steady-state/transient hydrogen plasma up to a base surface temperature of ~2220 K, and up to 5000 transient pulses for 1000 s using the linear plasma generator Magnum-PSI. The applied heat loads were characterized by combining sheath physics, thermographic information and finite element analyses, with which the thermal stress was evaluated. Combining microstructural investigation and thermo-mechanical numerical analyses, a physical picture of fracture is developed. The transient heat loads drive surface crack initiation, whose depth can be estimated by a simple analytical model for pure tungsten, while the cooling period following the steady-state heat load induces tensile stresses, opening existing surface cracks deeper. The fracture process is mediated by the microstructure whereby the ceramic particles stabilize the microstructure but promote surface crack initiation due to suppressed plasticity at the grain boundaries and the particle-matrix interfaces. The surface cracks relieve the subsequent cycles of transient thermal stress but intensify the steady-state thermal stress, therefore, promoting deep crack propagation. These results help to understand failure mechanisms in PFCs under extreme operation conditions which are valuable for developing advanced PFCs.

A direct random sampling method for the Fourier amplitude sensitivity test of nonuniformly distributed uncertainty inputs and its application in C/C nozzles

In this paper, the applicability of the conventional random balanced design method for the Fourier amplitude sensitivity test (RBD-FAST) is extended to uncertainty parameters with nonuniform distributions. The latter is a more general premise in real-world applications. The Halton low discrepancy sequence is proposed for direct random sampling (DRS) in RBD-FAST. The correctness of the method is verified with two benchmark problems, i.e., the G function and the flood model. DRS can alleviate the cumbersome mathematical derivation of sampling functions in the conventional FAST, and a higher accuracy level is observed with the DRS-RBD-FAST. The proposed method is employed in the global sensitivity analysis (GSA) of a C/C nozzle where 24 input parameters with normal distributions are considered. The key uncertainties contributing to the transient thermal stress of the C/C nozzle are identified, including the coefficient of thermal expansion, the wall thickness of the nozzle, the coefficient of thermal conductivity, the Poisson's ratios, and Young's moduli. The Poisson's ratios are identified as more sensitive parameters than the Young's moduli, which would not be identified without the higher accuracy level of the proposed DRS method. The proposed method can be used for widespread applications.