Thermal Stress Intensity Research Articles

Augmented human thermal discomfort in urban centers of the Arabian Peninsula

Anthropogenic climate change has amplified human thermal discomfort in urban environments. Despite the considerable risks posed to public health, there is a lack of comprehensive research, evaluating the spatiotemporal changes in human thermal discomfort and its characteristics in hot-hyper arid regions, such as the Arabian Peninsula (AP). The current study analyzes spatiotemporal changes in human thermal discomfort categories and their characteristics in AP, using the newly developed high-resolution gridded ERA5-HEAT (Human thErmAl comforT) dataset for the period 1979–2022. In addition, the study assesses the interplay between the Universal Thermal Climate Index (UTCI) and El Niño-Southern Oscillation (ENSO) indices for the study period. The results reveal a significant increase in human thermal discomfort and its characteristics, with higher spatial variability in the AP region. The major urban centers in the southwestern, central, and southeastern parts of AP have experienced significant increases in human thermal discomfort (0.4–0.8 °C), with higher frequency and intensity of thermal stress during the study period. The temporal distribution demonstrates a linear increase in UTCI indices and their frequencies and intensities, particularly from 1998 onward, signifying a transition towards a hotter climate characterized by frequent, intense, and prolonged heat stress conditions. Moreover, the UTCI and ENSO indices exhibit a dipole pattern of correlation with a positive (negative) pattern in the southwestern (eastern parts) of AP. The study’s findings suggest that policymakers and urban planners need to prioritize public health and well-being in AP’s urban areas, especially for vulnerable groups, by implementing climate change adaptation and mitigation strategies, and carefully designing future cities to mitigate the effects of heat stress.

Thermal stress information as a tourism-oriented climate product: Performance analysis for selected urban destinations in Romania and Italy

The study addresses the characteristics of a climate service targeting tourists and discusses the evaluation of its products with a particular focus on the thermal stress information. Furthermore, an assessment of the impact of input data on the accuracy and relevance of the thermal stress product is presented. The thermal stress is expressed through UTCI (Universal Thermal Climate Index) and it is computed from UERRA regional reanalysis and E-OBS gridded dataset, for summer season during 2011–2018. The analysis targets 10 cities with different characteristics located in Romania and Italy. It focuses on the impact of three temperature-related input data (instantaneous temperature at 12:00 UTC, daily maximum and daily mean temperature) on the thermal stress intensity. The results show that differences up to 4 days in the pronounced thermal stress category may appear when employing daily maximum temperature compared to the use 12:00 UTC instantaneous temperature, while the use of daily mean temperature leads to strong underestimation of thermal stress in this category. The findings are of interest in defining the technical choices of products to be incorporated in a climate service for tourism in order to assure a good user uptake.

Unveiling microbiome changes in Mediterranean octocorals during the 2022 marine heatwaves: quantifying key bacterial symbionts and potential pathogens

BackgroundClimate change has accelerated the occurrence and severity of heatwaves in the Mediterranean Sea and poses a significant threat to the octocoral species that form the foundation of marine animal forests (MAFs). As coral health intricately relies on the symbiotic relationships established between corals and microbial communities, our goal was to gain a deeper understanding of the role of bacteria in the observed tissue loss of key octocoral species following the unprecedented heatwaves in 2022.ResultsUsing amplicon sequencing and taxon-specific qPCR analyses, we unexpectedly found that the absolute abundance of the major bacterial symbionts, Spirochaetaceae (C. rubrum) and Endozoicomonas (P. clavata), remained, in most cases, unchanged between colonies with 0% and 90% tissue loss. These results suggest that the impairment of coral health was not due to the loss of the main bacterial symbionts. However, we observed a significant increase in the total abundance of bacterial opportunists, including putative pathogens such as Vibrio, which was not evident when only their relative abundance was considered. In addition, there was no clear relation between bacterial symbiont loss and the intensity of thermal stress, suggesting that factors other than temperature may have influenced the differential response of octocoral microbiomes at different sampling sites.ConclusionsOur results indicate that tissue loss in octocorals is not directly caused by the decline of the main bacterial symbionts but by the proliferation of opportunistic and pathogenic bacteria. Our findings thus underscore the significance of considering both relative and absolute quantification approaches when evaluating the impact of stressors on coral microbiome as the relative quantification does not accurately depict the actual changes in the microbiome. Consequently, this research enhances our comprehension of the intricate interplay between host organisms, their microbiomes, and environmental stressors, while offering valuable insights into the ecological implications of heatwaves on marine animal forests.5dDfKCEABnCL_GGsw4qbDQVideo

Cumulative bleaching undermines systemic resilience of the Great Barrier Reef

Climate change and ENSO have triggered five mass coral bleaching events on Australia's Great Barrier Reef (GBR), three of which occurred in the last 5 years.1-5 Here, we explore the cumulative nature of recent impacts and how they fragment the reef's connectivity. The coverage and intensity of thermal stress have increased steadily over time. Cumulative bleaching in 2016, 2017, and 2020 is predicted to have reduced systemic larval supply by 26%, 50%, and 71%, respectively. Larval disruption is patchy and can guide interventions. The majority of severely bleached reefs (75%) are predicted to have experienced an 80%-100% loss of larval supply. Yet restoration would not be cost-effective in the 2% of such reefs (∼30) that still experience high larval supply. Managing such climate change impacts will benefit from emerging theory on the facilitation of genetic adaptation,6,7 which requires the existence of regions with predictably high or low thermal stress. We find that a third of reefs constitute warm spots that have consistently experienced bleaching stress. Moreover, 13% of the GBR are potential refugia that avoid significant warming more than expected by chance, with a modest proportion (14%) within highly protected areas. Coral connectivity is likely to become increasingly disrupted given the predicted escalation of climate-driven disturbances,8 but the existence of thermal refugia, potentially capable of delivering larvae to 58% of the GBR, may provide pockets of systemic resilience in the near-term. Theories of conservation planning for climate change will need to consider a shifting portfolio of thermal environments over time.

Acclimation, duration and intensity of cold exposure determine the rate of cold stress accumulation and mortality in Drosophila suzukii

The spotted wing drosophila (SWD), Drosophila suzukii, is a major invasive fruit pest. There is strong consensus that low temperature is among the main drivers of SWD population distribution, and the invasion success of SWD is also linked to its thermal plasticity. Most studies on ectotherm cold tolerance focus on exposure to a single stressful temperature but here we investigated how cold stress intensity affected survival duration across a broad range of low temperatures (−7 to +3 °C). The analysis of Lt50 at different stressful temperatures (Thermal Death Time curve - TDT) is based on the suggestion that cold injury accumulation rate increases exponentially with the intensity of thermal stress. In accordance with the hypothesis, Lt50 of SWD decreased exponentially with temperature. Further, comparison of TDT curves from flies acclimated to 15, 19 and 23 °C, respectively, showed an almost full compensation with acclimation such that the temperature required to induce mortality over a fixed time decreased almost 1 °C per °C lowering of acclimation temperature. Importantly, this change in cold tolerance with acclimation was uniform across the range of moderate to intense cold stress exposures examined.To understand if cold stress at moderate and intense exposures affects the same physiological systems we examined how physiological markers/symptoms of chill injury developed at different intensities of the cold stress. Specifically, hsp23 expression and extracellular [K+] were measured in flies exposed to different intensities of cold stress (−6, −2 and +2 °C) and at various time points corresponding to the same progression of injury (equivalent to 1/3, 2/3 or 3/3 of Lt50). The different cold stress intensities all triggered hsp23 expression following 2 h of recovery, but patterns of expression differed. At the most intense cold stress (−6 and −2 °C) a gradual increase with time was found. In contrast, at +2 °C an initial increase was followed by a dissipating expression. A gradual perturbation of ion balance (hyperkalemia) was also found at all three cold stress intensities examined, with only slight dissimilarities between treatment temperatures. Despite some differences between the three cold intensities examined, the results generally support the hypothesis that intense and moderate cold stress induces the same physiological perturbation. This suggests that cold stress experienced during natural fluctuating conditions is additive and the results also illustrate that the rate of injury accumulation increases dramatically (exponentially) with decreasing temperature (increasing stress).

Experimental evolution on heat tolerance and thermal performance curves under contrasting thermal selection in Drosophila subobscura.

Ectotherms can respond to global warming via evolutionary change of their upper thermal limits (CTmax ). Thus, the estimation of CTmax and its evolutionary potential is crucial to determine their vulnerability to global warming. However, CTmax estimations depend on the thermal stress intensity, and it is not completely clear whether its evolutionary capacity can be affected. Here, we performed an artificial selection experiment to increase heat tolerance using fast- and slow-ramping selection protocols in Drosophila subobscura. We found that heat tolerance evolved in both selection protocols, exhibiting similar evolutionary change rates and realized heritabilities. Additionally, we estimated the thermal performance curves (TPC) to evaluate correlated responses to selection on heat tolerance. We detected that thermal optimum increased in fast-ramping selection lines, but with a cost at the thermal performance breadth. Conversely, we did not detect changes in the TPC for the slow-ramping selection lines, indicating that thermal stress intensity has important effects on the evolution of thermal physiology of ectotherms. These findings, together with previous studies in D.subobscura reporting interpopulation variability and significant heritabilities for heat tolerance, suggest that evolutionary change can contribute to insect persistence in thermally changing environments and adaptation to global warming conditions.

Thermal Stress Analysis of Tube Plate and Tube Bundle of Multi-Tube Pass Spirally Corrugated Tubes Heat Exchanger

This paper analyses the thermal stress of multi-tube heat exchanger with spirally corrugated tubes using numerical simulations. The simulations are focused on the thermal stress of the tube bundle and tube plate, which have large temperature difference. In this paper, the heat exchanger design software HTRI is creatively used to calculated the temperature boundary conditions of the heat exchanger, which is difficult to obtain. Based on the indirect coupling method of ANSYS, the thermal stress intensity and thermal deformation between the tube bundle and the tube plate of the heat exchanger are caculated. And the calculation results can provide important references for the design and optimization of the heat exchanger.

Effect of Temperature on the Mechanical Properties of Carbon Composites

The purpose of this research is to investigate and analyze the effect of temperature on the mechanical properties of carbon composites, aluminum foam, and carbon nanotube reinforced aluminum foam. For this analysis, fatigue behavior of aluminum foam has been discussed, and interlaminar shear stress between single-walled carbon nanotube reinforced aluminum foam and multiwalled carbon nanotube reinforced aluminum foam has been compared. The comparison has shown that the interlaminar shear stress within the interface of single-walled carbon nanotube and aluminum foam is higher than that within the interface of multiwalled carbon nanotube and aluminum foam. Hence, the probability of stress concentration and crack initiation within the interface of single-walled carbon nanotube and aluminum foam is higher than that within the interface of multiwalled carbon nanotube and aluminum foam. Furthermore, thermal fatigue lives of different single-walled carbon nanotube reinforced matrix nanocomposites have been evaluated. Additionally, interaction between carbon and molten aluminum has been analyzed. Finally, a new relation for the thermal interlaminar shear stress intensity factor to predict the crack initiation sites on fiber/matrix interface has been introduced.

Eliminating Fractures in Large Lanthanum Bromide Crystal Packages

Cerium-activated lanthanum bromide scintillator crystals have low thermal diffusivity and low fracture strength under tension. This combination makes LaBr <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> (Ce) susceptible to fracturing while cooling from high temperatures ( ≥ 175°C). Large crystals with low surface area-to-volume ratios are especially susceptible. When the cooling rate cannot be controlled, large temperature gradients can form between the crystal core and the crystal surface. The resulting tensile stress is often enough to fracture the crystal. Eliminating such fractures is important for applications involving large and rapid thermal excursions, such as oil well logging and space flight. Fractures can be mitigated through proper design of detector packaging. Measurements were taken to quantify the variability in fracture strength and fracture toughness of LaBr <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> (Ce). Corresponding packaging experiments exploring the tradeoffs in detector performance versus required surface feature size and compression have been performed. When external compression (>1.3 MPa) is combined with small surface features (R <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">v</sub> <; 20 μm), the thermal stress intensity can be reduced below the fracture toughness limit and allow even large crystals (> 200 cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup> ) to survive rapid thermal ramps ( <; -2°C/min.).

Analysis of Thermal Stress Intensity Factors for Edge Cracked Bimaterial System

The thermo elastic edge-cracking problem in bimaterial systems subjected to convective heating is considered. The medium is assumed to be insulated on one surface and exposed to sudden convective heating on another surface containing the edge crack. Superposition and uncoupled quasi-static thermoelasticity principles are adopted to formulate the problem. Thermal stress distribution and stress intensity factor values had been determined using the finite element software ANSYS for two different bi-material systems containing edge crack normal to the interface.

Analysis of Thermal Stress and Stress Intensity Factor of Pressurized Cylindrical Shell with Crack under Laser Irradiation

Analysis of Thermal Stress and Stress Intensity Factor of Pressurized Cylindrical Shell with Crack under Laser Irradiation

Callus Induction, Proliferation, and Plantlets Regeneration of Two Bread Wheat (Triticum aestivumL.) Genotypes under Saline and Heat Stress Conditions

Response of two genotypes of bread wheat (Triticum aestivum), Mahon-Demias (MD) and Hidhab (HD1220), to mature embryo culture, callus production, andin vitrosalt and heat tolerance was evaluated. For assessment of genotypes to salt and heat tolerance, growing morphogenic calli were exposed to different concentrations of NaCl (0, 5, 10, and 15 g·L−1) and under different thermal stress intensities (25, 30, 35, and 40°C). Comparison of the two genotypes was reported for callus induction efficiency from mature embryo. While, for salt and heat tolerance, the proliferation efficiency, embryonic efficiency, and regeneration efficiency were used. The results show significant medium and genotype effects for the embryogenesis capacity of calluses induction and plantlets regeneration under saline and thermal stresses. Mahon-Demias showed good callus induction and ability to proliferate and regenerate seedling under heat and salt stress conditions compared to Hidhab. No sizeable differences were observed between the two genotypes at higher salt stress rates. This study will serve as a base line forin vitroscreening of several elite wheat cultivars for their ability to induce callus and regenerate plants from mature embryos, and to start selection for tolerance to salinity.

Thermal Weight Functions and Stress Intensity Factors for Bonded Dissimilar Media Using Body Analogy

In this study, an analytical method is presented for the computation of thermal weight functions in two dimensional bi-material elastic bodies containing a crack at the interface and subjected to thermal loads using body analogy method. The thermal weight functions are derived for two problems of infinite bonded dissimilar media, one with a semi-infinite crack and the other with a finite crack along the interface. The derived thermal weight functions are shown to reduce to the already known expressions of thermal weight functions available in the literature for the respective homogeneous elastic body. Using these thermal weight functions, the stress intensity factors are computed for the above interface crack problems when subjected to an instantaneous heat source.

Thermoelectromechanical Response of a Piezoelectric Strip with Two Parallel Cracks of Different Lengths

This work is concerned with the thermoelectromechanical fracture behavior of two parallel cracks of different lengths in a piezoelectric material strip under thermal loading. The crack faces are assumed to be insulated thermally and electrically. Fourier transform techniques are used to reduce the mixed boundary value problems to two systems of singular integral equations. Numerical calculations are carried out, and detailed results are presented to illustrate the influence of the geometric parameters on the thermal stress and electric displacement intensity factors.

A Practical Approach for Evaluation of Thermal Shock SIF's in Flexibly Restrained Edge-Cracked Plates

A practical method to evaluate the thermal shock stress intensity factors (TS-SIF`s) associated with a flexibly restrained edge-cracked plate (FRECP) is outlined. It is assumed that the edge crack can be represented with a spring couple, and the deformations of the edge-cracked plate are consistent with Euler-Bernoulli deformation theory. It is then demonstrated how a compliance analysis of this simplified representation can be used with a finite element analysis of equivalent crack free plates to evaluate to TS-SIF`s associated with a FRECP. The accuracy of this method is shown to be excellent by comparing it against a direct fracture mechanic finite element analysis. This method is therefore advantageous to a fracture mechanic finite element analysis as it does not require an explicit analysis of a FRECP.

On the Use of Mechanical Weight Functions for Practical Evaluation of Thermal Shock SIF's in Flexibly Restrained Edge-Cracked Plates

Two practical methods have been used to estimate thermal shock stress intensity factors (TS-SIF`s) associated with a flexibly restrained cracked plate. The first method used a traditional mechanical weight function (MWF) methodology in conjunction with the MWF derived for an equivalent freely restrained cracked component. The second method used a traditional MWF methodology in conjunction with the MWF derived for an equivalent rigidly restrained cracked component. Fracture mechanic finite element analyses were also undertaken to construct a comparative benchmark for the TS-SIF`s associated with a flexibly restrained cracked plate. The results of this comparison demonstrate the errors associated with these MWF methods to be acceptable, if and only if, the crack size is small, the crack component aspect ratio is large or the flexible boundary restraint stiffness are deemed negligible or near rigid. In addition, the curves derived with these MWF methods do not intersect and there is no obvious transition to distinguish which MWF method would be more appropriate for a given a particular flexible boundary restraint configuration. In effect, this means that these MWF methods cannot be confidently used to evaluate the TS-SIF`s associated with a flexibly restrained cracked component.

Thermo-Mechanical Analysis of Alumina-Zirconia Composites by a Hybrid Finite Element Method

In the present work a hybrid finite element method, based on the Voronoi Cell method, is proposed for the thermo-mechanical analysis of heterogeneous materials containing cracks. The proposed method uses two hybrid elements to model the second phase heterogeneities of the material and the crack tips. The method was used to analyze alumina-zirconia ceramic materials; specifically, effective elastic moduli, thermal expansion coefficients and stress intensity factors were calculated. The effects due to zirconia t → m phase transformation and thermal stresses, which develop during the cooling stage of sintering, were also taken into account in calculating the stress intensity factor.

Viabilidade e vigor de sementes de paineira após armazenamento, condicionamento e estresses salino e térmico

O objetivo deste trabalho foi avaliar o efeito do condicionamento e dos estresses salino e térmico sobre o vigor e a viabilidade de sementes de paineira (Chorisia speciosa St.-Hil) armazenadas em geladeira, em embalagens impermeáveis, durante três anos. Sementes com e sem punção do tegumento foram condicionadas em água destilada e em soluções de KNO3 a 0,1 M e 0,2 M, durante 24 horas, a 27ºC. O estresse salino foi simulado com soluções de NaCl em potenciais osmóticos variando de 0,0 a -1,2 MPa, a 27ºC. O estresse térmico de diferentes intensidades foi aplicado em sementes secas, que germinaram a 27ºC. Houve diminuição da viabilidade e do vigor das sementes com o aumento da intensidade dos estresses salino e térmico. Nas sementes condicionadas e intactas, o limite máximo de tolerância à salinidade não foi reduzido, porém houve diminuição da tolerância ao estresse térmico, em sementes condicionadas com ou sem punção. O teste de condutividade elétrica indicou as sementes condicionadas em água e KNO3 0,1 M como as de maior vigor. Sementes condicionadas em água apresentaram maior velocidade de germinação sob estresses salino e térmico. O condicionamento substituiu a punção do tegumento, que não é recomendada para sementes armazenadas.

IMPORTANCE OF INERTIA TERM IN DYNAMIC CRACK PROBLEMS CONSIDERING LORD–SHULMAN THEORY OF THERMOELASTICITY

A numerical technique is presented for the accurate calculation of stress intensity factors as a function of time for generalized coupled thermoelastic problems. In this task, the effect of the inertia term is investigated, considering different theories of thermoelasticity, and its importance is shown. A boundary element method using the Laplace transform in time domain is developed for the analysis of fracture mechanics; dynamic coupled thermoelasticity problems with relaxation time are considered in the two-dimensional finite domain. The Laplace transform method is applied to the time domain and the resulting equations in the transformed field are discretized using the boundary element method. Actual physical quantities in the time domain are obtained using the numerical inversion of the Laplace transform method. The singular behavior of the temperature and displacement fields in the vicinity of the crack tip is modeled by quarter-point elements. The thermal dynamic stress intensity factor for mode I is evaluated using the J-integral method. The accuracy of the method is investigated through comparison of the results with the data available in literature. The J integral, which represents the dynamic energy release rate for propagating cracks, contains a boundary integral and a domain integral. The boundary integral contains strain energy, tractions, and strains whereas the domain integral contains inertia and strains. The J-integral method allows these two terms to be calculated separately. In this way, the importance of each term may be investigated by considering different theories of dynamic thermoelasticity.

TRANSIENT THERMAL FRACTURE OF A PIEZOELECTRIC CYLINDER

ABSTRACT This paper investigates the fracture mechanics problem of a piezoelectric cylinder under a sudden heating on its outer surface. The temperature field and the associated thermal stresses and electric displacements are obtained first. These stresses and electric displacements are added to the crack surface to form a mixed-mode boundary-value problem for the electromechanical coupling fracture. Both electrically impermeable and permeable crack-face boundary conditions are considered. An exact and closed-form solution for the thermally induced crack-tip field is obtained for infinitesimal cracking. Also obtained are the analytical expressions for the crack opening displacement and the electric displacement on the crack faces as a function of time. The maximum thermal stress and electric displacement inside the medium and the maximum thermal stress and electric displacement intensity factors near the crack border are given. These results are useful for the strength evaluation of piezoelectric materials under transient thermal environments.