Cyclic Temperature Changes Research Articles

Quantification and characterization of the microstructural damage of recycled aggregate self-compacting concrete under cyclic temperature changes

Recycled Aggregate (RA) usually increases porosity and weakens Interfacial Transition Zones (ITZs) of concrete, which favors the appearance of internal thermal damage. Four Self-Compacting Concrete (SCC) mixes with coarse and fine RA were subjected to positive and negative cyclic temperature variations to characterize their thermal damage and quantify its effects. Two damage mechanisms were found. On the one hand, micro-cracks appeared in the ITZs. On the other hand, micro-cracks arose from the micro-pores and propagated through the cementitious matrix. Both damage mechanisms were promoted by the use of coarse and fine RA, respectively. The damage was most notable at sub-zero temperatures and when adding coarse RA. Furthermore, it primarily affected compressive strength, although ultrasonic pulse velocity and hardened density also decreased, which served as non-destructive indicators to indirectly quantify the level of thermal internal damage of SCC.

Testing Electromechanical Sensors to Ensure Reliability in Hot Environments

In the world there are various methods of testing vehicles and its components used by various car manufacturing companies. Many methods are given in the UNECE regulatory documents in the field of transport, but these documents do not take into account the hot and climatic conditions of car operation. This article presents the road and climatic conditions of Central Asia, which is characterized by peculiar characteristics. The test methods are designed in such a way that, when operating cars in hot climatic conditions, the reliability of the sensors should be ensured when the car runs at least 250,000 km. It is established that in order to ensure the normal operability of sensors operating in hot climates, it is necessary to conduct tests at a nominal ambient temperature 45±5 °C, based on this parameter, a test procedure is built. The test methods are designed in such a way that all tests are carried out in accordance with the current standards in the field of electromagnetic, electromechanical and other electrical parameters of the automotive industry. Schematic diagrams of test benches are also given. The scientific work substantiates the methodology of accelerated reliability tests, in which the temperature is set as the accelerating factor. The tests fully reflect the operational characteristics of the movement of cars in a sharply continental climate with a hot slope of ambient temperature with sharp temperature changes, i. e. the impact of cyclical temperature changes. Based on the conducted research, conclusions are drawn, which reflects the results obtained.

Thermo-mechanical behaviour of energy piles in overconsolidated clay under various mechanical loading levels and thermal cycles

Energy pile foundations play the dual role of providing structural support to buildings and acting as heat exchanger units. Thus, they are subjected to different mechanical loads from the buildings and the cyclic temperature changes encountered in optimized hybrid systems. However, the effects of mechanical loading levels on the thermo-mechanical behaviour of energy piles under cyclic temperature changes are still to be investigated fully. This paper fills this knowledge gap through a series of model scale tests where the effects of different mechanical loading levels were investigated over multiple cooling-heating cycles in over-consolidated saturated clay. In this respect, ten cooling-heating cycles were applied while the pile's head load was maintained at 0, 25%, and 50% of the pile's ultimate bearing capacity, respectively. After ten thermal cycles, the pile's normalized settlement reached 0.05%, 0.37%, and 1.19%, respectively. The ultimate bearing capacity was 555 N, 535 N, and 520 N, respectively. The results indicate that the increase in load levels exacerbates the irreversible settlement while reducing the bearing capacity of the piles. Moreover, it also affects the stress distribution within the pile and further develops internal tension. The results from this study can be used for qualitative analysis of energy pile design.

A new aspect of post-depositional alterations of lithic artefacts: the case of Medzhibozh Lower Palaeolithic assemblages

Flint artefacts have been identified in the materials of the Lower Palaeolithic sites of Medzhibozh, which have experienced the effects of post-depositional alterations (PDA). We suggest a particular combination of anthropogenic and natural effects on lithic artefacts. In the vicinity of Medzhibozh in the Khmelnytskyi region in the West of Ukraine, several multilayered stratified Lower Palaeolithic sites are currently known. Artefacts and accompanying fauna have been identified in subaerial buried soils, initial hydromorphic soils, and alluvial deposits. The ages of the artefact-bearing sediments are preliminarily estimated to be between 1.2 and 0.4 Ma. The lithic assemblages of all horizons contain technologically and typologically archaic artefacts, the industry being referred to as Mode 1. Various types of rock were used as raw materials, including locally occurring flints in the form of pebbles and flattened nodules. Flint products from many assemblages are characterized by rounding and sheen due to their extended exposure to water-permeable horizons. Most of the flint artefacts belonging to a particular assemblage are of a similar type of preservation. The assemblages also contain artefacts with surfaces of different states of preservation, suggesting that they are of different ages. These could either be products of reutilisation or natural alterations. However, more recent surfaces tend to be isolated and do not form a removals system. Moreover, most of the individual PDA pieces show a technological and morphological consistency of differently preserved surfaces, indicating that a force initiating detachment was applied simultaneously. We, therefore, consider artefacts showing a variate state of scar preservation to be PDA products. We assume we are dealing with a new aspect of post-depositional alterations of lithic artefacts. Natural alteration had subjected artefacts, which received internal damage to the structure earlier when processed by man. The bipolar-on-anvil technique was actively used at Medzhibozh. Many artefacts show signs of multiple attempts of knapping, accompanied by a change in the position of the segmenting item. Such signs are impact pits, visible cracks, and Herzian cones disturbing the rock's texture. We believe that the internal cracks that appeared in the area of the not detached spall contribute to the accelerated natural alteration of the item in this area and, ultimately, to the detachment of the flake. The probability of spalling depends on the intensity of the internal distress, the structure of the rock, the climatic conditions, and the post-depositional environment. The most responsible factor for the effect of the “time-delayed spalling” seems to be repeated cycles of temperature changes. A comprehensive study of post-depositional modifications of lithic artefacts is essential in studies of Lower Palaeolithic sites, particularly the technological Mode 1 (Oldowan). This is due to the highly heterogeneous raw materials used, the bipolar-on-anvil knapping technique, and a long period of post-discard behaviour of artefacts. Key words: Lower Palaeolithic, Medzhibozh, stone artefacts, post-depositional alterations, time-delayed spalling, taphonomy.

Effect of atmospheric temperature on underground radon: A laboratory experiment

The effect of atmospheric temperature on underground radon flow was investigated in a customized climate-controlled laboratory (CCL) system, which enabled us to isolate the impact of ambient atmospheric temperature variations on underground radon transport. The soil thermal gradients that developed, following atmospheric warming, acted as the driving force for the diffusive radon flow, resulting in a decrease in the radon concentration along the experimental column setup at a rate of ∼70 Bq∙m−3 per oC∙m−1 (∼0.4% of the radon concentration). When the ambient temperature decreased, compared to the soil temperature, an air-soil temperature difference developed along the column, which acted as a driving force for radon to flow along the column and promptly increased the radon concentration at a rate of ∼140 Bq∙m−3 per oC (∼0.8% of the radon concentration). The overall radon concentration changes under the experimental conditions were up to 30%. The changes in the molecular diffusion coefficient in the experimental temperature range were ∼7%, with thermal diffusion as a possible additional mechanism contributing to radon transport due to temperature. The cyclic changes in ambient temperature in the forced conditions experiments were found to be directly correlated with underground radon oscillations. The same frequency for ambient temperature and radon concentration, along the experimental column in low frequency warming-cooling cycles (i.e., 4–8 days), was found. This good correlation was lost at higher frequencies (two days or more), due to the asymmetrical response of radon to atmospheric warming and cooling. The results of this study explain some of the field observations in underground radon monitoring.

Evaluation of Frost Impact on Traditional Ceramic Building Materials Utilized in Facing Walls.

This paper takes into consideration the performance of traditional bricks as part of a building exterior wall finish. Exterior wall materials change their properties when exposed to external environment. This process is extended over time and its intensity is closely related to microstructure, moisture and freeze–thaw cycles. Two methods of freeze–thaw durability tests were used in this study: standard and defined by the authors. The authors’ method incorporated the actual conditions of masonry unit function in exterior wall finish, i.e., cyclical effects of precipitation water, changes in temperature and air humidity. The laboratory test study included 50 freeze–thaw cycles. Three characteristic ranges of pore dimensions were indicated in the analysis: below 0.1 µm, between 0.1 and 3.0 µm and above 3 µm. Based on the method of freeze–thaw durability testing, the areas of microstructure changes were determined. The obtained results were related to the absorption of ceramic building materials. The authors’ method confirms the usage of traditional ceramic building materials designed for use in protected walls against water penetration in unprotected exterior wall finish. The critical water saturation method of masonry units (standard) based on extreme environmental conditions generates significant changes in porosity distribution that do not reflect real, i.e., moderate, conditions. This method is appropriate for masonry units operating in severe conditions, i.e., F2. The aim of this study is to suggest a methodology for durability tests of traditional ceramic masonry units to cyclic freezing and thawing, which are only exposed to F1 (moderate) conditions during operation. Changes in the microstructure of the ceramic building materials were used as the primary evaluation criterion. In order to determine the effect of cyclic temperature changes, the freeze–thaw durability test was performed according to generally accepted standard procedures and in-house methodology. The purpose of the study is to point out the individual approach for the analysis of the material–environment system. At the same time, it should inspire researchers to innovative methods which use external conditions in a laboratory environment.

Soil Thermal Response to Temperature Cycles and End Boundary Conditions of Energy Piles

This paper explores the influence of building cover and pile toe boundary conditions on ground temperature distributions surrounding energy piles. Experimental and numerical studies were conducted on two isolated cast-in-place energy piles installed in dense unsaturated sand, one exposed to the atmosphere at the ground surface (diameter=0.6 m and length=16.1 m) and the other installed under a six-story building (diameter=0.6 m and length=10 m). Investigations were conducted for monotonic heating and daily cyclic temperature changes of the piles ranging between 10°C and 35°C. The changes in ground temperature decreased as radial distance increased from the edge of both piles. Cyclic temperatures in both piles induced lower ground temperature changes and decreased the radial thermal influence zone compared with monotonic heating. However, the radial thermal zone in cyclic operating mode can be influenced by different ratios of heating to cooling times and hence should be selected carefully to avoid unexpected ground temperature changes. Atmospheric effects were observed up to a depth of 2 m for the energy pile exposed to the atmosphere. The insulation provided by the building footprint slightly decreased the impacts of ground-atmosphere interaction on the soil temperature distribution with depth near the surface compared to the energy pile exposed to the atmosphere. The ground temperature variations were dominant along the length of the heat exchanger loops for both piles. However, they were negligible near the pile toe below the heat exchanger loops for both piles.

Analysis of optical fiber connector contact damage caused by fluctuations in ambient temperatures of spacecraft

In this study, considering the cyclic changes in the ambient temperature of a spacecraft, the variation in the internal stress on the optical fiber connector contact with temperature was simulated to verify the reliable application of the connector. Thus, the potential damage to the contact caused by the ambient temperature was analyzed and verified. The results show that when the ambient temperature exceeds a certain range, microcracks occur on the contact as the internal stresses increase. It was experimentally verified that the traditional optical fiber contact is safe for use in spacecraft within the temperature range of − 65 to 100 °C. For the extensive application of optical fiber connectors on the spacecraft, the internal structure of the contact must be improved to reduce the maximum stress at extreme temperatures.

Research on the bending damage of concrete in areas with large temperature differences based on 3D‐Digital Image Correlation

AbstractDigital Image Correlation (DIC) technique is used to collect the whole‐field strain of concrete subjected to bending loads under different temperature change cycles, cooling rates, and water‐binder ratio. The bending damage behavior of concrete under large‐difference temperature circulation is analyzed with the whole‐field strain cloud map and data. In addition, with the whole‐field strain obtained by 3D‐DIC technology, the strain‐based damage variable is defined. Furthermore, the damage degree of concrete specimen in the bending process is quantified, and the bending damage evolution process of concrete under the action of temperature circulation is discussed. The results show that the damage of concrete in areas with large temperature differences is related to the number of temperature change cycles as well as the cooling rate. Moreover, the increase in the number of temperature change cycles and the cooling rate will aggravate the bending damage of the concrete. Additionally, the higher the water‐binder ratio, the more serious the adverse effect of temperature circulation on the concrete. This paper provide certain reference for the evaluation of concrete bending deformation damage in areas with a large temperature difference.

Self-Loosening of a 3D-Printed Bolt by Using Three Different Materials under Cyclical Temperature Changes

Three-dimensional printing can bring huge advantages when fabricating difficult structures and components in industry. This technology is also used commonly for printing threaded fasteners in the engineering field. The main disadvantage of threated fasteners is self-loosening. In this study, an International Organization for Standardization (ISO) standard M12 × 1.75 bolt and nut were printed by using a 3D printer and three types of 3D printing materials: acrylonitrile butadiene styrene (ABS-2), poly lactic acid (PLA), and glass. Following this, a test system for self-loosening of the 3D-printed bolts under cyclical temperature variations was constructed, and self-loosening of the bolted joints was observed by measuring the bolt preload using a load cell and the rotation displacement of the nut using a dial indicator according to temperature changes (from 10 °C up to 40 °C and 80 °C). The experimental results show that the ABS-2 bolt has good performance in terms of self-loosening phenomena under cyclical temperature changes, while the PLA bolt has poor performance in low temperature changes. The glass bolt indicated the lowest performance in high temperature changes.

Influence of neighbouring tube expansion on the residual stress of tubesheet with single-row holes

Abstract 1 The expansion joint is a commonly used method of connection tube and tubesheet in the pressure vessel industry. This paper established the rationality of the numerical simulation method by comparing with the analytical model. On this basis, the effect of neighbouring tube expansion on the residual stress of tubesheet with single-row holes was investigated, as well as the effect of the cyclic joint temperature changes on the tubesheet stress amplitude. Finally, preliminary work was conducted to determine the fatigue life of pressure vessels considering expansion factors. The results indicated that as the model was extended from one hole to 10 holes, the maximum and average stresses of each hole increased gradually and stabilized at a limit value when the model reached 10 holes, and the maximum and average stress in the expanded cases were approximately 13% and 10% higher than those in the unexpanded case, respectively. Residual stress results will lead to the change of stress distribution and the increase of stress amplitude, and then affect the fatigue life of the pressure vessel equipment. •Multilinear kinematic hardening model are used to exhibits the Bauschinger effect. •Numerical simulation method is validated by the analytical model. •Expansion process has a great influence on the stress level of the tube holes. •Residual stress leads to a significant change of tubesheet stress distribution. •Residual stress increases the stress amplitude and affects fatigue life.

Memory and rejuvenation effect on the cluster-glass phase of 1-D spin-chain compound Ca3Co2–xBixO6

We studied the structural, static, and dynamic properties of Ca3Co2–xBixO6 (x = 0 and 0.2) by means of powder X-ray diffraction and magnetization measurements. We reveal the rejuvenation phenomena in magnetic relaxation under cyclic temperature change and quenching below T c2. The reproduced step in the memory curve confirms the striking feature of rejuvenation effect in these samples. The observed memory and rejuvenation effects are discussed in the framework of hierarchical model of glassy phase.

Structure, Impermeability and Durability of Cement Concrete

The paper presents the main hypotheses of frost destruction of cement concrete. The influence of cyclic temperature changes and the effect of static and dynamic (shock) loads on concrete on changes in the structure and strength of concreteis considered. The paper provides results of comparative tests of frost resistance of concrete containing a porous additive and a plasticizer, which contribute to an increase in the density and impermeability of its structure. It has been shown experimentally that the introduction of air-entraining additives with an additional effect of hydrophobization is productive from the standpoint of ensuring frost resistance of concrete of relatively low classes (up to C30/37), compressive strength up to 50 MPa and water absorption by mass more than 4.0 %. It is advisable to increase the frost resistance of concrete with greater impermeability and strength by increasing these indicators, in particular, due to the maximum decrease in the initial water content and high-quality compaction. This conclusion is experimentally confirmed by the data presented in the paper, since the “mechanism” of frost destruction of cement concrete is multifactorial, and the growth of its density (impermeability) and strength provide a higher ability to resist “force” effects associated with repeated alternating deformations of concrete, as well as the action of external loads, accumulation of fatigue phenomena, hydrodynamics of liquid filtration under the influence of changing temperature fields, etc. A comparative assessment of concrete frost resistance has been carried out using standardized and patented techniques containing a porous (air-entraining) additive, as well as plasticizing and mineral additives of amorphous micro-silica, introduced into concrete in order to increase its density, impermeability and strength and on this basis – increasing frost resistance. Experimental data are presented, reflecting the relationship and patterns of decrease in frost resistance of concrete subjected to the simultaneous action of static (for compression – different levels from the corresponding indicator of concrete strength) and shock, concentratedly applied dynamic loads. The regularity of the relationship between the accelerated frost destruction of concrete and the action of mechanical loads that cause cracking in its structure has been confirmed.

Geomechanische Auswirkungen saisonaler Wärmespeicherung in stillgelegten Bergwerken

AbstractFor the transition to sustainable heat sources, storage infrastructure is required to provide heat evenly throughout the year. Solar heat is typically produced in the summer and can be stored in underground heat reservoirs for the winter. Flooded coal mines, e.g., are potential heat reservoirs. To assess whether the geomechanical integrity of a colliery and the surrounding rock mass are affected by seasonally stored heat, a numerical case study was performed at ”Zeche Dannenbaum“ in the Ruhr valley, Germany. During summer, hot water was injected into level 8 of the colliery while cold water was produced from level 4. This process was reversed in winter. Detailed subsurface models of the colliery, rock mass and tectonic faults were used to numerically simulate the cyclical changes in pore pressure and temperature and the resulting stress changes. The displacement of the land surface, and geomechanically critical regions in the rock mass were derived. Moreover, the reactivation potential of the fault zones and the risk of induced seismicity were evaluated. The high injection temperatures induce strong thermoelastic effects, which could potentially lead to fault reactivation and induced seismicity. Surface displacements, however, are negligeable.

Dynamics of plankton biocenoses under water level fluctuations in steppe lakes

Barun-Torey and Zun-Torey lakes are located in the arid steppe zone of the Central (Inner) Asia, Eastern Siberia, Russia. The Torey lakes are characterizes unstable hydrological regime. The water level variation is explained by the periodic filling and drying of the lakes due to cyclical climatic changes in humidity and temperature. We conducted our studies various water level phases of the climatic cycle: from high water level (1999, 2003) to drying out and the initial filling phase (2007, 2011, 2014, 2016, 2018, and 2020). The aim of this paper is to present long-term research results on changes in the plankton biocenoses of the Torey lakes during a climate cycle, the drying and initial filling of basins. Succession of plankton dominant species is in the direction of: diatoms+green algae and rotifers+crustaceans → green algae and crustaceans → green algae+cyanobacteria and crustaceans → no planktonic algae and invertebrates → cyanobacteria+diatoms+green algae and rotifers+cladocerans+copepods.

Membrane Homeoviscous Adaptation in Sinorhizobium Submitted to a Stressful Thermal Cycle Contributes to the Maintenance of the Symbiotic Plant-Bacteria Interaction.

Here, we estimate fast changes in the fluidity of Sinorhizobium meliloti membranes submitted to cyclic temperature changes (10°C–40°C–10°C) by monitoring the fluorescence polarization (P) of DPH and TMA-DPH of the whole cell (WC) as well as in its outer (OM) and inner (IM) membranes. Additionally, the long-term response to thermal changes is demonstrated through the dynamics of the phospholipid and fatty acid composition in each membrane. This allowed membrane homeoviscous adaptation by the return to optimal fluidity levels as measured by the PDPH/TMA-DPH in WC, OM, IM, and multilamellar vesicles of lipids extracted from OM and IM. Due to probe-partitioning preferences and membranes’ compositional characteristics, DPH and TMA-DPH exhibit different behaviors in IM and OM. The rapid effect of cyclic temperature changes on the P was the opposite in both membranes with the IM being the one that exhibited the thermal behavior expected for lipid bilayers. Interestingly, only after the incubation at 40°C, cells were unable to recover the membrane preheating P levels when cooled up to 10°C. Solely in this condition, the formation of threads and nodular structures in Medicago sativa infected with S. meliloti were delayed, indicating that the symbiotic interaction was partially altered but not halted.

Physical processes simulation in a precision device for liquid samples thermal cycling

An urgent task is the development of devices that provide a precision temperature change. The devices used in the real-time polymerase chain reaction method require not only repeated cyclic temperature changes with high accuracy, but also the temperature gradient minimization over the working fluid. In this article, the modeling of the working processes taking place in the thermal block of the device with the previously proposed thermohydraulic system, which ensures the temperature change together with the Peltier elements, is carried out. A mathematical model is formulated and a differential equation, boundary and initial conditions are substantiated. Numerical methods for solving the mathematical model in the Elcut software were applied. An experimental setup was developed and a study of heat exchange processes in the thermal block of a nucleic acid analyzer with a thermohydraulic system was carried out, confirming the adequacy of the developed mathematical model.

Investigation of the Thermal Shock Behavior of Mo‐Containing TiAl Alloys

TiAl alloys undergo cyclic temperature changes during use, the process of which can be simulated by the thermal shock test. A systematic investigation of the thermal shock behavior of four Mo‐containing TiAl alloys is conducted. The increase in Mo content from 1.0% to 4.0% causes the gradual decrease in the volume fraction of γ/α2 lamellar colony, while the volume fraction of equiaxed γ and βo phases gradually increases. At the same time, the thermal shock resistance of the TiAl alloys decreases as the Mo content increases. After thermal shock, cracks often occur within the lamellae and extend in a zigzag manner for TiAl−1.0Mo and TiAl−1.5Mo alloys. Their thermal shock resistance is enhanced by crack deflection, bridging, and microcrack shielding. For TiAl−2.0Mo and TiAl−4.0Mo alloys, cracks occur at the grain boundaries or within the γ phase and extend straight, with the result that these two alloys have worse thermal shock resistance than the other two alloys due to the limited effect of microcrack shielding. In addition, the microstructure stability of TiAl alloys after thermal shock is discussed, and there is a critical value of Mo content between 3.13% and 5.67%, which inhibits the βo → ω phase transition.

Effect of mastication simulation on the phase transformation of posterior 3-unit monolithic zirconia fixed dental prostheses

Statement of problemMonolithic zirconia restorations are directly exposed to cyclic loads and temperature changes in the oral cavity after cementation. These stresses may reduce the long-term success of the material by causing uncontrolled phase transformations within the zirconia. PurposeThe purpose of this in vitro study was to evaluate the effect of mastication simulation and different measurement points on the phase transformation of posterior 3-unit monolithic zirconia partial fixed dental prostheses (FDPs) in the posterior region. Material and methodsPosterior 3-unit FDPs of monolithic yttria-stabilized tetragonal zirconia polycrystalline (Y-TZP), including BruxZir Shaded (group B), FireZr (group F), and Upcera (group U) (n=10), were machined from presintered blocks. All specimens were exposed to mastication simulation (240 000 cycles/1.7 Hz/50 N). The monoclinic phase content was evaluated by X-ray diffraction (XRD). Phase transformation was measured at the mesial connector (group M), distal connector (group D), and pontic regions (group P) before and after mastication simulation. The relative monoclinic phase amount (Xm) was calculated for all specimens. The data were analyzed by ANOVA and post hoc tests (α=.05). ResultsAccording to XRD analysis, Xm for all groups and regions showed higher results after aging than before aging (P<.05). Group B has the lowest Xm among the groups. Group B showed a statistically significant difference compared with both group F and group U (P<.05). There was no significant difference between group F and group U (P>.05). When the regions were evaluated regardless of brand and the groups were evaluated in terms of regions, no statistically significant difference was observed between connectors and the pontic region (P>.05). ConclusionsMastication simulation causes an increase in the Xm. However, this increase was unlikely to be clinically significant. There may be differences in phase transformation depending on the contents of the brands and sintering procedures. Variations in the phase quantity were independent of the connector regions and pontic for FDPs.

Resistance investigation of diamond-like carbon coatings to cyclic temperature changes

Optical elements used in outer space must be designed considering the effects of such factors as space vacuum, atomic oxygen in low Earth orbit, solar and space radiation, large temperature drops, gas release of spacecraft materials and structural elements, space dust and debris. In order to harden and protect mirror surfaces of optical elements from external factors, it has been promisingly applied diamond-like carbon coatings on their surface. These coatings are characterized by high strength and wear-resistant properties, in particular, high hardness, low friction coefficient, high wear resistance and chemical inertness. This leads to their widespread use in various fields of science and technology, including optical instrumentation. This paper presents the results of testing an aluminum mirror with a diamondlike carbon coating under the effect of cyclic temperature changes for determining their ability to withstand a rapid cyclic ambient temperature change, and specifically, to maintain optical and mechanical properties.