•LITS of concrete and its components are clearly identified and defined.•LITS is a markedly confinement-dependent phenomenon.•Multiaxial tests for temperatures higher than 250°C are needed.•3D models ...capturing LITS dependency on the stress confinement have to be formulated.
Extensive research has been carried out over the past four decades on the behaviour of mechanically loaded concrete under transient thermal conditions. The purpose of this paper is to provide a concise review of the existing experimental and analytical works with a strong focus on the load-induced thermal strain (LITS) component. In order to eliminate ambiguities in definitions, the existing terms used to describe the strain components that develop in concrete under a transient thermal regime are compared and a clear definition of LITS and its components is given. The analysis of the existing experimental work shows that LITS is: a strain occurring only during first heating of loaded concrete to a given temperature; significantly influenced by the moisture flux in the temperature range 100–250°C; and independent of aggregate type for temperatures up to about 400°C. Examination of the existing multiaxial test data demonstrates that LITS is the result of markedly confinement-dependent phenomenon and that experiments on concrete subjected to triaxial compression and transient temperatures above 250°C are needed. In the light of the experimental evidence, for temperatures up to about 400°C LITS seems to be mainly due to chemical reactions and microstructural changes taking place in the cement paste, such as dehydration, drying and rearrangement of the water molecules within the cement paste. By contrast, for higher temperatures, thermomechanical damage due to thermal incompatibility between cement paste and aggregates is believed to contribute significantly to the development of LITS. Moreover, the necessity for modelling explicitly the LITS component in the case of Heating-Cooling (HC) cycles is discussed. Finally, a review of the main existing uniaxial and multiaxial explicit LITS models is given, and the advantages and drawbacks of each model are outlined.
Embedded FBG strain sensor is fixed on the measured object when monitoring strain, and the wavelength variation of FBG caused by the thermal strain of the measured object is coupled with the ...wavelength variation caused by external force. In order to reveal the basic situation of the thermal-force coupling, three embedded FBG strain sensors were prepared. The suspended temperature compensation FBGs and packaged temperature compensation FBGs were arranged inside these sensors. Then these sensors were placed in the air and reinforced concrete respectively to conduct sensing and temperature characteristic experiments. The sensing characteristic experiment proves the effectiveness and good repeatability of the strain measurement of the sensor. The temperature experiments prove that the packaged temperature compensation method is obviously better than the suspended temperature compensation method; And after being embedded in reinforced concrete, these sensors are incompletely suppressed by the thermal expansion of the reinforced concrete, the temperature sensitivities of three strain FBGs have decreased by 1.594pm/°C, 1.664pm/°C, 1.365pm/°C, respectively, while the temperature sensitivities of temperature compensation FBGs are basically unchanged.
In Vivo Multithread Ultrasound Thermal Strain Imaging Yin, Chuhao; Dong, Fansong; Su, Huajin ...
IEEE transactions on ultrasonics, ferroelectrics, and frequency control,
08/2023, Volume:
70, Issue:
8
Journal Article
Peer reviewed
While thermal therapy is increasingly applied in clinics, real-time temperature monitoring in the target tissue can facilitate improvements in the planning, controlling, and evaluating of therapeutic ...procedures. Thermal strain imaging (TSI), based on tracking the echo shifts in ultrasound images, has great potential for temperature estimation as is demonstrated in vitro. However, due to physiological motion-induced artifacts and estimation errors, employing TSI for in vivo thermometry is still challenging. Building on our earlier development of respiration-separated TSI (RS-TSI), a multithread TSI (MT-TSI) approach is proposed as the first part of a bigger plan. A flag image frame is first identified by analyzing the correlation between ultrasound images. Then, the quasi-periodic phase profile of respiration is determined and split into multiple parallelly distributed periodical subranges. Multiple threads of independent TSI calculations are thus established, with image matching, motion compensation, and thermal strain estimation performed in each thread. Finally, after applying temporal extrapolation, spatial alignment, and interthread noise suppression, the TSI results obtained in different threads are averaged to obtain the merged output. In microwave (MW) heating experiments targeting porcine perirenal fat, the thermometry accuracy of MT-TSI is comparable to that of RS-TSI, while the former exhibits lower noise and higher temporal density.
Thermal strain imaging (TSI) uses echo shifts in ultrasonic B-scan images to estimate changes in temperature which is of great values for thermotherapies. However, for in vivo applications, it is ...difficult to overcome the artifacts and errors arising from physiological motions. Here, a respiration separated TSI (RS-TSI) method is proposed, which can be considered as carrying out TSI in each of the exhalation and inhalation phases and then combining the results. Normalized cross correlation (NXcorr) coefficient between RF images along the timeline are used to extract the respiratory frequency, after which reference frames are selected to identify the exhalation and inhalation phases, and the two phases are divided quasi-periodically. RF images belonging to both phases are selected by applying NXcorr thresholds, and motion compensation together with a second frame selection helps to obtain two finely matched image sequences. After TSI calculations for each phase, the two processes are merged into one through extrapolation and interphase averaging. Compared to TSI based on dynamic frame selection (DFS), RS-TSI ensures that frames are selected during both the exhalation and inhalation phases while setting the frame selection range according to the respiratory frequency helps to improve motion compensation. The temporal intervals of TSI output are approximately half that employing DFS.
Transient Thermal Deformations (TTD) of High Performance Concrete (HPC) having various temperature and compressive loading histories in sealed conditions are investigated experimentally. The aim is ...to provide accurate data to quantify the transient thermal strain and to specify the conditions required to give rise to the phenomenon. The results are commented and hypotheses proposed to advise practitioners dealing with concrete structures concerned by the conditions of environment and loading that lead to Transient Thermal Deformation.
Abstract Aiming at the measurement problems such as strain in high temperature environment, this paper builds an optical fiber sensor that is suitable for high temperature environment. A test system ...platform that can provide a high temperature environment of 1000 °C both dynamic and static strain loading is designed. The platform includes a high-temperature furnace, constant-strength beams and excitation devices. Based on the test system platform, the thermal strain and loading strain tests of the high temperature fiber optic sensor are completed.
With the aim to increase the overall heat transfer performance and reliability of tube receiver for parabolic trough solar collector system, asymmetric outward convex corrugated tube is introduced as ...the metal tube of parabolic trough receiver. An optical-thermal-structural sequential coupled method was developed to study the heat transfer performance and thermal strain of tube receiver for parabolic trough solar collector system. Heat transfer performance and thermal strain comparisons between conventional tube receiver and asymmetric outward convex corrugated tube receiver are conducted. The researches indicated that the usage of asymmetric outward convex corrugated tube as receiver can enhance the heat transfer performance and reduce the thermal strain effectively. By using asymmetric outward convex corrugated tube as receiver, the maximum enhancement of overall heat transfer performance factor is 148% and the maximum restrain of von-Mises thermal strain is 26.8%.
•Asymmetric outward convex corrugated tube receiver is introduced as the metal tube of PTR.•Overall heat transfer performance factor is increased up to 148% by using ACPTR.•Regression equations are put forward for Nusselt number and Fanning friction factor.•Asymmetric outward convex corrugated tube can increase reliability of PTR effectively.
•Transient thermal strain is considered in the model of ultra-high strength concrete encased steel columns (UHSCESC).•Steel section has a lower temperature than its critical value after 150 min’s ...heating in standard fire.•The fire behavior of UHSCESC is governed evenly by steel section and core concrete.•The slenderness ratio, section size and load ratio are three key influencing factors.•EC4 is not applicable to UHSCESC leading to unconservative fire resistances up to 66 min.
Ultra-high strength concrete has been applied in concrete encased steel column to enhance strength and reduce usage of concrete. However, there are limited specifications in current design codes on ultra-high strength concrete encased steel columns (UHSCESC), particularly for fire effects. This paper presents numerical simulation of fire behaviour of UHSCESC exposed to standard fires. A thermo-mechanical model of UHSCESC is established by considering the effect of transient thermal strain and validated against experimental results. The effect of slenderness ratio, section size, load ratio, concrete strength, steel strength, reinforcement ratio and steel ratio on the fire behaviour of UHSCESC is investigated through parametric studies. The predicted fire resistance of UHSCESC is finally compared to EC4 results. It is found that the temperature of the steel section is lower than its critical value, and the load bearing capacity of UHSCESC is almost evenly provided by the core concrete and steel section. The slenderness, section size and load ratio have significant effects on fire resistance of UHSCESC, leading to a wide range more than 300 min. The EC4 method is not applicable to UHSCESC which may provide unconservative fire resistances up to one hour and over-conservative results of nearly four hours.
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