•Critical buckling loads for a concrete arch under temperature field are derived.•Transient thermal strain and basic creep strain are incorporated into analysis.•Behaviour contrasts that as in steel ...arches under same loading conditions.•Transient thermal strain significantly reduces buckling strength in concrete arches.•Basic creep strain has a minor effect, only slightly reducing stability boundaries.
In this paper, non-linear elastic pre-buckling and in-plane buckling analysis for a circular shallow concrete arch subjected to a uniformly distributed load and time-varying uniform temperature field is performed. Transient thermal strain and basic creep strain are considered, the latter modelled using a fractional derivative creep law, to investigate the coupling effects of time, temperature and geometric non-linearity on mechanical behaviour and stability boundaries. The first correspondence principle is invoked allowing the problem to be treated elastically and statically, with the non-linear equilibrium equations derived using the principle of virtual work. Numerical solutions to the variable order fractional derivatives are obtained through a finite-difference based discretisation scheme. Results show that the coupling effect between transient thermal strain and geometric non-linearity is significant as it influences pre-buckling behaviour and reduces buckling strength. Basic creep strain is less influential, causing a slight enhancement of the effects of transient thermal strain.
Fibre Bragg grating (FBG) sensors have been known as one of the smart localized and globalized Structural Health Monitoring (SHM) devices for various structural applications specifically those ...utilize composite materials. In recent decades the use of advanced composite materials green manufacturing methods has increased the requirement to provide effective means of performing experimental investigations to support analytical and numerical analyses. The main objective of this article is to analyse the performance of additively manufactured (AM) Carbon Fibre Reinforced Polymer (CFRP) sample with FBG sensors under the influence of environmental factors (temperature, relative humidity). The sample was manufactured using continuous carbon fibre applying Fused Deposition Modelling (FDM) technique. During the AM process one FBG sensor was embedded in the middle of the sample, while the second FBG sensor was attached to the finished sample surface. The environmental tests were conducted to investigate the durability of AM elements and influences of embedded FBG sensors on the composite specimen. Additionally, the behaviour of composite materials under environmental loading was modelled using the Finite Element Method (FEM) through an Abaqus software. It allows to achieve a more complex picture of embedded fibre optic influences on AM composite material durability.
•Symmetric outward convex corrugated tube is introduced as the metal tube of PTR.•Effective heat transfer coefficient can be increased up to 8.4% when SCPTR is used.•Regression equation is put ...forward for heat transfer coefficient and Nusselt number.•Corrugated tube can enhance thermal performance and reliability of PTR effectively.
A symmetric outward convex corrugated tube design is introduced for parabolic trough receivers with the aim of increasing their heat transfer performance and reliability. An optical–thermal–structural sequential coupled method was developed to analyze the heat transfer performance and thermal deformation of the glass cover and metal tube of the parabolic trough receiver. The developed coupled method has been validated with experimental results conducted in the DISS test facility in Spain. The numerical results indicated that the introduction of a symmetric outward convex corrugated tube design for the metal tube of the parabolic trough receiver can effectively enhance the heat transfer performance and decrease the thermal strain. The effective heat transfer coefficient can be increased up to 8.4% and the maximum thermal strain of metal tube can be decreased up to 13.1% when symmetric outward convex corrugated tube is used at Re=81728, p/D=4.3. In addition, regression correlations are put forward in order to find an effective heat transfer coefficient and effective Nusselt number for the fluid flow in the parabolic trough receiver.
Mechanical strain measurement at high temperature is a challenge due to thermal strain interference caused by material thermal expansion. In this paper, a novel hybrid sensor possessing unlimited ...cavity length was developed to eliminate thermal strain interference in mechanical strain measurement at high temperature. The sensor was composed by an extrinsic Fabry-Perot interferometric (EFPI) with unlimited cavity length which performs large strain measurement, and a gold-coated regenerative fiber Bragg grating (RFBG) with high reflectivity to fulfil temperature sensing. Sensing performance was tested on a ceramic cantilever. Firstly cantilever and the sensor was heated from room temperature to 800 °C without mechanical load. Pure thermal strain as large as <inline-formula> <tex-math notation="LaTeX">6500~\mu \varepsilon </tex-math></inline-formula> was measured by EFPI. At the same time temperature was measured by RFBG with a sensitivity of (10.98+0.00831T) pm/°C. Thermal strain data was fitted as a quadratic equation of temperature with a thermal strain-temperature coefficient of (6.407+0.00542T) <inline-formula> <tex-math notation="LaTeX">\mu \varepsilon /^{\circ }\text{C} </tex-math></inline-formula>. This relation still stands when mechanical load is introduced along with heating. In that case, temperature could be recorded by RFBG to get thermal strain, and total strain (containing thermal strain and mechanical strain) be measured by EFPI. By subtracting thermal strain from total strain, mechanical strain could be obtained. To verify the method mechanical load of 300, 500 and 600 <inline-formula> <tex-math notation="LaTeX">\mu \varepsilon </tex-math></inline-formula> was measured under randomly heating or cooling the cantilever. Deviation between measured and actual loaded mechanical strain was less than 10%, indicating the reliability of the sensor in eliminating thermal strain interference in mechanical strain measurement at high temperature.
Additively manufactured parts are often distorted because of spatially variable heating and cooling. Currently there is no practical way to select process variables based on scientific principles to ...alleviate distortion. Here we develop a roadmap to mitigate distortion during additive manufacturing using a strain parameter and a well-tested, three-dimensional, numerical heat transfer and fluid flow model. The computed results uncover the effects of both the key process variables such as power, scanning speed, and important non-dimensional parameters such as Marangoni and Fourier numbers and non-dimensional peak temperature on thermal strain. Recommendations are provided to mitigate distortion based on the results.
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Thermal and autogenous deformations of high-performance concrete at early ages have significant impact on the performance, serviceability, and durability of concrete structures. While substantial ...past research has significantly improved our fundamental understanding of the autogenous shrinkage and of the coefficient of thermal expansion (CTE) of cement paste and mortar, such understanding for concrete, especially modern types of high-performance concrete at early ages, remains inadequate. Accordingly, a new Temperature Stress Testing Machine (TSTM) capable of generating reliable data on autogenous shrinkage and CTE of concrete from very early ages has been built. After a review of relevant major aspects, key features of the newly-built TSTM are reported, with a focus on advanced thermal regulation and deformation capturing systems. The outcomes of a study using the newly-developed TSTM on autogenous deformation and CTE of early-age concrete (two mixtures with water-to-binder ratio of 0.35 and 0.42) subject to different curing temperatures (23, 35 and 45 °C) are then presented. Higher curing temperatures significantly accelerate the development of autogenous shrinkage at very early ages, whereas after the initial period, the magnitude of autogenous shrinkage cured at the intermediate temperature of 35 °C gradually becomes the largest. Despite this cross-over, the maturity concept appears appropriate to approximate the effect of curing temperature on autogenous shrinkage of concrete at early ages. The linear CTE of early-age concrete, obtained using stepped temperature profiles, follows a clear rising trend after setting. Based on the newly-measured CTE, an attempt was made to separate thermal strain and self-desiccation shrinkage, in which the presence of non-negligible delayed thermal strain became evident.
This study aimed to evaluate complex cognitive function, manual dexterity and psycho-physiological parameters in tradesmen working outdoors in the mining industry during summer and winter.
Twenty-six ...males working in a mining village in the north-west of Australia were assessed pre- and post-an 11-h shift at the start, middle, and end of a 14-day swing in summer (average daily temperature: 33.9°C, 38% RH;
= 12) and winter (24.3°C, 36% RH;
= 14).
Working memory performance did not differ between seasons, over the swing or shift (
≥ 0.053). Processing efficiency and manual dexterity performance did not differ between seasons (
≥ 0.243), yet improved over the course of the swing (
≤ 0.001) and shift (
≤ 0.001). Core temperature, heart rate, thermal comfort, rating of perceived exertion and thermal sensation were not significantly different between seasons (
≥ 0.076); however, average shift dehydration was greater in winter compared to summer (1.021 ± 0.005 vs. 1.018 ± 0.006;
= 0.014).
The ability to self-regulate the intensity of activity likely helped outdoor workers to thermoregulate effectively, minimising thermal strain during their swings and shifts, in turn explaining unaltered cognitive function and manual dexterity performance between seasons. Regardless of season, workers should receive education on dehydration and workplace risks to protect their health.
•A novel moisture-dependent thermal strain model for concrete is presented.•The moisture-dependent parts of concrete thermal strain are modelled explicitly.•The presented model is verified and ...validated against published experiments.•Nuclear vessels are affected by the moisture-dependency of concrete thermal strain.
This paper presents a constitutive model for concrete able to capture the effects of the moisture content of the material on its mechanical behaviour under compressive loads and high transient temperatures. The model is the first to account for the experimentally demonstrated effect of moisture content on the two components of thermal strain, Load Induced Thermal Strain (LITS) and Free Thermal Strain (FTS). Both LITS and FTS are formulated as functions of the water content of the material at the beginning of the thermal transient. First, the theoretical formulation and numerical implementation of the model are presented. Then, the model is verified and validated against published transient tests on concrete specimens having different initial moisture contents. Finally, it is employed to assess a representative nuclear pressure vessel subjected to fault conditions. The results show that the model allows the moisture dependent behaviour of concrete heated under mechanical load to be accurately captured. Furthermore, it is shown the introduction of moisture-dependent thermal strain components is crucial to capture the behaviour of nuclear pressure vessels subjected to fault conditions. If the moisture-dependency of thermal strain of concrete is not considered, non-conservative results may be obtained.
In a typical Nb 3 Sn cable for fusion applications, the knowledge of the strain state of Nb 3 Sn filaments is important to predict and interpret the conductor performance in operation. Amongst the ...relevant strain sources, the predominant is the thermal strain that arises during the cool-down of the conductor to operating temperature, due to the different expansion of Nb 3 Sn and copper in the cable and the stainless steel conduit. This work addresses the characterization of Nb 3 Sn thermal strain in the React & Wind prototype (RW2) developed by EPFL-SPC for the toroidal field coil and the central solenoid of the EUROfusion DEMO fusion reactor. AC susceptibility measurements were performed on the RW2 prototype to assess the thermal strain distribution in the cable cross-section, before and after undergoing electromagnetic and thermal cyclic loading. The results of the analysis have shown that RW2 exhibits a significantly lower absolute mean strain value (about −0.3%), compared to many Wind & React ITER conductor samples investigated with the same method. In addition, the analysis highlighted that the assessed thermal strain distribution does not vary significantly before and after the electromagnetic and thermal cycles, confirming the small performance degradation in the RW2 conductor that has been recently reported.
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