Thermal Dilatation Research Articles

Thermomechanical modeling of nonlinear internal hysteresis due to incomplete phase transformation in pseudoelastic shape memory alloys

This paper presents a thermomechanical model for pseudoelastic shape memory alloys (SMAs) accounting for internal hysteresis effect due to incomplete phase transformation. The model is developed within the finite-strain framework, wherein the deformation gradient is multiplicatively decomposed into thermal dilation, rigid body rotation, elastic and transformation parts. Helmholtz free energy density comprises three components: the reversible thermodynamic process , the irreversible thermodynamic process and the physical constraints of both. In order to capture the multiple internal hysteresis loops in SMA, two internal variables representing the transition points of the forward and reverse phase transformation, $$\phi _s^f$$ and $$\phi _s^r$$ , are introduced to describe the incomplete phase transformation process. Evolution equations of the internal variables are derived and linked to the phase transformation. Numerical implementation of the model features an Euler discretization and a cutting-plane algorithm. After validation of the model against the experimental data, numerical examples are presented, involving a SMA-based vibration system and a crack SMA specimen subjected to partial loading–unloading case. Simulation results well demonstrate the internal hysteresis and free vibration behavior of SMA.

Time Series Deformation Monitoring over Large Infrastructures around Dongting Lake Using X‐Band PSI with a Combined Thermal Expansion and Seasonal Model

The long‐term spatial‐temporal deformation monitoring of densely distributed infrastructures near the lake area is of great significance to understand the urban health status and prevent the potential traffic safety problems. In this paper, the permanent scatterer interferometry (PSI) technology with TerraSAR‐X imagery over the area around Dongting Lake was utilized to generate the long‐term spatial‐temporal deformation. Since the X‐band SAR interferometric phases are highly influenced by the thermal dilation of the observed objects, and the deformation of large infrastructures are highly related to external temperature, a combined deformation model considering the thermal expansion and the seasonal environmental factors was proposed to model the temporal variations of the deformation. The time series deformation and the thermal dilation parameter over the area were obtained, and a comparative study with the traditional linear model was conducted. The Dongting Lake Bridge and the typical feature points distributed around the lake were analyzed in details. In order to compensate for the unavailability of external in situ measurements over the area, phase residuals and the subsidence generated through Differential Interferometric Synthetic Aperture Radar (D‐InSAR) were utilized to verify the accuracy of the obtained deformation time series. Experiment results suggested that the proposed model is suitable and suggested for the selected study site. The root mean square error (RMSE) of the residual phase was estimated as 0.32 rad, and the RMSE compared with D‐InSAR derived deformation was ±1.1 mm.

OCLeaS – A tomographic PSI Algorithm using Orthogonal Matching Pursuit and Complex Least Squares

This letter describes an algorithm using Compressive Sensing to analyse a stack of SAR images to monitor small urban areas. It uses the combination of the Orthogonal Matching Pursuit and Complex Least Squares, in order to estimate the residual height, thermal dilation coefficient and the displacement rate associated with one or multiple dominant persistent scatterers in a SAR resolution cell. It can be interpreted as a hybrid tomographic-PSI algorithm. The proposed method is tested with simulated data over single and double PS. Then it is applied to a stack of 79 SAR scenes over the Central Business District of the city of Perth in Australia. The results are compared to a conventional algorithm.

An engineering approach for Prepreg characterization

Characterizing prepregs for process-simulation purposes is expensive. The present paper reports on a novel approach for thermoset prepreg characterization. It focusses on determining key-parameters which allow for comparing prepregs from a process-induced distortion (PID) perspective. The approach uses conventional thermo-mechanical-analysis (TMA) devices for data generation. It analyzes through-thickness strains along the whole curing process, which are the dominant driver for spring-in distortions. The measured data is utilized in a parameter-fitting scenario, allowing for characterizing compaction, chemical shrinkage and thermal dilation. Aside from magnitudes, the approach also provides information when chemical-shrinkage occurs during the process. The approach is applied here for quasi-isotropic carbon-fiber-epoxy-resin samples made from (QI) 8552/AS4 while selected comparisons with a corresponding M21E/IMA sample are provided for sake of capability demonstration.

The effect of shrinkage reducing admixtures on drying shrinkage, autogenous deformation, and early age stress development of concrete

AbstractThe current study investigates the effect of shrinkage reducing admixtures (SRA) on volume changes that may lead to shrinkage cracking and early age cracking. Drying shrinkage (DS) and autogenous deformation (AD), the impetus for shrinkage cracking, were measured over 2.5 years for three concretes with and without 1% SRA addition: an ordinary Portland concrete, a fly ash concrete and a slag concrete. The latter two concretes were also tested in the Temperature‐stress testing machine (TSTM), which measures AD, thermal dilation (TD) and restrained stress development for a concrete subjected to realistic temperature curing conditions. SRA was found to have a substantial and permanent impact on DS and AD for all three concretes (up to 32% reduction of the total deformation after 2.5 years). The higher the shrinkage, the higher the effect of SRA. For the slag concrete, where AD was found to be the main impetus of early age volume changes, SRA had a clear beneficial effect on the cracking tendency. For the fly ash concrete, where TD provided the main contribution to the volume changes, SRA had a less pronounced effect. The test results were also compared with AD and DS modeled by Model Code 2010.

Heat source and voiding signatures of Mullins damage in filled EPDM

The thermomechanical coupling of Mullins damage in filled EPDM has been investigated by analysing the self-heating via Infrared thermography (IR) and the voiding fraction by Digital Image Correlation (DIC). The volumetric strain measured during the rubber deformation is found to be predominantly associated with damage, while thermal dilatation caused by self-heating has a negligible contribution. On this basis, the thermomechanical coupling of Mullins phenomena has been identified by evaluating the strain and time dependence of the following criteria: the tangent modulus, the voiding rate and the heat sources. The tangent modulus that reaches a maximum at the strain transition from a series of cycle to another is found to be an appropriate mechanical signature of Mullin softening. At the same strain transition, both voiding rate upturn and heat source upturn are observed. These signatures suggest the Mullins damage to be mainly associated at high strain rate with the (re)-activation of dissipative cavitation mechanisms, by nucleation of new cavities and/or acceleration of cavities growth.

Effect of Annealing Process on Microstructure, Texture, and Mechanical Properties of a Fe-Si-Cr-Mo-C Deep Drawing Dual-Phase Steel

Dual phase steel generally has poor deep drawing property with a low r value less than 1.0, making it difficult to be used for deep drawing automotive parts. In order to improve the mechanical properties of the steel through heat treatment, effect of heat treatments with different conditions on a Fe-Si-Cr-Mo-C deep drawing dual-phase steel was investigated with the aim of identifying effective heat treatment parameters for effective modification towards optimal properties. Relevant thermal dilation and heat treatment experiments were performed. Corresponding characters were investigated. The results show that island martensite can be obtained at low cooling rate. With the increase of cooling rate, the formation of pearlite and bainite is favored. During annealing at low temperatures, recrystallization of the steel is incomplete with the presence of the shear bands. With the increase of annealing temperature, the recrystallization process is gradually complete, and the number of high angle grain boundaries increases significantly. The ratio of gamma orientation components to alpha orientation components decreases first and then increases with the increase of annealing temperature. The strain hardening exponent and r value show an upward trend with respect to annealing temperature, and the r value is as high as 1.15.

SELF-ADAPTING FAÇADE SYSTEMS: EXPERIMENTATION REGARDING THE EXPLOITATION OF THERMAL DILATION

ABSTRACT An original and innovative solar device orientation system is illustrated, together with the results of research and experimentation. The system proposed uses only the force generated by natural thermal dilation, without the help of motors, computerized devices or external energy sources, thus overcoming some critical aspects of the self-adaptive type of building envelopes used up until now. In the course of the research a mathematical model was developed to correlate the variation of the environmental temperature with the consequent expansion of the dilating elements of the system. The results of the tests carried out confirmed an excellent correspondence between the theoretical results and the experimentation. The state of the art of the research has all its theoretical aspects defined and some partial prototypes created. It is planned to build some complete prototypes with the realistic prospect of productive development.

Dependence of the elastic band structure of a helical medium on thermal dilatation

We consider an elastic helical medium formed by uniformly rotating a triclinic crystal around a given axis to constitute a helical medium giving rise to a material whose tensor stiffness rotates uniformly and varies along the helix axis. A detailed analysis of its elastic properties has been done previously. Here, we are concerned in analyzing the role of thermal coupling with heat flow through the dilatation tensor. Starting from a general dynamic description of the thermoelastic phenomena which takes into account the finite speed of propagation of thermal waves, we establish a set of equations for the strains, stresses, temperature and heat flow. These equations allow to calculate the band structure and the logarithmic ratio between longitudinal and transverse strains. We express our results for different values of the thermoelastic coupling and period of the helix which show remarkable modifications when compared with the case in which no thermoelastic coupling is present.

Contactless Characterization of Metals’ Thermal Expansion Coefficient by a Free-Space RF Measurement

In this communication, a novel method to characterize the thermal dilatation of metals using a contactless measurement of the frequency-dependent reflection coefficient of a resonator is introduced. This wireless technique allows extracting the thermal expansion coefficient of the material without the need of any calibration. Two antennas, a VNA, and a scatterer fabricated with the under-test material are required. All the measurements have been achieved using a climatic chamber with absorbers to control the scatterer's temperature. The measured values for thermal expansion coefficients are in good agreement with the values provided by the manufacturer which is confirmed by a sensibility study.

Improvement of toughness and hardness in BR1500HS steel by ultrafine martensite

AbstractTo obtain the ultrafine martensite for BR1500HS ultra-high-strength steel, a new preparation process of cyclic heat treatment (CHT) with descending heat temperature and holding time along with cycle steps was developed. First, a series of thermal dilation tests were conducted with the temperature range of 420–730°C and the heat rate of 5 K/s on a Gleeble-3800 thermomechanical physical simulator. According to the experimental data, the temperature ranges and the optimal holding time to completely austenitize BR1500HS were determined. Then, to confirm the optimal parameters of CHT for BR1500HS, several tests with various temperatures and cycle steps were conducted and analyzed by optical microscope and scanning electron microscope. Subsequently, the CHTs with decreasing heating temperature and holding time were studied due to the increasing internal energy of steel along with the CHT process. The lath width was measured as a criterion to evaluate the refinement degree in this article. After several loops of heat treatment, the lath width is reduced to 0.268 µm. Finally, the hardness evolution of the specimens subjected to CHT in this study was analyzed and compared with the lath width test results, which justified the effectiveness of the new developed process.

Spectroscopic assessment of a simple hybrid si-Au cell metasurface-based sensor in the mid-infrared domain

In this paper, we theoretically investigate the spectroscopic properties of a simple hybrid metasurface consisting in a periodic array of a Si-Au pattern in the mid-infrared spectral region. Our simulations show that our hybrid metasurface exhibits a strong spectral absorption band in the 5.5μm−10μm region, by comparison to the typical Au-Au counterpart. A considerable improvement to the full-metal metasurface approach is that resonance in the mid-infrared is obtained with a pattern cell of just λ/1.5 instead of the typical λ/5 to λ/8 requirement that occurs in full-metal structures, which relaxes the manufacturing constraints. To fully characterize the surface around resonance, we also performed wave propagation and thermal deposition investigations, the latter of which allows predictions of the shift in the resonance frequency caused by thermal dilation. The proposed metasurface constitutes a good candidate for use in mid-infrared and thermal detection devices, and benefits from the advantages of on-chip integration and scalability in THz generation-detection systems.

From Interferometric to Tomographic SAR: A Review of Synthetic Aperture Radar Tomography-Processing Techniques for Scatterer Unmixing in Urban Areas

Cross-track synthetic aperture radar (SAR) interferometry is a powerful technique that analyzes the phase shift each pixel undergoes between acquisitions of the same scene with just a slight change of viewpoint. These phase shifts provide information about the topography and, when more than two acquisitions are available at different dates, about possible slow motions along the line of sight, related to subsidence and/or thermal dilation, of the dominant scatterer in the resolution cell. However, interferometric processing exploits phase-only data, does not provide scatterer distribution in the vertical direction, and is not able to separate multiple scatterers lying in the same range/azimuth resolution cell.

Oedometric compression and thermal volume behavior of compacted Gaomiaozi bentonite saturated with salt solution

Saline solution has considerable influence on the thermo-hydro-mechanical behavior of compacted bentonite. In this study, the effects of NaCl solution on the swelling deformation, oedometric compression, and thermal volume behavior of compacted Gaomiaozi bentonite were investigated. Results show that compressibility of the specimens decreases with increasing NaCl concentration of the presaturation solution. At an overconsolidation ratio OCR=1 with a vertical pressure σv=0.1 MPa and at OCR=3 with σv=0.1 MPa, the specimens exhibited contraction during heating below the transition temperature, followed by dilation. A larger vertical pressure led to a higher transition temperature (at which the thermal strain turns from contraction to dilation). However, the specimens exhibited only thermal dilation at OCR=10 with σv=0.1 MPa and at OCR=2 with σv=0.5MPa. Additionally, for a given vertical pressure and presaturation solution, the specimens with a higher OCR exhibited a larger irreversible dilation after a thermal cycle. Moreover, the influence of the presaturation solution on the thermal volume change is non-monotonic. A dilute solution (NaCl solution of 0.1 mol/L) and high salinity solution (NaCl solution of 1.0 mol/L) markedly promote the thermal expansion. These experimental trends can be attributed to the fact that attenuation of the diffused double layer repulsion and electrostatic interaction as well as the reduction of the free water at high saline conditions harden the soil.

Finite element based micro modelling of masonry walls subjected to fire exposure: Framework validation and structural implications

This paper presents a 2-D finite element (FE) based micro modelling framework for thermo-mechanical response history analysis of solid brick masonry structures subjected to fire. The 2-D FE framework considers geometric and material nonlinearities, and transient states of strain in conjunction with the temperature-dependent material properties. Material nonlinearity within the 2-D FE model is considered by the temperature-dependent total strain rotating crack model. The FE framework is validated against the thermo-mechanical response of a half-scale masonry wall subjected to one-sided fire exposure, and it is observed that the predictions of the FE framework are reasonably accurate. Utilizing the validated FE framework, thermo-mechanical response history characterization is performed on a full-scale masonry wall subjected to one-sided fire exposure. Critical physical phenomena which include thermal bowing, heat diffusion, unit-mortar thermo-mechanical interaction, cracking and stress profiles within the masonry structures are studied intricately. Furthermore, thermo-mechanics within representative volumes enclosing unit as well as mortar and their correlation with the global thermo-mechanical response is studied. Such 2-D micro-scale thermo-mechanical computations on masonry walls followed by a detailed discussion on their thermo-mechanics are one of the novel features of the present study. It is observed that thermal bowing resulted from a complex interaction between thermal dilation and cracking and crushing in the mortar and unit within the masonry structure.

Multi-Scale Contact Localization and Dynamic Instability Related to Brake Squeal

Friction-induced vibrations (brake squeal) produced during braking applications have been one of the major problems in the transportation for many years. It can be the most troublesome for passengers because of its high frequency and acoustic pressure. The role of frictional contact surface geometry on the occurrence of squeal was investigated recently by some researchers. However, it has never been systematically studied at different scales simultaneously. Contact localizations are induced on the one hand by macro effects such as thermal dilatation (macroscopic scale) and on the other hand, by the heterogeneity of third body (tribolayer) generated by friction (mesoscopic scale). The aim of this paper is to investigate the effect of contact localization at both scales through stability analysis on a simplified pad on disc system. The model has been developed numerically by the finite element method (FEM) to introduce a non-uniform contact at macroscopic and mesoscopic scales. The results showed a strong dependency between squeal frequencies and effective contact zone at macroscopic and mesoscopic scales for the investigated configuration. Especially, it is found that squeal frequencies depend on the contact area at a macroscopic scale whereas the probability of occurrence of squeal frequency strongly relies on mesoscopic contact distribution.

Seasonal Deformation and Accelerated Motion of Infrastructure Monitoring Using a Generalized Differential SAR Tomography

Differential synthetic aperture radar tomography (D-TomoSAR) has proven an effective method for retrieving the elevations and deformations of both terrains and urban infrastructures. Particularly, D-TomoSAR with high-resolution X-band SAR data provides even higher accuracy for monitoring of deformations of the man-made structures. However, higher frequency increases the sensitivity of the system to the minute deformations causing a mismatch with the conventional linear deformation model. Currently, the traditional D-TomoSAR system has been extended to higher order versions to extract the seasonal deformation caused by the thermal dilation of structures. Nevertheless, the accelerated motion of scatterers representing another minute deformation component was neglected. As a result, the current D-TomoSAR model cannot accurately retrieve the linear, seasonal, and accelerated motions of the scatterers at the same time. In this letter, a generalized D-TomoSAR system model is proposed by a combination of the polynomial and the seasonal deformation model. Then, an effective algorithm for simultaneously retrieving the multiple deformation components based on the quasi-maximum likelihood (QML) technology is proposed. Finally, numerical simulations and experimental results with real data verify the effectiveness of the proposed system model and algorithm.

The effect of curing temperature on autogenous deformation of fly ash concretes

For concrete subjected to restrained conditions, autogenous deformation (AD) and thermal dilation (TD) are the main driving forces behind stress development in the hardening phase. Generally, AD in concrete is modelled by model codes or measured in the laboratory under 20 °C isothermal conditions, and then used as basis for stress calculations under realistic temperature conditions. To evaluate this common simplification, the current study investigated the effect of curing temperature on the AD of a series of fly ash concretes. A comprehensive test program was performed for fly ash concretes subjected to various temperature curing conditions. The model codes and measurements under 20 °C isothermal conditions provided AD developments in the same order of magnitude. However, when subjected to a realistic temperature history during curing, major changes in the AD developments were observed, emphasising that AD must be determined under relevant temperature conditions.

Linearno toplotno širenje građevinskog kamena poreklom iz plutonskih magmatskih kompleksa Eksterne vardarske zone Srbije

Thermal properties of the building stone used for cladding and flooring, especially in exteriors, are significant for durability and lifespan of buildings' surfaces covered with it, but also their aesthetic properties in the sense of integrity. Linear thermal expansion of natural stone units is determined in laboratory examinations, aiming to provide the value of yield between the units as free space for their dilatation and contraction upon temperature oscillations. Where this space is not provided, diurnal changes, especially temperature increase, create stone expansion and tension which can lead to deformations of stone units and mar units' and covered surfaces' integrity and aesthetics. Data on linear thermal expansion values of natural stone, especially from Serbia, are very rare in the literature, so our aim is to contribute to this type of knowledge. Examination of thermal dilatation of stone originating from eight plutonic massifs in External Vardar zone of Serbia has shown that the values are very small, parts of millimetres, and lower than those of the similar rock types originating from China, Brazil and Eastern Serbia. A clear grouping of the values of thermal expansion of the stone according to the genetic groups to which the plutons belong to can be observed. Mineral composition, grain size and presence of metallic minerals in samples have shown no clear influence on thermal dilatation values, but fabric inhomogeneity appears to cause the increase of these values.

Мембраны из сплавов палладия для получения особочистого водорода

In the present study, using the improved technology, high-quality vacuum-tight foils 10 – 20 µm in thickness were prepared from effective Pd – 6 wt. % In – 0.5 wt. % Ru, Pd – 6 wt. % Ru, Pd – 40 wt. % Cu palladium alloys. Using a combination of deformation and annealing modes, the Pd – 40 wt. % Cu alloy foil consisting of the ordered β-phase (97%) with the CsCl-type structure that exhibits the maximum hydrogen permeability in this system. The mechanical properties and hydrogen permeability of the prepared foils were studied and compared with those of alloy foils 50 µm thickness. The thermal concentration dilatation in hydrogen was studied at different temperatures. Data on the dilatation of palladium-based membranes are of primary importance for designing membrane filtering elements and selection of optimal conditions for their operation, since these data determine the operation life membranes. Based on the Pd – 6 wt. % In – 0.5 wt. % Ru alloy, the Pd – 6 wt. % In – 0.5 wt. % Ru – 1.25 wt. % Co alloy was developed; it is characterized by increased strength characteristics and lower α ↔ β hydride transition temperature.