Metastable effects on martensitic transformation in SMA

The use of Shape Memory Alloys (SMA) in technical applications as damping in civil engineering structures requires the characterization of the alloy for each specific application. This involves the evolution of the mechanical properties and damping capacity with the number of cycles, frequency, maximum deformation, applied stresses, and the evolution of the alloy with aging time and temperature. In particular, the temperature effects associated to self-heating need to be evaluated. In continuous cycling the effects of latent heat, the associated dissipation induced by the hysteresis, the heat flow to surroundings and the cycling frequency induce different states of temperature in the specimen, which in turn produces changes in the transformation-retransformation stresses. In this article, the temperature effects associated to cycling are outlined for different cycling frequencies. The results show that, for relatively faster frequency the temperature arrives at an oscillatory state superimposed to an exponential increase. For lower frequencies, some parts of the sample attain temperatures below room temperature. The experimental results are represented with an elementary model (the 1-body model or the Tian equation used in calorimetric representation) of heat transfer. For the higher fracture where life requirements are associated to damping in stayed cables for bridges, the results show (for the NiTi alloy) a reduction of the hysteresis width as the frequency increases for deformations up to 8%. For reduced deformation, under 2% appears an asymptotic behavior where the frictional area is practically independent of the cycling frequency (up to 20 Hz). In addition, it is shown that more than 4 million of working cycles can be attained if the maximum applied stress is kept below a threshold of about 200 MPa. Although under this condition the deformation must remain lower than 2% a reasonable damping capacity can still be obtained.     

The effects of rigid polystyrene particles on the glass transition characteristics and mechanical wave attenuation of styrene‐butadiene rubber: Particle size and acoustic mismatch

Glass transition characteristics and mechanical wave attenuation of the neat and filled styrene‐butadiene rubber (SBR) containing 10 wt % of rigid monosize polystyrene particles of various diameters from several hundred microns down to several tens of nanometers were investigated by dynamic mechanical thermal analysis, impedance tube, and ultrasonic spectroscopy. The results showed the matrix damping capacity and the breadth of glass transition increase by reducing the size of rigid particles due to the matrix‐particles interfacial area increase as the major governing parameter. Matrix glass transition broadening toward higher temperatures was attributed to the increased dynamic heterogeneity induced by fillers, whereas the damping capacity increase was assigned to contribution of interfacial friction loss mechanism. The proposed postulation was confirmed based on the calculated temperature distribution of the relaxing matrix volume fraction. Sound wave attenuation by the matrix and PS particles filled systems led to a broad absorption peak for the former and appearance of a secondary absorption peak at lower frequencies for the latter. Intensity of this secondary peak was highest for the system containing PS nanoparticles. Finally, ultrasonic attenuation enhanced by the PS particle size to wavelength ratio increase according to α_sca ～ (d/λ)^0.38 scaling law and declined by replacing the dense particles with larger hollow PS particles. Comparison of the normalized attenuation of the PS particle filled SBR in various mechanical wave attenuation regimes implied low sensitivity to particle size in vibration, mild differentiation in the sound, and finally severe differentiation in the ultrasound regimes. © 2009 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 48: 82–88, 2010     

Fire safety evaluation of expanded polystyrene foam by multi-scale methods

Microscale thermal analysis, bench scale cone calorimetric and real scale burning tests were conducted to evaluated fire safety performance of expanded polystyrene (EPS) foam. Simultaneous thermal analysis was used to study the thermal degradation of the foam in nitrogen, air, and oxygen environments at four heating rates. An endothermic effect is observed only in nitrogen environment, while two exothermic effects are observed in oxygen and air environments. In the nitrogen environment, the onset temperature of the endothermic effect and the endothermic peak temperature are much higher than that of the exothermic processes observed in air and oxygen environments. The Flynn–Wall–Ozawa method is utilized to analyze the degradation kinetics of the non-isothermal thermogravimetry. The activation energies calculated for an air environment, in a conversion range α = 20–70 %, are lower than those for an oxygen environment. The temperature range for this conversion range is 275–371 °C. The enthalpies of the first exothermic effect exceed that of the oxygen environment by 10–45 %. Bench scale cone calorimetric tests were carried out at incident heat flux of 25, 35, and 50 kW m^?2 with two sets of cone equipment. Heat release rate, ignition time, effective heat of combustion, and critical heat flux required for ignition is obtained. In real scale burning tests, the EPS boards were ignited in sandwich structures. Fire spread speeds were derived from temperature measurement inside sandwich structure.     

Calorimetric studies of poly(ethylene terephthalate) stretching over a wide temperature range

Heat effects and structural transformations in amorphous crystallizable poly(ethylene terephthalate) (PET) during uniaxial stretching accompanied by neck formation, have been investigated by calorimetric and x-ray methods over a wide range of temperatures and deformation rates. At small deformation (not exceeding 1–2%) and at temperatures below the glass transition temperature of the polymer, PET behaves as an elastic body. Upon stretching at a constant rate, constant heat power is absorbed, heat effects during loading and unloading coincide completely, and no hysteresis is observed. At large deformations (of the order of 50%), cold drawing develops in this temperature range. The internal energy change in cold drawing is zero within experimental error. A periodic heat release during the self-oscillation regime of drawing PET corresponds to periodic changes in stress, in the rate of the neck formation, and in the appearance of the sample. The temperature limits of the region where crystallization resulting from an uniaxial drawing of the polymer is possible, have been determined, and the heat effect of this phase transition has been measured. Orientation crystallization develops only from 70 to 94°C. These limits are insensitive to changes in deformation rate within one decimal order. The structure of PET in this temperature range has been investigated. The heat of phase transition of orientation crystallization of PET has been determined from the relationship between the measured values of the internal energy change during this process and the limiting degree of crystallinity for the stretched samples. This heat proves to be 5.5 ± 0.1 cal/g.     

On the use of a four-cameras stereovision system to characterize large 3D deformation in elastomers

The mechanical behavior and volume change of filled elastomers were studied thanks to a four-cameras stereovision system. The device allows measuring simultaneously the displacement field on two faces of the sample using 3D Digital Image Correlation (3D DIC). Subset size, step size and filter size, associated with DIC calculations, are carefully calibrated to ensure efficient analysis of the displacement fields. The smoothing parameter (i.e. filter size times step size) appears to be a discriminating criterion with an upper limit below which the strain field can be appreciably estimated. Within the appropriate choice of analysis parameters, volume changes under large deformation can be evaluated. For sufficiently large deformation, volume change exhibits an upturn during stretching which could be the sign of a significant increase of void fraction. Volume change appears to be reversible during unloading phase when maximum stretch ratio is low enough. So cavities that could have been open under tension are closed when elastic deformation is released. Conversely, for high stretching ratio, volume change exhibits a hysteresis loop-like evolution indicating that either some plastic cavities remained or closure kinetics is slower.     

Mechanocaloric properties of poly(dimethylsiloxane) and ethylene–propylene rubbers

We measured the temperature change in strips of poly(dimethylsiloxane) (PDMS) and ethylene–propylene rubbers that occurred as they were stretched and allowed to shrink by a factor of 3.5–4.5, along with the tensile force that effected the deformation. Main results obtained are as follows: (1) the temperature change is fully reversible in E–P rubber and slightly but definitely irreversible in PDMS rubber. The temperature rise in the latter on stretching is larger than the fall on shrinking by ca. 20 %. (2) The reversible part of heat that evolves from or is absorbed by PDMS rubber is smaller than, but close to, the mechanical energy expended. For E–P rubber, the heat generated greatly exceeds the expended mechanical energy. (3) The entropy of extension as a function of extension is reproduced well by Wang and Guth calculation for PDMS rubber, but not for E–P rubber.     

In-situ Study of Charge and Discharge of Ni-MH Battery Using the Combined Method of Electrochemistry and Microcalorimetry

An apparatus to study the battery system has been set up. The thermal effects of charge and discharge of Ni-MH batteries have been studied. The calorimetric measurements indicate that the net heat dissipation during charging is larger than that during discharging. It is observed that the ratio of heat dissipation to charging energy varies with charging capacity, and almost 90 percent of charging energy is lost as heat dissipation near the end of the charging process at 97.7 mA. A jump of thermal curve near the end of discharge due to a secondary electrode reaction has been observed.This revised version was published online in November 2005 with corrections to the Cover Date.     

Study on the hydrolytic degradation of the segmented GL-b-[GL-co-TMC-co-CL]-b-GL copolymer with application as monofilar surgical suture

The hydrolytic degradation of Monosyn™, a segmented copolymer derived from glycolide, trimethylene carbonate and ε-caprolactone, has been evaluated in buffered aqueous media at different pH and temperature. Degradation processes have been followed by considering mass loss and molecular weight profiles as well as the changes on ¹H NMR and FTIR spectra, morphology and both calorimetric and mechanical properties during exposure to the selected media and temperature.     

Mechanical properties of dual-phase polymer electrolytes prepared from poly(styrene-co-butadiene) rubber/poly(acrylonitrile-co-butadiene) rubber mixed latices

Mechanical properties of two dual-phase polymer electrolytes (DPEs), prepared from poly(styrene-co-butadiene) rubber (SBR) and poly(acrylonitrile-co-butadiene) rubber (NBR) latices, are studied. Both DPEs are composed of an SBR supporting phase and an ionconductive phase of NBR/lithium salt solution. The first DPE maintains a tensile strength of 0.5 MPa and elongation of 280% with an ionic conductivity of 10^?3 S/cm. Although the glass transition relaxations based on the dual-phase structure are not resolved in this DPE because of the proximity of the glass transition temperatures of the SBR and NBR, the glass transition shifts to a lower temperature due to the plasticization by the lithium salt solution. In the second DPE, two distinctive glass transition relaxations, corresponding to the SBR and NBR phases, are observed in the viscoelasticity versus temperature measurement, indicating the dual-phase structure. A simple equivalent mechanical model, which is modified from the Takayanagi model, is introduced to elucidate the mechanical behavior of the dual-phase structure in the second DPE. According to this model, 8% of DPE is a mechanically continuous SBR phase in the tensile direction, which effectively gives mechanical support to the DPE. © 1995 John Wiley & Sons, Inc.     

Influence of Liquid Isoprene Rubber on Strain Softening of Carbon Black Filled Isoprene Rubber Nanocomposites

The reinforcement of rubbers by nanoparticles is always accompanied with enhanced dissipation of mechanical energy upon large deformations. Methods for solving the contradiction between improving reinforcement and reducing energy dissipation for rubber nanocomposites have not been well developed. Herein carbon black(CB) filled isoprene rubber(IR)/liquid isoprene rubber(LR) blend nanocomposites with similar crosslink density(ν_e) are prepared and influence of LR on the strain softening behaviors including Payne effect under large amplitude shear deformation and Mullins effect under cyclic uniaxial deformation is investigated. The introduction of LR could improve the frequency sensitivity of loss modulus and reduce critical strain amplitude for Payne effect and loss modulus at the low amplitudes.Meanwhile, tuning ν_e and LR content allows reducing mechanical hysteresis in Mullins effect without significant impact on the mechanical performances. The investigation is illuminating for manufacturing nanocomposite vulcanizates with balanced mechanical hysteresis and reinforcement effect.     

Microbial desulfurization of SBR ground rubber by Sphingomonas sp. and its utilization as filler in NR compounds

Microbial desulfurization of waste tyre rubber has been investigated with great efforts since 1990s, because waste rubber has created serious ecological and environmental problems. A microbial desulfurization technique for SBR ground rubber has been developed by a novel sulfur‐oxidizing bacterium Sphingomonas sp. The adaptability of Sphingomonas sp. with SBR ground rubber was tested with the amounts of SBR ground rubber varying from 0.5 to 4% g/l. The sol fraction of desulfurized SBR ground rubber increased 70%, compared with SBR ground rubber without desulfurization. Fourier transform infrared spectroscopy‐attenuated total reflectance (FTIR‐ATR) spectrum and X‐ray photoelectron spectroscopy (XPS) analysis of the desulfurized surface of vulcanized SBR flakes revealed that not only the oxidation of crosslinked S? S and S? C bonds, but also the rupture of C?C double bonds had happened to SBR vulcanizates during microbial desulfurization. The cure characteristics, such as scorch time and optimum cure time of natural rubber (NR) vulcanizates filled, were found to decrease with increasing contents of desulfurized SBR ground rubber, due to some reactive groups on its surface. NR vulcanizates filled with desulfurized SBR ground rubber had lower crosslink density and hardness, higher tensile strength and elongation at break, compared with those filled with SBR ground rubber of the same amount. Dynamic mechanical properties indicated that there were better crosslink distribution and stronger interfacial bonding between NR matrix and desulfurized SBR ground rubber. Scanning electron microscope (SEM) photographs showed that the fracture surfaces of NR vulcanizates filled with desulfurized SBR ground rubber had more smooth morphologies. Copyright © 2010 John Wiley & Sons, Ltd.     

Dual-Phase structure of polymer electrolytes comprised of NBR/SBR latex films swollen with lithium salt solution

Dual-phase polymer electrolytes (DPE) that have high ionic conductivity (> 10^?3 S/cm) and good mechanical strength were prepared by mixing NBR and SBR latices and casting films. The latex films absorbed large quantities of lithium salt solution (e.g., 1M lithium perchlorate in γ-butyrolactone) to obtain DPE films but did not dissolve with swelling. The NBR phase is polar and was impregnated selectively with the polar lithium salt solution, whereas the SBR phase is nonpolar and formed a mechanically-supportive matrix. Transmission electron microscopic (TEM), electron energy loss spectral (EELS), and energy-dispersive x-ray (EDX) analyses showed microscopically the dual-phase structure. Evidence for swelling by lithium salt solution was found only in the NBR phase and not in the SBR phase by EDX microanalysis. Ionic conductivity as a function of NBR content or swelling degree showed clearly that a percolation threshold for ionic conductivity exists. © 1994 John Wiley & Sons, Inc.     

Morphology and mechanical and viscoelastic properties of natural rubber and styrene butadiene rubber latex blends

The morphology and mechanical and viscoelastic properties of a series of blends of natural rubber (NR) and styrene butadiene rubber (SBR) latex blends were studied in the uncrosslinked and crosslinked state. The morphology of the NR/SBR blends was analyzed using a scanning electron microscope. The morphology of the blends indicated a two phase structure in which SBR is dispersed as domains in the continuous NR matrix when its content is less than 50%. A cocontinuous morphology was obtained at a 50/50 NR/SBR ratio and phase inversion was seen beyond 50% SBR when NR formed the dispersed phase. The mechanical properties of the blends were studied with special reference to the effect of the blend ratio, surface active agents, vulcanizing system, and time for prevulcanization. As the NR content and time of prevulcanization increased, the mechanical properties such as the tensile strength, modulus, elongation at break, and hardness increased. This was due to the increased degree of crosslinking that leads to the strengthening of the 3‐dimensional network. In most cases the tear strength values increased as the prevulcanization time increased. The mechanical data were compared with theoretical predictions. The effects of the blend ratio and prevulcanization on the dynamic mechanical properties of the blends were investigated at different temperatures and frequencies. All the blends showed two distinct glass‐transition temperatures, indicating that the system is immiscible. It was also found that the glass‐transition temperatures of vulcanized blends are higher than those of unvulcanized blends. The time–temperature superposition and Cole–Cole analysis were made to understand the phase behavior of the blends. The tensile and tear fracture surfaces were examined by a scanning electron microscope to gain an insight into the failure mechanism. © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 38: 2189–2211, 2000     

Electrochemical heat flow calorimeter

A device designed for research of heat phenomena occurring in chemical power sources (CPS) is described. The device includes two functional blocks: electrochemical and calorimetrical, operating under single control, which allows simultaneously performing electrochemical and calorimetric measurements. The calorimetric block is a heat flow calorimeter. The calorimetric chamber design provides the possibility of studying thermal processes in laboratory electrochemical cells and CPS of planar, disk, and prismatic design. The absolute measurement error of the heat flow is ±50 μW at the resolution of 1 μW. The operating temperature range of the calorimetric chamber is 0–90°C. The basis of the electrochemical block is a module of a four–range potentiostat–galvanostat. The maximum polarizing current of the potentiostat is ±200 mA at the maximum voltage on the auxiliary electrode of ±10 V. Multiuser remote access from the user computers over Ethernet to the device is provided for control and treatment of experimental data. Digital deconvolution filters allowing to compensate the response rate of the heat flow meter are used for processing primary data of calorimetric measurements.     

高分子力学阻尼材料的研究——Ⅰ.填料对氯化丁基橡胶的力学阻尼行为的影响

本文研究了填料对氯化丁基橡胶在玻璃化转变温度以上的温度范围里的力学阻尼行为的影响。在T_g-36℃的范围里,通过测定填料表面吸附的结合橡胶和填料的表面积,用填料-橡胶界面积函数和单位重量橡胶在填料表面占据的表面积等参数,研究了填料-橡胶相互作用对氯化丁基橡胶的力学阻尼行为的影响;用界面积函数和填充胶中填料的体积份数之积研究填料-填料相互摩擦对它的力学阻尼行为的影响。发现在填料浓度低时,氯化丁基橡胶的力学阻尼行为主要受填料-橡胶相互作用的影响,高浓度时,填料-填料相互摩擦显著地改善了它的力学阻尼行为。     

Photosynthetic energy conversion in the diatom <Emphasis Type="Italic">Phaeodactylum tricornutum</Emphasis>

Isothermal microcalorimetry can be used to investigate the photosynthetic energy conversion of autotrophic organisms. In this study, for the first time a diatom alga was used to compare the calorimetrically measured heat flux with measurements of the photosynthetic performance by oxygen evolution and pulse-amplitude modulated fluorescence. The presented experimental setup proved suitable to compare calorimetric data with those of conventional methods of the determination of photosynthesis rates. Special attention was paid to the contribution of energy dissipation via non-photochemical quenching (NPQ) of chlorophyll fluorescence to the metabolic energy balance. This was achieved by a combination of different light conditions and the use of an inhibitor of NPQ. Although NPQ is an important photoprotective mechanism in diatoms, the inhibition of NPQ resulted in an activation of alternative, energy dissipating pathways for absorbed radiation which completely compensated for the fraction of energy dissipation by NPQ.     

Effect of heating rate on the thermal properties and devolatilisation of coal

The apparent specific heat of coal was measured by employing a computational calorimetric technique during continuous pyrolysis at heating rates of 10, 25 and 100°C min^-1. For all of the examined heating rates, the apparent specific heat was found to be approximately 1.4 kJ kg^-1 K^-1 at room temperature. When the sample reached decomposition temperature (~410°C), the specific heat increased to 1.9 kJ kg^-1 K^-1. From this point, the apparent specific heat was greatly influenced by the coal reaction mechanism. For this purpose a detailed gas analysis was carried out for the three examined heating rates. It was found that with increased heating rates, the devolatilisation reactions were shifted to higher temperatures, as reflected in the measured apparent specific heat. This revised version was published online in July 2006 with corrections to the Cover Date.     

A calorimetric setup for measuring heat effects of processes in solutions

A calorimetric setup was developed to determine the heat effects of chemical processes in solutions with a sensitivity of ～10^?5 K and an accuracy of temperature control in the thermostat of better than ±0.001 K. The performance of the calorimeter was tested by measuring the heat effects of solution of 1-propanol (m = 0.02–0.08 mol/kg), potassium chloride (m = 0.01–0.73 mol/kg), and L-phenylalanine (m = 0.0008–0.03 mol/kg) in water at 25°C.     

Prevention of oxide aging acceleration by nano-dispersed clay in styrene-butadiene rubber matrix

In order to minimize the oxidative degradation of SBR at high temperature, the nano-dispersed clay layers were introduced by using the SBR/clay (100/80) nanocompound to prepare SBR/clay/carbon black (CB) nanocomposites, then the effects of nano-clay on the properties of SBR nanocomposites are investigated. The clay layers and CB are uniformly dispersed in the SBR matrix at nano-scale. The mechanical properties of the SBR/clay/CB nanocomposites mostly decrease with the increase of clay loading, however, with the increase of clay loading, the change rate of the mechanical properties of the nanocomposites decreases and the aging coefficient of the nanocomposites rises, and the length and depth of the cracks of the aged nanocomposites after bending decrease, which means that the clay layers can provide the nanocomposites excellent thermal aging resistance and heat resistance. The experiment of aging with air and without air proved the importance of oxygen during rubber aging process. The FTIR spectra show the generation of oxygen-containing group on the external surface of the nanocomposites during aging. The DSC results indicate the differences between the internal layer and the external layer of the aged nanocomposites.     

Raman spectroscopy and thermal analysis of gum and silica-filled NR/SBR blends prepared from latex system

Natural rubber/styrene-butadiene rubber (NR/SBR) blends, with and without silica, were prepared by co-coagulating the mixture of rubber latices and various amounts of well-dispersed silica suspension. An attempt to predict blend compositions was made using Raman spectroscopy in association with differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA). It was found that the intensity of each Raman characteristic peak was strongly dependent on the blend composition, but there was no significant evolution with the presence of silica. Also, TGA results revealed an improvement in thermal stability of NR/SBR blends with increasing both SBR and silica contents due to the dilution effect. Two distinct glass transition temperatures (T_g) were observed in DSC thermograms of all blends, and their T_g values were independent on both blend composition and silica content. This indicated a physical blend formation, which agreed well with no shifts in Raman peaks of the blends in comparison with those of the individual rubbers. Linear regression with R² quality factor close to 0.99 was achieved when plotting intensity ratio at 1371/1302 cm^?1 versus blend ratios. On the other hand, the peak height ratio and heat capacity ratio from TGA and DSC analysis, respectively, yielded quadratic equations as a function of blend ratios.