Influence Of Measurement Temperature Research Articles

Influence of temperature dependent matrix properties on the high-rate impact performance of thin glass fiber reinforced composites

The influence of measurement temperature on the high velocity (>100 m/s) impact performance was investigated for three thermosetting epoxy resin S-2 glass composite systems. These three model resins were chemically similar but have different glass transition temperatures (Tg) and molecular weights between crosslinks (Mc) through the use of different diamine curing agents (Jeffamine® D230, D400, and D2000). Impact performance was quantified by the projectile kinetic energy absorbed (KE50) as calculated from the characteristic ballistic velocity (V50) of the composites during high velocity impact. Among the resin systems, the KE50 remained essentially constant over a broad range of temperatures for each composite set and modestly increased with decreasing Mc. The superficial damage area associated with delamination showed remarkable sigmoidal behavior as a function of the testing temperature relative to the Tg (T-Tg). Damage was high for low T-Tg values (glassy resin) and decreased as the resin traversed its Tg into the rubbery region. These damage area trends were found to depend on the resin Mc, with higher Mc values resulting in lower overall damage area and a lower inflection point temperature. High speed videography of the back surface of the samples showed that lower damage areas correlated with an increased back face deflection, which enabled energy absorption with relatively less delamination. Composite mechanical tests were performed to validate the impact performance and explain the deformation mechanisms observed during impact energy dissipation. Our results illustrate the critical importance of the resin architecture and temperature-dependent viscoelastic behavior on the impact properties of composites for impact-resistance applications.

Impact of the testing protocol on the mechanical characterization of small diameter electrospun vascular grafts

AimFor the proper function of small diameter vascular grafts their mechanical properties are essential. A variety of testing methods and protocols exists to measure tensile strength, compliance and viscoelastic material behavior. In this study the impact of the measurement protocol in hoop tensile tests on the measured compliance and tensile strength was investigated. MethodsVascular grafts made out of two different materials, a thermoplastic polyurethane (PUR) and polylactid acid (PLLA), with three different wall thicknesses were produced by electrospinning. Samples were tested with a measurement protocol that allowed the comparison of dynamic sample loading to a common quasistatic tensile test. Influence of measurement temperature, preconditioning cycles and the influence of a high number of loading cycles was also investigated. Compliance and tensile strength were evaluated and compared between the different samples and the different load cases. ResultsIn all samples a significant difference in the measured compliance was seen between an unloaded sample and a sample that was already in a preloaded state. For example in the PUR group with 100 μm wall thickness at 37 °C, the first compliance was 32.6 ± 9.6%/100 mmHg, which reduced to 15.4 ± 2.9%/100 mmHg at preloaded state. The PLLA group showed 7.5 ± 4.3%/100 mmHg vs. 0.94 ± 0.11%/100 mmHg respectively. The measurements showed the importance of dynamic testing, as the samples viscoelastic behavior had a considerable influence on the measured compliance. The quasistatic ultimate tensile test alone was not able to predict the sample's in vivo compliance. The measurement temperature had a significant influence on tensile strength and compliance. Both, the number of preconditioning cycles and the high number of loading cycles had a minor influence on the sample's compliance. ConclusionWith a quasistatic tensile tests alone, overestimated compliance values are measured in viscoelastic electrospun vascular samples, therefore dynamic loading cycles are required. Measurements at 37 °C are mandatory, as temperature has a significant influence on the mechanical properties.

Measurement of phagocyte activity in heterotherms

The heterotherm immune system undergoes significant variation in response to life cycle periodicity and torpor. As heterothermic bats are important reservoirs of zoonotic agents and modulation of immune activity can affect host-pathogen interactions, this work aimed at developing a suitable method for assessing heterotherm phagocyte activity. Chemiluminescence measurements were evaluated by mathematical and mechanistic approaches, both of which yielded comparable results in time-related parameters of phagocyte activity. Using a mathematical method, however, we developed a model that can be applied to particular specimens. The proposed equation offers a simple and reliable tool for comparing phagocyte activity, the values of which can be used for further analysis. While time-related parameters of bat phagocyte activity varied with measurement temperature, with the onset of respiratory burst at 38 °C being quicker than at 25 °C, quantitative values ​​of phagocyte activity were not influenced by measurement temperature. Further, homeotherm phagocyte activity parameters were more variable at 25 °C. Considering there was no influence of measurement temperature on the total volume of heterotherm phagocyte activity, we suggest that parameters measured at 25 °C are more representative of the immune status adapted to physiological extremes at low body temperatures.

Influence of measurement temperature on the luminescence properties of (113) defects in oxygen-implanted silicon

Influence of the measurement temperature in the range 5–130 K on the photoluminescence spectra of (113) defects in Si implanted with 350-keV oxygen ions at doses of 3.7 × 1014 cm–2 and annealed at a temperature of 700°C for 1 h in a chlorine-containing atmosphere is studied. The temperature dependence of the line intensity is characterized by portions of intensity increase with an activation energy of 23.1 meV and intensity quenching with activation energies of 41.9 and 178.3 meV. With increasing temperature, the lines are shifted to longer wavelengths and their FWHM increases.

Time-resolved optically stimulated luminescence and spectral emission features of α-Al2O3:C

This report is concerned with the influence of measurement temperature on luminescence lifetime and on the spectral emission features of luminescence from α-Al2O3:C. The lifetimes were determined from time-resolved luminescence spectra. Spectral measurements were done using thermoluminescence and X-ray excited optical luminescence. The emission spectra of α-Al2O3:C studied in this work shows prominent bands at 330, 380 and 420nm associated with vacancies in the oxygen sub-lattice in α-Al2O3:C and an additional band at 695nm due to Cr substitution for Al. Emission bands below 500nm are independent of temperature below 125°C but widen with temperature. Direct evidence of thermal quenching of the 420nm emission band is provided. Beyond 200°C, the 380 and 420nm bands merge and widen, with the 420nm emission dominant. Before the onset of thermal quenching, luminescence lifetimes are affected by retrapping both in the shallow- and in the main electron trap. This was deduced from features of time-resolved luminescence spectra measured from samples with and without the shallow trap. Additional measurements with temperature decreasing from 160 to 20°C, after phototransfer as well as after a considerable delay between irradiation and measurement, suggest that the change in lifetimes could also be related to other factors including slight shifts in emission wavelength for the 380 and 420nm emissions.

Luminescence lifetimes in natural quartz annealed beyond its second phase inversion temperature

The influence of annealing, irradiation dose, preheating and measurement temperature on luminescence lifetimes has been studied in quartz annealed at 1000 °C. The measurements were supplemented by studies on quartz annealed at 900 and 800 °C. Lifetimes increase with dose as well as with temperature and duration of annealing between 800 and 1000 °C. Preheating produces the same effect. The changes are accounted for in terms of hole-transfer from the non-radiative luminescence centre to and between radiative centres. The influence of measurement temperature on lifetimes depends on whether the stimulation is carried out from ambient to 200 °C or otherwise. This result is unlike that in quartz annealed at or below 500 °C where lifetimes are independent of the direction of heating. In particular, lifetimes decrease monotonically when measurements are made from 20 to 200 °C but not when recorded from 200 to 20 °C. The latter produces a pattern resembling that in quartz annealed up to 500 °C. The results are concluded as evidence of thermal effects on separate luminescence centres. In support of this, different values of the activation energy for thermal quenching were found for each supposed luminescence centre. The change of the corresponding luminescence intensity with temperature is also qualitatively consistent with this notion.

Influence of measurement temperature on the rheological and microstructural properties of glucomannan gels with different thermal histories

Samples of 3% glucomannan gels made with 0.6M KOH and preheated at Tht: 25°C (A), 50°C (B), 70°C (C) and 90°C (D) were studied at two measurement temperatures (Tm: 50 and 70°C) and compared to Tm: 25°C. Samples B and C were gels more thermo-stable at high measurement temperatures. This means that a preliminary heating at 50 and 70°C would be needed to retain their structural integrity of these gels. When the preheated gels were subjected to high deformation (puncture test), rigidity increased with increasing Tm. Similarly, small deformation tests showed that at Tm: 50°C and 70°C, the C sample had better gel characteristics than the others: i.e. higher elasticity and lower frequency-dependence of viscoelastic moduli. This means that there was more particle aggregation, so that when gels C were heated they would maintain a high degree of internal cohesion and connectivity. Mechanical and rheological analyses were consistent with the structures shown in SEM photographs.

Influence of observation temperature on light scattering of poly-N-isopropylacrylamide hydrogels

Static and dynamic light scattering methods were applied to characterize the microstructure of gels synthesized by cross-linking copolymerization of N-isopropylacrylamide, with particular emphasis on the influence of measurement temperature. The total scattering intensity was divided into two parts: thermal scattering due to Brownian motion and static scattering due to topological or spatial inhomogeneity. Different methods of data evaluation, i.e. the non-ergodic and the partial heterodyne approaches, were carefully compared. We obtained consistent results clearly demonstrating that both parts of the scattering rise markedly upon increasing the observation temperature from 10 to 27.5 °C thus approaching the lower critical solution temperature. While the temperature dependence of the thermal scattering component is well understood, we attribute the rise of the static component to the establishment of local swelling equilibrium in a gel whose cross-link density features some inhomogeneity. This means that with rising temperature the more densely cross-linked regions deswell at the expense of the less densely cross-linked ones. As a result, the scattering contrast is enhanced thus leading to a larger static scattering intensity.

Novel characteristic parameters for oil-paper insulation assessment from differential time-domain spectroscopy based on polarization and depolarization current measurement

For achieving the aging characteristic parameters of transformer oil-paper insulation, oil impregnated pressboard samples are acceleratedly thermally aged at high temperature (~150°C) in laboratory, and on the same sample before and after being aged, polarization and depolarization current (PDC) tests are performed at different temperatures (30, 40, 50 and 60°C), respectively. Besides analyzing the PDC results, the differential time-domain spectroscopy (DTDS) technique is introduced to investigate the aging status of oil-paper insulation and the influence of measurement temperature. The DTDS parameters such as polarization component Qn, polarization response time τn and line-shape parameter anare extracted with DTDS unscrambling method based on PDC data. It is revealed that DTDS represents similar polarization process and mechanism to PDC, and all the DTDS curves calculated with the obtained parameters (Qn, τn,αn) are in good fit with those measured. By analyzing the effect of temperature and aging, two types of relaxation polarization mechanism are observed, i.e., the interfacial polarizations between oil and paper insulation and inside the pressboard. The polarization components, response speeds and line-shape parameters of both the polarization mechanisms increase evidently on the whole with temperature rising or sample aging. It is demonstrated that, the DTDS theory is suitable for oil-paper insulation material, the DTDS unscrambling method is effective and objective, and such DTDS parameters are sensitive and can quantitatively reflect the changing of temperature and aging condition with regularity. Consequently, the parameters (Qn, τn, αn) can be considered as the novel characteristic parameters for aging condition estimation of oil-paper insulation to upgrade the application effect of PDC curves.

Positron and luminescence lifetimes in annealed synthetic quartz

The amount of luminescence that can be measured from quartz changes significantly as do the corresponding luminescence lifetimes if the quartz is annealed before pulsed optical stimulation. Owing to its importance in retrospective dosimetry, natural quartz has been the subject of most such thermal studies. In this work, the influence of annealing and beta irradiation on luminescence lifetimes determined from time-resolved luminescence spectra and positron lifetimes evaluated from positron annihilation spectra has been investigated in synthetic quartz, a material with eclectic applications including dosimetry and defect-physics studies. Measurements on the influence of stimulation temperature on luminescence lifetimes and luminescence intensity are also reported. Luminescence lifetimes are independent of annealing up to about 500 °C but increase thereafter suggesting the increasing importance of higher-lifetime luminescence centres. This interpretation is based on the energy band model for quartz used to explain luminescence lifetimes in which annealing induces the transfer of holes from a non-radiative luminescence center to and between radiative luminescence centres as is discussed in the text. Regarding the influence of measurement temperature on luminescence lifetimes, it was observed that lifetimes are strongly affected by measurement temperature particularly between about 120 and 200 °C in a manner consistent with thermal quenching. On the other hand, the luminescence intensity determined from the same time-resolved luminescence spectra goes through a peak as a function of measurement temperature. The initial increase in luminescence intensity is attributed to thermal assistance to optical stimulation whereas the subsequent decrease is ascribed to thermal quenching of the luminescence. Values of the activation energy for thermal assistance and thermal quenching are given. Positron lifetimes in unannealed quartz and quartz annealed at 500 °C are similar and independent of dose showing that irradiation or annealing did not produce new types of defects. The aim of this study is to improve understanding of the physical processes responsible for luminescence in synthetic quartz.

On the dose-dependence of luminescence lifetimes in natural quartz

The influence of irradiation dose on luminescence lifetimes has been studied in suites of natural quartz from Brazil, Nigeria and South Korea. The lifetimes were evaluated from time-resolved luminescence spectra measured from quartz pulse-stimulated at 470 nm and detected between 360 and 380 nm. The effect of irradiation varied between materials, decreasing with dose in the Brazilian quartz, independent of dose in the samples from South Korea, and increasing with dose in the quartz from Nigeria. The dose-related effects are accounted for with reference to an energy band scheme for quartz in which the luminescence lifetime is associated with a primary radiative recombination centre at which most capture of holes produced during irradiation and associated hole re-trapping takes place. The measurements on the effect of irradiation dose on luminescence lifetimes were augmented by investigations concerned with the influence of measurement temperature between 20 and 200°C on luminescence lifetimes in the same materials. It was observed that the luminescence lifetimes decrease continuously with temperature of stimulation and in a manner suggestive of increased thermal quenching of the corresponding luminescence. However, better consistency with the Mott–Seitz configurational coordinate model of thermal quenching is only apparent at temperatures greater than 120°C. The discrepancy is attributed to the model used to derive the formulae for luminescence lifetimes in which any re-trapping of stimulated charge is assumed negligible. However, it is argued that if re-trapping were in fact not negligible then the decrease of luminescence lifetimes with measurement temperature would be evidence of the progressive reduction of the re-trapping as the measurement temperature were increased with the overall effect being the monotonic decrease in luminescence lifetimes as observed.