Transient High Temperatures Research Articles

Gradient enhanced thermo‐mechanical damage model for concrete at high temperatures including transient thermal creep

AbstractA thermo‐mechanical model for concrete under transient high temperatures is presented. Particular emphasis is placed on the transient thermal creep model, which can be seen as an extension of Thelandersson's formulation, and the gradient‐enhanced damage model that has been extended here to include temperature dependency. Degradation of the material stiffness due to exposure to elevated temperatures is included via a simple thermal damage model. The model's performance is illustrated on several benchmark problems under both transient and steady state heating conditions. Copyright © 2004 John Wiley & Sons, Ltd.

Transient high temperatures in mantle plume heads inferred from magnesian olivines in Phanerozoic picrites.

Both scaled laboratory experiments and numerical models of terrestrial mantle plumes produce 'balloon-on-a-string' structures, with a bulbous head followed by a stem-like tail. Discussions have focused on whether their initial upwelling heads are hotter than the tails or cooler, as a result of entrainment of ambient mantle during ascent, and also on whether initial plume upwelling is a newtonian or non-newtonian process. The temperature of the mantle delivered to the base of the lithosphere is a critical parameter in such debates. Dry continental magmas can normally contribute little to this topic because their hottest (ultramafic) examples can be expected to be trapped, owing to their density, beneath the Moho. Here we report a rare case in which olivine (with 93.3% forsterite; Mg2SiO4) phenocrysts, precipitated from an unerupted komatiitic melt (approximately 24% MgO) of the Tristan mantle plume head 132 Myr ago, were carried to upper-crust levels in northwest Namibia by less Mg-rich (9.6-18.5% MgO) magmas. We infer that the hidden melt, generated when the plume impinged on the base of the lithosphere, originated in the mantle with a potential temperature of approximately 1,700 degrees C. This is approximately 400 degrees C above ambient and much hotter than the temperatures previously calculated for steady-state Phanerozoic mantle plumes. Published data show that the same conclusion can be reached for the initial Iceland and Galapagos plumes.

Transient high temperatures during seed growth in narrow-leafed lupin (Lupinus angustifolius L.) II. Injuriously high pod temperatures are likely in Western Australia

Studies under controlled environment conditions indicate that transient high temperatures (34-38˚C) during grain filling can significantly reduce weight per seed in narrow-leafed lupin (Lupinus angustifolius L.). This study has shown that on average, lupin pods reach temperatures about 3-5˚C higher than the maximum daily air temperature during seed filling under field cropping conditions. These differences do not appear to be markedly influenced by the amount of radiation intercepted by the canopy, stage of pod development, or position of the pods in the canopy, but fluctuate more as a result of differences in radiation intensity, wind speed, and water availability. Trickle irrigation reduced the difference between pod and air temperature by about 2˚C. Lupin species with larger pods (L. cosentinii and L. atlanticus) reached higher maximum daily temperatures than those of L. angustifolius. Long-term meteorological data indicate that air temperatures during seed filling of lupins in Western Australia are likely to exceed 30˚ C and will occasionally exceed 35˚ C. In lupin-growing areas of Western Australia, pod temperatures exceeding 33-35˚ C can be expected about 1 year in every 3, and more rarely (about 1 in 10 years), pod temperatures exceeding 38-40˚ C can be expected. These transient high temperatures are likely to increase significantly the year to year variation in yields of lupin grain.

Transient high temperatures during seed growth in narrow-leafed lupin (Lupinus angustifolius L.) I. High temperatures reduce seed weight

Highly variable yields are a weakness of narrow-leafed lupins. Yield variability could be caused by many factors, including hot days during seed filling. This paper investigates the effects of 2 hot days at various stages of seed filling in L. angustifoliusL. cv. Merrit. Exposing adequately watered plants to a total of 6 h at 34, 36, or 38˚C, compared with 20˚C, over 2 consecutive days reduced weight per seed by 4, 8, or 12% at maturity, respectively. The 38˚C treatment, applied when seeds averaged 4% of their final weight, also caused significant seed abortion. High temperatures reduced weight per seed at all stages of seed growth, except when seeds were <5-12 mg dry weight (3 and 6% of final seed dry weight, Expts 1 and 2, respectively). The reductions in weight per seed were not associated with reduced assimilate supply because: (a) neither photosynthesis nor leaf longevity were reduced by heat treatment; (b) competing inflorescences and branches were not allowed to develop; (c) the plants produced very large seeds for this cultivar (174-190 mg); and (d) leaves remained green well after the pods had matured. Seed N concentration decreased and fat concentration increased by small, although statistically significant, amounts in response to heat treatment at the last stage of seed development tested (57% of final weight per seed when treated) but not at earlier stages. This study indicates that hot days with pod temperatures as low as 34-36˚C during seed development can cause reductions in weight per seed, and hence yields, in narrow-leafed lupin crops.

Measurement of transient high temperatures by the modulated probe beam reflection technique

Measurement of transient high temperatures by the modulated probe beam reflection technique

Structural behavior of reinforced concrete structures at high temperatures

To establish a method to predict the behavior of reinforced concrete structures subjected simultaneously to high temperatures and external loads, this paper presents the results obtained in several series of tests carried out recently in Japan. This paper reports on the material properties of concrete and steel bars under high temperatures. It also considers the heat transfer properties of thick concrete walls under transient high temperatures, and the structural behavior of reinforced concrete beams subjected to high temperatures. In the tests, data up to 800 °C were obtained for use in developing a computational method to estimate the non-linear behavior of reinforced concrete structures exposed to high temperatures.

Anatomical anomalies in crop formation plants

Crop formations consist of geometrically organized regions ranging from 2 to 80 m diameter, in which the plants (primarily grain crops) are flattened in a horizontal position. Plants from crop formations display anatomical alterations which cannot be accounted for by assuming the formations are hoaxes. Near the soil surface the curved stems often form complex swirls with ‘vortex’ type patterns. In the present paper, evidence is presented which indicates that structural and cellular alterations take place in plants exposed within the confines of the ‘circle’ type formations, differences which were determined to be statistically significant when compared with control plants taken outside the formations. These transformations were manifested at the macroscopic‐level as abnormal nodal swelling, gross malformations during embryogenesis. and charred epidermal tissue. Significant changes in seed germination and development were found, and at the microscopic level differences were observed in cell wall pit structures. Affected plants also have characteristics suggesting the involvement of transient high temperatures.

Magmatism during and after continental break-up

Abstract Magmatism accompanying continental break-up is caused primarily by decompression melting of the underlying mantle as it wells up beneath the rift. The amount of melt produced depends mainly on the temperature of the asthenospheric mantle and on the rate of rifting. Break-up above normal mantle generates only small amounts of melt, reaching a maximum of 7 km in fully oceanic crust. If extension lasts for 10 Ma or more, as on many such ‘non-volcanic’ continental margins, then still less melt is generated because the slowly upwelling mantle cools by conductive heat loss. Break-up above abnormally hot mantle surrounding mantle plumes generates much larger melt volumes and ‘volcanic’ continental margins. The largest melt volumes occur when rifting is above a newly initiated mantle plume, with its transient high excess temperatures and flow rates. This creates flood basalt provinces. The resultant basalt may flow distances of over 1000 km, both as surface flows and as dykes and sills intruded laterally in the crust. Only about one-quarter of the melt reaches the surface, the remainder underplating or intruding the lower crust. The excess gravitational potential provided by mantle plumes assists rifting, though plumes do not always cause continental break-up.

Measurements of transient high temperatures during the deformation of polymers

Measurements of transient high temperatures during the deformation of polymers

Measurements of transient high temperatures during the deformation of polymers

A novel and simple technique for the measurement of the magnitude and spatial distribution of transient high temperatures is described. The technique is applied to the measurement of the temperatures produced during the deformation under impact of a range of polymers. It is found that very high temperatures (up to 700‡ C) can be obtained in materials which undergo catastrophic failure, and that the temperatures obtained are related to the material's thermal and mechanical properties.

Pyrotechnic reaction of lead monoxide and silicon: measurement of reaction temperature

The measurement of transient high temperatures, from the fast pyrotechnic reaction of lead monoxide and silicon, using an automatic recording pyrometer and optical focussing system is described. The measured temperatures are compared with calculated reaction temperatures with which agreement is good. Practical difficulties are discussed with regard to thermocouple and pyrometer temperature measurements in pyrotechnic systems. Infra-red pyrometers have advantages over thermocouple systems e.g. response time and ability to make non-contact measurements. This work indicates that they can be put to practical use in the field of pyrotechnics.

Influence of Temperature and Photoperiod on the Annual Ovarian Cycle in the Lizard Anolis carolinensis

Female Anolis carolinensis resemble males of the species in showing some dependence on both photoperiod and temperature for the regulation of seasonal reproductive activity. In both sexes, photoperiodism is a transient seasonal phenomenon and high temperatures appear to be one of the major stimuli for the onset of gonadal activity in the spring. Development of ovaries may require higher temperatures than the testes, helping to insure that males will be reproductively mature before egg production begins. Sperm retention is effective in female A. carolinensis but seems to be relatively inefficient for fertilizing eggs produced more than a few months after copulation. Unlike the males, females do not appear to have the potential for continuous reproductive activity: ovarian regression could not be prevented by manipulation of photoperiod and temperature. Also, females show a more marked refractoriness to photo-thermal stimulation in fall. In these respects, female A. carolinensis differ from females of tropical congeneric species; instead, they resemble temperate-zone lizards that have been studied. Photoperiod and temperature appear to be only two of several important exogenous stimuli that regulate the timing of seasonal changes in ovarian activity; moisture and social interactions are probably also important.

Phenolic resin char-formation during hyperthermal ablation

Ablation is a self-regulating heat and mass transfer process in which incident thermal energy is expended by sacrificial loss of material 1 1 ASTM (E 349)30. . The surface of a carbonaceous char is lost during the ablation of fiber-reinforced phenolic resin composites. The transient high temperatures penetrate deeply, resulting in an underlying pyrolysis zone with rapid pyrolysis rates and a high char interface temperature. Phenolic resin char-formation at high heating rates and high temperatures was studied using thermogravimetry (TG). The specialized thermobalance permitted runs in helium at rates of 3–430°C/min up to 1400°C. Computer code analysis provided rate parameters for an Arrhenius type correlation. The parameters represented well the parent TG run but were not independent of heating rate. A complex correlation was considered necessary for universal use. The attractive alternative was parameter evaluation at high heating rates using TG.

Optical strain determination at transient high temperatures in stainless steel

Type 304 stainless-steel plates 0.24×2.25×4 in. in size were subjected to stagnation heating in an oxyacetylene-flame apparatus. Transient thermal strains at temperatures up to 2000°F were measured with a water-cooled Tuckerman optical strain gage shielded from heat transfer by a cooled radiant-heat shield. The general equations of thermoelasticity are used for a flat homogeneous plate which is subjected to a particular transient three-dimensional temperature distribution. The optically measured strains on the unheated surfaces of the specimens were in close agreement with the thermal strains from the analytical solution using experimentally obtained temperature distributions in the specimens.