DETERMINATION OF CROSS-GRAIN PROPERTIES OF CLEARWOOD SAMPLES UNDER KILN-DRYING CONDITIONS AT TEMPERATURE UP TO 140° C

ABSTRACT

Small specimens of Pinus radiata have been tested to determine the creep strain that occurs during the kiln drying of boards. The samples have been tested over a range of temperatures from 20°C to 140°C. The samples, measuring 150 × 50 × 5 mm, were conditioned at various relative humidities in a pilot-plant kiln, in which the experiments at constant moisture content (MC) in the range of 5-20% MC were undertaken to eliminate mechano-sorptive strains. To determine the creep strain, the samples were brought to their equilibrium moisture content (EMC), then mechanically loaded under tension in the direction perpendicular to the grain. The strain was measured using small linear position sensors (LPS) which detect any elongation or shrinkage in the sample. The instantaneous compliance was measured within 60 sec of the application of the load (stress). The subsequent creep was monitored by the continued logging of strain data from the LPS units.

The results of these experiments are consistent with previous studies of Wu and Milota (1995) on Douglas-fir ( Pseudotsuga menziesii ). An increase in temperature or moisture content causes a rise in the creep straw while the sample is under tension. Values for the instantaneous compliance range from 1.7 × 10^?3 to 1.28 × 10^?7 MPa^?1 at temperatures between 20°C and 140°C and moisture content in the range of 5-20%. The rates of change of the creep strains are in the Order of magnitude 10^?7to10^?8s^?1 for these temperatures and moisture contents. The experimental data have been fitted to the constitutive equations of Wu and Miloia (1996) for Douglas-fir to give material parameters for the instantaneous and Creep strain components for Pinus radiata.     

CORRELATION OF GLUCOSE (DEXTROSE) DEGRADATION AT 90 TO 190°C IN 0.4 TO 20% ACID

Decomposition of glucose is described over a wide range of acid concentrations and temperatures by a correlation based on an Arrhenius type model combined with a modified Debye-Huckel equation. Degradation depends on temperature and acid concentration, represented by hydrogen ion activity. Kinetic data from our laboratory for 4 and 12 wt% glucose were combined with literature data to establish this model. Alternative non-linear mechanisms were compared by regression analysis of the published data as well as data developed in this study. Values of the degradation constant vary from 0.109 hr^-1 (at 20 wt% acid and 190°C) to 4.18 × 10^-7 (at 0.4 wt% acid and 100°C). This result will be useful to model glucose degradation in acid hydrolysis of celluloses, sterilization of fermentor feeds, and stripping of fermentation ethanol.     

MEASUREMENT OF HUMIDITY ABOVE TEMPERATURE OF 100°C WITH A DOUBLE-WICK WET BULB PSYCHROMETER

A need exists for a simple device to measure the psychrometric properties of high temperature and high humidity air. To meet this need, a small laboratory double-wick psychrometer was developed and tested which showed good results to 175°C dry bulb temperature and 100°C wet bulb temperature. Based on the results of the laboratory unit, a portable prototype psychrometric system was designed and built. The overall design provided quick measurement and indication of wet bulb temperature, dry bulb temperature, humidity, and enthalpy of a high temperature air stream.     

Al2O3/SiC复相陶瓷的高温蠕变与持久强度

采用三点弯曲方法分别研究了两种的位反应烧结的氧化铝／碳化硅复相陶瓷在１０００℃和１２００℃的高温蠕变性能和失效特性,探讨了不同温度和加载时间对有速率的影响,并分析了静载何上高温失效机理和持久强度,对常温力学性能和高温力学性能进行了测试,并对不同条件下的断口进行了显微分析和对比。研究表明复相陶瓷在高温静载荷下的损伤过程是由于晶骨移引起的蠕变和断裂纹扩展以及高温等综合过程,任何一种因素单独作用或多种因     

EQUILIBRIUM MOISTURE CONTENT OF DRIED BLOOD FLOUR FN THE TEMPERATURE RANGE OF 20 - 50°C

The paper presents results of water sorption tests of dried blood flour carried out tinder laboratory conditions and mathematical analyses of sorption isotherms obtained. Moisture equilibrium data were investigated at air temperatures in the range of 20-50°C and water activity ranging from 0 4 to 0 99. The experimental procedure used was a gravimetric dynamic method with continuous registration of sample weight changes. Sorption capacity decreases as temperature increases. Rehydration of the dried material results in hysteresis but this phenomenon was small. Four models of equilibrium moisture content/equilibrium relative air humidity (Chung—Pfost. Halsey. Henderson, and Oswin) were evaluated for their ability to fit data for the samples of dried blood. The modified Henderson equation was a good model for moisture adsorption and desorption of dried blood flour     

MODELLING OF STRESS DEVELOPMENT DURING DRYING AND RELIEF DURING STEAMING IN PINUS RADIATA LUMBER

ABSTRACT

A one-dimensional stress model was proposed for drying of radiata pine lumber, which has considered wood moisture shrinkage, instantaneous stress-strain relationships, mechano-sorptive creep, time-induced creep and temperature effects. In addition, wood hardening behaviour in the plastic region and differences between stress increase and decrease have been taken into account. The proposed Stress model can predict stress development and relief in a drying cycle once the required wood mechanical and Theological properties have been quantified.

Drying experiments were performed to dry Pinus radiata sap wood boards of 100×40×590 mm in a tunnel dryer. In the experiment, wood temperature, moisture content gradient and residual stress through board thickness were measured. The drying cycle included HT drying, cooling and final steam conditioning. The measured stress patterns were in agreement with the model predictions. However, more accurate calculations will be made once the detailed experimental data for radiata pine wood mechanical and rheological properties are available.     

轴棒法C／C复合材料室温及高温拉伸性能研究

研究了轴棒法C／C复合材料在室温及高温下的轴向拉伸性能,并用扫描电镜观察了高温拉伸试样的断口形貌。结果表明,轴棒法C／C复合材料在室温及高温下的断裂模式不同,且高温下的拉伸强度高于室温下的拉伸强度;以常压炭化结束的C／C复合材料开孔率变大,室温及高温下的拉伸强度小于以高压炭化结束的C／C复合材料。     

Some aspects of the mechanical response of BMI 5250‐4 neat resin at 191°C: Experiment and modeling

The inelastic deformation behavior of BMI‐5250‐4 neat resin, a high‐temperature polymer, was investigated at 191°C. The effects of loading rate on monotonic stress–strain behavior as well as the effect of prior stress rate on creep behavior were explored. Positive nonlinear rate sensitivity was observed in monotonic loading. Creep response was found to be significantly influenced by prior stress rate. Effect of loading history on creep was studied in stepwise creep tests, where specimens were subjected to a constant stress rate loading followed by unloading to zero stress with intermittent creep periods during both loading and unloading. The strain‐time behavior was strongly influenced by prior deformation history. Negative creep was observed on the unloading path. In addition, the behavior of the material was characterized in terms of a nonlinear viscoelastic model by means of creep and recovery tests at 191°C. The model was employed to predict the response of the material under monotonic loading/unloading and multi‐step load histories. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Effects of prior aging at 288°C in argon environment on time‐dependent deformation behavior of a thermoset polymer at elevated temperature,part 1: Experiments

The inelastic deformation behavior of PMR‐15 neat resin, a high‐temperature thermoset polymer, aged at 288°C in argon environment for up to 2000 h was investigated. The experimental program was designed to explore the in?uence of prior isothermal aging on monotonic loading and unloading at various strain rates. In addition, the relaxation response and the creep behavior of specimens subjected to prior aging of various durations were evaluated. All tests were performed at 288°C. The time‐dependent mechanical behavior of the PMR‐15 polymer is strongly influenced by prior isothermal aging. The elastic modulus increased and the departure from quasi‐linear behavior was delayed with prior aging time. Stress levels in the region of inelastic flow increased with prior aging time. Furthermore, prior aging significantly decreased the polymer's capacity for inelastic straining, including the material's capacity to accumulate creep strain. Conversely, the relaxation response was not affected by the prior aging. © 2009 Wiley Periodicals, Inc.? J Appl Polym Sci, 2009     

Experimental study on critical breakage stress of float glass with different thicknesses under conditions with temperatures of 25 and 200°C

The objective of this study is to directly measure the critical breakage stress for glass through mechanical tensile experiments based on MTS 810 apparatus. Two series of experiments were, respectively, conducted under the condition with a room temperature (25°C) and a hot environment (200°C) for float glass. The results show that the critical breakage stresses of 6, 8, 10 and 12 mm float glass are, respectively, 74, 127, 158 and 198% larger than that of 4 mm float glass under the condition with a room temperature (25°C). Similarly, the critical breakage stresses of 6, 10 and 12 mm float glass are, respectively, 29, 72 and 93% larger than 4 mm glass in the hot environment (200°C). In addition, through the comparison between the two series of experiments, it suggests that the critical breakage stresses of 6, 8, 10 and 12 mm thick float glass in a hot environment are, respectively, 7, 48, 16 and 19% smaller than that in a room temperature. It is suggested that the measured critical breakage stress of float glass here is relatively smaller than those in the previous measurements. Copyright © 2010 John Wiley & Sons, Ltd.