Intermittent drying of initially saturated porous materials

The aim of this paper is to examine the advantages of convective non-stationary (intermittent) drying and the possibility of its application to materials susceptible to crack formation (wood and ceramics). The notion “non-stationary” means here drying with periodically changeable parameters (air temperature and humidity). The drying time, energy consumption, and quality of dried samples are examined at different schedules of intermittent drying. The acoustic emission (AE) method is applied to monitor on line the material behavior and to detect the commencement of material cracking, and thus to find the moment at which the changes in drying conditions should be initiated. The mathematical model is developed to describe and imitate the intermittent drying kinetics determined experimentally. This model is used next for numerical calculation of the net energy used for drying, and to compare it with the measured total electric energy consumption. The tests were carried out on cylindrically shaped samples of wood and kaolin-clay. The benefits of non-stationary drying with respect to that performed in constant conditions were assessed. Such a formulated subject is a novelty in drying area.     

A study on drying models and internal stresses of the rice kernel during infrared drying

Due to the limited penetration of infrared, it is very difficult to develop an infrared drying model of rice kernels. In this study, two kinds of simplified drying models, which assumed the penetration depth is infinity and zero, were developed to investigate the effects of penetration on drying characteristics of thin layer infrared drying. The results show each model can predict temperature and moisture contents (MC) accurately. The maximum temperature difference of rice kernels in both models was always less than 1.5°C, so it is reasonable to exclude the influence of thermal stresses due to nonuniform temperature. This study also developed the internal stresses model with the mechanical properties from literatures. Mechanical properties were with the changes of temperature and MC. These models were solved with COMSOL Multiphysics and there are two stress concentration areas. One is near the surface of the endosperm, another close to the center. Comparison between the von Mises stress distribution and the moisture gradient was made after the simulation. The maximum MC in the endosperm appeared at its surface, which reached 190 1/m at 110?s, and the maximum stress appeared at the same place, which, a little later, reached 7?MPa at 160?s. Moisture gradient at the center was zero due to the existence of symmetry, while there was a significant stress, which reached 3.2?MPa during drying.     

Mechanical Effects in Saturated Capillary-Porous Materials during Convective and Microwave Drying

The differences are analyzed in distribution and time evolution of the temperature, moisture content, and drying-induced stresses generated by convective and microwave drying. The theoretical analysis of the drying induced stresses and the deformations of dried materials is based on the elastic and viscoelastic constitutive models. The theoretical predictions are confronted with the experimental data obtained by the acoustic emission (AE) method, which enable monitoring on line the development of the drying induced stresses. The system of double coupled differential equations of the thermomechanical drying model is solved numerically using the finite element (FEM) and the finite difference (FDM) methods. A cylindrical sample made of kaolin was chosen to compare experimental data with the model solution. Essential differences were identified in the analyzed items for convective and microwave drying as well as a significant difference in stress distribution was noted for elastic and viscoelastic constitutive models.     

Comparison of the viscous and elastic components of two ABS materials with creep,stress relaxation and constant strain rate measurements using the universal viscoelastic model

In general, the universal viscoelastic model evaluated in this study was found to adequately predict constant strain rate, creep, and/or stress relaxation measurements from the constants determined from constant strain rate measurements. The elastic and viscous components for two acrylonitrile–butadiene–styrene (ABS) viscoelastic materials were also easily isolated using this new universal viscoelastic model. The creep measurements for ABS‐A (25383‐A) and ABS‐N (LL‐4102‐N) at three different stresses allowed elucidation of the common creep intercept strain of the calculated creep slopes that was designated as the “projected elastic limit.” Once the values for n and β were evaluated from creep measurements, then the creep variation of the universal viscoelastic model yielded a reasonably good fit of the measured creep data for both ABS‐A and ABS‐N. The extensional viscosity constant λ_E was found to be 7.2% greater for ABS‐A than for ABS‐N. Consequently, ABS‐N was found to have a lower extensional viscosity in secondary creep than that of ABS‐A at any specific strain rate. The value of the efficiency of yield energy dissipation n for ABS‐N as determined from creep measurements was also 37.6% larger than the value of n for ABS‐A. In addition, the projected elastic limit ?_I for ABS‐A was 2% greater than the projected elastic limit for ABS‐N. These observations indicated that ABS‐A should be slightly more solidlike than ABS‐N. However, both ABS‐A and ABS‐N were significantly more solidlike than liquidlike because both of their values for the efficiency of yield energy dissipation n were very close to zero. In general, values of n range from 0 < n < 1 with a material characterized as being essentially pure elastic having a value of n = 0. Using the yield strain as the failure condition for constant strain rate and stress relaxation measurements and the strain at critical creep, the failure condition for creep, it was found that the universal viscoelastic model allowed these failure criteria to yield remarkably good agreement on a projected time scale. This agreement resulted even though separate and independent data were used to evaluate these three different techniques for both ABS‐A and ABS‐N. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 90: 1298–1318, 2003     

Analysis of the development of isotropic residual stresses in a bismaleimide/spiro orthocarbonate thermosetting resin for composite materials

In this article, we extend our model of isotropic residual stress development in thermosets to a novel thermosetting resin system: bismaleimide/spiro orthocarbonate. In this system, the cure shrinkage and resulting isotropic residual stresses are reduced through a ring‐opening reaction that occurs independently of the addition reaction. The modeling effort includes a parametric analysis of the effects of various parameters, including the volume changes involved in the reactions, the relative rates and orders of the reactions, the cure history, and the values of the bulk moduli and thermal expansion coefficients. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 88: 227–244, 2003     

Damage and failure analysis of a SiCf/SiC ceramic matrix composite using digital image correlation and acoustic emission

The analysis of failure behaviors of continuous fiber-reinforced ceramic matrix composites (CMCs) requires the characterization of the damage evolution process. In service environments, CMCs exhibit complex damage mechanisms and failure modes, which are affected by constituent materials, meso architecture, inherent defects, and loading conditions. In this paper, the in-plane tensile mechanical behavior of a plain woven SiC_f/SiC CMC was investigated, and damage evolution and failure process were studied in detail by digital image correlation (DIC) and acoustic emission (AE) methods. The results show that: the initiation of macro-matrix cracks have obvious local characteristic, and the propagation paths are periodically distributed on the material surface; different damage modes (matrix cracking and fiber fracture) would affect the AE energy signal and can be observed in real-time; the significant increase of AE accumulated energy indicates that serious damage occurs inside the material, and the macroscopic mechanical behavior exhibits nonlinear characteristic, which corresponds to the proportional limit stress (PLS) of the material.     

Mechanical properties of thin and thick coatings applied to various substrates. Part II. Young's modulus determination of coating materials*

To determine Young's modulus of coating materials when they are applied to substrates, theoretical and experimental analyses are performed. Significant residual stresses are generated within thin and thick coatings applied to substrates. As a result of these stresses, the bi-material strip assumes a certain curvature. The curved beam theory was used to establish the equivalent bending stiffness of bi-layer materials as functions of (a) the initial radius of curvature generated by residual stresses, (b) the mechanical radius of curvature during flexure testing, and (c) mechanical (Young's moduli) and geometrical (widths and thicknesses) characteristics of bi-layered systems. The relevant expression was transformed to a second- or third-order equation in order to calculate Young's modulus of the coating undergoing residual stresses (using models developed in Part I and by Stoney, Röll, and Inoue).     

Numerical simulations of flow behavior of gas and particles in spouted beds using frictional-kinetic stresses model

Flow behavior of gas and particles is simulated in the spouted beds using a Eulerian-Eulerian two-fluid model on the basis of kinetic theory of granular flow. The kinetic-frictional constitutive model for dense assemblies of solids is incorporated. The kinetic stress is modeled using the kinetic theory of granular flow, while the friction stress is from the combination of the normal frictional stress model proposed by Johnson and Jackson (1987) and the frictional shear viscosity model proposed by Schaeffer (1987) to account for strain rate fluctuations and slow relaxation of the assembly to the yield surface. An inverse tangent function is used to provide a smooth transitioning from the plastic and viscous regimes. The distributions of concentration, velocity and granular temperature of particles are obtained in the spouted bed. Calculated particle velocities and concentrations in spouted beds are in agreement with the experimental data obtained by He et al. (1994a, b). Simulated results indicate that flow behavior of particles is affected by the concentration of the transition point in spouted beds.     

Yield in Adhesive Joints and Design of Zones with Constant Elastic Shear Stresses

Yield in adhesive joints has been investigated by several scientists among whom L. J. Hart-Smith¹ especially is to be mentioned.

In the following, a method is demonstrated which is based on a simple elastic-plastic model. It shows the distribution of stresses in the adhesive and gives a total picture of the development of the length of the yield zones and their strain as a function of load.

Methods are given for the design of adhesive joints with constant elastic shear stresses at their ends or throughout their whole length. These stresses are obtained by varying the thickness of the adherends, the adhesive, or a combination of both. The constant elastic shear stress zones can be designed to take into consideration all known factors as temperature and hardening stresses, moments, etc. The characteristic yield properties as well as internal stresses after yield and unloading are determined together with the modified stress distribution for a new load.     

Antioxidative and Anti-Inflammatory Activities of Chrysin and Naringenin in a Drug-Induced Bone Loss Model in Rats

Oxidative stress (OS) mediators, together with the inflammatory processes, are considered as threatening factors for bone health. The aim of this study was to investigate effects of flavonoids naringenin and chrysin on OS, inflammation, and bone degradation in retinoic acid (13cRA)-induced secondary osteoporosis (OP) in rats. We analysed changes in body and uterine weight, biochemical bone parameters (bone mineral density (BMD), bone mineral content (BMC), markers of bone turnover), bone geometry parameters, bone histology, OS parameters, biochemical and haematological parameters, and levels of inflammatory cytokines. Osteoporotic rats had reduced bone Ca and P levels, BMD, BMC, and expression of markers of bone turnover, and increased values of serum enzymes alkaline phosphatase (ALP) and lactate dehydrogenase (LDH). Malondialdehyde (MDA) production in liver, kidney, and ovary was increased, while the glutathione (GSH) content and activities of antioxidant enzymes were reduced and accompanied with the enhanced release of inflammatory mediators TNF-α, IL-1β, IL-6, and RANTES chemokine (regulated on activation normal T cell expressed and secreted) in serum. Treatment with chrysin or naringenin improved bone quality, reduced bone resorption, and bone mineral deposition, although with a lower efficacy compared with alendronate. However, flavonoids exhibited more pronounced antioxidative, anti-inflammatory and phytoestrogenic activities, indicating their great potential in attenuating bone loss and prevention of OP.     

Nonlinear stress relaxation in palladium(II) complexes with triblock copolymers of styrene and butadiene

Above 200% strain, the mechanical response of triblock copolymers which contain styrene and butadiene is modified significantly by complexation with dichlorobis(acetonitrile)palladium(II). This pseudosquare‐planar transition metal salt forms π‐complexes with, and catalyzes the dimerization of, alkene groups in the main chain and the side group of Kraton's butadiene midblock. Between 10 and 100% strain, the plastic flow regime is similar for undiluted Kraton? and its Pd²⁺ complexes, but the level of engineering stress is approximately twofold larger for the complex that contains 4 mol % palladium(II) [Pd(II)]. Nonlinear stress relaxation measurements in the plastic flow regime (i.e., beyond the yield point but before the large upturn in stress) are analyzed at several different levels of strain. Transient relaxation moduli were modeled by a three‐parameter biexponential decay with two viscoelastic time constants. The longer relaxation time for Kraton? increases at higher strain, and in the presence of 4 mol % palladium chloride. A phenomenological model is proposed to describe the effect of strain on relaxation times. This model is consistent with the fact that greater length scales are required for cooperative segmental reorganization at larger strain. The resistance Ω to conformational reorganization during stress relaxation is estimated via integration of the normalized relaxation modulus versus time data. This resistance increases at higher initial jump strain because conformational rearrangements are influenced strongly by knots and entanglements at larger strain. The effect of strain on Ω is analyzed in terms of time‐strain separability of the relaxation modulus. Linear behavior is observed for Ω versus inverse strain (i.e., 1/ε), and the magnitude of the slope [i.e., ?dΩ/d(1/ε)] is threefold larger in the absence of PdCl₂(CH₃CN)₂. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 93: 1329–1336, 2004     

壳牌煤气化磨煤干燥系统设备故障分析及处理

神华煤直接液化项目采用壳牌煤气化装置。介绍了壳牌煤气化装置磨煤干燥系统的工艺原理和工艺流程;分析了磨煤机、称重给料机、循环风机、助燃空气风机、煤粉收集器、碎煤仓的故障原因,提出了相应的处理措施和技改方案。     

防氧化脱碳涂料对钢铁材料热处理的保护研究

分别研究了硅酸盐防氧化脱碳涂料对45#钢和40Cr钢热处理时的保护效果。1 100℃下保温时间对钢样氧化失重率的影响实验表明,随着保温时间的延长,无涂料保护的钢样的氧化失重率迅速增大,但有涂料保护的钢样其氧化失重率变化不大。钢样经1 100℃×2 h热处理后油淬的金相照片显示,45#钢的氧化脱碳程度比40Cr钢更严重,而有涂料保护的钢样其氧化脱碳作用明显减少。经过860℃×4 h与1 100℃×4 h热处理后淬火脱落的涂层其截面SEM形貌显示,涂层的内侧出现较厚的致密层,并呈明显的烧结状态,由能谱分析可知,它应为基体上的氧化膜或氧化膜与涂层成分的反应产物。初步探讨了涂料的防护原理,指出涂层不能避免钢样氧化,而轻微氧化形成的氧化膜能与涂层成分反应形成复杂的氧化物,从而达到较好的防护效果。     

The Effect of Superimposed Dynamic and Static Stresses on the Stress Relaxation Rates of Model Epoxy Resins

Model epoxy resins with controlled crosslinking densities were prepared from a commercially available DGEBA (Epon Resin 825® from Shell Chemical) and α,ω-aliphatic diamines having different lengths of the aliphatic chain. The mixtures were always prepared in stoichiometric ratio. Dumbbell specimens, either with a cylindrical (with thin walls) or a rectangular cross section, have been subjected to combined static tensile strains (applied vertically) and dynamic torsional strains (applied horizontally). The experiments were performed at temperatures encompassing the glassy and the rubbery range of each investigated resin. The apparatus, by which the combined dynamic and static stresses were applied, was equipped with load cells for measurement of stresses developed in the specimens, both in tension and in shear. In this paper, results concerning the effect of the above combinations of stresses on stress relaxation rates in tension are shown. The main conclusion of this study is that combinations of dynamic and static stresses affect the network chain mobility, as it is expressed by the stress relaxation rate, in a way depending on temperature and frequency of torsional oscillations, as well as the crosslinking density of the polymer. For the most flexible epoxy resins investigated in this work, the superimposed stressing experiments led to a stiffening of the structure in the glassy state, while an opposite effect has been observed for the most rigid resins in similar conditions. It seems that the behavior of the investigated epoxy resins in complex fields of stresses is governed by a balance between two competitive processes: free volume increase (by a strain-induced dilatation mechanism), and physical aging and short range orientation.     

N-Acetylcysteine and Aripiprazole Improve Social Behavior and Cognition and Modulate Brain BDNF Levels in a Rat Model of Schizophrenia

Treatment of negative symptoms and cognitive disorders in patients with schizophrenia is still a serious clinical problem. The aim of our study was to compare the efficacy of chronic administration of the atypical antipsychotic drug aripiprazole (7-{4-[4-(2,3-dichlorophenyl)-1-piperazinyl] butoxy}-3,4-dihydro-2(1H)-quinolinone; ARI) and the well-known antioxidant N-acetylcysteine (NAC) both in alleviating schizophrenia-like social and cognitive deficits and in reducing the decreases in the levels of the brain-derived neurotrophic factor (BDNF) in the prefrontal cortex (PFC) and hippocampus (HIP) of adult Sprague-Dawley rats, that have been induced by chronic administration of the model compound L-buthionine-(S, R)-sulfoximine (BSO) during the early postnatal development (p5–p16). ARI was administered at doses of 0.1 and 0.3 mg/kg while NAC at doses of 10 and 30 mg/kg, alone or in combination. Administration of higher doses of ARI or NAC alone, or co-treatment with lower, ineffective doses of these drugs significantly improved social and cognitive performance as assessed in behavioral tests. Both doses of NAC and 0.3 mg/kg of ARI increased the expression of BDNF mRNA in the PFC, while all doses of these drugs and their combinations enhanced the levels of BDNF protein in this brain structure. In the HIP, only 0,3 mg/kg ARI increased the levels of both BDNF mRNA and its protein. These data show that in the rat BSO-induced neurodevelopmental model of schizophrenia, ARI and NAC differently modulated BDNF levels in the PFC and HIP.     

Comparison Between Experimental and Theoretical Analysis of Stress Distribution in Adhesively-Bonded Joints: Tenon and Mortise Joints and Single-Lap Joints

We have studied the agreement between theoretical computations and experimental results of surface strains of bonded joints of two types: tenon and mortise, and single-lap joints, for different lengths of the lap. For instance, with the single-lap joint, we have tested four lengths of the overlap from 14 mm to 88 mm. Surface strains are measured by an extensometrical method with electrical gauges, when the specimen is loaded in uniaxial traction on a universal testing machine.

Experimental results and computations made by an improved method, such as the asymptotic expansions method, agree but only if the global traction load applied on the specimen is low, or if the overlap in respect with the others dimensions of the section of test specimen is long.

In these joints, effectively, stress fields are disrupted near the butts and become very difficult to compute. Actually, near the ends of the overlap, stresses can reach high limits with only low global load applied on the test specimen. With a short length of the overlap, linear behaviour disappears almost totally because of a strong interaction of the two perturbed fields. On the contrary, with a high length of overlap, stress fields become linear on the major part of the overlap, even with a high tensile load applied on the specimen. So, the length of the overlap has a great effect on the linear behaviour of the joint.     

高职教育校企合作运行机制模型及其现实改进

针对传统校企合作模式存在的人才培养质量不高、师资队伍发展缓慢、基地建设资源浪费以及社会认可度较低等一些列深层次的问题,利用头脑风暴法构建了基于企业发展方式转变的校企合作运行机制模型,并对要素之间的关系作了分析,最后提出了运行机制完善的相关建议。     

催化裂化装置烟机入口管线及其膨胀节事故失效分析有限元计算

针对某公司重油催化裂化装置能量回收系统中烟机入口管线上,相继发生管道、法兰、阀门等焊缝处断裂、摆式支架失衡及膨胀节断裂等失效事故,对该段管线及失效的膨胀节进行了有限元计算与分析,且提出了改进措施和建议。     

Analysis of stability of the interphase front with evaporation and exothermic reaction in the porous catalyst slab

Using a two-dimensional mathematical model and a number of simplifying assumptions, the analytical (linear) analysis of stability of the reaction-evaporation front inside the half-wetted porous catalyst slab was made. Based on the obtained spectral equation, the effect of different parameters on possible types of instability was studied.