Accelerated characterization of a chopped fiber composite using a strain energy failure criterion

The creep and creep rupture response of a chopped fiber composite material (SMC-R50) were investigated experimentally and analytically. The goal of this research was to use the short time laboratory data to predict long time creep and creep rupture behavior. The creep response data up to 200 min duration were obtained at various constant temperature and stress levels. The short time creep data were then modeled using a modified power law equation. The modified power law equation contains the parameters of the so-called accelerated characterization procedure. Using this power law equation, the short time creep response at the elevated temperatures were able to successfully predict the long time creep response at a lower temperature and stress level. To predict the creep rupture behavior, the modified power law equation was then coupled with a strain energy based failure criterion. It was found that the same parameters that were used in the prediction of the long-time creep response can also be used to predict the creep rupture. At a given temperature level, the strain energy density related to creep rupture was found to be a constant. Furthermore, this strain energy density was found to increase with an increase in temperature. With a limited amount of data, it was found that the strain energy based failure criterion coupled with the modified power law equation can be used to predict long time creep rupture behavior.     

Coupling of dry matter and nitrogen accumulation in ryegrass

The logistic model has proven very useful in relating dry matter production of warm season perennial forage grasses to applied nitrogen. A recent extension of the model coupled dry matter and plant N accumulation through a common response coefficient c. The objective of this analysis was to apply the extended logistic model to cool season Gulf annual ryegrass (Lolium multiflorum Lam.) and to establish a common response coefficient c between accumulation of dry matter and plant N. Analysis of variance established the validity of this hypothesis. The model accurately described response of dry matter, plant N removal, and plant N concentration to applied N, with an overall correlation coefficient of 0.9954. Furthermore, the model closely described the relationship between yield and plant N removal, as well as between plant N concentration and plant N removal. The logistic equation is well-behaved and simple to use on a pocket calculator. It can be used to estimate yields and plant N removal in evaluation of agricultural production and environmental quality.     

Compression-Permeability Properties of Compressed Bed of Superabsorbent Hydrogel Particles

The average pore size of the gel network of a superabsorbent hydrogel particle was evaluated based on the data of the permeation rate of water through the compressed bed of gels obtained with the use of a compression-permeability cell (C-P cell). The pore size evaluated based on the Happel's cell model using the C-P cell data was compared with that obtained from the Kozeny-Carman equation in which the Kozeny constant k was assumed to be 5.0. It was clarified that the use of k = 5.0 in Kozeny-Carman equation underestimated the pore size compared to the calculations using the Happel's cell model. Moreover, the effect of bound water in the gel was clarified.     

阶跃与方波示踪法测量气体的有效扩散系数

建立阶跃与方波示踪测量气体有效扩散系数的实验装置,并提出了扩散系数计算中所涉及的超越方程特征根的求解方法。采用稳态法,脉冲、方波和阶跃示踪动态法测量气体的有效扩散系数,对以扩散池为主体的各种实验方法进行评价。实验结果表明,当颗粒内的孔隙主要由大孔构成时,各种方法所得结果相近。阶跃与方波示踪法可以可靠地用来测量气体的有效扩散系数。     

卧式双轴T型搅拌器在非牛顿流体中的搅拌功率特性

考察了卧式双轴Ｔ型搅拌在非牛顿流体中的搅拌功率与表观雷诺数（Ｒｅ＾＊）、弗劳德数（Ｆｒ）以及加料量的变化关系,实验结果表明：Ｍｅｔｚｎｅｒ常数Ｋｓ随加料量的减少而急剧增加;在层流区域,Ｎｐ．Ｒｅ＝Ｋｐ关系仍然成立且非牛顿流体功率曲线与牛顿流体重合。对实验数据进行关联得到了非牛顿流体搅拌功率准数关联式。     

Compression-Permeability Properties of Compressed Bed of Superabsorbent Hydrogel Particles

The average pore size of the gel network of a superabsorbent hydrogel particle was evaluated based on the data of the permeation rate of water through the compressed bed of gels obtained with the use of a compression-permeability cell (C-P cell). The pore size evaluated based on the Happel's cell model using the C-P cell data was compared with that obtained from the Kozeny-Carman equation in which the Kozeny constant k was assumed to be 5.0. It was clarified that the use of k = 5.0 in Kozeny-Carman equation underestimated the pore size compared to the calculations using the Happel's cell model. Moreover, the effect of bound water in the gel was clarified.     

The effect of density profile on the flexural properties of structural foams

In this study, a comparison is made on the models available to predict the flexural modulus of structural polymer foams. Skin thickness and density profile in the core zone are taken into account to better relate foam morphology with mechanical response. It was found that including skin thickness is not sufficient to predict flexural moduli with high levels of precision and thus a transition zone between the skin and the core must be included. To this end, a single continuous equation is proposed to represent the complete density profile, which enabled us to predict our experimental data within 3%. POLYM. ENG. SCI., 47:1459–1468, 2007. © 2007 Society of Plastics Engineers     

卧式双轴T型搅拌器在牛顿流体中的功率消耗

以苯乙烯间规聚合反应过程为背景 ,采用卧式双轴 T型自清洁搅拌反应器 ,研究了它在牛顿流体中的搅拌功率和流型与转速、加料量的关系。实验结果表明 ,在层流区域 ,Np·Re=Kp 关系仍然成立 ,加料量对搅拌流型和搅拌功率影响较大。通过对实验数据关联得到牛顿流体功率准数关联式。     

响应曲面法优化啮合同向双螺杆挤出机固体输送段主机功率消耗和固体输送量的研究(Ⅱ)

采用响应曲面法(RSM)中Box-Behnken方法设计实验并分析,建立了啮合同向双螺杆挤出机固体输送段,单导程螺纹元件粉料输送的功率消耗和固体输送量的多因素二次多项式数学模型.探讨了主要因素对功率和输送量的影响及其交互作用.验证了模型的有效性,模型所预测的功率消耗和输送量与实验得到的数据误差小于10%.利用实验所得功...     

Fatigue life prediction of matrix dominated polymer composite materials

Fatigue life prediction is investigated analytically for matrix dominated polymer composite laminates having nonlinear stress/strain response, based on the fatigue modulus concept. Fatigue modulus degardation rate at any fatigue cycle was assumed as a power function of number of fatigue cycles. A new stress function describing the relation of initial fatigue modulus and elastic modulus was used to account for material non‐linearity at the first cycle. It was assumed that fatigue modulus at failure is proportional to the applied stress level. A new fatigue life prediction equation as a function of applied stress is proposed. The prediction was verified experimentally using cross‐ply carbon/epoxy laminate (CFRP) tube under torsional fatigue loading. It is shown that the proposed equation has wide applicability and agrees well with experimental data.     

THE RELEASE OF STRAIN IN GLASS*

Measurements of strain release¹ showed that check results were obtained only when the previous history of the samples was the same. Moreover, it was found that the release of strain was more rapid at first than could be accounted for by the equation of Adams and Williamson. This paper discusscs the effect of previous history on the measurements, describes an improved device for loading the specimens, and suggests a logarithmic equation which, in general, fits the observations better than that of Adams and Williamson. Tests of the equation are made both on data obtained from the modified apparatus described and on the data of Adams and Williamson. It is indicated that the Adams and Williamson equation gives too long an annealing time at higher temperatures and too short an annealing time at lower temperatures. It appears that the rate of release of strain depends on some power of the strain which varies from unity at high temperatures where the glass is a viscous fluid to a higher power at low temperatures where the release of strain is elastico-viscous in character. With a siugle specimen at any fixed temperature in the annealing range, however, it appears that the release of strain in various parts of the specimen takes place at a rate which is proportional to the strain, but that the rate undergoes continual change with time.     

Estimation of current efficiency in ion-exchange membrane chlor-alkali cells

A generalized current efficiency equation was derived from material balance considerations to estimate the caustic current efficiency in ion exchange chlor-alkali membrane cells taking into account the presence of NaHCO₃, Na₂CO₃, and NaOH in the feed brine. The validity and the accuracy of this equation was established by comparing the ‘gas analysis’ results with the data obtained from caustic collection measurements. It is also shown that this general expression can be easily extended to deduce the current efficiency applicable for diaphragm cell operations.     

茂金属聚乙烯交联反应挤出流动模型分析

在研究茂金属聚乙烯在双螺杆挤出机中进行的复合交联反应挤出过程流动模型时,在三参数关联流动模型中引入了第4个参数,获得了更好的停留时间分布曲线拟合效果。但是,其物理意义难以确定。为此,根据双螺杆挤出机的结构特点提出了RDBFC模型,获得了较好的拟合效果,物理意义更加合理。     

Control of stationary and transportation fuel cell systems: Progress and opportunities

Fuel cell power systems have witnessed intense development in the recent years as they offer a clean and efficient alternative for power generation in stationary and transportation applications. In this paper, we present an overview of recent work on dynamic modeling and control design for stationary and transportation fuel cell systems including the research at United Technologies Corporation.The use of equation oriented modeling framework for system level dynamic modeling enabled by tools, such as Dymola and gPROMS is described. It is demonstrated that the non-linear system level models readily allow linear model derivation and the application of advanced control analysis and design techniques that provide more insight into the system level dynamic and control issues in fuel cell systems. The dynamic modeling and advanced control design research performed at UTC for a hydrogen fed PEMFC power plant for a bus and a natural gas fed PEMFC power plant for stationary power generation is described.We also identify, for future research, the challenges and opportunities in several areas relating to fuel cell systems ranging from power management and freeze startup to system level modeling, control, diagnostics and hardware-in-the-loop validation of the control system. The emphasis is on polymer electrolyte membrane fuel cell (PEMFC) systems but phosphoric acid fuel cell (PAFC) systems are also briefly discussed.     

Characterization of the granular-to-fluid state process during mixing by power evolution in a planetary concrete mixer

Adding product into the mixer exerts a strong and rapid impact during concrete mixing. Experimental data obtained from a planetary mixer in a full-scale concrete plant under laboratory conditions show that the state of mixture progress with mixing time is well described by the mixing power evolution. More specifically, a reliable method for detecting the time corresponding to the transformation of a mixture from a cohesive granular material into a granular paste (i.e. the so-called “transition time”), through use of a mixing power measurement, will be presented herein. Moreover, once this transition has been achieved, mixing power consumption will be related to mixture rheology and then to mixer geometry by means of a simplified hypothesis. This equation can also be obtained via a dimensionless analysis. Lastly, it will be shown that mixture behavior beyond the transition point is well fitted by a hyperbolic equation. The corresponding mixing power evolution can then be predicted by the level of power at this transition time. These results are suitable for application to online process monitoring.     

分子热力学理论模型—氩模型与液体粘度的理论计算

应用张克武气体氩模型理论微分方程，导出液体粘度理论方程和“正烷烃沸点下的粘度值相同”的定理。本法以40种不同构型258种无机、有机、强缔合性的醇、酸、二醇及非极性纯质1528个实验数据检验，平均误差1．85％。其精度比著名的Van Velxen et al．法高倍以上达到实验允许误差范围内。解决了近百年来在无法精确计算的液体粘度这个技术科学上的关键难题。有重大理论意义和重要应用价值。     

Cell migration and proliferation during monolayer formation and wound healing

The interaction of living cells with surfaces is important in applications of biomaterials, such as tissue engineering. Characterising and modelling the attachment, migration and proliferation of cells on materials used for tissue engineering provides valuable insight into their potential applications as well as a means of objective comparison. In this study, proliferation and migration of NIH-3T3 fibroblast cells on tissue culture plastic in vitro were quantified. The development of randomly scattered individual cells into confluent cell monolayers proceeded with cell density following a logistic growth pattern. Travelling cell wavefronts produced in a wound healing assay were modelled with a modified Fisher equation incorporating both diffusion and logistic growth. The diffusivity and growth rates thus determined could be used for comparison with cell behaviour on other surfaces or under different conditions. Cell tracking showed that the average effective velocity of cells varied inversely with cell density, supporting contact inhibition of cell movement.     

Segregation kinetics in the rapid gravity flow of granular materials

An experimental analytical method for determining the kinetic segregation coefficient in the rapid gravity flow of a granular material down a rough incline is proposed. It is found that it is possible to predict the velocity of transverse displacement of individual large and small particles in the rapid gravity flow using a single kinetic segregation coefficient for different particle sizes and structural and kinematic characteristics of the flow. A previously proposed equation of segregation kinetics is refined, and its predictive power is analyzed.     

Modelling of performance of PEM fuel cells with conventional and interdigitated flow fields

A simple mathematical model is developed to investigate the superiority of the interdigitated flow field design over the conventional one, especially in terms of maximum power density. Darcy's equation for porous media and the standard diffusion equation with effective diffusivity are used in the gas diffuser, and a coupled boundary condition given by the Butler–Volmer equation is used at the catalyst layer interface. The performance of PEM fuel cells with a conventional flow field and an interdigitated flow field is studied with other appropriate boundary conditions. The theoretical results show that the limiting current density of a fuel cell with an interdigitated flow field is about three times the current density of a fuel cell with a conventional flow field. The results also demonstrate that the interdigitated flow field design can double the maximum power density of a PEM fuel cell. The modelling results compared well with experimental data in the literature.