Load and temperature interaction modeling of fatigue crack growth in a Ni-base superalloy

An approach was developed to predict the thermo-mechanical fatigue crack growth rates under typical gas turbine engine spectrum loading conditions. The material studied in the development of this model was a polycrystalline superalloy, Inconel 100. Load interaction effects were determined to have a major effect on the crack growth life. A yield zone load interaction life prediction model was modified to include temperature dependent properties. Multiple overload effects were included in the model to incorporate enhanced retardation compared to single overload retardation behavior. Temperature interaction effects were included and proved to be very important because of the wide temperature ranges to which turbine engine components are subjected. The effects of oxidation and temperature changes were accounted for in the model by accelerating crack growth in regions that had been previously affected by elevated temperatures. Experimental data of isolated, first order effects were used to calibrate and verify the model. Temperature dependent mechanical properties were determined and were essential in the model’s development. Parametric studies were performed using this model to assess the sensitivity of specific crack growth variables on life predictions.     

CVI工艺建模研究进展

CVI工艺是制备碳基及陶瓷基复合材料的重要工艺.本文利用系统建模思想对CVI工艺模拟研究进行了综述和分析,归纳总结了三类CVI工艺模型:机理模型,辩识模型和定性推理模型;机理模型从传质传热、沉积动力学和孔隙演变三个方面进行了分析和总结,同时,分析CVI工艺三类模型存在的不足,并指出了进一步努力的方向.     

蓄能器在舰船液压操舵系统中抗冲击作用仿真

在介绍基于Modelica语言和规范的多领域物理统一建模工具MWorks的基础上,进一步对其采用的蓄能器数学模型的形式进行归纳,给出在仿真过程中采用的蓄能器的基本模型、改进模型以及关于时间常数[τ]的讨论。在以往建立的舰船液压操舵系统的仿真模型中,增加蓄能器模型,进行两种模型中换向阀进、出口压力值的对比。仿真结果表明,蓄能器在系统中起到抗液压冲击的作用,能够大大降低系统换向时阀口的压力峰值。     

Scatchard-Hildebrand热力学模型在PA印刷层迁移预测中的应用

目的探讨Scatchard-Hildebrand热力学模型对塑料印刷层中有害物质迁移分配系数预测的适用性和准确性。方法以聚酰胺(PA)印刷层中5种迁移物为代表,选取相关文献中PA印刷层中有害物质向不同模拟液中迁移的实验测试结果数据,对分配系数实验值Fexp与模型预测计算值Fsim作对比分析,并用实验数据对Scatchard-Hildebrand统计热力学模型进行校正,研究了模型修正系数Ks(Ks=ln(Fsim/Fexp))与迁移物相对分子质量(M)及其醇-水分配系数(log P)以及模拟液极性(Ps)间的关系。结果 PA印刷层中有害物质迁移分配系数的预测模型修正系数Ks与M和Ps间呈现显著的线性关系,得到了修正后的分配系数预测模型。结论修正后的Scatchard-Hildebrand热力学模型对预测塑料PA印刷层中有害物质迁移分配系数具有一定的适用性。     

Latent risk and trend models for the evolution of annual fatality numbers in 30 European countries

In this paper a unified methodology is presented for the modelling of the evolution of road safety in 30 European countries. For each country, annual data of the best available exposure indicator and of the number of fatalities were simultaneously analysed with the bivariate latent risk time series model. This model is based on the assumption that the amount of exposure and the number of fatalities are intrinsically related. It captures the dynamic evolution in the fatalities as the product of the dynamic evolution in two latent trends: the trend in the fatality risk and the trend in the exposure to that risk. Before applying the latent risk model to the different countries it was first investigated and tested whether the exposure indicator at hand and the fatalities in each country were in fact related at all. If they were, the latent risk model was applied to that country; if not, a univariate local linear trend model was applied to the fatalities series only, unless the latent risk time series model was found to yield better forecasts than the univariate local linear trend model. In either case, the temporal structure of the unobserved components of the optimal model was established, and structural breaks in the trends related to external events were identified and captured by adding intervention variables to the appropriate components of the model. As a final step, for each country the optimally modelled developments were projected into the future, thus yielding forecasts for the number of fatalities up to and including 2020.     

高层斜交网格结构体系的性能研究

为研究钢管混凝土柱的轴向恢复力模型,设计制作了8个钢管混凝土柱试件并对其进行轴向往复加载,分析其受力机理和恢复力特性。基于试验结果,选用退化三线型模型,建立了钢管混凝土柱无量纲骨架曲线模型,并提出其轴拉与轴压方向的峰值承载力和位移的计算方法。鉴于钢管混凝土试件在轴拉与轴压方向受力机理的差异,对滞回曲线的正负向选用不同的滞回规则,建立了相应的卸载刚度函数。据此提出了钢管混凝土柱的轴向恢复力模型,并与试验滞回曲线进行对比,验证了恢复力模型的合理性,所建立的恢复力模型可为斜交网格结构体系的弹塑性分析提供依据。     

Structural modeling of contrast sensitivity in adulthood.

Structural equation modeling was used to assess the utility of the sensorineural model of contrast sensitivity proposed by Sekuler et al. [Vision Res. 24, 689 (1984)] to account for spatial vision in adulthood. In Study 1, visual acuity and contrast sensitivity (1.5-18 c/deg) were measured in 84 people between the ages of 19 and 81 yr. No three-filter model fitted the data well. Although a two-filter model was associated with good fit indices, parameter estimates for both filters were inconsistent with physiological and behavioral data. In Study 2, acuity and contrast sensitivity (1.5-18 c/deg) were assessed in 95 observers between the ages of 23 and 73 yr. All measures were gathered once per month over a three-month period. The Sekuler et al. three-filter model did not fit the data from any time of measure, but a two-filter, bandpass model provided a consistent and excellent fit for all three waves. The model suggests that age-related change in the neural mechanisms underlying contrast sensitivity is minimal once acuity is controlled. Discrepancies between this conclusion and that reported by Sekuler et al. may be related to test type, psychophysical method, reliability, and sample selection.     

A New Analysis of Hydrogen Diffusion in Metals with Trapping

A new model of hydrogen diffusion in metalshas been developed,it is more efficient todescribe the hydrogen diffusion with trappingin metals.In the model newly developed an impli-cit dependence on time of hydrogen diffusioncoefficient in metals with trapping was firstlybuilt and it is shown that hydrogen diffusioncoefficient will be different at different posi-tions in a dynamic process of hydrogen diffusionin a metal.Numerical solutions of the present modelwere obtained by finite difference method.Bychanging the parameters in the model the diffusionof hydrogen in a metal and the effect of trappingwere described and discussed.And the comparisonbetween the well known McNabb and Foster's modeland the present model was also made.     

Moisture diffusion in composite sandwich structures

The mechanical properties of polymer core materials in sandwich structures are often degraded by moisture that is absorbed during storage. To date, there is no reliable model to predict the amount of moisture that is present in these sandwich core materials. A multi-layer diffusion model applicable to these sandwich structures is described in this report. Inputs to this model are: (1) diffusivities of core and face sheet materials as functions of temperature, (2) moisture saturation data as a function of relative humidity, and (3) sandwich structure exposure history. The output is a prediction of the amounts of moisture in the core material and face sheets as a function of time.

In order to validate this model, moisture diffusion experiments were performed on a sandwich material consisting of graphite–epoxy face sheets and a core of Rohacell^® polymethacrylimide 200WF foam. Samples of this material were dried, and then hydrated at either 32 °C or 65 °C at either 83% or 100% relative humidity. The face sheets were separated from the core and each component was weighed, dried, and weighed again in order to determine the moisture distribution in the sandwich structure. The results were then compared with the model predictions.     

论模型制作及在工业设计中的应用

通过从不同材料和各个设计过程等方面对模型进行分析,探讨不同类型的模型对工业设计的作用,使设计师能全面了解模型的意义及内涵,更好地把握模型制作这一重要设计过程,从而提高自身的综合素质和设计能力,共同推进工业设计的研发过程,促进设计的整体发展.     

Model for practical prediction of natural carbonation in reinforced concrete: Part 1-formulation

A model is proposed for prediction of natural carbonation in reinforced concrete (RC) structures, and is potentially applicable to existing and new RC structures. The major components of the model comprise mathematical functions applied to predict the influence of concrete composition, and environmental factors on natural carbonation.This paper introduces the model concept and explains its structure including derivation, optimization and calibration. Over 163 data sets taken from a 10-year carbonation study were used in the model development and calibration. Only the experimental data that were based on outdoor natural exposure environment were employed in this research. Also in this study, the proposed model is compared with fib-Model Code 2010 using carbonation predictions generated from 346 data sets involving real world, highway structures. It is shown that the proposed model is comparably accurate and involves mainly basic tests with no major anticipated costs.     

Influencing factors for railroad-highway grade crossing accidents in Florida

Multiple regression was used to investigate the influence of physical factors on accident rates at 1,140 rail-highway grade crossings in Florida. Selection of the final model involved examination of residuals, transformation of variables. dummy variables and interaction terms. Variables in the final model were functions of average daily traffic, type of crossing protection, maximum train speed, trains per day. crossing speed limit, and number of lanes of traffic. Transformations were made to return estimates to the original scale of the data. Suggestions were made for improving the model and the data.     

Statistical modeling of fatigue crack growth rate in pre-strained 7475-T7351 aluminum alloy

In this study, 7475-T7351 aluminum strips were subjected to two tensile pre-strain levels of 3% and 5%. Using compact tension C(T) specimens, fatigue crack growth tests were conducted under constant amplitude loading at stress ratios of 0.1 and 0.5 in air and at room temperature. Three fatigue crack growth rate (FCGR) models, namely, Collipriest, Priddle, and NASGRO were examined. To handle the effect of stress ratio on FCGR, Walker equivalent stress intensity factor model was used. Consequently, generalized Collipriest (GC), generalized Priddle (GP), and generalized NASGRO (GN) models were developed and fitted to the FCGR data. It was shown that both GC and GP models fit the FCGR data in a similar fashion. However, the GP model provided a better fit than the GC model. The GN model was found to be the most appropriate model for the data. Therefore, this model may be suggested for use in critical applications, such as aeronautical structural design.     

A nonlinear contact algorithm predicting facet joint contribution in the lumbar spine of a specific person

The objective of this study was to realistically include the effect of facet loading in an EMG-assisted lumbar biomechanical model. Most biomechanical models lack detailed facet geometry, the inclusion of cartilage, and fail to model the full lumbar spine. Several new facet-specific components were added to an EMG-assisted biomechanical model, including realistic geometry and facet-specific contact algorithms. These algorithms defined nonlinear contact between each lumbar spine facet. Subject-specific data were applied to the model for assessment. As expected, resultant disc loads were generally lower in the model with facets. This information improves our understanding of how loads are distributed in the spine, and it can lead to a better understanding of causal pathways. If we understand those pathways, we then realise how to design better ergonomic interventions.     

Effective Thermal Conductivity in a Radial-Flow Packed-Bed Reactor

In this work a theoretical and experimental study of the heat transfer process in a radial flow reactor was carried out under steady- and non-steady-state conditions in order to determine the effective thermal conductivity (k _e). One of the mathematical models proposed was a pseudohomogeneous model in which the effective thermal conductivity varies with radial position. The second model studied was a two-phase model with different thermal conductivities for gas and solid. For the pseudohomogeneous model, an analytical solution was obtained using the method of separation of variables and series approximation. In the two-phase model, the gas and solid temperature profiles were obtained by two numerical methods: orthogonal collocation and Runge–Kutta. Several experiments were performed by changing particle diameter, gas flow and temperature input, and reactor size and time-operation condition: steady and nonsteady. Theoretical results were compared with experimental data in order to calculate the effective thermal conductivity. The values of k _e agree in general with the literature data. At low Reynolds numbers there is no appreciable difference between a pseudohomogeneous model and a two-phase equation model. Constant thermal properties can be used at Re;5 with enough accuracy to predict the thermal behavior of a radial-flow reactor.     

3D打印技术在展示设计模型定制化中的应用研究

目的 对3D打印技术在展示设计模型定制化中的应用进行探讨与研究,总结具体实施方法,达到普及3D打印技术并将其服务于展示设计模型定制化的目的。方法 本文采用调查法、观察法、实验法。调研3D打印技术及相关服务行业,了解模型制作在展示设计专业起到的关键性作用,以及传统展示设计模型制作的局限和不足。以3D打印技术为基础,观察、分析该技术在展示设计模型定制化中的优势特征;通过在展示设计的作品中运用三维数字建模结合3D打印技术的方法,定制了用传统模型制作方式几乎无法实现的,有大量弧度曲度的复杂造型的模型,总结出定制化设计的程序方法。结论 3D打印技术拓展了模型定制化的视觉效果和精细程度,让展示设计模型摆脱了传统制作手段繁琐的束缚,体现出制作工序简单、使用方便快捷、造型精准、成本可控等优势特征,因此3D打印技术将成为展示设计模型定制化未来发展的主要形式,研究其应用具有重要的理论与实践意义。     

Feasibility of an in vitro microbiological model as an alternative to the rabbit eye model.

Ocular inserts of gentamicin sulfate with polyvinyl alcohol (PVA) 1.5%, 2.0%, and 2.5% and a combination of methyl cellulose 2% and Eudragit NE 30D 30%, 35%, and 40% w/w of methyl cellulose were fabricated by a casting technique. The inserts were sterilized by gamma radiation at 25 kGy and tested for sterility. The microbiological efficacy of the ocular inserts against Staphylococcus aureus ATCC 6538P and Pseudomonas aeruginosa NCIM 2200 was evaluated by developing an in vitro microbiological model and an in vivo noninvasive rabbit eye model. Parameters of the in vitro microbiological model were varied, and the results correlated with a noninvasive rabbit eye model. The in vitro model proved to be a viable alternative to the rabbit eye model in evaluating the microbiological efficacy of gentamicin sulfate ocular inserts.     

The stribeck curve in cold flat rolling

Cold flat rolling of lubricated steel strips was studied. The three-component system of rolling - the mill, the rolled strip and their interface - was analyzed using a two-step mathematical model, a 1D model and flat rolling experiments. The utilized experimental data have been taken from McConnell and Lenard [1]. The objective of the study was the examination of the interactions of the three components and the development of the Stribeck curve. In the first part of the work, a two-dimensional finite element model was used in which the elastic deformation of the work roll and the elastic–plastic deformation of the strip were considered. Special attention was paid to the events at the lubricated interface where an upgraded version of Levanov’s model was utilized. The model was developed to analyze the local variables at the roll-strip interface. The parameters of the model were determined in an iterative manner, minimizing the differences of the measured and computed roll force and torque. Thus, the relative velocity between the roll and the strip, the roll pressure, the interfacial shear stress and the temperature were obtained. The effect of the temperature on the material parameters of the constitutive equations was also taken into account. Another model was then employed to consider the effects of the local variables on the lubricant’s viscosity. These were then used to obtain the local values of the Sommerfeld number, which in turn led to its average value and to the traditional shape of the Stribeck curve. Further, a simple 1D model of the flat rolling process was also tested for its ability to lead to the Stribeck curve. It was concluded that while both advanced and simple models allowed the development of the curve, removing the simplifying assumptions yielded a more reliable plot.     

Productivity enhancement strategies in North American automotive industry

The aim of this study is to define a robust estimation model of the most dominant labour productivity measurement, Hours per Vehicle (HPV), in the auto industry. Data utilised in this study were from 10 different multinational North American carmakers from 1999 to 2007. Through a comprehensive literature review and practical consideration, 13 important variables that affect HPV were defined and developed. Several robust and advanced statistical methods were utilised to determine the best possible HPV regression equations. The MM estimator, multiple M-estimator, was defined as the best method to perform the data analysis and to derive the robust regression model to estimate HPV. Depending on the car class, the vehicle variety, model types, annual working days, car assembly utilisation and launching a new model penalise HPV; however, annual production volume, flexible manufacturing and year of production improve HPV. Moreover, Japanese plants are the benchmark regarding HPV followed by joint ventures, and American plants.