Components of a Variance Model for the Analysis of Repeated Measurements in Fixed-Point Comparisons

Experimental design is a statistical tool concerned with the planning of experiments to obtain the maximum amount of information from the available resources. This tool may be applied to metrology, especially for the analysis of a large number of repeated measurements (replicates) of short-term repeatability and the medium-term and long-term reproducibilities, enabling the inclusion of these “time-dependent sources of variability” in the uncertainty budget. The realization of the International Temperature Scale of 1990 (ITS-90) scale requires that laboratories usually have more than one cell for each fixed point, for comparison on a regular basis. The calculation of the uncertainty of such comparisons is considered here, taking into account these time-dependent sources of variability. These components of the uncertainty evaluated by a Type A method are obtained by the statistical analysis of the experimental results using the components of a variance model for designs consisting of nested or hierarchical sequences of measurements, as foreseen by the mainstream GUM. An application example of a balanced nested structure in the comparison of two fixed-point cells is presented.     

Design of a composite tube to analyze the compressive behavior of CFRP

A dumbbell-shaped tube is designed in order to study the compression of composites in the direction of the fibers. Three conditions are defined that ensure the validity of the experimental procedure: the cracks appear in the middle of the specimen, the strain field is homogeneous in the gauge area, and buckling must be avoided. Several tubes are manufactured and then analyzed to verify that they satisfy these three conditions. It turns out that a [0°]₁₁ woven carbon/epoxy (G939/M18) tube reinforced with [90°] unbalanced woven glass/epoxy tabs (1055/ES18) is suitable for compression tests.The non linear elastic behavior of the material is then identified. The values of the parameters are close to those identified in a pure bending test.     

双侧延伸端板半刚性组合节点的抗震性能(1):试验研究

与钢结构相比,相同延性下,组合结构具有较高的刚度及较好的抗火性能。因此,在地震高发区大量采用组合结构。研究了双侧延伸端板半刚性组合节点的抗震性能,对节点进行单调、循环、准静力试验,以描述这种节点的抗震性能。试验包括内节点和外节点,并提供了关于节点延性、能量耗散、退化影响的实用数据。采用这些数据构建和校验基于构件的节点模型。节点由双向弹簧组成,其中一个代表剪切板的性能,另一个代表连接的性能。模型能精确模拟节点的性能及在循环荷载下的破坏形式。     

基于TRIZ和田口方法的集成化设计方法研究

为给产品创新设计提供更好的方法,在分析比较目前国外相对成熟的发明问题解决理论TRIZ与田口方法的特点及内在联系的基础上,提出了首先通过TRIZ避免创新设计方案的技术冲突,再运用田口方法选择最佳方案的产品优化设计思路,并将这一思路应用于汽车消声器优化的设计.     

Creep deformation and damage evaluation of service exposed reformer tube

Abstract

This paper aims at studying the creep deformation behaviour and quantifying creep damage of ～11 years service exposed primary hydrogen reformer tube made of HP40 grade of steel in a petrochemical industry, in terms of Kachanov’s continuum damage mechanics model (K model) and Bogdanoff model (B model) based on Markov process. Hot tensile, conventional creep deformation under identical test conditions, optical microscopy and fractography were extensively carried out. The as received tubes did not possess any sign of degradation including voids or creep cavitations and decarburisation. There was indeed loss of tensile strength from room temperature to 870°C for the bottom portion of the tube due to aging and overheating. Accumulation of damage due to creep has been quantified through microstructural studies in terms of two damage parameters A and A*. Experimental scatter observed in creep deformation and creep strain rate curves of the material at 870°C and at various stress conditions, is probably due to scatter in creep cavitations/voids and also due to variation in the mode of fracture in top as well as bottom portion of the tube. From statistical point of view, Weibull distribution pattern for analysing probability of rupture due to void area, shifts with increase in true strain towards the higher population of void. The estimation of average time to reach a specific damage state from K model and B model is in close agreement with that of experimental data and can describe the sudden changes of the creep damage in the tertiary region as well.     

Finite element analysis and experimental study on high strength bolted friction grip connections in steel bridges

High strength bolted friction grip (HSFG) joints are widely used in steel bridges. Through finite element analysis (FEA) and experimental study, the mechanical behavior including slip-load relationship, load transfer factors, stress state, and friction stress distribution of this type of joints was studied in detail. Both FEA results and experimental results show that the loads resisted by bolts in the edge rows are larger than the ones by bolts in the middle rows. The stress distributions in the connected plate and cover plate are wave-like with large stress and small stress alternate in different locations. Good agreements existed between the test results and the FEA results which verified the accuracy of the FEA. The numerical simulation method of the HSFG joints is proved to be a feasible and time efficient method for connection design.     

Application and validation of algebraic methods to predict the behaviour of crystalline silicon PV modules in Mediterranean climates

Predicting both PV module and generator performances under natural sunlight is a key issue for designers and installers. Five simple algebraic methods addressed to predict this behaviour in Mediterranean climates have been empirically validated. Firstly, the calibration in STC of all significant electrical parameters of both a monocrystalline and a polycrystalline silicon PV modules was entrusted to an accredited independent laboratory. Then, a 12-month test and measurement campaign carried out on these modules in the city of Jaén (Spain, latitude 38°N, longitude 3°W) has provided the necessary experimental data. Results show that (a) crystalline silicon PV module outdoors performance may be described with sufficient accuracy – for PV engineering purposes – only taking into account incident global irradiance, cell temperature, and using any one of two simple algebraic methods tried in this paper and (b) regardless the used method, poor results may be achieved if the PV specimens under study are not electrically characterised in STC prior to analysing their outdoors performance. Even so, the methods recommended in (a) perform best.     

Determining the boundary conditions by estimating RDOFs CMS for piping system

It is difficult to obtain boundary conditioners for air conditioner piping system by FE model. An estimating rotational degree of freedoms (RDOFs) component mode synthesis (CMS) method is presented and used to determine the boundary conditions. This paper presents the method to determine the boundary conditions of the piping system from experimental data. A piping system of the air conditioner is carried out as an example using MSC. Nastran, and the comparisons between the results and the experimental ones show the achievements.     

教学实验设备的规划建设

针对高等学校的教学实验设备规划建设，介绍了制定规划的依据，规划目标的确定、保证计划司标实现的措施以及效益评估等，对高校建设具有重要的意义。     

液体静压主轴热特性分析与试验研究

有效的热变形仿真分析是机床热平衡设计以及热误差补偿的基础。为了提高热变形仿真的精度,通过优化发热量等计算方法以及合理设计分析流程,基于ANSYS Workbench对超硬车数控车床液体静压主轴箱系统进行热特性仿真分析以及温升测试试验。热特性仿真与测试试验结果表明:温度场仿真与试验结果误差在5%以内,保证了热变形仿真的有效性。由变形仿真分析知:主轴3个方向上的热变形及主轴前端最大变形为5μm,为热误差补偿提供理论基础。由试验结果得到了同一转速下各热源处温升随时间的变化曲线,为合理预热、提高加工精度提供理论基础。