Computer modelling application in life prediction of high temperature components

Defects introduced in pressure vessel components during fabrication processes act as potential sources for damage accumulation and subsequent catastrophic failure. Cracks nucleate at these stress risers and propagate aided by fatigue type of loading, corrosion and creep. Analysis of crack growth under conditions of ‘time-dependent fatigue’ is very important for the life prediction of pressure vessel components. In this paper the interaction of creep-hot corrosion and low cycle fatigue is analyzed based on the energy expended for the nucleation of damage at the advancing crack front. The total damage accumulation is divided into that due to (i) fatigue, (ii) corrosion and (iii) creep for modelling purpose. The analysis yields a relation in terms ofJ-integral which is applicable to both crack propagation and final failure. A corrosion-creep parameter (F _i ) has been introduced at the crack propagation stage and raw data from different sources have been analyzed for different types of loading and compared with the theoretical predictions. The total energy in tension which includes the tension going time, appears to be a good parameter for the prediction of time-dependent fatigue life.     

Quantifying uncertainty in multicriteria concept selection methods

Decision support for concept selection in engineering design ranges from simple pairwise comparison techniques to methods that consider multiple criteria. The Analytic Hierarchy Process, or AHP, is an example of a multicriteria selection tool with wide-spread industry application. It is recognized by responsible practitioners that AHP, like other decision support methods, is best used not as an optimization tool, but as a means of clarifying individual or group attitudes; the numerical rankings that are its output are not definitive. This paper offers a means to quantify how differently two alternatives must be ranked by AHP to instill confidence that one is truly better than the other, a question that is in practice always answered using intuition. The quantification of uncertainty in AHP relies on the extension of concepts from statistical hypothesis testing. The procedure is not stochastic in the same way that physical measurement is, so probability distributions are created over relevant parameters. The quantified uncertainty depends, as in all statistical analysis, upon the assumed distributions. The uncertainty in AHP is quantified from two distinct points of view. The first makes the assumption that AHP is structurally correct but subject to measurement “error” in the pairwise comparisons, while the second quantifies the uncertainties introduced by AHP’s failure to consider different level of compensation in trade-offs among criteria.     

Elements in the determination of instability in the intensity of laser radiation

The article presents a formula for estimating the component of uncertainty in the measurement of the relative statistical fluctuation of the power of laser radiation caused by a finite number of measurements of power on the basis of which instability is determined. The influence of drift on the measured radiation power is established and a formula for adding the drift and fluctuation components of the relative statistical fluctuation is checked. __________ Translated from Izmeritel’naya Tekhnika, No. 11, pp. 28–32, November, 2006     

Temperature-Resolved Infrared Spectral Emissivity of SiC and Pt–10Rh for Temperatures up to 900°C

This article reports the first comprehensive results obtained from a fully functional, recently established infrared spectral-emissivity measurement facility at the National Institute of Standards and Technology (NIST). First, sample surface temperatures are obtained with a radiometer using actual emittance values from a newly designed sphere reflectometer and a comparison between the radiometer temperatures and contact thermometry results is presented. Spectral emissivity measurements are made by comparison of the sample spectral radiance to that of a reference blackbody at a similar (but not identical) temperature. Initial materials selected for measurement are potential candidates for use as spectral emissivity standards or are of particular technical interest. Temperature-resolved measurements of the spectral directional emissivity of SiC and Pt–10Rh are performed in the spectral range of 2–20 μm, over a temperature range from 300 to 900°C at normal incidence. Further, a careful study of the uncertainty components of this measurement is presented.     

Methods of calculating emissions of pollutants into the atmosphere and estimating their uncertainty

The main sources of uncertainty when calculating emissions of pollutants into the atmosphere are considered. An Ishikawa cause and effect diagram is used for a qualitative analysis of the uncertainty factors. The particular features of different methods of calculating the emissions are considered and the values of the overall uncertainty of the results of calculations and their main components are estimated. Translated from Izmeritel’naya Tekhnika, No. 2, pp. 55–60, February, 2009.     

Current Work on Furnaces and Data Analysis to Improve the Uniformity and Noise Levels for Metal Fixed Points

Ongoing work to improve the uniformity of vertically mounted furnaces, manufactured by Carbolite (e.g., Type TZF12/75—three-zone furnace capable of 1200 °C, with 75 mm inner bore) along the axis and across the working tube and/or equalizing block is reported. This involves adjusting the size of the end zones, the position of the control thermometers, and the use of cascade-control methods. Means regularly used at NPL to reduce electrical noise in some commercially available ac furnaces through a reduction in the voltage used to “fire” the heaters, and better use of thyristor controllers (by extending their cycle time) are described. The need to shield the controllers from local magnetic fields is described. With these measures, the electrical noise from ac furnaces can approach that of dc furnaces, without the large cost of a dc power supply. The application of new data analysis techniques (Allan deviation) will be shown to improve the representation of uninterrupted fixed-point traces (as used in ingot verification rather than PRT calibration). Reduction of statistical noise on the temperature measurements has been achieved for data on the freezing plateau by determining the statistically optimum averaging time. This shows that the statistical uncertainty in the determination of the temperature of a particular freezing plateau is less than 25 μK and that noise (drift) from other sources, possibly due to variations in room temperature, starts to become appreciable over periods longer than a few tens of minutes. The measurement of freezing and melting plateaux at this level is aided by the introduction of new ASL-F900 bridge(s), and quieter/larger standard resistor baths.     

Correct evaluation of type-B standard uncertainty

The evaluation of uncertainty components “by means other than the statistical analysis of series of observations” (type-B evaluation) is considered. The problem comes down to selection of an appropriate a priori probability distribution of a random quantity within specified limits on the basis of all available information. Typical situations are indicated that lead to simple model distributions: rectangular (uniform), triangular, normal, and arcsine. Attention is drawn to the unjustified use of the iniform distribution model in examples of measurement-uncertainty evaluation. Translated from Izmeritel'naya Tekhnika, No. 5, pp. 33–34, May, 2000.     

Determination of stray light at the PTB goniophotometer facility

For improved luminous flux measurements, the Physikalisch-Technische Bundesanstalt (PTB) was equipped with a new robotic goniophotometer. In order to characterize this instrument, to reduce the combined measurement uncertainty, and to determine the respective uncertainty components, the influence of stray light on the measurement results was investigated. Considering the specific structure of the robotic goniophotometer, stray light was measured on-line by means of a purpose-built “back-looking” photometer. By this means, the influence of the luminous intensity distribution of each individual light source with regard to its stray light could be considered. Before the first experimental application, the invented procedure was tested by means of calculations using mathematical models. In this paper, the mathematical model for the calculation of stray light in the goniophotometer room is presented together with the calculation results and the results of the first measurements. The achieved results indicate that the recommended stray light measurements can decrease the total relative standard measurement uncertainty of luminous flux measurements down to 2 × 10⁻³.     

Accounting for Dependence in a Flexible Multivariate Receptor Model

Formulation and evaluation of environmental policy depends on receptor models that are used to assess the number and nature of pollution sources affecting the air quality for a region of interest. Different approaches have been developed for situations in which no information is available about the number and nature of these sources (e.g., exploratory factor analysis) and the composition of these sources is assumed known (e.g., regression and measurement error models). We propose a flexible approach for fitting the receptor model when only partial pollution source information is available. The use of latent variable modeling allows the direct incorporation of subject matter knowledge into the model, including known physical constraints and partial pollution source information obtained from laboratory measurements or past studies. Because air quality data often exhibit temporal and/or spatial dependence, we consider the importance of accounting for such correlation in estimating model parameters and making valid statistical inferences. We propose an approach for incorporating dependence structure directly into estimation and inference procedures via a new nested block bootstrap method that adjusts for bias in estimating moment matrices. A goodness-of-fit test that is valid in the presence of such dependence is proposed. The application of the approach is facilitated by a new multivariate extension of an existing block size determination algorithm. The proposed approaches are evaluated by simulation and illustrated with an analysis of hourly measurements of volatile organic compounds in the El Paso, Texas/Ciudad Juarez, Mexico area.     

Evaluation of Measurement Uncertainty for Absolute Flatness Measurement by Using Fizeau Interferometer with Phase-Shifting Capability

It is important to precisely measure flatness of the optical flats, as many industries use these as reference standards to ensure the quality of precision measurements and fabricated components. This paper describes identification of sources of error and measurement uncertainty evaluation for three flat test. Three flat test is used for absolute flatness measurement of optical flats, with the help of Fizeau interferometer (VerifireXP/D, with phase shift interferometry) established recently at National Physical Laboratory, India (NPL-I). The absolute profile of reference flat with higher accuracy can be determined using liquid level reference but liquid flat reference is more difficult to realize practically. Therefore three flat test is frequently adopted in standard interferometric measurements and traceability of this test can also be established by using a traceable laser head. This paper describes three flat method in detail along with observations and evaluation of measurement uncertainty as per ISO GUM is also done. Factors contributing to uncertainty of measurement of surface flatness have been indentified and detailed evaluation of uncertainty in measurements has been reported here.     

Design optimization of an artificial lateral line system incorporating flow and sensor uncertainties

An artificial lateral line (ALL) system consists of a set of flow sensors around a fish-like body. An ALL system aims to identify surrounding moving objects, a common example of which is a vibrating sphere, called a dipole. Accurate identification of a vibrating dipole is a challenging task because of the presence of different types of uncertainty in measurements or in the underlying flow model. Proper selection of design parameters of the ALL system, including the shape, size, number and location of the sensors, can highly influence the identification accuracy. This study aims to find such an optimum design by developing a specialized bi-level optimization methodology. It identifies and simulates different sources of uncertainty in the problem formulation. A parametric fitness function addresses computational and practical goals and encompasses the effect of different sources of uncertainty. It can also analyse the trade-off between localization accuracy and the number of sensors. Comparison of the results for different extents of uncertainty reveals that the optimized design strongly depends on the amount of uncertainty as well as the number of sensors. Consequently, these factors must be considered in the design of an ALL system. Another highlight of the proposed bi-level optimization methodology is that it is generic and can be readily extended to solve other noisy and nested optimization problems.     

Uncertainty Budgets for Calibration of Radiation Thermometers below the Silver Point

Below the freezing point of silver, radiation thermometers are generally calibrated by implementing the multi-point interpolation method using blackbody measurements at three or more calibration points, rather than the ITS-90 extrapolation technique. The interpolation method eliminates the need to measure the spectral responsivity and provides greater accuracy at the longer wavelengths required below the silver point. This article identifies all the sources of uncertainty associated with the interpolation method, in particular, those related to the reference blackbody temperatures (either variable-temperature or fixed-point blackbodies) and to the measured thermometer signals at these points. Estimates are given of the ‘normal’ and ‘best’ uncertainties currently achievable. A model of the thermometer response is used to propagate all the uncertainties at the reference points and provide a total uncertainty at any temperature within the calibration range. The multi-point method has the effect of constraining the total uncertainty over this range, unlike the ITS-90 technique for which the uncertainties propagate as T ². This article is a joint effort of the working group on radiation thermometry of the Consultative Committee for Thermometry (CCT), summarizing the knowledge and experience of all experts in this field.     

噪声对阶跃信号上升时间测量不确定度的影响

为了更准确地反映阶跃信号上升时间测量过程中可能存在的不确定度来源、提高测量结果的可信度,对噪声引入的阶跃信号上升时间测量不确定度分量开展了数值仿真和试验分析。结果表明,信噪比对上升时间测量不确定度存在显著影响,在信噪比较低的情况下,噪声引起的上升时间测量不确定度成为主要来源。通过比较Savitzky?Golay平滑算法和移动平均平滑算法在阶跃信号上升时间计算中的应用效果,发现采用适当的平滑算法可以降低噪声引入的不确定度分量,其中,移动平均平滑算法的效果更好。本研究有助于提高动态信号测量结果的可靠性和准确性,对航空、航天、汽车等领域的动态信号测试不确定度分析具有重要的参考价值。     

Dynamic Measurements of the Temperature Coefficient of Resistance in the Transient Plane Source Sensor

The extended dynamic plane source (EDPS) method is one of the transient methods for measurements of the thermal conductivity and thermal diffusivity in solids. This technique uses a transient plane source (TPS) sensor, which serves as the heat source and thermometer. Its calibration consists of measuring the temperature dependence of the TPS sensor resistance and computing the temperature coefficient of resistance (TCR) using least-squares (LS) estimation. The goal of this study is to calibrate the TPS sensor directly in the apparatus for the EDPS method. The article presents an uncertainty assessment of the TCR measurement. The main sources of uncertainty stem from resistance measurements of the constant resistor and platinum thermometer calibration. The LS estimate of the TCR in a nickel TPS sensor is 4.83 × 10⁻³ K⁻¹ at 20 °C and 4.57 × 10⁻³ K⁻¹ at 45 °C with a combined standard uncertainty better than 0.04 × 10⁻³ K⁻¹, which is 0.7 %.     

A Nickel–Carbon Eutectic Cell for Contact and Non-contact Thermometry

The highest-temperature, defining fixed point of the International Temperature Scale of 1990 (ITS-90) is the copper freezing point (1,084.62°C). Many international metrology institutes are investigating the use of transition temperatures of metal–carbon alloys as references for the calibration of temperature measuring instruments above the copper point, making it possible to reduce the calibration uncertainty of pyrometers in radiation thermometry and thermocouples in contact thermometry. This research is being performed mainly by radiation thermometry laboratories that have developed specific cells with blackbody cavities containing relatively small quantities of metal–carbon alloys. Parallel to this, some laboratories have also developed cells with these same alloys, but of a different design, suitable for the calibration of thermocouples. This report concerns the development of a nickel–carbon eutectic cell (≅1,329°C) at Inmetro, with which either a radiation thermometer or thermocouple can be calibrated. The measurements of the temperature of this cell were performed using the reference radiation thermometer of the Pyrometry Laboratory and Pt/Pd thermocouples that were constructed, stabilized, and calibrated at the Thermometry Laboratory. Details of the cell fabrication, as well as the instrumentation used for the measurements are given. The results of a comparison between the two different types of measurement are reported, including the uncertainty budgets of both methods.     

Analysis of an open-ended coaxial probe with lift-off fornondestructive testing

The open-ended coaxial probe with lift-off is studied using a full-wave analysis, and an uncertainty analysis is presented. The field equations for the following terminations are worked out: (1) the sample extends to ∞ in the positive axial direction, (2) the sample is backed by a well-characterized material, and (3) the sample is backed by a short-circuit termination. The equations are valid for both dielectric and magnetic materials. The model allows the study of the open-ended coaxial probe as a nondestructive testing tool. The analysis allows a study of the effects of air gaps on probe measurements. The reflection coefficient and phase are studied as a function of lift-off, coaxial line size, permittivity, permeability, and frequency. Numerical results indicate that the probe is very sensitive to lift-off. For medium to high permittivity values and electrically small probes, gaps on the order of fractions of a millimeter strongly influence the reflection coefficient. In order for the field to penetrate through the air gap, larger size coaxial line or higher frequencies need to be used. A comparison of the theory to experiment is presented. The results are in close agreement. A differential uncertainty analysis is also included     

Effects of a priori parameter selection in minimum relative entropy method on inverse electrocardiography problem

The goal in inverse electrocardiography (ECG) is to reconstruct cardiac electrical sources from body surface measurements and a mathematical model of torso–heart geometry that relates the sources to the measurements. This problem is ill-posed due to attenuation and smoothing that occur inside the thorax, and small errors in the measurements yield large reconstruction errors. To overcome this, ill-posedness, traditional regularization methods such as Tikhonov regularization and truncated singular value decomposition and statistical approaches such as Bayesian Maximum A Posteriori estimation and Kalman filter have been applied. Statistical methods have yielded accurate inverse solutions; however, they require knowledge of a good a priori probability density function, or state transition definition. Minimum relative entropy (MRE) is an approach for inferring probability density function from a set of constraints and prior information, and may be an alternative to those statistical methods since it operates with more simple prior information definitions. However, success of the MRE method also depends on good choice of prior parameters in the form of upper and lower bound values, expected uncertainty in the model and the prior mean. In this paper, we explore the effects of each of these parameters on the solution of inverse ECG problem and discuss the limitations of the method. Our results show that the prior expected value is the most influential of the three MRE parameters.     

Uncertainty analysis of the high vacuum part of the orifice-flow-type pressure standard

The orifice-flow-type pressure standard is commonly accepted as primary standard for vacuum gauge calibration in the high vacuum gas pressure range. It consists of two parts—a high vacuum part and a flowmeter. Practical questions arising at design of the standard have to be answered based on the standard uncertainty analysis.The analysis of the uncertainty sources in the high vacuum part except deviations from the Maxwellian distribution is given in the paper. Uncertainty of a precise flowmeter is taken from references for comparison. It follows from the analysis that uncertainties caused by some sources at routinely achievable parameters are negligibly small and further improvement brings no benefit. The crucial quantities influencing the total uncertainty are the temperature of the chamber and the flowmeter, the outgassing rate from the inner surfaces, the ultimate pressure of the pump and the additional (detrimental) pumping speed. The pumping speed of the main pump has to be “sufficiently higher” than the orifice conductance.