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Norbert Ulbrich - One of the best experts on this subject based on the ideXlab platform.
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wind tunnel Strain Gage balance calibration data analysis using a weighted least squares approach
33rd AIAA Aerodynamic Measurement Technology and Ground Testing Conference, 2017Co-Authors: Norbert Ulbrich, Thomas VoldenAbstract:A new approach is presented that uses a weighted least squares fit to analyze wind tunnel Strain-Gage balance calibration data. The weighted least squares fit is specifically designed to increase the influence of single-component loadings during the regression analysis. The weighted least squares fit also reduces the impact of calibration load schedule asymmetries on the predicted primary sensitivities of the balance Gages. A weighting factor between zero and one is assigned to each calibration data point that depends on a simple count of its intentionally loaded load components or Gages. The greater the number of a data point's intentionally loaded load components or Gages is, the smaller its weighting factor becomes. The proposed approach is applicable to both the Iterative and Non-Iterative Methods that are used for the analysis of Strain-Gage balance calibration data in the aerospace testing community. The Iterative Method uses a reasonable estimate of the tare corrected load set as input for the determination of the weighting factors. The Non-Iterative Method, on the other hand, uses Gage output differences relative to the natural zeros as input for the determination of the weighting factors. Machine calibration data of a six-component force balance is used to illustrate benefits of the proposed weighted least squares fit. In addition, a detailed derivation of the PRESS residuals associated with a weighted least squares fit is given in the appendices of the paper as this information could not be found in the literature. These PRESS residuals may be needed to evaluate the predictive capabilities of the final regression models that result from a weighted least squares fit of the balance calibration data.
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A Universal Tare Load Prediction Algorithm for Strain-Gage Balance Calibration Data Analysis
47th AIAA ASME SAE ASEE Joint Propulsion Conference & Exhibit, 2011Co-Authors: Norbert UlbrichAbstract:An algorithm is discussed that may be used to estimate tare loads of wind tunnel Strain–Gage balance calibration data. The algorithm was originally developed by R. Galway of IAR/NRC Canada and has been described in the literature for the iterative analysis technique. Basic ideas of Galway’s algorithm, however, are universally applicable and work for both the iterative and the non–iterative analysis technique. A recent modification of Galway’s algorithm is presented that improves the convergence behavior of the tare load prediction process if it is used in combination with the non–iterative analysis technique. The modified algorithm allows an analyst to use an alternate method for the calculation of intermediate non–linear tare load estimates whenever Galway’s original approach does not lead to a convergence of the tare load iterations. It is also shown in detail how Galway’s algorithm may be applied to the non–iterative analysis technique. Hand load data from the calibration of a six–component force balance is used to illustrate the application of the original and modified tare load prediction method. During the analysis of the data both the iterative and the non–iterative analysis technique were applied. Overall, predicted tare loads for combinations of the two tare load prediction methods and the two balance data analysis techniques showed excellent agreement as long as the tare load iterations converged. The modified algorithm, however, appears to have an advantage over the original algorithm when absolute voltage measurements of Gage outputs are processed using the non–iterative analysis technique. In these situations only the modified algorithm converged because it uses an exact solution of the intermediate non–linear tare load estimate for the tare load iteration.
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Iterative Strain-Gage Balance Calibration Data Analysis for Extended Independent Variable Sets
49th AIAA Aerospace Sciences Meeting including the New Horizons Forum and Aerospace Exposition, 2011Co-Authors: Norbert UlbrichAbstract:A new method was developed that makes it possible to use an extended set of independent calibration variables for an iterative analysis of wind tunnel Strain–Gage balance calibration data. The new method permits the application of the iterative analysis method whenever the total number of balance loads and other independent calibration variables is greater than the total number of measured Strain–Gage outputs. Iteration equations used by the iterative analysis method have the limitation that the number of independent and dependent variables must match. The new method circumvents this limitation. It simply adds a missing dependent variable to the original data set by using an additional independent variable also as an additional dependent variable. Then, the desired solution of the regression analysis problem can be obtained that fits each Gage output as a function of both the original and additional independent calibration variables. The final regression coefficients can be converted to data reduction matrix coefficients because the missing dependent variables were added to the data set without changing the regression analysis result for each Gage output. Therefore, the new method still supports the application of the two load iteration equation choices that the iterative method traditionally uses for the prediction of balance loads during a wind tunnel test. An example is discussed in the paper that illustrates the application of the new method to a realistic simulation of temperature dependent calibration data set of a six–component balance.
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Regression Model Term Selection for the Analysis of Strain-Gage Balance Calibration Data
27th AIAA Aerodynamic Measurement Technology and Ground Testing Conference, 2010Co-Authors: Norbert Ulbrich, Tormod VoldenAbstract:The paper discusses the selection of regression model terms for the analysis of wind tunnel Strain–Gage balance calibration data. Different function class combinations are presented that may be used to analyze calibration data using either a non–iterative or an iterative method. The role of the intercept term in a regression model of calibration data is reviewed. In addition, useful algorithms and metrics originating from linear algebra and statistics are recommended that will help an analyst (i) to identify and avoid both linear and near–linear dependencies between regression model terms and (ii) to make sure that the selected regression model of the calibration data uses only statistically significant terms. Three different tests are suggested that may be used to objectively assess the predictive capability of the final regression model of the calibration data. These tests use both the original data points and regression model independent confirmation points. Finally, data from a simplified manual calibration of the Ames MK40 balance is used to illustrate the application of some of the metrics and tests to a realistic calibration data set.
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combined load diagram for a wind tunnel Strain Gage balance
27th AIAA Aerodynamic Measurement Technology and Ground Testing Conference, 2010Co-Authors: Norbert UlbrichAbstract:Combined Load Diagrams for Direct–Read, Force, and Moment Balances are discussed in great detail in the paper. The diagrams, if compared with a corresponding combined load plot of a balance calibration data set, may be used to visualize and interpret basic relationships between the applied balance calibration loads and the load components at the forward and aft Gage of a Strain–Gage balance. Lines of constant total force and moment are identified in the diagrams. In addition, the lines of pure force and pure moment are highlighted. Finally, lines of constant moment arm are depicted. It is also demonstrated that each quadrant of a Combined Load Diagram has specific regions where the applied total calibration force is at, between, or outside of the balance Gage locations. Data from the manual calibration of a Force Balance is used to illustrate the application of a Combined Load Diagram to a realistic data set.
Debabrata Chakraborty - One of the best experts on this subject based on the ideXlab platform.
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influence of the notch length on the optimal radial location of Strain Gage in a single edged notched plate
2020Co-Authors: P J Paul, K S R K Murthy, Debabrata ChakrabortyAbstract:For estimation of accurate mode I stress intensity factor in a single edged notched plate, it is important to place the Strain Gage within a maximum permissible radial distance \( r_{\hbox{max} } \) [14]. In the present paper, it is aimed to study how the notch length affects this parameter \( r_{\hbox{max} } \). A finite element based procedure is developed based on theoretical formulation analogous to Dally and Sanford technique [16] for cracks. Results show that both notch length and the net ligament length have significant influence on \( r_{\hbox{max} } \) and some interesting observations have been reported.
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a Strain Gage technique for the determination of mixed mode stress intensity factors of orthotropic materials
Composite Structures, 2017Co-Authors: Debaleena Chakraborty, Debabrata Chakraborty, K S R K MurthyAbstract:Abstract A theoretical frame work is developed for Strain Gage based determination of mixed mode (KI/KII) stress intensity factors (SIFs) in slant edge cracked plate (SECP) made of orthotropic materials. Using three parameter Strain series around the crack tip and appropriate stress functions, the present formulation shows that mixed mode SIFs in orthotropic materials could be determined using only four Strain Gages. A finite element based methodology is developed to determine the upper bound on the radial location (rmax) of Strain Gages ensuring accurate determination of SIFs. Proposed technique is applied to numerical simulation of [02/90]2S and [0/±45/90]S glass-epoxy SECP laminates to demonstrate accurate determination of mixed mode SIFs by placing the Gages within rmax. Results from the present work provide clear guidelines in terms of number of Strain Gages and their suggested locations for accurate determination of mixed mode SIFs in orthotropic materials.
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a new single Strain Gage technique for the accurate determination of mode i stress intensity factor in orthotropic composite materials
Engineering Fracture Mechanics, 2014Co-Authors: Debaleena Chakraborty, K S R K Murthy, Debabrata ChakrabortyAbstract:Abstract The present work proposes a new single Strain Gage technique for the accurate determination of mode I stress intensity factor (SIF) in orthotropic composite materials. This work also aims at showing the existence of valid or optimal Gage locations for the accurate determination of SIFs in orthotropic composites. Accordingly, a finite element based general approach is developed for the estimation of such optimal Gage locations. Results of numerical examples show that the proposed Strain Gage technique can yield highly accurate value of SIF for orthotropic laminates when the Gage is placed within the valid locations.
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experimental verification of optimal Strain Gage locations for the accurate determination of mode i stress intensity factors
Engineering Fracture Mechanics, 2013Co-Authors: Hrushikesh Sarangi, K S R K Murthy, Debabrata ChakrabortyAbstract:Abstract The present work focuses on the experimental verification of optimal Strain Gage locations and their importance in accurate determination of mode I stress intensity factors (SIFs) using Dally and Sanford’s single Strain Gage technique (DS technique). The results of the present experimental study are also used to substantiate the efficacy of the methodology for determination of maximum permissible Strain Gage radial location rmax proposed earlier by the same authors for locating the optimal Strain Gage locations. Present results clearly demonstrate that highly accurate values of SIFs can be determined if the Strain Gages are placed at the optimal locations.
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optimum Strain Gage locations for accurate determination of the mixed mode stress intensity factors
Engineering Fracture Mechanics, 2012Co-Authors: Hrushikesh Sarangi, K S R K Murthy, Debabrata ChakrabortyAbstract:Abstract Assessment of proper radial location for Strain Gages is extremely important in accurate experimental determination of mixed mode stress intensity factors (SIFs) and is an open problem. The present work proposes a methodology for accurate estimation of maximum permissible radial location (rmax) and also suggests a new Strain Gage method for experimental determination of the mixed mode SIFs (KI and KII). The effect of crack length to width ratio and state of stress on the rmax has also been investigated in this work. Numerical results obtained from the present investigation are observed to be in accordance with the theoretical predictions.
Chuanpu Liu - One of the best experts on this subject based on the ideXlab platform.
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optimizing the edm hole drilling Strain Gage method for the measurement of residual stress
Journal of Materials Processing Technology, 2009Co-Authors: Hwateng Lee, Chuanpu LiuAbstract:Abstract When using the electrical discharge machining (EDM) hole-drilling Strain Gage method to measure the residual stress within a component, the metallurgical transformation layer formed on the wall of the EDMed hole induces an extra stress, which can lead to significant measurement errors. Accordingly, the objective of the present work was to explore and determine the optimal EDM parameters which reduce the thickness of the metallurgical transformation layer and therefore minimize the magnitude of the hole-drilling induced stress. The experimental results demonstrated that by maintaining the relative stability coefficient of the discharge duty ratio at a value greater than 0.99, the induced stress emerged in EDM hole-drilling measurement can be reduced substantially and becomes insensitive to the parameters of the pulse current and pulse-on duration. Further investigations revealed that when the residual stress is to be measured accurately, using a hollow electrode instead of the usual solid electrode and the following parameters are recommended. The pulse current and pulse-on duration are in the ranges of 4–12 A and 9–23 μs, respectively, and the pulse-off duration needs to be longer than the value required to ensure that the relative stability coefficient of the discharge duty ratio exceeds 0.99.
K S R K Murthy - One of the best experts on this subject based on the ideXlab platform.
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influence of the notch length on the optimal radial location of Strain Gage in a single edged notched plate
2020Co-Authors: P J Paul, K S R K Murthy, Debabrata ChakrabortyAbstract:For estimation of accurate mode I stress intensity factor in a single edged notched plate, it is important to place the Strain Gage within a maximum permissible radial distance \( r_{\hbox{max} } \) [14]. In the present paper, it is aimed to study how the notch length affects this parameter \( r_{\hbox{max} } \). A finite element based procedure is developed based on theoretical formulation analogous to Dally and Sanford technique [16] for cracks. Results show that both notch length and the net ligament length have significant influence on \( r_{\hbox{max} } \) and some interesting observations have been reported.
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a Strain Gage technique for mode i notch stress intensity factor of sharp v notched configurations
Theoretical and Applied Fracture Mechanics, 2018Co-Authors: P J Paul, K S R K Murthy, Debaleena ChakrabortyAbstract:Abstract A simple and robust single Strain Gage technique for accurate measurement of mode I notch stress intensity factor (NSIF) for sharp V-notched configurations has been proposed. The technique is supported by strong theoretical foundation, and it allows the Strain Gage to be placed reasonably away from the notch tip thus avoiding various problems associated with singularities. Importantly, in contrast to the available techniques, the present Strain Gage technique also prescribes proper radial locations (optimal locations) for the Strain Gage which are extremely useful in accurate measurement of NSIFs. A general theory and procedure has been developed for the estimation of these Gage locations a priori for any given sharp V-notched configuration. These locations are shown to be dependent on the notch angle and notch length to width ratio. Experiments have been conducted using linear Strain Gages of 1 mm Gage length and the results show that accurate NSIFs can be measured using the proposed single Strain Gage technique. The numerical results of the present investigation clearly show that very accurate (of the order of less than 1% error) mode I NSIF can be measured using the proposed single Strain Gage technique if the Gages are placed at the optimal locations. The present results also demonstrate that highly inaccurate (of the order of 45% error) and unacceptable NSIFs would result if the Gages are placed at non-optimal Gage locations.
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a Strain Gage technique for the determination of mixed mode stress intensity factors of orthotropic materials
Composite Structures, 2017Co-Authors: Debaleena Chakraborty, Debabrata Chakraborty, K S R K MurthyAbstract:Abstract A theoretical frame work is developed for Strain Gage based determination of mixed mode (KI/KII) stress intensity factors (SIFs) in slant edge cracked plate (SECP) made of orthotropic materials. Using three parameter Strain series around the crack tip and appropriate stress functions, the present formulation shows that mixed mode SIFs in orthotropic materials could be determined using only four Strain Gages. A finite element based methodology is developed to determine the upper bound on the radial location (rmax) of Strain Gages ensuring accurate determination of SIFs. Proposed technique is applied to numerical simulation of [02/90]2S and [0/±45/90]S glass-epoxy SECP laminates to demonstrate accurate determination of mixed mode SIFs by placing the Gages within rmax. Results from the present work provide clear guidelines in terms of number of Strain Gages and their suggested locations for accurate determination of mixed mode SIFs in orthotropic materials.
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a new single Strain Gage technique for the accurate determination of mode i stress intensity factor in orthotropic composite materials
Engineering Fracture Mechanics, 2014Co-Authors: Debaleena Chakraborty, K S R K Murthy, Debabrata ChakrabortyAbstract:Abstract The present work proposes a new single Strain Gage technique for the accurate determination of mode I stress intensity factor (SIF) in orthotropic composite materials. This work also aims at showing the existence of valid or optimal Gage locations for the accurate determination of SIFs in orthotropic composites. Accordingly, a finite element based general approach is developed for the estimation of such optimal Gage locations. Results of numerical examples show that the proposed Strain Gage technique can yield highly accurate value of SIF for orthotropic laminates when the Gage is placed within the valid locations.
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experimental verification of optimal Strain Gage locations for the accurate determination of mode i stress intensity factors
Engineering Fracture Mechanics, 2013Co-Authors: Hrushikesh Sarangi, K S R K Murthy, Debabrata ChakrabortyAbstract:Abstract The present work focuses on the experimental verification of optimal Strain Gage locations and their importance in accurate determination of mode I stress intensity factors (SIFs) using Dally and Sanford’s single Strain Gage technique (DS technique). The results of the present experimental study are also used to substantiate the efficacy of the methodology for determination of maximum permissible Strain Gage radial location rmax proposed earlier by the same authors for locating the optimal Strain Gage locations. Present results clearly demonstrate that highly accurate values of SIFs can be determined if the Strain Gages are placed at the optimal locations.
Thomas Volden - One of the best experts on this subject based on the ideXlab platform.
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wind tunnel Strain Gage balance calibration data analysis using a weighted least squares approach
33rd AIAA Aerodynamic Measurement Technology and Ground Testing Conference, 2017Co-Authors: Norbert Ulbrich, Thomas VoldenAbstract:A new approach is presented that uses a weighted least squares fit to analyze wind tunnel Strain-Gage balance calibration data. The weighted least squares fit is specifically designed to increase the influence of single-component loadings during the regression analysis. The weighted least squares fit also reduces the impact of calibration load schedule asymmetries on the predicted primary sensitivities of the balance Gages. A weighting factor between zero and one is assigned to each calibration data point that depends on a simple count of its intentionally loaded load components or Gages. The greater the number of a data point's intentionally loaded load components or Gages is, the smaller its weighting factor becomes. The proposed approach is applicable to both the Iterative and Non-Iterative Methods that are used for the analysis of Strain-Gage balance calibration data in the aerospace testing community. The Iterative Method uses a reasonable estimate of the tare corrected load set as input for the determination of the weighting factors. The Non-Iterative Method, on the other hand, uses Gage output differences relative to the natural zeros as input for the determination of the weighting factors. Machine calibration data of a six-component force balance is used to illustrate benefits of the proposed weighted least squares fit. In addition, a detailed derivation of the PRESS residuals associated with a weighted least squares fit is given in the appendices of the paper as this information could not be found in the literature. These PRESS residuals may be needed to evaluate the predictive capabilities of the final regression models that result from a weighted least squares fit of the balance calibration data.
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Strain Gage balance calibration analysis using automatically selected math models
41st AIAA ASME SAE ASEE Joint Propulsion Conference & Exhibit, 2005Co-Authors: Norbert Ulbrich, Thomas VoldenAbstract:A technique is presented that determines a set of candidate math models in order to analyze Strain–Gage balance calibration data using global regression. At first, a permitted and a required math model are defined in order to bound possible candidate math models. In the second step, starting with the permitted math model, families of possible candidate math models are created by generating all possible math term combinations for a fixed number of terms. Then, after the global regression has been applied to the calibration data using each family member, the next candidate math model is found by comparing the standard deviation of the response residual. This process is repeated for each Gage using the updated candidate math model until only the required math model remains. A three component balance calibration data set is used to illustrate the determination of candidate math models. In addition, results from a six component balance calibration are discussed in order to show the application of the proposed method to realistic balance calibration data.
