Time Dependent FLC Determination Comparison of Different Algorithms to Detect the Onset of Unstable Necking before Fracture

2013 ◽  
Vol 549 ◽  
pp. 397-404 ◽  
Author(s):  
Walter Hotz ◽  
Marion Merklein ◽  
Andreas Kuppert ◽  
Harald Friebe ◽  
Markus Klein
Keyword(s):  
Correlation Coefficient ◽  
Work Group ◽  
Time History ◽  
Time Dependent ◽  
Forming Limit ◽  
Iso Standard ◽  
Modified Method ◽  
History Of ◽  
Forming Limit Curves

The ISO standard 12004-2:2008E for the determination of forming limit curves based on the section method was approved in 2008. About 4 years of measuring experience in different laboratories has shown advantages and weaknesses of the standard and is leading to some minor changes in the specification. In the years from the development of this standard until today a further technical development of the optical measuring devices occurred, so that it is now possible to determine forming limit curves using the time history of the test. This procedure of determination is referred to a time dependent technique and could be the basis of the ISO 12004 part 2 proposal worked out by the work group Erweiterung FLC ISO 12004 of the German group of the IDDRG. This publication recapitulates existing work which was carried out from the IDDRG work group regarding the determination of forming limit curves for sheet metal materials. On one hand known issues with the current section based approach are discussed and on the other hand it deals with a comparison of different algorithms to determine the FLC from the time history of the Nakajima test using strategies to identify the instant of onset of instable necking. The different time dependent algorithms [ utilised are automatically selecting the area where necking is leading to fracture and then analyze the time history of such points using the first or the second time derivative of the true major strain, or of the true thinning strain using methods like: correlation coefficient (modified method based on [2]), gliding correlation coefficient, linear best fit (modified method based on [3]) and gliding difference of mean to median. The resulting experimental FLC points are compared with the results from the section technique described in ISO 12004 part 2 and with the maximum strain values measured in each test. Further a large number of forming limit curves were determined and used for a comparison of these different methods to define the most promising time dependent algorithm, which was selected as a suggestion for the working group defining the new proposed ISO standard 12004 part 2.

Time Dependent Magnetic Switching in Spin Valve Structures

1995 ◽  
Vol 384 ◽  
Author(s):  
J. B. Restorff ◽  
M. Wun-Fogle ◽  
S. F. Cheng ◽  
K. B. Hathaway
Keyword(s):  
Giant Magnetoresistance ◽  
Spin Valve ◽  
Time History ◽  
Time Dependent ◽  
Si Substrates ◽  
Magnetic Switching ◽  
Magnetic Aftereffect ◽  
Magnetron Sputter Deposition ◽  
History Of ◽  
Time Required

ABSTRACTWe have observed time dependent magnetic switching in spin-valve sandwich structures of Cu/Co/Cu/Fe films grown on silicon and Kapton substrates and Permalloy/Co/Cu/Co films grown on NiO or NiO/CoO coated Si substrates. The giant magnetoresistance (MR) values ranged from 1 to 3 percent at room temperature. The films were grown by DC magnetron sputter deposition. Measurements were made on the time required for the MR to stabilize to about 1 part in 104 after the applied field was incremented. This time depends almost linearly on the amplitude of the timedependent MR change with a slope (time / ΔMR) of 20 000 to 30 000 s. Some samples took as long as 70 s to stabilize. The time dependent effects may be important for devices operating in these regions of the magnetoresistance curve. In addition, measurements were made on the time history of the MR value for a period of 75 s following a step change in the field from saturation. We observed that the time dependent behavior of the MR values of both experiments produced an excellent fit to a function of the form ΔMR(t) = α + β;ln(t) where ɑ and β are constants. This time dependence was consistent with the behavior of the magnetic aftereffect.

scholarly journals Tracking patchy pulsating aurora through all-sky images

2017 ◽  
Vol 35 (4) ◽  
pp. 777-784 ◽  
Author(s):  
Eric Grono ◽  
Eric Donovan ◽  
Kyle R. Murphy
Keyword(s):  
Time History ◽  
Image Data ◽  
Auroral Oval ◽  
Automatic Identification ◽  
Inner Magnetosphere ◽  
Wide Range ◽  
History Of ◽  
Initial Results ◽  
Automatic Technique

Abstract. Pulsating aurora is frequently observed in the evening and morning sector auroral oval. While the precipitating electrons span a wide range of energies, there is increasing evidence that the shape of pulsating auroral patches is controlled by structures in near-equatorial cold plasma; these patches appear to move with convection, for example. Given the tremendous and rapidly increasing amount of auroral image data from which the velocity of these patches can be inferred, it is timely to develop and implement techniques for the automatic identification of pulsating auroral patch events in these data and for the automatic determination of the velocity of individual patches from that data. As a first step towards this, we have implemented an automatic technique for determining patch velocities from sequences of images from the Time History of Events and Macroscale Interactions during Substorms (THEMIS) all-sky imager (ASI) and applied it to many pulsating aurora events. Here we demonstrate the use of this technique and present the initial results, including a comparison between ewograms (east–west keograms) and time series of patch position as determined by the algorithm. We discuss the implications of this technique for remote sensing convection in the inner magnetosphere.

Thermal Influences on Deep Drawing Process of Ferritic and Metastable Austenitic Stainless Steels

2013 ◽  
Vol 769 ◽  
pp. 221-228 ◽  
Author(s):  
Philipp Schmid
Keyword(s):  
Stainless Steels ◽  
Deep Drawing ◽  
Austenitic Stainless Steels ◽  
Forming Limit ◽  
Martensite Formation ◽  
Forming Process ◽  
High Dependency ◽  
Forming Tools ◽  
Forming Limit Curves

Sheet metal forming processes, in particular deep drawing processes, are highly influenced by occurrence of latent and friction heat. Especially when forming metastable austenitic stainless steels, strain-induced martensite formation is suppressed by higher temperatures and therefore influences the material behavior and so called TRIP-effect. This study gives an overview about thermal influences on the deep drawing forming process of metastable austenitic CrNi-steel 1.4301 in comparison with ferritic stainless steels such as 1.4016. Measurements on serial and evaluation tools were carried out to determine occurring temperatures within forming tools. Attention is paid to effects on tribological aspects such as behavior of lubricants at higher temperatures, influence of temperature development on the martensite formation, mechanical properties, forming limit curves as well as heat flow within the forming tools. Lubricants with different temperature stability were compared to each other with determination of friction coefficient in strip drawing tests. Martensite and temperature development during forming of material was measured in non-isothermal tensile tests approving a high dependency of martensite formation on temperature. Forming limit curves for temperatures determined from RT to 140°C for EN 1.4301 are showing high dependency of necking behavior especially under plain strain conditions. Determination of thermal contact conductance coefficients for process and tool relevant material combinations allows interpreting heat flow mechanisms in forming tools and improving forming process to higher robustness. Results of this paper can be used to individually set boundary conditions for thermo-mechanical coupled forming simulation of austenitic stainless steel and process layout of tool temperature control systems.

Time dependent determination of forming limit diagrams

CIRP Annals ◽  
2010 ◽  
Vol 59 (1) ◽  
pp. 295-298 ◽  
Author(s):  
M. Merklein ◽  
A. Kuppert ◽  
M. Geiger
Keyword(s):  
Time Dependent ◽  
Forming Limit ◽  
Forming Limit Diagrams

scholarly journals Advanced calibration of magnetometers on spin-stabilized spacecraft based on parameter decoupling

2019 ◽  
Vol 8 (1) ◽  
pp. 63-76 ◽  
Author(s):  
Ferdinand Plaschke ◽  
Hans-Ulrich Auster ◽  
David Fischer ◽  
Karl-Heinz Fornaçon ◽  
Werner Magnes ◽  
...  
Keyword(s):  
Time History ◽  
Field Measurements ◽  
Incorrect Choice ◽  
University Of Technology ◽  
Solar System Bodies ◽  
History Of ◽  
Determination Of Parameters ◽  
Calibration Equations ◽  
Calibration Parameters

Abstract. Magnetometers are key instruments on board spacecraft that probe the plasma environments of planets and other solar system bodies. The linear conversion of raw magnetometer outputs to fully calibrated magnetic field measurements requires the accurate knowledge of 12 calibration parameters: six angles, three gain factors, and three offset values. The in-flight determination of 8 of those 12 parameters is enormously supported if the spacecraft is spin-stabilized, as an incorrect choice of those parameters will lead to systematic spin harmonic disturbances in the calibrated data. We show that published equations and algorithms for the determination of the eight spin-related parameters are far from optimal, as they do not take into account the physical behavior of science-grade magnetometers and the influence of a varying spacecraft attitude on the in-flight calibration process. Here, we address these issues. Based on decade-long developments and experience in calibration activities at the Braunschweig University of Technology, we introduce advanced calibration equations, parameters, and algorithms. With their help, it is possible to decouple different effects on the calibration parameters, originating from the spacecraft or the magnetometer itself. A key point of the algorithms is the bulk determination of parameters and associated uncertainties. The lowest uncertainties are expected under parameter-specific conditions. By application to THEMIS-C (Time History of Events and Macroscale Interactions during Substorms) magnetometer measurements, we show where these conditions are fulfilled along a highly elliptical orbit around Earth.

Lift and Moment Prediction For an Oscillating Airfoil With a Moving Separation Point

1974 ◽  
Vol 96 (4) ◽  
pp. 372-378 ◽  
Author(s):  
P. V. K. Perumal ◽  
F. Sisto
Keyword(s):  
Flat Plate ◽  
Analytical Method ◽  
Time History ◽  
Experimental Results ◽  
Time Dependent ◽  
Separation Point ◽  
Empirical Knowledge ◽  
Torsional Mode ◽  
History Of ◽  
Dependent Point

An analytical method for predicting the perturbed aerodynamic reactions of a harmonically oscillating flat plate airfoil with time dependent point of separation is presented. It is shown that this method in conjunction with an empirical knowledge of the time history of the separation point can predict stall-flutter. Numerical results are presented and compared with existing theoretical and experimental results with special emphasis on torsional mode of oscillation.

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