Sven Eck

Calibration, Measurement and Error Analysis of Optical Temperature Measurement via Laser Induced Fluorescence

This paper describes a measurement device for optical temperature measurement. The temperature measurement is based on light induced fluorescence, and hence the device is partly physical and partly theoretical in nature. Rather that estimating a single calibration curve for the measurement, as is the norm with optical measurement, we perform the calibration pixel-wise, which accounts for systematic non-uniformity over the images and measurement cell. With this approach, the measurement is less susceptible to gross outliers. A measurement device can hardly be called such, if the measurement is not accompanied by a measure of its accuracy. We therefore undertake the error propagation throughout the theoretical portion of the measurement device, which leads to a measure of the accuracy of the optical temperature measurement. The analysis not only gives insight into the measurement process, but facilitates the amelioration of the experimental apparatus.

Experimental Observation of Convection during Equiaxed Solidification of Transparent Alloys

3D samples of NH4Cl-H2O solutions were solidified under defined experimental conditions. The occurring melt convection was investigated by Particle Image Velocimetry (PIV). The occurrence of NH4Cl crystals was observed optically and first attempts were made to quantitatively measure its number density, size distribution and sedimentation rate by PIV and Particle Tracking (PT). In order to prove the reproducibility of the results several experimental runs with equal and slightly modified conditions were analyzed.

In Situ Observation of Solidification in an Organic Peritectic Alloy System

Up to date very few organic substances have been reported that show a non-faceted/non-faceted (nf/nf) peritectic phase diagram in a temperature range suitable for direct observation in a micro Bridgman furnace setup. Sturz et al. [1] and Barrio et al. [2] studied the peritectic phase diagram for the organic model alloy TRIS (Tris(hydroxymenthyl)aminomethane) - NPG (Neopentylglycol). The phase diagram is based on thermal analysis by means of DSC measurements [1, 2] and evaluation of lattice parameters measured with x-ray diffractometry [2]. In the current work we present investigations on the system TRIS – NPG that have been obtained by optical investigations of directional solidification in a micro Bridgman-furnace with various initial alloy concentrations and pulling rates in a fixed temperature gradient. The phase diagram [1, 2] was confirmed by direct comparison of DSC measurements and optical investigations. Furthermore we present in situ observations of solidification in the peritectic region. They show a solidification behavior that was clearly distinguishable from the solidification in hyper- and hypoperitectic regions of the phase diagram.

Towards condition monitoring of railway points: Instrumentation, measurement and signal processing

This paper presents the instrumentation and signal processing required to measure the strain occurring on the frog of a railway turnout. The aim is to enable the automatic estimation of the cumulative load exhibited on the element; this is relevant with respect to perdurant changes, safety and maintenance planning. Furthermore, the measurement system enables the identification of irregularities at rolling stock. The frog is instrumented with four strain gauges, housed in robust stainless steel casings. The measured strain signal is partitioned into three portions: a) a section prior to the train reaching the frog; b) the time during which the train traverses the turnout and c) a post train period. Statistical analysis is applied to the signal prior to the train arriving to determine characteristic perturbation behavior. This also enables a numerically efficient method of identifying irregularities at rolling stock. The specific measured strain pattern permits the grouping of the measurements according to train type. Dynamic time warping with local polynomial resampling is applied to each measurement so that a consensus curve can be computed for the strain associated with each train type. Long-term changes in the consensus curve reveal perdurant changes on the frog; while single trains with a significant deviation from the consensus curve can also be identified. The pre- and post-train measurements are compared to determine if there is a durative change in residual-strain. All methods used are derived and pseudo-code is presented for the critical algorithms. Measurement and analysis results are presented for six types of train. An exemplary detailed analysis is presented for multiple traversing of a Talent train.

A finite element model for carburisation of surface densified PM components

The primary purpose of case hardening is to provide a hard, wear and fatigue resistant surface while maintaining a soft ductile core. PM structural parts play an increasing role in the automotive industry, especially for complex shaped parts like gears. In recent years, several studies have been published concerning surface densification of PM transmission gears containing both experimental studies and finite element-based numerical investigations of the densification process. Furthermore, a series of papers has recently been published dealing with the finite element (FE)-based simulation of the heat treatment of a PM part. The focus was on the influence of the porosity on the solid-solid phase transformation during the heat treatment. Case hardening of surface densified PM structural parts, however, has not been considered so far. The subject of the work presented here was to study the influence of the local density of a surface densified gear on the carburisation process.

Numerical and Experimental Investigation of NH4Cl Solidification

This paper deals with the validation of a volume averaged multiphase solidification model based on a benchmark experiment using NH4Cl-H2O as model alloy and Particle Image Velocimetry (PIV) as optical measurement method. For the numerical modelling of the solidification, different phases (e.g. liquid, equiaxed grains and columnar dendrite trunks) have been considered. The mass, momentum, energy conservation and species transport equations for each phase have been solved. The Eulerian-Eulerian model equations have been implemented in the commercial Finite Volume Method based software FLUENT-ANSYS v6.3 using User-Defined Functions (UDF). The mass transfer has been modelled by diffusion controlled crystal growth. The simulation of the NH4Cl-H2O solidification has been numerically investigated as a two-dimensional unsteady process in the cross-section of a 100 x 80 x 10 (mm3) experimental benchmark. Since during the experiment both columnar and equiaxed growth of NH4Cl have been observed, both phenomena have been considered in the simulation. The predicted distribution of the solidification front and the measured thickness of the mushy zone have been compared with the measurements.

Experimental and numerical investigations of NH4Cl solidification in a mould Part 2: numerical results

Abstract This paper deals with the validation of a multiphase solidification model based on a benchmark experiment presented in Part 1. For the numerical modelling of NH4Cl–H2O solidification, the three different phases liquid, columnar dendrite trunks and equiaxed grains have been considered. The mass, momentum, energy conservation and species transport equations for each phase have been solved. The multiphase Eulerian-Eulerian model equations have been implemented in the Finite Volume Method based commercial software FLUENT-ANSYS using User-Defined Functions (UDF). The simulation of the NH4Cl–H2O solidification has been numerically investigated as a twodimensional unsteady process representing a cross-section of a 100 × 80 × 10 mm experimental benchmark. During the experiment both columnar and equiaxed growth of NH4Cl were observed, therefore both phenomena were considered in the simulation. The predicted distribution of the solidification front has been compared with the measurements.

Experimental and numerical modelling of the flow field in a CuxSny direct chill caster

Abstract To investigate the influence of the casting speed on the flow field and the shape of the solidification front in an industrial bronze caster, numerical calculations have been performed and experimental flow field measurements were used to validate the numerical model. Both numerical and experimental model represented 1:1 the real caster geometry of 820 × 250 × 800 mm3. A steady-state calculation, considering solidification and turbulent flow, was performed. Furthermore, a 1:1 water model of the industrial bronze caster has been built and combined with a Particle Image Velocity (PIV) setup to measure the apparent flow fields. Amongst other parameters, the numerical model provided information on the influence of the casting speed on the solidification front shape. The water model gave the experimentalist the facility to adjust the shape of the solidification front to the one predicted by the numerical model and compare the resulting flow field with the numerical prediction. This work presents a comparison of the results of both numerical and experimental models for different casting speeds with the same numerical parameters and boundary conditions.