Hernan Alberto González Rojas

THERMOMECHANICAL ANALYSIS OF AN ELECTRICALLY-ASSISTED WIRE DRAWING PROCESS

Electrically-assisted wire drawing process is a hybrid manufacturing process characterized by enhancement of the formability, ductility and elongation of the wire drawn specimen. A thermomechanical model to describe the change of the mechanical response due to the thermal contribution is proposed in this work. Additionally, a numerical simulation was conducted to study the potential and limitations of this hybrid process by using two different hardening laws: a phenomenological and a dislocationbased hardening laws. The results show how the flow stress, the effective plastic strain and residual stresses behave under the electroplusing effect. In addition, Electron Backscattered Diffraction was used to study the electropulsing treatments on the microstructure during cold drawing. It is observed a decrease of the high and low angle grain boundaries for samples deformed with electropulsing. This detwinning process has a strong influence on the strain hardening by improving the material formability. It was shown that the two proposed hardening laws adequately describe the electrically-assisted wire drawing process showing a similar mechanical behavior. Nevertheless, the dislocation-based hardening law has the potential to be generalized to many other material and process configurations without extensive number of material tests as the phenomenological hardening law would require.

Differential diagnosis between Parkinson's disease and essential tremor using the smartphone's accelerometer

Background The differential diagnosis between patients with essential tremor (ET) and those with Parkinson’s disease (PD) whose main manifestation is tremor may be difficult unless using complex neuroimaging techniques such as 123I-FP-CIT SPECT. We considered that using smartphone’s accelerometer to stablish a diagnostic test based on time-frequency differences between PD an ET could support the clinical diagnosis. Methods The study was carried out in 17 patients with PD, 16 patients with ET, 12 healthy volunteers and 7 patients with tremor of undecided diagnosis (TUD), who were re-evaluated one year after the first visit to reach the definite diagnosis. The smartphone was placed over the hand dorsum to record epochs of 30 s at rest and 30 s during arm stretching. We generated frequency power spectra and calculated receiver operating characteristics curves (ROC) curves of total spectral power, to establish a threshold to separate subjects with and without tremor. In patients with PD and ET, we found that the ROC curve of relative energy was the feature discriminating better between the two groups. This threshold was then used to classify the TUD patients. Results We could correctly classify 49 out of 52 subjects in the category with/without tremor (97.96% sensitivity and 83.3% specificity) and 27 out of 32 patients in the category PD/ET (84.38% discrimination accuracy). Among TUD patients, 2 of 2 PD and 2 of 4 ET were correctly classified, and one patient having PD plus ET was classified as PD. Conclusions Based on the analysis of smartphone accelerometer recordings, we found several kinematic features in the analysis of tremor that distinguished first between healthy subjects and patients and, ultimately, between PD and ET patients. The proposed method can give immediate results for the clinician to gain valuable information for the diagnosis of tremor. This can be useful in environments where more sophisticated diagnostic techniques are unavailable.

Influence of the Regime of Electropulsing-Assisted Machining on the Plastic Deformation of the Layer Being Cut

In this article, the influence of electropulsing on the machinability of steel S235 and aluminium 6060 has been studied during conventional and electropulsing-assisted turning processes. The machinability indices such as chip compression ratio ξ, shear plane angle ϕ and specific cutting energy (SCE) are investigated by using different cutting parameters such as cutting speed, cutting feed and depth of cut during electrically-assisted turning process. The results and analysis of this work indicated that the electrically-assisted turning process improves the machinability of steel S235, whereas the machinability of aluminium 6060 gets worse. Finally, due to electropluses (EPs), the chip compression ratio ξ increases with the increase in cutting speed during turning of aluminium 6060 and the SCE decreases during turning of steel S235.

Estimation of the polishing time for different metallic alloys in surface texture removal

ABSTRACT The aim of this work is to propose a novel analytical model for predicting the polishing time and behavior of the surface texture removal in different metal alloys. The surface texture, resulting from a previous milling process, is characterized and investigated by the Abbott–Firestone curve, the relative speed of the abrasive material, the applied force, the type of material and the size of the abrasive grains. Consequently, a model that predicts the surface texture evolution based on the mechanism of abrasion is proposed, in which a constant of the wear model is found to behave linearly with the size of the abrasive grain for each metal alloy. Based on the good agreement between the experimental and the estimated values (R2 equal to 0.993), operational parameters are recommended to predict the required surface texture for AlCu4PbMg, 30CrNiMo8, C45E and X6CrNiMo8 when using abrasive grade between P180 and P1200.

Time measurement characterization of stand-to-sit and sit-to-stand transitions by using a smartphone

The aim of this study is to analyze a common method to measure the acceleration of a daily activity pattern by using a smartphone. In this sense, a numerical approach is proposed to transform the relative acceleration signal, recorded by a triaxial accelerometer, into an acceleration referred to an inertial reference. The integration of this acceleration allows to determine the velocity and position with respect to an inertial reference. Two different kinematic parameters are suggested to characterize the profile of the velocity during the sit-to-stand and stand-to-sit transitions for Parkinson and control subjects. The results show that a dimensionless kinematic parameter, which is linked to the time of sit-to-stand and stand-to-sit transitions, has the potential to differentiate between Parkinson and control subjects.