Machining Simulation of Ti6Al4V under Dry and Cryogenic Conditions

Abstract Nowadays, numerical modeling is becoming a valuable and powerful tool for designing and optimizing the production process, as well as improving the machined components quality. Particularly, the Finite Element Method permits to increase the knowledge on the machinability of difficult-to-cut metals, such as the titanium alloys. The aim of this work is to develop a 3D FE model as a tool for predicting cutting forces, temperature, and machining-induced microstructural alterations during semi-finishing turning Ti6Al4 V under dry and cryogenic conditions. The numerical model is experimentally calibrated and validated

Analysis of the Surface Integrity in Cryogenic Turning of Ti6Al4 v Produced by Direct Melting Laser Sintering

The Ti6Al4V is widely utilized in the biomedical field thanks to its high biocompatibility, however, due to its low machinability, is classified as a difficult-to-cut material. With the goal of improving the surface quality of biomedical components made of Ti6Al4V produced by the DMLS additive manufacturing technology and later on machined, Liquid Nitrogen was tested as a coolant in semi-finishing turning. The integrity of the machined surfaces is evaluated in terms of surface defects and topography as well as residual stresses. The obtained results showed that the cryogenic machining assured a lower amount of surface defects and higher values of the residual compressive stressed compared to dry cutting, but a general worsening of the surface topography was detected

Training Support Vector Machines Using Frank-Wolfe Optimization Methods

Training a Support Vector Machine (SVM) requires the solution of a quadratic programming problem (QP) whose computational complexity becomes prohibitively expensive for large scale datasets. Traditional optimization methods cannot be directly applied in these cases, mainly due to memory restrictions. By adopting a slightly different objective function and under mild conditions on the kernel used within the model, efficient algorithms to train SVMs have been devised under the name of Core Vector Machines (CVMs). This framework exploits the equivalence of the resulting learning problem with the task of building a Minimal Enclosing Ball (MEB) problem in a feature space, where data is implicitly embedded by a kernel function. In this paper, we improve on the CVM approach by proposing two novel methods to build SVMs based on the Frank-Wolfe algorithm, recently revisited as a fast method to approximate the solution of a MEB problem. In contrast to CVMs, our algorithms do not require to compute the solutions of a sequence of increasingly complex QPs and are defined by using only analytic optimization steps. Experiments on a large collection of datasets show that our methods scale better than CVMs in most cases, sometimes at the price of a slightly lower accuracy. As CVMs, the proposed methods can be easily extended to machine learning problems other than binary classification. However, effective classifiers are also obtained using kernels which do not satisfy the condition required by CVMs and can thus be used for a wider set of problems

Neonatal Cortical Auditory Evoked Potentials Are Affected by Clinical Conditions Occurring in Early Prematurity

Purpose: Cortical auditory evoked potentials may serve as an early indicator of developmental problems in the auditory cortex. The aim of the study was to determine the effect on neonatal cortical auditory processing of clinical conditions occurring in early prematurity. Methods: Sixty-seven preterm infants born at 29 weeks mean gestational age (range, 23\u201334 weeks) were recorded at a mean postconception age of 35 weeks, before discharge from the third level neonatal intensive care unit. The average of 330 responses to standard 1000 Hz pure tones delivered in an oddball paradigm was recorded at frontal location. Data of 45 of 67 recruited premature infants were available for analysis. Mean amplitudes calculated from the data points of 30 milliseconds centered on P1 and N2 peaks in the waveforms of each subject were measured. The effect of perinatal clinical factors on cortical auditory evoked responses was evaluated. Results: The amplitude of P1 component was significantly lower in infants with bronco-pulmonary dysplasia (P \ubc 0.004) and retinopathy of prematurity (P \ubc 0.03). The multivariate analysis, done to evaluate the relative weight of gestational age and bronco-pulmonary dysplasia and/or retinopathy of prematurity on cortical auditory evoked potentials components, showed an effect of clinical factors on P1 (P \ubc 0.005) and of gestational age on N2 (P \ubc 0.02). Conclusions: Cortical auditory processing seems to be influenced by clinical conditions complicating extremely preterm birth

SVILUPPO DI UN METODO DIGITALE PER L’ANALISI DELLE SOLLECITAZIONI IN COMPONENTI MECCANICI FORTEMENTE INTAGLIATI

The thesis proposed a experimental method for the assessment of the Notch Stress Intensity Factors (NSIF) of V-notches under mixed mode loadings without the use of particular techniques of experimental type in the preparation of the specimen and the use of sophisticated optical equipment laboratory. The NSIFs are calculated on the basis of a comparison of two digital photos of a calculation grid placed in the area of maximum stress concentration taken whit a digital camera. The photos are calculated to different load conditions and taken with a commercial digital camera. The method is particularly flexible in order to effect the introduction of an innovative compensation system errors and misalignments. The function performed by the compensation system can also seen as a calibration performed on the image and not a priori. The position of each dot in the refinement mesh is read automatically by the software. By using the parameter JV (J-integral applied to the V-grooves) provides directly NSIF of the notch under mixed mode (I and II). A mesh of dark spots is created on the surface near the notch tip and yhr spots have a diameter of abaut 20 pixel which is equivalent to a few tenths of a millimetre in standard applications. The technique is also applicable to plane models that reproduce the resistant section of a weld, in particular will be considered classical form of cruciform joints. Staric measurements were performed with normale tensile loads on speciments PVC or Aluminium. Is finally proposed an alternative employment of the technique for direct application on the surface instead of the notch in section for measuring the KI. This application is interesting because it potentially also be applied directly to the components in use. The accuracy of the experimental method with respect to the FE analysis is around then per cent

Tractor cabin ergonomics analyses by means of Kinect motion capture technology

Kinect is the de facto standard for real-time depth sensing and motion capture cameras. The sensor is here proposed for exploiting body tracking during driving operations. The motion capture system was developed taking advantage of the Microsoft software development kit (SDK), and implemented for real-time monitoring of body movements of a beginner and an expert tractor drivers, on different tracks (straight and with curves) and with different driving conditions (manual and assisted steering). Tests show how analyses can be done not only in terms of absolute movements, but also in terms of relative shifts, allowing for quantification of angular displacements or rotations

Virtual water trade and country vulnerability: A network perspective

In this paper, we analyze the link between virtual water trade, that is, the flow of water embodied in the international trade of agricultural goods, and vulnerability to external shocks from the vantage point of network analysis. While a large body of work has shown that virtual water trade can enhance water saving on a global scale, being especially beneficial to arid countries, there are increasing concerns that more openness makes countries more dependent on foreign food suppliers and especially more susceptible to external shocks. Our evidence reveals that the increased globalization witnessed in the last 30 years is not associated with the increased frequency of adverse shocks (in either precipitation or food production). Furthermore, building on recent advances in network analysis that connect the stability of a complex system to the interaction between the distribution of shocks and the network topology, we find that the world is more interconnected, but not necessarily less stable