The analysis of tool life and wear mechanisms in spindle speed variation machining

Regenerative chatter vibrations generally limit the achievable material removal rate in machining. The diffusion of spindle speed variation (SSV) as a chatter suppression strategy is mainly restricted to academy and research centers. A lack of knowledge concerning the effects of non-stationary machining is still limiting its use in real shop floors. This research is focused on the effects of spindle speed variation technique on tool duration and on wear mechanisms. No previous researches have been performed on this specific topic. Tool wear tests in turning were carried out following a factorial design: cutting speed and cutting speed modulation were the investigated factors. The carbide life was the observed process response. A statistical approach was used to analyze the effects of the factors on the tool life. Moreover, the analysis was extended to the wear mechanisms involved during both constant speed machining and SSV. The worn-out carbide surfaces were examined under a scanning electron microscope equipped with an energy dispersive X-ray spectrometer. Significant differences were appreciated. It was observed that SSV tends to detach the coatings of the inserts, entailing a mechanism that is quite unusual in wet steel turning and thus fostering the wear of the tool. The performed analysis allowed to deduce that the intensified tool wear (in SSV cutting) is mainly due to thermo-mechanical fatigue

A novel application of cryogenics in dieless sheet metal piercing

In tube punching, if the internal die is necessary to properly pierce the tube avoiding its collapse, it also represents a bottleneck to a rapid change of the punching set. In this research an innovative dieless tube punching approach has been conceived and studied. The use of a cryogenic fluid to force the material ductile-brittle transition is a way to limit the sheet deformation during the piercing process. The analysis of the innovative cryogenic punching was carried out both adopting numerical and experimental methodologies. A finite element FE model of the cryogenic punching was developed and updated in two stages. First, experimental tensile tests, performed at cryogenic temperatures, were used to characterize some material properties. Secondly, some piercing tests in cryogenic conditions were performed at different velocities and temperatures to fine update the model. A validation session was carried out to assess the model and the process feasibility. It was found that the FE model reproduced the experimental results within a maximum estimation error of 10% on both the punching force and tube deflection. Results showed that both the increment of the punching velocity and especially the decrement of the punching temperature could be the only viable solution for making the tube dieless punching industrially feasible

Volcaniclastic sedimentation in a closed, marginal rift basin: the case of the Melka Kunture area (Upper Awash, ethiopia)

The upper Awash runs across a volcano-sedimentary succession dated from the Early to Middle Pleistocene and located on the western margin of the northern portion of the Main Ethiopian Rift. The succession lies above Late Miocene to Pliocene lava flows, domes and large volume ignimbrites. The succession formed within a fluvial system that developed within transversal rift faults. The stratigraphy consists of primary volcanic deposits interbedded with reworked sediments emplaced in a low-energy floodplain developed in a subsiding area. The lower part of the volcaniclastic sequence is dominated by a 1.2 Ma old, low aspect ratio, pyroclastic density current deposit (Kella ignimbrite). This eruption was followed by an eruptive stasis and reorganization of the drainage system. Tephra deposition in the floodplain climaxed again between 0.9 and 0.7 Ma and was associated with extensive tephra reworking. Sedimentation rates significantly decreased after 0.6 myr ago, probably owing to declining volcanic activity. Dynamic interaction between tectonics and volcanic activity created a complex sedimentary environment preserving numerous artefacts (lithic tools), animal and hominin remains. Stratigraphic correlation is based on the interpretation of the basin evolution and has relevance for the reconstruction of the palaeoenvironment and the interpretation of the palaeontological and archaeological data

Caracterización superficial de pigmentos sobre artefactos paleolíticos de la zona de los Montes Albanos (Roma, Italia) por microscopía óptica y espectroscopía raman

Preliminary results of the characterization of red pigmentations on paleolithic artefacts from the southern area of Montes Albanos (Rome, Italy) are presented. The set of materials consists of three decorated rounded pebblestones and a cortical flint blade typologically attributable to the Upper Paleolithic (Final Epigravetense, 14,000-12,000 cal BP). The findings were observed with optical microscope Nikon SMZ 1000/800 with magnifications of 1x to 6.3x. In two pebblestones, one decorated with parallel engravings, residues of ocher were detected in association with traces of use. In the third one, stained red dye was observed to form geometric patterns. Finally, reddish pigmentations were located on the cortical dorsal surface of a flint blade. To characterize chemically the coloring agent detected, macro-microscopically, Raman spectroscopy was used, a technique that allowed the study of the nature of the residues and the detection of additional organic materials whose presence must be related to post-depositional contaminations produced by the manipulation or/and surface exposure of artifacts

Electron-phonon interaction in the solid form of the smallest fullerene C20_{20}

The electron-phonon coupling of a theoretically devised carbon phase made by assembling the smallest fullerenes C$_{20}$ is calculated from first principles. The structure consists of C$_{20}$ cages in an {\it fcc} lattice interlinked by two bridging carbon atoms in the interstitial tetrahedral sites ({\it fcc}-C$_{22}$). The crystal is insulating but can be made metallic by doping with interstitial alkali atoms. In the compound NaC$_{22}$ the calculated coupling constant $\lambda/N(0)$ is 0.28 eV, a value much larger than in C$_{60}$, as expected from the larger curvature of C$_{20}$. On the basis of the McMillan's formula, the calculated $\lambda$=1.12 and a $\mu^*$ assumed in the range 0.3-0.1 a superconducting T$_c$ in the range 15-55 K is predicted.Comment: 7 page

Association of Body Mass Index of HIV-1-Infected Pregnant Women and Infant Weight, Body Mass Index, Length, and Head Circumference: The NISDI Perinatal Study.

This study assessed the relationship between the body mass index (BMI) of HIV-1-infected women and their infants' perinatal outcomes. The study population consisted of women enrolled in the NICHD International Site Development Initiative (NISDI) Perinatal Study with data allowing calculation of the BMI adjusted for length of gestation (adjBMI), who delivered singleton infants. Outcome variables included infant growth parameters at birth (weight, BMI, length and head circumference) and gestational age. Of 697 women from Argentina, the Bahamas, Brazil and Mexico who were included in the analysis, the adjBMI was classified as underweight for 109 (15.6%), normal for 418 (60.0%), overweight for 88 (12.6%) and obese for 82 (11.8%). Median infant birth weight, BMI, birth length and head circumference differed significantly according to maternal adjBMI (P</=0.0002). Underweight mothers gave birth to infants with lower weight, lower BMI, shorter length and smaller head circumference, while infants born to normal, overweight and obese mothers were of similar size

EVALUATION OF THE CYTOTOXICITY OF PULP FLOOR PERFORATION FILLING MATERIALS BY USING IN PARALLEL 2D AND 3D CULTURE MODELS

Oral Communication presented at the ";Forum des Jeunes Chercheurs";, Brest (France) 2011