ULTRASONIC ASSISTED TURNING OF HARDENED STEEL WITH MONOCRYSTALLINE DIAMOND
INTRODUCTION The demand for ultra-precise steel parts with optical surface qualities and complex shaped geometries is increasing and could be applied for plastic injection molding or precision glass molding processes. Nowadays optical molds for injection molding are coated with a nickel layer, in order to be able to machine the surface with diamond tools. Directly machined steel parts would decrease manufacturing time, making the coating process step unnecessary. Additionally, the life time of the mold is increased dramatically. Uncoated steel tools have a higher scratch resistance and no risk of delamination. Therefore the potential of directly machining steel with monocrystalline diamond is exceptionally high.
Theoretical modeling of tool mean temperature during ultrasonically assisted turning
This article summarizes the results of theoretical and experimental studies of average tool temperature in ultrasonic-assisted turning of aerospace aluminum using Al2O3-coated tools. In theoretical study, thermal modeling of heat source at the tool–work interface and the temperature distribution in the cutting tool are presented. To determine the actual performance, the sticking and slipping tool–chip contact lengths (lc and ls) are experimentally measured and then heat source at the tool–work interface is modeled according to the analogy between shear stress distribution and heat source distribution on the rake face. Then, with respect to the kinematics of the process, the cutting velocity model is presented. The velocity model is used to define the heat flux equation and shear strain rate in ultrasonic-assisted turning. Using heat flux function and Johnson–Cook model, the temperature distribution in a semi-infinite rectangular corner, as a function of time and distance from tool tip, is presented. The analysis results are compared with experimental measurements of average cutting temperature from ultrasonic-assisted turning tests on 7075 aluminum using K-type Testo 735 thermocouple. On the other hand, results show that ultrasonic-assisted turning does not necessarily lower the average cutting temperature in all cases. The effectiveness of the technique is highly dependent on the value of vibration amplitude, work velocity, and feed rate. At low feed rates and amplitudes, the average tool temperature for ultrasonic-assisted turning is 60% of the conventional turning value while growing with an increase in feed rate and amplitude.
Exposure to violence in incarcerated youth from the city of São Paulo.
OBJECTIVE
This study aimed to determine the extent of exposure to community violence among delinquent Brazilian youth in the 12-month period prior to their incarceration and to identify factors associated with this exposure.


METHOD
With an oversampling of girls, a cross-section of youth under 18 years of age from juvenile detention units in the city of São Paulo, Brazil completed a structured interview. Key items related to exposure to violence (witnessed and experienced) were drawn from the Social and Health Assessment questionnaire to cover the 12-month period prior to incarceration.


RESULTS
Participants (n = 325, 89% boys) reported high rates of exposure to violence with largely similar levels for boys and girls. Being threatened with physical harm, being beaten or mugged and/or shot at were the most common forms of violence experienced. After controlling for demographic and family variables, the fact of having peers involved in risk behavior, easy access to guns and previous involvement with the justice system were associated with witnessed violence; whereas having slept on the street was the only variable associated with experienced violence.


CONCLUSION
This group of youth was exposed to high levels of violence and other adverse experiences. Future research should examine the effectiveness of strategies aimed at reducing the exposure to violence of high-risk youth.