Mechanism investigation of friction-related effects in single point incremental forming using a developed oblique roller-ball tool

Single point incremental forming (SPIF) is a highly versatile and flexible process for rapid manufacturing of complex sheet metal parts. In the SPIF process, a ball nose tool moves along a predefined tool path to form the sheet to desired shapes. Due to its unique ability in local deformation of sheet metal, the friction condition between the tool and sheet plays a significant role in material deformation. The effects of friction on surface finish, forming load, material deformation and formability are studied using a newly developed oblique roller ball (ORB) tool. Four grades of aluminum sheet including AA1100, AA2024, AA5052 and AA6111 are employed in the experiments. The material deformation under both the ORB tool and conventional rigid tool are studied by drilling a small hole in the sheet. The experimental results suggest that by reducing the friction resistance using the ORB tool, better surface quality, reduced forming load, smaller through-the-thickness-shear and higher formability can be achieved. To obtain a better understanding of the frictional effect, an analytical model is developed based on the analysis of the stress state in the SPIF deformation zone. Using the developed model, an explicit relationship between the stress state and forming parameters is established. The experimental observations are in good agreement with the developed model. The model can also be used to explain two contrary effects of friction and corresponding through-the-thickness-shear: increase of friction would potentially enhance the forming stability and suppress the necking; however, increase of friction would also increase the stress triaxiality and decrease the formability. The final role of the friction effect depends on the significance of each effect in SPIF process

From Mexico to Beijing: "Women in Development" Twenty Five Years On

During the past twenty five years the Women in Development (WID)approach has become an increasingly important issue in the literature on Third World development. WID issues and related activities have now been incorporated into the aid practice of most development agencies. This paper critically analyses the diverse and conflicting ideologies that have emerged in the WID literature since the early seventies

Charge carrier transport in boron doped poly Si

The influence of the used substrate and the boron doping concentration of the charge-transport properties of solid-phase crystallized polycrystalline silicon (poly-Si) is explored. The samples were characterized using temperature dependent transport measurements to determine mobility, carrier concentration, and conductivity. While Arrhenius plots of the hole concentration cannot be used to determine the position of the Fermi energy, a detailed analysis of the temperature dependent carrier concentration shows a Meyer–Neldel and an anti-Meyer–Neldel rule. Charge transport in poly-Si on SiN coated Borofloat glass with a boron concentraion [B] &lt; 1016 cm–3 is limited by phonon scattering. On the other hand, for all poly-Si samples on Corning glass and poly-Si on SiN coated Borofloat glass with [B] &gt; 1016 cm–3 charge-carrier transport is governed by thermionic emission over potential barriers. The data are discussed in terms of the Baccarani transport model. </jats:p

Angle-resolved photoemission spectroscopy of tetragonal CuO: Evidence for intralayer coupling between cupratelike sublattices

We investigate by angle-resolved photoemission the electronic structure of in situ grown tetragonal CuO, a synthetic quasi-two-dimensional edge-sharing cuprate. We show that, in spite of the very different nature of the copper oxide layers, with twice as many Cu in the CuO layers of tetragonal CuO as compared to the CuO2 layers of the high-Tc cuprates, the low-energy electronic excitations are surprisingly similar, with a Zhang-Rice singlet dispersing on weakly coupled cupratelike sublattices. This system should thus be considered as a member of the high-Tc cuprate family, with, however, interesting differences due to the intralayer coupling between the cupratelike sublattices.1991sciescopu

Ticket-splitting and strategic voting under mixed electoral rules: Evidence from Germany

"There is more to strategic voting than simply avoiding wasting one’s vote if one is liberated from the corset of studying voting behavior in plurality systems. Mixed electoral systems provide different voters with diverse incentives to cast a strategic vote.They not only determine the degree of strategic voting, but also the kind of strategies voters employ. Strategic voters employ either a wasted-vote or a coalition insurance strategy, but do not automatically cast their vote for large parties as the current literature suggest. This has important implications for the consolidation of party systems. Moreover, even when facing the same institutional incentives, voters vary in their proclivity to vote strategically." (author's abstract