Ball-burnishing process influence on hardness ans residual stresses of aluminium A92017

The ball-burnishing process is done firstly, to improve the surface finish of workpieces that have been previously machined and secondly, to obtain a harder surface with a compressive residual stress map. In this way we will obtain a surface that is more resistant to wear and fatigue. In this paper we present results of tests performed with this process that was applied to workpieces with a convex surface of aluminium A92017. An experiment to do tests was designed. Measurement results of surface hardness and residual stress are presented in this paper as well. These results are compared to those measured in the workpieces before being burnished. Finally conclusions are drawn about the improvement of these properties applied to workpieces through the ball burnishing process. The main innovation of this paper is that we work on convex geometries. We also obtain a table of recommended parameter values for the process

Effects of a ball-burnishing process assisted by vibrations in G10380 steel specimens

This paper explores the effects on the surface roughness, hardness and residual stress of G10380 steel specimens milled and treated with a ball-burnishing process assisted by vibrations. These vibrations are incorporated through the attachment of an induced coil module to a conventional burnishing tool, with forces transmitted through a pre-loaded spring. A positive effect of vibrations on the improvement and efficiency of the burnishing treatment is demonstrated, empirically proving that the vibrations introduce additional energy into the system that aids with displacements along the surface of the material to reallocate the crystalline structure. Significant results are found in terms of final surface roughness, which is highly improved in comparison to conventional burnishing treatments, even with fewer passes and a significant time reduction. Less robust results are observed in terms of specimen hardness and residual stress, but future improvements could be derived with a thorough development of the vibration system

Study of a ball-burnishing vibration-assisted process

This study refers to the study of the ball-burnishing process assisted by vibration. This study begins by considering that this vibration helps to make the development of this finishing process easier because it helps to deform the workpiece material more easily. Because a similar tool is not available in the market, a tool that can perform the study needed to be designed, characterised and manufactured to conduct the study by considering the critical components that are involved in the design and the physical model that characterises the operation. For these criteria, the tool operation is also characterised by evaluating the surface roughness that remains after the process occurs. Workpieces of aluminium and steel were used for the experimental validation. These results were compared to those obtained using the same tool without vibration. The roughness results obtained using the ball-burnishing vibration-assisted process improve compared to those obtained using the process without assistance for both materials tested

Experimental Study on the Mechanical Effects of the Vibration-Assisted Ball-Burnishing Process

Burnishing processes are effective methods for treating pieces to increase their durability and roughness. Studies reveal that traditional burnishing can be strongly improved with the assistance of external energy sources. A vibrating module was attached to a classical burnishing tool and was tested on aluminum specimens to find the optimal vibrationassisted burnishing parameters. Vibration caused roughness improvements of the specimens and decreased the processing time by fivefold compared to traditional burnishing. At the tested frequency, no significant consequences were found on hardness and residual stresses

Search for new physics with same-sign isolated dilepton events with jets and missing transverse energy

A search for new physics is performed in events with two same-sign isolated leptons, hadronic jets, and missing transverse energy in the final state. The analysis is based on a data sample corresponding to an integrated luminosity of 4.98 inverse femtobarns produced in pp collisions at a center-of-mass energy of 7 TeV collected by the CMS experiment at the LHC. This constitutes a factor of 140 increase in integrated luminosity over previously published results. The observed yields agree with the standard model predictions and thus no evidence for new physics is found. The observations are used to set upper limits on possible new physics contributions and to constrain supersymmetric models. To facilitate the interpretation of the data in a broader range of new physics scenarios, information on the event selection, detector response, and efficiencies is provided.Comment: Published in Physical Review Letter

Search for a W' boson decaying to a bottom quark and a top quark in pp collisions at sqrt(s) = 7 TeV

Results are presented from a search for a W' boson using a dataset corresponding to 5.0 inverse femtobarns of integrated luminosity collected during 2011 by the CMS experiment at the LHC in pp collisions at sqrt(s)=7 TeV. The W' boson is modeled as a heavy W boson, but different scenarios for the couplings to fermions are considered, involving both left-handed and right-handed chiral projections of the fermions, as well as an arbitrary mixture of the two. The search is performed in the decay channel W' to t b, leading to a final state signature with a single lepton (e, mu), missing transverse energy, and jets, at least one of which is tagged as a b-jet. A W' boson that couples to fermions with the same coupling constant as the W, but to the right-handed rather than left-handed chiral projections, is excluded for masses below 1.85 TeV at the 95% confidence level. For the first time using LHC data, constraints on the W' gauge coupling for a set of left- and right-handed coupling combinations have been placed. These results represent a significant improvement over previously published limits.Comment: Submitted to Physics Letters B. Replaced with version publishe

Combined search for the quarks of a sequential fourth generation

Results are presented from a search for a fourth generation of quarks produced singly or in pairs in a data set corresponding to an integrated luminosity of 5 inverse femtobarns recorded by the CMS experiment at the LHC in 2011. A novel strategy has been developed for a combined search for quarks of the up and down type in decay channels with at least one isolated muon or electron. Limits on the mass of the fourth-generation quarks and the relevant Cabibbo-Kobayashi-Maskawa matrix elements are derived in the context of a simple extension of the standard model with a sequential fourth generation of fermions. The existence of mass-degenerate fourth-generation quarks with masses below 685 GeV is excluded at 95% confidence level for minimal off-diagonal mixing between the third- and the fourth-generation quarks. With a mass difference of 25 GeV between the quark masses, the obtained limit on the masses of the fourth-generation quarks shifts by about +/- 20 GeV. These results significantly reduce the allowed parameter space for a fourth generation of fermions.Comment: Replaced with published version. Added journal reference and DO

Measurement of the t t-bar production cross section in the dilepton channel in pp collisions at sqrt(s) = 7 TeV

The t t-bar production cross section (sigma[t t-bar]) is measured in proton-proton collisions at sqrt(s) = 7 TeV in data collected by the CMS experiment, corresponding to an integrated luminosity of 2.3 inverse femtobarns. The measurement is performed in events with two leptons (electrons or muons) in the final state, at least two jets identified as jets originating from b quarks, and the presence of an imbalance in transverse momentum. The measured value of sigma[t t-bar] for a top-quark mass of 172.5 GeV is 161.9 +/- 2.5 (stat.) +5.1/-5.0 (syst.) +/- 3.6(lumi.) pb, consistent with the prediction of the standard model.Comment: Replaced with published version. Included journal reference and DO

Compressed representation of a partially defined integer function over multiple arguments

In OLAP (OnLine Analitical Processing) data are analysed in an n-dimensional cube. The cube may be represented as a partially defined function over n arguments. Considering that often the function is not defined everywhere, we ask: is there a known way of representing the function or the points in which it is defined, in a more compact manner than the trivial one