INFLUENCE OF SIZE EFFECTS ON SURFACE GENERATION DURING FINISH MACHINING AND SURFACE INTEGRITY IN TI-6AL-4V

Finish machining is an essential manufacturing process that is used to enhance the mechanical characteristics of critical components. The deformation that occurs at the tool and workpiece interface in finish machining significantly affects a host of component properties, commonly referred to as “surface integrity” properties. Surface roughness is a machining deformation-affected characteristic that is of high relevance in contemporary manufacturing. However, over recent decades it has been made clear that the material properties of the deformed surface layers are relevant to component performance as well. Predicting the overall surface quality of a machined component is of great relevance to the manufacturing industry. Current state-of-the-art predictive models in the area of machining-induced surface integrity are typically founded in two-dimensional F.E.M. analysis. These investigations frequently show the advantages of tool geometry manipulation. However, most efforts focus solely on the prediction of two-dimensional surface integrity qualities such as those found in orthogonal machining. Indeed, most recent models largely ignore three-dimensional properties such as surface roughness, and do not incorporate three-dimensional machining parameters that are highly relevant to the surface integrity state of typical finished components. In light of these shortcomings, the nature of surface integrity in three-dimensional machining is explored, and a physics-based geometric model of surface generation is applied to some areas of surface integrity prediction. The main focus of this work is to investigate and model the relationship between the more dominant parameters in finish turning (feed, nose radius, and edge geometry) and the surface generation phenomena that occur in the application of tools with varied geometries of this scope. The presented geometric model is derived from unique assumptions that allow for the close approximation of surface generation. The model is subsequently validated with experiments that utilize modified turning inserts of precise edge geometry, as well as pedigreed data from previous literature. Good agreement with experimental roughness results is obtained, thus verifying the validity of the surface generation assumptions. In addition, subsurface properties are found to correlate well with the geometry of ploughed areas predicted by the modeling methodology presented in this text

The Effect of Cutting Edge Geometry, Nose Radius and Feed on Surface Integrity in Finish Turning of Ti-6Al4V

While the respective effects of nose radius, feed and cutting edge geometry on surface integrity have each been studied at depth, coupling between these effects is not yet sufficiently understood. Recent studies have clearly established that cutting edge micro-geometries may not only have positive effects on tool-life, but can also be used to tailor surface integrity characteristics, such as surface roughness and near-surface severe plastic deformation. To further a more fundamental understanding of the effects of cutting edge micro-geometries on surface integrity, experimental turning data was generated for a varied range of cutting tool geometries and feeds. Scanning laser interferometry was used in conjunction with a recently developed profile-analysis algorithm to analyze, characterize, and verify the geometry of complex cutting edge micro-geometries. Near surface nanostructure, and surface roughness of the produced surfaces were characterized and correlated to the varied tool geometries. An interaction between two geometry characteristics, predicted kinematic roughness and hone size, was discovered. Scanning laser interferometry analysis of the surfaces revealed that large hones provided either an increase or decrease in roughness, depending on predicted kinematic roughness

An Iterative Size Effect Model of Surface Generation in Finish Machining

In this work, a geometric model for surface generation of finish machining was developed in MATLAB, and subsequently verified by experimental surface roughness data gathered from turning tests in Ti-6Al4V. The present model predicts the behavior of surface roughness at multiple length scales, depending on feed, nose radius, tool edge radius, machine tool error, and material-dependent parameters—in particular, the minimum effective rake angle. Experimental tests were conducted on a commercial lathe with slightly modified conventional tooling to provide relevant results. Additionally, the model-predicted roughness was compared against pedigreed surface roughness data from previous efforts that included materials 51CrV4 and AL 1075. Previously obscure machine tool error effects have been identified and can be modeled within the proposed framework. Preliminary findings of the model’s relevance to subsurface properties have also been presented. The proposed model has been shown to accurately predict roughness values for both long and short surface roughness evaluation lengths, which implies its utility not only as a surface roughness prediction tool, but as a basis for understanding three-dimensional surface generation in ductile-machining materials, and the properties derived therefrom

Long-chain omega-3 PUFAs and their role in healthy ageing

The effects of various fat subtypes can have a profound influence on our health and performance, not only in the early years of life but also as we age. The long-chain omega-3s docosahexaenoic and eicosapentaenoic acid appear to have a positive role in our mental and physical health

Computationally Efficient, Multi-Domain Hybrid Modeling of Surface Integrity in Machining and Related Thermomechanical Finishing Processes

In order to enable more widespread implementation of sophisticated process modeling, a novel, rapidly deployable multi-physics hybrid model of surface integrity in finishing operations is proposed. Rather than modeling detailed chip formation mechanics, as is common in numerical models, the proposed models integrates existing analytical and semi-empirical models of the plastic, elastic, thermal and thermodynamic domains. Using this approach, highly complex surface integrity phenomena such as residual stresses, grain size, phase composition, microhardness profile, etc. can be accurately predicted in a manner of seconds. It is envisioned that this highly efficient modeling scheme will drive new innovations in surface engineering

Gauge Invariant Variational Approach with Fermions: the Schwinger Model

We extend the gauge invariant variational approach of Phys. Rev. D52 (1995) 3719, hep-th/9408081, to theories with fermions. As the simplest example we consider the massless Schwinger model in 1+1 dimensions. We show that in this solvable model the simple variational calculation gives exact results.Comment: 14 pages, 1 figur

Conditions for the spectrum associated with a leaky wire to contain the interval [− α2/4, ∞)

The method of singular sequences is used to provide a simple and, in some respects, a more general proof of a known spectral result for leaky wires. The method introduces a new concept of asymptotic straightness

Symmetry improvement of 3PI effective actions for O(N) scalar field theory

[Abridged] n-Particle Irreducible Effective Actions ($n$PIEA) are a powerful tool for extracting non-perturbative and non-equilibrium physics from quantum field theories. Unfortunately, practical truncations of $n$PIEA can unphysically violate symmetries. Pilaftsis and Teresi (PT) addressed this by introducing a "symmetry improvement" scheme in the context of the 2PIEA for an O(2) scalar theory, ensuring that the Goldstone boson is massless in the broken symmetry phase [A. Pilaftsis and D. Teresi, Nuc.Phys. B 874, 2 (2013), pp. 594--619]. We extend this by introducing a symmetry improved 3PIEA for O(N) theories, for which the basic variables are the 1-, 2- and 3-point correlation functions. This requires the imposition of a Ward identity involving the 3-point function. The method leads to an infinity of physically distinct schemes, though an analogue of d'Alembert's principle is used to single out a unique scheme. The standard equivalence hierarchy of $n$PIEA no longer holds with symmetry improvement and we investigate the difference between the symmetry improved 3PIEA and 2PIEA. We present renormalized equations of motion and counter-terms for 2 and 3 loop truncations of the effective action, leaving their numerical solution to future work. We solve the Hartree-Fock approximation and find that our method achieves a middle ground between the unimproved 2PIEA and PT methods. The phase transition predicted by our method is weakly first order and the Goldstone theorem is satisfied. We also show that, in contrast to PT, the symmetry improved 3PIEA at 2 loops does not predict the correct Higgs decay rate, but does at 3 loops. These results suggest that symmetry improvement should not be applied to $n$PIEA truncated to $<n$ loops. We also show that symmetry improvement is compatible with the Coleman-Mermin-Wagner theorem, a check on the consistency of the formalism.Comment: 27 pages, 15 figures, 2 supplemental Mathematica notebooks. REVTeX 4.1 with amsmath. Updated with minor corrections. Accepted for publication in Phys. Rev.

Robust data-driven identification of risk factors and their interactions : A simulation and a study of parental and demographic risk factors for schizophrenia

Objectives Few interactions between risk factors for schizophrenia have been replicated, but fitting all such interactions is difficult due to high-dimensionality. Our aims are to examine significant main and interaction effects for schizophrenia and the performance of our approach using simulated data. Methods We apply the machine learning technique elastic net to a high-dimensional logistic regression model to produce a sparse set of predictors, and then assess the significance of odds ratios (OR) with Bonferroni-corrected p-values and confidence intervals (CI). We introduce a simulation model that resembles a Finnish nested case-control study of schizophrenia which uses national registers to identify cases (n = 1,468) and controls (n = 2,975). The predictors include nine sociodemographic factors and all interactions (31 predictors). Results In the simulation, interactions with OR = 3 and prevalence = 4% were identified with = 80% power. None of the studied interactions were significantly associated with schizophrenia, but main effects of parental psychosis (OR = 5.2, CI 2.9-9.7; p = 35 (1.3, 1.004-1.6; p = .04) were significant. Conclusions We have provided an analytic pipeline for data-driven identification of main and interaction effects in case-control data. We identified highly replicated main effects for schizophrenia, but no interactions.Peer reviewe

Compact QED3 with theta term and axionic confining strings

We discuss three dimensional compact QED with a theta term due to an axionic field. The variational gauge invariant functional is considered and it is shown that the ground state energy is independent of theta in a leading approximation. The mass gap of the axionic field is found to be dependent upon theta, the mass gap of the photon field and the scalar potential. The vacuum expectation of the Wilson loop is shown to be independent of theta in a leading approximation, to obey the area law and to lead to confinement. We also briefly discuss the properties of axionic confining strings.Comment: 35 pages, LaTex, typing error correcte