Reduction of the mesh size influence on the results of a lagrangian finite element machining mode

Mesh dependence of the results of a finite element model are well known in many fields such as in structural design. This problem is however not much addressed in the literature for machining modelling although it is crucial for the quality of the results and the predictive aspect of the model. In this work, an orthogonal cutting model of the titanium alloy Ti6Al4V is exploited. The model formulation is Lagrangian and a damage criterion with eroding elements is used. A strong sensitivity of the results to the size of the elements is observed and the results do not converge when the size of the mesh decreases. To address this issue, a non-local damage criterion that reduces the mesh dependence of the results is introduced. The results show a strong decrease of their dependence to the size of the mesh. The recommendation is to use elements length that is not too far from the size of the grains of the material to avoid a dramatic increase of the computing time for very small elements and the absence of converged results for too large elements

Boson and neutron stars with increased density

We discuss boson stars and neutron stars, respectively, in a scalar-tensor gravity model with an explicitly time-dependent real scalar field. While the boson stars in our model -- in contrast to the neutron stars -- do not possess a hard core, we find that the qualitative effects of the formation of scalar hair are similar in both cases : the presence of the gravity scalar allows both type of stars to exist for larger central density as well as larger mass at given radius than their General Relativity counterparts. In particular, we find new types of neutron stars with scalar hair which have radii very close to the corresponding Schwarzschild radius and hence are comparable in density to black holes. This new branch of solutions is stable with respect to the decay into individual baryons.Comment: Matches version published in Phys. Lett.

Coupled Eulerian-Lagrangian (CEL) simulation for modelling of chip formation in AA2024-T3

Aluminium alloys are of the most used alloys in the aeronautic industry. Increasing knowledge in machining and prediction of chip formation in these materials is crucially important to design better components with enhanced functional performance. To achieve this, a new finite element modelling strategy is developed to incorporate material damage and softening in the Coupled Eulerian-Lagrangian (CEL) formulation for the machining of AA2024 alloy. The CEL modelling technique is adopted to simulate chip formation at high cutting speeds. An orthogonal cutting setup is used to compare the modelling predictions with experimentally measured cutting forces and chips sections. The proposed model shows a good ability to reproduce the experimental results and to predict the trends induced by variations in the cutting conditions

Distinctive Features of Hairy Black Holes in Teleparallel Gauss-Bonnet Gravity

We examine the teleparallel formulation of non-minimally coupled scalar Einstein-Gauss-Bonnet gravity. In the teleparallel formulation, gravity is described by torsion instead of curvature, causing the usual Gauss-Bonnet invariant expressed through curvature to decay into two separate invariants built from torsion. Consequently, the teleparallel formulation permits broader possibilities for non-minimal couplings between spacetime geometry and the scalar field. In our teleparallel theory, there are two different branches of equations in spherical symmetry depending on how one solves the antisymmetric part of the field equations, leading to a real and a complex tetrad. We first show that the real tetrad seems to be incompatible with the regularity of the equations at the event horizon, which is a symptom that scalarized black hole solutions beyond the Riemannian Einstein-Gauss-Bonnet theory might not exist. Therefore, we concentrate our study on the complex tetrad. This leads to the emergence of scalarized black hole solutions, where the torsion acts as the scalar field source. Extending our previous work, we study monomial non-minimal couplings of degrees one and two, which are intensively studied in conventional, curvature-based, scalar Einstein-Gauss-Bonnet gravity. We discover that the inclusion of torsion can potentially alter the stability of the resulting scalarized black holes. Specifically, our findings indicate that for a quadratic coupling, which is entirely unstable in the pure curvature formulation, the solutions induced by torsion may exhibit stability within certain regions of the parameter space. In a limiting case, we were also able to find black holes with a strong scalar field close to the horizon but with a vanishing scalar charge.Comment: 14 pages, 14 figures. Matches published version in PR

Recent advances in modelling and simulation of surface integrity in machining - A review

Machining is one of the final steps in the manufacturing value chain, where the dimensional tolerances are fine-tuned, and the functional surfaces are generated. Many factors such as the process type, cutting parameters, tool geometry and wear can influence the surface integrity (SI) in machining. Being able to predict and monitor the influence of different parameters on surface integrity provides an opportunity to produce surfaces with predetermined properties. This paper presents an overview of the recent advances in computational and artificial intelligence methods for modelling and simulation of surface integrity in machining and the future research and development trends are highlighted