Wyniki wyszukiwania - BazTech

1

Effect of the cutting speed on the chip morphology and the cutting forces

Daymi A., Boujelbene M., Ben Salem S., Hadj Sassi B., Torbaty S.

Archives of Computational Materials Science and Surface Engineering

|

2009

|

Vol. 1, nr 2

77-83

EN

Purpose: The aim of this research is to make a first experimental analysis of the effect of the cutting speed on the chip morphology, and of the cutting forces in the orthogonal turning process of the titanium alloys Ti-6Al-4V. Design/methodology/approach: The methodology has consisted of proving a series of parameters combinations: f, feed rate, Vc, cutting speeds are explored in a range from 50 to 250 m/min, and is analyzing the different types of chips and the evolution cutting forces appeared during each one them, and determined the analytical model of plastic deformation ratio. Findings: Tests achieved have shown three main types of chips: Continuous chip at 50 m/min, Flow chip for speeds ranging around 100 m/min, and Shear localized chip starting from the transition speed of 125 m/min and above. The modification of the mechanism of chip formation is associated with the appearance of shearing instability. Chip segmentation by shear localisation is an important process which is observed within a certain range of cutting speeds. This phenomenon might be desirable in reducing the level of the cutting forces by improving chip's evacuation. Research limitations/implications: A possible future work would be the development of a general the phenomenal of the thermo mechanical of the cutting high speed machining. The behavior is of the thermo - visco - plastic studies are planed in the future. Practical implications: The relationship found between high speed machining and chip morphology and the cutting forces and work piece surface finish has an important practical implication since it allows selecting the best cutting condition combination from the points of view both the security and the economy for the established requirements in each case. Results are of great importance in for aerospace, biomedical and automotive industry. Originality/value: The paper is original since the bibliographical review has allowed testing that, although works about these themes exist, none approaches the problem like it has been made in work.

2

Adiabatic heat evaluation for dynamic plastic localization

Longere P., Dragon A.

Journal of Theoretical and Applied Mechanics

|

2007

|

Vol. 45 nr 2

203-223

EN

In most cases, adiabatic plastic heating is evaluated using the inelastic heat fraction coefficient, also known as Taylor-Quinney coefficient, which is usually assumed to be constant. From the thermodynamic viewpoint, this method consists in neglecting (or including some part of) various thermomechanical couplings in the heat equation. Nevertheless this coarse method can lead to over-estimation of the temperature rise. In this paper, adiabatic shear banding incipience is considered in the context of thermal instability. It is shown that the accuracy in the prediction of favourable conditions for the onset of this plastic localization is strongly dependent on the technique retained for evaluating the plasticity induced heating. This paper aims at showing the influence of various levels of simplification of the thermal equation on the critical conditions at localization onset, the latter being obtained from a criterion based on the linear perturbation method.

PL

Adiabatyczne ogrzewanie w stanie plastycznym jest w większości przypadków opisywane za pomocą ułamkowego ciepła zwanego współczynnikiem Taylora-Quinney'a, zwykle przyjmowanego jako parametr o stałej wartości. Opis taki, z punktu widzenia termodynamiki, zasadza się na pomijaniu (lub uwzględnianiu jedynie pewnej części) sprzężeń termomechanicznych w równaniu definiującym bilans cieplny. Taki zgrubny opis może prowadzić do przeszacowania wzrostu temperatury w obliczeniach dotyczących plastycznego ogrzewania. W pracy przedstawiono proces adiabatycznego formowania pasm ścinania wynikający z termicznej niestabilności. Pokazano, że dokładność w przewidywaniu korzystnych czynników dla inicjacji procesu lokalizacji odkształceń plastycznych silnie zależy od metody szacowania ciepła powstającego wskutek uplastycznienia. Celem rozważań jest pokazanie wpływu różnego stopnia uproszczeń przyjętych w równaniu bilansu cieplnego na warunki odpowiadające za pojawienie się lokalizacji odkształceń plastycznych. Te ostatnie wyznaczono za pomocą kryterium opartego na liniowej metodzie perturbacyjnej.

3

Modelling adiabatic shear banding via damage mechanics approach

Longere P., Dragon A., Trumel H., Resseguier T. de, Deprince X., Petitpas E.

Archives of Mechanics

|

2003

|

Vol. 55, nr 1

3-38

EN

During dynamic loading processes, large plastic deformation associated with high strain rates leads, for a broad class of ductile metals, to degradation and failure by adiabatic shear banding. The paper presents an attempt to model some salient features of this process viewed as an anisotropic damage mechanism coupled with thermo--elastic/viscoplastic deformation. The model is destined to be applied in the context of high velocity impact and penetration mechanism. The methodology employed within the framework of the internal state variable structure strives to keep a middle way between extensive description of complex viscoplastic flow and damage events and application-oriented accessibility requirements. Model capabilities are prelaminarily illustrated for shear loading process.