Genetic adaptability of durum wheat to salinity level at germination stage

Faculty of Sciences, University of Tunis El Manar, Tunis from April to May 2010 to improve salt tolerance during germination stage. For this purpose, two crosses and their progenies (F1, F2, BC1Ps and BC1Pr) were used based on shoot length at different salinity levels (0, 50, 75, 100, 150 and 200 mmol/L). Significant differences for salt tolerance between means of generations were observed in all the treatments. Separate generation means analysis indicated that inheritance of resistance to salt at germination stage was dependent upon the level of salinity. With low salinity level (50 and 75 mmol/L), only additive and dominance effects were implicated in the genetic control of this trait. For moderate salinity level (100 and 150 mmol/L) in the two crosses, genetic interactions were solicited and the digenic epistatic model was sufficient to explain variation in generation means. However, for the 200 mmol/L treatment, none of these models explained the variations in generation means and probably, higher order interactions or genes linkage were solicited. The estimated values of narrow-sense heritability were dependent on the cross and the salinity level and ranged between 29 and 90%. The results of this study indicated that selection in specific environments is useful for enhancing resistance to salt, but it may not be effective in providing resistance across a wide range of environments.Keys words: Durum wheat, genetic-adaptability, salinity level

Performance of nano-structured multilayer PVD coating TiAlN/VN in dry high speed milling of aerospace aluminium 7010-T7651

A low-friction and wear resistant TiAlN/VN multilayer coating with TiAlN/VN bilayer thickness 3 nm has been grown by using the combined cathodic arc etching and unbalanced magnetron sputtering deposition on high speed steel tools for dry cutting of aluminium alloys. In this paper, in-lab and industrial high speed milling tests have been performed on an aerospace aluminium alloy 7010-T7651. The results show that the TiAlN/VN coated tools achieved lower cutting forces, lower metal surface roughness, and significantly longer tool lifetime by three times over the uncoated tools as a result of the low friction and eliminated tool-metal adhesion. Under the same conditions, a TiAlN based multicomponent coating TiAlCrYN also increased the tool lifetime by up to 100% despite the high cutting forces measured

Toward a better understanding of tool wear effect through a comparison between experiments and SPH numerical modelling of machining hard materials

The aim of this study is to improve the general understanding of tungsten carbide (WC–Co) tool wear under dry machining of the hard-to-cut titanium alloy Ti6Al4V. The chosen approach includes experimental and numerical tests. The experimental part is designed to identify wear mechanisms using cutting force measurements, scanning electron microscope observations and optical profilometer analysis. Machining tests were conducted in the orthogonal cutting framework and showed a strong evolution of the cutting forces and the chip profiles with tool wear. Then, a numerical method has been used in order to model the machining process with both new and worn tools. The use of smoothed particle hydrodynamics model (SPH model) as a numerical tool for a better understanding of the chip formation with worn tools is a key aspect of this work. The redicted chip morphology and the cutting force evolution with respect to the tool wear are qualitatively compared with experimental trends. The chip formation mechanisms during dry cutting process are shown to be quite dependent from the worn tool geometry. These mechanisms explain the high variation of the experimental and numerical feed force between new and worn tools

Comparative study between wear of uncoated and TiAlN-coated carbide tools in milling of Ti6Al4V

As is recognized widely, tool wear is a major problem in the machining of difficult-to-cut titanium alloys. Therefore, it is of significant interest and importance to understand and determine quantitatively and qualitatively tool wear evolution and the underlying wear mechanisms. The main aim of this paper is to investigate and analyse wear, wear mechanisms and surface and chip generation of uncoated and TiAlN-coated carbide tools in a dry milling of Ti6Al4V alloys. The quantitative flank wear and roughness were measured and recorded. Optical and scanning electron microscopy (SEM) observations of the tool cutting edge, machined surface and chips were conducted. The results show that the TiAlN-coated tool exhibits an approximately 44% longer tool life than the uncoated tool at a cutting distance of 16 m. A more regular progressive abrasion between the flank face of the tool and the workpiece is found to be the underlying wear mechanism. The TiAlN-coated tool generates a smooth machined surface with 31% lower roughness than the uncoated tool. As is expected, both tools generate serrated chips. However, the burnt chips with blue color are noticed for the uncoated tool as the cutting continues further. The results are shown to be consistent with observation of other researchers, and further imply that coated tools with appropriate combinations of cutting parameters would be able to increase the tool life in cutting of titanium alloys

3D Finite Element Modelling of Cutting Forces in Drilling Fibre Metal Laminates and Experimental Hole Quality Analysis

Machining Glass fibre aluminium reinforced epoxy (GLARE) is cumbersome due to distinctively different mechanical and thermal properties of its constituents, which makes it challenging to achieve damage-free holes with the acceptable surface quality. The proposed work focuses on the study of the machinability of thin (~2.5 mm) GLARE laminate. Drilling trials were conducted to analyse the effect of feed rate and spindle speed on the cutting forces and hole quality. The resulting hole quality metrics (surface roughness, hole size, circularity error, burr formation and delamination) were assessed using surface profilometry and optical scanning techniques. A three dimensional (3D) finite-element (FE) model of drilling GLARE laminate was also developed using ABAQUS/Explicit to help understand the mechanism of drilling GLARE. The homogenised ply-level response of GLARE laminate was considered in the FE model to predict cutting forces in the drilling process

Tool wear in high speed machining

High speed machining has received an important interest because it leads to an increase of productivity and a better workpiece surface quality. However, at high cutting speeds, the tool wear increases dramatically due to the high temperature at the tool-workpiece interface. There are three major processes of wear : abrasion wear, adhesion wear and diffusion wear. The last one is predominant at large temperature. Chemical diffusion produces a transfer of the tool constituents towards the chip. The loss of some of those constituents reduces the tool mechanical resistance and its efficiency. That is why an important objective of metal cutting research has been the assessment of tool wear and the evaluation of tool-life. This paper describes diffusion wear and presents an analytical model which allows to calculate the concentration of the diffused substances. The mass which is lost by the tool is obtained according to the cutting conditions such as cutting speed, rake angle and depth of cut. The model includes the physical and chemical parameters of the tool and of the workpiece

Influence of the tribological phenomenon on the tool wear in dry drilling of aluminum alloy AA2024 T351

In machining, the formation of chip and tool wear is controlled by the tribological phenomenon at the tool-chip interface. Investigations show that the contact between the tool and the chip tends to change from a sliding contact to a sticking contact. When the cutting speed is increased, the tool rake face temperature can attain large values (sometimes of the order of 1000 °C in the case of machining steels). Without the use of coolants and lubricants, this temperature can be higher. These high temperatures are due to the important deformation work associated with large shear strains in the primary shear zone, and to the friction effects along the tool-chip interface. An experimental analysis of the tool wear for dry machining of aeronautic aluminum alloy AA2024 T351 is proposed. The change in the tribological conditions at the tool-chip interface is discussed

Analysis of tribological parameters during machining

In this paper, a hybrid analytical-numerical approach is performed for the orthogonal cutting process. The modelling of the thermomechanical material flow in the primary shear zone, the tool-chip contact length and the sliding-sticking zones are obtained from an analytical approach. In addition, the Finite Element method is used to solve the non linear thermal problem in the chip. Our aim is to propose an approach which can easily be used to identify the main parameters governing tool wear and to explain the experimental trends. The effects of cutting conditions and material behaviour on the sliding-sticking zones and on the temperature distribution along the tool-chip interface can be evaluated from this approach. It has been found that the sliding-sticking zones at the tool-chip interface strongly control the local conditions of stress, velocity and temperatur