A predictive hybrid force modeling in turning: application to stainless steel dry machining with a coated groove tool

The International Journal of Advanced Manufacturing Technology - This paper presents an hybrid numerical/analytical modeling for estimation of cutting forces in machining process. The approach...     

A micromechanical constitutive model for dynamic damage and fracture of ductile materials

This paper proposes a detailed theoretical analysis of the development of dynamic damage in plate impact experiments for the case of high-purity tantalum. Our micro-mechanical model of damage is based on physical mechanisms (void nucleation and growth). The model is aimed to be general enough to be applied to a variety of ductile materials subjected to high tensile pressure loading. In this respect, the work of Czarnota et al. (J Mech Phys Solids 56:1624–1650, 2008) has been extended by introducing the concept of nucleation law and by entering a nonlinear formulation of the elastic response based on the Mie-Grüneisen equation of state. This later aspect allows us to consider high impact velocities. All model parameters are directly assessed by experimental measurements to the exception of the nucleation law which is characterized by the way of an inverse identification method using three free-surface velocity profiles (at low, intermediate and high impact velocities). It is shown that the nucleation law can be consistently determined in the range of operating pressures. The nucleation law being identified, the development of internal damage happens to be a natural outcome of the modelling. The model is applied to predict damage development and free-surface velocity profiles for various test conditions. The variety and the quality of results support the physical basis (in particular micro-inertia effects) upon which the proposed model of dynamic damage is based.     

Modeling of velocity-dependent chip flow angle and experimental analysis when machining 304L austenitic stainless steel with groove coated-carbide tools

This paper presents an analysis of experimental cutting forces and the study of the chip flow angle when machining 304L austenitic steel with a groove coated tool under dry condition. Experiments were conducted on a wide range of cutting conditions with a particular attention to ensure a great confidence in the obtained results. A detailed analysis of experimental cutting forces and the identification of empirical cutting force equations similar to that usually used for flat tools are proposed. The main focus of this work is on the study of chip flow angle deduced here from experimental cutting forces, considering that the chip flow direction is collinear to the friction force. From a comparison between experiments and two often used approaches, it appears that the experimental chip flow angle estimation, based on neglecting the complex tool geometry and adopting a zero rake angle, is bounded by the two considered modelings that renders useful for the proposed study. From experiments it is also observed an increase of the chip flow angle as the cutting velocity is increased. A velocity-dependent modeling with two distinct strategies of identification is then proposed in order to capture the cutting velocity effect on the chip flow angle.     

Involvement of Ceramide Signalling in Radiation-Induced Tumour Vascular Effects and Vascular-Targeted Therapy

Sphingolipids are well-recognized critical components in several biological processes. Ceramides constitute a class of sphingolipid metabolites that are involved in important signal transduction pathways that play key roles in determining the fate of cells to survive or die. Ceramide accumulated in cells causes apoptosis; however, ceramide metabolized to sphingosine promotes cell survival and angiogenesis. Studies suggest that vascular-targeted therapies increase endothelial cell ceramide resulting in apoptosis that leads to tumour cure. Specifically, ultrasound-stimulated microbubbles (USMB) used as vascular disrupting agents can perturb endothelial cells, eliciting acid sphingomyelinase (ASMase) activation accompanied by ceramide release. This phenomenon results in endothelial cell death and vascular collapse and is synergistic with other antitumour treatments such as radiation. In contrast, blocking the generation of ceramide using multiple approaches, including the conversion of ceramide to sphingosine-1-phosphate (S1P), abrogates this process. The ceramide-based cell survival “rheostat” between these opposing signalling metabolites is essential in the mechanotransductive vascular targeting following USMB treatment. In this review, we aim to summarize the past and latest findings on ceramide-based vascular-targeted strategies, including novel mechanotransductive methodologies.     

Ultrasonic biomicroscopy of viable, dead and apoptotic cells

The densities of feline epidermal dendritic cells expressing CD18, MHC class II and CD1a antigens were determined for four anatomical locations in 19 cats of European breed in blind conditions. The densities (+/- SD) of CD1a+ Langerhans cells in the skin of the abdominal wall (269 +/- 68 cells/mm2), the back (363 +/- 19), the internal side of the ear (572 +/- 30) and the external side of the ear (502 +/- 32) were significantly different, with young and old animals displaying less stained cells than adults. No significant differences in the mean densities were found with regard to sex, colour or antibody used.     

Selected aspects of epoxy adhesive compositions curing process

The paper focuses on selected parameters of curing process – temperature and time. The tests aimed at evaluating the impact of short-term thermal recuring on 1050A and 2017A aluminium alloy sheet adhesive joints strength. Joints were formed with two different adhesives, the main component of which was in both cases epoxy resin Epidian 53 and two different cure agents – poliamineamide C (PAC) and triethylenetetraamine (PF) curing agents. Curing conditions – first curing time, recuring time and recuring temperature – were modified for each of the four tests conducted. For the sake of comparative analysis, adhesive joints were subjected to a single-stage cure cycle at ambient temperature. A two-stage cure cycle of both Epidian 53 compositions at 80?°C for 1 and 2?h produces a material of different mechanical properties than the same material which submits a single-stage cure cycle at ambient temperature, as well as at 60?°C for 30?min. Simultaneously, Epidian 53/PF/100:50 composition proves to produce higher joint strength after recuring than Epidian 53/PAC/100:80; the strength of a joint formed with the former composition increases up to 50% when compared with joints subjected to a single-stage cure cycle. Moreover, tests show that recuring of the adhesive joint formed with both compositions at 60?°C for 30?min does not have a considerable influence on either 1050A or 2017A aluminium adhesive joint strength.     

Quantitative measurements of apoptotic cell properties using acoustic microscopy

Time-resolved acoustic microscopy was used to measure properties of cells such as the thickness, sound velocity, acoustic impedance, density, bulk modulus, and attenuation, before and after apoptosis. A total of 12 cells were measured, 5 apoptotic and 7 non-apoptotic. Measurements made at 375 MHz showed a statistically significant increase in the cell thickness from 13.6 ± 3.1 μm to 17.3 ± 1.6 μm, and in the attenuation from 1.08 ± 0.21 dB/cm/MHz to 1.74 ± 0.36 dB/cm/MHz. The other parameters, such as the sound velocity, density, acoustic impedance, and bulk modulus remained similar within experimental error. Acoustic images obtained at 1.0 GHz showed increased RF-signal backscatter and a clear delineation of the nucleus and cytoplasm from apoptotic cells compared with non-apoptotic cells. Extensive activity was observed optically and acoustically within apoptotic cells. Acoustic measurements made one minute apart showed variations in the ultrasonic backscatter but not attenuation in the cells, which indicated rapid structural changes were occurring but not changes in bulk composition. The normalized crosscorrelation coefficient was used to quantify the variations in the backscatter RF-signal during apoptosis by comparing the first RF signal measured to each successive RF signal every 10 s. A coefficient of 1 indicates strong correlation, whereas a coefficient of 0 indicates no correlation. An average correlation coefficient of 0.93 ± 0.05 was measured for non-apoptotic cells, compared with 0.68 ± 0.17 for apoptotic cells, indicating that the RF signal as a function of time varied rapidly during apoptosis.     

Finite element modelling of the thermo-mechanical behavior of coatings under extreme contact loading in dry machining

During metal cutting processes, intensive friction and high temperature generated at the tool chip interface affect the cutting zone of the tool, by inducing damage and wear. To improve the cutting tool's life, thin hard coatings, synthesized by physical or chemical vapor deposition (PVD or CVD) techniques, are often used as protective layers. In this work, numerical/theoretical analysis of dry machining has been performed to study the impact of different coating layers on the machining process. Four cases are considered: an uncoated tool made of tungsten carbide (WC-Co) and coated tungsten carbides in three different configurations. The first one is made of one layer namely TiN, the second one (hypothetical carbide insert) is composed of two layers (Al₂O₃ and TiN), and the last one has three layers (TiCN, Al₂O₃ and TiN). The workpiece material is an AISI 316L stainless steel. All cutting conditions are fixed in order to highlight the effect of coatings independently from others influencing parameters. The analysis has shown the impact of the different configurations of coatings on the temperature level inside the tool and on its surface, on the pressure and also on the cutting and feed forces.     

The in situ architecture of Escherichia coli ribosomal RNA derived by electron spectroscopic imaging and three-dimensional reconstruction

The structures of the large and small ribosomal subunits of Escherichia coli were reconstructed using spectroscopic electron microscopy and quaternion-assisted angular reconstitution to resolutions of better than 4 nm. In addition, the distributions of phosphorus within these complexes were reconstructed. The three-dimensional reconstruction of the distribution of this atomic element is an extension of microanalysis (in two dimensions) for phosphorus identification and mapping, as a signature of the arrangement of the phosphate backbones of the constituent ribosomal RNAs. The results on both the phosphorus reconstructions and the total reconstructions (protein and ribosomal RNA) reveal several passageways through both subunits. The structures correspond favourably with other independent reconstructions of the whole E. coli ribosome from cryoelectron micrographs and their accompanying models of translation (Frank et al ., Nature , 376, 441–444, 1995; Stark et al ., Structure , 3, 815–821, 1995). The overall reconstructions in conjunction with the phosphorus (rRNA) distributions are the first to be achieved synchronously for this nucleoprotein complex.     

Evaluation of Root Exudates of Seven Sorghum Accessions

Seven sorghum accessions were evaluated quantitatively and qualitatively for the composition of their root exudates. Utilizing a unique capillary mat growing system, root exudates were collected from all sorghum accessions. Exudates were subjected to TLC and HPLC analysis to evaluate their chemical composition. Within each sorghum accession, variation existed in the amount of exudate produced and the chemical constituents of each exudate. Sorgoleone was the predominant constituent identified in each accession's exudate. Other closely related compounds, including 5-ethoxysorgoleone, 2,5-dimethoxysorgoleone, three other minor components (MW = 364, 388, and 402), and one unidentified component comprised the minor constituents of the root exudate. Our past work has shown that several of these compounds have potent phytotoxic activity as photosystem II inhibitors, thereby lending further support to the concept that Sorghum spp. are allelopathic and weed suppressive.