Showing papers by "Mines ParisTech published in 1982"

Plastic deformation and solid-phase transformation in polybutene-1

Abstract: The stress-strain behaviour under uniaxial tension was investigated for polybutene-1 specimens crystallized in Modification II with various types of spherulitic microstructure and degrees of crystallinity. As for Modification I, the tensile properties were found to depend greatly on the initial microstructure, but Modification II specimens exhibit a much more pronounced plastic behaviour than specimens fully transformed into Modification I prior to deformation. The deformation of spherulites within the samples was followed either by direct microscopic observation or by means of small-angle light scattering patterns. In situ microscopic observations of individual spherulites showed that the characteristic dark band, which appeared in the early stages of the deformation of Modification I spherulites and which corresponds to the whitening of the strained samples when observed with reflected light, occurred for much larger strains in the case of specimens initially crystallized in Modification II. Differential scanning calorimetry and wide-angle X-ray scattering experiments performed before and after the tensile tests ensured that the unstable tetragonal Modification II was transformed into the stable hexagonal Modification I during the plastic deformation. Eventually, the evolution of this phase transformation was determined as a function of the applied tensile strain by use of X-ray diffractometry.

Propagation of fatigue cracks under polymodal loading

Abstract: — The influence of steady mode III on mode I fatigue growth behavior is investigated in four materials–a plain carbon steel, a Ni–Cr–Mo–V rotor steel, and titanium alloys, TA6V and TA5E ELI. It is shown that these loading conditions give rise to two main effects: (i) a strong reduction in propagation rate and (ii) a modification in crack path, the fatigue crack adopting a characteristic “factory-roof’ aspect. In 2024 Al alloy, it is shown that the superimposition of steady mode II to cyclic mode I leads to crack bifurcation, the angle θ being a function of Ka/Ktmax. These observations are discussed in the light of a new criterion which is introduced. This criterion is based on two main assumptions: (i) Fatigue cracking is assumed to occur only under the effect of local mode I opening. (ii) It is postulated that a fatigue crack grows in a direction where the crack propagation rate is maximum. A number of limitations of this approach, associated with crack closure phenomenon, are discussed.

The Use of Torsion Testing to Assess Material Formability

Abstract: The accurate conversion of the torque/twist data obtained from torsion tests into equivalent stress/equivalent strain data is required for reliable formability predictions, particularly at large strains. The first stage in this process is the derivation of the shear stress/shear strain curve from the torque/twist data. A new method is proposed which performs this first operation. It is based on the observation that the radii of cylindrical bars remain straight during testing, and also on the hypothesis that the state of the material at a given radius is not influenced by the state of the surrounding layers. This method appears to reduce significantly the errors inherent in the previous methods. The second stage involves converting the shear stress/strain curve into an equivalent stress/equivalent strain relationship, with due consideration for the very large strains involved. For this purpose, the equivalent strain ∈ e q is calculated from the incremental changes in the strain components during torsion. This analysis leads to the relation ∈ e q = γ/√3 where γ is the shear strain at the radius of interest. This solution is the same as for small deformations, and thus conflicts with the result of Eichinger and Siebel, which is different for large strains. It is also shown that, when the corrected conversions are used, the rate of work hardening calculated from torsion tests is lower than that obtained from uniaxial testing. This discrepancy is attributed to three causes: (a) at low strains, the torsion equivalent stresses calculated using the von Mises relationship are 6.5 percent lower than those obtained from the crystallographically based Bishop and Hill formulation, which is judged to be more accurate; (b) the difference in the textures developed in torsional and tensile deformation leads to Taylor factors that evolve differently with strain, and which cause the tension and torsion equivalent stresses to diverge at large strains, even if the true rates of work hardening (in terms of the critical resolved shear stresses) are the same in the two modes of deformation; (c) there is a possibility that there is less dislocation accumulation at large strains in torsion than in tension because less dislocation intersection is required by the torsion as opposed to the tension end textures. The lower work hardening rates determined in torsion lead in turn to lower forming limit predictions for deformation along other strain paths.

Quantitative analysis of 5-fluorouracil and 5,6-dihydrofluorouracil in plasma by gas chromatography mass spectrometry

Abstract: 5-Fluorouracil and 5,6-dihydro-5-fluorouracil were analysed in the plasma of patients by combined gas chromatography mass spectrometry. 5-Bromouracil was the internal standard. After extraction from plasma with an isopropanol-diethyl ether mixture (20/80) the components were pentylated and the derivatives produced extracted into diethyl ether. Electron impact mass spectrometry was used for the simultaneous quantitative determinations of 5-fluorouracil and 5,6-dihydro-5-fluorouracil (detection limit 10 ng ml-1 5-fluorouracil, 80 ng ml-1 5,6-dihydro-5-fluorouracil). Chemical ionization was utilized to measure 5,6-dihydro-5-fluorouracil concentrations less than 80 ng ml-1 (sensitivity 10 ng ml-1). The biological applicability of these two techniques was demonstrated by analysing plasma samples from patients after administration of 5-fluorouracil or 5'-deoxyfluorouridine by intravenous injections and infusions.

How to measure the degree of independence of a research system

Abstract: The French bibliographic data-base PASCAL is used to study relations between Research Systems in terms of dependance of a periphery upon a Center.The deployment of disciplines, the productivity and the use of mother tongue of 9 developped countries are quantified (on the Life Science file only).This dependance is also quantified by reference to who studies whom, and in which language the results are available. A search in Life Science and Earth Science files by means of subject terms added by PASCAL indexers at input to papers published by 5 developped countries working on fourteen Latino-american and African countries.

Determination of the plastic and viscoelastic properties of a metallic soap by a hot hardness measurement

Abstract: An analysis of an indentation test in the case of mixed plastic—viscoelastic behaviour, as is met in metallic soaps, is described. The viscoelastic part of the strain is described in terms of a Burgers model whose five rheological parameters are then a yield stress,σ0, two elasticity moduli,G0 andG1, and two viscosities,η0 andη1. This analysis is applied to a hot hardness experiment on a compacted metallic soap, calcium stearate, between 20 and 130° C. By fitting the model to the experimental curves, values ofσ0,η0,η1,G0 andG1 as a function of temperature, have been derived. It is shown that plastic strain is much greater than viscous strain at low temperature, sinceη0 is very high. The material is therefore a solid. It is also shown that, as temperature increases, viscous strain increases and plasticity vanishes (above a transition temperature,σ0=0, and only viscoelasticity remains). The curvesη0(T),η1 (T),G0(T) andG1 (T) have marked slope changes at about 90° C (which is the crystal—crystal phase transition temperature of calcium stearate), and the viscosities fall at 123° C, which is the first crystal mesomorphic phase-transition temperature. This test seems to be a good simple rheological measurement for bodies exhibiting simultaneous plasticity and viscosity or viscoelasticity.

An Evaluation of the Plane Strain Compression Test. II. Experimental Study of the Friction Test: Role of Transfer Layers in Boundary Lubrication

Abstract: The Plane Strain Compression Test is used to measure the mean friction shear stress at the sheet-die interfaces. It is found that the shear-stress level is strongly influenced by transfer film formation on the dies. The thickness of these films, and their elementary chemical composition, have been determined by Auger Electron Spectroscopy and rugosimetry. The effect of contact mechanics and lubricant parameters on transfer film formation is discussed.

EFFECT OF STRESS AND STRAIN ON MARTENSITIC TRANSFORMATION IN A Fe-Ni-Mo-C ALLOY WITH A HIGH Ms TEMPERATURE

Abstract: The interactions between stress and martensitic transformation are studied for a low alloyed steel (60NCD11) with a Ms temperature of 230°C. For tensile tests carried out at temperatures just above Ms, the transformation doesn't exhibit the stress-assisted behavior expected for athermal martensitic transformation. In contrast, for "static" tests, Ms is enhanced even at low stresses, but this enhancement is cooling-rate dependant. A comparison has been made with an Fe-Ni-C-Cr alloy obtained by adding Nickel to the 60NCD11 steel and an Fe-20 Ni - 0.5 C alloy. For these two alloys Ms is below room temperature. A classical scheme with stress-assisted martensite and strain-induced martensite is observed for the Fe - 20 Ni - 0.5 C alloy but an intermediate behaviour is obtained for the Fe-Ni-C-Cr alloy.

An indirect adaptive control scheme for disturbed MIMO systems

Abstract: An adaptive on line pole placement control scheme is presented which involves at each step identification of the unknown system matrices followed by a nonlinear computation of the adaptive feedback matrices. We show that a priori knowledge of an upperbound of the degree of the numerator, and of column degrees of a column proper denominator is sufficient to get local boundedness even when the system is corrupted by bounded disturbances.

The Relationship Between Structure, Properties and Processing in Powder Metallurgy Superalloys

Abstract: After a review of the influence of composition, powder production technique and processing parameters on mechanical properties and on weldability, the effects described are interpreted in the light of microstructural and analytical observations on both loose particles and consolidated products.

Towards a direct adaptive control scheme for general disturbed mimo systems

Abstract: The existence of direct adaptive control schemes for not necessarily minimum phase Multiinput-Multioutput systems is stated. This result is based on identification of a model with a bilinear structure when on line pole placement is to be achieved. We establish global boundedness even when the norm of the residuals between the true plant and the assumed linear model is bounded from above by the norm of the signals.