Showing papers by "Mines ParisTech published in 1983"

A Local Criterion for Cleavage Fracture of a Nuclear Pressure Vessel Steel

Abstract: Experiments were performed on three heats of A508 class 3 steel in order to determine the mechanical conditions for cleavage fracture. These tests were carried out on various geometries including 4-point bend specimens and axisymmetric notched tensile bars with different notch radii which have been modelized using the finite element method. In one heat, the temperature range investigated was from 77 K to 233 K. It is shown that the cleavage resistance is increased by tensile straining. Moreover, the probability of fracture obeys the Weibull statistical distribution. All the results can be accounted for in terms of a local criterion based on Weibull theory and which takes into account the effect of plastic strain. In this criterion, the parameters which were experimentally determined are found to be temperature independent over the range 77 K to 170 K. The applicability of the approach proposed for cleavage fracture at the crack tip is also examined. It is shown that the experimental results published in the literature giving the variation of fracture toughness with temperature can be explained by the proposed criterion which predicts reasonably well both the scatter in the experimental results and theKICtemperature dependence.

A linear-system-theoretic view of discrete-event processes

Abstract: A discrete-event system is a system whose behavior can be described by means of a set of time-consuming activities, performed according to a prescribed ordering. Events correspond to starting or ending some activity. An analogy between linear systems and a class of discrete-event systems is developed. Following this analogy, such discrete-event systems can be viewed as linear, in the sense of an appropriate algebra. The periodical behavior of closed discrete-event systems, i.e. involving a set of repeatedly performed activities, can be totally characterized by solving an eigenvalue and eigenvector equation in this algebra. This problem is numerically solved by an efficient algorithm which basically consists in finding the shortest paths from one node to all other nodes in a graph. The potentiality of this approach for the performance evaluation of repetitive production processes is illustrated on an example.

Fatigue oxidation interaction in a superalloy—application to life prediction in high temperature low cycle fatigue

Abstract: A study of the interaction between fatigue and oxidation has been carried out in the case of a cast cobalt base superalloy MARM 509 tested in laboratory air at 900 °C. The influence of fatigue cycling on oxidation of this alloy has been studied by quantitative metallography on polished specimens exposed to air in a furnace and on strain-cycled low-cycle fatigue specimens. The oxidation kinetics were determined by thickness measurements for matrix oxidation and by oxidized depth measurements for the preferential oxidation of MC carbides. In both cases the oxidation kinetics were found to be dramatically enhanced by cycling for the matrix oxidation according to a linear relationship with plastic strain amplitude and less dramatically for carbides according to an exponential relationship with the maximum cyclic stress. From these observations a damage equation which describes fatigue damage as a crack growth process has been proposed: the elementary crack advance is a summation of a mechanical contribution due to the fatigue process itself which is described by Tomkins’ equation and of an oxidation contribution which has been evaluated from metallographic measurements. Integration of this crack growth equation gives predicted fatigue lives which are in good agreement with experimental results within a factor of two.

Effect of stress triaxiality on neck propagation during the tensile stretching of solid polymers

Abstract: Cylindrical samples of high density polyethylene were tested in tension at 21° C and a nominal strain rate of 8.5 × 10−4 sec−1. The occurrence of necking in the centre of the specimens was provoked by the introduction of area defects of various sizes. The stabilization of this constriction and its propagation towards the ends of the specimens was studied photographically. An analytical method for the description of neck development is outlined, based on the use of strain and strain rate gradients. The times corresponding to neck initiation and stabilization are shown to be associated with critical values of the local strain hardening coefficient of the material. The role of area, strength and temperature inhomogeneities in the kinetics of strain localization is discussed. A further inhomogeneity term based on the axial variation of the Bridgman triaxiality factor FT is introduced. It is shown that the transverse compressive stresses associated with the shoulders of the neck can play a significant role in neck propagation in otherwise homogeneous materials.

The Role of Colloids in Nuclear Waste Disposal

Abstract: Aspects of formation and characterization of a radioactive colloidal fraction released by the waste form or produced by association with microcolloids naturally existing in ground water or produced either by corrosion of container material or by degradation of backfill material are discussed. A filtration model has been developed in order to describe colloidal transport under field conditions. Comparison between data obtained with laboratory column experiments and theoretical evaluations is presented.

Short crack propagation and closure effects in a508 steel

Abstract: — Fatigue crack growth measurements are usually made on standard specimens containing long cracks (∼10 mm) although in most practical situations, a large part of the fatigue life is spent with much shorter dimensions. The purpose of the present study is a comparison of crack growth behaviour for long cracks (∼13–16 mm) in CT specimens and smaller ones (∼0.3–0.5 mm) in four point bend specimens. Large effects are noticed indicating that, at a given stress intensity factor amplitude, the crack growth rate is significantly higher in specimens with short cracks. Mouth displacement measurements for both specimen configurations show that the crack closure phenomenon accounts for the observed effect. Crack closure is likely to be associated with fracture surface roughness as shown by partly machining the material left behind the crack tip in CT specimens.

Crystalline defects in M7C3 carbides

Abstract: M7C2, carbides prepared in various conditions have been observed by electron microscopy and diffraction. Examinations of the first-order Laue zone with crystals having the c axis parallel to the electron beam demonstrate that the unit cell describing the structure of these carbides is the orthorhombic cell proposed by Fruchart and Rouault. This cell can be considered as an ordered cell of an average hexagonal cell and can have three orientations at 120° from each other. It contains metal atom tetrahedra whose local environment in prismatic interstices containing carbon atoms is typical and is never destroyed, whatever the conditions of preparation may be. Thus, in primary carbides present in cast irons and steels, the state of crystallization is such that a long-range order of the environment is established : ortho-rhombic domains are separated by {1I00} twins and antiphase boundaries. In Fe7C3 carbides crystallized from amorphous iron-carbon alloys, the local environments are only short...

Scientific Basis of Water Resource Management

Abstract: The least that one can say about the report is that it is very enjoyable reading. Every chapter has been carefully written, and the literary merit of some chapters is outstanding (particularly those by Klemes, ‘Empirical and Causal Models in Hydrology,’ and by Baker, ‘Geology, Determinism, and Risk Assessment’). The best that one can say about the report is that it does meet its stated objectives of (1) evaluation of the adequacy of present hydrologic knowledge and of the appropriateness of present research programs to provide information for decision making and (2) description of the impact of hydrologic knowledge on the planning and management of water resources. The worst that one can say about the report is that it is not particularly original and that there are few really fresh new arguments developed in it. One notable exception is provided in Chapter 11, by Matalas, Landwehr, and Wolman, which challenges the traditional (implicit) assumption that ‘human activity is an external perturbation of the hydrologic cycle.’ Though not the explicit intent of chapter 4, by Bredehoeft, Papadopulos, and Cooper, with the explosion of the water-budget myth in groundwater, this chapter illustrates clearly the profound interaction of man (through wells) in the hydrologic cycle, a situation that cannot be comprehended from a study of the system free from human influence.

Crack Initiation Under Low-Cycle Multiaxial Fatigue in Type 316L Stainless Steel

Abstract: Low-cycle fatigue tests corresponding to fatigue life range between 103 and 105 cycles were carried out at room temperature on one heat of 316 L austenitic stainless steel. These tests included: (i) reversed tension-compression, (ii) reversed tension-compression with a superimposed steady torque, (iii) pulsated tension-compression with a stress ratio (R σ ) such that −0.5

Les Minéralisations Manganésifères Volcano-Sedimentaires du Blafo-Guéto (Côte d'Ivoire) — Paragénèses — Altération Climatique

Abstract: Les indices manganesiferes des collines Blafo et Gueto sont rencontres dans les quartzites et les schistes sericiteux associes aux epanchements rhyolitiques d'une serie volcano-sedimentaire birrimienne. La mineralisation, epigenetique, est une impregnation d'oxydes de fer (goethite) et de manganese (essentiellement MnO2-cryptomelane et nsutite), surimposee a une paragenese initiale a magnetite, pyrophanite et localement ottrelite et grenat. L'alteration meteorique n'a provoque de transformations notables que dans les materiaux associes a deux surfaces d'aplanissement. L'une est conservee sous forme de petits temoins bauxitises au sommet des collines et des minerais enrichis sont associes a la gibbsite et la kaolinite. L'autre est un glacis de piemont et le manganese s'y disperse dans une cuirasse ferrugineuse.

Dislocation mobility measurements : an essential tool for understanding the atomic and electronic core structures of dislocations i n semiconductors

Abstract: Thanks to the exploration of a wider range of stress and temperature, and to better instrumental resolution, new phenomena have been investigated and are reviewed here. Deviations to Schmid's law at high stresses and low temperatures, changes in the activation energy at high temperatures, influence on dislocation velocities of dislocation lengths, impurities and point defects and illunlination are reported and discussed in terms of kink nucleation and migration, core structures and reconstruction defects. Some new experiments are also proposed.

Statistical Distribution of Solar Radiation (Hourly Sums): Cumulative Frequency Curves

Abstract: Cumulative Frequency Curves of solar irradiance are a suitable climatic input for solar systems sizing simplified methods. From this study they will be available for various european locations and types of surfaces (orientation and tilting).

Deformation and Fracture Behaviour of a Dual-phase Cr-V Steel

Abstract: Dual-phase structure in an HSLA steel containing 1% Cr and 0.2% V was produced by cooling from austenite field to the (α+γ) region, then quenching in iced brine. The quenched steels were tempered at 700°C. Linear equations were proposed to express the effect of martensite volume fraction and tensile strength on uniform elongation, products of tensile strength and uniform or total elongation. Cleavage and/or void coalescence was the operating mode of fracture for quenched steels, whereas void coalescence was the main mechanism after tempering. The size of the voids was found to be affected by the steel plasticity.

EXAFS Study of Co1−xBx Glasses

Abstract: The usefulness of EXAFS in studying the local order around the atom probe is now clearly demonstrated by an increasing number of papers. However, in disordered materials, this technique does not reproduce the average pair distances measured by other methods such as X-ray diffraction unless the asymmetry of the pair potential is taken into account.

Heliosat Project : Estimation of Global Radiation from Satellite Using a Statistical Approach

Abstract: The global objective of the HELIOSAT project is to develop an operational system for estimating the global hourly radiation from the geostationnary satellite METEOSAT, using a low-cost SDUS receiving station.