Showing papers by "Francis Delannay published in 1996"

Influence of test parameters on the measurement of the essential work of fracture of zinc sheets

Abstract: The Essential Work of Fracture (EWF) concept is used to characterize the fracture of thin plates of a zinc alloy. The consistency and applicability of the EWF approach are discussed. The successive stages of the fracture process were studied: the evolution of the shape of the crack tip was observed with a scanning electron microscope, the shape of the plastic zone and the evolution of necking in the ligament ahead of the crack tip were measured using a laser profilometer and the onset of cracking in the ligament was detected by means of a TV camera coupled with acoustic emission recording. The influence of both test parameters and material parameters on the Essential Work of Fracture (We) and on the CTOD (δc) are elucidated. The effects of specimen geometry, deformation rate, texture and grain size are especially investigated. The main advantages and drawbacks of the EWF method are highlighted.

Experimental and numerical investigation of fracture in double-edge notched steel plates

Abstract: Double-edge notched (DENT) steel plates were pulled until complete fracture and several experimental observations were made (using profilometry and scanning electron microscopy). The essential work of fracture (EWF) model was found to be well verified. Numerical simulations - up to the maximum load only - of some experiments were performed using the finite element method (FEM), and incorporating geometric and material non-linearities (large deformation elasto-plasticity). Some experimental measurements were compared with the corresponding numerical computations and excellent agreement was found.

Application of Local Damage and Fracture Models to Notched Round Copper Bars

Abstract: The Rice & Tracey, damage work, and Lemaitre & Chaboche models were investigated on cylindrical notched extruded copper bars. The values of the two constant factors appearing in the expression of the void growth rate in the Rice & Tracey model were reevaluated by combining experiments (porosity measurements and tensile tests) and numerical computations of uniaxial tensile tests and of tensile tests on notched round bars. The values of the critical void growth rates (Beremin approach) and critical damage works were found to be independent on triaxiality. The application of the Lemaitre & Chaboche model allows to predict the softening appearing at initiation for lower triaxialities. Difficulties were encountered to physically identify the parameters of the model.

Critical assessment of the application of the J-integral and CTOD concepts to circumferentially cracked copper bars

Abstract: The aim of this work is to explore experimentally the validity of the concepts of J-integral and crack tip opening displacement for characterizing the stress and strain state at the tip of an axisymmetrical crack in a bar undergoing large plastic strain before crack extension. The tests are made on extruded copper round bars presenting a very high ductility. Three different analytical formulations of the J-integral proposed in the literature for circumferentially cracked bars are compared at initiation of cracking. The limit between shallow crack and deep crack geometries is experimentally demonstrated. It is found that, in neither of these geometries, J and delta CTOD are dominant. However, the ratio J(c)/delta(c) is constant for deep cracks, which suggests an alternative fracture criterion consisting in postulating the dissipation of an average critical energy per unit volume until crack extension.

Critical assessment of the process of growth of a layer on

Abstract: A layer of YBa2Cu3O7-delta (123) can be grown on a Y2BaCuO5 (211) substrate by reaction with a mixture of 3BaCuO(2) + 2CuO. This reaction has been studied in the temperature range of 930 to 980 degrees C. The reaction is never complete but levels off when the CuO present in the reactant mixture is exhausted, The liquid dissolves an excess of CuO and the 211 substrate becomes covered by co-precipitation of 123 grains and CuO inclusions. The formation of 124 and related polytypoids is favoured by the Cu-rich stoichiometry of the reactant liquid. The growth of the 123 grains follows a parabolic law. The presence of a thermal gradient during reaction does not affect the orientation of the grains but has an influence on the thickness of the 123 layer.