[en] Several recent theoretical studies have considered the problem of the probability of fast fracture in pressure vessels due to induced flaws. These studies assume all relevant quantities to be randomly distributed and independent, whereas service experience suggests that the presence of defects and inferior-toughness material may be correlated to some degree. The lack of statistical data on spatial distributions of material properties precludes a detailed analysis, but it is possible to develop simplified models to examine some aspects of the problem. In particular it is possible to devise an upper bound on the influence of correlation effects, making minimal use of statistical information. A lower bound on failure probability is given by the analysis based on completely randomly distributed properties. It can be shown that in some applications the effects of correlation are not significant, without necessarily knowing what correlation exists. In other instances the effect of correlation is to introduce a common-mode element which significantly increases the failure probability. (orig.)

[en] The C-E ALWR is an upgrade of the proven System 80 NSSS standard design and so is referred to as System 80+. Both plants are rated at 3817 Mwt, but System 80+ incorporates a number of modifications to the design. A best-estimate small break study addressed the economic concern of how large a break size can be tolerated without the two-phase fluid level falling below the top of the core. With a best-estimate analytical procedure and no single failure the core was shown to remain covered for breaks up to, and including, that of a 10 in. dia. break. A large break licensing analysis confirms that adequate reflood exists following the end of SIT discharge without a LPSI system

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[en] In this paper, the development of advanced analytical capabilities for the treatment of piping systems is reported. It is a three-dimensional structural-response analysis of piping systems that considers both the hoop and flexural stresses, including bending in both planes. The analysis is also coupled with modified fluid-flow algorithms that takes into account the three-dimensional motion of the piping systems. A three-dimensional uniform cross-section pipe element with eight degrees of freedom at each node is described. The degrees of freedom are: three displacements along three orthogonal directions, three rotations about the three axes (one torsional and two bending rotations), pipe shell hoop displacement and pipe shell bending rotation. Thus, hoop, flexural, axial, and torsional modes of response are considered in the element. (orig.)

[en] Analysis of the response of high energy lines after the occurence of pipe rupture has received considerable attention in recent past, with an array of different modelling techniques proposed and available in the literature. Information on relative merits of such methods is scarce and the present study provides tentative guidelines to the designer confronted with the selection of an appropriate model for a given system. The criteria of evaluation are, implicitly, the time required for analysis and the computer cost involved and, explicitly, the degree of accuracy of the solutions. The models compared are grouped into four classes: (i) one-degree-of-freedom-systems that introduce a stationary plastic hinge and require simple hand calculations, (ii) kinematic models incorporating the concept of a travelling hinge, easily analysed by means of inexpensive computer programs, (iii) engineering beam models considering elasto-plastic pipe behavior and (iv) two dimensional finite element systems based on plane stress theory. The kinematic model, proposed earlier by the authors, is used to conduct a qualitative analysis of the response as a function of the magnitude of external force, gap size and rigidity of the restraint. The engineering beam model gives results that practically coincide with those generated by the plane stress approach, although consistently a little higher than the latter. The methods were applied to typical configurations with bilinear restraints and the results obtained prove that the single-degree-of-freedom model may lead to non conservative solutions whereas the straight application of the kinematic model would always underestimate the maximum deformation of the restraint. (orig.)

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[en] In several recent investigations, experimental studies on the effect of normal stress on the hydraulic conductivity of a single fracture were made on three rock specimens ranging in cross-sectional area from 0.02 m² to over 1.0 m². At the maximum stress levels that could be attained (10 to 20 MPa), minimum values of the fracture hydraulic conductivity were not the same for each rock specimen. These minimum values increased with specimen size, indicating that the determination of fracture conductivity may be significantly influenced by a size effect. The implications of these results are important. Cores collected in the field are normally not larger than 0.15 m in diameter. However, the results of this work suggest that when this size core is used for laboratory investigations, the results may be nonconservative in that fracture permeabilities will be significantly lower than will be found in the field. 6 figures

[en] We combine the asynchronous spacetime discontinuous Galerkin (aSDG) method, an interfacial-damage fracture model, and a dynamic contact model to simulate dynamic fracture and crack closure in brittle materials. The contact model enforces specialized Riemann solutions for bonded, separation, slip and stick conditions while preserving elastodynamic characteristic structure across fracture interfaces. Powerful adaptive spacetime meshing tracks dynamic evolution of fracture-surface networks and captures moving solution features. We present numerical examples to demonstrate the model’s ability to reveal fine details of fracture response in problems that range from dynamic crack initiation, growth, closure, and arrest along a pre-defined planar path to fragmentation of rock by an explosively loaded wellbore with stochastic nucleation, free propagation, and coalescence of fracture surfaces.

[en] We present a theoretical study of the sub-critical fracture of heterogeneous materials under a constant external load. A generic fiber bundle model is proposed, which provides a direct connection between the microscopic fracture mechanisms and the macroscopic time evolution of the sub-critical system. In the model, material elements either fail due to immediate breaking or undergo a damage accumulating ageing process. On the macrolevel the model reproduces the empirical Basquin law of rupture life, and it makes it possible to derive a generic scaling form for the deformation histories of different load values. On the microlevel we found that sub-critical fracture is accompanied by crackling noise, i.e. the competition of the two failure modes of fibers gives rise to a complex bursting activity, where slow damage sequences trigger bursts of breaking events. When the load is equally distributed over the fibers, the size of damage sequences and of bursts, as well as the waiting times in between, are characterized by universal power law distributions, where only the cutoffs have material dependence. When stress concentrations arise in the vicinity of failed regions, the power law distributions of noise characteristics prevail but the exponents are different from their equal load sharing counterparts. In the presence of stress concentration the failure process accelerates resulting in a higher value of the waiting time exponent compared to the case of homogeneous stress distribution