102,116 research outputs found
Non-destructive Mechanical Testing of Pipelines
No full textStrategic infrastructures made of pipelines transporting hydrocarbons across theworld are exposed to the risk of failure due to damage accumulation during operation. The degradation process is promoted by material aging and enhanced by harsh service conditions. Severe consequences can be prevented by the long-life monitoring and integrity assessment of materials and components. Structural diagnosis can be assisted by non-destructive mechanical testing. This chapter provides an overview on the procedures at present available for pipeline steels in this context.
The information content of hardness and instrumented indentation tests is specifically addressed. The focus is on the reliability of the predictions that can be provided by small sampling sizes when experimental information and numerical simulations are combined. The significance of such methodology for the evaluation of the current
properties of exercised pipelines is illustrated together with the relevant validation studies. The gains resulting from the progressive technological advancements are also evidenced
Experimental and computing strategies in advanced material characterization problems
No full textThe mechanical characterization of materials relies more and more often on sophisticated experimental
methods that permit to acquire a large amount of data and, contemporarily, to reduce the invasiveness of the tests. This
evolution accompanies the growing demand of non-destructive diagnostic tools that assess the safety level of components
in use in structures and infrastructures, for instance in the strategic energy sector. Advanced material systems and
properties that are not amenable to traditional techniques, for instance thin layered structures and their adhesion on the
relevant substrates, can be also characterized by means of combined experimental-numerical tools elaborating data
acquired by full-field measurement techniques. In this context, parameter identification procedures involve the repeated
simulation of the laboratory or in situ tests by sophisticated and usually expensive non-linear analyses while, in some
situation, reliable and accurate results would be required in real time. The effectiveness and the filtering capabilities of
reduced models based on decomposition and interpolation techniques can be profitably used to meet these conflicting
requirements. This communication intends to summarize some results recently achieved in this field by the author and
her co-workers. The aim is to foster further interaction between engineering and mathematical communities
Hybrid finite element approach to quasi-brittle fracture
No full textThe modelling of quasi-brittle fracture processes by a hybrid finite element formulation is introduced. Both the nodal displacements defined in the whole domain of the problem and the equivalent nodal forces defined on the fracture interfaces, where all nonlinearities are supposed to be concentrated, are introduced first as independent variables. The displacements are then eliminated by static condensation, and only the degrees of freedom which represent the dual generalized (in Prager's sense) variables (tractions and opening displacements) defined on the interfaces are retained. These generalized variables are related to each other through a softening cohesive law, enforced in a suitable weighted averaged sense. The comparison with the standard finite element methods based on displacements only, with other mixed finite element formulations, as well as with the symmetrical version of the boundary element method is also pointed out, mainly for the discussion on the stability and bifurcation of quasi-brittle fracture processes
An approximate method for fatigue-life prediction of framed structures
No full textThe propagation of fatigue cracks in framed metal structures, usually described by Linear Elastic Fracture Mechanics, is analyzed here and described by a numerical method based on classical beam theory. A procedure to be used in practice for the evaluation of stiffness degradation and energy release rate is presented. The procedure uses formulae which are explicitly given for statistically determinate beam structures that are being progressively damaged. If implemented into any beam-oriented finite element code as shown here, the proposed approach allows one to deal also with redundant structures
The Blatz-Ko material model and homogenization
No full textA hyperelastic constitutive model for compressible materials undergoing large deformations is introduced from the evaluation, by homogenization, of the strain energy density function of periodic porous rubber composites. For infinitesimal deformations the proposed material model remains unidentifiable from the Blatz-Ko one, but it is shown that, at higher stretching levels, these models differ substantiall
Derivation of hyperelastic incompressible material constitutive tensor within a total lagrangian framework
No full textA tridimensional non-linear elastic constitutive relationship of the hyperelastic incompressible materials is derived from the Mooney-Rivlin strain energy density function. This works within large displacement theory, in the total Lagrangian formulation. Several applications, referring to the implementation in a non-linear computer code, are also described
Thermal effects in partially saturated soils: a constitutive model
No full textThe present paper is centred on the assessment of an elastic-plastic model for partially saturated soils, earlier proposed by the authors, for its predictive capability with respect to temperature changes, on the light of available experimental results. The model is cast within a constitutive framework that uses Bishop's stress and suction as main variables governing the volumetric response of the material. Some enhancement to the original temperature-independent formulation is proposed. In particular, functions describing the yield surface and the compressibility modulus are modified to account for the shrinking of the elastic domain and for the increase of irreversible volumetric strain with heating. Some examples illustrate the main features of the present proposal. Comparison with some experimental results is also included
Modelli elastici non-lineari per l'analisi di membrane secondo un approccio di tipo misto
No full textAccuracy Check of Road’s Cross Slope Evaluation Using MMS Vehicle
Get PDFDepartment of Civil Engineering (DCE), seat of Topography and Photogrammetry – Pisa University, cooperating with Excellence Centre for Telegeomatics Research of the Trieste University, is developing several methods in order to evaluate road’s cross slope.
This measure is performed by use of instrumentation integrated on MMS vehicle GIGI One. In particular two different approaches are followed. The first one preview using of low cost monoaxial laser scanner IBEO Automotive LD GmbH, synchronized with Applanix POS LV system. With the second one cross slope is calculated by only inertial system data, using a simplified algorithm that describes vehicle dynamics.
This paper will present an accuracy control of both methods. This control is realised on two different datasets, relating to the s.s. 58 Strada Nuova per Opicina, joining Trieste to Opicina and the s.s.1 Aurelia between Rosignano and Campolecciano, near Livorno.
The control compares the two method’s results systematically and preview several single point check by tests realised with classic topographic instrumentation
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