Mechanical characterization of metal-ceramic composites

Metal-ceramic composites represent a class of quasi-brittle materials for advanced structural applications that require adequate mechanical characterization. Difficulties and costs associated with material production and specimen extraction prevent the execution of a statistically meaningful number of standard laboratory tests. Parameter calibration methodologies based on instrumented indentation and inverse analysis represent fast and reliable identification procedures in the present context, as shown by the present contribution, based on some experience achieved in the framework of the European Network of Excellence on ‘Knowledge-based Multi-component Materials for durable and safe performance’ (KMM-NoE)

Mechanical characterization of metal-ceramic composites

Metal-ceramic composites represent a class of quasi-brittle materials for advanced structural applications that require adequate mechanical characterization. Difficulties and costs associated with material production and specimen extraction prevent the execution of a statistically meaningful number of standard laboratory tests. Parameter calibration methodologies based on instrumented indentation and inverse analysis represent fast and reliable identification procedures in the present context, as shown by the present contribution, based on some experience achieved in the framework of the European Network of Excellence on ‘Knowledge-based Multi-component Materials for durable and safe performance’ (KMM-NoE)

A method to calculate the support length of beams resting on masonry walls

Rehabilitation, strengthening, and retrofitting of existing masonry buildings represent an important challenge for the construction engineering field. Often, slab strengthening/retrofitting is performed by replacing existing timber and steel beams or by adding new beams to improve the slab load-carrying capacity. The computation of the stresses at the beam–masonry interface (i.e., the contact pressure) is crucial to properly design the beam support length, preventing local failure of masonry and beam. This paper presents a simple analytical procedure to compute the contact pressure at the beam–masonry interface. The analytical procedure is validated by comparison between analytical and corresponding numerical results obtained by finite element modeling. Different types of beam (solid and laminated timber beams and steel beams) were considered, as well as different support conditions (simply resting on the wall considering different support lengths or fully embedded). The results obtained show that the method proposed is simple and reliable, which makes it suitable for professional practice

A new cohesive law for the simulation of crack propagation under cyclic loading. Application to steel- and concrete-FRP bonded interface

This paper presents a new cohesive law for modelling interfaces under mixed-mode cyclic loading. The formulation is based on the definition of a free energy function which governs the interface behaviour under monotonic loading, which is then extended to cyclic-driven decohesion through the introduction of a scalar damage variable, whose evolution in time is governed by a phenomenological rate equation. The cohesive model is formulated for a mixed-mode problem and then it is applied for the simulation of debonding phenomena occurring at the interface under a pure a shear stress state. Experimental results available in literature, related to single-lap shear tests, performed on both concrete and steel specimens reinforced by fibre reinforced composite (FRP), are used to validate the proposed model and to show its effectiveness to simulate very closely the observed experimental behaviour

A rate dependent cohesive model for the analysis of concrete-FRP bonded interfaces under dynamic loadings

Reinforced concrete structures, strengthened with fibre-reinforced polymers materials (FRP), are frequently subjected to dynamic loadings, due to, e.g., earthquake, blast, or impact events. The definition of proper cohesive laws to model the bond between the fibre-reinforced polymer sheet and concrete, under high deformation rates, is a crucial issue because the typical failure mode of these joints is debonding of the composite from the concrete substrate. Although numerous studies have already investigated the quasi-static interface response, experimental and numerical investigations, concerning the effect of deformation rate on the bond behaviour between a fibre-reinforced polymer sheet and concrete, are still few. This paper presents a cohesive law for the modelling of interfaces under mixed-mode dynamic loadings, considering the effect of deformation rate. The formulation is based on the decomposition of the discontinuity displacement vector across the interface into elastic and viscoplastic components, with the evolution of the latter being governed by a viscoplastic law formulated according to the overstress approach. Experimental results available in literature, related to double- and single-lap shear tests, performed on FRP reinforced concrete specimens, are exploited to validate the proposed model and to show its capacity to simulate closely the experimental behaviour

Service behaviour of composite steel-concrete slabs with a simplified approach and a hygro-thermo-chemical-mechanical model for the non-uniform shrinkage evaluation

Composite steel-concrete floors are widely used throughout the world for building applications. These floors usually consist of composite slabs supported by steel beams in steel framed construction and of post-tensioned composite slabs carried by band beams in concrete buildings. The design of composite floors is commonly governed by serviceability limit state associated with deflection limits. Recent research has pointed out that a non-uniform shrinkage profile occurs in slabs cast on profiled steel sheeting. In this context, this paper provides a brief overview of the main factors influencing the service behavior of composite slabs and of a model capable of predicting their long-term deflections considering two approaches for the evaluation of the non-uniform shrinkage profiles, i.e. a simplified approach and a hygro-thermo-chemicalmechanical model. The adequacy of the proposed prediction models is then outlined by comparing the longterm deflections calculated with the proposed approach and those measured experimentally from long-term tests carried out on selected composite and post-tensioned composite slab samples that have been reported in the literature

Bound between FRP bars and concrete: experimental and numerical investigations

In this paper are detailed the results obtained by a numerical model, based on a cohesive law, able to simulate the adhesion between concrete and FRP bars. The FRP bars considered were obtained by pultrusion of unidirectional glass (GFRP) and carbon (CFRP) fibres. The numerical analyses are compared to experimental pull-out tests

Stochastic and recursive estimation of the hygro-thermo-chemical-mechanical parameters of concrete through Monte Carlo analysis and extended Kalman filter

Hygro-thermo-chemical-mechanical models, used to determine the variations over time of temperature, relative humidity and shrinkage induced deformations in concrete components, are characterised by the presence of a large number of input parameters. Some of these parameters can be evaluated on the basis of the concrete mix specifications or from literature data, while the others present a large variability and, in some cases, do not have a precise physical meaning and, for this reason, require the implementation of proper identification strategies. The experimental work involved for this characterisation can be time-consuming and costly because based on the long-term monitoring of the time evolution of the field quantities in specific positions within concrete components. The aim of this paper is to propose and validate recursive identification strategies that exploit, in a step by step fashion, the information coming from the experimentation for the identification of the model input parameters. The influence of different exposure conditions and of different concrete thicknesses are investigated and, for each scenario considered, the expected identification error of each parameter is estimated, within a stochastic context implemented through Monte Carlo analyses and Kalman Filter, as a function of the monitored time

Indentation and imprint mapping for the identification of constitutive parameters of thin layers on substrate: perfectly bonded interfaces

Indentation tests are at present frequently employed for the identification of material parameters at different scales. The indentation curve provides experimental data for the calibration of mechanical models through traditional semi-empirical formulae or through simulation of the test and inverse analysis. A recently proposed innovative inverse analysis technique combines the traditional indentation test with the mapping of the residual deformations (imprint), thus providing experimental data apt to be used to identify isotropic and anisotropic material parameters in more accurate fashion and in larger number. In this paper, such new methodology is employed for the identification of material properties in film–substrate systems. The film and a significant portion of the underlying bulk material are incorporated in the finite element models built up to simulate the indentation test in finite strain regime. The substrate material properties are considered among the unknown parameters to be identified through inverse analysis, carried out by a batch, deterministic approach, using conventional optimisation algorithms for the minimisation of a suitably defined discrepancy norm. Several numerical examples are discussed in order to test the performance of the proposed methodology in terms of result accuracy and computing effort