A FE-Meshless Multiscale Approach for Masonry Materials

Abstract A FE-Meshless multiscale computational strategy for the analysis of running bond masonry is presented. The Meshless Method (MM) is adopted to solve the boundary value problem (BVP) at the mesoscopic level. The representative unit cell is composed by the aggregate and the surrounding joints, the former assumed to behave elastically while the latter are simulated as non-associated elastic-plastic zero-thickness interfaces with a softening response. Macroscopic localization of plastic bands is obtained performing a spectral analysis of the tangent stiffness matrix. Localized plastic bands are embedded into the quadrature points area of the macroscopic finite elements.

Mesoscopic aspects of the computational homogenization with meshless modeling for masonry material

The multiscale homogenization scheme is becoming a diffused tool for the analysis of heterogeneous materials as masonry since it allows dealing with the complexity of formulating closed-form constitutive laws by retrieving the material response from the solution of a unit cell (UC) boundary value problem (BVP). The robustness of multiscale simulations depends on the robustness of the nested macroscopic and mesoscopic models. In this study, specific attention is paid to the meshless solution of the UC BVP under plane stress conditions, comparing performances related to the application of linear displacement or periodic boundary conditions (BCs). The effect of the geometry of the UC is also i…

The FE-Meshless multiscale approach applied to masonry structures

Heterogeneous structures have an overall response that is strongly dependent on the inelastic events developing at the local level. In these structures, the most relevant kinematical and mechanical phenomena take place at a scale which is small if compared to the dimensions of the entire structure. In literature, a mesoscopic and a macroscopic scales of interest are distinguished, directly linked to as many theoretical approaches. The mesoscopic approach [1] considers materials and their interfaces individually, but many difficulties arise in the mesh creation and a fine discretization of the structure is needed, which leads to prohibitive computational costs. The macroscopic approach consi…

Adhesive debonding detection of FRP reinforcement by the ultrasonic non-destructive technique

Fiber reinforced polymer (FRP) composite systems are extensively used for repairing and reinforc- ing structurally inefficient concrete structures. The performance of an FRP rehabilitation system is highly influenced by its integrity. In particular, the presence of defects, e.g. voids, inclusions, debonds, improper cure and delaminations, caused by an inaccurately manufacture and installation, may affect the capability of the rehabilitated structure. For this reason, non-destructive (ND) meth- ods could be used to assess the quality of the reinforcement [1,2]. In this work an ultrasonic ND technique for detecting delamination defects in FRP reinforcement is presented. The technique couples …

Numerical and Experimental Assessment of FRP-Concrete Bond System

Fiber reinforced polymer (FRP) composite systems are widely used to repair structurally deficient constructions thanks to their good corrosion resistance, light weight and high strength. The quality of the FRP-substrate interface bond is a crucial parameter affecting the performance of retrofitted structures. In this study, ultrasonic testing have been used to assess the quality of the bonding. In the case of FRP laminates adhesively bonded to concrete, high scattering attenuation occurs due to the presence of concrete heterogeneities. The substrate material behaves almost like a perfect absorber generating a considerable number of short-spaced echo peaks that make the defect echo not disti…

On the use of the electromechanical impedance technique for the assessment of dental implant stability: Modeling and experimentation

We propose the electromechanical impedance technique to monitor the stability of dental implants. The technique consists of bonding one wafer-type piezoelectric transducers to the implant system. When subjected to an electric field, the transducer induces structural excitations which, in turn, affect the transducer’s electrical admittance. The hypothesis is that the health of the bone surrounding the implant affects the sensor’s admittance. A three-dimensional finite element model of a transducer bonded to the abutment of a dental implant placed in a host bone site was created to simulate the progress of the tissue healing that occurs after surgery. The healing was modeled by changing the …

CH of masonry materials via meshless meso-modeling

In the present study a multi-scale computational strategy for the analysis of masonry structures is presented. The structural macroscopic behaviour is obtained making use of the Computational Homogenization (CH) technique based on the solution of the boundary value problem (BVP) of a detailed Unit Cell (UC) chosen at the meso-scale and representative of the heterogeneous material. The smallest UC is composed by a brick and half of its surrounding joints, the former assumed to behave elastically while the latter considered with an elastoplastic softening response. The governing equations at the macroscopic level are formulated in the framework of finite element method while the Meshless Meth…

Efficient finite difference formulation of a geometrically nonlinear beam element

The article is focused on a two-dimensional geometrically nonlinear formulation of a Bernoulli beam element that can accommodate arbitrarily large rotations of cross sections. The formulation is based on the integrated form of equilibrium equations, which are combined with the kinematic equations and generalized material equations, leading to a set of three first-order differential equations. These equations are then discretized by finite differences and the boundary value problem is converted into an initial value problem using a technique inspired by the shooting method. Accuracy of the numerical approximation is conveniently increased by refining the integration scheme on the element lev…

Electromechanical Impedance Method to Assess the Stability of Dental Implants

In this paper we illustrate the application of the electromechanical impedance (EMI) technique, popular in structural health monitoring, to assess the stability of dental implants. The technique consists of bonding a piezoelectric transducer to the element to be monitored. When subjected to an electric field, the transducer induces low to high frequency structural excitations which, in turn, affect the transducer's electrical admittance. As the structural vibrations depend on the mechanical impedance of the host structure (in this case the implant secured to the jaw), the measurement of the PZT's admittance can infer the progress of the osseointegration process. In the study presented in th…

FE·Meshless multiscale modeling of heterogeneous periodic materials

The computational mutiscale modeling of periodic heterogeneous materials, characterized by the assembly of units and joints, represents a compromise between the inaccuracy resulting from the macro modeling approach and the computational effort of the meso modeling. Assuming that the heterogeneities are orders of magnitude smaller than the structure dimensions, according to the multiscale approach, the macroscopic stresses and strains around a certain point can be found by averaging the stresses and the strains in a small representative part of the microstructure or a representative volume element (RVE) attributed to that point. A first-order two-scale scheme has been used to model heterogen…

Assessment of bonding defects in FRP reinforced structures via ultrasonic technique

Fiber reinforced polymer (FRP) composite systems are widely used for the rehabilitation of concrete structures such as building that need to resist to seismic loads, bridges that have to carry heavier traffic loads. The technique consists in bonding the composite plate to the concrete surface element in order to increase the flexural capacity. A proper attachment of the FRP plate to the concrete surface is necessary for the efficiency of the load transfer between the reinforcement and the substrate. In this work, the quality of composite bonding is characterized through ultrasonic testing. The proposed technique is relative to a time domain analysis of the ultrasonic signals and couples the…

A noninvasive approach for the assessment of dental implants stability

We propose the Electromechanical Impedance (EMI) technique to monitor the stability of dental implants. The technique consists of bonding one wafer-type piezoelectric transducers to the implant system. When subjected to an electric field, the transducer induces structural excitations which, in turn, affect the transducer’s electrical admittance. The hypothesis is that the health of the bone surrounding the implant affects the sensor’s admittance. In this paper we present the results of an experiment where a sensor is bonded to an abutment screwed to implants secured into bovine bone samples. The results show that the EMI technique can be used to monitor the stability of dental implants alth…

Ultrasonic inspection for the detection of debonding in CFRP-reinforced concrete

Fibre-reinforced plastic (FRP) composites are extensively used to retrofit civil structures. However, the quality and the characteristics of the bond between the FRP and the structure are critical to ensure the efficacy of the retrofit. For this reason, effective non-destructive evaluation (NDE) methods are often necessary to assess the bonding conditions. This article presents an ultrasonic technique for detecting defects at the FRP-substrate interface. The technique uses the Akaike Information Criterion, to detect automatically the onset of the ultrasonic signals, and the novel Equivalent Time Lenght (ETL) parameter, to quantify the energy of the propagating ultrasonic signals along the i…

Advancements on the FE·Meshless CH for the analysis of heterogeneous periodic materials

Over the last few years, the intrinsic role of different spatial scales in the mechanics of materials has been well recognized. Generally, two main different scales can be identified in the heterogeneous materials: the macroscopic level, which coincides with the global structural one, and the mesoscopic level, that is the scale at which the heterogeneities can be identified and where the most relevant nonlinear mechanical phenomena occur. In this framework, substantial progress has been made in the two-scale computational homogenization (CH). This method is essentially based on the on the fly assessment of the macroscopic constitutive behavior from the boundary value problem (BVP) of a stat…

A phase-field model for strain localization

Strain localization in quasi-brittle materials occurs when a material is subjected to a high level of mechanical solicitations and inelastic strains develop in relatively narrow zone where micro-cracks appear. The gradual evolution of the micro-cracks results in the formation of localized bands up to the development of stress-free cracks. The localized zone or plastic band is generally associated to a faster growth of strain and is characterized by inelastic phenomena such as opening and propaga- tion of cracks, initiation and growth of voids. Conversely, outside of this zone, the material unloads elastically. Extensive research has been carried out to address issues related to the modeling…

On the use of EMI for the assessment of dental implant stability

The achievement and the maintenance of dental implant stability are prerequisites for the long-term success of the osseointegration process. Since implant stability occurs at different stages, it is clinically required to monitor an implant over time, i.e. between the surgery and the placement of the artificial tooth. In this framework, non-invasive tests able to assess the degree of osseointegration are necessary. In this paper, the electromechanical impedance (EMI) method is proposed to monitor the stability of dental implants. A 3D finite element model of a piezoceramic transducer (PZT) bonded to a dental implant placed into the bone was created, considering the presence of a bone- impla…

Modeling the electromechanical impedance technique for the assessment of dental implant stability

We simulated the electromechanical impedance (EMI) technique to assess the stability of dental implants. The technique consists of bonding a piezoelectric transducer to the element to be monitored. When subjected to an electric field, the transducer induces structural excitations which, in turn, affect the transducer's electrical admittance. As the structural vibrations depend on the mechanical impedance of the element, the measurement of the transducer's admittance can be exploited to assess the element's health. In the study presented in this paper, we created a 3D finite element model to mimic a transducer bonded to the abutment of a dental implant placed in a host bone site. We simulate…

BEAM ELEMENT UNDER FINITE ROTATIONS

The present work focuses on the 2-D formulation of a nonlinear beam model for slender structures that can exhibit large rotations of the cross sections while remaining in the small-strain regime. Bernoulli-Euler hypothesis that plane sections remain plane and perpendicular to the deformed beam centerline is combined with a linear elastic stress-strain law. The formulation is based on the integrated form of equilibrium equations and leads to a set of three first-order differential equations for the displacements and rotation, which are numerically integrated using a special version of the shooting method. The element has been implemented into an open-source finite element code to ease comput…

Granular chains for the assessment of thermal stress in slender structures

Slender beams subjected to compressive stress are common in civil and mechanical engineering. The rapid in-situ measurement of this stress may prevent structural anomalies. In this paper, we describe the coupling mechanism between highly nonlinear solitary waves (HNSWs) propagating along an L-shaped granular system and a beam in contact with the granular medium. We evaluate the use of HNSWs as a tool to measure stress in thermally loaded structures and to estimate the neutral temperature, i.e. the temperature at which this stress is null. We investigated numerically and experimentally one and two L-shaped chains of spherical particles in contact with a prismatic beam subjected to heat. We f…

Modelling the Electromechanical Impedance Method for the Prediction of the Biomechanical Behavior of Dental Implant Stability

Abstract We propose the electromechanical impedance (EMI) technique to assess the stability of dental implants. The technique consists of bonding a piezoelectric transducer to the element to be monitored. Conventionally, electromechanical admittance is used to diagnose structural damage. In this study, we created a 3D finite element model to mimic a transducer bonded to the abutment of a dental implant placed in a host bone site. We simulated the healing after surgery by changing the Young's modulus of the bone-implant interface. The results show that as the Young's modulus of the interface increases, the electromechanical characteristic of the transducer changes.

FE-Meshless multiscale non linear analysis of masonry structures

Efficient formulation of a two-noded geometrically exact curved beam element

The article extends the formulation of a 2D geometrically exact beam element proposed by Jirasek et al. (2021) to curved elastic beams. This formulation is based on equilibrium equations in their integrated form, combined with the kinematic relations and sectional equations that link the internal forces to sectional deformation variables. The resulting first-order differential equations are approximated by the finite difference scheme and the boundary value problem is converted to an initial value problem using the shooting method. The article develops the theoretical framework based on the Navier-Bernoulli hypothesis, with a possible extension to shear-flexible beams. Numerical procedures …

Highly nonlinear solitary waves for the NDT of slender beams

Slender beams subjected to compressive load are common in civil engineering. The rapid in-situ measurement of this stress may help preventing structural anomalies. In this article we describe the coupling mechanism between Highly Nonlinear Solitary Waves (HNSWs) propagating along a granular system in contact with a beam subjected to thermal stress. We evaluate the use of these waves to measure stress in thermally loaded structures and to estimate the neutral temperature, i.e. the temperature at which the stress is null. We investigate numerically and experimentally one and two L-shaped chains of spherical particles in contact with a prismatic beam subjected to heat. We find that certain fea…

An integrated structural health monitoring system based on electromechanical impedance and guided ultrasonic waves

We propose a structural health monitoring (SHM) paradigm based on the simultaneous use of ultrasounds and electromechanical impedance (EMI) to monitor waveguides. Methods based on the propagation of guided ultrasonic waves (GUWs) are increasingly used in all those SHM applications that benefit from built-in transduction, moderately large inspection ranges, and high sensitivity to small flaws. Meantime, impedance-based SHM promises to adequately assess locally the structural integrity of simple waveguides and complex structures such as bolted connections. As both methods utilize piezoelectric transducers bonded or embedded to the structure of interest, this paper describes a unified SHM para…

Interphase Model and Phase-Field Approach for Strain Localization

Quasi-brittle materials subjected to a high level of mechanical solicitations see the development in relatively narrow zone of micro-cracks that coalesce into stress free cracks. In this work, the problem of strain localization in elastoplastic materials exhibiting softening has been approached by applying the interphase model together with the phase-field theory. In particular, the narrow zone where strains concentrate, usually named process zone or localization band, is kinematically modeled using the interphase model, while the phase-field variable is introduced to regularize the contact strains at the interface between the plastic strain band and the surrounding material. This correspon…

On the coupling dynamics between thermally stressed beams and granular chains

The in-situ measurement of thermal stress in slender beams, or long continuous welded rails, may prevent structural anomalies. With this aim, we investigated the coupling dynamics between a beam and the highly nonlinear solitary waves propagating along a straight granular chain in contact with the beam. We hypothesized that these waves can be used to measure the stress of thermally loaded structures, or to infer the neutral temperature, i.e., the temperature at which this stress is null. We studied numerically and experimentally the mechanical interaction of one and two straight chains of spherical particles in contact with a prismatic beam that is subjected to heat. The results show that c…

A phase-field model for strain localization analysis in softening elastoplastic materials

Abstract The present paper deals with the localization of strains in those structures consisting of materials exhibiting plastic softening response. It is assumed that strain localization develops in a finite thickness band separated from the remaining part of the structure by weak discontinuity surfaces. In view of the small thickness of the band with respect to the dimensions of the structure, the interphase concept is used for the mechanical modeling of the localization phenomenon. We propose a formulation for the quasi-static modeling of strain localization based on a phase-field approach. In this sense, the localization band is smeared over the volume of the structure and a smooth tran…