3,095 research outputs found
Bond characterization of monolithic and layered glass panels and ultrasonic tests to control glued surfaces
No full textAn experimental investigation is presented regarding the compressive and shear strength of monolithic and PVB laminated glass elements connected by acrylic glue. Ultrasonic tests were also used to control the efficiency of glued surfaces of glass panels.
Twenty-four triplets composed of three float glass elements glued with acrylic adhesive were prepared to perform bond tests. Of these twelve triplets were made with monolithic glass elements with a nominal thickness of 20 mm, while twelve were made with layered glass elements 20 mm thick. Three single elements of monolithic glass and three of layered glass were tested for compressive strength. Ultrasonic tests were performed on a sample made by gluing two layered glass panels 200 × 300 × 20 mm in thickness in which defects in glued surfaces were generated artificially. Experimental stress-strain curves in compression for glass elements and shear stress-slippage curves from bond tests were also derived with crack patterns at rupture
Mixed mode failure analysis of bonded joints with rate dependent interface models
No full textThe recent developments in joining technologies and the increasing use of composites materials in structural design justify the wide interest of structural mechanics researchers in bonded joints. Joints often represent the weakness zone of the structure and appropriate and rigorous mechanical models are required in order to describe deformation, durability and failure. The present work is devoted to the theoretical formulation and numerical implementation of an interface model suitable to simulate the time-dependent behaviour of bonded joints. The interface laws are formulated in the framework of viscoplasticity for generalized standard materials and describe the softening response of the joint along its decohesion process in presence of shear and tensile normal tractions. These laws are derived in a thermodynamic consistent manner and take into account the rate dependency modifications of the fracture process zone making use of a sort of non-local instantaneous dissipation. The interface constitutive laws are expressed both in rate and discrete incremental form for the purpose of numerical implementation. The consistent tangent matrix is derived. Finally, the problem of model parameters identification is approached making use of the finite element method for the experiments simulation and of an evolution strategy to solve the constrained optimization problem which mathematically represents the parameter identification inverse problem
Fractional Viscoelastic Transversally Isotropic Timoshenko Beam
No full textIn this paper the viscoelastic behavior of pultruded beams has been examined. Pultruded beams are constituted by a polymer infilled with reinforcement in longitudinal direction, while in the orthogonal direction no fiber are present for technological reasons. As a consequence the material has two different behaviors in longitudinal and in orthogonal directions. It follows that pultruded beams are transversally isotropic, and the shear deformation may not be neglected. Based upon the previous observations and assuming for Creep and/or Relaxation test the power law, the constitutive equations are ruled by fractional operators. From constitutive laws, and assuming the Timoshenko beam theory to account for the shear, the equations of the beam are derived. Experimental test performed on the specimen of the pultruded beam have been carried out confirming the validity of the fractional differential equations here derived
Interphase Model and Phase-Field Approach for Strain Localization
No full textQuasi-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 corresponds to
diffuse the interphase in the volume of the solid body.
The formulation of the problem has been developed in a classical way using the principles of thermodynamics. A key point consists in a Reuss/Sachs type homogenization of the inelastic contact strains through a weak Dirac delta function which takes the shape of the Mumford-Shah
functional. The introduction of this kinematical hypothesis consistently leads to the complete set of the governing equations for a localized body.
The model has been tested by means of analytical applications. The results show that the introduced strain regularization does not affect substantially the structural behavior, also the model can be easily used to replicate experimental results.
The application of the proposed model may involve different contexts as the strain localization in soil mechanics, plastic hinge formation in reinforced concrete frames and delamination in composite materials. It should be noted that the calibration of model parameters for the comparison between numerical end experimental results can be performed easily, since no additional mechanical parameters are needed with respect to those that characterize the elastoplastic behavior
Non linear analysis of blocky structures in presence of anisotropy of friction and wear of contact surfaces
No full textAn Interface Model for the Analysis of Anisotropy of Friction and Wear of Contact Surfaces
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Multi-objective parameter identification via ACOR algorithm
No full textThe spreading of advanced constituive models, needed to model complex phenomena, makes necessary to solve difficult parameter identification problems. The need of multiple tests to fully characterize the experimental behaviour makes the parameter identification problem a multi objective one. Unlike conventional techniques, based on the formulation of an aggregate scalar ob- jective function, in the present work the problem is addressed using a new multi objective algorithm obtained extending the continuous Ant Colony Optimization algorithm. Mathematical tests and ap- plication to a real world problem are performed and different performance measures are used to asses the performance of the approach
INTERFACE MODEL FOR THE NONLINEAR ANALYSIS OF BLOCKY STRUCTURES OF ANCIENT GREEK TEMPLES
No full textThe presence of singularity surfaces with reference to the displacement field is a characteristic of a number of structural systems. Strong discontinuities are present in old masonry structures where dry joints connect the blocks or the mortar ageing suggests to neglect the adhesion properties.
These structures cannot be considered a continuum but rather an assembly of blocks. These discontinuous structures could be modelled as an assembly of blocks interacting trough frictional joints whose mechanical behaviour is described by appropriate interface laws.
In the present work an interface model present in literature is adopted, the double asperity model, which has been implemented in a standard finite element code with the principal aim to develop structural analysis of old monumental masonry structures.
The interface model is briefly illustrated and the numerical implementation of the interface laws is described in detail.
Numerical examples are presented to simulate the behaviour of a couple of greek temples of Agrigento Italy.
These old monumental structures, IV-VI sec. BC, are inserted in the world heritage list by Unesco
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