37 research outputs found
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
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
Non linear analysis of blocky structures in presence of anisotropy of friction and wear of contact surfaces
No full textMulti-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
An Interface Model for the Analysis of Anisotropy of Friction and Wear of Contact Surfaces
No full textAn Hypervolume based constraint handling technique for multi-objective optimization problems
No full textFormulation of structural optimization problems usually leads to the individuation of one or more objective functions to be minimized under different constraints. Many multi-objective evolutionary algorithms are approached by a Pareto-compliant ranking method, where no a priori information on the problem is needed and the concept of non-dominated solutions is used. In this paper a constraint handling technique based on the concept of hypervolume indicator is presented. Initially proposed to compare different multi-objective algorithms hypervolume indicator is the only single set quality measure to reflects the dominance of solution’s sets. The constraint handling technique proposed use an extension of stochastic ranking approach for single-objective optimization problem to multi-objective ones. The extension proposed use the hypervolume indicator to compares different solutions and is tested on a structural constrained multi-objective problems. Results show the suitability of the proposed 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
