Raffaele Zinno

INTERLAMINAR DAMAGE MODEL FOR POLYMER MATRIX COMPOSITES

A constitutive model for fiber-reinforced composite materials with damage and unrecoverable deformation, which for the first time accounts for interlaminar damage, is presented. The formulation is based on Continuous Damage Mechanics coupled with Classical Plasticity Theory in a consistent thermodynamic framework using internal state variables. In-plane damage and novel formulation of interlaminar damage are included in order to describe the main failure modes of laminates structures. A novel implementation of the constitutive model into a finite element formulation incorporating geometric nonlinearity is presented. The model uses a small number of adjustable parameters, which are identified from available experimental data. Comparisons with experimental data for composite laminates under torsion loading are shown to validate the model for interlaminar damage. Coupled material and geometrical nonlinear analysis with simultaneous in-plane and interlaminar damage is demonstrated. The effect of warping on interlaminar damage is shown to be significant.

Damage evolution in bimodular laminated composites under cyclic loading

This work deals with layered composite structures under cyclic loading. In particular, bimodular material laminates are considered and the Bert model is adopted. The analysis is developed using a finite element procedure based on a theory which takes into account the shear deformability (layer-wise deformation plate theory). The adoption of this theory is important to improve the stress evaluation by obtaining a better utilisation of the polynomial failure criteria for the identification of the cracked zones. To determine the stiffness reduction due to the damage evolution, the Laws et al. formulas are adopted for two types of crack (penny-shaped and slit-aligned). The analysis of the structures under cyclic loading is carried out by adopting some reasonable hypotheses on the reduction of the mechanical parameters and on the crack detection.

An analytical delamination model for laminated plates including bridging effects

A penalised interface model, whose strain energy is the penalty functional related to interface adhesion constraint, is introduced in conjunction with a damageable interface whose local constitutive law, in turn, represents bridging stress effects, in order to analyse delamination and bridging phenomena in laminated plates. The laminate is modelled by means of first-order shear deformable layer-wise kinematics and the governing equations are formulated in the form of a non-linear differential system with moving intermediate boundary conditions related to opportune delamination and bridging growth conditions. The problem is solved through an analytical approach. The model leads to an accurate and self-consistent evaluation of the energy release rate and its mode components due to the inclusion of significant contributions arising from coupling between in-plane and transverse shear stresses, and to an asymptotic estimate of interlaminar stresses. The salient features of the proposed model are investigated in the context of an energy balance approach and of a J-integral formulation, thus providing simple results useful to model delamination growth and bridging behaviour when mixed mode loading is involved. The accuracy of the proposed model is substantiated through comparisons with results from continuum analysis obtained by a finite element (FE) procedure. The effectiveness of the proposed model is highlighted by showing the solution of a two-layered plate scheme subjected to pure and mixed mode loading conditions and to fibre bridging stresses. The results point out that the present model, despite its low computational cost in comparison with more complex FE analyses, is an efficient tool to predict delamination and bridging evolution.

Total Lagrangian formulation for laminated composite plates analysed by three-dimensional finite elements with two-dimensional kinematic constraints

A three-dimensional element with two-dimensional kinematic constraints is developed for the geometric nonlinear analysis of laminated composite plates. The Newton-Raphson iterative method is adopted to trace the nonlinear equilibrium path. Maximum accuracy in the computation of stresses is achieved by postprocessing the stress results from constitutive equations with the aid of the equilibrium equations. Some numerical examples are presented to demonstrate the efficiency and the validity of the proposed element. A total Lagrangian description and the principle of virtual displacements is used to formulate the equilibrium equations.

Finite element analysis and parametric study of steel-concrete composite beams

Abstract A finite element model is presented to predict the stresses and deformations in steel-concrete composite beams. The model takes into account the effect of cracking and tension-stiffening in the tensed concrete, and of longitudinal slip between the steel beam and the concrete slab due to the ‘partial interaction’ of theconnectors. Some comparisons with experimental data available in literature are reported to validate the efficiency of the proposed model. Finally, a parametric study was done to investigate the effects of the geometric and mechanical variables as boundary conditions and the slip modulus of the connectors.

Typical Failures, Seismic Behavior and Safety of the “Bourbon System” with Timber Framing

All the research on the behavior and failure of specimens of the Bourbon System, masonry with timber framing, has been done on early 1900 C photographic records. The photos show some case baraccate damaged by the 1905 and 1908 seismic events. The damage is recorded also in the official documents of the technicians sent from Rome, just like Commissione del Genio Civile [, including Canevazzi and Panetti. More data come from Baratta punctual description [ who visited Calabrian towns damaged in the 1908 earthquake. Other news has been taken out from some old chronicles regarding timber frame buildings before 1783.

First-ply failure of laminated composite plates

Abstract Composite laminates offer superior load carrying capacity. Reliable application of structures requires a knowledge of their stress/strain and failure behavior. past treatments involved assumptions in both the stress and failure analyses; they become increasingly more difficult when the failure of the microstructure constituents is to be included in the continuum analysis of the laminates. Recognizing the conventional failure criteria used for composite material analyses, this work adopts the first-ply failure criterion by application of a polynomial function and the finite element procedure. The laminates are modeled by the Reissner-Mindlin plate theory that accounts for moderate rotation. This is because shear effects are more pronounced in composite laminates whose transverse shear modulus is low relative to the Youngs modulus. Failure loads are obtained for different laminate thicknesses, stacking sequences and aspect ratios and different failure criteria. The results show that predictions made from the maximum stress criterion are nearly the same as the others, except for those obtained by the Hill criterion.

Behaviour of the Borbone Constructive System Under Cyclic Loading: Preliminary Report

The Borbone constructive system, constituted by masonry reinforced with timber frames, was conceived in the Calabria region after the earthquake of 1783. In fact, subsequently to this catastrophic event Ferdinando of Borbone the IV immediately drew up an anti-seismic code in which prescribed, among the other rules, the buildings reconstruction to be carried out with the reinforcement of a skeleton of timber elements. Also the residence of the Bishop of Diocese of Mileto-Nicotera-Tropea was built in Mileto (Vv), at the end of 18th c., adopting the Borbone anti-seismic system. This “baracca” of the Bishop was investigated with an accurate dimensional and structural survey, supported by petrographic and chemical analysis of mortars and stones and by assessment of the wood species of the inner members of the load bearing system. All these data allowed the designers to realize an “imperfectly” identical copy of the bishop’s building wall. The paper will present the results of quasi-static cyclic tests according to UNI EN 12512:2003, on the full scale specimen of the Mileto masonry reinforced with timber framing. Furthermore, the hysteretic behaviour (ductility, energy dissipation, equivalent viscous damping ratio, strength impairment) of the Borbone constructive system will be discussed in the document, with a special focus on the single anti-seismic contribution of masonry and timber frame to the overall cyclic stiffness.

In-Plane Versus Out-of-Plane “Behavior” of an Italian Timber Framed System—The Borbone Constructive System: Historical Analysis and Experimental Evaluation

The Borbone system, elaborated after the terrible earthquake that in 1783 hit the southern part of the Calabria Region, is constituted by masonry reinforced with timber frames. It represents the synthesis of the most advanced anti-seismic criteria of the time, the Age of the Enlightenment. With the present study based on pictures and reports of the time as well as on the results of experimental trials on real scale (1:1) models, the authors intend to contribute to the interpretation of the behavior to seismic actions of the cited Borbone system and decoding the answer of the system to horizontal forces both parallel (by means of experimental analysis) and perpendicular to the walls (relied on historical data). The values collected in the cyclic tests—such as ductility, strength impairment, equivalent viscous damping, and energy dissipation, conducted on two samples: masonry wall reinforced by timber frames and timber framed wall without infill)—have been compared with the experimental data concerning other framed masonry systems (Gaiola and Dhajji Dewari) bringing out the constructive and mechanical differences as well as similarities.

Koiter asymptotic analysis of thin-walled cold-formed steel members

Abstract An imperfection sensitivity analysis of cold-formed steel members in compression is presented. The analysis is based on Koiter’s approach and Monte Carlo simulation. If the modes interaction is correctly accounted, than the limit load and the erosion of critical buckling load can be easily evaluated. Thousands of imperfection can be analysed with very low computational cost and an effective statistical evaluation of limit performance can be carried out. The analysis is done on pallet rack uprights in compression, based on an intensive experimental study carried out at the Politehnica University of Timisoara.