Renato Barboni

A finite element evaluation of single-layer and multi-layer theories for the analysis of laminated plates

Abstract A layerwise polynomial expansion along the thickness direction for displacements is assumed to analyse the behaviour of an arbitrary laminated composite plate. In contrast with other proposed approaches and in order to take into account the transverse normal stress distribution, out-of-plane displacements are not assumed to be constant along the thickness. Based on the proposed kinematic assumptions the continuity of the interlaminar stress components at the interface can be also achieved. A finite element procedure is established and plate models are derived in which the stress field is obtained directly from the constitutive relations and not by the integration of the three-dimensional equilibrium equations. Comparisons among the numerical results obtained with the proposed layerwise models, single-layer models, the classical laminate theory and exact three-dimensional elasticity solutions are presented and briefly discussed.

Optimal placement of PZT actuators for the control of beam dynamics

The dynamics of a flexural beam actuated by induced strain surface bonded (piezoelectric) actuators is considered. The bending moment produced by the single actuator is evaluated by means of the pin-force model. A modal approach is then used to build special dynamic influence functions which explicitly account for the size and the position of the actuator. Simple optimal geometrical conditions are then obtained and illustrated for several cases with different boundary conditions.

Impact Testing on Composites Laminates and Sandwich Panels

The purpose of this work was the evaluation of the behavior of fiber-reinforced composites and sandwich panels for aeronautical applications under impact. Experimental tests were performed on several specimen configurations, based on different quasi-isotropic lay-up and materials such CFRP, CFRTP and a syntactic foam as the core of sandwich panels. Considering the high specific mechanics characteristics of such a foam and its cocurability with the facesheet material, symmetric and non-symmetric sandwich configurations have been tested. The study has pointed out the advantages for aeronautic constructions of different materials and the influence of the core position along the panel thickness. The impact tests were performed with a falling weight machine, which allowed the most important dynamic and kinetic parameters, such as the contact force, impactor velocity and displacement and perforation energy to be measured. Delamination areas of each specimen were also measured using N.D.I. reflection ultrasonic techniques. In order to determine the residual strength, Compression After Impact tests were performed on specimens that have an indentation of approximately 0.3-0.4 mm. A numerical simulation was performed using a transient dynamic Finite Element Analysis. The main goal of this analysis was to define the controlling factors for high velocity impact simulation, such as the increase of geometric non-linearity and the delamination effects. Moreover, the delamination areas and positions were determined taking in account the different boundary conditions. The study have pointed out the behavior of thermoset, thermoplastic and unsymmetric sandwich panels.

Pin-force and Euler-Bernoulli models for analysis of intelligent structures

The relationship between these two methods is discussed, especially for the case of one side only actuation layer. For both models the static response of hte system is obtained for different geometrical, elastic, and piezoelectric characteristics in the cases of one and two (to and bottom surface bonded) actuation layers

Vibration control of an active laminated beam

The dynamic response of a carbon fibre reinforced plastic [0/ + 45/ − 450]s active laminated beam covered by piezoelectric layers is considered. A simple collocated displacement control strategy is implemented by letting the active layers work as actuators and sensors and by constructing an analogue control circuit the characteristics of which are given in some detail. The open- and closed-loop steady-state response of the cantilever beam are then experimentally tested in the range of 40–2000 Hz and the effectiveness of the control mechanism is successfully demonstrated.

A class of C0 finite elements for the static and dynamic analysis of laminated plates

Abstract A general higher-order deformation theory is developed to analyse the behaviour of an arbitrary laminated fibre-reinforced composite plate. Three-dimensional effects such as the warping of sections and the presence of interlaminar stress field components are taken into account assuming a power series expansion of displacements along the thickness. A class of C0 finite element models based on this theory is then developed for mono- and bi-dimensional elements. Applications of the models to bending and vibration of laminated plates are then discussed. The present solutions are compared with those obtained using the three-dimensional elasticity theory, classical laminate theory and other higher-order theories.

A three-dimensional analysis of edge effects in composite laminates with circular holes

Abstract A three-dimensional (3D) displacement approach is developed in order to account for 3D effects of stress concentration in critical areas of composite laminates (free edges, free and loaded holes, notches, etc.). A finite element procedure is set up both for monodimensional and for bidimensional elements. First the problem of interlaminar stress prediction in a composite laminate with straight free edges under uniaxial loading is critically examined. The stress analysis of a holed composite plate under in-plane action is then studied in the case of a free hole and of a loaded hole. The importance of stacking sequence and of some geometrical parameters, such as the radius to the thickness ratio R/h, on the stress field around the hole are also investigated.

On the use of a multilayer higher-order theory for the stress analysis around a circular hole of laminates under tension

Many single layer and multilayer higher-order theories were recently proposed for the analysis of the three-dimensional stress field that usually occurs in composite laminates especially in critical areas such as free edges. In this paper a finite element analysis based on a multilayer theory is performed in order to predict the complicated pattern of the stress field around the hole of laminates under tension. The numerical results are compared with the ones obtained with other modelling approaches, including single layer higher-order theories. The analysis shows that multilayer-theory-based finite elements can be effectively used in the prediction of the stress response of composite structures in cases of practical interests.

Analysis of a glass-fibre sandwich panel for car body constructions

The analysis of a glass-fibre sandwich panel for railway applications is considered. The influence of a special fire-resistant treatment on the mechanical properties of the structure is analysed for static and cycling loadings. The main design and simulation issues are first highlighted. The failure loads of the composite panel are then evaluated from a numerical and an experimental point of view both for the laminated skin of the sandwich and for the entire structure.

The Effects of Delamination on the Fatigue Behavior of Composite Structures

The aim of the present study is to investigate the role played by delamination on the fatigue behavior of centrally holed CFRP laminates. To reach this objective, both theoretical and experimental studies were performed. As to the theoretical analysis and the relevant numerical predictions of the 3D state of stress, the study proposes the use of a finite element procedure based on a multi-layer higher-order laminate theory developed by the authors in conjunction with the application of an interlaminar failure criterion. The approach assumes that significant information on the fatigue life of holed laminate can be obtained by performing a static prediction only. Two types of rectangular laminates with stacking sequences [+45)4/(-45)4] s , and [0/90] 3 manufactured with T300/934 are examined. The static and the fatigue failure of the above mentioned laminates were then investigated in a series of experiments in order to verify the initiation of delamination both in the static case and during the fatigue loading process, ultrasonic nondestructive inspections were also made. The obtained results show a significant correspondence between the experimental static and fatigue behavior of the laminates and the theoretical predictions. They show also that an efficient numerical tool of the 3D state of stress prediction is used.