I. Crivelli Visconti

A Note on Specially Orthotropic Laminates

A particular class of composite laminates is presented, where coupling ef fects are rigorously zero.

Composite materials response under low-velocity impact

Abstract A simple model, based on energy considerations, has been tested to predict the maximum contact force during a low-velocity impact between an impactor and a composite plate. Three different composites, i.e. glass cloth-polyester, carbon cloth-polyester and nylon cloth-polyester, were examined. The results reported here, obtained using an instrumented apparatus, show that the total energy applied during the impact is the governing parameter of the phenomenon, rather than the impactor speed or mass. All the composites under evaluation did not show any variation of elastic modulus with impact velocity. Moreover, the dynamic behaviour of carbon-polyester and nylon-polyester composites can be predicted by simple static tests, because of their insensitivity to rate-dependent phenomena; for these materials a simulation of impact tests by static tests is therefore suggested. Glass-polyester composites did show a rate-dependent behaviour, by an increase in strength of about 70% with respect to the static case; a small number of dynamic tests is, however, sufficient to characterise their behaviour under impact conditions.

The Wear Behaviour of Composite Materials with Epoxy Matrix Filled with Hard Powder

The wear behaviour of composite materials, sliding under dry conditions against smooth steel counterface, has been investigated. The composite materials consisted of glass woven fabric reinforcing three different systems of matrix: epoxy resin, epoxy resin filled with powders of silica and epoxy resin filled with powders of tungsten carbide. The powders were mixed in a volumetric fraction of 6% with the epoxy resin. Three laminates were manufactured by hand lay up technology. The sliding tests have been conducted on the specimens, cut from the three laminates, with a pin on disk apparatus. The results put in evidence different wear behaviours of the composite materials observed at different values of sliding speed and pressure. The presence of different wear mechanisms has been appreciated by SEM-micrographic examinations.

Elastic behaviour of composite structures under low velocity impact

Abstract The results of a study on the behaviour of glass cloth/polyester panels under low velocity impact are reported. The experimental load/time curve in the elastic region showed good agreement with that predicted by a simple analytical model, based on energy considerations, using elastic properties obtained by static tests. The structural rigidity of the panels was not significantly affected by premature local shear damage, due to the concentration of load, even after first fibre failure. The strength of the material was found to be strongly rate-dependent; as a consequence the response of the structure in the post-elastic region cannot be predicted from the results of static tests.

Analysis of Transversal Permeability for Different Types of Glass Fiber Reinforcement

In some of the new processes to produce elements in composite materials, the innovation is due to the fact that the resin flow is perpendicular to the plane of the reinforcement during the impregnation.So a very important parameter is the transversal permeability of the reinforcing materials used in these processes. In fact for a high value of this parameter it is possible to increase the product quality and to reduce the process time.In this work, using Darcys law and a particular permeameter, the transversal permeability of preforms constituted by fabric and mat layers of fiber glass has been valued for different injection pressures. In particular, the permeability of two types of preform, consisting respectively of only mat layers and of only fabric layers, have been determined by tests and calculated by Kozeny–Carman equation. The research has been also focalised on the evaluation of the permeability of preforms constituted by a mix of the two different types of reinforcement. Furthermore an analytical model has been studied to calculate the permeability of preforms consisting of layers of different reinforcement types, starting from the permeability data characterizing the single reinforcement type and determined by the tests or by Kozeny–Carman equation.

Overview of Composites: Their Uses and Technology Trends

Abstract Too many review papers have been and are still being written on the topic of advanced composites, with regard to the state of their application. It is not useful, therefore, to restate well-known opinions about the degree of consumption of different types of fibers, or about projections in the next 10 years, while considering that the present use of composites is not as wide as was assumed some 10–15 years ago. It has been preferred, instead, to search among some of the principal parameters that do affect the know-how and applications of composites in order to trace a guideline of the possible trends of the development of composite technologies including basic science and final applications. To do that, this article analyzes a number of points which are believed to be in continuous evolution, trying to look at those criteria or aspects that clearly could indicate the evolution trends.

Design of Continuous Fiber Composite Structures

Not differently from any human new adventure, the history of composites begun once upon a time (or at least it seems so now) certainly with the idea to provide something with new properties, new aspects, new challenges, able to solve old problems.

Quality evaluation of thermoplastic composite material single-lap joints

Publisher Summary The joining of glass fiber reinforced polymer (GFRP) matrix composite materials by structural bonding still presents difficulties because of the adopted bonding process, the interface properties, and the control of the adhesive thickness. This chapter presents the first results of a study on the characterization of single lap bonded joints made of glass fiber reinforced propylene thermoplastic matrix composite laminates. Two different adhesive types commercially available for thermoplastic polymers are utilized. A planned development of this work provides for the utilization of neural network based UT image analysis procedures to automatically recognize the possible poor quality of the bond in industrial bonding procedures of thermoplastic composite material assemblies. The considered factors are the joint static strength and the joint quality evaluated through advanced ultrasonic nondestructive evaluation.

Flow Front Analysis In Resin Infusion Process

Publisher Summary The Resin Infusion under Flexible Tool (RIFT) is a closed mold technology to manufacture composite material and particularly large component. This chapter presents the analysis of impregnating flow of a thermosetting resin in a RIFT process and the simulation of the process for the manufacturing of the laminate of simple geometry. Starting from the analysis of the impregnating flow, an analytical model based on the electrical analogy is developed to calculate the value of an equivalent permeability of the fibrous reinforcement. The value of this parameter is requested to realize the process in simulation by FEM. The results of the simulations are compared with the results obtained by experimental tests carried out using a preform of fiberglass reinforcement and epoxy resin to manufacture plane laminate in composite materials.

APPLICATION OF ACOUSTIC EMISSION TECHNIQUES FOR THE INVESTIGATION OF THE MECHANICAL BEHAVIOUR OF GRP COMPOSITE MATERIALS

Abstract - Acoustic emission (A.E.) represents very attractive and promising technique for detecting flaws, studying material degradation and monitoring crack initiation and formation. Composite materials, moreover, appear to be ideal for the exploitation of A.E. techniques as several brittle failure modes occur before the catastrophic failure. What this paper means to produce is an investigation into the behaviour of glass fibre reinforced plastic (GFRP) specimens with different fibre orientation by means of rising load tests, and to eventually infer some relationships between A.E. data and the stresses responsible for the various failure modes in the material being tested.