M. Tarfaoui

Prediction of Damage in Composite Cylinders After Impact

This paper presents the results from a study in two parts. The first part involves the identification and modeling of damage initiation and development in glass-reinforced epoxy composite cylinders subjected to drop weight impact. The second is concerned with the evaluation of the influence of this damage on the residual strength under hydrostatic pressure loading. Original results showing the influence of damage on implosion pressure are presented. The improved understanding of these phenomena and the development of predictive tools is part of an ongoing effort to improve the long-term integrity of composite structures for underwater applications.

Scale and Size Effects on Dynamic Response and Damage of Glass/Epoxy Tubular Structures

The impact behavior of composite materials has been extensively studied but interest has been centered on flat plates. For underwater applications, thick composite cylinders are employed and several questions must be addressed concerning the influence of accidental impact. The aim of this work is to study the dynamic response of tubular structures. Such structures find many applications but the damage upon impact is not taken into account during their dimensioning. However, at the time of their handling or in service the damage introduced by accidental impact can compromise their capacity to fulfill their function. The cylinders are thick and consist of epoxy matrix and glass fiber reinforcement. After having observed the nature of the damage related to the static and dynamic loading, the scale and size effects on dynamic response and damage are examined. The studies reveal that the dynamic responses show a satisfactory correlation with predictions based on rules of similitude.

Residual Strength of Damaged Glass/Epoxy Tubular Structures

This article presents results from static and dynamic tests on thick filament wound glass/epoxy tubes. The first part involves the identification of damage initiation and its development. Ultrasonic inspection was employed first to determine projected damage areas. A large number of samples were then sectioned and polished and the true damage area was revealed by a dye penetrant technique. This has made possible detailed descriptions of damage development. The true damage area is roughly 10 times the projected area. The second part of the article is concerned with the evaluation of the influence of this damage on residual strength under hydrostatic pressure loading. The improved understanding of these phenomena and the development of predictive tools is part of an ongoing effort to improve the long-term integrity of composite structures for underwater applications.

Comparative study of mechanical properties and damage kinetics of two- and three-dimensional woven composites under high-strain rate dynamic compressive loading

The in-plane compressive behavior of two- and three-dimensional woven composite was investigated at high strain rates. The Split Hopkinson Pressure Bar is employed to test the high strain rate dynamic mechanical properties of E-glass vinylester composite material. For three-dimensional woven composite, two configurations were tested: compression responses along the stitched direction and orthogonal to the stitched direction. Dynamic compression properties for two- and three-dimensional are determined and compared. Experimental results show that the strain rate has a significant effect on the two- and three-dimensional woven composite response. It is observed that the three-dimensional woven composite has higher compression strength and dynamic modulus than the two-dimensional composite at high strain rate. For this study, a high-speed camera was used to determine the damage kinetics under dynamic load. The two-dimensional woven composite is mainly damaged in a mode of matrix cracks and severe delamination, while the mode for three-dimensional woven composite is mainly cracking of matrix and delamination for in-plane along to the stitched direction and shear banding failure for in-plane orthogonal to the stitched direction.

Dynamical characterisation and damage mechanisms of E-glass/vinylester woven composites at high strain rates compression

Within the EUCLID project, ‘Survivability, Durability and Performance of Naval Composite Structures’, one task is to develop improved fibre composite joints for naval ship superstructures. In many practical situations, the structures are subjected to loading at very high strain rates like slamming, impact, underwater explosions or blast effect. Material and structural response vary significantly under such loading as compared to static loading. In this paper, the results from a series of Split Hopkinson Pressure Bar tests on the woven composites are presented. These tests were done in two configurations: in-plane and out-of-plan compression test. It is observed that the failure strength varies with the different loading directions. The results indicate that the stress–strain curves, maximum engineering stresses and strains evolve as strain rate changes. The woven composites have higher values of engineering stress and dynamic stiffness for in-plane than for out-of-plane compression at the same strain rate; however, the in-plane strain at maximum stress is higher than that of out-of-plane compression. During the experiments, a high speed camera was used to determine the damage mechanisms. The specimens are mainly damaged in a crushing and shear failure mode under out-of-plane loading, as for in-plane test, the failure was dominated by fibre buckling and delamination.

Numerical Evaluation of Dynamic Response for Flexible Composite Structures under Slamming Impact for Naval Applications

The deformable composite structures subjected to water-entry impact can be caused a phenomenon called hydroelastic effect, which can modified the fluid flow and estimated hydrodynamic loads comparing with rigid body. This is considered very important for ship design engineers to predict the global and the local hydrodynamic loads. This paper presents a numerical model to simulate the slamming water impact of flexible composite panels using an explicit finite element method. In order to better describe the hydroelastic influence and mechanical properties, composite materials panels with different stiffness and under different impact velocities with deadrise angle of 100 have been studied. In the other hand, the inertia effect was observed in the early stage of the impact that relative to the loading rate. Simulation results have been indicated that the lower stiffness panel has a higher hydroelastic effect and becomes more important when decreasing of the deadrise angle and increasing the impact velocity. Finally, the simulation results were compared with the experimental data and the analytical approaches of the rigid body to describe the behavior of the hydroelastic influence.

Simulation of Mechanical Behavior and Damage of a Large Composite Wind Turbine Blade under Critical Loads

AbstractaIssues such as energy generation/transmission and greenhouse gas emissions are the two energy problems we face today. In this context, renewable energy sources are a necessary part of the solution essentially winds power, which is one of the most profitable sources of competition with new fossil energy facilities. This paper present the simulation of mechanical behavior and damage of a 48xa0m composite wind turbine blade under critical wind loads. The finite element analysis was performed by using ABAQUS code to predict the most critical damage behavior and to apprehend and obtain knowledge of the complex structural behavior of wind turbine blades. The approach developed based on the nonlinear FE analysis using mean values for the material properties and the failure criteria of Tsai-Hill to predict failure modes in large structures and to identify the sensitive zones.

Experimental study of the out-of-plane dynamic behaviour of adhesively bonded composite joints using split Hopkinson pressure bars

The effect of the strain rate on the mechanical behavior and the damage of adhesively bonded joints is one of the most important factors to consider in designing them. Vast research has been carried out on the dynamic behaviour of adhesives at different strain rates; however, the investigation about the dynamic behaviour of the adhesively bonded joints is limited. In this paper, the main objective is to study and assess the effect of the strain rate on the out-of-plane mechanical behaviour of adhesively bonded joints under dynamic compression using Hopkinson bars. These joints are studied using glass/vinylester composite materials which are commonly used in naval applications. The experimantal results have shown a strong material sensitivity to strain rates. Moreover, damage investigations have revealed that the failure mainly occurred in the adhesive/adherent interface because of the brittle nature of the polymeric adhesive. Results have shown good agreement with the dependency of the dynamic parameters on strain rates.

Computational Homogenization of Mechanical Properties for Laminate Composites Reinforced with Thin Film Made of Carbon Nanotubes

Elastic properties of laminate composites based Carbone Nanotubes (CNTs), used in military applications, were estimated using homogenization techniques and compared to the experimental data. The composite consists of three phases: T300 6k carbon fibers fabric with 5HS (satin) weave, baseline pure Epoxy matrix and CNTs added with 0.5%, 1%, 2% and 4%. Two step homogenization methods based RVE model were employed. The objective of this paper is to determine the elastic properties of structure starting from the knowledge of those of constituents (CNTs, Epoxy and carbon fibers fabric). It is assumed that the composites have a geometric periodicity and the homogenization model can be represented by a representative volume element (RVE). For multi-scale analysis, finite element modeling of unit cell based two step homogenization method is used. The first step gives the properties of thin film made of epoxy and CNTs and the second is used for homogenization of laminate composite. The fabric unit cell is chosen using a set of microscopic observation and then identified by its ability to enclose the characteristic periodic repeat in the fabric weave. The unit cell model of 5-Harness satin weave fabric textile composite is identified for numerical approach and their dimensions are chosen based on some microstructural measurements. Finally, a good comparison was obtained between the predicted elastic properties using numerical homogenization approach and the obtained experimental data with experimental tests.

Self-heating and deicing epoxy/glass fiber based carbon nanotubes buckypaper composite

The recent developments in the aeronautical structure industry have seen a sharp rise in the use of polymer composite materials. The performances of all aerodynamic surfaces are heavily dependent on the shape and the surface form. The modification of these surfaces due to condensation and melting of ice can cause catastrophic decreases in the aerodynamic performance. In this study polymer composite materials as heater were made and studied. The feasibility of using advanced polymer composites for de-icing application was validated and studied through experiments. It consists of thin carbon nanotubes (CNTs) Bucky paper placed between two glass fibers veils and then infiltrated with an epoxy polymer resin and cured. The composite can be heated up very quickly using an electrical power source. The idea of using this new material as a heater and de-icing material was explored experimentally. For that purpose, the temperature distribution was monitored at different positions of the panel using thermal imaging. Experimental results show that the surface temperature of the panel increases gradually as the heating time increases. This temperature increased in a short time period of heating time, implying that the composite panels with CNTs Bucky paper display an excellent heating performance.