Pierre Mertiny

Influence of the filament winding tension on physical and mechanical properties of reinforced composites

Abstract In this experimental investigation the influence of the applied tow tension during filament winding on the physical and mechanical properties of glass-fibre reinforced polymeric composite tubulars, was studied. Pressure retaining tubular products used in the transportation/storage of fluids are generally subjected to a variety of loading conditions during their service life; thus tubular specimens were tested under different biaxial loading ratios. The stress/strain response was recorded and functional and structural failure envelopes were developed. These envelopes indicate the leakage and final failure characteristics of the components, respectively. The mechanical properties were analysed in conjunction with the measured physical properties: ‘fibre volume fraction’ and ‘effective wall thickness’. Experimental findings demonstrate that the component strength depends on the degree of fibre tensioning. Under fibre-dominated loading conditions, higher winding tension leads to an improved resistance against failure of tubular components, whereas under matrix-dominated loading failure is delayed by reduced fibre tensioning.

An experimental investigation on the effect of multi-angle filament winding on the strength of tubular composite structures

Computer-controlled winding procedures are a state-of-the-art production method for tubular structures with filament reinforced polymer composites. Such structures are often subjected to complex states of stress during installation and/or operation. Modern computerised equipment allows for the design and production of multi-angle lay-up configurations. Using internal pressure and axial force, experiments under biaxial tensile stress ratios were carried out to investigate the performance of multi-angle filament wound structures. Results in terms of stresses at failure, observable modes of failure and stress-strain curves were compared to those of a baseline configuration made from a ±α angle-ply lay-up. Multi-angle wound structures exhibited an overall better performance in resisting damage when subjected to a variety of loading conditions. Thus, the present investigation concludes that multi-angle winding technology may provide considerable advantages over pure angle-ply lay-ups.

Tunneling Conductivity and Piezoresistivity of Composites Containing Randomly Dispersed Conductive Nano-Platelets

In this study, a three-dimensional continuum percolation model was developed based on a Monte Carlo simulation approach to investigate the percolation behavior of an electrically insulating matrix reinforced with conductive nano-platelet fillers. The conductivity behavior of composites rendered conductive by randomly dispersed conductive platelets was modeled by developing a three-dimensional finite element resistor network. Parameters related to the percolation threshold and a power-low describing the conductivity behavior were determined. The piezoresistivity behavior of conductive composites was studied employing a reoriented resistor network emulating a conductive composite subjected to mechanical strain. The effects of the governing parameters, i.e., electron tunneling distance, conductive particle aspect ratio and size effects on conductivity behavior were examined.

Representative volume element to estimate buckling behavior of graphene/polymer nanocomposite.

The aim of the research article is to develop a representative volume element using finite elements to study the buckling stability of graphene/polymer nanocomposites. Research work exploring the full potential of graphene as filler for nanocomposites is limited in part due to the complex processes associated with the mixing of graphene in polymer. To overcome some of these issues, a multiscale modeling technique has been proposed in this numerical work. Graphene was herein modeled in the atomistic scale, whereas the polymer deformation was analyzed as a continuum. Separate representative volume element models were developed for investigating buckling in neat polymer and graphene/polymer nanocomposites. Significant improvements in buckling strength were observed under applied compressive loading when compared with the buckling stability of neat polymer.

A Review of Thermal Spray Metallization of Polymer-Based Structures

A literature review on the thermal spray deposition of metals onto polymer-based structures is presented. The deposition of metals onto polymer-based structures has been developed to enhance the thermal and electrical properties of the resulting metal-polymer material system. First, the description of the thermal spray metallization processes and technologies for polymer-based materials are outlined. Then, polymer surface preparation methods and the deposition of metal bond-coats are explored. Moreover, the thermal spray process parameters that affect the properties of metal deposits on polymers are described, followed by studies on the temperature distribution within the polymer substrate during the thermal spray process. The objective of this review is devoted to testing and potential applications of thermal-sprayed metal coatings deposited onto polymer-based substrates. This review aims to summarize the state-of-the-art contributions to research on the thermal spray metallization of polymer-based materials, which has gained recent attention for potential and novel applications.

Stacking Sequence Effect of Multi–angle Filament Wound Tubular Composite Structures:

Pressure–retaining tubular structures made from polymer fibre reinforced composites are commonly wound with uniform winding angles. Modern production equipment allows for the fabrication of multi–angle layup configurations. Performance improvements of multi–angle layups in comparison to those with uniform winding angles have been reported for structures that are operated under variable biaxial stress states. Designing components with multi–angle layups is a complex task, as the proper winding angles as well as stacking sequence need to be determined. In this study, the influence of the stacking sequence on the strength of multi–angle filament wound tubes was investigated experimentally. Applying axial force and internal pressure, tubes of a certain layup and tubes with the inverted stacking sequence were subjected to different biaxial stress states. Stresses/strains at failure and failure modes were compared. Certain combinations of stacking sequence and biaxial stress state were found to result in increased strength. To confirm experimental findings, an analytical investigation is included in this study.

Effect of nanocomposite structures on fracture behavior of epoxy-clay nanocomposites prepared by different dispersion methods

The effects of organic modifier and processing method on morphology and mechanical properties of epoxy-clay nanocomposites were investigated. In this study, the preparation of nanocomposites by exfoliation-adsorption method involved an ultrasonic mixing procedure, and mechanical blending was used for in situ intercalative polymerization. The microstructure study revealed that the organoclay, which was ultrasonically mixed with the epoxy, partially exfoliated and intercalated. In contrast, organoclay remained in phase-separated and flocculated state after the mechanical blending process. Tensile stiffness increased significantly for the nanocomposite prepared by ultrasonic dispersion method through realizing the reinforcing potential of exfoliated silicate layers. Nanocomposites with exfoliated and intercalated nanoclay morphology were ineffective in enhancing the fracture toughness whereas nanocomposites with phase-separated and flocculated morphology have improved crack resistance predominantly by crack deflecting and pinning mechanisms.

Study of Mode I Fracture of Graphene Sheets Using Atomistic Based Finite Element Modeling and Virtual Crack Closure Technique

In this letter a finite element based atomistic model is proposed. This model was employed to study the mode I fracture characteristics of graphene monolayers. The proposed model was found to be less numerically intensive with fewer degrees of freedom in comparison to other numerical techniques, such as Monte Carlo and molecular dynamics modeling. An approach based on the virtual crack closure technique was employed to develop the atomistic formulation for estimating strain energy release rates for graphene sheets under opening mode.

Deposition of Electrically Conductive Coatings on Castable Polyurethane Elastomers by the Flame Spraying Process

Deposition of metallic coatings on elastomeric polymers is a challenging task due to the heat sensitivity and soft nature of these materials and the high temperatures in thermal spraying processes. In this study, a flame spraying process was employed to deposit conductive coatings of aluminum-12silicon on polyurethane elastomers. The effect of process parameters, i.e., stand-off distance and air added to the flame spray torch, on temperature distribution and corresponding effects on coating characteristics, including electrical resistivity, were investigated. An analytical model based on a Green’s function approach was employed to determine the temperature distribution within the substrate. It was found that the coating porosity and electrical resistance decreased by increasing the pressure of the air injected into the flame spray torch during deposition. The latter also allowed for a reduction of the stand-off distance of the flame spray torch. Dynamic mechanical analysis was performed to investigate the effect of the increase in temperature within the substrate on its dynamic mechanical properties. It was found that the spraying process did not significantly change the storage modulus of the polyurethane substrate material.

Multiscale model to investigate the effect of graphene on the fracture characteristics of graphene/polymer nanocomposites.

In this theoretical research work, the fracture characteristics of graphene-modified polymer nanocomposites were studied. A three-dimensional representative volume element-based multiscale model was developed in a finite element environment. Graphene sheets were modeled in an atomistic state, whereas the polymer matrix was modeled as a continuum. Van der Waals interactions between the matrix and graphene sheets were simulated employing truss elements. Fracture characteristics of graphene/polymer nanocomposites were investigated in conjunction with the virtual crack closure technique. The results demonstrate that fracture characteristics in terms of the strain energy release rate were affected for a crack lying in a polymer reinforced with graphene. A shielding effect from the crack driving forces is considered to be the reason for enhanced fracture resistance in graphene-modified polymer nanocomposites.