Eric Lafranche

Prediction of injection-moulded flax fibre reinforced polypropylene tensile properties through a micro-morphology analysis

Micromechanical models usually applied to predict the mechanical properties of short glass fibre reinforced composites were used to evaluate the Young’s modulus and tensile strength of flax fibre reinforced polypropylene. Due to lack of accuracy between the experimental results and the existing models, a new adjustment to the Kelly-Tyson model was proposed. The changes were based on the understanding of the microstructure obtained in polypropylene/flax fibre composites produced by injection moulding with different flax fibre content. The mechanical properties were interpreted based on real fibre loading, fibre orientation, fibre dimension distribution and morphology of the composites. Lack of fibre/matrix adhesion, strong fibre damage and changes on the crystallization behaviour of polypropylene in the presence of flax fibres affect the mechanical strength, stiffness and elongation of the composites. The Kelly-Tyson’s model used for tensile strength prediction was modified to take into consideration the fibre property variability due to the large distribution of fibre shape ratio induced by the process. Finally, matrix modulus has been adjusted to take into account the change of crystallinity with fibre content. A better description of the mechanical properties is obtained using the proposed approach, resulting indeed in an excellent approximation to the modulus of the composite.

Injection Moulding of Long-glass-fibre-reinforced Poly(ethylene Terephthalate): Influence of Processing Conditions on Flexural and Impact Strengths

This paper aims to identify the main parameters that influence the mechanical properties of long-glass-fibre-reinforced poly(ethylene terephtalate) parts in order to optimise the potential of these composites. A Taguchi design of experiments (DOE) was used for this purpose. The shape of the injection-moulded specimen was representative of the complexity of industrial parts (presence of sharp frontal and tangential steps). The mechanical properties (bending and Charpy impact tests) were measured at different locations in the part in order to highlight anisotropy. Variance analysis has shown that holding pressure, injection speed, and mould temperature are the most effective processing parameters. It has also shown that the optimised parameter sets that lead to the highest flexural strength on the one hand and the highest impact strength on the other hand are different, the polymer melt and mould temperatures being opposite. Finally, microstructure analysis has shown a fibre content gradient along the flow axis, which is greatly amplified by the presence of geometrical accidents (frontal and tangential steps) including the reorientation of fibres in the flow direction at the end of the parts.

Thermal Modeling in Composite Transmission Laser Welding Process: Light Scattering and Absorption Phenomena Coupling

In previous studies [1, , we have presented a detailed formulation of a macroscopic analytical model of the optical propagation of laser beams in the case of unidirectional thermoplastic composites materials. This analytical model presented a first step which concerns the estimation of the laser beam intensity at the welding interface. It describes the laser light path in scattering transparent composites (first component) by introducing light scattering ratio and scattering standard deviation. The absorption was assumed to be negligible in regard to the scattering effect. In this current paper, in order to describe completely the laser welding process in composite materials, we introduce the absorption phenomenon in the model, in the absorbing material (second component), in order to determine the radiative heat source generated at the welding interface. Finally, we will be able to perform a three dimensional temperature field calculation using a commercial FEM software. In laser welding process, the temperature distribution inside the irradiated materials is essential in order to optimize the process. Experimental measurements will be performed in order to valid the analytical model.

Thin wall injection-overmoulding of polyamide 6/polypropylene multilayer parts: influence of processing conditions on thermomechanical properties of the layer assembly

Plastic packaging has many development drivers: providing enhanced functionalities, better barrier properties, and longer shelf life while taking into account the environment and respecting criteria of thermo-mechanical performance. As a single polymer cannot satisfy all these requirements, plastic products are often made of more than one polymer and/or more than one single layer, each one having different but complementary properties. This work aims at investigating the over-moulding of PA6 over PP-g-MA in order to optimise the adhesion of multilayer PP/PA6 injection-moulded parts, as PP and PA6 are not miscible. Among the processing parameters, the holding pressure was found to be the main parameter governing the peeling strength of the multilayer assembly. The change of the polymer structure was evaluated by optical microscopy coupled to infrared spectroscopy and scanning electron microcopy. The PA6/PP-g-MA interfacial properties were investigated by dynamic rheology and assessed in term of quadratic distance of diffusion through the interface. For this purpose, the variation of the temperature field of the assembly during the cooling stage of the manufacturing process was simulated using the heat transfer module of a finite elements software package.

A microstructural approach for modelling flexural properties of long glass fibre reinforced polyamide6.6

This paper focuses on the development and the validation of flexural modulus and flexural strength predictive models of long glass fibre reinforced polyamide 6.6 (PA66). Based on previous injection moulding optimization of 40u2009wt% long glass fibre PA66, a microstructure analysis was investigated on glass fibre reinforced PA66 by varying the parameters of the material (fibre length, fibre content, fibre diameter). In a first phase, analytical models established within the framework of the processing condition limits previously determined have been elaborated. These models lead to a good experimental/calculation correlation but remain limited to a mould and part design. In a second phase the flexural modulus and maximal flexural stress have been then estimated from structural models based on a five layer morphological description of the composites (local residual fibre length, local fibre content and fibre orientations). The long glass fibre PA66 composites were characterized in terms of fibre content distribution model and fibre orientation model through the part thickness. The experimental/model correlation was achieved whatever the process variability is (mould, material and processing conditions) both for the flexural modulus or flexural strength. The models have been then validated with an industrial part. Finally, a correlation between the two studied properties has been revealed depending on the nature of the composite matrix (PA66, PA6 or PP).

Effect of the Interdiffusion at the Polymer/Polymer Interface on the Flexural Properties of Over-Moulded Short Glass Fibre/Glass Fabric Reinforced PA6 Composites

The injection over-moulding of 30wt% short glass fibre reinforced PA6 (SGF from Solvay Engineering Plastics) onto consolidated unbalanced (87/13) 70wt% glass fabric reinforced PA6 (Continuous Fibre Reinforced Thermoplastic (CFRT) from Solvay Engineering Plastics) was investigated with the objective to optimise the flexural and interlaminar shearing of the complex. Among the processing parameters, the temperature of the fabric before injection and the over-moulded melt temperature associated to the mould temperature (cooling rate of the complex) were revealed as the main parameters directing the mechanical properties of the complex. Moreover, the flexural modulus and the apparent interlaminar shear strength fall down critically in the main direction (chain direction of the fabric) under a CFRT temperature of 150°C. The effect of the SGF/CFRT interface was quantified in term of quadratic distance of diffusion through the interface. First, the 1D cooling of the complex was simulated according to the heat transfer module of COMSOL Multiphysics® in order to determinate the variation of the temperature field during the cooling stage of process. The calculations were achieved with an initial CFRT temperature of 23, 100, 150 and 200°C, the mould and SGF melt temperatures were kept constant. The diffusion theory has then been applied to calculate the variation of the auto-diffusion coefficient through the thickness during the complex cooling, the diffusion is supposed occurring only at a temperature above the PA6 crystallisation temperature (185°C). The calculation of the quadratic distance of diffusion through the thickness confirmed the mechanical results. Under a CFRT temperature of 150°C, the ability to the molecular diffusion at the interface becomes non-existent. The melt temperature of the SGF PA6 has to be sufficient to melt the CFRT PA6 interface, the time of diffusion directed by both the CFRT and mould temperatures (cooling rate) has to be long enough to allow the molecular diffusion from the material to the other.

Prediction of Tensile Properties of Injection Moulding Flax Fibre Reinforced Polypropylene from Morphology Analysis

The Young modulus and tensile strength of flax fibre reinforced polypropylene were determined and compared with the micromechanical models usually used in the case of short glass fibre reinforced composites. The fibre length and fibre diameter distributions of the injected reinforced of 2, 4, 8 and 22vol% compound were determined and used to the models in order to evaluate the expected properties of the composites. The mechanical properties were interpreted on the base of real fibre content, fibre orientation, fibre length and diameter distributions and morphology of the composites. The Kelly-Tyson’s model of the tensile strength prediction has been modified to take in consideration the fibre property variability due to the large distribution of fibre shape ratio induced by the process. Finally matrix modulus has been adjusted to take into account the change of crystallinity with fibre content.

Processing-induced morphology : Its relationship with tensile- impact behaviour in injection-moulded polypropylene

This paper aims at identifying the main parameters that govern the tensile-impact strength of injection-moulded polypropylene. A Taguchi Design of Experiments (DOE) analysis has shown that the key parameters in both flow and transverse directions are the polymer melt and mould temperatures and the volumetric flow rate. The differences in high-speed mechanical behaviour have been explained on the basis of an investigation of the processing-induced morphology/tensile-impact behaviour relationship. The microstructure of parts manufactured under two extreme sets of moulding conditions has been analysed through-the-thickness by means of microscopy observations and by measurements of crystallinity, molecular orientation and thermal expansion. The impact brittleness originates from the skin layers, the major influential parameters being the skin/core ratio and the crystalline structure. The crack initiation energy increases with the oriented skin layer thickness, whereas the brittleness increases with the crystallinity level and the spherulite size.

Infrared welding process on composite: Effect of interdiffusion at the welding interface

In this study, the effects of the welding temperature field developed during the infrared assembly process on the joining properties of glass fibre reinforced polycarbonate/ unreinforced polycarbonate with carbon black were investigated. The temperature field and the contact time govern together the quality of the adhesion at the welding interface. The effect of the semi-transparent glass fibre reinforced polycarbonate composite / unreinforced polycarbonate composite with carbon black interface was quantified in term of quadratic distance of diffusion or diffusion depth through the welding interface. The microstructural characterizations were investigated in order to inspect the welding zones quality and to observe their failure modes. The diffusion theory has then been applied to calculate the variation of the quadratic distance of diffusion versus time at different locations. The complete self-diffusion is supposed occurring only at temperature above the polycarbonate glass transition temperature (140°C) and with a quadratic distance of diffusion superior to the mean square end-to-end distance.