Glass Fibre Content of PP Plates and their Properties: Part II: Tensile Mechanical Properties (original) (raw)
Related papers
2014
A validation of the fibre orientation and fibre length attrition prediction for long fibrereinforced thermoplastics Abstract Long glass fibre (LGF) composites are extensively used in manufacturing to produce components with enhanced mechanical properties. Long fibres with length 12 to 25mm are added to a thermoplastic matrix. However severe fibre breakage can occur in the injection moulding process resulting in shorter fibre length distribution (FLD). The majority of this breakage occurs due to the melt experiencing extreme shear stress during the preparation and injection stage. Care should be taken to ensure that the longer fibres make it through the injection moulding process without their length being significantly degraded. This study is based on commercial 12 mm long glass-fibre reinforced polypropylene (PP) and short glass fibre Nylon. Due to the semi-flexiable behaviour of long glass fibres, the fibre orientation distribution (FOD) will differ from the orientation distribution of short glass fibre in an injection molded part. In order to investigate the effect the change in fibre length has on the fibre orientation distribution or vice versa, FOD data was measured using the 2D section image analyser. The overall purpose of the research is to show how the orientation distribution chnages in an injection moulded centre gated disc and end gated plaque geometry and to compare this data against fibre orientation predictions obtained from Autodesk M oldflow Simulation Insight.
Shear anisotropy of short glass fibre reinforced thermoplastics injection mouldings
Fibre Science and Technology, 1979
Examination of the stiffness in shear of two glass fibre reinforced thermoplastics (G FTP) injection mouldings via the rail shear and plate-twisting techniques indicates that there is little anisotropy in shear as a function of orientation in GFTP. Comparison of experimental data with theories which predict the stiffness behaviour of composites having a distribution o f fibre lengths and fibre orientations shows that the Halpin et al. laminate analogy provides a good correlation both in tension and shear. It appears that a circular plate-twisting experiment may provide a useful and rapid measure of the anisotropy of shear stiffness.
Composites Part A: Applied Science and Manufacturing, 2018
Rapid heat cycle molding (RHCM) of reinforced thermoplastics is increasingly used in order to obtain high surface quality on structural parts. In this work, the effect of RHCM on both microstructure and ultimate tensile strength of polypropylene reinforced with 30 wt.% long glass fibers was investigated. Micro X-ray computed tomography was employed to allow a non-destructive assessment of fibers orientation and internal porosity, while optical measurements were used to evaluate the residual fibers length distribution. The experimental results indicated that an increase of injection velocity always results in a decrease of ultimate tensile stress, due to higher fiber breakage. This effect is partly attenuated at low mold temperature, due to an increase of fiber orientation. On the other hand, when using RHCM an increase of injection velocity results in a greater decrease of ultimate tensile stress, due to the reduction of both fiber length and fiber orientation.
Mechanical properties of glass fiber reinforced polypropylene injection molded with a rotation mold
Polymer Engineering & Science, 2006
A special mold (Rotation, Compression, and Expansion Mold) was used to impose a controlled shear action during injection molding of short glass fiber reinforced polypropylene discs. This was achieved by superimposing an external rotation to the pressure-driven advancing flow front during the mold filling stage. Central gated discs were molded with different cavity rotation velocities, inducing distinct levels of fiber orientation through the thickness. The mechanical behavior of the moldings was assessed, in tensile and flexural modes on specimens cut at different locations along the flow path. Complete discs were also tested in four-point flexural and in impact tests. The respective results are analyzed and discussed in terms of relationships between the developed fiber orientation level and the mechanical properties. The experimental results confirm that mechanical properties of the moldings depend strongly on fiber orientation and can thus be tailored by the imposed rotation during molding. POLYM. ENG. SCI., 46:1598 -1607,
An experimental study was conducted to investigateanisotropy effects on tensile properties of two short glass fiber reinforced thermoplastics. Tensile tests were performed in various mold flow directions and with two thicknesses. A shell-core morphology resulting from orientation distribution of fibers influenced the degree of anisotropy. Tensile strength andelastic modulus nonlinearly decreased with specimen angle and Tsai-Hill criterion was found to correlate variation of these properties with the fiber orientation.Variation of tensile toughness with fiber orientation and strain rate wasevaluated and mechanisms of failure were identified based on fracture surface microscopic analysis and crack propagation paths. Fiber length, diameter, and orientation distribution mathematical models were also used along with analytical approaches to predict tensile strength and elastic modulus form tensile properties of constituent materials. Laminate analogy and modified Tsai-Hill criteria provided satisfactory predictions of elastic modulus and tensile strength, respectively.
Reprocessing of glass fibre reinforced polypropylene through Injection moulding: Investigation of mechanical, physical and rheological properties, 2010
An investigation is conducted to determine the effect of reprocessing, through injection moulding, short glass fibre filled (20 wt %) polypropylene. Key mechanical and physical properties are monitored throughout the successive reprocessing phases in order to quantify the changes to the material. The fibre length is known to influence the mechanical properties and here the fibre length distribution is measured, again over the successive processing steps. This distribution is observed to show a reduction in average fibre length even within the first processing stage using virgin material. Processing parameters linked with melt plastication (screw rotation rate and back pressure) are observed to influence the average fibre length of the material entering the mould.
Morphological investigations of injection moulded fibre-reinforced thermoplastic polymers
Composites, 1991
Fibres affect the matrix morphology in fibre-reinforced composites. Especially in semi-crystalline melts the fibres can act as nucleation rods causing a structure known as transcrystallinity. Transcrystalline structures are also found in injection moulded parts. They affect the structure of fracture surfaces especially in the case of long fibre-reinforced polymers with good fibre/matrix adhesion. Transcrystalline structures are usually generated and investigated in a microscope with a hot stage. For injection moulded parts this is an inadequate method. The morphological results presented here were obtained from plasma-etched inner surfaces and thin sections by means of light and contrast interference microscopy accompanied by scanning electron microscopy of fracture surfaces. Plasma etching is a well suited preparation technique to reveal both morphological superstructures and damage such as voids, debonding and fibre cracks in composites.
We present a study of thermorheological behavior of thermoplastic composites reinforced polypropylene with different rates of short hemp fibers (PP/short HF) during industrial conditions of injection molding. The online rheometer fitted to the injection molding machine, was used to study the different rheological properties of composites, such as viscosity and elasticity, under real conditions of injection processing without disruption of the injection cycle and a minimum time and with high accuracy. We have highlighted the impact processing conditions such as the control temperature of injection machine, screw speed rotation and the shear rate on the viscosity and elasticity of the composite. The mastery of the rheological behavior of composites ''PP short Hemp fibers'', during industrial conditions of the injection molding, allows both the quality control of the material and self-regulation of the machine and the optimization of injection cycle parameters, therefore a better production.
Express Polymer Letters, 2007
Based on a previous optimisation of set-up parameters for injection moulding of polyamide 6-6 (PA 6-6) reinforced with 40-wt% of 10 mm long glass fibre, the aim of this paper is to define suitable guidelines to further improve the mechanical performances of PA 6-6 / glass Long Fibre Thermoplastic (LFT) injection mouldings. Different solutions have been considered: screw and non-return valve design modification so as to adapt them to LFT processing, increase of the initial fibre content (up to 50-wt%) and length (up to 25 mm) in the LFT pellets. Using a LFT dedicated plasticating unit has allowed decreasing the fibre breakage amount by about 80% at the nozzle exit, however without improving the flexural properties. Increasing the initial fibre content has logically permitted to improve the flexural properties. Increasing the initial fibre length has not brought any improvement of the properties and has even amplified the structural heterogeneities and anisotropy of the parts. These trends have been explained on the basis of cavity pressure records highlighting significantly different rheological behaviours, and of resulting residual fibre lengths and through-the-thickness fibre orientation profiles modifications.