Structure-property relationships in glass-reinforced polyamide, part 1: The effects of fiber content

We present the results of an extensive study of the performance of injection-molded glass-fiber reinforced polyamide 66 with glass content between 0 and 40% and based on two chopped glass products both sized with polyamide compatible sizing. Mechanical properties generally improved with increasing glass content, modulus linearly, strength with a maximum at 40-50% glass content, and impact showing an initial decrease from the resin value with a minimum at 4% glass content before increasing at higher glass contents. Residual fiber length decreased linearly with increasing glass content. Interfacial strength was found to be in the range of 30-36 MPa, and no significant differences in dry as molded performance was found between the 123D and 173X sizings. Conditioning these composites in either boiling water or water/glycol mixtures leads to a dramatic drop in both tensile modulus and tensile strength. This is most likely due to the high level of matrix plasticization. After conditioning, the 173X sized glass delivered a significantly higher level of tensile elongation at all fiber contents. Excellent agreement was obtained between the experimental data and the theoretical predictions of the rule of mixtures model for modulus and the Kelly-Tyson model for strength over the range of fiber concentrations studied

The influence of fibre length, diameter and concentration on the strength and strain to failure of glass fibre-reinforced polyamide 6,6

Results of an investigation of the mechanical performance of injection moulded long glass fibre-reinforced polyamide 6,6 composites are presented. The glass fibre content in these composites was varied over the range 10-50% by weight using fibres with average diameters of 10, 14, and 17 μm. Mechanical testing and analysis of the apparent interfacial shear strength was carried out at 23 and 150 °C on dry-as-moulded and boiling water conditioned samples. The results from these composites are compared with standard extrusion compounded short glass fibre materials. The influence of fibre diameter and concentration on the residual fibre length, fibre orientation distribution and composite strength and elongation to failure is presented and discussed in comparison to the predictions of some of the available micromechanical models

Structure-property relationships in glass reinforced polyamide, part 2: The effects of average fiber diameter and diameter distribution

We present the results of an extensive study of the influence of average fibre diameter and the width of the diameter distribution on the performance of injection moulded glass-fibre reinforced polyamide 66. In the average fibre diameter range from 9-18m dry-as-moulded (DaM) composite unnotched impact and tensile strength decreased significantly. The composite notched impact performance and tensile modulus showed little dependence on fibre diameter. The influence of broadening the fibre diameter distribution by blending glass fibre samples of different average diameter was found to be particularly negative on the level of composite unnotched impact when compared at equal number average diameter. After hydrolysis treatment the composite tensile strength and modulus exhibited a large drop compared to the DaM results. In contrast, the unnotched impact results became insensitive to fibre diameter after hydrolysis. The average level of unnotched impact after hydrolysis was sufficiently high to show an increase over DaM when the fibre diameter was above 14m. Residual fibre length correlated significantly with fibre diameter with a lower average length for thinner fibres. The interfacial shear strength was found to be in the range of 26-34 MPa for DaM composites. There was a highly significant inverse correlation between the DaM interfacial strength and the average fibre diameter. It is shown that results from both tensile and unnotched impact measurements can be brought back to single trend lines by using a Z average value for the average fibre diameter which is more heavily weighted to the thicker fibres in the distribution

Interfacial strength in thermoplastic composites - at last an industry friendly measurement method?

Many elegant techniques have been developed for the quantification of composite micro-mechanical parameters in recent years. Unfortunately, most of these techniques have found little enthusiastic support in the industrial product development environment, where they are viewed as time consuming, complex, inefficient, labour intensive, and in many cases unproven or inapplicable in 'real' systems. Despite this reaction, there is a real need for a 'user-friendly' micro-mechanics to aid the composites industry to move to the next level of development. A method for deriving values for τ (the interfacial shear strength) and ηo (a fibre orientation factor) from a simple combination of the composite tensile stress-strain curve and the fibre length distribution has been available for some time. Despite the recent wealth of activity in the development of micro-mechanical test techniques, there has been little follow-up on this older technique. In this paper we explore this analysis by its application to injection moulded glass-fibre-reinforced thermoplastic composites produced using three matrices (polypropylene, polyamide 6,6 and polybutyleneterephthalate) and containing different levels of glass-fibre. We furthermore show how the analysis can be extended to obtain another important micro-mechanics parameter, σuf, the fibre stress at composite failure. Values of τ and ηo obtained using this improved version of the original model are presented and discussed

The influence of fibre length, diameter and concentration on the impact performance of long glass-fibre reinforced polyamide 6,6

Results of an investigation of the mechanical performance of injection moulded long glass-fibre reinforced polyamide 6,6 composites are presented. The glass-fibre content in these composites was varied over the range of 10-50% by weight using fibres with average diameters of 10, 14 and 17 μm. Impact testing was carried out at −40, 23 and 80 °C on dry-as-moulded and boiling water conditioned samples. The results from these long fibre composites are compared with standard extrusion compounded short glass-fibre materials. Data on the influence of fibre diameter, fibre concentration, residual fibre length, hydrothermal conditioning and testing temperature on the composite performance in notched and unnotched pendulum impact tests and multiaxial instrumented impact tests are presented and discussed. All of the above parameters are shown to have significant influence on impact performance. However, the level of these effects is shown to depend on which type of impact test is being considered

The influence of fibre length and concentration on the properties of glass fibre reinforced polypropylene : 6. the properties of injection moulded long fibre PP at high fibre content

The results of an investigation of the mechanical performance of injection moulded long glass fibre reinforced polypropylene with a glass fibre content in the range 0-73 weight % are presented. The composite modulus exhibited a linear dependence on fibre content over the full range of the study. Composite strength and impact resistance exhibited a maximum in performance in the 40-50 weight % reinforcement content range. The residual fibre length and fibre orientation in the samples has also been characterised. These parameters were also found to be fibre concentration dependent. Modeling of the composite strength using the measured fibre length and orientation data did enable a maximum in strength to be predicted. However, the position and absolute level of the predicted maximum did not correlate well with the experimental data. Further analysis indicated that deeper investigation of the dependence of the interfacial shear strength and fibre stress at composite failure on the fibre content are required to fully elucidate these results

Interfaces and interfacial effects in glass reinforced thermoplastics - Keynote Presentation

Optimization of the fibre-matrix interphase region is critical to achieving the required performance level in thermoplastic matrix composites. Due to its initial location on the fibre surface, the sizing layer is an important component in the formation and properties of the composite interphase. Consequently, any attempt to understand the science of the composite interphase must encompass an understanding of the science of sizing. In this paper the role of sizings from fibre manufacture through to performance of composite parts is reviewed. In particular the role of organosilane coupling agents and how the formation of a polysiloxane interphase is influenced by the surface properties of the fibre is examined. The influence of the sizing film former in terms of its level of interaction with the silane coupling agent is also examined. The importance of residual stresses in thermoplastic composites in the values obtained for the apparent adhesion levels in these systems is highlighted. These residual stresses are shown to play a significant role in determining the level of interfacial strength in thermoplastic composites and in particular in polyolefin matrices. By applying some of the available models for this phenomenon this analysis is extended to explore the effect of the anisotropic fibre microstructure of carbon, aramid and natural fibres on the apparent interfacial strength in thermoplastic composites

Interfacial strength in fibre reinforced thermoplastics

There has been a rapid growth in the development and application of fibre-reinforced thermoplastic polymer composites in recent years. Parallel to this growth has been the increasing recognition of the need to better understand and measure the micro-mechanical parameters which control the structure-property relationships in such composites. The properties of thermoplastic composites result from a combination of the fibre and matrix properties and the ability to transfer stresses across the fibre-matrix interphase. Optimization of the stress transfer capability of the fibre-matrix interphase region is critical to achieving the required performance level in thermoplastic matrix composites

Anisotropy of reinforcement fibres and its influence on the apparent interfacial shear strength in thermoplastic composites

Optimization of the stress transfer capability of the fibre-matrix interphase region is critical to achieving the required performance level in thermoplastic matrix composites. Despite the ever increasing diversity of the reinforcements available for polymer composites, glass fibres still account for 95% of fibre reinforcements used in the composites industry, primarily due to of their highly attractive performance/price ratio. Due to its initial location on the glass fibre surface, the sizing layer is an important component in the formation and properties of the composite interphase. A large proportion of the research published on interphase optimization in these materials has focussed on the role of the organosilane coupling agents which are almost universally present in glass fibre sizing. Perhaps due to their common name of "coupling agents", perhaps due to their reactive nature or even perhaps due to the early focus of composites research on chemically reactive thermosetting matrices, there exists a dominant mindset in the composites research community to approach the interphase from a chemical bonding viewpoint. While this approach may very well be justified in thermosetting matrix composites it is not at all clear that this is also the case for reinforced thermoplastics, in particular for the commercially important polyolefin based composites

The influence of fibre length and concentration on the properties of glass fibre reinforced polypropylene: 5. Injection moulded long and short fibre PP

We present results of a step by step comparison of the mechanical performance of injection moulded 'long' (LF-PP) and 'short' (SF-PP) previous termglass fibre-polypropylenenext term compounds. The study allows direct comparison of the mechanical performance of long and short previous termfibrenext term systems in the same resin at the same previous termfibrenext term diameter, and the effect of previous termfibrenext term diameter in short previous termfibrenext term compounds. Furthermore, the comparison of these three systems has been made over the 0-40 wt% previous termfibrenext term content range. At the same previous termfibrenext term diameter and previous termfibrenext term content LF-PP gives significant improvements in room temperature tensile and flexural strength, notched and unnotched impact resistance. The improvement in impact resistance is higher still at lower test temperature. LF-PP also gives increasingly higher modulus over SF-PP as the strain is increased. The effect of lowering the previous termfibrenext term diameter in SF-PP has been shown to increase both strength and unnotched impact, but not to the levels obtained with LF-PP at higher previous termfibrenext term diameter. Notched impact and modulus of SF-PP were relatively unaffected by reduction of the previous termfibrenext term diameter. The relative mechanical data are shown to conform well to available models. The results are discussed in terms of the relevant micro-mechanical parameters of these materials