On crystallisation and fracture toughness of poly(phenylene sulphide) under tape placement conditions

Abstract

Fibre reinforced thermoplastic tapes are subjected to high heating and cooling rates during the tape placement process. Such high cooling rates can significantly inhibit the crystallisation of the thermoplastic polymer and thereby affect its mechanical properties, such as strength or toughness. In the present work, the crystallisation of poly(phenylene sulphide) (PPS) subjected to high cooling rates was investigated using a fast scanning calorimeter. The PPS was found to be unable to crystallise when subjected to cooling rates higher than 20uC s 21. The influence of the degree of crystallinity on fracture toughness was investigated using an essential work of fracture approach. The amount of plastic work during the fracture process was found to decrease after moderate annealing.Keywords: Thermoplastic composites, Tape placement, Crystallisation, Fracture toughness Introduction Background and motivationThe laser assisted tape placement process, schematically illustrated in Fig. 1, is a promising manufacturing technique for thermoplastic composites, combining in situ consolidation with high productivity.1 Unidirectionally (UD) fibre reinforced thermoplastic tapes can be deposited at high rates onto a pre-consolidated (in some cases double curved) laminate. This laminate can be produced by either the tape placement process itself or by an alternative, more conventional, manufacturing technique. The mechanical properties of the final component can be tailored to a high degree by incrementally placing the tapes in the desired orientation. The process shows great potential for automation, which makes it attractive for the aerospace or automotive manufacturing industries. Moreover, the tapes can potentially be welded in situ, that is without an energy consuming consolidation step in an autoclave.1 Currently, however, such a post-consolidation step is still required in order to obtain the desired mechanical properties. Much effort is spent optimising the process in order to omit this expensive step and reach truly in situ tape placement. Such an optimisation procedure requires a thorough understanding of the interrelation between processing parameters, constituent material properties and final component performance.The characteristic process time, i.e. the time available for consolidation, is extremely short for the tape placement process. Such short process times can only be achieved when the material is subjected to extremely high heating and cooling rates, 2,3 which can easily exceed 400uC s 21. In the case of semicrystalline polymers, these high rates can significantly influence the resulting degree of crystallinity of the matrix material, and thereby the final product properties. The emergence of these fast manufacturing processes calls for an improved understanding of the crystallisation under highly non-isothermal conditions. Moreover, the influence of the degree of crystallinity on the material properties also becomes of increased interest.The present work focuses on poly(phenylene sulphide) (PPS), which is a the...

Mechanical characterisation of carbon fibre–PEEK manufactured by laser-assisted automated-tape-placement and autoclave

“…In LATP the elevated temperature induced by the laser at the nip point coupled with high dynamic shear forces (induced by the consolidation roller operating at relatively fast lay-down speeds) lower the viscosity of the matrix, and the applied roller pressure promotes inter-ply bonding. Early work [23][24][25][26] on LATP has been followed by renewed interest in recent years [11,12,16,19,[27][28][29][30][31][32][33][34][35]. This is largely due to its potential in terms of energy efficiency and precise control when compared to alternative heat sources such as hot-gas [16,31,32].…”

“…For example, 94% of autoclave level properties were achieved for CF/PEEK using a diode laser processing head running at 6 m/min with heated tooling [16]. Grouve et al working with a semi-crystalline CF/PPS tape reported that excellent toughness could be achieved using low laser power, high placement speeds and with the laser biased towards the incoming tape [27][28][29][30]. The high toughness was attributed to a largely amorphous morphology, as PPS was found to be unable to crystallise when subjected to high cooling rates (>20°C/min) inherent in the LATP process.…”

Non-uniform crystallinity and temperature distribution during adjacent laser-assisted tape winding process of carbon/PA12 pipes

“…Also, the mechanical performance of the composite pipes was studied for various loading conditions [24][25][26]. The degree of crystallinity (DoC) is another temperature-dependent structural parameter which affects the mechanical performance of the crystalline FRP products [27][28][29][30][31][32]. The desired DoC depends on the application of the manufactured thermoplastic part.…”

“…For the parts with a high interlaminar fracture toughness and large plastic deformation, a low level of DoC is required. Whereas for the parts with high tensile modulus and strength, a high DoC is desired [29,32]. During the LATW process, multiple intensive heating and cooling cycles take place due to a localized heat input by the high-powered laser which affect the final DoC throughout the product.…”

Processing of thermoplastic matrix composites through automated fiber placement and tape laying methods

“…10 A closely related process, derived from filament winding, is the tape winding process, which has a low-cost setup without a robotic or gantry-mounted head, and involves a mandrel/tool having a cylindrical shape so that circular rings can be processed. Both flat laminates 9,10,13,16,17,19,21,22,25,30,31,33,35 –69 and circular rings 20,55,70,71 –84 were investigated as well as elliptical rings. 76 Although a promising technique, ATP process still has many challenges to be overcome before it can be ful...…”