Polyetheretherketone Laminates Research Articles

Modelling of Bond Formation during Overprinting of PEEK Laminates.

The rapid technological progress of large-scale CNC (computer numerical control) systems for Screw Extrusion Additive Manufacturing (SEAM) has made the overprinting of composite laminates a much-discussed topic. It offers the potential to efficiently produce functionalised high-performance structures. However, bonding the 3D-printed structure to the laminate has proven to be a critical point. In particular, the bonding mechanisms must be precisely understood and controlled to ensure in situ bonding. This work investigates the applicability of healing models from 3D printing to the overprinting of thermoplastic laminates using semi-crystalline, high-performance material like PEEK (polyether ether ketone). For this purpose, a simulation methodology for predicting the bonding behaviour is developed and tested using experimental data from a previous study. The simulation consists of a transient heat analysis and a diffusion healing model. Using this model, a qualitative prediction of the bond strength could be made by considering the influence of wetting. It was shown that the thermal history of the interface and, in particular, the tolerance of the deposition of the first layer are decisive for in situ bonding. The results show basic requirements for future process and component developments and should further advance the maturation of overprinting.

Mechanical Characterisation of Bond Formation during Overprinting of PEEK Laminates.

The latest generation of high-temperature 3D printers enables the production of complex structural components from aerospace-grade thermoplastics such as PEEK (polyether ether ketone). However, adding long or continuous fibres is currently limited, and thermal stresses introduced during the process restrict the maximum part dimensions. Combining 3D-printed components with continuous fibre-reinforced components into one hybrid structure has the potential to overcome such limitations. This work aims to determine whether in situ bonding between PEEK laminates and PEEK 3D printing during overprinting is feasible and which process parameters are significantly responsible for the bonding quality. To this end, the bonding is analysed experimentally in two steps. Firstly, the influence of the process parameters on the thermal history and the strength of the bond is investigated. In the second step, a detailed investigation of the most critical parameters is carried out. The investigation showed the feasibility of overprinting with bonding strengths of up to 15 MPa. It was shown that the bonding strength depends primarily on the temperature in the interface. Additionally, the critical parameters to control the process were identified. The process influences that were displayed form the basis for future hybrid component and process designs.

Enhanced interlaminar fracture toughness of CF/PEEK laminates by interleaving CNT-decorated PEEK films

The weak interlaminar properties severely hinder the high-property applications of carbon fiber (CF) reinforced thermoplastic composites. Here, interlaminar properties were significantly enhanced by introducing carbon nanotube (CNT) decorated polyether ether ketone (PEEK) films into the interlayer. PEEK films decorated with different CNT contents were fabricated by the spraying and thermoforming processes. Tensile test results show that the films with a CNT surface density of 45 mg/m2 exhibit superior tensile strength and Young's modulus due to the higher crystallinity and larger crystalline size. The introduction of this modified film into unidirectional CF reinforced PEEK laminates leads to an increase by 101% to 1.67 kJ/m2 in interlaminar fracture toughness, while the interlaminar shear strength is retained. Fractographic analysis reveals that the increase in interlayer resin content and crack path deflection are primary factors contributing to interlaminar toughening. Molecular dynamics simulation demonstrates that incorporating CNT in the interlayer resin significantly improved the interfacial bonding strength between fiber and resin, thus resulting in crack path deflection.

In situ tensile behavior of hybrid carbon and glass fibers reinforced PEEK laminates: Isothermal or fire testing conditions

This work aims at investigating the thermo-mechanical coupling under critical temperature conditions in hybrid carbon/glass fibers reinforced Poly Ether Ether Ketone (PEEK) laminates. Two testing conditions have been considered: (i) isothermal and (ii) fire condition. A tensile loading was applied in homogeneous and isothermal temperature distribution (Room temperature – 350 and 500 °C) by means of a high-temperature furnace to quantify the influence of temperature on the mechanical response and properties. Regarding the fire conditions, a one-of-a-kind bench-scale fire test combining an in situ tensile mechanical loading and a kerosene burner (a flame temperature of 1100 °C ± 80 °C and a heat flux of 116 kW/m2 ± 10 kW/m2) has been designed and instrumented to induce anisothermal temperature conditions. This prototype allows the evolution of various physical quantities to be tracked as a function of the flame exposure time (5-10-15 min). These include temperature, loss of mass, deformation, stress, which are fundamental for understanding the mechanisms brought into play. The decrease of the tensile properties under isothermal conditions is −38% ± 0.6% (axial stiffness) and −54% ± 0.3% (axial strength) with respect to the values obtained at room temperature. The tensile response under fire is similar to the one obtained in isothermal conditions at 500 °C. The creep behavior of CG/PEEK laminates was also investigated with different boundary conditions (with or without a protective shield reducing the delirious effect of flame in terms of damages within the laminates). Compared to virgin specimens, the residual tensile mechanical properties significantly decrease as a function of the flame exposure time (5-10-15 min): 30% ± 1.1% and −55% ± 1.6% in axial stiffness and strength, respectively.

Influence of temperature degradation on the low velocity impact behavior of hybrid thermoplastic PEEK laminates

To evaluate the severity of thermal degradation on the impact response of carbon (C) and glass (G) fibers reinforced PolyEther Ether Ketone (PEEK) laminates, low velocity impact tests were conducted at a temperature higher than the glass transition temperature Tg (150°C) and after exposure to a kerosene flame (5-10-15′). The first important effect resulting from temperature increase was a reduction of the impact energy required to induce BVID (Barely Visible Impact Damage). The second effect was that matrix ductility (enhanced at T>Tg) contributes to significantly modify the permanent indentation. Not surprisingly, the plastic and viscoplastic deformation mechanisms being ruled by the PEEK matrix behavior at high temperature, the permanent indentation increases by almost 40% for all impact energies. Contrary to the external damage represented by permanent indentation, temperature has a tremendous influence on the internal damage as there was virtually no delamination in the CG/PEEK laminates impacted at Room Temperature (RT) and 150°C. At last, impact tests conducted on specimens exposed to a kerosene flame implied that the impact bearing capabilities of CG/PEEK laminates dramatically decreased after a 5′ exposure and became even critical after 10′ as perforation was observed. For 40 J impacts, the permanent indentation was multiplied by 3–9 with respect to the as-received specimens.

Multi-axial damage and failure of medical grade carbon fibre reinforced PEEK laminates: Experimental testing and computational modelling.

Orthopaedic devices using unidirectional carbon fibre reinforced poly-ether-ether-ketone (PEEK) laminates potentially offer several benefits over metallic implants including: anisotropic material properties; radiolucency and strength to weight ratio. However, despite FDA clearance of PEEK-OPTIMA™ Ultra-Reinforced, no investigation of the mechanical properties or failure mechanisms of a medical grade unidirectional laminate material has been published to date, thus hindering the development of first-generation laminated orthopaedic devices. This study presents the first investigation of the mechanical behaviour and failure mechanisms of PEEK-OPTIMA™ Ultra-Reinforced. The following multi-axial suite of experimental tests are presented: 0° and 90° tension and compression, in-plane shear, mode I and mode II fracture toughness, compression of ±45° laminates and flexure of 0°, 90° and ±45° laminates. Three damage mechanisms are uncovered: (1) inter-laminar delamination, (2) intra-laminar cracking and (3) anisotropic plasticity. A computational damage and failure model that incorporates all three damage mechanisms is developed. The model accurately predicts the complex multi-mode failure mechanisms observed experimentally. The ability of a model to predict diverse damage mechanisms under multiple loading directions conditions is critical for the safe design of fibre reinforced laminated orthopaedic devices subjected to complex physiological loading conditions.

Stochastic analysis of inter- and intra-laminar damage in notched PEEK laminates

This paper presents a finite element model to predict the progressive damage mechanisms in open-hole PEEK (Poly-Ether-Ether-Ketone) laminates. The stochastic laminate's properties with non-uniform stress distribution are consid- ered from element to element using the Gaussian distribution function. The failure modes considered are: fiber tension/ compression, matrix tension/compression, fiber/matrix shear, and delamination damage. The onset of damage initiation and propagation are predicted and compared with three different failure criteria: strain-based damage criterion, Hashin-based degradation approach and stress-based damage criterion which is proposed by the authors of the present work. The inter- laminar damage modes associated with fiber/matrix shearing and delamination are modeled using the cohesive elements technique in ABAQUS™ with fracture energy evolution law. Mesh sensitivity and the effect of various viscous regulariza- tion factors are investigated. Damage propagation and failure path are examined by re-running the program for several times.

Heat transfer effects on the processing‐structure relationships of polyetheretherketone (PEEK) based composites

AbstractAn analytical methodology was developed capable of describing interrelations between thermal processing and polymer structure for thermoplastic based composite laminates. Specifically, this modeling methodology was used to describe experimental results generated with a specially designed match die quench mold by processing both neat PEEK polymer and carbon fiber reinforced laminate samples at different cooling rates. The developed model accurately predicted temperature profiles for PEEK laminates of different thicknesses, under normal as well as extreme quenching conditions of 114°C/s. surface cooling rates that are possible to generate with the quench mold. In general, the modeling methodology is capable of predicting a part's thermal profile during processing in terms of the composite's microscopic intrinsic properties (fiber and matrix), composition, and lamina orientation. Furthermore, by coupling to the thermal profile description, a previously developed crystallization kinetics model for PEEK polymer and its carbon reinforced composite, a quantitative description of structural development during processing was obtained. Thus, with this analytical methodology, a skin‐core crystallinity profile, where the crystallinity varies with part‐thickness as a result of uneven cooling experienced during processing, was predicted both for the neat PEEK polymer and its carbon reinforced laminate forms. Finally, the developed methodology clearly established the interplay of both microscopic heat transfer and kinetics of crystallization/solidification of the matrix that must be accounted for in predicting the final structure of a carbon fiber reinforced laminate that will, in turn, govern microscopic and macroscopic performance.