Thermoplastic Matrix Composites Research Articles

Fatigue Delamination Behavior of PEEK Thermoplastic Composite Laminates

Edge delamination tension fatigue tests were conducted on AS4/PEEK composite lami nates to determine the fatigue delamination behavior of these graphite reinforced, semi crystalline thermoplastic matrix composites. The strain at onset of edge delamination, ∈ c, observed during fatigue tests of (35n/ — 35 n/0n/90n)s laminates, where n = 1,2, was plotted as a function of fatigue cycles, N. The delamination onset strain decreased dramatically with fatigue cycles and then began to level off to an endurance limit at 106 cycles. The delamination onset strains were used to calculate critical strain energy release rate, Gc, values as a function of fatigue cycles to provide a more generic representation of the fa tigue delamination behavior of the material, i.e., one that is independent of layup and ply thickness. Although the static interlaminar fracture toughness of the AS4/PEEK compos ite is much greater than the toughness of graphite epoxy composites, the delamination fa tigue Gc threshold, calculated from the cyclic strain endurance limit at 106 cycles, was only slightly greater than the delamination fatigue threshold for graphite epoxy composites. This comparison, however, was based only on the contribution of mechanical strain to the strain energy released. An asymmetric (0 2/906)T AS4/PEEK curved panel was heated in an oven to determine the stress free temperature of the composite, and quantify the contri bution of residual thermal stresses to the strain energy release rate at delamination onset. The contribution of residual thermal stresses to delamination in AS4/PEEK was substan tial due to the large temperature range between manufacture and room temperature. More work is needed to fully characterize the influence of residual thermal and moisture stresses, and the degree of crystallinity of the PEEK matrix, on the strain energy release rate for delamination growth, and the interlaminar fracture toughness of the composite.

Thermoplastic matrix sheet composites

AbstractUntil recently, most high performance composites have been made with low‐viscosity thermosetting polymers. These polymers are ideally suited for producing composites in low production quantities because a wide variety of custom shapes can be manufactured without a high degree of mechanization. As the demand for composites increases, there is a need to develop high‐volume production techniques. Thermoplastic polymer‐based composites are better suited to high‐volume production than thermoset‐based composites because only heat and pressure are needed to form parts; no chemical reaction is required. Thermoplastic matrix composites are not well suited for low‐volume production runs because the need to handle high temperatures and pressures demands equipment that is best utilized for large production runs. In addition to processing advantages, thermoplastic matrix composites exhibit improved impact strength and chemical resistance over most thermoset‐based composites. In the course of this work, composites reinforced with long and continuous glass fibers were produced that had tensile strengths as high as 270 MPa, tensile moduli of 16.2 GPa, and notched Izod impact strengths of 11.1 J/cm.

A micrographic study of bending failure in five thermoplastic-carbon fibre composite laminates

The local deformation and failure sequences of five thermoplastic matrix composites were microscopically observed while bending the samples in a small fixture attached to a microscope stage. The thermoplastics are polycarbonate, polysulphone, polyphenylenesulphide, polyethersulphone and polyetheretherketone. The composites made from these plastics contain a variety of carbon fibres, though all with similar properties, and have fibre volume fractions ranging from 32 to 66%. Comparison is made to an epoxy matrix composite, 5208-T-300. Laminates tested are (0/90)2S, with outer ply fibres parallel to the beam axis. Four-point bending is used at a typical span-to-thickness ratio of 39:1. A shallow notch is put in the samples at mid-span to avoid failure under the loading pins. It was found that all the thermoplastic composites failed by abrupt longitudinal compression buckling of the outer ply. Very little precursory damage was observed. Micrographs reveal typical fibre kinking associated with longitudinal compression failure. Curved fracture surfaces on the fibres suggest they failed in bending rather than direct compression. Delamination was suppressed in the thermoplastic composites, and the delamination that did occur was found to be the result of compression buckling, rather than vice versa. Microbuckling also caused other subsequent damage such as ply splitting, transverse ply shear failure, fibre tensile failure, and transverse ply cracking.

High Performance Thermoplastic Matrix Composites

Most high performance composites utilize thermosetting polymers as the matrix material. These low viscosity liquid prepolymers are easily impregnated into reinforcing fibers and then crosslinked to form a solid structure. Polymers which have a low viscosity at room temperature are ideally suited for low production runs because a wide variety of individualized shapes can be manufactured without a high degree of automation. As the demand for composites increases the need for high volume production techmques has developed. Thermoplastic polymers are more appropriately suited for automated produc tion than thermosets because they require only the application of heat and pressure to form parts. No chemical reaction is required with thermoplastic composites. Thermoplastic matrix composites are not appropriate for low volume production runs because the high temperatures and pressures required to process the composites utilizes equipment which is appropriate for large production runs. In addition to high volume processing advantages, thermoplastic matrix composites exhibit improved impact strength and chemical resis tance over most thermset based composites. The composites produced in this investigation had tensile strengths as high as 270 MPa, tensile moduli of 16.2 GPa, and notched Izod impact strengths of 11.1 J/cm.

Experimental Investigation of Laser-Assisted Thermoplastic Tape Consolidation

An experimental investigation of a novel approach for manufacturing of thermoplastic matrix composites, is described. The technique is based on using laser energy as the focused heat source to melt the matrix material for subsequent consolidation, and appears to be particularly suited for thermoplastic filament winding operations. An experimental set up is defined to produce multi ply rings, and the feasibility of this technique is demon strated by discussing several samples that were produced using Ryton AC40-60 prepreg tapes. The quality of consolidation is examined through cross-sectional micrographs.

A Model of the Manufacturing Process of Thermoplastic Matrix Composites

A model is presented of the steps involved in the manufacturing process of semicrystal line thermoplastic matrix composites. The model relates the temperature and pressure ap plied during processing to a) the flow of the matrix into the fiber tow, b) the formation of contact and bond between adjacent plies, and c) the crystallinity. The results of the model were verified by tests performed with PEEK 150P polymer and APC-2 graphite/PEEK composite.

Thermoplastic matrix continuous filament composites of Kevlar® aramid or graphite fiber

Key static mechanical properties and laminating processes of thermoplastic matrix continuous filament composites reinforced with Kevlar® aramid or graphite fibers are presented and discussed. A tow of Kevlar or graphite impregnated with a thermoplastic matrix from a proprietary melt-coating process involving injection of a melted thermoplastic polymer can be consolidated into a sound, void-free composite laminate by compression molding. The unidirectional composites of Kevlar 49 or graphite from the melt-coated tows possess mechanical properties superior to those of similar composites prepared by other processes such as yarn cowinding and film laminating. The unidirectional composites of Kevlar 49 with thermoplastic matrices prepared from the melt-coated tows are equivalent or superior to those using Epon® epoxies or polyvinylester in flexural, shear and compressive strengths. Using J-polymer, a polyamide copolymer and a proprietary Du Pont resin candidate as a thermoplastic matrix model, a static mechanical test data base has been developed for graphite/thermoplastic matrix composites showing significant advantages in damage tolerance, compression after impact, and interlaminar fracture toughness. Although the unidirectional compressive strength of graphite/epoxy composites has been shown to correlate with matrix modulus, the thermoplastic matrix composites show no such correlation.