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Applied Composite Materials: An International Journal for the Science and Application of Composite Materials (v.7, #4)
Residual Compression Stress Profile in High-Modulus Carbon Fiber Embedded in Isotactic Polypropylene by Micro-Raman Spectroscopy by H. D. Wagner; M. S. Amer; L. S. Schadler (pp. 209-217).
Raman spectroscopy was used to investigate the compressive fragmentation process and the interface behavior in ultra high modulus (UHM) (750 GPa Modulus) pitch-based graphite/polypropylene composites upon cooling from processing temperature to room temperature. It is found that bulging is the primary mechanism of failure in these fibers, and Raman peak position measurements show that not all visually detected features represent real fiber failure. However, at real break locations, the fiber strain is found to drop to zero.
Keywords: compressive fragmentation; interfacial shear stress; polypropylene; polymer composite
Design of Composite Wing Access Cover Under Impact Loads by A. F. Johnson; G. Kempe; J. Simon (pp. 219-229).
The paper describes a design concept and prototype development study for a composite wing access cover panel which may be subjected to high velocity impact loads from burst tyre fragments. A number of design variants were fabricated in unidirectional (UD) carbon fibre reinforced polyetheretherketone (CF/PEEK) using the vacuum forming method. Emphasis in the paper is on the use of impact simulations at the design stage to assess various design concepts for the composite panel using finite element (FE) simulation techniques. These predict a damage state in the structure after impact loading, which allows the panel concepts to be ranked for impact resistance. This led to a successful design concept, which was verified by structural impact tests, in which the CF/PEEK access panel had an impact resistant liner of high performance polyethylene fabric.
Keywords: aircraft structures; carbon fibre/PEEK; impact simulation; impact damage; high performance polyethylene fibres
Micromechanical Modelling Coupled to a Reliability Approach for Damage Evolution Prediction in Composite Materials by F. Desrumaux; F. Meraghni; M. L. Benzeggagh (pp. 231-250).
This work is based on Mori and Tanaka"s work combined with statistical tensile strength theories for the computation of the effective properties of composites. In order to describe the entire behaviour of composite materials, statistical local damage criteria are introduced representing interface, fibres amd matrix. The damage accumulation process is described by the microcrack density, which increases according to probabilistic considerations. In fact, the Weibull distribution applied at the microscale level arises as a key model for the strength of composite materials. In addition, the representation of the failure processes of each constituent gives a more accurate prediction of composite material behaviour. Specific results are given for composites reinforced by aligned or randomly oriented fibres and for particulate material called Twintex®, developed by Vetrotex©.
Keywords: self-consistent analysis; probabilistic fracture; Weibull law; damage mechanism
NCG Reinforced MMC Fabricated by the Squeeze Casting Method by Y. M. Ryu; E. P. Yoon; M. H. Rhee (pp. 251-267).
In order to increase the wettability between carbon fiber and aluminum matrix, pure nickel was applied as coating on carbon fiber. And scanning electron microscopy was used to characterize the microstructure of the coating, fiber and matrix. The tensile tests of carbon fiber and aluminum matrix were done to examine how the behavior of nickel layers with variation of applied pressure make an effect on the mechanical properties of composites. As the applied pressure increases, nickel layers were resolved into the aluminum matrix and ultimate tensile strength of the composite decreased. This was due to premature fracture of the reaction layer acting as a surface notch.
Keywords: carbon fiber; nickel; aluminum; squeeze casting; resolution; tensile property