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Applied Composite Materials: An International Journal for the Science and Application of Composite Materials (v.6, #1)
Nanoscale Indentation and Scratch of Short Carbon Fiber Reinforced PEEK/PTFE Composite Blend by Atomic Force Microscope Lithography by Yanchun Han; Stefan Schmitt; Klaus Friedrich (pp. 1-18).
The atomic force microscope (AFM) has become a popular tool for characterizing surfaces of different types of materials. In this paper a new technology of AFM–SPM lithography was used to conduct nanoscale scratch and indentation tests on a short carbon fiber reinforced PEEK/PTFE composite blend. In the scratch test, by moving the tip across the surface at constant velocity and fixed applied force, grooves with nanometer scale dimensions were fabricated on the PEEK matrix surfaces. The grooves consisted of a central trough with pile-ups on each side. These grooves provided information about deformation mechanisms and scratch resistance of the individual phases. In the nanoscale indentation and scratch of the polymeric phases, microploughing and microcutting are the dominant wear mechanisms. The harder phases, i.e., graphite and carbon fibers, get worn by microcracking events.
Keywords: atomic force microscope (AFM); SPM lithography; short carbon fiber reinforced PEEK/ PTFE composite blend; nanoscale scratch and indentation tests
Effect of Consolidation Method on the Mechanical Properties of Nonwoven Fabric Reinforced Composites by Youjiang Wang (pp. 19-34).
Nonwoven fabrics provide low cost reinforcement for composites. The consolidation behavior of E-glass nonwoven preforms and the mechanical properties of the resulting composites are studied. The reinforcement structures include stitch-bonded chopped-strand mat, powder-bonded chopped-strand mat, and continuous-strand mat. A woven fabric is also included for comparison. The bulkiness of the fabric influences their processibility in the hand lay-up and resin transfer molding (RTM) processes. Mechanical properties of specimens from the hand lay-up and the RTM processes are evaluated in tensile, compressive, and flexural tests. The test results and failure mechanisms are reported, and the effect of consolidation condition on the mechanical properties are analyzed. Theoretical analysis of the elastic properties of nonwoven composites are discussed. The tensile moduli from the experiment for such composites are compared with theoretical predictions and good agreement is observed.
Keywords: nonwoven fabrics; composites; mechanical properties; consolidation; resin transfer molding; analysis
An Experimental Study of Resistance Welding of Carbon Fibre Fabric Reinforced Polyetherimide (CF Fabric/PEI) Composite Material by M. Hou; L. Ye; Y.-W. Mai (pp. 35-49).
This paper presents an experimental investigation of resistance welding of carbon fibre fabric reinforced polyetherimide composites (CF fabric/PEI). The heating elements were made from a single CF fabric/PEI prepreg sheet with neat PEI films co-moulded to both surfaces. Welding was conducted on a welding area of 25 mm × 12 mm. The quality of the welded specimens was studied using a non-destructive evaluation technique (C-scan) as well as a mechanical test (lap shear strength). The relationships between input power, input energy, welding time and consolidation pressure were studied. Experimental results indicated that sufficient joining was obtained at a power level from 80 to 160 kW/m2, under an initial welding pressure of 0.15 to 0.40 MPa. The maximum lap shear strength achieved through resistance welding was equivalent to that of the compression moulded benchmark. The fracture surfaces of welded specimens showed mostly cohesive-failure or intralaminar failure. An optimum processing window is proposed for the resistance welding of CF fabric/PEI composite system.
Keywords: joining; thermoplastic; composites; resistance welding; carbon fiber; polyetherimide
X-ray Analysis of Residual Stresses in C/SiC Composites by M. Broda; A. Pyzalla; W. Reimers (pp. 51-66).
The residual stress state of C/SiC-composites, which are manufactured by a pyrolytical process is analysed by X-ray diffraction. The residual stress state in the composites results from the superposition of the shrinkage of the matrix material during the pyrolytical process and from effects of the thermal mismatch between fibres and matrix. The dependence of the residual stress state on the fibre coating and the process parameters of the pyrolytical process is determined. Furthermore, the change of the stress state in the samples submitting them to mechanical and thermal loads is analysed.
Keywords: X-rays; residual stresses; C/SiC composites; fibre reinforced ceramic composites