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Applied Composite Materials: An International Journal for the Science and Application of Composite Materials (v.5, #2)
Towards a Predictive Design Methodology Based on the Physical Modelling of the Fracture of Fiber Composites by S. Mark Spearing; Peter W. R. Beaumont (pp. 69-94).
A predictive design methodology based on modelling the fracture stress (notched tensile strength) and post-fatigue residual strength of laminated fiber composites is presented. The approach is based explicitly on the development of models of the physical processes by which damage accumulates at a notch-tip and the application of these models to cross-ply laminates for a variety of material systems, including thermosetting and thermoplastic matrices containing carbon, glass and Kevlar fiber reinforcements. The effects of temperature and humidity on composite fracture can also be examined in the context of this modelling strategy.A pre-requisite of the model is that it has to be calibrated for each material system by performing tensile tests on notched and unnotched cross-ply laminate. From this initial calibration, which takes relatively little time, it is possible to apply the model to a prediction of the dependence of fracture stress on notch size; to an understanding of the effects of laminate stacking sequence (within the same cross-ply family) on fracture stress; and to provide insight into the effects of thermal or load cycling history on fatigue damage-growth and residual or fatigue strength.The advantages and deficiencies of this modelling strategy are assessed, as well as the applicability of such a physical modelling approach to the predictive design and failure of composite materials in general.
Keywords: modelling; notch strength; damage; fatigue; environment; temperature; prediction; design
The Influence of Interface Structure and Composition on the Response of Single-Fiber SiC/Ti-6Al-4V Composites to Transverse Tension by D. B. Gundel; D. B. Miracle (pp. 95-108).
The cruciform specimen geometry has recently been established to investigate the transverse tensile behavior of single-fiber or multiple-fiber titanium matrix composites; however, the results on only relatively few commercially-available fibers have been reported to date. The present study reports the transverse behavior of a range of SiC fibers prepared by different manufacturers and with different surface coatings. The mechanical response of the composite and the damage present at the interfacial region have been documented. In general, the stress–strain behavior was found to be sensitive to the chemical and structural nature of the fiber–matrix interfacial region. Fibers with carbon-rich coatings were found to have a range of interfacial strengths depending on the structure of the interface layers, while uncoated fiber interfaces have a high strength. This study demonstrates the value of the single-fiber transverse cruciform test for quantitatively comparing the behavior of various fibers and coatings, and shows that it can be useful for coating development studies.
Keywords: cruciform specimen geometry; interface strength; interface structure; transverse tensile testing; fiber coatings; titanium matrix composites; SiC fibers; damage; failure
Strengthening Efficiency of E-Glass Fibre Composite Jackets of Different Architectures for Concrete Columns by Lin Ye; Shi Zhang; Yiu-Wing Mai (pp. 109-122).
E-glass woven roving (WR), combined with chopped strand mat (CSM), glass fibre tape (GFT) and a vinyl-ester resin, was used to restrain concrete columns using a wrapping procedure with different architectures. The results indicate that great reinforcing efficiency can be obtained through tailoring the architectures of composite jackets. An experimental study on the retrofitting efficiency of damaged concrete columns was also conducted, using a group of damaged concrete columns wrapped with the composite jackets. The results show that the original load-carrying capacity can be restored with a large ultimate displacement for the damaged concrete columns.
Keywords: concrete columns; wrapping technique; glass fibre composite; civil engineering
Effect of Remote Ply Orientation on the Perceived Mode I and Mode II Toughness of θ/θ and θ/−θ interfaces by Ryan C. Hudson; Barry D. Davidson; Jonathan J. Polaha (pp. 123-138).
Results are presented from an investigation of the effect of remote ply orientation on the perceived mode I and mode II toughness of a laminated graphite/epoxy. Experimental and numerical studies were conducted on four commonly used stacking sequences. Each sequence contained a midplane delamination and was subjected to bending loads that produced either predominantly mode I or predominately mode II conditions. Of the four sequences, two contained delaminations at 30/30 interfaces, and two contained delamination at 30/-30 interfaces. For each interface type, one stacking sequence exhibited a relatively small transverse curvature under the applied loadings but a relatively large twisting curvature, whereas the other sequence exhibited a small twisting curvature but a large transverse curvature. For the two types of loadings (mode I and mode II), each of the four sequences was analyzed by three dimensional finite element analyses and tested in precracked and non-precracked configurations. Using appropriate nondimensional parameters, the results of this study are combined with the results of companion numerical investigations to make recommendations regarding the choice of stacking sequences for the determination of the toughness of arbitrary interfaces.
Keywords: delamination; fracture mechanics; double cantilever beam; end-notched flexure; mode I; mode II; multidirectional interface; graphite/epoxy