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Experimental and analytical procedures are used to ascertain the inplane behavior of a class of ribbon-reinforced composites containing different combinations of ribbon width, pattern, volume fraction, and amount of ribbon overlap. The rationale and description of four types of unidirectional and cross-ply composites are also given. One of the objectives of this study is to determine whether the analytical tools, based on classical laminated plate theory, developed for filamentary composites are suitable for the characterization of unnotched ribbon-reinforced composites.
The experimental results of the principal properties of the unidirectional composites indicate that the materials are orthotropic. In the longitudinal direction, the response is not affected by the ribbon width, pattern, and amount of ribbon overlap: however, influences of these parameters are observed in the transverse and in-plane shear directions. The transverse-to-longitudinal ratios (E22/E11 and σ22/σ11, modulus and strength ratios respectively) of the laminates containing 1.27-cm ribbons were found to vary from 0.78 to 0.91 for the modulus and 0.67 to 0.78 for the strength, depending on the ribbon pattern used. Good overall correlations are observed between the off-axis results and analyses.
The axial stress-strain response of all cross-ply laminates is always between the longitudinal and transverse response curves. This averaging behavior of the cross-ply laminates is due to the substantial contribution of the 90-deg laminae to the axial response of the composite. Further in-plane studies on the cross-ply laminates indicate that the trends of the moduli and strengths, for laminates containing ribbons which are packed hexagonally, are parabolic with respect to the inclination of the 0-deg laminae and the axial load. For cross-ply laminates containing ribbons packed in a staggered manner, the properties may be assumed to be isotropic. The average axial-to-longitudinal ratios (Ex/E11 and σx/σ11) for the cross-ply laminate are 0.91 for the modulus and 0.82 for the strength. The correlations between experiment and analysis show that the predictions are generally conservative, especially in terms of strengths. This is primarily due to the presence of interlaminar reinforcing effects, which are not considered in the analysis. In addition, variations in stacking sequence do not affect the response of all the laminates tested. Based on macroscopic and microscopic observations of the fractured specimens and the results presented here, it would be conclusive to say that freeedge effects are substantially reduced when ribbon reinforcement is used.
composite materials, Metglas, ribbons, modulus, Poisson's ratio, strength, iron-nickel alloy, failure, evaluation
Senior Engineering Scientist, Research Division, AMP Incorporated, Harrisburg, Pa.