Interlaminar Shear Strength of Fibre-Reinforced

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Interlaminar shear strength of fi bre- reinforced com posites M. F. M A R K H A M and D. DAWSON An analysis is given of the stress distribution between two grooves cut on opposite faces of a fibre-reinforced composite when a tensile stress is applied to the ends. If this loading system is used to produce failure in shear, it has been shown that the fracture surface is always on the centre plane of the test piece. Hence, values of the interlaminar shear strength derived from this technique are found to be more consistent than those resulting from the widely used 3-point short beam bend test where the fracture pattern can be complex. Examples of the measurement of interlaminar shear stress for several types of fibre reinforced composites are given using the technique and analysis described in this paper. Several methods have been suggested for the measurement of interlaminar shear strength of fibre-reinforced composites. That most commonly used is to subject a short thick beam to 3-point loading until failure occurs by shear on the central plane. For this test to succeed, the ratio of beam length to thickness must be five or less, or failure in bending may supervene. Also the presence of defects in the beam may precipitate failure in a manner other than pure shear along the mid-plane. Moreover, the distribution of shear stress along this plane is not well authenticated in the literature, and is highly sensitive to variation in the detail of the rollers or knife edges used to apply the loads. Dukes and Barnett, in a review article i state that, at present, there is no recognised procedure for the short beam test in this country, although a span-to-depth ratio of five appears to be widely used. If the ratio is much lower, there is a probability that cracking could occur at the points of loading. According to a report by Sturgeon, 2 the short beam method cannot be
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