| Abstract: | The primary aim of this investigation was to establish the strength characteristics of S-glass fiber bundles and composites subjected to quasi-static loading. Ten glass-bundle specimens and glass-fiber unilayer specimens, each containing thirty-one approximately equally spaced fibers (S-glass, 0.00485-in. diameter) were prepared and tested in an Instron machine at three strain rates (0.0265 in./in./min, 0.66 in./in./min and 26.5 in./in./ min). Grid lines were placed on composite specimen producing interference moiré fringes with a reference master grid placed in front of the specimen. The specimens were observed photographically during deformation. The experimental bundle strength compares well with that obtained on the basis of Daniels' theory. The experimental standard deviation is, however, much larger than that predicted theoretically. The experimental mean composite strength is compatible with that obtained on the basis of rule of mixtures and Gücer-Gurland models. The Zweben crack-propagation criterion E 2(f C )=1] gives too low a value for the composite strength. A new criterion E 3(fC)=1] is suggested for the present test series. Due to the rather large standard deviation and the small number of test samples it was not possible to quantitatively evaluate the effect of rate of straining. However, it is observed that, within the range of strain rates employed, the effect of strain rate on bundle and composite strengths does not exceed 20 percent and 10 percent, respectively. |
