Igor Palley

A fracture mechanics approach to the single fiber pull-out problem as applied to the evaluation of the adhesion strength between the fiber and the matrix

—A fracture mechanics approach to the problem of single fiber pull-out is formulated in terms of the critical energy release rate. The solution is more general than that of Outwater and Murphy [1] since the matrix compressive and shear rigidities are more realistic and stress distribution is taken into consideration. The model also takes into account frictional forces between the filament and the matrix along the debonded surface. The shear-lag method is used for stress analysis. A relationship between the filament pull-out force, the critical value of the energy release rate and the position of the tip of the cylindrical crack is established. Numerical examples show the effects of fiber and matrix rigidities and diameters on the apparent average debonding stress predicted by the model. The results of a computer study on the relationship between the pull-out force and the notch size are presented along with the analysis of the model sensitivity to different parameters.

Tensile creep in ceramics using four-point bending test

A new model of ceramic creep in four point bending is proposed to determine the tensile creep rate which is difficult to test. Based on the assumption that ceramics creep only in tension and there is no creep in compression, the tensile creep rate of six ceramics is calculated in a simple way. The six ceramic compositions SiC, Al2O3/SiC, Mullite, Al2O3/Si3N4, Sialon and TZ-6Y, were subjected to a constant load which corresponded to initial maximum stress level of 135 MPa in four point bending. All test were performed at 1100°C for about 180 min. which is a time showing a steady short-time transient creep. Certain levels of creep, in terms of measured displacement, were observed in all the tested materials. The experiment shows that the lowest level of creep among the tested materials is in SiC, the highest is in TZ-6Y. The creep rate is expressed in terms of measured displacement and the calculated tensile creep rate at the apparent steady state is given for all tested materials.

A Fracture Mechanics Approach to Interlaminar Failure of Unidirectionally Reinforced Composites

Models are proposed for initiation and completion of failure in unidirec tionally reinforced composites under longitudinal shear. The models allow characteriza tion of the effect of fiber volume content on the average shear strength of composites con sidered as homogeneous material. Results are compared with experiments.

New Method for Evaluation of Fiber/Matrix Adhesion

Abstract There are several well-known methods for evaluating the level of fiber-to-matrix adhesion. For example, the single filament pull out test is the most direct way of measuring the level of the debonding strength. However, the method is not always applicable because Of fiber brittleness or the geometry and/or size of the fibers. Incorporation of fibers in a fiber/matrix composite and arranging the composite failure in such a way that fiberlmatrix debonding is the dominant failure mode is another well-known method for evaluating the interfacial adhesion level. The short beam shear method, popular because of convenience, is an example of this class of methods.