Date of Graduation

2003

Document Type

Thesis

Degree Type

MS

Committee Chair

Samir N. Shoukry

Abstract

Three-Dimensional Finite Element Unit Cell Models (UCM) have been extensively used in modeling Continuous Fiber reinforced Metal Matrix Composites (CFMMC). They are effective means to predict transverse stiffness or strength properties, as well as residual stresses that develop during the fabrication process of such materials. The boundary conditions of the unit cell are chosen so that all compatibility conditions are satisfied along its interfaces with the surrounding system of fibers and matrix. past applications of such Unit Cell Models neglect the effect of interactions with the neighboring fibers, as well as local bond stresses at the fiber-matrix interfaces. The various limitations of such UCM’s lead to poor correlations with experimental results. It has been reported that UCM’s may overestimate residual stresses in MMC materials by about 30 percent. Their predictions also indicate large levels of scatter and variability when estimating transverse stiffness properties. In this thesis two Multi Fiber Models (MFM) of a unit cell were developed, in an attempt to reduce the current discrepancies between finite element predictions and experimental data. The boundary conditions of the unit cell were shifted in these models away from the fiber-matrix interface, in order to account for the effects of neighboring fibers on the distribution of stresses through the MFM. The results generated by the proposed models were examined by assuming two different scenarios of conditions at the fiber-matrix interface: unbonded and fully bonded. The models developed in this study were used to predict the residual stresses and the transverse stiffness of Alumina/Titanium (Al2O3/Ti-6Al-4Va) composite. The finite element results were compared with those obtained from the classical Unit Cell Models. The accuracy of the models developed in this thesis, is reflected through a good agreement with the experimental results available from published literature. A parametric study was conducted to investigate the effect of fiber volume fraction on the magnitudes and distributions of residual stresses. The influence of fiber packing pattern on the transverse stiffness of CFMMC materials is also studied in this thesis, both for square array packing and hexagonal array packing.

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