Inelastic Deformation Of Metal Matrix Composites

A theoretical model capable of predicting the thermomechanical response of continuously reinforced metal matrix composite laminates subjected to multiaxial loading was developed. A micromechanical model is used in conjunction with nonlinear lamination theory to determine inelastic laminae response. Matrix viscoplasticity, residual stresses, and damage to the fiber/matrix interfacial zone are explicitly included in the model. The representative cell of the micromechanical model is considered to be in a state of generalized plane strain, enabling a quasi two-dimensional analysis to be performed. Constant strain finite elements are formulated with elastic-viscoplastic constitutive equations. Interfacial debonding is incorporated into the model through interface elements based on the interfacial debonding theory originally presented by Needleman, and modified by Tvergaard. Nonlinear interfacial constitutive equations relate interfacial tractions to displacement discontinuities at the interface. Theoretical predictions are compared with the results of an experimental program conducted on silicon carbide/titanium (SiC/Ti) unidirectional, (O4), and angle-ply, (+34)(sub s), tubular specimens. Multiaxial loading included increments of axial tension, compression, torque, and internal pressure. Loadings were chosen in an effort to distinguish inelastic deformation due to damage from matrix plasticity and separate time-dependent effects from time-independent effects. Results show that fiber/matrix debonding is nonuniform throughout the composite and is a major factor in the effective response. Also, significant creep behavior occurs at relatively low applied stress levels at room temperature. Lissenden, C. J. and Herakovich, C. T. and Pindera, M-J. Unspecified Center NASA-CR-191522, AM-93-03, NAS 1.26:191522 NAG1-745; RTOP 506-73-43-03...

The deformation mechanisms of a Ti 15-3/SCS6 (SiC fiber) metal matrix composite (MMC) were investigated using a combination of mechanical measurements and microstructural analysis. The objectives were to evaluate the contributions of plasticity and damage to the overall inelastic response, and to confirm the mechanisms by rigorous microstructural evaluations. The results of room temperature experiments performed on 0 degree and 90 degree systems primarily are reported in this report. Results of experiments performed on other laminate systems and at high temperatures will be provided in a forthcoming report. Inelastic deformation of the 0 degree MMC (fibers parallel to load direction) was dominated by the plasticity of the matrix. In contrast, inelastic deformations of the 90 degree composite (fibers perpendicular to loading direction) occurred by both damage and plasticity. The predictions of a continuum elastic plastic model were compared with experimental data. The model was adequate for predicting the 0 degree response; however, it was inadequate for predicting the 90 degree response largely because it neglected damage. The importance of validating constitutive models using a combination of mechanical measurements and microstructural analysis is pointed out. The deformation mechanisms, and the likely sequence of events associated with the inelastic deformation of MMCs, are indicated in this paper. Majumdar, B. S. and Newaz, G. M. Unspecified Center...

This book contains fifteen papers based on the presentations made at the symposium on "Inelasticity and Micromechanics of Metal Matrix Composites" held at the University of Washington, USA, in mid-1994. The papers represent the most recent work conducted on inelasticity and micromechanics of metal matrix composites. The book is divided into two parts: Part I deals with the study of inelastic deformation in metal matrix composites, while Part II tackles the micromechanical aspects of metal matrix composites. The articles discuss different aspects of these two topics ranging from purely theoretical treatments to extensive experimental investigations. Many of the papers are by prominent researchers working in this area.

Polymer composites were introduced for the aerospace industry as light, strong, stiff materials, and adopted by the construction and automobile industries, among others. Meanwhile, composite materials have been introduced to fulfill the uses that these conventional materials could not, such as in extreme environments. The research for new composites includes not only new polymer systems, but metals, ceramics and intermetallic systems as well. This volume contains a selection of recent work by leading researchers in micromechanics on the topics of prediction of overall properties of elastic, perfectly bonded systems, problems associated with inelastic deformation of the phase, debonding at interfaces and growth of distributed damage. Many familiar aspects of mechanical behavior, such as fatigue, fracture, strength and buckling, etc. have been reexamined and adapted for these new systems.