Fatigue Testing and Damage Development in Continuous Fiber Reinforced Metal Matrix Composites

Abstract

SUMMARYContinuous fiber reinforced metal matrix composites (MMC) are projected for use in high temperature, stiffness critical parts that will be subjected to cyclic loadings. This paper presents a general overview of the fatigue behavior of MMC. The objectives of this paper are twofold. The first objective is to present experimental procedures and techniques for conducting a meaningful fatigue test to detect and quantify fatigue damage in MMC. These techniques include interpretation of stress-strain responses, acid etching of the matrix, edge replicas of the specimen under load, radiography, and micrographs of the failure surfaces. In addition, the paper will show how stiffness loss in continuous fiber reinforced metal matrix composites can be a useful parameter for detecting fatigue damage initiation and accumulation. Second, numerous examples of how fatigue damage can initiate and grow in various MMC are given. Depending on the relative fatigue behavior of the fiber and matrix, and the interface properties, the failure modes of MMC can be grouped into four categories: (1.) matrix dominated, (2.) fiber dominated, (3.) self-similar damage growth, and (4.) fiber/matrix interfacial failures. These four types of damage will be discussed and illustrated by examples with the emphasis on the fatigue of unnotched laminates.

Deformation and fracture of Ti- and Ti3Al-matrix composites

“…It was found that an SCS-6 fiber may have a fatigue endurance limit around 1.3 GPa. 32 These results imply that the fatigue endurance crack deflection and branching, fiber breakage, and fiber sliding as well as pull-out. For this type of composite, the crack exhibits a nonplanar crack-propagation behavior.…”

A Creep Cavity Growth Model for Creep-Fatigue Life Prediction of a Unidirectional W/Cu Composite

“…Matrix dominated fatigue failure of a continuous-fiber-reinforced composite likely occurs if the matrix material has a lower fatigue endurance than the reinforcing fiber (ref. 15). Matrix dominated failure of 9 vol.% tungsten fiber reinforced copper at elevated temperature would be expected due to the known high temperature mechanical behavior of copper and the relatively low volume fraction of the reinforcing fiber.…”

Prediction of Matrix Fatigue Crack Initiation in Notched SCS-6/Ti-15-3 Metal Matrix Composites

“…The maximumstrain next to the notch can be written as Maximum local strain = Kt_ max +°r/E (2) where _max = maximumnominal value of applied strain E = Young's modulus of the matrixmaterial.…”

“…In room temperature fatigue tests of unnotched specimens,Johnson [2] also observed that at higher applied loads, the fibers failed before matrixfatigue cracksdeveloped. At lower loads and longer life (50,000cyclesplus), the matrix material fatigue cracks prior to fiber failure.…”