Heterogeneous Fracture Mechanics Representations of the Effects of Defects from Manufacturing to End of Life

Abstract

Composite materials are essential for many modern applications, including airplanes and cars, energy conversion and storage devices, medical prosthetics, and civil structures. The strength and life of such materials are determined by a complex sequence of progressive nucleation, accumulation, and coalescence of micro-damage that is always related to the micro-morphology of the constituents and their properties. Although detecting and modeling all of the discrete events in that sequence is quite difficult, and in some cases not feasible, it would be very useful to identify observable parameters that indicate the onset of different stages of damage development so that remaining strength and life could be estimated. Recently, the authors have developed a method of following the effect of multi-defect nucleation, growth, coalescence, and fracture plane development based on the measurement of dielectric response of composite materials. The method also enables the prediction of as-manufactured individual sample strength, suggesting that the birth-to-death effect of defects can be followed and interpreted. The present paper postulatesthe construction of a fundamental fracture mechanics methodology based on this general set of observables that could enable the consistent relationship of all defect and material states during the processing and application life of composite materials as a foundation for a birth-to-death assessment of the effect of defects. The “heterogeneous fracture mechanics” concept is defined and discussed with example data and observations that indicate the success and limitation of the method for as manufactured materials, static and fatigue loadings.