Quantifying Damage Precursor Using Microcontinuum Physics

Abstract

It is quite challenging to quantify the precursor to damage state in composite materials. Interaction between intrinsic material state and ultrasonic wave signal is evident from many literatures. But, quantifying such state, before their manifestation, has not been investigated properly. It has been found that the fluctuation in time of flight (TOF) of dominant wave modes in structures are possible to be detected, if measured using equipment with the capability to measure at least nano to pico second fluctuations. Therefore, it is imperative to quantify such fluctuations by understanding of the physics behind such changes. Microcontinuum approach provides the tool to explain the nano to pico second fluctuations of wave modes at early stage of damage. In this paper Bi-Helmholtz type nonlocal parameters are used to quantify the damage state in carbon fiber composite specimens and subsequently the state is verified using high frequency scanning acoustic microscopy imaging. Two carbon fiber composite specimens were tested under fatigue loading and the damage state is quantified every 500 cycles. It has been found that before actual visible damage the new damage parameter is able to indicate the precursor to damage state.