Composite machining damage quantification using thermoelastic stress analysis

Abstract A new experimental method is presented for quantifying machining damage in polymer matrix composites. The method consists of capturing infrared images of machined samples and using thermoelastic stress analysis to quantify damage from the machining event. A modified stress concentration factor is presented as an easily measured and useful damage parameter. Circular holes were drilled into the center of plate specimens fabricated from a commercially available glass fiber reinforced composite. A standard drill bit, brad point drill bit, and abrasive water jet machining were the three machine tools investigated. Infrared images were used to quantify the machining damage by assigning a thermoelastic stress analysis based stress concentration factor (mSCF) to each machined hole. The mSCF was then used to rank the damage inherent to each machining method. Optical and electron microscopy were utilized to identify the types of damage associated with the three machining methods. Finally, each sample was fatigued to failure to substantiate the IR results. The ranking of damage based upon the mSCF was in good agreement with the fatigue lifetime rankings: higher mSCF is associated with shorter fatigue lifetimes.