Response of adhesively bonded composite joints to low velocity impact

by Pillai, Govind Ramakrishna.

Adhesively bonded composite joints are widely used in modern lightweight flight and space vehicle structures and will be widely used in the next generation aircrafts such as Unmanned Aerial Vehicles (UAV) and Joint Strike Fighters (JSF). Designing of adhesively bonded composite joints is a challenging task as the characteristics of the composite laminate adherends have an effect on their performance. Wide use of composite materials is attributed to their superior properties such as high specific stiffness, excellent fatigue properties as well as resistance to environmental conditions. Although they possess such superior properties, their relatively low through thickness strength and susceptibility to impact have a significant concern preventing designer from using in areas which are prone to impact damage. In this experimental study, impact testing was done on adhesively bonded composite laminates. Hysol EA 9394 was the adhesive used for bonding the composite laminates. Glass/Epoxy, Carbon Plain Weave/Epoxy and Carbon Unitape/Epoxy were the composite laminate adherends used for the formation of the lap joint. Quasi-isotropic laypup sequence was used for manufacture of the composite adherends. Lap joints formed using the above said adherends were impacted at the center of the joint using an Instron Dynatup drop tower with impactors of different diameters as well as with different energy levels. The impacted specimens were then non-destructively inspected using through transmission ultrasonic C-scan. Residual indendation on the impacted specimen is also recorded. Impact force, total energy absorbed, duration of impact and impactor displacement were the important parameters which were used to quantify impact response of the adhesively bonded composite joints. In addition to the above said parameters, damage area obtained from through transmission ultrasonic C-scanning was also used to quantify the impact response of the v adhesively bonded composite joints. Residual indentation measurement combining with visual inspection was made use for preliminary damage detection. vi