Prediction of residual strength and delamination growth of thin CFRP laminates with re-infiltrated Barely-Visible-Impact-Damage

Abstract

Thin-walled Carbon-Fiber-Reinforced-Plastics (CFRP) laminates are becoming one of the composite materials most widely used in aeronautical industry for structural parts because of their high specific stiffness and strength. Nevertheless, the impact strength is one of its main drawbacks. Consequently, even low-energy impacts (the most frequent ones) such as accidental tool falls during ground services can cause instances of damage. Mainly, low-energy impacts induce internal damage patterns made of matrix cracks and delaminations in the laminates. They are classified as Barely-Visible-Impact-Damage (BVID) and present a stochastic nature. The pristine properties of laminates with BVIDs can be completely restored by gluing together the internal cracks. Nowadays, the technique that can perform such repair is known as re-infiltration. But, in the aeronautical industry there is no certification process available for primary structural repairs with this technique. In order to certify gluing repairs of damage with a stochastic nature, aeronautical approval authorities demand to prove the load bearing capacity (residual strength and damage growth) by means of experimental tests and numerical predictions. Therefore, the goal of this thesis is to investigate numerical models and methods capable to predict the residual strength and delamination growth of thin-walled CFRP laminates with re-infiltrated BVID. The numerical models will be based on Abaqus finite element code and validated experimentally. Furthermore, in order to perform the repairs, the re-infiltration method will be further developed. Finally, the Non-Destructive-Testing techniques based on ultrasonic scans and computer tomography will be used to model the internal damage patterns in the finite element models.