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The use of mechanical fasteners is still main assembling method for CFRP sub-structures in aircrafts and helicopters. However, this type of joint introduces complex stress field in the hole surroundings producing failures risk. In this work, a progressive damage 3D model of the riveted joint has been implemented to predict the residual strength and compliance after first damage signs and reproduce the final failure of composite joints under tensile test. Two 3D FEM Models were used and results are compared to experimental tests. The junction stiffness under load was evaluated and preliminary analysis shows both the coefficient of friction and preload induce not significant alteration of the composite joint behaviour. On refined model, a 3D Hashin-type failure criterion was used to analyze damage of matrix and fibers, beginning in the hole where contact conditions with the bolt pin and head are more severe and is evenly distributed in various plies, leading to final rupture of second or third one. Successively, delaminations were introduced with cohesive model, since is considered to produce reliable results, because the initial compression collapse in critical layers in contact with rivet is proved to affect shear and compression load transfer to other layers, giving rise to localized internal delaminations, propagating successively in width.

This paper describes the application of active pulsed Thermography (PT) as a Non-Destructive Test (NDT) method for the investigation of CFRP aeronautical components. The analyzed specimens include T-shaped stringers, previously monitored by ultrasonic analysis, and laminated flat plates with internal production defects. Several set-up tests allowed to identify optimal configurations for the defect detection, according to specimen geometry and defect location. A custom post-processing algorithm has been developed to improve thermographic data for more precise defect characterization, whilst a successive full-field contrast mapping allows to achieve a reliable defect distribution map and a better definition on larger areas. Detection of defects was studied with a specific thermal contrast evaluation, with a suitable choice of undamaged reference area during the transient cooling phase. The influence of heating time and experimental set-up on the thermal contrast results has also been studied; moreover, the ability of thermographic technique to detect real small production defects with accuracy and reliability is verified for CFRP aeronautical components.

In this work the mechanical behaviour of CFRP laminates having an artificial wrinkle introduced in the critical section has been studied in the Open Hole Tension and Open Hole Compression configuration. The experimental test allowed determining the failure mechanism and the knockdown of the ultimate strength in five different configurations.