Stepped lap repairs of thick composites
Topic(s) : Special Sessions
Co-authors :
Xue PENG (JAPAN), George SOTIRIADIS (GREECE), Maelle SERGOLLE (FRANCE), Emilien BILLAUDEAU (FRANCE), Vassilis KOSTOPOULOS (GREECE)Abstract :
The design and evaluation of different composite repair technics, for the purpose of forming an optimum patch design, is a complex and time-consuming process. Also, the effectiveness of a repair patch depends on various parameters, such as the shape and the bonding quality. The integrity of the patch is of most importance when referring to thick composites as these are used in critical areas of a structure.
In the present work, the effectiveness of stepped repair to thick damaged CFRP composite plates that are 16 mm in thickness was investigated by using a dedicated test campaign in conjunction with validated FE numerical models. The main goal was to recover a significant portion of the original strength of the pristine specimens and identify the influence of laser assisted repairs in comparison with conventional methods. For this reason, two methods of machining/treatment were used for the material removal in order to confirm which one provides better surfaces to enhance adhesive bonding;
•Milling, as conventional machining
•Laser beam treatment of the machined surfaces. The expected result is that the laser treated surface will provide a smoother activated surface, which enhances bonding.
As the 16mm specimens would imply high loads to fail, three point bending tests of pristine and repaired specimens were performed up to final failure. All samples per each case were tested and post failure analysis was performed.
In conjunction with the test campaign, FE models were created in order to be validated for the selection of the ideal patch geometry (d/t ratio, where d is the length of the step and t the ply thickness). The cohesive zone model properties in all the cases were quantified in order to use them in the FEM models. The quality of bonding was evaluated by using step repaired specimens in order to address the quality of bonding between the patch and the primary structure. For this reason, a dedicated test campaign with stepped repaired coupons of 3 mm thickness was performed by testing them in tension, as can be seen in the figure. Then, the validated model parameters were used for the three-point tests of the thick specimens.
The FE models were capable of predicting the failure load of the specimens as well as the way they failed. The outcome was that the stepped scarf repair campaign was able to unveil the advantage of the lasers added value to repair procedure with main advantage based on the strength of the repaired specimens in comparison with the conventional repairs.
In the present work, the effectiveness of stepped repair to thick damaged CFRP composite plates that are 16 mm in thickness was investigated by using a dedicated test campaign in conjunction with validated FE numerical models. The main goal was to recover a significant portion of the original strength of the pristine specimens and identify the influence of laser assisted repairs in comparison with conventional methods. For this reason, two methods of machining/treatment were used for the material removal in order to confirm which one provides better surfaces to enhance adhesive bonding;
•Milling, as conventional machining
•Laser beam treatment of the machined surfaces. The expected result is that the laser treated surface will provide a smoother activated surface, which enhances bonding.
As the 16mm specimens would imply high loads to fail, three point bending tests of pristine and repaired specimens were performed up to final failure. All samples per each case were tested and post failure analysis was performed.
In conjunction with the test campaign, FE models were created in order to be validated for the selection of the ideal patch geometry (d/t ratio, where d is the length of the step and t the ply thickness). The cohesive zone model properties in all the cases were quantified in order to use them in the FEM models. The quality of bonding was evaluated by using step repaired specimens in order to address the quality of bonding between the patch and the primary structure. For this reason, a dedicated test campaign with stepped repaired coupons of 3 mm thickness was performed by testing them in tension, as can be seen in the figure. Then, the validated model parameters were used for the three-point tests of the thick specimens.
The FE models were capable of predicting the failure load of the specimens as well as the way they failed. The outcome was that the stepped scarf repair campaign was able to unveil the advantage of the lasers added value to repair procedure with main advantage based on the strength of the repaired specimens in comparison with the conventional repairs.