A Non-Destructive Method to Classify the Correct Installation of Blind Bolts

Aerospace manufacturing requires efficient manufacturing processes. Composite materials are extensively used and manufacturing processes must evolve to overcome composite constraints for manufacturing and joining. Bolting is an extended joining process for composite materials in which a deformable blind bolt is stressed until joining forces are high enough to cause bolt breakage and ensure sufficient compression forces in the joint. Among bolting methods, blind bolting is an efficient composite joining method that enables the construction of aerospace composite structures accessing joints from a single side of the joint (front side), thus allowing for constructing closed structures where accessing the back side (blind side) is not possible. However, not being able to access the deformed head at the blind side prevents to perform a quality control and ensure a proper bolt deformation and a proper installation. In this research work a nondestructive method for blind bolt installation is developed. Several potential inspection techniques (shearography, thermography, frequency response methods and ultrasonic methods) are tested for blind bolting inspection suitability assessment. An ultrasonic measurement technique is identified as partially capable of classifying bolt installation. A further development, combining ultrasonic methods and process monitoring data, has led to a bind bolt installation classification method with a hit rate >95% on tested samples.