Materials Science and Engineering

Context of the test: The Direction Générale de l’Armement (French military direction) is a major actor of aeronautical airworthiness. One of its tasks is to ensure the ability of operational conditions of French military systems. In this context, DGA Techniques aéronautiques performed mechanical tests on elementary and technological specimens to extend the flight-life of a fighter aircraft. 278 stress specimens were tested for this qualification program, with a lifetime of 10,000 to 500,000 cycles. One kind of those specimens were made of two steel parts clamped by a carbon plate and screw fasteners. Until now, regular visual inspections were performed to detect crack ignition. Those operations were very time-consuming and they mobilized technical staff during several years for the whole campaign. Therefore, a test method was developed to automatize this inspection.

 

Description of the adopted solution: DGA TA has developed an automated crack control system by the means of a camera and an image analysis, allowing the tests to be performed without operator (except for the set up) during days, nights and weekends. The set up includes four cameras, an analyze computer and a mechanical testing machine. A program for image processing was developed with Datalogic software. Every one thousand cycles, a picture per fastener was taken and those pictures were compared with a reference state, which is the beginning of the test. A crack criterion was defined on a given area. A difference greater than 100 pixels with respect to the initial state correspond to the crack ignition. Afterwards, a signal was sent to the machine to switch the test off. At the end, the operator visually inspected the specimen and decided to continue or terminate the test.