Research at UC3M Improves the Bolted Joints in Airplanes

A research project at Universidad Carlos III de Madrid (UC3M) that analyses the bolted joints used in the aeronautical industry has determined the optimum force that should be applied so that they may better withstand the variations in temperature that aircraft are subjected to. This advance could improve airplane design, weight and safety. (OIC/UC3M).

The researchers have analyzed the performance of these bolted joints in aeronautical structures in which mechanical elements (screws, nuts, washers) are used to join parts that are made of composite materials. Specifically, the scientists at UC3M have analyzed the influence of bolt torque (the force with which the bolt is tightened) and temperature, which varies from -50ºC, when the airplane is flying at an altitude of 10,000 meters, to 90ºC, the temperature to which a bolted joint may be exposed when it is close to a heat source. To do this, they developed a numerical model and analyzed the behavior of these joints under different conditions. "The main conclusion that we drew is that the torque of each joint should be estimated taking into account the range of temperatures to which the plate is going to be subjected, because current industry standards that are applied to determine torque do not take this effect into account", explains one of the authors of the study, Professor Enrique Barbero, head of the Advanced Materials Mechanics research group of the Department of Continuum Mechanics and Structural Analysis at UC3M.

The main type of failure that they found was the crushing of carbon fiber plates against the shaft of the bolt, which is made more likely by low temperatures or by low torque levels. "At -50ºC the volume of the panels is reduced and the effect of the torque is diminished, so the joints that are subjected to these temperatures, such as those that form part of the fuselage and the external structure of the airplane, should have a greater torque so that its effect is maintained even under very low temperatures", affirms Professor Carlos Santiuste. The opposite effect can also be dangerous, the researchers point out, because when temperatures are high or when the torque is too great, the panels made of composite materials may be damaged by being compressed between the head of the bolt and the washer.

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