Analyse the stress in thread fastener by finite elements to predict the contact damage

In the assembly of the fasteners, high temperature can be generated from the friction between internal and external threads under some conditions of extreme pressure which may cause cold weld bounding. In fact, during the... [ view full abstract ]

In the assembly of the fasteners, high temperature can be generated from the friction between internal and external threads under some conditions of extreme pressure which may cause cold weld bounding. In fact, during the application of torque, the cold weld bounding is most likely to appear on the sliding surface of threads if the combination of pressure and heat are sufficient to enable the bounding process. This simulation evaluates the contact between internal and external thread to help better understand the mechanics of cold weld bonding in threaded fastener by the use of the multi-axial criteria of Crossland over the geometry of Unified National threads standard. Another view we consider is the plastic flow between the sliding surfaces under movement after the cold weld bounding has been initiated and when threads are seized for other reasons than bounding. The seizing of threads due to the closing clearance produced by the corrosion and the oxidation phenomena is another topic that the simulation aims to address and eventually, the modeling could be extended to predict the damage by contact fatigue in some alternating loads in lead screws and the nut. In fact, so many factors could trigger premature damage on the thread’s sliding surfaces that it is difficult to investigate the root cause from the only observations of damages made on the physical parts. To help explore the sensitivity of threaded fasteners to the aforementioned failures, we intend to show a numerical approach that makes use of Finite Element Analysis specifically focused on the thread’s sliding surface. We aim to predict the damage by combining the tolerance of thread’s profile, the loading modes, the coefficient of friction, the prevailing torque from the reduced clearance of the self-locking features, the temperature raise from friction, as well as other threads distortions such as the presence of corrosion/oxidation interfering with the thread’s clearance. The outcome of this study is to design a characterization plan for the selection of thread’s profile, alloy type, lubricant/coating type and the driving speed of torque management systems on free running and self-locking fasteners to avoid galling and fatigue damage.