Abstract
Friction joints with high-strength fasteners are widely used in construction, heavy machinery and aircraft construction. The reliability and operability of structures with friction joints depends on the tightening force of the fastener used. In the domestic industry, the tightening force is controlled either by the torque, which is measured using a calibrated torque wrench, or by the angle of rotation of the nut at the final stage of tightening. The above-mentioned methods of controlling the tightening force have increased labor intensity. Friction joints with control of the tightening force of fasteners for deformation of individual elements are widely used abroad. In Japan and the USA, high-strength bolts are used with the control of the tightening force on the twisting of the end element. Another effective way to control the tightening force of friction joints is to use a special washer with end-mounted protrusions that deform during tightening. The tightening force is controlled by measuring the gap between the washers. The gap is measured during the tightening of the fastener with a special probe. Using the finite element method based on the "DEFORM-3D" software package, the modeling of the stamping process of the washer protrusion, which is deposited during tightening, is performed. The mechanical properties of the material of the stamped workpiece (steel 35) were set from the database of the software package, and the die tool (matrix and punch) they were considered as absolutely solid bodies. Based on the results of the calculations performed, a graph of the dependence of the punching force F of the deposited protrusion of the washer on the movement of the punch is constructed. To approximate the resulting curve F = f(Δh), a polynomial of the 5th degree was used.
Keywords:
friction joints, high-strength fasteners, bolt, nut, washer, fastener tightening force, modeling of the stamping process, finite element method, stamping forces.