Complex screw joint under the action of the separation force and a skew torque

Abstract

be disregarded if the surface quality of the rod is no worse than class 5 (with microprojections of mean height less than 2.5-5.0 μm) and with a work ing load no greater than 0.5-0.6 of the tensile force.In the present work, we consider in more detail the influence of contact pliability with different surface quality of the contact surfaces on the load distribution within a complex screw joint under a central force and a skew torque, when the flanges are flexurally rigid.The rigidity of flanged joints tightened by screws was measured experimentally in [2]. Specifically, the flexure f of the basic beams ( Fig. 1a) and the flexure f a of their analogs ( Fig. 1b) was measured under a load F r = 1.2 kN. The basic beam consists of two parts tightened by four M8 screws; the tightening force on each screw is F ti = 7 kN; the total length L = 450 mm; the distance from the force F r to the butt joint is l 0 = 280 mm; the flange diameter D = 110 mm; the rod diameter d ro = 20 mm; and the diameter of the circle where the screws lie is D scr = 80 mm. In other words, the distance between the screws l scr = 57 mm. Struc tures with flanges of different thickness are tested: h = 10, 16, and 25 mm. The roughness of the contacting surfaces Ra = 0.4 μm. The analogs are one piece beams with the same overall dimensions as the com posite beams.In Fig. 2, we show experimental data from [2]. Spe cifically, we show the influence of the flange thickness on the rigidity of the joint for the basic beam (c = F r /f) and the analog (c a = F r /f a ) and also on the skew ϕ of the butt joint. The flanges are made of steel (continuous curves) or cast iron (dashed curves).With fixed flange thickness h, the skew ϕ of the joint takes the form Values of c and c a were given in [2].With sufficient flange thickness (h min = 16 mm for steel and h min = 22 mm for cast iron), ϕ hardly depends on h, according to [2] (Fig. 2). This indicates that the contact surface is not buckled or distorted. Thus, when h ≥ h min , the flanges have sufficient flexural rigidity.In the present case, with a screw diameter d = 8 mm, h min /d = 2 for steel and h min /d = 2.75 for cast iron. Correspondingly, l scr /h min ≈ 3.6 and 2.6.A condition for the absence of flexural strain was proposed in [3]: 2h/(D -d ro ) ≥ 1.The experimental apparatus developed for study of a complex screw joint 1 (Fig. 3) consists of two coils with flanges of height h = 25 mm. The external diam eter of the flange D 1 = 100 mm; the internal diameter ϕ f f a -( )/l 0 Abstract-The influence of pliability of the rough contact layer on the load distribution over the screws in a complex joint under the action of a separation force and a skew torque is investigated experimentally.