Calculations of contact stresses of mating screw surfaces

Due to stress concentration in the contact area, there is a great deal of strain, which results in the local plastic deformation and destruction. Contact stresses take up some 80% of the total amount of stresses in strength esti-mation of screw mating surfaces. It is difficult to determine nominal contact stresses, so the calculations are performed by the elasticity theory methods. The contact stresses have been calculated by Hertz formulas in the longitudinal screw cross-section of a screw mechanism. The need to calculate contact stresses in the longitudinal screw cross-section is caused by total stresses of the screw, coil and contact stresses (a complex calculation tech-nique of the stress state screw surfaces). Energy deformation analysis (the fourth theory of strength) is used as the contact strength criterion; its applicability has been proved by the experimental data. It is advisable to apply this contact stress calculation technique to all types of point-contact gearing as well as friction gearing.