MODELING OF ADHESIVE-PRESS CONNECTION OF HOLLOW FIBERGLASS SUCKER RODS

Abstract

Hollow sucker rods made of polymer composite materials (PCM) have high fatigue strength, but require improvement and ensuring the strength of the connection of the composite body with a steel nipple. The design of such connections is complicated by the fact that the PCM body has orthotropic characteristics of elasticity and strength and low interlayer strength. Morphological analysis has shown that a promising direction for improving such connections is the combination of adhesive-wedge, press and threaded connection methods in one design. This allows to increase strength, improve manufacturability, and prevent the penetration of the medium into the contact zone. The annular hole of the steel nipple with a screw thread is filled with glue and a smooth rod is screwed into it to form a tight fit. The polymerized glue forms a system of wedges that provide additional strength. A finite element axisymmetric model of such a connection has been developed with simulation of contact, ductility of the nipple material and orthotropy of the body material. Two simulation steps are performed. In the first, tension and polymerization of wedges are simulated. In the second step, the connection is gradually loaded with a tensile force, which is simulated by axial movement of the body end. The moment of failure of the connection is determined by the maximum value of the stress in the body. The simulation confirmed the effectiveness of the proposed design. The considered variant withstands tensile stresses up to 709 MPa, and the equivalent stresses in the body after tension formation are close to 500 MPa. The parametric model and macro for it can be used to study and optimize the parameters of such a connection for different types of PCM (fiberglass, carbon fiber, etc.). Increasing the tension and length of the contact zone does not solve the problem of stress concentration. Optimization of other geometric parameters is necessary. Promising solutions may include the creation of an additional screw thread on the opposite contact surface, additional crimping with dies, special surface treatment, the use of a variable hole diameter, pitch and other screw thread parameters along the axis.