Three dimensional threaded fastener meshing algorithm

Abstract

Understanding the stresses in the root of a thread of a bolt has never been easy. Ideally one would like to put a strain gage right at the root and measure them directly, but the placement of the gage and its wires are impossible without changing the insitu environment. Engineers then turned to analytical models, but soon discovered that two dimensional models where not giving the correct results because the geometry is not axis symmetric and three dimensional models where too difficult to mesh with today's CAD tools. A team consisting of Ford engineers and computer programers developed a program that will automatically generate a full three dimensional model of a thread fastener and mating threaded block by using a combination of cylindrical meshing techniques and a method of revolving “profiles” in a helical coordinate system. The bolt meshing program is able to input parameters about the thread fastener and block: diameter, pitch, length, etc., and output a complete three dimensional model in the form of an ABAQUS or NASTRAN finite element input deck. This model can then run through the ABAQUS finite element program and the resulting stress field computed. This paper will focus on the algorithm used to generate the mesh.