Plane Spline Function Method for Curve Fitting and Automatic Drwing of Specimen Boundary Contour in Photoelastic Image Data.

Abstract

In spite of the importance of determining the specimen boundary in experimental stress analysis, no efficient or successful method for extraction of the boundary contour deformed under load in photoelastic image data has yet been proposed because of several difficulties both in the construction and drawing of an approximate plane curve. This paper discusses a new method for plane curve fitting by use of a plane spline function (PSF) and its automatic drawing only from a small number of selected data points, extending the well-known spline function method of one variable into a new planar spline function method of two variables. In this method, separating the boundary contour into several branches of a simple arc, an algebraic plane curve is fitted to the set of dispersed data invo1ved in each branch. Then, the boundary contour of the specimen edge is efficiently constructed and drawn on the basis of the concept of Frenet's dynamic frame.