DESCRIPTION OF THE MATHEMATICAL LAW THAT DEFINES THE RELAXATION OF BOVINE PERICARDIUM SUBJECTED TO STRESS

A material subjected to traction stress increases in length; if we mai ntain the elongation constant, the stress varies over a period of time . This phenomenon has been referred to as relaxation. The purpose of t his study was to define a mathematical law that relates the variation in stress to time when elongation remains constant in bovine pericardi um. The mathematical function obtained after assaying 34 samples to th e point of relaxation, subjected to initial stresses ranging from 0.17 -10.07 MPa, responds to the following equation: y = -0.0252 + 0.953 al pha - (0.0165 + 0.015 alpha)lnt, where y is the stress withstood at an instant in time, t, after initial stress alpha. A normogram, validate d by assays of up to 6,340 min duration (4.40 days), is presented for graphic calculation, permitting the computation of the loss of stress due to relaxation of this biomaterial, with initial stresses ranging f rom 1-10 MPa. (C) 1994 John Wiley & Sons, Inc.