Introduction to the Variational Formulation in Mechanics

5Materials Exhibiting Creep

5.1 Introduction

The existence of components in engines and mechanisms subjected to high temperatures is commonplace. Therefore, understanding the mechanical properties of constitutive materials is fundamental in order to predict the behavior of the component during its useful life.

When materials are subjected to high temperatures, the strains that take place over long periods of time, phenomenon known as creep, become relevant. Hence, it is necessary to determine the mechanical models which are capable of representing the behavior of such materials to estimate the strains and stresses developed in the components.

5.2 Phenomenological Aspects of Creep in Metals

Although L. T. Vicat carried out systematic observations of slow strains in metallic bars in the 19th century [302], in general it is widely acknowledged that the phenomenological theory of fluency (also known as creep), started at the beginning of the 20th century with the contributions of the English physicist E. N. Andrade [4, 5], who introduced the terminology used these days in the description of the different phases of the creep phenomenon.

A typical creep experiment aimed at establishing a relation between the uniaxial deformation and the stress , through time , at a given temperature ...