Preface

This book contains chapters with original and innovative research studies in the issues related to the broadly defined creep effect, which concerns not only the area of construction materials but also natural phenomena. In classical terms, creep is defined as a process that takes place under constant load, which ensures that stresses are usually within the Hooke's law range, and at elevated temperature. The loads applied to products working under creep conditions cause stresses and strains whose values may change over time, not only as a result of overloads occurring during service, but mainly at the time when loading remains unchanged and result in stresses lower than the yield strength.

In the creep of materials, both plastic and reversible strain occurs. As a result of the process, their shapes and dimensions change constantly during service. After the elapse of sufficient time of working under creep conditions, the components are degraded and their further service is prevented. The degradation processes start at the moment when the rate of strain changes from its minimum and proportional values to disproportional ones as it is increasing.

The development of materials for operation under creep conditions and the related manufacture of products with improved performance are a result of the dynamic worldwide demand for new technologies, and recently also those related to environmental protection. The result of the above-mentioned conditions is the extensive investigations of the properties of new materials carried out by scientists and researchers all over the world. This mainly concerns the components working under the so-called creep conditions, which are characterised by a slow change in the shape of material due to the operation of mainly prolonged permanent stresses, which are lower than the elastic limit of material.

The aim of next book from the series is to provide readers, students and PhD students, as well as research personnel and professional engineers involved in the operation of devices with comprehensive information on their changes in performance during work. Additionally, collection in one place of not only studies the phenomenon of creep but also the practical application of the discussed methods on specific examples and technological solutions. The chapters of this book will be developed by renowned and respected researchers and specialists from around the world.

> **Tomasz Tański and Marek Sroka** Silesian University of Technology, Poland

**Adam Zieliński** Institute for Ferrous Metallurgy, Poland

**Grzegorz Golański** Czestochowa University of Technology, Poland

**1**

inspection.

area is required.

procedure, is also important.

**Chapter 1**

*and Grzegorz Golański*

**1. Introduction**

Introductory Chapter: Creep - An

*Adam Zieliński, Marek Sroka, Tomasz Tański*

tional values to disproportional ones as it is increasing [6].

Overview of New Research Results

In classical terms, creep is defined as a process that takes place under constant load, which ensures that stresses are usually within the Hooke's law range, and at elevated temperature. The loads applied to products working under creep conditions cause stresses and strains whose values may change over time, not only as a result of overloads occurring during service, but mainly at the time when loading remains unchanged and results in stresses lower than the yield strength [1]. A characteristic feature of creep is that after strain relief of the material in service, the strain decreases and the so-called strain recovery takes place [2].

In the creep of materials, both plastic and reversible strains occur. As a result of the process, their shapes and dimensions change constantly during service. After the elapse of sufficient time of working under creep conditions, the components are degraded and their further service is prevented [3–5]. The degradation processes start at the moment when the rate of strain changes from its minimum and propor-

The service within the time as assumed by designers as well as the extension of the lifetime of the materials and products made from them which have worked the design service life are most often determined by the calculation method based on creep strength data and positive results of comprehensive mechanical tests [7–11]. Among materials, the products operating under creep conditions are of particular importance. In their evaluation, the condition assessment of their materials is important and necessary [12–16]. It is carried out using destructive and nondestructive materials testing the result of which is referred to the available characteristics of materials both in the as-received condition and after service [17–22]. The results of these tests, supported by the extensive material characteristics database, allow for good estimation of the material condition and degree of exhaustion and determination of the time of further trouble-free service until the next scheduled

However, in a number of cases, to reach the design service life for products working under creep conditions, not only good estimation of their service life but also its determination based on destructive tests in a selected representative test

Yet, it is not always possible in practice. Therefore, the aspect of knowledge (experience), frequently acquired during long-term scientific and industrial practice, and also supported by thorough cost-effectiveness calculation made for such a

The problem in evaluation of creep resistance of materials operated under creep conditions for a long time is the time necessary to perform creep tests for
