Introduction

Abstract

The word “system” is used here for a technical construction (object) in its operational environment from, for instance, civil, mechanical, automotive, coastal, ship, or aerospace engineering. The forces acting on the system during its utilization affect the system’s properties. An example is the stiffness degradation through a crack due to cyclic forcing, and the hardening effect of high static forces at the beginning of a fatigue test. If the system property changes reduce safety, lifetime or other aspects of performance, and comfort, then failures (defects, faults, damage) can occur. Because the safety effects of failures can be catastrophic, early failure detection, localization and assessment are necessary during the system’s life.