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Numerous industrial sectors request the permanently monitoring for damage of components with the least possible number of sensors. These industrial fields are construction engineering (e.g. bridge monitoring), renewable energies (e.g. monitoring of wind turbine rotor blades), chemical industry (e.g. monitoring of pipelines and storage tanks), mechanical engineering, vehicle manufacturing, aerospace industry (e.g. monitoring of lightweight structures) and others more. The diagnosis of components for internal failures can be carried out with different NDE methods depending on the material and the defect size. Examples of such methods are X-ray, the pulse-echo-ultrasonic method, for certain kinds of materials magnetic particle inspection, eddy current methods, as well as radar and Terahertz methods. However, these methods are of limited suitability for permanent monitoring because of their limited range within the material to be monitored. For permanent monitoring of components guided acoustic waves (also called Lamb waves) are most useful because of their large range within solid materials. Changes inside the material have great influences on the propagation conditions of the guided waves. Acoustic sensors are able to monitor large components even at a great distance from each other. Sensors and devices for the measurement of guided waves are already available. However, precise instructions for the use of these systems and the description of substitute defects are missing. The aim of the government-funded research project QuantSHM is now to overcome these constraints of monitoring systems in order to allow the monitoring methods to be widely accepted. Basically, research results of two fields of application will be presented. In particular these are acousto ultrasonic methods for isotropic materials (e.g. steel, pipelines) and acoustic emission methods for anisotropic materials (e.g. composites, rotor blades). Defect sizes can be clearly correlated with the defect size for isotropic materials whereas damaged areas are better addressed by acoustic emission for anisotropic materials.

Nowadays, long welded railway rails are achieved by means of aluminothermic and flush-butt welding processes. Compared to bolted joints, welds proved to be effective in terms of reduced wheel damage, ride comfort and maintenance. However, even if the event is inexplicably not considered in relevant standards, surface cracks often initiate within the welded and the heat affected regions of the foot, leading to brittle failure. On the subject, a recent work developed a probabilistic methodology for determining day-by-day failure probability. However, apart from this structural integrity study and few others, a complete damage tolerance approach should also consider the capability of nondestructive inspections. The latter is recognized as an essential input to define maintenance inspection intervals. The present work is focused on the capability assessment of Phased Array ultrasonic inspection applied to aluminothermic-welded joints by means of Probability of Detection curves, as a result of experimental and Model Assisted data samples.