Setting Discrete Yield-stress Sensors for Recording Early Component Loading Using Eddy-current Array Technology and Induction Thermography

Problematic requirements, regarding the assessment of the integrity of highly loaded components require that modern methods be developed to record the component's loading history during its life cycle. New developments are moving towards a continuous monitoring of loading history using sensors as well as towards determing the material's or component's state during its service. This requires integrating the load sensors into the component in order to record the component's loading online. Based on the physical material properties of metastable austenitic steels, a novel design is developed for implementing local, component-inherent load sensors; so-called directionally-sensitive yield-stress sensors. The appropriate strengths and yield stresses, corresponding to the component loading to be monitored, can be specifically set by locally heat treating the selected, cold-worked sensor's region using a fibre-laser. Electromagnetic testing methods, such as eddy current technology and imaging induction thermography are developed to rapidly collect the technical data of such microstructures which possess modified physical material properties. The measuring technology is developed and adapted to the testing task via modelling. FEM computation are also performed both for describing the domain's scope and the eddy current distribution, as well as for simulating the magnetising processes as well as the chronological formation of temperature fields in the component's edge region

Eddy Current Detection of the Martensitic Transformation in AISI304 Induced upon Cryogenic Cutting

The combination of a hard subsurface layer and a ductile component core is advantageous for many applications. Steels are often heat treated to create such a hardened subsurface, which is both time- and energy-consuming. It is of great advantage to create a hardened subsurface directly within the machining process, as the production line of most components includes such a process to produce the desired geometric dimensions and surface quality. To achieve a martensitic subsurface layer within the machining process, cryogenic, external turning using a metastable AISI304 austenitic steel is used herein. Herein eddy current testing and the analysis of higher harmonics are used for the detection of the ferromagnetic, martensitic phase in the parent austenite. A good correlation is found between the martensite content and the amplitude of the signals measured. Therefore, eddy current testing is considered as a suitable real-time, nondestructive testing method, which forms the basis for the generation of a tailored, deformation-induced martensitic subsurface layer during external turning