Dynamic magnetostriction for material characterisation of micro structure states of degraded structural steel

The magnetostriction effect has been known for over 100 years. The first observation was made by Joule in 1842; while applying a magnetic field to a nickel rod specimen the length changed. Magnetostriction is the change of the dimensions and the Young modulus of a magnetic material caused by a change in its magnetic state. Magnetostriction is classified as linear or longitudinal; transverse and volume magnetostriction. Linear magnetostriction is also referred to as Joule magnetostriction, where deformation occurs in the direction of the applied field while the volume of the distorted magnetic domains remain constant. During transverse magnetostriction the dimension change is perpendicular to the applied field. Volume magnetostriction is mainly caused by the increase of distance between the atoms by the applied magnetic field. If the volume of an iron-based material expands with an increase in magnetisation the volume magnetostriction is defined as positive. The magnetisation state of a material can also be changed by temperature variations or by applied mechanical stress. Spins in excited state can transfer their excess energy to the lattice so a disturbance of the coupled magnetic and crystal lattice affects the magnetostriction. Moreover, in Joule magnetostriction the dimensional change is associated with the distribution of distorted magnetic domains so it could be expected that domain movement hindrance would affect magnetostriction. Magnetisation state changes can cause a strain just as strain can cause a change in the magnetisation state. Thus magnetostriction effects are reciprocal causing a magnetostrictive material to behave as piezoelectric materials due to magneto elastic interaction. A sound wave is generated by the change in the magnetic state while the sound wave strains change the magnetisation state of the material. This principle of the reciprocity of magnetic state - strain was used as the theoretical background of the dynamic magnetostriction test. By applying the dynamic magnetostriction test the effect of the precipitates on the crystalline of a ferromagnetic polycrystalline can be recognised by its interaction on the magnetisation state. Dynamic magnetostriction tests have been further developed at the Fraunhofer Institute for NDT, Saarbrücken, in order to define material properties. A 15NiCuMoNb5 copper content ferritic steel material was submitted to isothermal thermal ageing and the material properties changing because of copper precipitation were studied. Mechanical and physical properties, e.g. hardness, electrical conductivity were tested. The objective was to provide a basis for developing a non-destructive testing technique for this type of steel, which is widely used in the energy industry as pipeline and vessel material. This contribution discusses the physical background, the NDE-approach and the results

Characterization of precipitation-induced embrittlement of 15 NiCuMoNb 5 steel using micromagnetic techniques

The low-alloy, heat-resistant steel 15 NiCuMoNb 5 (WB 36, material number 1.6368) is used as piping and vessel material in boiling water reactor (BWR) and pressurized water reactor (PWR) nuclear power plants in Germany. After long-term service exposure at temperatures above 320°C, damage was observed during operation (and in one case during in-service hydro-testing). Small-angle neutron scattering (SANS) measurements (performed by MPA Stuttgart) concluded that the service-induced hardening and decrease in toughness of WB 36 materials was caused by the precipitation of copper particles ranging from 1 to 3 nm in size. For the non-destructive characterization of the precipitation-induced property changes in WB 36, service exposure was simulated on a set of tensile test samples. The material's hardness was observed to rise by as much as 40 HV 10 as a result of the simulated service exposure. However, as conventional Vickers hardness measurements are not applicable repetitively and area-wide in this case, and as spot tests require information about critical test areas, early-detecting the hardness increase non-destructively is a most favourable solution of this problem. This way, electromagnetic surveillance of power plant components can inform the provider about the aging processes. Therefore, the suitability of micromagnetic NDE techniques for the characterization of the Vickers hardness was investigated. A measurement system was successfully calibrated for the prediction of HV 10 by Barkhausen noise and field upper harmonics analysis

Nieniszcząca charakteryzacja uszkodzenia materiału w odniesieniu do termicznego starzenia, degradacji neutronowej i zmęczenia

Nondestructive Testing (NDT) in the engineering community is normally associated with the objective to detect, to classify and to size material nonconformities - for instance beginning with nonmetallic inclusions of a size of some ten $\mu$m in steel or Aluminum alloys up to so-called 'material defects' like macroscopic cracks of some mm size. This objective, however, is at the top of the list of activities concerning the number of applications in nondestructive material testing worldwide. Methodologies like UT (Ultrasonic Testing) and RT (Radiographic Testing) or MT (Magnetic Testing) are well introduced in a wide field of product and component examination standards. In the last 15 to 20 years, the NDT technology was also developed for characterizing materials, for instance in terms of microstructure parameters, i.e. lattice defects, like distributions and densities of dislocations, precipitates, micro-voids, in order to describe strengthening and/or softening in materials, mainly in metal alloys, but also to measure the applied and residual stresses (Dobmann et al., 1989).Badania nieniszczące (NDT) są zwykle, w społeczności inżynierskiej, wiązane ze zdolnością do wykrycia, klasyfikacji i wymiarowania niezgodności materiałowych - na przykład z początkiem niemetelicznych wtrąceń o rozmiarach kilku dziesiątek mikrometra dla stali lub stopów aluminium, aż do tak zwanych "defektów materiałowych" w rodzaju pęknięć makroskopowych o rozmiarach kilku milimetrów. Cel ten jest jednak na szczycie listy podejmowanych działań w szeroko rozumianych nieniszczących badaniach materiałowych. Metodologie w rodzaju BU (badań ultradźwiękowych), BR (badań radiograficznych) czy BM (badań magnetycznych) są dobrze wprowadzone w szerokiej dziedzinie standardowych badań wyrobów i ich składników. W ostatnich 15-20 latach techniki nieniszczące rozwijano również w odniesieniu do charakteryzacji materiału na przykład w zakresie parametrów mikrostruktury, tzn. do defektów sieciowych typu rozkładów i gęstości dyslokacji, wtrąceń, mikropustek, aby opisać wzmocnienie i/lub osłabienie materiałów, głównie stopów metali, ale również do mierzenia przyłożonych i resztkowych naprężeń (Dobmann et al., 1989)

Vorrichtung zur Rissedetektion

DE 102007022053 A1 UPAB: 20081126 NOVELTY - The device has a sensor unit with a magnetometer (7) i.e. giant magneto resistive (GMR)-sensor, and a control unit for controlling sensor electronics and signal processing. The sensor unit and the control unit are separably connected with each other in a non-elastic manner. The control unit comprises a micro-controller (10) with an integrated analog to digital (A/D)-converter. A measuring signal that is measured by the sensor unit is amplified by the control unit. The control unit comprises a signaling device (11) for acoustic display i.e. miniature loud speaker, of measuring result. USE - Device for measuring a magnetic field and/or gradient of the magnetic field for testing ferro-magnetic material to detect crack in the material. ADVANTAGE - The device can be manufactured in a simple manner with reduced construction units so as to reduce the dimension of the device, thus increasing the mobility of the device and allows fast and universal applicability of the device. The device reliable measures the magnetic field and/or its gradient in a fast manner and with reduced material and personal expenditure. The increased mobility of the device allows fast, simple and economical testing of the ferro-magnetic material with respect to the crack surfaces

Nondestructive characterization of dielectric materials with scanning terahertz spectroscopy

Terahertz time domain spectroscopy (THz TDS) has a wide variety of applications regarding characterization and inspection of dielectric materials such as plastics, ceramics and wood. Market prices for high-performance equipment have decreased below a hundred thousand Euros already and will soon reach levels where a wide range of industrial applications can be envisaged. Besides the detection of flaws and foreign bodies in many types of plastics and measurement of coating thickness, THz TDS can detect diffusion of water into plastics due to the high absorption coefficient of water in the THz range. This contribution regards imaging of water diffusion into a sheet of polyamide 6.6 with scanning THz TDS equipment in transmission mode. The weight increase of the water-exposed part of the sample due to water absorption was about 3% after about 300 hours of immersion, and the exposed area showed a significant decrease of the transmitted THz amplitude. Future work aims at reconstructing the moisture gradient into depth by means of inverse profiling algorithms

Nondestructive evaluation of structural change due to creep degradation in P91 steel by micromagnetic properties

In this study, to evaluate the structural change due to creep degradation in P91 steels nondestructively by means of the micromagnetic multiparameter microstructure and stress analysis (3MA) device, information of dislocation density change is extracted from micromagnetic properties. Micromagnetic properties of the creep and thermal aging samples are measured by 3MA device. The relationship between measured micromagnetic properties and the low-angle grain boundary length of the samples quantified as the alternative value of dislocation density by Electron Back Scatter Diffraction (EBSD) equipment are investigated. Change of dislocation density due to creep degradation can be evaluated by some micromagnetic properties which are independent on precipitation change

Verfahren zur zerstörungsfreien quantitativen Bestimmung der Mikroeigenspannung II. und/oder III. Art

The method involves performing removal of the specimen to exclusive formation of coherent copper precipitates. The load voltage value is determined. The load voltage is dependence of the maximum Barkhausen noise amplitude for a test piece and a maximum cooling. The withdrawal of the specimen to the Ostwald ripening is performed. The load voltage value is determined. The load voltage is dependence of the maximum Barkhausen noise amplitude for a test piece after the removal to Ostwald ripening and cooling. The micro residual stress of the specimen is determined

Terahertz amplitude polynomial principle component regression for aramid-basalt hybrid composite laminate inspection

As an emerging nondestructive diagnostic and monitoring technique, terahertz time-domain spectroscopy (THz-TDS) imagery is attracting more attention. In this regard, new THz image processing algorithms based on infrared thermography (IRT) concepts are greatly needed, since most IRT imagery modalities are fast for in-line industrial inspection. However, this scenario is difficult due to some physical constraints to be reached, although this idea should be followed to avoid the loss of useful information during image processing. In this paper, a novel THz amplitude polynomial principle component regression (APPCR) algorithm is proposed for the inspection of aramid-basalt hybrid composite laminates. This algorithm segments THz amplitude-frequency curves to simulate heating-up and cooling-down behaviors as in IRT; in addition, it uses an empirical orthogonal functions-based principle component regression modality to simplify the THz image analysis procedure. This experimental and analytical study shows that APPCR can, first, simplify the THz image analysis procedure, and second, enhance image contrast and spatial resolution. A theoretical analysis was conducted as experimental explanation, while the IRT imagery results were used for comparative purposes. In addition, signal-to-noise ratio analysis was used to evaluate quantitatively the image enhancement. Finally, it is possible to conclude that THz is more suitable to inspect transparent or semitransparent materials. Advantages and disadvantages of THz-TDS and IRT are summarized in the text