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This work demonstrates that an artificial scaffold structure can be designed to exhibit mechanical properties close to the ones of real bone tissue, thus highly reducing the stress-shielding phenomenon. In this study the scan of lumbar vertebra fragment was reproduced to create a numerical 3D model (this model was called the reference bone sample). New nine 3D scaffold samples were designed and their numerical models were created. Using the finite element analysis, a static compression test was performed to assess the effective Young modulus of each tested sample. Also, two important metrics of each sample were assessed: relative density and surface area. Each new designed 3D scaffold sample was analyzed by considering two types of material properties: metal alloy properties (Ti-6Al-4V) and ABS polymer properties. Numerical analysis results of this study confirms that 3D scaffold used to design a periodic structure, either based on interconnected beams (A, B, C, D, E and F units) or made by removing regular shapes from base solid cubes (G, H, I units), can be refined to obtain mechanical properties similar to the ones of trabecular bone tissue. Experimental validation was performed on seven scaffolds (A, B, C, D, E, F and H units) printed from ABS material without any support materials by using Fused Deposition Modeling (FMD) technology. Results of experimental Young modulus of each printed scaffold are also presented and discussed.

Magnetic flux leakage (MFL) distribution for three configurations of samples has been investigated in order to study the influence of notch and plastic deformation separately as well as together. Samples have been made of S355 steel. The MFL signal measurements were carried out along the longest dimension of the sample over a length of 120 mm. Two components of magnetic field were measured: 1) tangential to the main axis and 2) normal to the largest surface of the sample. Study has shown that geometrical effect, related to the notch presence, as well as plastic deformation with associated compressive macroresidual stresses, together are responsible for the specific MFL distribution above the sample. In order to confirm the assumption that the decrease of the permeability in the central part of the sample and the change of cross section are the main sources of the MFL anomaly, disrupting flux from demagnetization field, a series of simulations has been made. Simulation results coincide with those obtained experimentally and thus confirming the above hypothesis.

The effect of various combinations of conditions, i.e., presence of the Earth's magnetic field during and after deformation on the distribution of stray magnetic field of S355 steel sample, which is locally deformed, was investigated. Some of the stages of the experiment were carried out in zero magnetic field. Compensation of the Earth's magnetic field was obtained by the application of a pair of Helmholtz coils. These coils are able to produce homogeneous field compensating Earth's magnetic field over the full length of the sample. Stray magnetic field measurements were carried out along the longest dimension of the sample using the probe consisting of mutually perpendicular sensors allowing the simultaneous measurement of two magnetic field components, i.e., tangential and normal to a surface of the sample. Research has shown that there is a correlation between the level of plastic deformation of the investigated sample and the distribution of stray magnetic field. It was found that the nature of stray magnetic field of the sample depends on presence of external magnetic field during unloading. An attempt was also made, with the finite-element analysis, to verify experimentally obtained stray magnetic field distribution of undeformed sample.

The magnetic Barkhausen effect is useful for assessing 1D and 2D stress states of ferromagnetic steel objects. However, its extension to technically important materials, such as duplex anisotropic steels, remains challenging. The determination of magnetisation inside the studied object and the electromagnet for various geometries, materials and magnetisation angles is a key issue. Three-dimensional, dynamic finite element analysis has been applied to reproduce time-varying fields inside and outside the prototype of a double-core magnetising setup. Useful relationships between characteristics (peak height and location) and magnetic induction vector have been proposed. The qualitative plausibility of simulation has been validated with an experiment and an analytic formula of skin depth. The angular anisotropy of magnetic Barkhausen effect (MBN) in an isotropic sample has been shown in simulation and confirmed experimentally. The numerical model, despite some limitations, seems to be an efficient tool for calibrating stress/MBN relationships at least in isotropic structural steel components.

Experimental results are shown of magneto-acoustic emission (MAE) and Barkhausen effect (BE) for two ferritic steel plates of different dimensions. The paper presents preliminary results of modelling the MAE, based on the finite element method (FEM), taking into account the key role of the eddy currents. Explanations are suggested as to the effects of MAE peak maximum growth, shift, as well as the characteristic BE profiles at the bottom of the large plates.

As creep damage degradation proceeds in 304, 321, and 347 grade stainless steel boiler tubes, the tubes develop a ferro-magnetic component depending on length of service. Incipient creep damage occurs inside the steel, involving precipitation inside the grains, with precipitates getting larger and forming mostly at or near grain boundaries as degradation continues. This incipient creep damage eventually leads further to the development of cavities at grain boundaries, which in turn lead eventually to microcracking and cracking. The amount of ferromagnetic component has been correlated (albeit in a relatively small number of exploited specimens) to the amount of incipient creep damage. The ferromagnetic component appears to be primarily associated with the formation of ferromagnetic hard oxide scale on the outer surface of the boiler tube. The ferromagnetic part of the scale has been identified, using x-rays, as magnetite. This ferromagnetic oxide surface can be easily inspected in power plants using eddy current techniques. Because of the correlation with incipient creep damage, the suggestion is that measurement of the amount of ferromagnetic component can be used to nondestructively monitor the development of incipient creep damage in austenitic steel at stages of development well before cavitation and microcracking. We have found that a processed signal can be extracted from eddy current measurements, which is directly related to the amount of ferromagnetic component. We have shown mathematically why the signal behaves as it does. This same signal has been simulated using finite element modeling (FEM). Its linear dependence on the amount of ferromagnetic component is verified experimentally, mathematically, and by FEM. In addition, we also demonstrate a way in which frequency dependence of the eddy current signal can be used to separate out effects of conductivity from effects of change in permeability due to the ferromagnetic component, thereby reducing effects of experimental error in evaluating the amount of ferromagnetic component at low amounts of degradation. In the present year, the technique is now being tested via measurements at several power plant sites.Copyright © 2007 by ASME