Markku Moilanen

Improvement of the Barkhausen noise method for stress evaluation

Abstract Envelopes of Barkhausen noise bursts are measured for ferritic-pearlitic, tempered microalloyed, 3.5Ni and 9Ni steels in an unloaded state and under tensile stresses, and the area Ar, peak amplitude Vm and restricted area RAr of these envelopes are determined. RAr is evaluated from the portion of the signature which has simultaneously a high and unique dependence on stress. In the case of ferritic-pearlitic steels, tensile stress increases Barkhausen activity at the leading edge of the envelope which thus constitutes a convenient time range for determining RAr. Ar and Vm values suffer from a non-unique stress dependence in the tempered steel, i.e. the existence of a local maximum, but the stress response of RAr remains unique, with spatial scatter, at least up to 300 MPa. A directional contribution of the texture to noise values impairs the possibility for evaluating stress magnitudes in the 3.5Ni steel, while the 9Ni steel has a high stress response and pronounced spatial variation in noise. The RAr figures represent an improvement over Vm and Ar values as stress measurements, especially for tempered steels and to a lesser extent ferritic-pearlitic steels, whereas all the parameters mentioned have similar stress responses for Ni steels.

Measurement of lung-retained contaminants in vivo among workers exposed to metal aerosols

In Finland the amount of lung-retained contaminants has been measured among welders, foundry workers, and iron and steel factory workers. About 300 subjects have so far been measured since 1976. The method of measuring is based on the magnetic properties of metal aerosols. At the very beginning the method resembled the one suggested by D. Cohen. The original method was too slow, and data processing was not suitable for clinical or hygienic work. Therefore, the automatic and computerized instrument for measuring lung-retained contaminants was developed in cooperation with Outokumpu Oy. The resolution of the magnetic measurement is better than 0.05 nT corresponding to a sensitivity of 0.5 mg of magnetic contaminants in the lung in the form of magnetite. These figures mean that, in practice, a shipyard welder has enough contamination for measurement after one months exposure. In addition, the present paper reviews the magnetic properties of metal aerosols briefly and summarizes the results of measuring different occupational groups.

Coercivity and power spectrum of Barkhausen noise in structural steels

Abstract Relative coercivities and power spectra of Barkhausen noise are measured for ferritic pearlitic C-Mn, tempered microalloyed and 9% Ni steels under unstressed and tensile stressed conditions. Coercivity depends on the type of material, stress state, amounts of pearlite and grain boundary precipitates, grain size and dislocation density. The stress dependence of coercivity is extremely strong in the Ni steel, relatively strong in the tempered steel at low stress levels and small in the ferritic-pearlitic steels. The power spectra exhibit clustering in elementary magnetic transitions, which can be expressed in terms of the mean pulse duration ϱ τ 0 . This is inversely proportional to coercivity, incrasing as a function of grain size D approximately as D 1 2 . Tensile stress directed parallel to the magnetization prolongs ϱ τ 0 in the case of the ferritic- pearlitic and tempered steels but shortens it in the case of the Ni steel. The stress dependence of ϱ τ 0 and noise level are controlled by possible grain boundary phases and the amount of pearlite (lamellar carbides). Grain boundaries and lamellar precipitates tend to suppress displacements of the 90° domain walls, which increases the stress response of the noise at high stress level.

Detection of Thermal Cycling-Induced Failures in RF/Microwave BGA Assemblies

The purpose of this paper was to investigate the effect of thermal cycling on the high-frequency behavior of ball grid array (BGA) interconnection structures. In order to characterize the applicability of RF measurements in predicting interconnection breakdown, a broadband BGA transition structure between a radio frequency printed wiring board (RF-PWB) and a ceramic module was fabricated. In addition to basic assemblies consisting of two BGA transitions between the module and substrate, the designed transition was applied in a passband filter module to demonstrate the effect of thermal cycling on the performance of a practical device, as well. The BGA test modules mounted on the PWBs were exposed to thermal cycling testing over a temperature range of -40degC to + 125degC. To detect interconnection failures induced by cyclic thermal stresses, both dc resistance and scattering parameter measurements were performed on the test assemblies at specific intervals. Parallel to the electrical measurements, crack propagation in the vicinity of the BGA transition structure was investigated using scanning acoustic microscopy (SAM). Moreover, scanning electron microscopy (SEM) was used to determine the failure mechanisms of the test assemblies. Degradation of the signal transmission characteristics of the basic assemblies was first observed at higher microwave frequencies as an increase in signal return loss (|S11|) and/or a change in its phase. The effect of TCT on the filter assembly was more constant and clearer to observe in the phase than in the magnitude of S11 in the passband. The dc resistance measurements showed no indication of degradation in any of the tested assemblies.

Stress response of Barkhausen noise and coercive force in 9Ni steel

Abstract The stress response curves of barkhausen noise, coercive force and lattice parameter of ratained austenite are measured for 9Ni steel in as-received condition (quenched and tempered plate), in tempered states following annealing for 1 to 243 h at 590°C, and in a coarse-grained state after annealing at 1200°C. The stress response is strong in all cases, but depends on the content of retained austenite, exhibiting the strongest response at 3 to 5 vol% austenite. The total range of retained austenite content was from 1.5 to 11.1%. The coercive force rises from about 500 to 850 A/m at temperings from 1 to 243 h, and contains a major contribution from dislocation of the fresh martensite formed furing cooling. The figures for austenite content and the lattice parameter measurements reveal that the austenite begins to lose stability after a few of tempering.

Stress response of Barkhausen noise in a tempered C-Mn steel

Abstract The dependence of Barkhausen noise on tensile stress is measured in a high strength vanadium microalloyed C-Mn steel after tempering at 200, 400, 500, 600 and 650°C. Simultaneously, the coercive force and two field parameters related to the magnetic reversal curve are recorded for some of the specimens tempered at 500, 600 and 650°C. Tempering causes a maximum in Barkhausen noise vs. stress curve and minima in the field strength vs. stress curves. An increase in the impedimental force due to stress gradients experienced by domain walls is suggested as the cause of the maximum. Stress gradients with short “wavelenghts” are thought to be produced in lath-or plate-like martensitic/bainitic structures. The effect appears in the course of tempering, as recovery processes reduce the dislocation density, and vanishes as recrystallization leads to an almost complete elimination of these dislocations.

Estimation of individual dust exposure by magnetopneumography in stainless steel production

The objectives of the study were to measure the magnetic dust lung burden of workers in stainless steel production by magnetopneumography (MPG) and to investigate the relationship of the results with air-borne concentrations of dust, total and hexavalent chromium as well as urinary excretion of chromium. There were 128 workers from the chromite mine, sintering plant, ferrochrome smelter, stainless steel smelting shop, cold rolling mill and welding shop in the exposed groups and five persons from the office staff in the control group. The remanent magnetic field (RMF) in the lungs was slightly elevated among workers in the ferrochromium and steel smelting shops; the levels were, however, lower than those reported for welders earlier and those observed in the welding/repair shop. Workers in the mine, concentrator and sintering plants and in the cold rolling mill exhibited remanent magnetic fields comparable to the referents. There was a relationship between the RMF and the actual urinary chromium concentration. Miners and concentrator and sintering plant workers showed retarded relaxation rate (ReR) of the remanent magnetic field. However, the RMF of the first two of these groups were low (< 0.1 nT) and this made it difficult to measure the ReR accurately. The duration of exposure correlated weakly but significantly with the relaxation rate, while smoking was not related to it.

Enabling Remote Testing: Embedded Test Controller and Mixed-signal Test Architecture

Remote testing requires embedded test infrastructure, consisting of communication, test control and test access. This article presents an embedded test solution for a low-frequency audio board. Supporting analog testing, the solution consists of a measurement and calculation method for passive component characterization, analog test bus solution and an embedded test controller for controlling embedded tests and providing test stimuli. Moreover, the solution, which supports the presented test plan, was compared to a test plan supporting traditional testing. It was found that the embedded test solution provided a 29% test coverage of the audio board components and substituted flying probe testing included in the traditional test plan. Besides such benefits as improved fault diagnostics and lower manufacturing costs, the paper also discusses the drawbacks of the presented solution, including reduced measurement accuracy. This paper also presents a correction to a previously presented passive component measurement and calculation method.

Failure Detection of BGA Transition Structures at High Frequencies

The purpose of this paper was to investigate the effect of thermal cycling on the high frequency behavior of a BGA transition structure. A broadband microwave BGA transition structure between a RF-PWB and a ceramic module was designed and fabricated. The stand-off height of the composite BGA solder joints was 500 mum. The BGA test modules mounted on the PWBs were exposed to thermal cycling testing over a temperature range of -40...+125 degC. To detect interconnection failures induced by cyclic thermal stresses, both DC resistance and scattering parameter measurements (45 MHz-25 GHz) were performed on the test assemblies at specific intervals. Parallel to the electrical measurements, crack propagation in the vicinity of the BGA transition structure was investigated using scanning acoustic microscopy (SAM). Moreover, scanning electron microscopy (SEM) was used to determine the failure mechanisms of the test assemblies. Degradation in the signal transmission characteristics was first observed at higher microwave frequencies as an increase in signal return loss (|S11|). As the thermal cycling test proceeded, the reflected signal loss became more significant and gradually became pronounced at lower microwave frequencies. Pure DC resistance measurements showed no indication on the degradation of the transition structure

Dusts in a steel-making plant

SummaryA magnetic method for measuring the amount of metal contaminants retained in the lungs was applied to workers in an iron- and steelmaking plant.Knowledge of properties of airborne particles is required for the calibration of the measuring method and for the estimation of the biological activities of the particles.In this study chemical composition, morphology of typical particles, and magnetic properties of dusts and fumes from different parts of the plant are presented. The amounts of contaminants retained in the lungs of 27 workers representing typical occupations in the production process were measured. The levels of lung contamination of the iron and steel workers were compared with those of manual metal arc steel welders and with those of foundry workers.In the sintering department, the dust is generated by mechanical handling of raw materials. Iron content of the dust is low, and iron is mainly in the form of magnetite.Blast furnace fumes contain mainly iron in the form of iron oxides condensed from pig iron. According to X-ray diffraction analysis, electron micrographs, and magnetic measurements, fume particles have a hematite/ magnetite shell structure. Similar iron fume particles are generated in the continuous casting process.The main part of the converter dust is glass-like slag where iron is dissolved in form of iron 11 oxides.Concentrations of toxic metals in metal fumes were low, e.g., the highest concentration of lead was 0.2%.The iron concentration of dusts and fumes was 25–59% Fe. Typical saturation magnetic moment was 42Am2/kg varying between 15 and 92 Am2/ kg. The equation between saturation magnetic moment and the iron content for dusts in the iron and steel production process was: Ms = 0.66 × Fe % + 11,r = 0.79.The mean magnetic moments of the dusts and fumes in different parts of the plant were equal so that the same calibration coefficient can be used for all dusts when measuring the amount of contaminants retained in the lungs.The approximate amount of lung-retained contaminants varied from 20–200 mg in blast furnace workers, from 10–40 mg in sintering plant workers, and from 2–20 mg in workers in continuous casting process. The mean remanent magnetic fields were in the same groups 1.4 nT, 0.47 nT, and 0.29 nT, respectively.Comparison between different occupational groups exposed to metal aerosols in different iron-based processes indicated that the level of lung contamination was lowest among iron and steel workers, next highest among foundry workers, and highest among stainless steel manual metal arc welders.