Search

The development of magnetic Barkhausen noise methods for rapid detection of residual stress concentrations has implications for integrity assessment of submarine pressure hulls. However, the stress-response of Barkhausen noise in submarine hull steel, HY-80, is complicated by the influence of the material’s martensitic microstructure. The present work sheds light on the stress-dependent behavior of Barkhausen noise in HY-80 by comparing its signal characteristics with those of more common ferrite/pearlite steels. HY-80 and various ferrite/pearlite steel plates were uni-axially stressed up to and beyond the level for plastic deformation. Barkhausen noise measurements, performed using the same sensor under reproducible flux-controlled magnetization conditions, facilitated a direct comparison of material responses. Results showed that with the application of tensile stress, the Barkhausen noise signal of ferrite/pearlite steels linearly increased, reached a peak value and saturated in the elastic region. By contrast, HY-80 demonstrated a linear increase with tensile stress characterized by a transition from a lower to a seven times higher rate of change for stresses above 200 MPa up to its yield point. The different stress-response of HY-80 was attributed to its martensitic microstructure, which modifies the response of the domain structure under tensile stress conditions.

Fatigue cracks are prone to develop around fasteners found in multi-layer aluminum structures on aging aircraft. Probability of Detection (POD) studies using eddy current techniques within the bolt holes contribute to risk assessments used in evaluating the serviceability of these aircraft. The signal response to corner and mid-bore cracks by eddy current testing using standard split-D differential probes has been examined. The data indicate that split-D probes are primarily sensitive to cracks at the corners of the Ds and that this gives rise to a double maximum for small mid-bore cracks as the corners pass over the crack. The double signal is not seen for corner cracks because the excitation coil, which is almost completely out of the hole, excites almost no eddy currents when the second corner of the D is over the crack. However, the eddy current response is more sensitive to corner cracks. The a90/95 for corner cracks was measured to be 0.22 mm (length) compared to 0.34 mm (depth) and 0.62 mm (length) for mid-bore cracks. The enhanced detectability of corner cracks is attributed to the presence of the edge, which restricts passage of eddy currents around the crack.

Fatigue cracks are prone to develop around fasteners found in multi-layer aluminum structures on ageing aircraft such as the CC-130 Hercules and CP-140 Aurora (P-3 Orion). Probability of Detection (POD) studies using eddy current techniques within the bolt holes contribute to risk assessments used in evaluating the serviceability of these aircraft. Improving POD by optimizing the inspection system can reduce the required frequency of inspections, since assurance of detection of smaller crack sizes extends the interval for which growth of cracks to a critical size may occur. In this work signal analysis and POD of laboratory grown fatigue cracks in the corners of bolt holes of 7075-T6 aluminum is examined. A number of parameters that enhance crack detection are identified, including the use of intimate contact probes versus steel sheath (non-contact), higher frequencies and the use of C-Scan display. Results demonstrate better detectability at 1600 kHz, than at the normally used 400 kHz, and enhanced recognition and assurance of identification of peak crack signal for data recorded and displayed in a C-Scan format. Results are compared with a previous POD study, which used current field techniques for detection.

Fatigue cracks are prone to develop around the fasteners found in multilayer aluminum structures such as ageing aircraft. The determination of their probability of detection (POD) using eddy current techniques is critical for risk assessments used in evaluating serviceability. Normally, a large number of samples of both fatigue cracks and electric discharge machined notches are required for such a study. In this study, the use of quantitative fractography (QF) to efficiently gather POD data for bolt hole eddy current is demonstrated. The technique can be readily automated, significantly reducing man-hour requirements. The method is applied to mid-bore cracks, grown without starter notches, in order to simulate naturally occurring fatigue cracks. POD of the mid-bore cracks is examined using a probit analysis. An a 90/95 is the probability that 90% of the cracks of size a or larger will be detected 95% of the time. An a 90/95 of 0.34 mm was obtained for mid-bore crack depth. This value is consistent with sk...

Probability of detection (POD) of fatigue cracks and electric discharge machined (EDM) notches in 7075-T6 aluminum was evaluated for a bolt-hole eddy current inspection system. The POD study involved simulated bolt holes in coupons representative of wing areas on CC-130 and CP-140 aircraft. The data were obtained from 24 inspectors who inspected 468 coupons that contained a set of coupons with 45 EDM notches and 72 laboratory-grown fatigue cracks located at the inner surface corner of the bi-layer structures. A single point calibration based upon a 0.76 mm (0.030 inches) deep corner notch set to 20% of screen height (SH) was utilized. Large variability in detection capability between inspectors was observed. A portion of this variability was attributed to significant background noise on the order of 5% screen height (SH). Normalization of each inspector's data to signal amplitudes from notches at twice the depth (1.5 to 1.6 mm (0.060 inches)), close to 40% SH, reduced the relative variations and resulted ...

The use of the Smallest Half Volume (SHV) robust statistics method and the Mahalanobis distance to blindly distinguish fasteners with cracks from fasteners without is examined. Pulsed eddy current data obtained from CP140 Aurora wing structures is used to test the approach. It is shown that the method can achieve levels of detection very close to those obtained when the same measurement technique is applied with full knowledge of which fasteners have no cracks. The method is applicable to a broad range of similar situations when an objective hit/miss criterion is used.

An investigation of the sensitivity of magnetic Barkhausen noise (MBN) to changes in uniaxial tensile stress applied to mild steel under conditions of low, medium, and high excitation field amplitudes is presented. Field excitation in the lowest range that was tested produced the most sensitive response to change in stress for the squared-voltage-signal output integrated with respect to time (MBNenergy). The linear response extended to the highest applied stress of 220 MPa, which was 80% of yield strength. In this field range, the angle-dependent MBNenergy and distribution of pulse heights under applied stress conditions was observed to be consistent with previous measurements performed in the medium- to high-field amplitude ranges. However, the number of Barkhausen events was less, and increased linearly with applied stress up to 120 MPa. In contrast, at higher field amplitudes, the initial number of events was greater, but then decreased with increasing applied stress. The results at low field amplitudes are attributed to the additional 180deg domain wall activity, accompanied by increased magnetization level, which could be induced by tensile stress. The reduction in number of events at higher stresses and higher excitation field amplitudes, which corresponds to an increase in MBNenergy and broadened pulse-height distribution, is associated with increased collective Barkhausen behavior. These results demonstrate that improved sensitivity of Barkhausen signals to changes in stress can be achieved in mild steel if optimized field excitation is used.

The consistency of magnetic Barkhausen noise (MBN) measurements under applied sinusoidal magnetic field control and sinusoidal magnetic circuit flux control was investigated under variable circuit permeability conditions. A U-core electromagnet was used to provide the alternating magnetic excitation. The magnetic circuit permeability was changed by varying excitation magnet lift-off and by using samples with known magnetic anisotropy. By controlling the circuit magnetic flux, measured as the flux in one of the U-core poles near the sample, MBN measurements were found to be consistent and independent of the excitation magnet lift-off in both a Si–Fe steel sample and an interstitial free (IF) steel sample at peak sample flux densities greater than 1.16 T and 0.29 T respectively. Consistency within a 95% confidence level was demonstrated for lift-off values of 0.6 mm or less, with decreasing sensitivity to lift-off observed at higher fluxes. MBN anisotropy measurements were also performed using both field control and flux control. Under field control conditions a component of the anisotropy signal was found to be dependent on the magnetic circuit permeability. This permeability dependence was absent when using flux control. The results demonstrated that flux control should be used when performing MBN measurements on samples where lift-off may be an issue, as values obtained will have less dependence on the excitation magnet characteristics than when field control is used.

While most empirical studies of claim construction in the Federal Circuit focus on the set of all Federal Circuit claim construction cases, Professor Krause and Ms. Auyang focus on two revealing subsets of cases: cases involving dissents (“close cases”) and cases in which the Federal Circuit reverses the district court (“reversals”). This focus brings results-affecting differences in approach among the judges to light. The close cases data show a wide disparity among the Federal Circuit judges in terms of how likely they are to adopt a broadening (as opposed to a narrowing) claim construction, with some judges showing a “broadening rate” of over 90%, and some judges showing a narrowing rate of over 80%. The close cases data also shows how factors like “pro-patent” and “pro-affirm” vary widely across the judges. Until the Federal Circuit recognizes these internal differences and eradicates them, claim construction will continue to be panel dependent and unpredictable. The reversals data shows that district courts consistently vote in a narrowing direction, and, more specifically, in a direction that, much more often than not, enables them to dispose of cases on summary judgment. This tendency argues strongly against any proposals for broad deference for district courts in claim construction. The authors argue that the Federal Circuit judges should seek to understand the differences between each other within the court, and work to promote a single unified approach. As a teaching tool for district courts -- and to help keep track of where differences in approach exist -- the authors recommend that the Federal Circuit adopt a simple algorithm for claim construction cases, and they provide one such example of an algorithm.

The magnetization of the bulk superconducting transitions of Hg 3 NbF 6 and Hg 3 TaF 6 was measured in the temperature range from 0.1 to 1 K and in magnetic fields from 0 to 50 G. Measurements were performed on both samples in the zero-field-cooled (ZFC) and field-cooled (FC) modes. The magnetization was also measured as the sample warmed through its superconducting transition in the same field in which it had been cooled; this was referred to as the return-warming (RW) mode. A large difference in magnitude between the ZFC and FC modes for both samples indicated the presence of multiply connected regions (or type-II superconductivity). Evidence for both samples of the trapping of flux due to inhomogeneities and defects was provided by the hysteresis measured between the FC and RW modes

Probe design parameters affecting depth of penetration of pulsed eddy currents in multi‐layer aluminum 2024‐T3 were examined. Several probe designs were evaluated for their ability to detect a discontinuity at the bottom of a stack of aluminum plates. The reflection type probes, consisting of pick‐up coil and encircling drive coil, were characterized based on their transient response to a square pulse excitation. Probes with longer fundamental time constants, equivalent to a lower driving frequency, generated greater depth of penetration. However, additional factors such as inductive and resistive load, and excessive coil heating were also factors that limited signal‐to‐noise response with increasing layer thickness.