Modelos de la inteligencia emocional

For each defect in table 6.4, a 1-5MHz chirp inspection was carried out and the maximum signal response from the defect was evaluated by measuring it’s critical features; peak amplitude (Smax), peak frequency (fmax), area under curve (A) and frequency of zero-crossing (fX) as defined in section 6.3.3. The results of the critical feature analysis are summarised in the following sections.

Amplitude Changes

The relationship between peak amplitude, Smax, and area under the curve,A, was examined for group A and B defect geometries in table 6.4. The results are separated into their sub-groups to show the behaviour of the chirp measurement as a function of varying different discontinuity dimensions (Figure 6.13).

For each subgroup a polynomial, best fit curve was plotted of the form,

y=p1x2+p2x+p3, (6.6)

wherey is the area axis and x is the peak amplitude axis. p3 was forced to zero so that the curves intersected the origin i.e. when the peak amplitude is zero, the area under the curve will also be zero.

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Figure 6.13: Peak amplitude, Smax, verses area under the background-subtracted frequency-sweep curve, A, for large machined defects (l dout) of varying dimen- sions and defects of finite length (l ≈ dout). Four plots show experimental data points and polynomial best fit curves for the chirp response parameters as a func- tion of varying depth (blue), varying gape (red), varying length (yellow) and varying size (purple). The numbers of the defects (as defined in table 6.4) are indicated next to each data point.

The area under the chirp curve, A, is shown in figure 6.14 as a function of the changes in defect area. The results are separated into two subplots of groups A (figure 6.14.a) and B (figure 6.14.b) and displayed as a function of the vari- able cross-sectional area for that group of defects. Group A is represented by the

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Figure 6.14: Area under the background-subtracted frequency-sweep curve (fre- quency summation) for machined defects of varying dimensions given in table 6.4. a) Infinitely long defects of constant surface length (l dout): comparing defects of varying depth and varying gape, and b) finite length defects of constant gape (0.10mm): comparing defects of varying length and varying overall size. The num- bers of the defects (as defined in table 6.4) are indicated next to each data point and the associated measurement error-bars shown.

cross-sectional area along the scan axis (see figure 6.12), and group B defects are represented by their cross-sectional area along the defect axis.

The results in figure 6.13 indicate that there is a distinct difference in how varying gape changes the relationship betweenSmaxandAwhen compared to depth or length. At small dimensions the amplitude trends become indistinguishable from one another so one would expect not to be able to differentiate between different de- fect dimension changes for defects smaller than the size of the probe coil. However, the measurements of the group A defects (figures 6.13 & 6.14), imply that ampli- tude changes can be used as a relative measure of changes in depth and gape. In figure 6.13 it appears that the changing gape of a discontinuity, with a fixed depth,

tends towards a plateau of the area under the curve, whilst the peak amplitude continues to increase for higher gapes. In contrast, the changing depth of a discon- tinuity leads to the inverse effect; plateauing peak amplitude whilst the area under the curve increases for increasing depths. These changes are a result of changes to the full frequency spectrum of the chirp measurement depending on the depth and gape. Lower frequencies penetrate deeper into the material and so an increase in defect depth would be expected to cause a change to ever lower frequencies in the spectrum thereby increasing the area under the chirp curve. Conversely, changes in gape for a fixed depth would not affect the lower frequencies of the spectrum and would only cause changes at higher frequencies i.e. the NERSE peak frequency.

Frequency Changes

The relationship between peak frequency, fmax, and peak amplitude, Smax, was examined for group A and B defect geometries in table 6.4. The results are separated into their sub-groups to show the behaviour of the chirp measurement as a function of varying different discontinuity dimensions (figure 6.15). No best fit functions were applied to the data.

No error bars are shown in the figure due to the difficulty in determining errors in the frequency measurement which was largely subjective. Larger discon- tinuities have sharper peaks and clear zero-crossing points, whereas smaller defects are more susceptible to background noise which led to less reliable signal analysis.

The results shown in figure 6.15 show the trajectories of the NERSE peaks signal in frequency-amplitude space. The scattered frequency positions of the dif- ferent defect group studies is a result of differences in the probe setup as discussed below.

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Figure 6.15: Experimental measurement of peak frequency verses peak amplitude of chirp measurements for the four groups of machined defects (defined in table 6.4). The numbers of each defect (as defined in table 6.4) are indicated next to each data point.