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THE METAL-BENDERS” by JOHN B. HASTED

The French research has concentrated on the metallurgical aspects of paranormal metal-bending. This has been a suitable approach, since the Pechiney laboratories are thoroughly familiar with the physical properties and structure of the aluminium alloys they have developed for aircraft such as Concorde and the Mirage fighters. The measurements which are commonly made on each specimen before and after exposure are as follows:

1 All the dimensions were measured, especially the deformation from straightness, and the thickness; for bars of circular cross-section the diameter was carefully studied. Accuracies of about a micron could be obtained.
2 The micro-hardness, which we have seen to be characteristic of the granular and dislocation structure of the metal, was regularly measured at a large number of points; for Vickers hardness, a diamond pyramid is forced into the metal and the diagonal dimensions of the square indentation measured under the microscope.
3 The residual strain profile in the metal was measured, using X-ray diffraction techniques which are a speciality of Dr Bouvaist. The principle of the technique is basically that of Bragg diffraction. There is a linear relationship between the proportional lattice strain (delta d)/d and sine squared psi, where psi is a certain angle measured in the X-ray diffractometer. The distance d defines a separation of planes within the crystal. The technique is used with polycrystalline metals, and is not much affected by grain size.
4 The grain boundaries - Foil specimens were often taken from the metal, and electron micrographic examination made at various magnifications. The grain boundaries are seen at low magnifications, and at high magnifications it is possible to study the forms of the dislocations and count the loop dislocations when these are seen.
5 The dislocation density  - the scanning electron microscope was used in the back-diffusion mode to obtain the dislocation density or plastic strain from the width of the channelling patterns or ‘Kikuchi lines’. These lines arise from the inelastic scattering of the electrons. Their absorption is different in different regions of the crystal, and their width can be related to the dislocation density below the surface.
6 The local composition of alloys - Electron probe microanalysis was used for obtaining the local composition of alloys. The X-ray spectrum arising from the electron bombardment was analysed not with a spectrometer but with an energy-sensitive solid state probe.

All these measurements show changes when a bar of metal is bent, either normally or paranormally. The differences between the two sets of measurements are such as would require examination by a metallurgist in order to give a full interpretation.

One thing that is clear from these studies is that in paranormal bending the ‘elastic component’ is largely suppressed. The dependence of applied stress, sigma, upon strain, epsilon, in a metal is typically of the form of Figure 13.1a. When increasing normal stress is applied the strain increases in such a way that a point travels along the curved graph in the direction of the arrow. When the metal is stressed beyond the yield point and the stress is suddenly relaxed at a point A at the apex of the graph, the metal behaves in such a way that the point moves downwards and to the left, reaching the axis of zero stress at B.

Thus there is a permanent strain or extension of the metal, but it is not as large as was the temporary strain at point A. If we were to plot a graph of the time variation of strain it would in a normal bend have the form of Figure 13.1b (full line). The elastic component contributes temporarily a large proportion of the strain. Ultimately the elastic component ceases to contribute, and it is only the internal stress which holds the metal under its condition of permanent strain.

However, in paranormal metal-bending it seems that the path taken from 0 to B is more direct; in Figure 13.1b a possible path is represented by the broken line. In Figure 13.1b one cannot easily know the path taken, but we have seen that some of the strain gauge signals are of the same form as the broken line of Figure 13.1b.
The stress that is operative in the no-touch paranormal metal-bending process is apparently an internal stress. The residual internal stresses were found by Dr Bouvaist to be somewhat different after a paranormal bend from those after a normal bend.

The residual internal strain profile is related to the profile of the applied stress. Consider the normal permanent deformation illustrated in Figure 13.2: the applied stress increases as one proceeds outwards from the neutral axis.

Between the surface and the broken line planes the stress is so large that the yield point is passed and the strain becomes plastic; by contrast, in the inner region, the strain is entirely elastic. This results in the setting up of reverse strain, so that the strain profile takes the form of the final part of Figure 13.2. The residual strain profile of a normally deformed metal bar is governed by these features. But the residual strains inside a paranormally deformed bar can be different. Dr Bouvaist has measured anomalous residual stress on metal bars exposed to the action of Jean-Pierre Girard.

[Figure 13.1 (a) Development of plastic strain epsilon p by application of stress sigma which increases from zero to a point represented by the solid circle A, and is relaxed to zero at solid circle B. (b) The time-dependence of strain developing to its final value epsilon p in a case such as Figure 13.1a. ]