Sketch of the definition of bending length λ.
Scheme of the measurement method. The wire is clamped on a rotary stage and supports a load which is free to move in the horizontal direction. When the bending point stays exactly on the axis of the rotary stage, the load does not move when the stage is rotated. The bending length can be evaluated as the distance between the clamp and the rotation axis.
Picture of the apparatus for the measurement of the bending point position. The coil actuator under the load was used for exciting the bouncing mode of the loaded mass.
Schematic view (left) and picture (right) of the rubber pipe used to damp the pendulum swing.
Example of the variation of the oscillation amplitude when the vertical position is changed. In this case, the wire head is displaced continuously with time, and the amplitude passes through a minimum.
Oscillation peak to peak amplitude of the steel wire with respect to the vertical displacement. Experimental points are fitted with a quadratic function. The resulting bending length is λ = 6.6 ± 0.1 mm.
Scheme of a typical silica wire produced to be assembled in the Virgo+ quasi-monolithic suspension.
Sketch of the steel cone holder blocking one end of the wire.
Oscillation peak to peak amplitude of the silica wire with respect to the vertical displacement. Experimental points are fitted with a quadratic function. The resulting bending length is λ = 33.9 ± 0.1 mm.
Simulated bending shape of the silica wire (blue line) and linear fit after the bending region (red line). The bending point, as from definition, is located at the crossing among the red line and the zero-deformation axis, that is, λ = 33.85 ± 0.05 mm.
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