Structural assessment and measurement of the elastic deformation of historical violins: The case study of the Guarneri ‘del Gesù’ violin (1743) known as the ‘Cannone’

Abstract This paper presents a deformative and structural study of the Guarneri ‘del Gesu’ violin (1743) known as the ‘ Cannone ’. A structural assessment is fundamental to understanding the violin's compatibility with its residual function of musical instrument. The tuning of the instrument to a modern playing pitch during concerts could, in fact, cause stress resulting in plastic deformations of its structure. In order to understand the stress level to which the violin is subjected when tuned, several tests were performed. The forces acting on the bridge were measured, the geometry of the un-strung and of the tuned violin were acquired with a tri-dimensional scanner, the violin deformation was assessed by means of the computed surface deviation mesh and by measuring the deformation in selected lines, several sections of the violin were cut from the digital model and stress exerted on the sections was computed. The stress exerted on the neck , scroll and body were found to be very limited. More significant, albeit at a low level, was the stress exerted under the bridge between the sound holes . Mechanical stress exerted after tuning was found to be safe for the violin, if applied for a limited amount of time. This does not mean that the violin can be played freely, because the real strength of the material used in the violin is not known and mechanical stress during a concert must be added to time (viscous behaviour), moisture content variation (mechano-sorptive behaviour) and hygro-thermal stress, thus worsening the condition. The method presented here could be applied to compute the level of stress of any violin.