There are various mechanical stresses that occur in the tissue of the vocal cords during phonation.
The destructive/damaging effect of each load depends not only on its size but also on the loading speed.
During phonation in the adductor phase, a chordal load occurs in the form of 'quasi-static' traction along the anterior-posterior direction of the cords.
This stress, when normal, ranges from a few to several hundred KPas. A normal stress is therefore represented by forces normal to the cross section, whereas pure stress involves forces parallel to the cross section. When the glottis closes, an impact stress occurs between the two folds with a magnitude of the order of 0.1 – 5 KPas, depending on the note. The impact produces a three-dimensional stress field that includes normal and tangential stresses.
The air flow on the subglottic wall imparts a combination of normal compressive and shear stresses of less than 5 KPas. The elastic shear forces in the rope are generated by dynamic movements of the covering layer (cover body), whereas the frequency-dependent inertial loads are caused by the acceleration and deceleration of the fabric mass.
Vocal nodules occur in the area just below the superficial layer; therefore, damaging loading occurs beneath the overburden in the form of shear loads. Vascular lesions, in contrast, occur on the upper surface of the vocal folds, where no physical contact occurs.
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