A ballistic instrument for measuring the work done in breaking a thread or bundie of filaments is described. The thread is mounted between two clamps, one of which is incorporated into a pendulum at its centre of percussion, the other rests on a ledge on the pendulum, the instrument being contrived so that this clamp is caught on fixed projections when the pendulum is at the lowest part of its swing. The energy absorbed in breaking a thread is measured in terms of the consequent decrease of the arc of swing of the pendulum after falling from a definite height. The extensometer described gives load-extension diagrams of single ultimate filaments of silk. Tensions on the filament under test produce torsions on a steel blade; these are recorded by the consequent deflections in a vertical plane of a beam of light which falls on a photographic film. The elongations of the filament corresponding to these tensions are proportional to the (corrected) horizontal movements of this film, which records load-extension diagrams with rectangular co-ordinates.
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Denham et al. (1928) studied this question.