Determining mechanical properties at the shear of the material of "T" type pressure fire hose based on torsion tests

Abstract

This paper reports the results of experimental studies into determining mechanical properties (elastic and dissipative) at the shear of the material of a pressure fire hose of the "T" type with the internal diameter of 77 mm using torsion tests. During the studies, a series of field experiments have been conducted on the torsion of the pressure fire hose samples with internal hydraulic pressure (P) in a hose of 0.2 МPа (Р1), 0.4 МPа (Р2), and 0.6 МPа (Р3) under conditions of static loading-unloading cycles. The tests consisted of 6 cycles – for each of the (P) loading-unloading cycles, which were carried out at a two-minute interval, the rigidity and elasticity modules at the shear of the material of a hose were determined by means of torsion tests. It was established that the numerical results of mechanical properties depend on the hose load "history", that is, the elasticity modules increased in the first two, three load cycles, and they stabilized only afterward at the level of 3.04 MPa for Р1, 4.35 МPа for Р2, 4.39 МPа for Р3. The above, together with a significant decrease in residual deformations, strengthens the elastic properties of the fire hose material. The results of the research have been approximated by the corresponding trend lines. The equation of dependence of the current torque on deformation was determined. The curves of the deformation of samples, which, under the conditions of cyclic loading-unloading, formed hysteresis loops, were established. The resulting hysteresis loops during the study in the first two modes undergo quantitative and qualitative changes, namely, the slope and its area decrease. The similarity of experimental studies at different internal pressures (P) was established. A change in the properties of the material of a fire hose at the consecutive loading-unloading deformation cycles is reverse, the gaps between the deformation cycles lead to a partial restoration of the mechanical characteristics, approximating them to the original values.