The behaviour of braided hydraulic hose reinforced with steel wires

Abstract

Measurements are reported of the variation with pressure of the elastic strain in the wires of the outer braid of a two-braid high pressure hydraulic hose. Strain measurements were made with a Solex pneumatic extensometer. The performance of the extensometer was checked by comparing the measured and calculated strains for the wires in a single braid hose. Good agreement was found. Surprisingly little hysteresis was observed in the wire tensions on loading and unloading. Hysteresis in the length changes of the hose was more marked. Measurement of the relative displacement of the edges of adjacent tapes of wires led to the conclusion that frictional forces at the points where braid wires cross is a major source of hysteresis. An analysis is presented which was used to calculate both the elastic strains in the braid wires and the length change of the hose on pressurisation. The analysis takes account of the compressibility of the rubber between the two braids but ignores constraints arising from friction or from the rubber. The measured strains and length changes agreed sufficiently well with the predicted values to justify the use of the analysis for hose design. Using this analysis, information is assembled about the effect of braid angle on wire tensions and length change; this leads to a proposal for the ideal values of the inner and outer braid angles in a particular case.