Preliminary results of the study of the effect of a multi-cycle load on the hardness of a high-pressure fuel pipe

Investigation of the effect of internal pressure on the distribution of hardness in the fuel pipe wall was conducted. In the high pressure circuits of Common Rail systems, the fuel pressure is much higher than the pressure level in conventional fuel systems. Thas is why it is of practical interest to change the mechanical properties of the component materials during operation. In the present work, an attempt was made to evaluate the influence of the multi-cycle loading of the fuel pipe with a high internal pressure on the hardness of the material from which the fuel line was made. The loading was carried out under the conditions of a non-motorized test bench with a pressure of diesel fuel of 160 MPa. The test duration was 500 hours. With the selected pump shaft speed and the response frequency of the electrohydraulic control valves this was equivalent to approximately 96x106 cycles. Before and after the tests, hardness measurements were made in the cross section of the fuel lines. The distributions of hardness values are obtained, which testify the existence, under the given loading conditions of a self-hardening process of the material. In the initial state, fuel lines are characterized by a certain anisotropy of hardness and, accordingly, strength characteristics. In this case, the inhomogeneity of the field of values of hardness decreases with decreasing radius of location of the material layer. Dispersion of hardness values takes place both along the axis of the fuel pipe and in the circumferential direction. Loading of fuel pipes of the Common Rail type with pulsating hydraulic pressure leads to a redistribution of the hardness values in the fuel pipe wall. It is found that in the layers of material located closer to the central channel of the fuel pipe, the hardness equalization occurs to a greater extent as it is used, than in layers located far from the central channel. In general, the hardness is increased, which can be interpreted as the hardening of the fuel line during operation.

hardness, pipe, cross section, result