Abstract
The impedance-graded material(IGM)systems can be used as a protective structure to attenuate the stress.Due to the fluidic oscillator of the down-the-hole(DTH)hammer made by cemented carbide was broken during the test,it is urgent to design a protective structure to decay the stress transferred to the fluidic oscillator.This paper studied the stress attenuation effect of Steel-Poly-ether-ether-ketone(PEEK)-layered-protective-structure(SPLPS)subjected to low-velocity impact loadings.The contact state of samples is measured by pressure-sensitive test paper.The experiments were carried out by the split Hopkinson pressure bar(SHPB)method.The stress attenuation effect of 5-layer SPLPS was tested at the different impact velocities.A three-dimensional numerical simulation model is established to simulate the SHPB experiments with the same boundary conditions.The stress attenuation effect of different layers of SPLPS is compared by numerical simulation.Besides,the influence of the thickness of steel-sheet and PEEK-sheet is investigated.And the SPLPS made for the DTH hammer has been tested in the hot dry rock drilling field.The results show that the data of numerical simulation are consistent with the SHPB experimental results.It is found that the different impact velocities do not change the contact state of the sample's end face.The stress attenuation ratio of 5-layer SPLPS in numerical simulation and experiment is 77%.The attenuation ratio increases rapidly when the number of SPLPS layers changes from 1 to 4.When the number of SPLPS layers exceed 4,the attenuation ratio does not increase significantly.Additionally,the thickness of 6 mm and 8 mm are suitable parameters for the SPLPS.The field test has proved that the SPLPS could protect the fluidic oscillator effectively.
NSTL