Study On Pressure Resistance Of Borehole Pressure Pillow For Mine

Borehole stressmeter for mine is a kind of measuring instrument for monitoring rock burst.It can provide real-time early warning of the dangerous zone and degree of rock burst.Borehole pressure pillow is the key components on the Borehole stressmeter for bearing pressure.Its structural size directly affects the accuracy of monitoring rock burst.Increasing the size of borehole pressure pillow,which can make borehole pressure pillow better fit the rock mass under the initial pressure to improve the accuracy of monitoring rock burst.However,with the increase of the size of borehole pressure pillow,the problem of insuficient pressure resistance will arise.In this study,the analysis of the pressure resistance of the large size borehole pressure pillow will have a more important practical engineering significance to improve its reliability and sensitivity.According to the working condition of borehole pressure pillow in the rock mass,the pressure test is carried out on the designed borehole pressure pillow.The pressure test is divided into two working conditions of independent and applying inclusion pressure test.The independent pressure test tests the deformation and pressure resistance of borehole pressure pillow under internal pressure,as the load increases,the thickness dimension of borehole pressure pillow shows an overall increasing trend,and its width dimension shows an overall decreasing trend.The applying inclusion pressure test tests the pressure resistance of borehole pressure pillow under the internal and external double loads,the change trend of internal pressure and external pressure are basically the same.The borehole pressure pillow is made of S30408 stainless steel,and its mechanical properties is tested by Small punch test(SPT)technology.Based on the extended finite element method(XFEM),using the finite element analysis software ABAQUS to simulate the fractured process of the specimen in the SPT.The fractured zone of the materials first undergoes thinning,and the thinned zone gradually produces larger plastic deformation,then the crack propagation is produced until it fractures.Based on the elastic-plastic theory,simulating the stress and strain characteristics of borehole pressure pillows of different thicknesses under the working conditions of pressure test.The relative error between the test value and the numerical simulation value is between 0.21%and 9.12%.With the increase of the thickness of borehole pressure pillows,the stress and strain show an overall downward trend.With the increase of the initial spacing of inclusion,the stress and strain show an overall upward trend.Borehole pressure pillow with a thickness of 1.6 mm can meet the pressure resistance requires of independent and large spacing of inclusion.The influence of welding residual stress on the pressure resistance of borehole pressure pillow is studied,the simulation results shows that the maximum welding equivalent residual stress of borehole pressure pillow is 254 MPa,and the welding residual stress will cause the actual stress distribution of borehole pressure pillow to be uneven under internal pressure load,further result in stress concentration.The dendrite structure of weld zone grows perpendicular to the fusion line.The fractured location is concentrated in the heat affected zone.From the direction of inside to outside of borehole pressure pillow,the fractography changes from ductile fracture to brittle fracture.The borehole pressure pillow cracks from inside to outside.The pressure resistance of borehole pressure pillow is mainly determined by structure size and welding quality.Using the finite element method to carry out numerical simulation of its withstand pressure,and analyzing the microstructure,composition and fractography of the welded joint,the pressure resistance of borehole pressure pillow can be studied more accurately.These studies provides a basis for structural design and welding process of borehole pressure pillow.