| Using sodium chloride grain jets to cut biological bone material is a crucial operation in surgery.This method eliminates the potential for thermal effects on tissue recovery associated with traditional processing methods and provides better biocompatibility of sodium chloride grains.As a "flexible" process,the deformation of the cortical bone by the attachment wall during cutting can make it difficult to control the surface quality of the process accurately,so it is essential to investigate the deformation of the cortical bone by the sodium chloride grain jet under the attachment wall and the effect of the deformation on the surface quality of the process.In order to avoid the influence of cortical bone opacity on the capture of jet beam deformation when cutting cortical bone by sodium chloride grain jet,a visual simulation experiment based on high-speed photographic of abrasive water jet cutting transparent PMMA was designed to analyze the deformation of the jet beam inside transparent PMMA,providing a theoretical basis for sodium chloride grain jet cutting cortical bone experiments.Combined with the roughness of the machined surface and the results of the inspection and analysis of the microscopic surface morphology,the following conclusions were tentatively drawn: The jet beam is not only deformed by deflection hysteresis due to the front sidewall constraint and divergence deformation due to the sidewall constraint on both sides,but also by increasing diameter deformation along the cutting feed direction due to the joint constraint of the front sidewall and the sidewall on both sides.The increased diameter deformation increases the sum of squares of the residuals obtained after fitting the curve of the surface roughness Ra along the depth of cut,indicating that this deformation leads to a reduction in the energy density of the jet beam,which is susceptible to fluctuations caused by external conditions.Based on a visual simulation of abrasive water jet cutting,an experiment was designed to cut cortical bone with a sodium chloride grain jet.Again,a high-speed camera was used to capture the jet beam morphology,and the parameters related to the jet beam deformation due to the constraint of the attached bone edge wall were analyzed when the sodium chloride grain jet beam was cutting cortical bone at different working pressures,target distances and feed rates,combined with the surface roughness and microscopic morphology of the cortical bone:(1)Verifies the conclusion reached in the simulations when cortical bone is cut by a sodium chloride grain jet,there is an increasing diameter deformation of the jet beam under the combined constraints of the front and side walls.The deformation leads to a reduction in the energy density of the jet beam,which is susceptible to fluctuations due to external conditions.(2)If we want to obtain better surface quality,and the geometry of the jet beam is conducive to jet collection and safety protection,we need to choose a larger working pressure,smaller target distance and feed rate,and the best working parameters in this experiment are p=340 MPa,d=1 mm and υ=10 mm/min.(3)The distinctive surface morphology of cortical bone caused by sodium chloride grain jets can be divided into four types: 1.Oblique stripes consisting of cut-through peaks and uncutthrough valleys that occur periodically on the surface as the depth of cut increases;2.Vertical scratches on the surface caused by anomalous sodium chloride grains with sharp edges and sharp corners;3.Transverse defects on the surface caused by lateral spalling of bone units stretching bridging fibres;4.Cavities existing in the bone tissue itself.(4)The degree of inclination of the oblique stripes present on the machined surface of the cortical bone is mainly influenced by the deflection hysteresis deformation of the jet beam;the structural characteristics of the bone tissue and the shape of the sodium chloride grains mainly influence the remaining three surface morphologies. |
