| Micro-grinding is a common and basic operation in clinical neurosurgery.Clinical neurosurgeons use drip-cooling with normal saline to remove bone tissue in bone grinding.This method has low cooling efficiency and poor visibility in the operation area.Adjusting the grinding parameters by experience can easily lead to the operation temperature being too high,while human bone,nerve and blood vessel are vulnerable to the influence of high temperature.Bone necrosis and irreversible thermal injury of nerve caused by excessive grinding temperature is one of the bottlenecks in osteosurgery.At the same time,as a kind of hard-brittle material with complex structure,biological bone tissue is accompanied by a large number of micro-cracks during grinding process,which are easy to expand and connect and lead to bone fracture.Bone crack injury caused by excessive mechanical stress(stress injury)is another technical bottleneck in surgical bone grinding,which severely restrict the application of micro-grinding in surgical operations.However,the essence and scientific origin of thermal and mechanical injuries during bone tissue removal can be attributed to thermodynamic problems in mechanical engineering.Based on this,a new technology of nanoparticle jet spray cooling(NJSC)bio-bone micro grinding is proposed in this paper,which can draw lessons from the inhibition measures of grinding thermal and mechanical injuries in mechanical engineering field,and solve the bottleneck of surgical bone surgery,providing theoretical guidance and technical support for clinical bone surgery to avoid or reduce thermal-mechanical injuries.Based on the above,the thermodynamic mechanism of NJSC bio-bone micro-grinding is studied in this paper.The mechanism of nanoparticle jet convective heat transfer in micro-grinding area is studied,the heat transfer mechanism of nano solid particles is revealed,and the mathematical model of convective heat transfer coefficient under NJSC is developed.The heat distribution mechanism in the micro grinding area is revealed,and the heat distribution coefficient model of the NJSC micro-grinding area is developed.The micro-grinding mechanical behavior ofhard-brittle bio-bone materials is studied,and the minimum chip thickness model under the size effect of bio-bone micro-grinding is developed.The stress transfer and crack propagation mechanism of hard-brittle bone materials are revealed,and the critical undeformed chip thickness model of ductile-brittle transition is developed,and the dynamic heat source distribution of removal in the ductile removal of bio-bone is revealed.On this basis,a temperature field dynamic model of NJSC of bio-bone micro-grinding is developed.The main jobs of the paper are as follows:(1)The mechanism of nanoparticle jet spray droplet convective heat transfer in micro-grinding area is studied,and the probability density distribution mechanism of spray droplet size is revealed,and the influence mechanism of jet parameters on spray boundary is explored.The dynamic behavior of droplets impacting on the surface of heat source is analyzed by Weber number and Laplace number,and the effective heat transfer droplet size is analyzed by probability statistics.Based on the study of the heat transfer coefficient of single nanofluid droplet,a convective heat transfer coefficient model for NJSC is developed,and the influence of jet parameters and droplet spreading parameters on convective heat transfer coefficient is explored.(2)A measurement system of convective heat transfer coefficient conforming to the spray cooling boundary condition is designed and built to solve the bottleneck that,the measurement of the convective heat transfer coefficient in-tube does not conform to the actual spray cooling condition,leading to the large of the measurement error of the spray cooling convective heat transfer coefficient.The measurement error of the measurement system is analyzed,and by measuring the convective heat transfer coefficient of pure saline spray and spray of different medical nanofluids,the error of theoretical model of convective heat transfer coefficient is analyzed.The mechanism of enhanced heat transfer of nano solid particles in micro grinding area is revealed.(3)The mechanism of ductile removal of hard-brittle materials is studied,the mechanical behavior of bone micro-grinding is revealed,and the threshold distribution of the undeformed chip thickness in the ductile removal of bio-bone micro-grinding is explored.Based on the theory of strain gradient plasticity,a mathematical model of minimum chip thickness under the size effect of bio-bone micro-grinding is developed.The mechanism of stress transfer and crack propagation in hard-brittle bone materials is revealed.Based on fracture mechanics theory,a mathematical model of critical undeformed chip thickness for ductile-brittle transition is developed.(4)A single abrasive scratch experiment platform is built to study the removal mechanism of the ductile removal of hard-brittle bone materials by using fresh bovine femur compact bone,which has the closest mechanical properties to human bone.The micro-grinding behavior of hard-brittle bone materials is determined by the variation trend of grinding force ratio,unit grinding force and specific grinding energy with the undeformed chip thickness of single abrasive.The accuracy of the minimum chip thickness and the critical undeformed chip thickness model for ductile-brittle transition of bio-bone materials is analyzed.The mechanism of nanoparticles' anti-wear and anti-friction mechanism on the threshold interval of undeformed chip thickness removal in the ductile removal of bio-bone materials is revealed.(5)The heat distribution mechanism in the micro-grinding zone is revealed,a heat distribution coefficient model is developed based on the convective heat transfer mechanism of nanoparticle jet.The influence mechanism of bio-bone material removal on energy generation and consumption in micro-grinding zone is analyzed,and the dynamic heat flux model for ductile removal is developed.On this basis,a temperature field dynamic model of bone micro-grinding with NJSC is developed,and the thermal injury domain of the grinding shaft is analyzed by finite difference method.(6)The temperature field of NJSC bio-bone micro grinding is studied,and the experimental platform of micro-grinding with NJSC is developed.By measuring the micro grinding force and the temperature of different measuring points on the bone surface,the accuracy of the dynamic model of NJSC bio-bone micro-grinding temperature field is analyzed.The dynamic characteristics of temperature field in micro-grinding of bone materials are studied.The influence mechanism of nanoparticle size and concentration on the micro-grinding temperature of bone is revealed. |
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