| A full-face tunnel boring machine(TBM)has the advantages of friendly construction environment,fast speed,safety,environmental protection,high economic benefit and strong geological adaptability,and is widely used in water conservancy and hydropower,municipal administration,high-speed railway tunnel,national defense and other underground engineering construction.As the "tooth" of TBM,the disc-shaped cutter is located at the front of the TBM and is in direct contact with the rock mass.The cutter-rock contact behavior directly affects the rock-cutting efficiency for the TBM and the construction progress.When a TBM is used in hard rock stratum,the normal force required for the cutter to penetrate a given depth into the rock increases sharply as the uniaxial compressive strength of the rock increases,resulting in the decrease of advance speed and the aggravation of cutter loss,which may have an adverse huge effect on TBM construction.The interaction between cutter and rock on the contact surface is the root cause of rock breakage and cutter loss,and cutter structure is one of the key determinants of cutter-rock contact behavior.The surface structure design of cutter is an important potential way to regulate the cutter-rock contact and improve the efficiency of cutter rock breaking,but the relevant research is still rare.This paper proposes for the a design scheme of a new type spiral groove cutter,and uses a hybrid discrete element model and a reduced scale rock-cutting experiment to evaluate from several key indexes the comprehensive performance of the proposed cutter,to verify the feasibility and effectiveness of the design scheme.Based on the results,the following conclusions were drawn:(1)Based on the control of the cutter-rock contact state,a new design concept of groove cutter was proposed.It was found that the existence of grooves can greatly reduce the cutting force of rock breaking cutter,but different grooves have different effects,among which the spiral groove cutter is more prominent in improving the efficiency of rock breaking.(2)The rock breaking efficiency of spiral groove cutter was evaluated by numerical simulation and laboratory test.The results show that the average normal force of the spiral groove cutter was reduced by at least 25%,and the average rolling force was reduced by at least 20% than that of the conventional constant cross-section flat-top cutter.The presence of the spiral grooves reduced the projected area of the cutter-rock contact region,and the degree of reduction was greater for the normal projected area than the tangential projected area.Thus,spiral grooves reduce more normal forces than rolling forces.At the same time,the rock breaking specific energy of cutter is significantly reduced,and the rock breaking energy utilization rate is improved.(3)The existence of spiral groove makes the cutter-rock contact become discontinuous,and the contact area changes constantly during the process of cutter movement,which reduces the average contact area,cutting force and rock breaking specific energy of spiral groove cutter.At the same time,the rock below the groove is through with each other by the cracks generated by two cutter teeth of the same cutter,forming smaller rock fragments(rather than rock powder).Which improves the rock breaking efficiency of the cutter(reducing the rock breaking specific energy of the cutter).(4)The structural parameters of cutter are the key factors affecting the cutter performance.A systematic study of the three key design parameters of the new cutter shows that the cutter width has the greatest effect on rock breaking efficiency,while the spiral angle of groove has the least effect.This is because the width of the cutter affects the contact area,contact state and stress distribution of the cutter-rock to the greatest extent.(5)Through the linear cutting test in the laboratory,it is found that the new spiral groove cutter shows excellent results when tested on two kinds of rocks with different macroscopic properties.This shows that the cutter can adapt to different formations,and shows better rock breaking performance than the conventional constant cross-section flat-top cutter.(6)The wear performance of new spiral groove cutter was studied by laboratory wear experiment.The results show that the wear appearance of spiral groove cutter tooth top is similar to that of the conventional constant cross-section flat-top cutter,and it is uniform wear rough surface.However,the helical groove cutter tooth tip part,because the cutter width is much smaller,and the use of no dip angle groove,resulting in weak strength,there are obvious plastic deformation and flaking phenomenon.But mainly concentrated in the early service,in the middle and late period,the material loss rate slowly slowed down or even less than the conventional constant cross-section flat-top cutter.(7)The plastic deformation degree of the conventional constant cross-section flat-top cutter and the top of the teeth of a spiral groove cutter is similar and small,mainly caused by hard mineral particles scratch or embedded generated two-body and three-body abrasive wear.The plastic deformation of the helical groove cutter increases exponentially along the direction of the tip of the cutter tooth.So the tip of the cutter tooth is a small amount of fatigue wear(i.e.cutter tooth flaking)on the tip of the cutter tooth in addition to the two-body and threebody wear.However,the spiral groove cutter can according to the needs by adjusting the structural design parameters,changing the shape of the groove section and chamfering the cutter tooth tip or other ways to alleviate the cutter use early service of plastic deformation and flaking,improve the service life of the spiral groove cutter. |
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