Piecewise model and experiment of power chuck's gripping force loss during high speed turning

High speed power chucks are important function units in high speed turning.The gripping force loss is the primary factor limiting the rotational speed of high-speed power chucks.This paper proposes a piecewise model considering the difference of wedge transmission's radial deformation between low-speed stage and medium-to-high-speed stage,the friction forces of chuck transmission,and the compressibility of hydraulic oil in rotary hydraulic cylinders.A corrected model of gripping force loss is also established for power chucks with asymmetric stiffness.The model is verified by experiment results.It is helpful to use the piecewise model to explain the experimental phenomenon that the overall loss coefficient of gripping force increases with the rotational speed increasing at medium and high speed stages.Besides,the loss coefficients of gripping force at each stage during speeding up and the critical rotational speed between two adjacent stages are discussed.For wedge power chucks with small wedge angel(α<20°) and ordinary lubrication(μ0>0.06),the local loss coefficient of gripping force at the low speed stage is about 70% of that at the medium to high speed stage.For wedge power chucks with larger wedge angel(α>20°) or low friction coefficient(μ0<0.06),the wedge transmissions cannot self-lock at high speed stage,and the gripping force loss at the high speed stage is related to the hydraulic lock and hydraulic oil in the rotary hydraulic cylinder;the local loss coefficients of gripping force at the third stage is about 1.75 to 2.13 times that at the second stage.This work is helpful to understand the mechanism of the gripping force loss thoroughly and to optimize power chucks.

Study on damage-stress loss coupling model of rock and prestressed anchor cable in dry-wet environment

The loss of anchoring force is one of the problems to be solved urgently.The anchorage loss is a key factor causing the failure of anchoring engineering,so it is crucial to study the time-dependent variation of anchoring force.Alternating dry and wet(D-W)conditions have a significant effect on deformation of rock.The anchoring system is composed of anchoring components and rock mass,and thus rock deformation has a significant impact on the loss of anchoring force.Quantifying rock deformation under the effects of D-W cycles is a prerequisite to understanding the factors that influence loss of anchoring force in anchor bolts.In this study,we designed an anchoring device that enabled real-time monitoring of the variation in strain during D-W periods and rock testing.Nuclear magnetic resonance(NMR)measurements showed that under D-W conditions,the increment in porosity was smaller for prestressed rock than unstressed rock.The trends of prestress loss and strain variation are consistent,which can be divided into three characteristic intervals:rapid attenuation stage,slow attenuation stage and relatively stable stage.At the same stress level,the rate of stress loss and strain for the soaking specimen was the highest,while that of the dried specimen was the lowest.In the same D-W cycling conditions,the greater the prestress,the smaller the strain loss rate of the rock,especially under soaking conditions.The characteristics of pore structure and physical mechanical parameters indicated that prestress could effectively suppress damage caused by erosion related to D-W cycles.The study reveals the fluctuation behavior of rock strain and prestress loss under D-W conditions,providing a reference for effectively controlling anchoring loss and ideas for inventing new anchoring components.

Adhesion is safe to the refractive surgeries: A theoretical analysis

Adhesion behavior,existed on the damaged interface,was responsible for the safety and stability of the postoperative cornea refer to the refractive surgeries.In this study,we inferred that the force loss generated by the post-operative cornea must do not surpass the interfacial adhesion force of the cornea.In case of that,the corneal flap(or cap)would trend to separate from the residual stromal bed,and then became a threat to the visual health of the corrected myopic patient.According to this inference,we derived the theoretical maximum ablated ratio,which was well matched with the empirically clinical safety standard employing the commonly programmed optical zone.