| Friction lining is an important part of the friction hoist.The friction generated by the viscoelastic deformation between the friction lining and the wire rope drives the hoist transmission.The viscoelastic deformation performance of friction lining is directly related to the friction between friction lining and wire rope,the lifting capacity,the working efficiency and the reliability of the friction hoist.Based on the experiment platform on dynamic micro slip friction of friction lining and wire rope,this thesis uses the digital image correlation method(DIC technology)to study strain fields of viscoelastic friction lining during the frictional drive process.The friction experiments under different dynamic working conditions were carried out.The distribution regularity of the internal strain field of the friction lining under different dynamic conditions was observed and quantified.The effects of different dynamic parameters on the internal strain field and friction properties were investigated.The coupling relationship between the the strain of the friction lining and friction force was established.(1)Based on the DIC technology,the process of dynamic contact between the wire rope and the friction lining was observed.With an increase in pressure and a change in the position of the contact point,the X strain changed from tensile to mixed tensile-compressive strain and the Y strain changed from mixed tensile-compressive to compressive strain.The friction experiments under static load revealed that the strain of the friction lining varied periodically due to reciprocating motion.The strain maximum and variation of strain decreased with an increase in distance from the contact surface.The calibration point 1mm away from the contact interface has the maximum Y strain at 3MPa,which is-0.061.The calibration points with coupled linear relationship between strain maximum and friction force for different pressures and sliding velocities were obtained.(2)Based on the DIC technology,the strain field distribution regularity of the lining under different alternating loads was observed.When the alternating load amplitudes and frequencies are high,the maximum strain value of each sliding cycle varies significantly.An alternating load amplitude of 1000 N and an alternating load frequency of 1/2Hz were identified as critical values in generating irregular strain in the friction lining.The calibration points with coupled linear relationship between strain maximum and friction force for different alternating load amplitudes and alternating load frequencies were obtained.(3)It was found that the highest accuracy of the maximum strain at the calibration point 4mm away from the contact interface is obtained when correlated with the friction force.The fitting results were all above 91%,which means that using the calibration point 4mm away from the contact interface for monitoring is the most suitable.Based on the DIC technology,the strain change of the calibration point 4mm away from the contact interface under different contact interface mediums and forms of lifting acceleration was observed.It was found the friction lining has the smallest strain variation,the smoother friction force and friction coefficient,the best friction transmission stability in the form of trapezoidal acceleration under different contact interface mediums.The highest values of the friction force,friction coefficient,and strain variation amplitude occur under dry friction conditions.The maximum strain is -0.016 and the friction force is 1260 N at a constant velocity stage.The lowest values occur under friction-enhancing grease medium.The maximum strain decreases by 45.6%,and the friction force decreases by 64.3%.(4)The appropriate two-dimensional area in the friction liner monitoring zone was identified using DIC technology.The Y strain of two-dimensional area was extracted.The variation law of Y strain under different dynamic parameters was investigated.The fitting equations of Y strain maximum and friction force for different dynamic parameters were obtained.The theoretical friction force is calculated from the strain value of the strain gauge.Compared with the actual friction force,it was found the theoretical friction force and actual friction force error was small.Error less than 10.6%. |
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