Research On High-speed Rolling Mechanical Property Of Vehicle Tire Based On Digital Image Correlation

Tire rolling deformation is an important part of tire mechanical property.The rolling deformation of the tire which is consisted of large rigid displacement and flexible deformation is the direct result of interaction between tire and road surface.Limited by the condition of high-speed tire rolling,the research on the mechanical property of high-speed rolling tire mainly focuses on the research of high-speed deformation characteristics of rolling tire.The accurate measurement and expression of nonlinear flexible large of rolling deformation play a important role in revealing high-speed rolling tire mechanical property,high-speed rolling tire deformation mechanism and optimized tire structure and so on.By now,the research of nonlinear flexible large deformation of rolling tire is still inadequate in the aspects of experiment measurement method,measurement result stability,influence degree of experiment environment and rolling deformation modeling,etc.In particular,the research on the nonlinear flexible large deformation of high-speed rolling tire is not enough.Three problems that have not yet been fully developed in the modeling and expression of nonlinear flexible large deformation of high-speed rolling tires,the acquisition of global flexible deformation and mechanical properties measurement are:(1)How to accurately express the nonlinear flexible large deformation characteristics and distribution law of high-speed rolling tire by means of theoretical model;(2)How to obtain full-field nonlinear flexible large deformation of rolling tire by the digital image measurement method;(3)How to accurately measure the contact patch length and rolling resistance coefficient of rolling tire by means of digital image of rolling tire deformation;This paper has carried out a lot of theoretical research,development analysis and experimental verification to solve problems.The main research contents of this dissertation are listed as follows:Firstly,the rigid ring tire model is used as a theoretical framework to establish a distributed load flexible ring tire model that takes into account the characteristics of arbitrary vertical load pressure distribution,the dynamic contact coupling between tire and road surface,and carcass flexibility.A tire modal experimental system is developed.The tangential stiffness,radial stiffness,bending stiffness and modal damping coefficients of the rolling tire model are identified by the tire modal analysis and frequency response function bandwidth method.On this basis,it is revealed that the tangential nonlinear flexible large deformation of high-speed rolling tire is similar sinusoidal in distribution and the radial nonlinear flexible large deformation is eccentric in rolling contact patch by the simulation of distributed load flexible ring tire model.Secondly,the absolute node coordinate formula of continuum mechanics theory is introduced into the digital image correlation measurement method,and an improved digitial image measurement method is proposed,which is suitable for the nonlinear large flexible deformation of rolling tire.This method has the characteristics of full-field,non-contact,easy to implement and stable measurement,and it could effectively solve the shortcomings of the inner-sensor measurement method of rolling tire.The monocular tread rubber block torsional deformation measuring device is developed to capture the digital image of continuous torsional deformation of tread rubber block.The digital image quality is evaluated by combination of the gray histogram,correlation coefficient and relative entropy.The torsional nonlinear large deformation characteristics and trend of tread rubber block are obtained by digital image processing and experimental measurement respectively to verify the validity of the improved digital image correlation method and determine the stick-slip state switching point of the tread rubber block.As can be seen from the image processing results,the influence mechanism of the torsional angular velocity on the trajectory morphology of the marker point is revealed.The larger the torsional angular velocity is,the more obvious the marker point hysteresis phenomenon is,and the larger the marker point hysteresis loop area is.On this basis,the global relative strain rate distribution cloud map is obtained by means of improved image correlation method,which more clearly reveals the evolution mechanism and influence mechanism of the global torsional deformation distribution of the tread rubber block.Furthermore,based on optimized digital image correlation method,the high-speed stereo-vision measurement system is established.The calibration of high-speed stereo-vision measurement system,the creation of random speckle pattern on tire surface and the quality analysis of rolling tire digital image have been completed.By combining the improved digital image correlation method and stereo matching calculation method,the sequence of captured high-speed rolling tire deformation speckle digital image is processed and analyzed to measure the single-point relative coupling displacement and full-field nonlinear large flexible deformation distribution characteristics and dynamic change law.A relative coupling displacement solution model based on improved digital image correlation method is proposed.In order to identify and separate the rigid body displacement and flexible deformation from the relative coupled displacement of high-speed rolling tire,the relative position transformation rotation matrix and translation matrix of high-speed rolling tire deformation image subset mesh node are calculated by the decoupling model under the generalized absolute node coordinates.It is helpful to reveal and analyze the changing characteristics of relative coupling displacement,relative rigid displacement and relative flexible large deformation of the marker point,as well as the distribution pattern and dynamic changing law of the relative full-field nonlinear flexible large deformation cloud map.The effects of load,pressure and speed on the distribution characteristics of nonlinear flexibility large deformation of high-speed rolling tires are studied.The experimental results show that the distributed load flexible ring tire model can accurately express the nonlinear flexible large deformation characteristics and distribution law of high-speed rolling tire.Finally,a rolling tire mechanics observation method is proposed based on digital image correlation.The relative flexible X-direction,Z-direction and shear strain rate distributions of marker point are obtained by digital image processing method,and the relative flexible principal strain rate distributions of marker points are calculated.The instantaneous endpoint position of the real-time contact mark length of the rolling tire is determined by identifying the mutation characteristics of the relatively flexible principal strain rate of the marker point.On this basis,the calculation of the time-varying contact footprint length of rolling tires based on digital images is completed.In the contact patch of rolling tire,the area difference of the strain rate between the endpoints of the contact mark and the theory center of the contact mark is calculated by analyzing the relative flexible principal strain rate distribution in the direction of the real-time contact patch length,and then the dynamic radial offset of the rolling tire is obtained.The evolution process of deformation and strain within the high-speed rolling contact patch and the hysteresis(offset)mechanism caused by the rolling resistance are more clearly revealed by analyzing the relative flexible deformation of marker point and the distribution of full-field deformation cloud map.In the contact patch of the rolling tire,the maximum point of the relative flexible deformation is identified.On this basis,the dynamic contact radius of the rolling tire is determined by combining the relative coupling displacement distribution of maximum point.Tire rolling resistance coefficient is obtained by dynamic radial offset and dynamic contact radius of rolling tire.The experimental results show that the non-contact measurement method of rolling resistance coefficient based on digital image of rolling tire deformation is feasible,stable and easy to implement.Major Innovations of the Dissertation:(1)A distributed load flexible ring tire model that is suitable for tire high-speed rolling dynamics analysis is established.In order to accurately express the flexible deformation characteristics and distribution rule of tire contact patch in the high-speed rolling condition,the model takes into account such factors as the distribution of arbitrary vertical load pressure,the contact relationship between tire and road surface,and the flexibility of tire carcass.It provides theoretical basis for the comprehensive observation of tire rolling mechanics based on digital image.(2)A relative coupling displacement solution model with improved digital image correlation is proposed.In view of the relative coupling displacement characteristics of the nodes of the rolling tire deformation digital image subset(superposition of rigid body large displacement and flexible body large deformation),the model is used to identity the relative flexible large deformation in the relative coupled displacement under the generalized absolute node coordinates.It solves the problem of full-field measurement and identification of nonlinear flexible large deformation of high-speed rolling tire.Which further expands the application scope of absolute node digital image correlation method.(3)The distribution characteristics and dynamic change law of the relatively nolinear flexible large deformation of the high-speed rolling tire are revealed and analyzed.Under the constant load variable tire pressure,with the increase of the tire pressure,the relatively flexible large deformation of the rolling tire changes in a decreasing trend,while under the constant tire pressure variable load,with the increase of the load,the rolling tire relatively flexible large deformation shows an increasing trend.According to the cloud map of the relative full-field flexible large deformation distribution of the rolling tire,At the periodic change point of the rolling tire,the relative full-field flexible large deformation is uniformly interphase distributed at the low speed,and the relative full-field flexible large deformation is concentrated distributed in a local area at the high-speed condition.(4)A rolling tire mechanics observation method is proposed based on digital image correlation.Based on stereo-vision digital image calculation,the rigid body displacement and flexibility deformation of marker point of the rolling tire are obtained.According to the deformation distribution of the marker points,the contact patch length and rolling resistance coefficient of the rolling tire are calculated.Based on this method,the physical observation of normal(Z direction)deformation distribution of the full-field of marker point patch is successfully obtained.Based on this distribution,ont only accurate measurement of rolling resistance and contact patch length is achieved,but also a clearer demonstration of the tire deformation,strain evolution process and hysteresis(offset)mechanism of rolling resistance during the tire rolling process.This provides a more direct evaluation method for the analysis of the tire rolling dynamics mechanism and the optimal design of tire drag reduction.It also provides data support for the mechanical calculation of the new-generation intelligent tire inner tire sensor.