Mechanical Testing And Parameter Study Of Wood-plastic Composite Sleeper

For many years,sleeper researchers mostly search for available raw materials at first,then use these materials to produce products,and finally check whether sleeper products are applicable on track lines.Few scholars consider this issue with reverse thinking,i.e.,at first study what are the best technical parameters of a railway sleeper,then look for materials and carry out the sleeper product design.Before the emergence of composite sleeper,the performance of traditional sleepers is limited by the raw material,which makes the reverse thinking unrealistic.However,with advent of designable composite materials and development of finite element analysis softwares,such a reverse technical route is becoming feasible.For example,elastic modulus of softwood sleeper is universally considered low,while elastic modulus of concrete sleeper is too high,so the ideal elastic modulus value of sleeper should be between the two of them,thus,for a "roadbed-ballast bed-sleeper-rail-train" system with specific traffic patterns,there is a optimal solution for sleeper elastic modulus,and this problem could be solved by using comprehensive knowledge of different subjects.Basing on the reverse thinking process above,this thesis comprehensively utilized design of experiment(DOE),analysis results of train line dynamic modeling,regression analysis and optimization theory to optimize technical parameters of proposed composite sleeper,and to study influence of these technical parameters on other components of track system,which is critical for understanding interaction relationship between sleeper parameters and performance of different components of track system.Besides,another innovation of the thsis is the use of laser holographic interferometry to study the deformation and failure mechanism of composite sleeper material.The main results of this thesis could be summed up in three aspects:(1)Studied crack resistance of proposed composite sleeper(uses sawdust as filler,timber beams as reinforcing components,polymer as matrix,pic.4.3)material samples(excluding timber beams)by conducting crack resistance test,analysed compressive strength and deformation characteristics of samples by conducting compression test and using method of laser holographic interferometry,obtained important data and images,which provide reference for further optimization design of the composite sleeper.(2)Basing on design of experiment(DOE),analysis results of train line dynamic modeling,regression analysis and optimization theory,with operation condition of locomotive type BJI-80,speed 80km/h,1520mm gauge railway line in straight line section,optimized sleeper bending coefficient,sleeper quality,elastic modulus in horizontal direction,elastic modulus in vertical direction of proposed composite sleeper.(3)By using design of experiment(DOE)and train line dynamic modeling analysis results,influence of sleeper bending coefficient,sleeper quality and elastic modulus of rail foundation in horizontal and vertical directions(which mainly rely on temperature)on response functions are studied by plotting their contour maps.Response functions include rail bottom stress,rail vertical deflection,sleeper vertical deflection,sleeper vertical acceleration,stress of ballast bed on top of surface,stress of subgrade on top of surface,rail vertical maximum dynamic load and stress of rail head.