The Study On The Critical Preload Of Composite Beam Of Hydraulic Press

Considering the restrictions of manufacture,transportation and installation conditions, the beams of large hydraulic press are generally designed as composite type. Compared to integral beams,apart from sufficient strength and stiffness, composite ones should also guarantee its loaded integrality. And the preload is the major method to guarantee the integrality of the composite beams. The integrality of the composite beams not only has a great influence on the working precision of the hydraulic press,, but also is critical to the service life of the body of the hydraulic press. Therefore, it has been one of the most important problems on the design of large hydraulic press, that to find a method which can accurately calculate the preload parameter to guarantee the integrality of the beams.In this article, a calculation model of the composite beam was established based on the composite lower beam of one large hydraulic press. Further more, the model was decomposed to a bending model and a prestressed model based on the mechanical and deformation characteristics of the composite beam. The computational problem of the critical preload of the composite beam was analyzed and researched by means of the methods of theory, simulation and experiment.As for the bending model of the composite beam, combing with shear deformation theory of beam, computational formula of bending normal stress was derived. After numerical simulation researching of the influence of load, span-depth ratio and loading range on the bending normal stress of the middle section, the conclusion was got that the most important influence factors are load and span-depth ratio. And the computational formula of bending normal stress of the most easily slotting place was amended according to the results of the numerical simulation.As for the prestressed model of the composite beam, with using the method of numerical simulation, it was researched that the influence of the position of the rods and the span-depth ratio on pressure stress of the middle section junction position of the under plate of the beams. And it turn out that span-depth ratio has a remarkable influence. However, the loading range has a relatively less influence. The computational formula of compressive stress of most easily slotting place was fitted out from the simulation result. On the basis of the above work, the computational formula of critical preload was derived based on superposition principle and critical condition.The experiment of critical preload force was also conducted on the composite beam in the article. The results of the experiment shown that the prestressed structure of the composite beam designed by the computing method of critical preload of the article can meet the demand of the integrality of the composite beams.