Allowable Load Analysis Of Box-like Telescopic Boom Truck Cranes

Although the track crane with a smaller structural dimension, its telescopic booms has a large hoisting capacity. On the premise of hoisting load is less than the allowable load, the truck crane can move rapidly, as well as obtain a longer working distance or a higher working height by extend its telescopic booms. Therefore, they are widely used in some engineering field, such as nuclear power plants, chemical industry, ports and so on. The telescopic booms of truck crane is the structure of suffer both-way composite actions of bending-compression and which is mainly suffer bending load, and sometimes they should bear the effect of torque. As a consequence, the force bearing status is very complex. The overlapping portion is the contact position of the nested telescopic booms, the distribution of contact stress is very complicated. The plastic yield deformation in the contact area is the primary factor to consider.The box-like telescopic boom structure is widely used in many engineering machinery, pre-estimate the allowable load quickly and accurately is an indispensable prerequisite and foundation. If we can use a method to pre-estimate the allowable load of telescopic booms accurately before use ANSYS to make more-refined simulation, thus we can save much trail calculation time. Based on upon, a contact model has been established in this thesis which is started from analytical method. The analysis of contact between slider and local cover plate of nested segment has been developed, and obtained the deflection status of local cover plate of the contact zone. Then acquired the regularities of stress distribution. And finally, conduct the strength analysis and stability analysis of the local cover plate, obtained the allowable load of the telescopic booms'truck crane. In addition, a contact simulation of the established local cover plate has been carried out by using ANSYS, and made a comparison of deflection value and Von Mises stress between analytical solution and ANSYS simulation. The specific research contents of this paper are as follows:To begin with, the recurrence formula of shearing force and bending moment on the cross section of multiple segment telescopic booms'truck crane has been derived when consider the self-weight of the telescopic booms. During extension movement or retraction movement of the telescopic booms, an analysis of time-history curve of the contact force between the slider and local cover plate was given by a numerical example. Theoretical analysis of cross-section's strength was developed when telescopic booms bear combined effect of bending and twisting.Secondly, the analysis of contact problem between telescopic booms of truck crane has been given in this graduation thesis. The relevant theoretical knowledge of thin plate has been introduced, then a local cover plate model has been established, which is four-sides-clamped, for the contact area between slider and cover plate of telescopic booms. The function of deflection surface of the localized cover plate has been obtained by using the virtual variational principle of energy. Then the strain, stress and internal force of local cover plate are derived by use the deflection surface function of localized cover plate. A description of contact zone of localized cover plate of telescopic booms by use an example which has given every parameter.Thirdly, the distribution function of Von Mises stress along each axis of the localized cover plate is developed according to the stress function of local cover plate contact area. The distribution regularity of Von Mises in each axis direction is determined by using a mathematical methodology for the obtained Von Mises stress function of the localized cover plate. Furthermore, the position of appear maximum Von Mises stress in upper-side local cover plate of basic boom and in lower-side local cover plate of secondary boom were found, they are the potential danger locations where most likely produce plastic yield in the cover plate. And a comparison between numerical result and the result of AN SYS simulation has been given.Then, be similar to the localized cover plate model which is a four-side-champed, an improved model, which is one pair of boundary is simply-supported and the other pair of boundary is champed, has been established. The processing method was similar to the four-side-champed localized cover plate model, the deflection surface function has been obtained, and the distribution rules of Von Mises stress along each axis of local cover plate and the position where appears maximum Von Mises stress value has been developed. Furthermore, made a comparison of deflection and Von Mises stress of localized cover plate between analytical method and ANSYS simulation, and analyzed the deviation of them. The result indicated that the second improved model is better than the first model.At last, according to the functional relationship between external load and maximum Von Mises stress at potential danger location in upper-side cover plate of basic boom and lower-side cover plate of secondary boom, respectively. The maximum hook load is determined based on the forth strength theory. The smaller value is chosen as the critical load of the telescopic booms, and it is the allowable load of truck crane. Furthermore, a stability analysis of the cover plate is developed when telescopic booms suffer critical load, the presented numerical simulation result verified the lower-side cover plate of basic boom meet the stability requirements when the truck crane hoisting the critical load. The allowable load of telescopic boom determined by second cover plate model is larger than the allowable load of telescopic boom determined by first cover plate model, and its'numerical solution is more closer to ANSYS simulation result.In addition, some effective method to enhance the bearing capacity of telescopic booms has been given in this graduation thesis, for certain cross-section's inner dimension of telescopic booms truck crane. The bearing capacity of telescopic booms can be further improved on the basis of original model by using the four methods which have been given in the thesis.