| Engineering vehicles are widely used in the field of construction, mining, transportation, farmland water conservancy and so on, which is belonging to off-road vehicle. Because of the high deadweight, the abominable working environment and the descending stability, engineering vehicles are prone to rolling over during working, which may cause personal injury even death once the accident happens. When wheel loader is rolling over, the most effective method to protect the diver is equipping engineering vehicle with roll-over protective structure (called ROPS for short). This paper based on"Digital design platform of safty for Roll-over and Falling-object of engineering vehicles"and"Roll-over safty technology for road-off vehicle", which supported by national 863 program and national natural science foundation program respectively. According to the key problems of dynamic test method and design method of ROPS, the dynamic response and the dynamic roll-over test method and the dynamic design method was discussed detailedly in this paper.According to characteristics of rolling engineering vehicles, the basic theory of dynamic response method of ROPS during rolling was discussed in this paper. Firstly the theories of geometric nonlinearity, material nonlinearity and contact nonlinearity of dynamic rolling response analysis were presented. Then according to the basic equations of explicit finite element method, the calculational accuracy and efficiency of the analysis were taken into consideration, such as the method of controlling time-step of explicit integration algorithm, the main algorithm of contact surface and the symmetric penalty function based on the contact force. The shell element which adapt to the impacted simulation of ROPS and the viscous damping hourglass-control method which adapt to the rolling simulation of ROPS were selected respectively.The method of analyzing dynamic rolling engineering vehicle was put forward in this paper. The finite element model of whole vehicle was established. Then the analysis in boundary conditions of typical rolling-over case was performed. According to the quantitative and qualitative comparisons among the kinetic energy, the impacted force of ROPS, the total internal energy, the internal energy of ROPS, the frictional energy, the deformation mode and the plastic hinge, the analyzed results can be summarized as following: rigid slope is more dangerous than tamped slope for engineering vehicle as the others conditions are the same; when engineering vehicle rolling over at the rigid slope and the tamped slope, the deformation modes of ROPS are the same but the positions of plastic hinge are different. Basing on these conclusions, the dynamic rolling simulation method of engineering vehicle ROPS was proposed in this paper.There are two types of test of ROPS: rolling test on site and test in the lab. Taking the economic status into consideration, the rolling test on site is impossible, so the dynamic test in the lab was performed basing on the model of wheel loader. Through the comparison between the results of test and computer simulation, we obtained conclusions that the computer simulation can simulate the rolling impacted force response of ROPS accurately and can obtain the formation law and the energy conservation of plastic hinge. The differences of material model and frictional coefficient resulted in deviation between the test results and the simulated results. Furthermore, the weld cracked during test, which was not taken into consideration during simulation and will be discuss in further research.The dynamic design method was proposed in this paper. According to the international standard of static test of ROPS, a four-post ROPS for a heavy wheel loader was developed. Then the static nonlinear test and the destructive test were performed, and the results showed that the ROPS could meet the static safety requirements of international standard. The dynamic rolling-over response analysises were performed in nine rolling-over cases. The simulated results showed that the wheel loader did not roll over more than 360°but slipped down to crash on the horizontal plane, except the case of which the inclination of slope is 45°and the frictional coefficient is 0.6. The wheel loader slipped down to crash on the horizontal plane in the case of which the frictional coefficient is 0.2 while the inclination of slope is 15°, and ROPS played a role to protect the driver. ROPS did not play a role while the inclination is 30°and 45°. While the inclination of slope is invariant, with increasing frictional coefficient, the impacted force of ROPS increased and the internal energy of ROPS increased respectively. The variation of internal energy is complicated while the frictional coefficient is invariant. When the frictional coefficient was set as 0.2, the internal energy is lowest while the inclination is 45°, and the internal energy is highest while the inclination is 30°. When the frictional coefficient was set as 0.4, the internal energy is lowest while the inclination is 15°, and the internal energy is highest while the inclination is 30°. When the frictional coefficient was set as 0.6, the internal energy increased with increasing inclination. So the deformation mode and the position and number of the plastic hinge are completely different in the two simulation method above.The strength, the stiffness and the energy of ROPS should be taken into consideration during designing the roll-over protect structure, and the energy design is the key point. In order to maximize the absorption of energy and prolong the acting time of impacted force, a new structure of ROPS which is easy to absorb the energy was proposed. Then the dynamic analysises in several cases were performed. Basing on the orthogonal test method, the energy absorbing structure was optimized. The results are as follows. (1) The inducing liners in the post and the beam could control the position of plastic hinge; (2) The new type of ROPS with absorbing structure could prolong the acting time of impacted force by 59.52 percent and reduce the acting time of peak force, while the carrying capacity of ROPS was invariant; (3) The peak of impacted force of new ROPS decreased by 2.84kN, and the maximum internal energy of ROPS increased by 14.97 percent; (4) The deformation of new ROPS was smaller than that of original ROPS; (5) For original ROPS, the positions of plastic hinge are different at different post, which are the same at the free end of inducing liner for new ROPS. That is to say, the inducing liners play a role in inducing deformation.The innovative points in this paper are as follows. (1) The roll-over safety daynamic simulation of engineering vehicles was performed in this paper, which according with the results of simulation proved that the simplification of model and the selection of elements were reasonable. The dynamic deformation mode of ROPS, the plastic hinge and the changing law of impacted force and internal energy of whole vehicle were discussed in this paper. (2) Several new laws of dynamic response of ROPS have been found by the research of dynamic response of whole vehicle. The engineering applications of a typical large wheel loader were performed, and a new method to develop ROPS of engineering vehicle was proposed based on dynamic design flow of ROPS. (3) A new ROPS with inducing liners was proposed. Meanwhile, the stiffness nearby the joints of ROPS and stiffeners has been improved. The contradiction between carrying capacity and energy absorption of ROPS has been solved by the energy absorbing structure.The results in this paper improved the theory of designing ROPS, which can provide theoretical basis and practical method for dynamic designing and testing. This paper has a great significance on improving of national engineering vehicle.
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