Computer Simulation And Experiment Study On The Performance Of Falling-object And Roll-over Protective Structures For Engineering Vehicles

Engineering vehicles are used in agricultural, mining, construction, water conservancy, road construction etc, including loaders, excavators, rollers, bulldozers, graders, loaders mining, industrial tractors and dump cars. Falling-object and roll-over accidents often happen because of the complexity of the road, poor working environment and they are difficult to avoid. The drivers'life is often threaded by such kind of accidents. Falling-object protective structure and roll-over protection structure (FOPS&ROPS) is a group structure installed outside the vehicle cab, and its main function is to safeguard the lives and safety of the drivers when the vehicles encountered falling-object or roll-over, and minimize the damage caused by these accidents. Along with the increasing requirements for safety performance of engineering vehicles in international, properties qualified with the FOPS&ROPS have become mandatory requirements in developed countries such as Europe and the United States. However, the current design methods for FOPS&ROPS are not yet perfect. To improve the design and manufacture quality of domestic FOPS&ROPS, also to improve the security of domestic FOPS&ROPS and promote China-made engineering vehicle to enter the international market, the study on the design theory and experiment methods of FOPS&ROPS has become a very urgent issue in engineering vehicle industry. Combining"the 10th five-year plan"project, the name of which is"Development of ZL 80G intelligent loader"from the item of"Revitalization of the Old Industrial Base in Northeast China"supported by the National Development and Reform Committee and the consigns of many domestic leading engineering vehicle enterprises, this dissertation studies performance computer simulation and experiment study on the FOPS&ROPS for engineering vehicles. On the basis of referring to relevant literatures extensively, this dissertation summarizes the study status and elaborates on the current international standards on the performance requirements and test methods of engineering vehicle FOPS&ROPS. Then it discusses the basic theory and the numerical simulation algorithm of performance computer simulations of FOPS&ROPS and does some computer simulations of typical of FOPS&ROPS. On the basis of a wide range of protective structure tests on the FOPS and ROPS test equipments according to the standard requirements, the simulation results are correct by comparing them to test data. By analyzing the test data of FOPS&ROPS, this dissertation summed up the deformation mode and failure mechanism of protective structures, points out the problems in the design and manufacture of FOPS&ROPS and gives some ways to improve them. On the basis of the computer simulation and experiment study on FOPS&ROPS, puts forward the optimization methods of FOPS&ROPS which are based on the neural networks and genetic algorithm, takes a small excavator for example, optimizes its falling-object protective structure parameters, the result proves that the quality of the protective structure can be reduced significantly under the premise of guaranteeing the performance requirements. The main contents of this dissertation are as follows:First, it introduces the current international standards on the performance requirements and test methods of engineering vehicle FOPS&ROPS. Then it discusses the basic theory of the computer simulations of FOPS&ROPS.Second, it puts forward the dynamic simulation methods of a falling-object protective structure which is impacted by drop hammer. Takes the integrative FOPS&ROPS and independent FOPS for example, it discusses the establishment of the finite element model, the choice of material properties, the disposal of boundary conditions, the algorithm of contact collision interface and the control of hourglass, etc, it also performs the dynamic simulation a FOPS and analyzes the influences of different structural parameters on the performance of anti-impact. At the same time, it studies the energies that are absorbed by every component, the results show the structural beams and the roof of the integrative FOPS&ROPS are the major components of energy absorption, the energy that are absorbed by pillars and strengthen beams is very little. The irrational structure parameters are improved through simulation.Third, the experimental research on many kinds of FOPS manufactured by leading enterprise is carried out, according to the international standards of performance requirement. Through comparing the experimental data with computer simulation results of FOPS it is found that the model and results of computer simulation are correct. Based on the large number of experiment on different types of engineering vehicle FOPS, the deformation mode and failure mechanism of protection structure are analyzed. It is pointed out that the flaws of FOPS&ROPS design and what should be paid attention to, which provides reference for the design and manufacture of FOPS.Forth, with the basic principle of large plastic deformation and non-linear finite element method, a ROPS simulation model of engineering vehicle is established and a numerical simulation is carried out. The principle of model simplification and the factors that can affect the calculation results are depicted, such as how to determine the element, material properties and boundary conditions and so on. Take a loader as an example, the method of establishing the finite element model is detailedly discussed. According to the international standards the simulation of lateral load, lateral energy absorption, vertical load and longitudinal load are completed. The results show that the roll-over protection structure meets all the standards of design index.Fifth, experimental study on multi-engineering vehicles from domestic leading enterprise is carried out, based on laboratory experiments and performance requirements of engineering vehicle ROPS. Through comparing the ROPS performance test data of the Loader with computer simulation results, it is found that the simulation model and arithmetic are correct. Despite the ROPS meets the international performance standard, the stiffness of ROPS usually is high. When reaching the lateral energy absorption, lateral load has already exceeded the standards too much. It is hard to provide a smooth cushion when the vehicle turns over, so the driver needs to bear strong impact. Such kind of ROPS is big and heavy. It not only makes the cost high, leads to steel waste, but also decreases the stability of the vehicle; affect the vision of driver, which increase the risk of rolling over. In this dissertation, the ratio of the largest lateral load of lateral energy absorption process to the minimum lateral load standard ruled is defined as a coefficient, which is taken as the evaluation index of ROPS buffer performance. And its value range is recommended. Based on the analysis of the deformation mode and failure mechanism of protection structure when lateral load, vertical load and longitudinal load proceeding, the method to improve ROPS design and manufacture is given. Finally, FOPS&ROPS should have the lowest weight when it meets the performance standard. This will decrease the cost and avoid dynamical falling and oil consumption increasing that caused by the heavy vehicles. In order to improve the protection ability of protection structure to driver and reduce manufacture cost and design cycles, the optimization mathematical model is established, where the quality is defined as objective function and the performance is taken as constraints condition. Because of the material non-linearity, geometry non-linearity and contact non-linearity between the design variable and performance, the explicit expression is hard to establish. And all the design program need to make a large amount of calculation for finite element analysis owing to non-linear, large deformation. In order to solve this problem, the optimization method based on neural network and genetic algorithm is put forward. It calculates the response of protection structure through selecting sample points, trains neural network to simulate the relations between design variable and performance, and utilize the genetic algorithm to solve the global optimal point. Take the excavator FOPS as an example for optimization design, the dissertation makes computer program and optimization program for FOPS is determined.This dissertation carries on a more systematic and in-depth study on the performance computer simulation, laboratory testing and optimization design of engineering vehicle FOPS&ROPS, the study results have applied in Guangxi LiuGong Machinery Co. Ltd. and XuGong Science&Technology Co. Ltd. and other leading engineering vehicle manufacture enterprises, raises the design standards of FOPS&ROPS, improves the protective structure performance, makes the performance of homemade engineering vehicle FOPS&ROPS in accordance with international safety standards, so the safety requirements of engineering vehicle FOPS&ROPS is not the barrier of entering American-European market yet. The theoretical research and experimental work provides a basis for the FOPS&ROPS design.