Study On The Performances Of The Rollover Potection System For Engineering Vehicles Based On Operator Injury

Engineering vehicles refer to off-highway mobile machinery applied in mines, architecture, water conservancy, road construction and other fields, including industrial tractors, loaders, excavators, rollers, bulldozers and dump trucks, etc.. Since the road surfaces are complex and the working environment is harsh, engineering vehicles are susceptible to rollover accidents, and once rollover happens, the engineering vehicle will inflict fatal damage to the operator.To protect the life safety of the operator, the current international method is to install a rollover protection structure (ROPS) on engineering vehicles, and the international standards have stipulated static lab test requirements in view of ROPS performance. However, facts have shown that the ROPS that meet the requirements of international standards cannot protect the operator's life safety upon rollover. The rollover of engineering vehicles is a dynamic impact process, during which the operator gets hurt due to the following reasons:1) Severe collision between the ROPS and the ground leads to high acceleration and a human body injury index beyond the threshold value of human body impact resistance; 2) Violent rebound in the collision results in repeated clashes between the operator and objects inside the vehicle, and aggravates the operator's injury; 3) Dramatic deformation of the operator's cab squeezes the operator and makes it hard for rescue, and thus causes severe injury or even death. The severity of the operator's injury depends on the flexibility of the system contacting and colliding the ground, the restraint between the operator and the vehicle body as well as the strength and stiffness of ROPS. The ROPS satisfying the requirements of international standards can only avoid the third case and are unable to provide sufficient buffering for the operator.In this paper, visual computer simulation and physical prototype test method have been adopted in combination with the project of National Natural Science Foundation program "Roll-over safety technology for off-road vehicle" (No.50775095) and the national "863" program "Digital design platform of safety for Roll-over and Falling-object of off-road vehicles (No.2007AA04Z126) to predict and evaluate the operator's injury after rollover, and to carry out numerical simulation and experimental study on a new type of buffer energy-absorption ROPS. Based on the findings of domestic and foreign researches on ROPS designs for engineering vehicles, car crash safety, motorcycle crash safety, a virtual prototype with the system of operator-vehicle-ground environment as the research object, body injure degree as evaluation index has been established to simulate rollover accidents of engineering vehicles by using multi-disciplinary knowledge including multi-body system dynamics, large deformation nonlinear finite element method, impact injury biomechanics, testing and sensor echnology and material science.Numerical simulation of the rollover process in the given (?)amps and ground conditions for typical engineering vehicle has been conducted; comprehensive simulation has been performed on human body response, energy absorption of the structure, strength and stiffness of the structure, buffer time and so on. Thus human body response, force exerted on various parts of the vehicle body and dynamic response have been extracted, and such parameters as parameters of vehicle body and seat, restraint form of seat belt, ground parameters, the influence of energy absorption and support mode ROPS on human body injury to evaluate human body injury have also been obtained.Based on the dynamic simulations and experiments of the rollover process of engineering vehicles and in combination with the lab test performance requirements in international standards for ROPS, the author has put forward a ROPS design method with the focus on human body injury. This design method starts from the perspective of protecting the operator and analyzes the movement of the operator and vehicle and their injury and damage in the way of accident reconstruction, on the basis of which safety design of rollover protection system has been conducted.In this paper, a new concept of protection structure has been proposed, which consists of buffer energy-absorption device and metal frame structure. The installation of buffer energy-absorption device on the traditional frame-type ROPS can not only absorb the kinetic energy generated by many rollovers, but also reduce deformation of ROPS itself, and thus solves the contradiction between the stiffness requirement and energy absorption requirement; besides, the buffer energy-absorption device can significantly weaken the peak value of acceleration due to the first collision between the protection structure and the ground. From the perspective of energy absorption, maximum collision load and structure light-weight design, thin-wall straight square pipes with hole-defect induced deformation are introduced into the ROPS design. According to the optimization theory and surrogate model, multi-objective anti-collision optimization analysis has been carried out on the thin-wall straight square pipe with hole-defect induced deformation by combining several means, namely, finite element analysis, experiment design, response surface method, genetic algorithm, and the optimal design parameters of ROPS have been obtained.The research findings of this dissertation improve the performance requirements for ROPS in current international standards from static lab tests to human body injury in dynamic rollover, and improve the individual assessment test on protection structures and seat belts, etc. stipulated by current international standards to the integrated test of human-vehicle-environment, which develops the safety design method for engineering vehicles and is of great importance to guaranteeing the operators' life safety of engineering vehicles and improving the competitiveness of China in engineering vehicle market.