Anti-fatigue And Lightweight Design For Frame Structure Of A Heavy Truck

Heavy truck is always being driven under full load even overload conditions.So on the complicated roads with adverse it is very easy to result in fatigue damage of the frame whose stress is the most complex on a truck.However the frame is a key component of a heavy truck,the merits and demerits of the fatigue life performance will directly affect the quality and safety of the heavy trucks.Therefore,the research on the fatigue characteristics of frame is particularly important.This paper takes the frame of a heavy truck as the research object and multi-objective topology optimization design of the frame is conducted based on variable density topology optimization theory.At the same time,anti-fatigue lightweight of the frame is researched.The main contents are as follows:(1)The topology optimization model of the frame is established.According to the quality of the parts and the full load of the heavy truck,the force of the frame is determined,and the restraint of the frame under the four typical conditions is analyzed.This paper uses the compromise programming method to transform the multi-objective optimization problem of multi-conditions stiffness and low-order frequencies into single-objective optimization problem.The weight coefficients of each sub-goal are calculated by AHP.The multi-objective topology optimization design is conducted based on variable density method,taking minimum compliance under static multi-conditions and maximum multi-low-order natural frequencies as the goal.(2)According to the topology optimization results and referring to the structure of the same type of heavy truck frame,the geometric model and finite element model of the frame are established.The static response of the frame is analyzed under the four typical conditions,which are bending condition,reversing condition,emergency braking condition and urgent turning condition.The stress distribution and deformation of the frame under the four typical conditions are obtained,and the strength of the frame is checked.The frame model analysis is conducted based on the modal theory,and the top ten order modal frequencies and corresponding model vibration mode are extracted.(3)A simplified dynamic model of the heavy truck is established based on the multi-body dynamics principle.Choosing the time-domain excitation signal of theC-level road as input,the load time history from the position where the frame and suspension connect is extracted.According to the material S-N curve,the load spectrum and the quasi-static stress results under unit load,the fatigue life of the frame is analyzed based on the nominal stress method and Miner’s linear cumulative damage method.(4)Taking the frame cross-beam and stiffener thickness as the design variables,the anti-fatigue lightweight model of the frame structure is established with the frame quality and the fatigue life as the optimization objectives.The anti-fatigue lightweight design of the frame is reached based on Kriging approximation model by using the multi-objective genetic algorithm(NSGA-II).The weight of optimized frame is reduced by 4.4% with the frame fatigue life slightly increased,and the frame still has good static and dynamic behavior.This paper completes a relatively comprehensive study on the anti-fatigue lightweight design of the heavy truck frame,and achieves the desired results.The research results of this paper have some significance on the actual development of the heavy truck frame.