Study On The Vibration Characteristics And Structural Optimal Design Of The Concrete Pump Truck

This paper, takes the arm set of the concrete pump truck as the object of study, aiming at the vibration and fatigue crack engineering problems, adopting the combinative method of theory, test and computer simulation, therefore the composite researches on the system are carried out. The hydraulic system simulation model, the FEM analysis model, the kinetics simulation model and the dynamic structural optimal design model are founded. Using the correlative software, the calculation and the analysis works are done and four large experimental researches are carried as well, and the reasons of the key problems are found out. Moreover, the dynamic optimal designs of the actual structure are completed and the modify projects are put forward. The main research contents can be summarized as follows:1. By the hydraulic impact simulation study and the experimental research, the fundamental reason of the arm's violent vibration is the hydraulic impact which caused by the improper matching between the response time of dividing circuit and the operation time of rod piston. It is the fist time to use the cooperating time graph of the "s" pipe value and the pumping cylinder to describe and analyze the perfect swing time of the pumping cylinder and the swing cylinder. At the same time, the concept of "the impact intensity" is put forward to describe the hydraulic impact. The relationship between the impact intensity and the work frequency, pressure, discharge rate, etc. are established. This gets the proper pump rate of the pump truck and provides enough accordance and test data for the analysis of hydraulic system. In order to solve the hydraulic impact, the method of adding multi-grade control electro-circuit is brought forward, which used to change the trigger time to cooperate with the exchange time of the dividing circuit.2. By the structural modal analysis and the experimental research, it is found that the work frequencies and the first inherent modal frequency of the arm set of the pump truck are partial overlapped, and this gives a cut-in point for us to solve the actual problems. There are two ways to reduce the vibration. First, by changing the dimension and the mass of the structure, we can improve or reduce the inherent modal frequency of the arm to keep away from the work frequencies. Second, we can improve and reduce the work frequency to keep away from the first inherent modal frequency of the arm.3. By changing the parameters of mass and stiffness and the hydraulic impact load, the kinetic vibration characteristic response simulation is accomplished. It is found that theresponse of vibration displacement of the arm coincides with the hydraulic impact load in shape and size, and the vibration displacement decreases with the reduction of the impact value. So, cutting the peak value of the hydraulic impact is an effective method to minimize the arm's vibration.4. Based on the theory of FEM, via MSC/NASTRAN software, the static and dynamic stress analysis and the experimental research of the concrete pump truck have been accomplished. The maximum stress points have been got. These provide the dependences for the structural fatigue design.5. By the contrast fatigue tests of different style weld joints of pump truck's main material, the fatigue strength S-N curve P-S-N fatigue curve and the Goodman fatigue endurance limit figure are set up. This provides the data for the fatigue design and calculation. The experimental results indicate that the yield strength and the tensile strength of the welded joints are much lower than that of the arm steel. Through scanning the fatigue fracture with the electron microscope, it is found that the fatigue points are at the welded collar and at the bottom of the welded seam which is not fully welded. So, the weld techniques should be reformed to improve the fatigue strength of the welded seam.6. Using the hydraulic experimental load and the P-S-N fatigue curve of welded joint, under the possibility of 50% and 95%, the fatigue life study on the arm of the pum...