- Detail

The semi-trailer tank car is a special vehicle for transporting liquid substances. Because of its flexibility, convenience, short manufacturing cycle and other advantages, it has become one of the main transportation equipment for water, fuel, acids, beverages, milk and so on. The environment of tank car is changeable during transportation, and the design and manufacturing requirements are high, so it must be reliable, economical and reasonable. The design and manufacture of tank is the most important factor, so it is necessary to analyze its strength. In view of this, this paper makes a finite element analysis on a cut-off point pressure insulated semi-trailer tank car developed by our company, which mainly meets the qualification standard, carries out a stress test on its hydraulic test, and compares the calculated value with the test value, so as to fully understand its stress distribution, and finally get a more safe and reasonable design scheme

2 finite element analysis

2.1 basic assumptions and simplification

(1) the tank is linear elastic or solvable. Researchers acknowledge that some limitations in the model solve some of the problem systems that cause this weather

(2) the tank body and the loading medium are isotropic, and the density is evenly distributed

(3) process factors such as small fillets in the structure are not considered

2.2 selection of element type

according to the basic theory of finite element analysis, whether the selection of element type is appropriate or not has a direct impact on the accuracy and speed of calculation. Plate and shell structure refers to a thin-walled structure whose size in one direction is much smaller than that in the other two directions. Generally, when the ratio of thickness t to the minimum dimension L in the other two directions is less than 1/10, it can be regarded as a thin-walled plate. Most of the components that make up the tank body and frame are thin-walled components, and the section thickness meets the assumption of thin-walled components compared with the length of the other two directions, so the use of plate and shell elements is appropriate. Comprehensively considering the structure and stress characteristics of the tank, the 4-node quadrilateral element shell181 element is selected. There are six degrees of freedom on each node of shell181 unit, namely, the displacement degrees of freedom UX, uy, UZ along the coordinate axis and the rotation degrees of freedom ROTx, ROTY, Rotz around the coordinate axis

the whole structure is basically symmetrical to the left and right, but considering the design of the wave plate inside the tank, a complete model of the whole vehicle is still established, as shown in Figure 1. The mesh division of the model can be conveniently and quickly divided by using the meshtool tool of ANSYS software and selecting the appropriate face and side length size

Figure 1 vehicle solid model

2.3 material characteristic parameters and boundary condition treatment

the vehicle is mainly composed of tank assembly and frame assembly. The materials used are SUS304 and Q345A respectively. See Table 1 for the characteristic parameters of materials. Table 1 brief table of material characteristic parameters

because the actual deformation of the car is very small relative to the deformation of the whole tank, the main purpose of this paper is to analyze the tank, so the influence of leaf springs is not considered here, and the following constraints are simply handled:

(1) fixed constraints are used at the corresponding position of the suspension

(2) adopt fixed restraint at the corresponding position of the traction pin

the calculation conditions correspond to 0.03mpa and 0.06mpa under full water pressure under hydraulic test respectively. The load is applied as:

(1) the gravity load generated by the self weight of the tank car, that is, the inertia load with the size of g=9.81m/s2 is applied in the negative direction of the Y axis

(2) apply the pressure load of liquid self weight, consider that the punching medium is water, and load according to the pressure gradient

2.4 analyze the calculation results

according to the calculation result picture, it can be found that the maximum stress of the tank body appears at the bending of the head. The stress of the rest of the tank is low. This is mainly caused by the unreasonable bending radius during the manufacture of dished heads. Under the working condition of hydraulic test (the pressure is greater than 2G load vertically downward), figure 2 shows that when the water is full of stamping 0.03mpa, the maximum stress of the tank is 214mpa, which has reached the yield limit of the material; When the water is full of 0.06mpa, the material has yielded in a small area of the head. Therefore, damage is more likely to occur at the bend of the head. In addition, the stress of the rest of the tank must be kept low to save resources, which is absolutely safe

Figure 2 cloud diagram of von Mises stress distribution when water is full stamping 0.03mpa

3 stress test

3.1 test process

when the static stress at a specific point on the tank body and frame of the car (with a rated load of 30t) is measured by electrical method, the wheels, insulation layer and guardrail of the tank car are removed, and special supports are made and placed at the corresponding positions of traction pin and suspension respectively

ye2539 static resistance strain gauge of Jiangsu Lianneng Electronic Technology Co., Ltd. is used as the measuring instrument. Before the test, according to the results of finite element software analysis and considering the actual situation, the measuring points are mainly arranged on the left half of the tank body, and a small number of strain gauges are pasted on the right half of the tank body

considering that the cross-section shape of the tank is composed of eight arc lines with different radius of curvature, the direction of the principal stress is easy to determine under the hydraulic test condition, so the unidirectional strain gauge is mainly arranged on the tank

3.2 analysis and comparison of test results

due to the large number of test data, we now take out the working condition of 0.06mpa full water stamping during the hydraulic test for comparison. In order to get the stress value of the measuring point, the stress of each point is calculated according to the formula of material mechanics

unidirectional stress σ= E ε

the analysis results of some test points corresponding to the electrical test under the same working conditions are extracted from the finite element model. The location and stress distribution of the points are shown in Fig. 4 ~ 6. Due to the different positions of patches, they need to be converted into local cylindrical coordinate system according to different structures. Compare it with the finite element calculation results, as shown in Table 2 (the data of all other test points are omitted). Figure 3 more clearly shows the relationship between the calculated value and the test value

Figure 3 Comparison of calculated and measured values

Figure 4 radial stress nephogram of head

Figure 5 radial stress nephogram of middle part of tank

Figure 6 radial stress nephogram of middle and lower part of tank

4 conclusion

(1) semi trailer tank car is a very important means of transportation, and the key point of its design is the design of tank body. The calculation results under hydraulic conditions are given by using the finite element software ANSYS, which verifies the reliability and feasibility of the design

(2) the stress of the liquid tank car is successfully tested by the electric measurement method. Under the same working conditions, the results are compared with the finite element calculation results, and the two data are in good agreement

(3) according to the calculation and test results, the tank design can be further optimized to make the design more reasonable and reliable, and improve the market competitiveness of products. (end)

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