Finite element analysis of the body frame of the h

Finite element analysis of bus body skeleton

I. preface

is an indispensable testing equipment for physical experiments, teaching research, quality control and so on

in recent years, the state has issued a policy to speed up the mandatory scrapping of large buses, which has promoted the strengthening of transportation and urban infrastructure construction in all regions, and the market demand for large and medium-sized urban buses required by bus passenger transport has gradually expanded, People's requirements for buses also tend to be high-speed, comfortable, stable and reliable. This puts forward higher requirements for the design of passenger cars. In order to meet the design requirements, optimize the passenger car design and shorten the design cycle, CAE technology plays an increasingly important role

the body frame is the main bearing structure of the bus, accounting for almost half of the weight of the whole vehicle. Whether its strength and stiffness meet the design requirements determines the rationality of the overall design of the bus. This paper mainly uses ANSYS finite element software to calculate and analyze the body frame of a 12 meter Yellow Sea bus

II. Establishment and simplification of finite element model

establishing the finite element model of the body framework should not only truthfully reflect the important mechanical characteristics of the actual structure of the bus body, but also try to use fewer elements and simple element forms to ensure high calculation accuracy and save calculation time. When establishing the finite element model of the body structure, according to the structure of the body and its bearing characteristics, some necessary simplifications are made: the body frame is simplified into a spatial frame structure, ignoring the influence of the body skin on the strength and stiffness of the overall structure of the body, and ignoring some non bearing elements that have little influence on the deformation and stress of the overall structure

according to the structural characteristics of the spatial bar structure of the bus skeleton, which is welded by rectangular steel tubes, the node is generally selected at the intersection of the members, and the member connecting the two nodes is regarded as a unit. Because the joints of the skeleton structure are generally used to transmit axial force, bending moment and shear force, the members are generally taken as beam elements in the calculation, which are simplified into a spatial rigid frame finite element calculation model composed of spatial beam elements. This modeling mainly adopts ANSYS beam 188 element and shell 181 element. The finite element model of the whole vehicle skeleton established by this analysis is shown in Figure 1

Figure 1 skeleton finite element model sketch

2.1 boundary constraint treatment

the characteristics of the semi loaded bus body are that the body skeleton is rigidly connected with the frame, and the frame is connected with the axle through the suspension system. Different suspension systems have a great impact on the strength and stiffness of the frame and bus frame. In order to make the boundary constraints more in line with the service conditions, the suspension elements and the frame are combined. The actual structure of suspension is simulated by beam element

2.2 load handling

the body bears a lot of loads. In terms of its load nature, the main loads the body receives are bending, torsion, lateral load and longitudinal load. In addition to the mass of the frame itself, there is an additional mass. The added mass includes the mass of body skin, glass, powertrain, spare tire, battery, radiator, compressor, fuel tank, driver's seat, passengers, luggage, chassis assemblies and engine, etc. Complete experimental reports and curves can be printed out immediately after processing; When loading, the mass of the body frame is uniformly distributed on all components of the frame; Passengers, the seat mass is equivalently allocated to the floor support according to the passenger car seat layout, and the corresponding nodes are set at the seats; The floor quality is treated according to the uniformly distributed load acting on the underframe; The mass of underframe assemblies, engines and attachments acts on the nodes at the support points

2.3 calculation conditions

considering the operation characteristics of the vehicle, this calculation and analysis mainly discusses eight working conditions: bending under dangerous full load conditions (i.e. there are equipment self weight, seats and standing passengers, a total of 80 people), bending with 2.5 times the dynamic load, right rear wheel suspension, left rear wheel suspension, braking, left turning, right turning, and starting

III. analysis of calculation results

because the car is a rear mounted car, the rear load is relatively large, and the center of gravity of the whole car is increased due to the recent installation of air conditioners, natural gas cylinders and other heavy objects on the top. We have carried out static simulation calculation and analysis of common vehicle operation conditions, and found that the local stress value is too large through trial calculation

3.1 the comparison of the maximum stress values under various working conditions is shown in Table 1: unit MPa Table 1: comparison of the maximum stress values under various working conditions

comparison of stress nephogram under typical working conditions (because there are many nephograms, only lifting working conditions and left turning working conditions are listed here):

from the stress distribution nephogram, we can also see that: under the suspension condition of left and right rear wheels, the transverse support beam at the rear of the frame is under great stress; Under the bending condition of 2.5 times the dynamic load coefficient, the stress value at the connection between the side wall column and the bracket is larger; The maximum stress value appears at the connection between the side beam and the fixed slot beam of the air conditioner under left and right rotation conditions The following is a list of the maximum stress values and positions of each assembly under various working conditions

4 comparison and analysis of the maximum stress value of each assembly

4.1 the comparison of the maximum stress value of each assembly is shown in Table 2 below: unit MPa

working condition the maximum stress value of the assembly (MPA) and position bending working condition the floor beam 43.203 left front wheel front floor right side wall 43.983 rear wheel rear bracket and side wall column connection left side wall 49.879 rear wheel rear bracket and side wall column connection top cover 43.812 left beam is bent at the air conditioning fixed channel beam connection (2.5 times the dynamic load) Working condition floor beam 108.007 left front wheel front floor right side wall 109.958 rear wheel rear bracket and side wall column connection left wall 124.697 rear wheel rear bracket and side wall column connection top cover 109.529 right beam at air conditioning fixed groove beam connection left rear wheel suspended working condition floor beam 103.421 left rear wheel rear support beam right wall 112.587 rear wheel rear bracket left wall 51.987 rear wheel rear bracket and side wall column connection top cover 66.717 left beam at air conditioning The right rear wheel at the connection of the fixed trough beam is suspended. The floor beam is 94.012. The speed of the right rear vehicle is about 300km/h when the train is running. The right side of the rear wheel floor is 49.481. The left side of the connection between the rear wheel bracket and the side wall column is 86.511. The top cover of the connection between the rear wheel bracket and the side wall column is 43.277. The left beam is at the connection of the fixed trough beam of the air conditioner. The left turning condition floor beam is 97.222. The right side of the rear wheel support beam is 92.734. The window column above the rear wheel is connected with the waist beam Connection left side wall 108.682 connection between rear wheel front bracket and bottom side beam top cover 128.997 connection between top cover ninth bent beam and right side wall right turning condition floor beam 103.856 right rear wheel rear floor support beam right side wall 104.117 connection between rear wheel front bracket and bottom side beam left side wall 101.619 connection between rear wheel upper window column and waist beam top cover 138.257 connection between top cover ninth bent beam and left side wall starting condition floor beam 44.941 right rear wheel rear floor right Side wall 57.78 connection between door column and top cover left side wall 50.931 connection between rear wheel bracket and side wall column top cover 38.924 left beam at the connection of fixed channel beam of air conditioner braking working condition floor beam 67.071 left rear wheel rear floor right side wall 47.386 rear window column left side wall 53.547 rear window column top cover 52.365 left beam at the connection of fixed channel beam of air conditioner

4.2 comparison of assembly stress nephogram under typical working conditions

4.2.1 starting working condition:

4.2.1 left Turning conditions:

4. Conclusion

through the static calculation of the vehicle under various operating conditions and the comparative analysis of the assembly stress under various operating conditions, it is found that there is a phenomenon of large stress value in local places. Because the calculation adopts the analysis under the limit state, the probability of this limit condition under normal operation is small, but because the vehicle is equipped with air conditioning and natural gas cylinders on the top, the center of gravity is high, In sharp turns and braking, there will be instantaneous excessive stress. Considering the road conditions of the vehicle, pay attention to several parts with large stress values in the calculation and the places where damage often occurs during the test. Carry out targeted two-wheel improvement design according to the test results. At the same time, pay attention to the vibration of the vehicle body when carrying out washboard pavement and cobble pavement, and see whether there is local resonance through the natural vibration shape of the vehicle body obtained from modal analysis. (end)