The stress-strain state of the universal chassis of the tractor trailer in T-Flex

This article discusses the calculation of the strength of the frame structure of the universal chassis of the tractor trailer in the T-Flex software package and the comparative analysis of the results with experimental data and model data based on the principle of virtual work (possible movements).


Introduction
It is well known that the cultivation, collection, and storage of agricultural products is one of the most important tasks for all countries, including our republic. As demand for products grows, an important factor in achieving this goal is the production of inexpensive, efficient, and durable equipment used to grow, harvest, and transport it. One of the ways to solve this goal is to develop trailers with a universal chassis. Several large world companies JOCKIN (Belgium), ANNABURGER MultiLandPlus (Germany), Fliegl Agrartechnik (Germany), Cargo (Germany), and others, are engaged in the development and production of trailers with a universal chassis [1]. Similar tractor trailers are planned to be produced in Uzbekistan at the Tashkent Agricultural Machinery Plant. Priyanka Ranu, Rajeev Singh Chauhan, Dr. V. N. Bartaria [3] used ANSYS to analyze the strength of the chassis frame with a force of 58860 N. The calculations were performed for 3 different materials: steel, fiberglass, and carbon fiber. Analysis showed that carbon fiber material caused less deformation and stretching compared to fiberglass and steel material.
Divyesh N. Chaudhari, prof. Vinod M. Makwana, prof. Dharmeet J. Patel [4] focused on optimizing the chassis frame design, taking into account the movement of wheeled vehicles under dynamic, static, and cyclic loads. The chassis frame model was created by computer programs. Based on the analysis of the model, the weight and material of the structure were changed.
Mohd Azizi Muhammad Nor and others [5] carried out a comparative analysis of the data on the chassis load of a 35-ton trailer in the CATIA V5R18 software package and the data analytical calculations. The results showed good agreement between the values of the maximum torsions and some difference in magnitude.
The T-FLEX CAD computer complex is widely used in the CIS countries [6]. T-FLEX CAD is a computer-aided design system (CAD) with all modern tools for developing projects of any complexity. The program has powerful parametric 3D modeling capabilities and combines documentation and design tools. It is professional CAD software that combines the powerful parametric capabilities of 2D and 3D modeling with tools for creating and designing drawings and design documentation for a unified design documentation system.
To theoretically substantiate the frame of the universal chassis of the tractor trailer, which is the main element of the chassis, we use the algorithmic program T-Flex.
There are several advantages to using the T-Flex software. First, the operating system of the program is in Russian and is user-friendly. Secondly, its standard library is large, and the elements used to comply with the standards used in our country.

Methods
Let calculated the stress-strain state of the universal chassis of the tractor trailer in T-Flex CAD and received comparative analysis of the results.
The virtual model of the universal tractor trailer chassis in the T-Flex software package is shown in figure 1.
T-Flex CAD uses the finite element method for structural analysis. The finite element analysis program generates a system of equations, assumed initial and boundary conditions. The system of equations is solved to unknowns and is the values of characteristics within the elements. The principles of virtual movement are used to create equilibrium equations. To perform computational work using the T-Flex CAD software package, the following values of the material used in the trailer frame, initial and boundary conditions were taken. Compressive strength: 3.99826E + 008 N / m2 Heat capacity: 440 J (kg • K) 2. Boundary conditions: Where the frame is connected to the springs, the rods are securely fixed on the turntable, the load F = 66000 N acts on 4 points of the frame, the temperature is T 0 = 298 K (25C). 3. Initial conditions: initial values of stress and displacement of frames are equal to zero. Dividing the model into finite elements in the form of a tetrahedron. The minimum and maximum values of stress, displacement, and equivalent frame deformation are presented in Table 1.  The system of general equations of forces and moments acting on the spar (taking into account bending and torsion) is as follows [8]: 12   6  12  6  0  0  3  2  3  2   6  4  6  2  0  0  2  2  1  1  12  6  12  6  1  1  0  0  3  2  3  2  2  2  6  2  6  4  2  2  0  0  2  2  1  1  k  k  2 2

Equivalent of deformation
shows the design diagram of the frame structure, taking into account the influence of elastic springs. When constructing the design scheme of a thin-walled bar, consider its "middle" surface, which passes through the middle of the elements that form the bar [9]. The trace of the middle surface in the plane of the cross-section forms the profile of the section ( figure 5). According to the profile outline, two types of rods are distinguished: -rods with a closed profile; -rods with an open profile. The system of equations was implemented in the Basic program. Based on the calculations of the frame of a tractor trailer with a carrying capacity of 4 tons, the maximum stress in the spar was determined, which was 106 MPa.
The experimental value of the maximum stress in the spar was 102 MPa, and the calculated maximum stress according to the T-Flex program was 104 MPa (figure 6).
The relative difference in the values of the maximum stresses in the side member of the tractor trailer frame is less than 4%.
The calculations were made for a static load, considering the safety factor k equal to 1.5 and the dynamic factor k d equal to 1.

Conclusions
Analysis of the graphs shows that the value of the maximum stress obtained using the T-Flex program is 104 MPa. If we take into account that for a spar with the material -steel 25 and a yield point σ Т = 274 MPa, the permissible stress when calculating for bending by a static load has a value [ ] = ⋅ д = 274 1,5⋅1 = 182. 7 MPa, where k is the safety factor; k d is a dynamic coefficient, then for the selected geometrical parameters of the spar of a 4-ton trailer satisfy the strength conditions when driving on an asphalt concrete road. Using this method, calculations were also carried out for cases where the safety factor is k = 1.5 and the dynamic factor is k d = 2.5. The maximum stress value for the T-Flex program was 234 MPa, for the Basic program, 237 MPa, and the experiment, 256 MPa. Comparative analysis shows that the results of the maximum stress in the spar obtained using the T-Flex program correlate well with the experimental data (8.6%) and the results obtained using the Basic program (1.3%). The maximum stress obtained for the adopted safety and dynamic factors satisfies the strength conditions. Thus, a comparative analysis of the results obtained showed that using the T-FlexCAD software package, it is possible to calculate, with an accuracy of 9%, the characteristics of the static (dynamic) strength of the frame structure of a tractor trailer of a universal chassis.