Design of natural- rubber panel railroad crossing using finite element method

Thailand has a railway system that is available throughout the country, so there are several railroad crossings. These crossings are generally made of concrete or logs with multiple constraints. There are some disadvantages of concrete railroad crossing, such as, crack, noise during car passing over. To overcome these disadvantages, the softer materials should be used instead. Therefore, this research proposes the natural rubber, widely grown throughout Thailand, panel railroad crossing. However, the natural rubber alone is not enough to withstand the harsh condition. Thus, it is necessary to have some addition ingredients that will enhance the natural rubber properties. The material used in this research is a rubber compound between Chloroprene Rubber (CR) 75% and Natural rubber (NR) 25% blend with additives such as carbon black (CB), magnesium oxide ( MgO) and sulfur ( S8) . The objectives of this article were to analyze the deformation of the natural rubber panel railroad crossing and to evaluate its safety factor, defined as the ratio of strain at break and the maximum equivalent strain, using finite element method. In the analysis, the applied loading of the model was obtained from the State Railway of Thailand. The analyzed results reveal that the deflection of rubber panels passes the standard from State Railway of Thailand. Safety factor of external rubber panel is 27.03 and for internal rubber panels are 9.12 and 15.29. The metal pads had elastically deformed and concrete railroad sleeper deformation was very small.


Introduction
Thailand in one of the countries that has the highest production capacity of rubber in the world. Although Thailand's rubber exports around 87% , export revenues are about 193,067 million Baht per year, but domestic processing about 13. 4% of rubber can generate about 230,000 million Baht annually. Thailand is experiencing several problems with natural rubber, such as the volatility of raw rubber prices, the problem of natural rubber production that does not meet the market demand, the problem of the quality of raw rubber, the problems of the rubber market and competitors from the other countries.
Therefore, Thailand focuses on the development of rubber processing industry in the country to increase the amount of rubber before selling, it will increase revenue for farmers. At present, the railroad industry is growing in the future due to investment in the development of the rail system in Thailand. The BTS network in Bangkok and the government's " nationwide double-track railway project ". According to the State Railway of Thailand. Currently, Thailand has a railroad track of approximately 4,346 kilometers. There are more than 2,500 railroad crossings across the country. Generally, these crossings are made of concrete or logs. The disadvantages of using these materials are lifetime limit, cracking problem, damaged concrete cushions due to impact with crossing panels. Additionally, there are problems in rainwater drainage and in noise generation during the cars passing through. The vehicle passing through must slow down, resulting in traffic problems at the intersection. Concrete and logs are brittle material that are not resistant to repetitive force. Breaking or cracking causes accidents and wastes the repair budget. The problem can be solved by finding materials that can withstand repeated repetitive forces. Rubber is a good choice. The advantages of using rubber to produce rubber crossing panels such as rubber are soft material, no rupture, good for vibration and silence while the car runs through. There are also promoting the use of rubber in Thailand, design and production of prototypes that are feasible to commercialize by Thai companies. The design of the workpiece should be appropriate for the actual use, including the finite element method for deformation and the estimated lifetime of the rubber panels. If the project is successful, it will be a key variable for the country and the government. As a result, the country's economic, social, agricultural and security development has increased. The Institute hopes that the project will be able to respond positively and significantly to the government.

Material properties
Initially, the analysis needed to determine the material properties. The material used is the compound rubber that has been researched and develop a formula for support the impact between the rails and concrete pillars. The chemical composition is given in Table 1. The mechanical properties of the rubber are derived from the tensile test data, as shown in Fig 1. Table 2 shows the derived mechanical properties. Moreover, the rubber hyperelastic properties were also considered in this paper and Yeoh's model was employed.  Yeoh 3 rd order model is the most suitable model that can predict behaviour of compound rubber and its constitutive model is given in equation 1.

Loading and Boundary condition
Analysis of 3D problems by finite element method was done using ANSYS workbench program. The load is coming from vehicle wheel. The load value is 22.  The contact relation between two internal rubbers are suppressed because the installation is done by inserting the two panels together without adhesive or fastener. The contact between rubber panels and metal pad was set as rough contact. For other contact relation set as bonded contact, they cannot separate from each other. The centre of contact between the two panels is wedge-shaped, which support assembly and allows the rubber to not separate from one another while the vehicle is passing.
The wheel on this model is assumed to be a rigid body.

Safety factor
The rubber panels safety factor calculates by equation 2.
The metal pad safety factor calculates by equation 3.   The equivalent strain of external rubber panel shows as sample because this part is most deflated. Unit of equivalent strain is mm/mm.   Maximum stress that occurs in metal pad is 83. 943 MPa at point 2 loading. But the yield stress of this component is 250 MPa, according to mechanic properties of structural steel. That' s metal pad just occurs elastic deformation and can be recovered to the initial shape. In case of the concrete railroad sleeper, it also has deformation from contact with metal pad. The deformation occurs very small section in millimeter unit but permanent. The most deformed area is loaded at point 1. Sample picture of the simulation results from loading on the external rubber panel shown below.

Conclusions
The rubber has suitable properties and can be used in real production the external rubber panel deflection is 27.332 mm. For internal rubber panels maximum deflection is 22. 614 mm from loading at point 2. Safety factor of external rubber panel is 27.03. Safety factor of internal rubber panels are 9.12 and 15.29. The deformation according to metal pads that support below rubber panels. Metal pads also deflection from load, but the deformation of metal pad occurs in elasticity period. The concrete railroad sleeper very small section. From the analysis result can be estimated that the model can be used.