The casting material of tractor gearbox housing is nodular cast iron QT450-10. The material properties are given to the meshed finite element model, and the material parameters are shown in the table.
| Part name | Material Science | Material properties | Poisson’s ratio | Modulus of elasticity / GPa | Density / kg / m3 | Mass / kg |
| Gearbox housing casting | QT450-10 | MAT1 | 0.27 | 169 | 7100 | 164.8 |
Nodular cast iron QT450-10 is composed of single crystals arranged irregularly in multiple directions. Its physical properties are identical and do not involve the influence of temperature. Therefore, the material property is defined as mat1. Its tensile strength and plastic properties are good. In terms of mechanical properties, its tensile strength is greater than 450MPa and its conditional yield strength is greater than 310mpa, indicating that it has strong fracture resistance and its elongation is greater than 10%. These parameters are the key parameters for static analysis and topology optimization.
In order to ensure the safety of the tractor gearbox housing casting in actual work and ensure that the maximum stress value of the tractor gearbox housing casting under various working conditions is less than the allowable stress of the material, an appropriate safety factor should be selected, as shown in the following formula:
Where:[σ]— Maximum allowable stress; σu – ultimate stress; Ns – safety factor.
The selection of safety factor needs to comprehensively consider the mechanical properties and economic problems. Generally, the value range of safety factor for static load is 1.2 ~ 2.5. Due to the complex working environment of tractor gearbox shell casting, the safety factor is 2.5. According to the formula, the allowable stress of QT450-10 material is 124mpa.