With the rapid development of China’s rail transit industry, as well as the new development concept of energy saving and environment-friendly, lightweight has become the focus of modern vehicle design and manufacturing. Carbon fiber composites have the characteristics of light weight, high strength, corrosion resistance, low cost, and easy to design, process and modify. It is an important means to realize the lightweight of car body.
- Material selection and structure design
The traditional subway cab cover is made of glass fiber reinforced plastic, which is made of carbon fiber foam sandwich material. It is made up of two thin and rigid carbon fiber composite panels as a light weight and high strength structure, which is composed of inner and outer panels and a thick and light foam core.
It has the characteristics of high specific strength, high specific modulus, good impact resistance, sound absorption, vibration absorption and heat insulation. The carbon fiber reinforced material is made of T700 and epoxy resin, and the sandwich core is T90.150 foam. The head cover of subway cab adopts the technology of autoclave integrated molding, and the windshield is installed in the middle, and the lamp mounting hole is reserved. In the sandwich sandwich structure of cab hood, the middle layer mainly plays the role of supporting panel and hood forming.
- Optimization of free size
According to the overall size layout of the inner and outer panels of the cab hood, the fiber orientation is arranged along the force transmission direction of the ply, and the shear and bending load requirements are integrated to maximize the high strength and rigidity of the fiber axial direction.
The number of ply directions should be as few as possible. Generally, four ply directions of 0 °, 90 ° and ± 45 ° are adopted. Among them, 0 ° ply is beneficial to the transmission and bearing capacity of axial force; ± 45 ° ply has buffering effect on shear load and has great help to improve process; 90 ° ply can control lateral stiffness and adjust Poisson’s ratio. In the actual structure fabrication of Bosch, the thickness of each layer is an integral multiple of the minimum single layer thickness, and a total of 16 layers of different shapes are used. The thickness of each layer is 0.15mm, and 6 / 6 / 2 layers of 0 °, 90 ° and ± 45 ° are respectively used.
3. Optimization of laying sequence
In the structural optimization design of carbon fiber composites based on laminates, it is necessary to optimize the stacking sequence. The stacking sequence of composite materials not only affects the mechanical properties of carbon fiber laminates, but also affects the process.
Because the shape of each layer is cut in the free size optimization, many of the layers are not fully covered in the inner and outer panels of the hood, so the layout of the laying sequence is the overall layout, and the actual laying in the local area of the hood will be different.
In order to improve the overall forming performance of the foam core sandwich structure of the cab hood and avoid the sudden change of the stepped thickness in the thickness change area of the laminate, the inner and outer surfaces of the sandwich laminates should be fully covered to cover the overall structure of the hood. At the same time, in order to improve the impact resistance of the head cover, a full-scale layer of ± 45 ° was added in the outermost and innermost layers of the optimization results of the stacking sequence.
4. Determination of optimization results
After a series of optimization design and continuous modification of laying technology, the final quality of the carbon fiber cab hood is 27%. The full-size and equal thickness structure before optimization is 188.4kg, and the optimized quality is reduced by about 137.5kg. The original fiberglass cab hood quality is 218.4kg, and the quality of the CFRP foam sandwich structure is adopted. It decreased by about 37%.
The structural redundancy can be avoided and the structural stress can be increased by optimizing the composite laminate structure, reasonably arranging the materials and exerting the potential properties of the materials. Under the condition of meeting the requirements of strength, stiffness and stability, the ideal lightweight effect is achieved.