Engineering Report

Chassis Design – Corvette C7

Type of Chassis: Tubular space frame chassis. Material used: AISI 4130. Manufacturing process: Metal inert gas (MIG) welding. Types of tubes used: Round tube, Square tube. Assumptions undertaken while designing:

1. The car will be rear wheel drive with engine and powertrain unit mounted in rear.

2. Independent double wishbone suspensions will be used as suspension system for the car.

3. Hard points for the independent suspension were chosen arbitrarily as main focus was on designing of chassis.

4. Tubular space frame chassis was designed according to dimensions of the Corvette c7 cad model provided.

Material choice for chassis: With the choice of material between AISI 1020 and AISI 4130 the latter was chosen for the construction of tubular space frame chassis based on following stat table.

Mehcanical Properties AISI 1020 AISI 4130 Tensile strength, ultimate 395Mpa 560 Mpa

Tensile strength, yield 295Mpa 460 Mpa Poissons ratio 0.29 0.27-0.30

Modulus of Elasticity 200 Gpa 210 Gpa

Density 7.9 g/cc 7.85 g/cc

From the above mentioned information it can inferred that AISI 4130 will have a higher strength to weight ratio compared to AISI 1020, this will contribute in increased torsional rigidity of the chassis while focusing on weight which will be relatively lighter compared to AISI 1020 tubular space frame. This is very much desirable for high performance sports car like Corvette C7 which led to choice of this material. Also AISI 4130 steel has good strength and toughness, weldability and machinability. Manufacturing processes: 1. Laser cutting: The round tubes will have to be laser cut to generate a fish mouth structure at the ends of the tube before assembly and welding. 2. Welding: Welding of AISI 4130 steel can be performed by all commercial methods. However MIG welding was chosen over other welding processes because of its high welding strength and also ease of welding. 3. Heat Treatment: Due to stress concentration at welded joints, AISI 4130 tubular space frame would be required to be heat treated to relieve all internal stresses and increases the strength of the chassis.

Selection of tubes and dimensions: Round and square tubes were used for designing of tubular space frame chassis. The dimensions of tubes used are as follows: 1. 25 x 2.5 mm – Round 2. 19 x 1.65mm - Round 3. 14 x 2 mm – Round 4. 20 x 15 mm – Square

The round tubes with dimensions 25 x 2.5 mm was chosen for main roll bars of the chassis. Main roll bars would be highly stressed under dynamic conditions of the chassis and these tubes were chosen to be with greatest outer diameter and thickness in the entire frame.

The round tubes with dimensions 19 x 1.65 mm was used to connect frontal impact structure, cockpit and rear engine bay and 14 x 2 mm round tube was used as triangulation tube to increase overall torsional rigidity of the structure.

The square tube with dimensions 20 x 15 mm was used as bottom rail of the frame as square tubes take greater bending loads such as of driver, engine and entire powertrain unit whereas round tubes have greater torsional resistance.

(*All tube dimensions were chosen in accordance with my past experience in FSAE design competition.) The Design: The design was done using 3d sketch and Weldment features of solidworks 2014 keeping in mind the rule of triangulation to avoid shear stresses and induce just tensile and compressive stresses in the frame.

Assembly:

Figure 1 Assembly of tubular space frame with the body (rear view)

Figure 2 Assembly of tubular space frame (Front view)