CHASSIS DESIGN
This particular blog deals with a brief introduction to chassis design. Most of the people find it very difficult to find precise and appropriate content related to chassis design . A lot also find it a little boring as it does not contain videos in it.Here, I will.. try to share some info. step wise so that you don't find it boring.
First I will start with some basic types of Chassis
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Backbone Chassis
Lotus developed a different kind of chassis for its Elan sports car. It ran a fully enclosed tubular member through the center of the vehicle. Though this method definetly is trying to make a fully enclosed tubular member which directly relates to underlying theory, but because of the small size it makes it difficult to create a very ridgid chassis by todays standards.
Lotus Tub
The Lotus Tub is a development which progressed from the backbone chassis. Though not a direct evolution it is related by Colin Chapman’s development into light weight and is also a rather unconventional chassis. It takes many small cross sectional extrustions and glues them together to create large beams that run the length of the vehicle. Unlike Ladder Frame design the passenger actually sits between these large beam members providing a strong passenger compartment protecting against impact. The weaker passenger compartment is stabalized by the front and rear area which heavily connects the sides. The Lotus Elise and variants such as the Vauxall VX220 are a good example of this type of vehicle. It should be noted that this platform has become very common for startup companies to base a sports car on. Notable’s include the Tesla Roadster, Venturi Fetish, Dodge EV, Zytek Elise, and several others. It has evolved into the 2 + 2 called the Evora.
Monocoque
A monocoque is similar to that of a skinned space frame but witout a any underlying support through the monocoque area. It may built up of a material reinforcing the skin or more commonly using double wall honeycomb techniques. Monocoques use the outter body as a load bearing structure but in some cases it refers more to that its constructed of continous panels. In the case of aluminum chassis one can be constructed by rivits, glue, spot welding, or seam welding, and in the case of a fiber composite it can be glued or rivited.
Angular Monocoque
The Angular Monocoque is a full monocoque but uses flat panels constructed out of sheet metal. The easiest way to turn an edge is with a hard corner with flat sections. Curvatures are difficult to build in low volumes repeatably without a press and die. One aspect to watch for is stress concentrations when simulating as these bends and edges are stress risers. The simulation software is going to assume that these have similar strength attributes but in reality this may not be the case as the metal would need to be have been either annealed or normalized. The forced bending with strengthen the material but bring it closer breaking and less resistant to fatigue. Welding will also cause differening behaviour based on the type of weld.
Carbon Fiber Monocoque
Carbon fiber monocoques are similar to angular monocoques but have very little compressive strength but high tensile strength. The carbon fiber techniques can be used for glass fiber and kevlar based monocoques as well. The emphasis is on carbon fiber in the industry now as it is stronger and more ridgid than kevlar and glass fiber and in this respect designs can be made stronger and lighter than any other. Using a fiber composite allows for low volume repeatability of designs but simulation is difficult as layup technique and directionality of the material changes the overall properties in different directions.
First I will start with some basic types of Chassis
Ladder Frame
Two long beams that run the length of the vehicle and provide a strong support for weight and originally based on a carriage design. Body on frame achitecture is a good example of this type of chassis.
Space Frame
A nodal triangulated truss network that attempts to distribute all loads into axial directions so that no part of the frame is subjected to the harsher bending forces. A good example of this type of chassis is most Formula SAE chassis or a Lamborgini Countach.
Audi Aluminum Space Frame
A technology that blends mass manufactured monocoque design with large cross section aluminum members. The Audi R8 or the Lamborgini Gallardo is a good example of this type of chassis.
Skinned Space Frame
Rather than triangulate all members, a sheet of metal is either welded or riveted to the area. This acts as a multi-directional axial member in the tensile directions. It provides little compressive resistance due to its ease of buckling but by the nature of the space frame design one primary direction is always in tension.Formula One transition vehicles are a good example of this type of chassis. The Ferrari 126c introduced in the early 80’s is of this type but was not sufficient to compete against the composite chassis at the time.Backbone Chassis
Lotus developed a different kind of chassis for its Elan sports car. It ran a fully enclosed tubular member through the center of the vehicle. Though this method definetly is trying to make a fully enclosed tubular member which directly relates to underlying theory, but because of the small size it makes it difficult to create a very ridgid chassis by todays standards.
Lotus Tub
The Lotus Tub is a development which progressed from the backbone chassis. Though not a direct evolution it is related by Colin Chapman’s development into light weight and is also a rather unconventional chassis. It takes many small cross sectional extrustions and glues them together to create large beams that run the length of the vehicle. Unlike Ladder Frame design the passenger actually sits between these large beam members providing a strong passenger compartment protecting against impact. The weaker passenger compartment is stabalized by the front and rear area which heavily connects the sides. The Lotus Elise and variants such as the Vauxall VX220 are a good example of this type of vehicle. It should be noted that this platform has become very common for startup companies to base a sports car on. Notable’s include the Tesla Roadster, Venturi Fetish, Dodge EV, Zytek Elise, and several others. It has evolved into the 2 + 2 called the Evora.
Monocoque
A monocoque is similar to that of a skinned space frame but witout a any underlying support through the monocoque area. It may built up of a material reinforcing the skin or more commonly using double wall honeycomb techniques. Monocoques use the outter body as a load bearing structure but in some cases it refers more to that its constructed of continous panels. In the case of aluminum chassis one can be constructed by rivits, glue, spot welding, or seam welding, and in the case of a fiber composite it can be glued or rivited.
Angular Monocoque
The Angular Monocoque is a full monocoque but uses flat panels constructed out of sheet metal. The easiest way to turn an edge is with a hard corner with flat sections. Curvatures are difficult to build in low volumes repeatably without a press and die. One aspect to watch for is stress concentrations when simulating as these bends and edges are stress risers. The simulation software is going to assume that these have similar strength attributes but in reality this may not be the case as the metal would need to be have been either annealed or normalized. The forced bending with strengthen the material but bring it closer breaking and less resistant to fatigue. Welding will also cause differening behaviour based on the type of weld.
Carbon Fiber Monocoque
Carbon fiber monocoques are similar to angular monocoques but have very little compressive strength but high tensile strength. The carbon fiber techniques can be used for glass fiber and kevlar based monocoques as well. The emphasis is on carbon fiber in the industry now as it is stronger and more ridgid than kevlar and glass fiber and in this respect designs can be made stronger and lighter than any other. Using a fiber composite allows for low volume repeatability of designs but simulation is difficult as layup technique and directionality of the material changes the overall properties in different directions.
The details of all these types of chssis will be discusses in the next blogs
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