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January2015
Plastics are the most commonly used type of polymer. Plastics include a very wide range of materials that can be used for everything from body panels to bonding metal. Below is a chart designed to make it easier to understand this group of materials. The list is not absolute but covers the principle automotive plastics.
| Material | Type | Properties | Uses | Commercial Names |
| ABS (Acrylonitrile Butadiene Styrene) |
Thermoplastic | Very strong and tough; good resistance to heat deformation; good electrical properties. | Bumpers, dashboards, interior door panels; generally used because of its resistance to wear and tear and good deformation properties. | Abson, Delta, Cycolac, Denka, Magnum, Novodur, Terluran, Toyolac |
| Acrylics (poly-methylmethacrylate) |
Thermoplastic | Average mechanical properties but excellent for transmitting light with good resistance to weathering. | Transparent features; previously used for dashboard lighting. Can be used with a light source to create interesting surfaces in low light. | |
| Fluorocarbons (PTFE / TFE) |
Thermoplastic | Very low coefficient of friction; very good electrical properies; chemically inert under virtually all conditions. Can be used up to 260ºC | High-temp electronic components; anti-adhesive coatings; anti-corrosive seals; bearings. Used generally to keep surfaces protected, clean and smooth. | |
| Polyamides (nylons) |
Thermoplastic | Strong and tough; resistant to abrasion; low coeffiecient of friction; absorbs water and several other liquids. | Bushes and light-loaded gears and bearings. | |
| Polycarbonates | Thermoplastic | Transparent; low water absorption; ductile; good resistance to impact; average chemical resistance. | Headlight lenses, non-shatter sports car windows. Hardness is insufficient for daily use for windows on production vehicles (surface deterioration). | |
| Polyethylene (PE) |
Thermoplastic | Low strength, poor resistance to weathering; low coefficient of friction; electrically insulating. | Battery parts; not substantial enough for most automotive applications. | |
| Polypropylene (PP) |
Thermoplastic | Cheap; good fatigue strength and electrical properties; chemically inert; poor UV resistance; resistant to heat distortion. | Bumpers | |
| Polystyrene | Thermoplastic | Interior trim; cheap alternative for low demand transparent applications (eg. interior light lenses). | ||
| Vinyls (usually Polyvinylchloride – PVC) |
Thermoplastic | |||
| Polyester (PET / PETE) | Thermoplastic | |||
| Epoxies | Thermoset | |||
| Phenolics | Thermoset | |||
| Polyesters | Thermoset | |||
Carbon fibre is a composite material made from embedding fibres of carbon in epoxy resin. The process, in its simplest form involves laminating layers of fibres (usually as matting) with epoxy before curing.
Carbon fibre has many particular advantages in weight and performance but is held back by expensive fabrication, repair and recycling processes. The beauty of carbon fibre is that it can be fabricated in such a way that directional performance (in terms of response to force applied) can be manipulated to give the best possible results in virtually every circumstance. Whilst a material such as steel will have desirable performance when subjected to forces in certain ways or from certain directions, weaknesses will remain. The ability to arrange fibres to suit the particular forces affecting a component mean more areas of weakness can be eliminated.
Carbon fibre is expensive to use for several key reasons:
- The raw materials are complicated and thus costly to produce.
- There is a relatively high level of wastage.
- Automated manufacture is difficult as most of the performance benefits come from the way components are built by hand to best suit force-distribution across a component.
- Fabrication and curing mean product cycle times and demand on resources are high.
Despite the significant production costs, carbon fibre is an extremely appealing material for high-performance applications where cost restrictions are not so tight. It is commonly stated that carbon fibre can offer the same tensile strength as steel for just 25% of the weight. This is subject to careful design and fabrication to ensure the best possible performance across a component.
In order to reduce costs, increase rates of production and produce more consistent results, some new processes are being introduced. In the Mercedes-Mclaren SLR this envolved producing blanks, moulds and utilising processes from the textile industry to weave fibres to create accurate, ready made elements.
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| “The longitudinal members of the front body structure consist of a central cross member and the encircling moulded part or internal web. The cross member comprises several layers of carbon fibre stitched together by a machine. After the form has been cut to shape, the web blank is inserted into a braided polystyrene core. This core element is clamped into a specially developed braiding machine that produces the longitudinal member from 25,000 ultra-fine carbon filaments that are unwound simultaneously from 48 reels. This process allows the fibres to be braided around the core at a precisely defined angle to create the desired contour. Several layers are overlapped in certain areas, depending on the thickness required.” – Mercedes McLaren |
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Performance in Impact
Relatively little is known about carbon fibre in crash situations. Material failure is difficult to model due to the complex nature of its composition and the variance in its construction when produced by hand. Failure is non-elastic and very different to standard automotive metals. Reinforcements are used to modify the characteristics of components to improve strength or elastic deformation characteristics. The Mercedes Mclaren SLR uses a roof made of a carbon fibre foam sandwich to improve crash-worthiness.
Fibre polymers can be drawn into filaments of a length at least 100 times greater than the diameter. Fibres are typically used for textiles and are used extensively in automotive interior applications. Additionally aramid fibres are used in composite materials.
More information on carbon fibre.
Fibres have commonly been sourced from mineral supply but are increasingly being obtained from natural sources. This offers particular benefits when considering vehicle end-of-life requirements and reliance on oil.
Fibres in the Automotive Industry
Fibres are used in cars and other vehicles for a wide range of purposes from component manufacture to passenger safety.
Fibres
Carpeting/Flooring
Mats
Trim
Headliners
Aramid Fibres
Belts / hosing
Fibre optic & electromechanical cables
Gaskets
Friction linings (eg. brake pads / clutch plates)
Adhesives
Sealants
Resources
Natural Fibres in Automotive Applications 
Plastic Optical Fibres in Cars
This section looks at some of the key materials that are and can be used in the production of road going vehicles.
Polymers
Metals
Composites
General
- Materials In Brief
- Recycling (Design for)
- Biodegrading
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A technician oversees the milling of this Hummer model. The image shows a full size model being milled from high-density foam by a machine that has been given three-dimensional data from previously completed CAD models. |
Computers have been used in the design of cars for many years. The automotive industry has been one of the leading forces for CAD development alongside aerospace and the military. In fact, some years ago, the British military research unit – DERA – and Ford initiated a joint development programme to investigate new computer design technologies.
As with all the things in the world of computers, things started big and expensive and eventually became cheaper and smaller. Although design studios may now have large CAD walls to visualise developing vehicles, it is also possible to work on the design of a car from a single PC. There are a few, core systems and programmes used in the automotive industry. In this section, we look at the key features of each ranging from specifications to usage.
Key CAD Programmes
Alias AutoStudio Alias SurfaceStudio
Also..
Digital Scanning of Clay Models (3D Digitising)
CMMs (Coordinate Measuring Machines)
Developing a vehicle is an arduous process of design and evaluation, trial and error – constant improvement and adaptation. Initial design concepts go through a range of stages to bring them closer to realisation and modelling is key to evaluating a design at each stage.
Modelling can take several forms. Traditionally, clay models have been used at various scales to help understand and resolve the form and proportions of a vehicle. To varying degrees, this has been supplemented, sometimes even replaced, by CAD modelling. Whilst clay is still a medium used to evaluate predominantly visual characteristics, CAD systems can additionally help evaluate other factors such as aerodynamics, impact scenarios and other physical considerations.
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Clay ModellingClay modelling is one of the most established 3D visualisation techniques used in the automotive industry. This section looks in detail at clay modelling – the process, history, current practices. |
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CAD ModellingComputers are now used to accelerate virtually every aspect of vehicle development. Computer aided design (CAD) modelling allows designers and engineers to resolve increasingly large amounts of a vehicle before even the first model is made. This section covers the principles and technology behind computer aided design. |
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Additional Modelling ProcessesThere are other processes involved in modelling, and sometimes entirely different approaches. We take a look at some of the more significant variants in this section. |
ergonomics
the scientific study of people and their working conditions, especially done in order to improve effectiveness
(Source: Cambridge Dictionary)
anthropometrics
Anthropometrics is the comparative study of human body measurements and properties.
(Source: University of Texas Online)
Ergonomics, or human factors engineering, is, loosely speaking, the science of designing for the human form and human behaviour. As a field, ergonomics covers everything from door handles and buttons to vehicle proportions and door apertures. With the increasing use of information technology within cars, ergonomics is becoming a major consideration in the design of user interfaces and information and entertainment systems.
Considering Humans
People vary dramatically in size and proportion around the world. Scandinavian men are amongst the tallest whilst far eastern women are among the shortest. Similar variations appear in other factors – width (at various points of the body), hand size, reach, weight and so on. Traditionally these factors have largely depended upon the geographical location of a person – and how humans have developed over thousands of years. However, lifestyle is increasingly affecting the physical attributes of people. A particular example is the increasing levels of obesity in western countries, especially the US. This dramatically affects average figures for dimensions such as width as well as movement and reach considerations.
Another very major issue affecting designers is the increasing life expectancy of people. This is particularly pertinant in developed countries but will increasingly affect all developing countries. As life expectancy increases, people perform tasks and activities for longer and later in life. At the same time, people may experience a deterioration in mobility and dexterity. Here lies another important ergonomic consideration – designing for people who may have trouble with awkward controls, openings and other features of a vehicle whilst still expecting to use the vehicle to its fullest. Changes in response to these concerns can be seen on almost every new car – exterior door handles are often larger, simpler and bolder than a decade or more previously.
Models and Mannequins
Within the automotive industry, representative models and mannequins are used to form the basis for vehicle size and form. Tradionally, these would be simple, actual size 2D models based on the Dreyfuss human dimension data. Henry Dreyfuss was a pioneer of human measurement and captured the first significant data on human measurement. This method has been superceded by computer models which have been developed from more recent data.
Traditionally, wind tunnel testing was a sizeable trial and error process, ongoing throughout the development of a vehicle. Today, with the high level of CAD prediction and pre-production evaluation, coupled with a greater human understanding of aerodynamics, wind tunnel testing often comes into the design process later. The wind tunnel is the proving ground for the vehicle’s form and allows engineers to obtain considerable amounts of advanced information within a controlled environment.
Whilst advanced design processes can anticipate a large proportion of aerodynamic performance, it is still crucial to assess a vehicle in the wind tunnel. Many elements of a vehicle’s form only reveal their behaviour in air flow when carefully tested and cannot be anticipated on computer. The reality of production, tolerances in components and accuracy of build can all play a part in affecting the aerodynamic behaviour of a car.
Aside from engineering concerns, manufacturers are increasingly looking to see how to improve the customer-side of aerodynamics. For example, wind noise from door mirrors is considered very undesirable and can only really be evaluated in a wind tunnel. Other, less obvious issues can also be examined – such as whether air flow forces water through seals or dirt into door apertures.
Sophisticated sound equipment is used in the wind tunnel to compile data on wind noise.
In this photograph, a stream of smoke travels over the vehicle in the wind tunnel as air passes from right to left. It can be clearly seen that laminar air flow remains attached until the very rear of the vehicle, emphasising just how carefully aerodynamic performance has been considered.
All images courtesy & © Ford Motor Company
Only recently have computers played such a substantial role in aerodynamics. Before sophisicated aerodynamic simulation, a vehicle would be designed with key principles in mind and then finalised in the wind tunnel through a process of trial and error. In these fantastic photos, the state of cutting edge aerodynamic development in 1967 has been captured for posterity. Ford’s GT design team can be seen working directly on a vehicle in the wind tunnel.
The photos illustrate how a vehicle would be modified and tested in a gradual process to improve aerodynamic performance. It appears that sensor panels have been placed under the wheels to measure pitch, roll and yaw; this would have been some of the most advanced equipment at the time but is now integrated into the floor of modern wind tunnels.
