Lesson 16 Monocoque Construction Body,Automotive bodies are generally formed out of sheet steel. The steel is alloyed with various elements to improve its ability to be formed into deeper depressions without wrinkling or tearing in manufacturing presses. Steel is used because of its general availability, low cost, and good workability. For certain applications, however, other materials, such as aluminum, fibreglass, and carbon-fibre reinforced plastic, are used because of their special properties.,Polyamide, polyester, polystyrene, polypropylene, and ethylene plastics have been formulated for greater toughness, dent resistance, and resistance to brittle deformation. These materials are used for body panels. Tooling for plastic components generally costs less and requires less time to develop than that for steel components and therefore may be changed by designers at a lower cost.,Most small passenger vehicles switched to monocoque construction in the 1960s, but the trend had started in the 1930s with cars like the Opel Olympia, and Citroen Traction Avant leaving just trucks, some bus manufacturers and large cars using conventional frames.,The switch continued for several decades - even small SUVs typically use this construction method today. Body-on-frame remains the preferred construction method for heavy-duty commercial vehicles, especially those which are intended to carry and pull heavy loads, such as trucks.,A halfway house to full monocoque construction was the semi-monocoque used by the Volkswagen Beetle and Citroen 2CV. These used a lightweight separate chassis made from pressed sheet steel panels forming a platform chassis, to give the benefits of a traditional chassis, but with lower weight and greater stiffness. Both of these chassis were used for several different models. Volkswagen made use of the bodyshell for structural strength as well as the chassis - hence semi-monocoque.,X-ray drawing of the 1942 Nash 600 body design.,Automobile designs originally used body-on-frame construction, where a load-bearing chassis consisting of frame, powertrain, and suspension formed the base vehicle, and supported a non-load-bearing body or coachwork. Over time, this was supplanted by monocoque designs, integrating the body and chassis into a single unit.,The external panels may be stressed, in such cases as the rocker panels, windshield frame and roof pillars, or non-stressed, as is often the case with fenders. Today, spot welded unit body is the dominant technique, although some vehicles (particularly trucks and buses) still use body-on-frame.,1 Early designs The first automotive application of the monocoque technique was 1923s Lancia Lambda, but it was not a true monocoque because it did not have a stressed roof, it was akin to a boat and has been described as punt type construction. In 1928 German motorcycle manufacturer DKW launched their first car, the P15 wood and fabric bodied monocoque car.,The Airflow and Traction Avant steel monocoque cars (with stressed roofs) were both launched in 1934. General Motors then followed with the Opel Olympia in 1935. In 1936, Lincoln introduced the Zephyr, a monocoque design which was as strong as the Airflow yet much lighter.,A halfway house to full monocoque construction was the semi-monocoque used by the 1930s designed Volkswagen Beetle. This used a lightweight separate chassis made from pressed sheet steel panels forming a platform chassis, to give the benefits of a traditional chassis, but with lower weight and greater stiffness4. This chassis was used for several different models. Volkswagen made use of the bodyshell for structural strength as well as the chassis - hence semi-monocoque.,Nash Motors introduced this type of construction in 1941 with the new 600, generally credited with being the first popular mass-produced unibody construction automobile made in the United States. The all-welded steel with sturdy bridge-like girders that arched front to rear made for improved strength, safety, and durability.,Nash engineers claimed that about 500 pounds of excess weight was cut out (compared to body-on-frame automobiles) and the bodys lower air drag helped it to achieve better gas mileage. The companys 1942 news release text attached to the X-ray drawing describes how . all auto bodies will be built . as this some day.,2 Post-war advancements After World War II, the technique became more widely used. The Alec Issigonis Morris Minor of 1948 featured a monocoque body, as did the Hudson Motor range of the same time. Other automakers incorporated this type of construction, and the terms unit body and unibody became more common in general use. The Ford Consul was the first Ford built in England using a unibody.,In 1960, a major breakthrough in unibody construction was reached in mass-produced Detroit vehicles with over 99% of Chrysler vehicles produced that year being fully unitized; some of the basic designs surviving almost untouched through the mid 1970s (EG