Fiberglass, SMC, and Carbon Fiber: History, Construction, and Beyond

Written by Sam Sanderson

Information Credit to Gregg Emmich

From water slides, traffic lights, helicopter rotor blades, circuit boards, boats, and of course automotive parts, composites have been used for a vast array of products, starting with the accidental discovery of fiberglass in 1932.  Games Slayter, a researcher at Owens-Illinois, discovered "fiberglas" when he directed a jet of compressed air at a stream of molten glass and produced glass fibers.  This original "fiberglas" was glass wool - strands of glass fibers entrapping a great deal of gas - which made it useful as an insulator, however it was not structurally strong.  It wasn't until 1936, when duPont produced a polyester resin designed to combine with the glass fibers, that the composite material we know today as fiberglass was developed.  This composite material was significantly stronger than the original glass wool "fiberglas", opening up a world of possibilities for designers, including those in the automotive industry.

History of the Fiberglass-Bodied Car:

  1946 Stout Scarab Experimental at the Gilmore Car Museum - 2011

1946 Stout Scarab Experimental at the Gilmore Car Museum - 2011

  Stout Scarab on display in Genoa, Italy

Stout Scarab on display in Genoa, Italy

Many people believe that the Chevrolet Corvette was the first car to be manufactured with a complete fiberglass body, but this is not the case.  Immediately following the end of World War II, Stout Motorcar Company of Detroit, Michigan, produced a prototype minivan called the Stout Scarab Experimental, also known as Project Y, that featured a body composed entirely of fiberglass.  This minivan also featured the world's first fully functioning air suspension, which had been developed in 1933 by Firestone.  Sadly, this minivan never went into production.  Due to the company's low production volume, it is believed that the Stout Scarab Experimental would have had a selling price around $10,000, well beyond the means of most potential buyers.  (Interesting side note:  the Stout Scarab is credited to be the world's first production minivan.  This minivan was constructed with an aluminum space frame unit body construction with steel frame parts and a steel body.  The Scarab was priced at $5,000 - comparable to $90,000 today - however very few would pay the hefty price for this innovative car, and so only 9 units were produced.  These 9 units were hand built, and no two Scarabs are identical.  Of the 9 units, five are known to survive today.)

  1954 Kaiser Darrin

1954 Kaiser Darrin

The Kaiser Darrin also preceded the debut of the Chevrolet Corvette.  It is rumored that Henry J Kaiser did not like the design of the Kaiser Darrin, however his wife Alyce proclaimed the Darrin as "the most beautiful thing I have ever seen", and so the Kaiser Darrin was scheduled for production.  The prototype Darrin was unveiled at the Los Angeles Motorama in September of 1952, beating the debut of the Corvette by two months.  Featuring a fiberglass body, a three position convertible top, and sliding "pocket" doors that slid on tracks into the front fender wells, it was hailed as the sports car that everyone was waiting for.  There were no factory records kept, however at least two of these cars were equipped with McCulloch Centrifugal Superchargers (one of these supercharged Darrin's was sold at Barrett-Jackson Scottsdale in 2010).  Due to production delays, the Kaiser Darrin did not reach showroom floors until January 1954, making the Chevrolet Corvette the first mass-produced all-fiberglass body car. Because of the production delays, slow sales once the car entered the consumer market, and the Darrin's unremarkable power when compared to the Corvette and other sports cars of the era, the production of the Kaiser Darrin was cancelled in August 1954.  Only 435 models were produced during the Darrin's production run.

  Pre-production Advertisement for the Kaiser Darrin
  1953 Chevrolet Corvette debuted at the New York Auto Show

1953 Chevrolet Corvette debuted at the New York Auto Show

While it may not be the only fiberglass-bodied car in history, the Chevrolet Corvette is definitely the most iconic.  The Corvette was originally designed as a show car for the January 17, 1953 Motorama display at the New York Auto Show.  After its debut, the Corvette generated enough interest to incite GM to begin mass production on June 30, 1953.  GM's designer Harley Earl used fiberglass to create the body of the Corvette because it was lightweight, rust-proof, and it offered an economical way to produce the Corvette without the expense of large sheet metal stamping dies.  The Corvette was produced using conventional fiberglass methods until the third generation in 1968, when the press-mold process was introduced. This process involved the fiberglass and resin being molded in a die-like tool that produced smoother parts more quickly.  This was a significant advancement in fiberglass production, and it laid the groundwork for the development of SMC, which was introduced in 1973.  All Corvettes from 1973 to 2004 used entirely SMC body panels, until the introduction of the carbon fiber hood on the special edition Z06 model in 2004.  Since 2004, Corvettes have continued to use SMC body panels, however more of an emphasis has been placed on carbon fiber panels due to its strength and weight advantages.

Fiberglass and SMC Construction:

  Fiberglass Mat

Fiberglass Mat

  Fiberglass Cloth

Fiberglass Cloth

The original process of making a fiberglass part involved hand laminating sheets of woven glass fibers on the inside of a mold.  These sheets could either be fiberglass mat - a sheet of loose glass fibers pressed together and held with a binder that is soluble in polyester resin - or fiberglass cloth - glass fibers that have been woven into a cloth material. Fiberglass cloth is available in a variety of weaves - plain, basket, and twill are the most common. Choosing a cloth is based on factors such as weight and strength needed for that particular part.  There are also pre-colored fiberglass cloths available that can be used to create a unique visual effect when combined with a clear resin and gel coat.  The fiberglass sheets are laid onto the mold and laminated with resin, layer by layer.  Once all desired layers have been applied, excess resin is removed and the fiberglass is allowed to harden in the mold.  During the curing process, the resin in the fiberglass composite may shrink 2-6% depending upon the resin used.  Because the glass fibers themselves do not contract, this may cause distortion in the part.  Curing time depends upon the type of resin and hardener used.

Hand laminating parts is an incredibly time consuming process.  The advent of the chopper gun made it easier to manufacture fiberglass parts, thus saving time and making it more cost effective.  The chopper gun is a hand held tool that mixes resin and catalyst, spraying the mixture with chopped glass fibers at the pull of a trigger to the inside of a mold.  Although this sped up the layup/laminating process, parts still had to stay in the mold until fully cured. 

The press mold-process, such as was used in the Corvette, further decreased the production time of fiberglass.  However, as with previous processes, it still took time for the part to cure.  Enter SMC.

  Damaged SMC

Damaged SMC

Sheet molded compound, otherwise known as SMC.  A machine process using both outside and inside molds that compress and heat the fiberglass composite, speeding the curing time of the resin and leaving smooth surfaces on both sides.  Fillers are added to the resin to further expedite the curing process, but this decreases the strength.  Because of this, SMC is typically reserved for cosmetic body panels, whereas boat construction still uses the one sided mold method.

The glass fibers are easily recognizable in damaged SMC, so it is often misidentified as fiberglass, resulting in technicians repairing the SMC on a 1973 Corvette the same way they repaired their own row boat.  Unfortunately, this leads to a failure of the repair.

Considering the weakened integrity of the SMC's resin due to the filler material and the poor adhesive properties of polyester resin, polyester resin is not appropriate for use when repairing SMC.  It is necessary to use a stronger resin, such as an epoxy resin, to compensate for SMC's weakness.  However, SMC can still be repaired using the hand laminating process.  Because of SMC's weakness, it's not uncommon for redamaged SMC to break around the perimeter of the repair.

Carbon Fiber - History, Construction, and Beyond:

  Carbon Fiber Cloth

Carbon Fiber Cloth

Carbon fiber was first discovered in 1860 by Sir Joseph Swan, a British physicist and chemist, for use in light bulbs.  However, it wasn't until 1980 when the McLaren Racing Team introduced the first carbon fiber-bodied race car in the Formula1 racing circuit that carbon fiber began to be used in the automotive industry. 

  Pre-preg Carbon Fiber

Pre-preg Carbon Fiber

Carbon fiber is composed of fibers of carbon that are woven to make a cloth.  It can be hand laid in a mold the same way that fiberglass is formed, however care has to be taken to ensure that too much resin is not applied.  If too much resin is used, it will cause a weaker final product.  Because of this, a new method was developed approximately 20 years ago involving the use of pre-preg (pre-impregnanted) carbon fiber.  Carbon fiber sheets are available with a specific amount of resin pre-impregnated into the carbon fiber, resulting in the maximum strength product.  These sheets come with a backing that is peeled off when ready to use, leaving a slightly sticky surface on the back of the carbon fiber.  While these sheets are more convenient and easier to use than conventional carbon fiber sheets, they must be strictly temperature controlled - sheets are transported frozen and should then be kept in a refrigerator until ready to be used - to prevent the resin from activating prematurely.  Once the pre-preg carbon fiber has been laid into a mold, there are several ways to cure the part.  The preferred method of curing is vacuum bagging and cooking in an oven or autoclave, however the part can also be allowed to cold cure.

Vacuum bagging is a process that can be used for curing fiberglass parts as well as carbon fiber.  Using this process, the part is sealed in a plastic bag and all of the air is evacuated, causing the pressure in the atmosphere to evenly press the carbon fiber or fiberglass onto the mold.  The part is then baked in an oven or an autoclave.  This method ensures that no air is trapped in the part and creates a strong uniform finished product.  The attached video from Koenigsegg shows how they use pre-preg carbon fiber and the vacuum forming method to construct the bodies and parts of their hypercars.

  Carbon fiber tub chassis and complete car of Alfa Romeo 4C

Carbon fiber tub chassis and complete car of Alfa Romeo 4C

Many parts are being manufactured using carbon fiber because it is considerably stronger and lighter when compared to SMC or fiberglass, however it is more difficult to manufacture carbon fiber, and so it is more expensive to produce carbon fiber parts as opposed to fiberglass or SMC.  Because of this, carbon fiber has generally been reserved for use in hypercars, supercars, and high-end sports cars.  However, it is hotly debated that carbon fiber parts will be the wave of the future.  As more pressure is applied within the automotive industry to improve fuel efficiency, there will be an increased need for lighter materials.  Daily advancements in carbon fiber production are making it ever more affordable for the production market. 

BMW recently created the i-series, a series of electric vehicles constructed with entirely carbon fiber body structures.  The range of electric vehicles is greatly affected by the weight of the vehicle, and so the use of carbon fiber gives their i-series electric vehicles an edge over the competition.  The introduction of the BMW I3 launched the all-carbon fiber car from the elite hypercar into the every day consumer market, providing weight to the argument that carbon fiber is the wave of the future.

With the production of the first fiberglass-bodied car back in 1946, composites have had a major influence in the automotive industry.  Will carbon fiber-bodied cars be the wave of the future? Only time will tell.