Composite-Bodied Electric Car Company Finished
Aptera Motors, a California company that was working on a revolutionary electric car is officially out of business. As reported at The Blaze, some videos recently came out that show employees destroying the composite bodies.
The headline reads:
Employees of Failed Electric Car Manufacturer Caught Destroying Car Frames…With Forklifts
The story describes how the company had hoped to revolutionize transportation with an electric car that was extremely efficient with its’ energy usage. Part of this included the use of lightweight construction materials to decrease the mass of the vehicle while allowing for maximum aerodynamics.
Edmunds did a report on the Aptera that is copyrighted 2009
The videos showing the destruction of the car bodies was posted by Youtube user KarenRei.
The bodies look weak in the video, but I am sure that fully-assembled vehicles were designed to have the doors strengthen the passenger areas for crash protection.
Non-Destructive Testing with Ultrasound
Composite materials can become damaged in many different ways. There can also be flaws in the original manufacturing process. Many times it is necessary to identify any damaged areas within the composites layers that cannot be detected with the eye.
Inspection of composites fiberglass and carbon fiber structures may be required for advanced critical applications of composites materials. Identifying any potential problems with the composites structure is extremely important.
Of course problems can be identified through destructive testing-drilling holes, making cuts, etc. It also may be necessary to do testing in a non-destructive manner, i.e. not cutting into the laminate that is being tested.
One method of accomplishing non-destructive testing of composites laminates is using ultrasound. This Youtube video demonstrates the use of this method.
As you can see, the damage is found in this carbon fiber laminate. This information is a flag that can be used to decide whether to make a repair or replace the structure.
Delamination within the fiberglass or carbon fiber part will result in a much weaker structure than the design intended. Other areas of the composites part will be further strained by weaknesses in other areas and may also fail.
This ultrasonic test can help to identify otherwise invisible problems with either the original manufacturing process or damage during the life cycle of the composite part.
NASA Composite Crew Module
NASA, the space agency for the U.S. government, has investigated the use of advanced composites for use in future vehicle programs. The Composite Crew Module (CCM) has been designed and built as a travel vehicle for astronauts in future space programs to travel. Drawing parallels to the Apollo program, this module will be launched on a rocket and break away as a module.
This technology and material are undergoing testing and evaluation before it is officially accepted for the Orion program. As a partnership between government agencies and public companies, this technology aims to reduce weight and improve performance of the manned vehicles.
From NASA’s website “Led by the NESC, the project team is a partnership between NASA and industry, including design, manufacturing, and tooling expertise. Partners are civil servants from nine NASA Centers – ARC, DFRC, GRC, GSFC, JSC, JPL, KSC, LaRC, and MSFC; the Air Force Research Laboratories; and contractors from Alcore, Alliant Techsystems, Bally Ribbon Mills, Collier Corporation, Genesis Engineering, Janicki Industries, Lockheed Martin, and Northrop Grumman. The CCM team operates in a virtual environment, electronically connecting participants across the country.”
This full-scale structure has strain gauges attached to monitor loads on the structure. It was announced on January 25 that it has passed a battery of stress tests to prove viability.
The structure appears to be made with carbon fiber materials, maybe with some graphite reinforcement and an epoxy resin system. Mention of aluminum honeycomb can be found in the online reading materials. The main pieces are autoclaved, while bonding of the large sections (upper and lower shells) is accomplished outside of the autoclave.
Composites technology is being developed for future space exploration structures and vehicles, and this is good news for the composites industry!
Panel Stiffness
Composites structures have requirements for stiffness to provide support and stability. Tests can be completed to identify the stiffness of a given area on a composites structure, i.e. how much it will bend for a given force.
The required stiffness of a section of a composites part depends upon the overall design and service expectations. Several factors, including the life expectancy of the object, the load rating of the composites surface, the inter-laminar bond strength, will help determine the threshold requirements. Testing is very important to determine the life expectancy of the part and whether it meets the requirements of its’ job.
Panel stiffness can be modified to meet these requirements using two basic methods. One way to increase the stiffness of an unsupported composites panel is to reduce the size of the panel through additional support structures. The other way is to increase the panel thickness across the same area. Choosing which method to use depends upon the engineering of the part and determining which method is acceptable with the surrounding part layout. If there is room to add supports, this is likely a quick and easy option. If there is room to increase the thickness, adding new or additional coring materials may be a simple solution.
Building a strong and stiff composites structure can be accomplished with the extremes of building a robust “skeleton” with small open areas and a thin skin, or having a basic, limited “skeleton” with a heavy duty cored laminate that supports itself.
A combination of the two usually works out best.
Home Workshop Supplies
Sometimes the most difficult aspects of working on fiberglass projects at home is obtaining the proper supplies. Now that we have the internet, this is greatly simplified, and many online stores exist to sell many different types of resin and reinforcement; tools and supplies. One of the problems with this is the cost of shipping the resins as hazardous materials. And actually seeing and handling the reinforcement will help in determining if it is up for your application.
Sometimes it is advantageous to buy supplies from a physical store. This saves time and money from shipping, and allows for better inspection of the purchased products. Local sources are not always easy to identify. Many times automotive bodyshop repair stores carry fiberglass resin. I have found that marine repair supply stores carry a more extensive repair supply, including epoxy, polyester, fiberglass sheeting, and even gelcoat and associated chemical additives.
When purchasing esins and gelcoats always keep in mind the shelflife. My experience has always been that polyester, vinylester, and gelcoat have about a six month shelflife from when it was manufactured. Be cautious at autobody supply houses that sell low volume amounts of resin and may have some old stock. Epoxy generally has a longer shelflife.
A good practice when obtaining new materials is to always do a test run in a small dixie cup, sometimes called a “Gel Test”. Mix the resin and hardener together and stir it up. Monitor the time it takes to start getting thick and lumpy. And time full hardness. As it gets towards full cure, there is potential to get hot enough to start a fire, so take proper precautions. This test will tell whether the resin and hardener are even compatible and what sort of working time to expect. This will make life much easier under actual fabrication conditions.
The Importance of Testing
The testing of properties for Composites laminates and structures can be tricky. Much of this is due to the complex base of ingredients and makeup of the laminate. When we are putting together a combination of resins, reinforcements, coring, fasteners, curing agents, fasteners, etc. we can radically affect the properties of the FRP structure. This can be beneficial and disadvantageous.
ASTM test specifications can be used to determine properties such as stiffness, chemical resistance, impact strength, etc. There are several designed specifically for FRP laminates. These can be very informative, especially when developing and comparing potential laminate designs.
House tests can also be developed to test for more specific properties on test panels and the overall structure. A flat and square test speciment may test out great for certain properties. When it is put into actual application, it may have differenet features which make it stronger or weaker than the flat test panel. Things such as holes, notches, square corners, curves, and other geometric shapes have a wide range of effects. They may increase localized thickness from overlap joints, may cause stress concentrators, or may have thin areas because of an area being difficult to reach.
One of the projects I worked on recently involved the conversion of the processing from hand layup to resin infusion processing. For product liability we wanted to prove that we tested the laminates for strength, and doing an overall structure test was out of the question. But testing flat and square infusion panels would just give us a number. So we setup a baseline with the same size flat and square test panels made with the old laminate schedule using hand layup. This old laminate schedule had been very suitable in its application. We just needed to ensure that the new infused laminate schedule exceeded the strength of the original hand laid laminate schedule.
We setup this direct comparison between laminates by removing the variables of the part shape itself. We also added some safety factor to ensure for any other variables that may be involved. Our supplier tested the panels for us, giving us official ASTM results. We worked through a few different scenarios with the new laminate schedule, received test results, and made our decision. Future inquiries into our engineering work can be backed up with technical testing data.
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