Most people are 'familiar' with ACMs through the 'fiberglass patch kits' that can be had at any automotive or hardware store. These kits typically come with a yard or so of light-weight, random-orientation glass fiber fabric, a can of a simple polyester resin, and a small tube of cream hardener. In use, one prepares a quantity of the resin by adding a small amount of the hardener to initiate the polymerization reaction. A piece of the fiberglass fabric is then mixed into or wetted in the activated resin, and the resulting wad of 'goop' is worked into a rough shape or form over a hole in some automotive bodywork or elsewhere. Once this patch has cured, it is typically then coerced into a more desirable final shape through the use of grinders, files, sandpaper, scrapers, or any other tool that the repairer may find close to hand and deem as being worth a try. A thin coat of polymer putty may then be applied and smoothed out to fill any irregularities in the fiberglass patch. A coat or two of spray paint then completes the job.

The 'fiberglass patch kit' has been around for a long time. It has been refine d somewhat, and it is pretty much 'fool proof' in that anyone can use one and obtain quite satisfactory results. Indeed, such a patch job, carried out with some care, may last for many years. The person who performed the work may be secure in the belief that he or she now understands how to work with ACMs.

It is a false security.

Picture this scenario: The young person who did that simple patch job, and perhaps a few other patch jobs as well, subsequently finds employment at a small local aircraft maintenance facility. The job entails cleaning small private aircraft, and assisting the owner/operator of the facility with minor repairs. As these repairs are typically carried out on low-performance private aircraft constructed with thin sheet metal skins, the repairs are fairly simple and straightforward. But then one day the owner of the facility secures a repair job on a helicopter that has developed a nasty crack in the engine intake cowl. He knows two things: he knows that the intake cowl is made of fiberglass-based composites, so the sheet metal repair techniques with which he is familiar will not work, and he knows that his helper has mentioned having carried out fiberglass repairs on many occasions. So the owner gives the go-ahead, and the helper proceeds with the repair using the fiberglass patch kit methods he knows. They are pleased to find that the repair seems to go quite easily. The hard, smooth surface of the intake cowl allows the woven fiberglass patch cloth to be pressed down very neatly, and the resin appears to bond very well to the surface. The cured patch is still a little rough around the edges, but with a little extra fine sanding and some glazing putty, it will look as good as new...

Or how about this scenario? An outdoors enthusiast wants to build a custom canoe. Some research has revealed the incredible impact resistance and light weight of aramid (Kevlar) fabric, so the do-it-yourselfer decides to build his c anoe using woven aramid with an easy-to-use polyester resin. Some time later, the new canoe looks great and is ready to go on the water in the rock-strewn northern rivers and lakes that the outdoorsman likes to explore...

And here's one more scenario to consider. A worker in a factory that produces small aircraft of composite construction is assigned the task of fastening cross members in the tail sections of the aircraft as they proceed along the production line. He has been taught the proper way to attach the cross members using the correct fasteners, and he carries out this task both well and unquestioningly. For some reason, his supply of the proper fasteners runs out, but being a bright fellow, he realizes that there are other techniques for fastening things together. He thinks for a moment or two, assembling the components of another technique from what he knows, then diligently sets to work. In place of the fasteners he is supposed to use, he now drills several pilo t holes in the cross members and secures them in place using expanding head or 'pop' rivets. His new method quickly has the members tightly fastened in place, and the production line moves along again with barely an interruption.

In these three scenarios, the resolutions may seem harmless enough to the untrained individual, but there is one facet of ACM structures that can not be overlooked or forgotten for a single moment: failure to work strictly within the principles that govern the performance of ACM structures is a fatal mistake. When dealing with ACM structures, mistakes are not forgiven. Each of these scenarios involve serious flaws that WILL result in the failure of the structure, with the loss of life being a near certain result.

In the first scenario, the repair procedure and materials were totally inappropriate. The engine intake cowl of the helicopter was indeed made with fiberglass, but in a high-performance thermosetting epoxy resin. This is entirely inco mpatible with the polyester resin 'patch kit' material that was used for the repair. Nor was the patching process used in any way appropriate to rebuilding the internal structure of the cowl itself. In effect, the patch was only stuck over the crack temporarily, like a band-aid, and was not bonded into the ACM structure of the cowl. At some point, most likely under full engine load in flight, the patch would have separated from the cowl and been drawn directly into the turbines of the helicopter engine. The engine would have been instantly and completely destroyed, and the helicopter would have crashed killing at least everyone on board at the time.

The outdoorsman's canoe, in the second scenario, would have worked out very well, at least for a time. While the aramid fiber would indeed have offered excellent resistance to impacts against rocks, the low-performance matrix would have become cracked and damaged immediately, allowing the aramid fibers to come into contact with the water. Some further research would have revealed that such contact would allow the aramid fibers to 'wick up' as much as twelve times their own weight of water. Where this happens, the composite structure is ruined and will require frequent repair at best. At the worst, the canoe would become heavier and heavier, losing its designed weight balance and perhaps dumping its occupants into the freezing waters of some cold northern lake.

The third scenario also seems to have an acceptable solution, but in reality it does not. ACMs and ACM structures are surprisingly fragile when exposed to forces they were not designed to accommodate, and like all such materials they are especially vulnerable to forces acting across the fibers rather than along the length of the fibers. The worker's "new" technique of fastening the cross members will work extremely well with other materials, such as sheet metal, but is completely unacceptable for joining structures made from ACMs. Examination of the members that had been fastened in this way revealed that the sideways pressures exerted against the composite material by the rivet heads as they were set into place had fractured and cracked both fibers and matrix at every instance. Under load, as in flight, the structures would have failed catastrophically. Every one of the airplanes in which this method of fastening the cross members had been used would have crashed.

All three of these scenarios are more than merely object lessons in an article. They are in fact actual true incidents that, fortunately, were caught in time by trained personnel who happened to spot the problems. The cured patch on the helicopter engine cowl was grasped lightly by the corner and unceremoniously jerked away by a composites expert when the young worker asked if his patch work was good; the outdoorsman was informed of the problems associated with aramid fiber and water, and was advised to use carbon fiber with a tough epoxy resin instead ; the damage caused by the faulty fastening technique was spotted and reported by a visiting composites expert who just happened to be walking through the plant to meet someone at the time.

Unfortunately, such incidents occur all too frequently due to a lack of proper training. People who are trusted by others to carry out certain tasks fall victim to the trap of simply not realizing that ACMs are completely different from any other materials that they have ever worked with. The basic rules that apply to all of those other materials do not apply to ACMs.  Proper training and a good appreciation of how ACMs work are essential to working with and applying them successfully. Proper training saves time, money, reputations, and even lives.

How much money can proper training save? A simple example, again taken from real life, offers a good indication. Carbon fiber "2 by 2" twill has become a very popular material for custom compo sites work, as much for its visual appeal as for its structural properties. A trainee at an international training facility once recounted his experience with a venture to produce custom decorative truck bumpers from this material. He required a mold in which to lay up the resin and fabric to form the new bumpers, and had proceeded to take a "splash" mold from a standard bumper. He used the correct materials and laid down strip after strip of unidirectional glass fiber and resin to capture the exact shape of the bumper. Several hours later, he removed his new mold, which immediately twisted out of shape. He then obtained a different resin in the mistaken belief that his choice of materials had been incorrect, and repeated the entire mold-making procedure. The results were the same, an unusable twisted mold. When the trainee learned about the principles and effects of fiber orientation, he realized (and said as much) that he had thrown away literally thousands of dollars in just th ose two mold-making attempts. Had he known about these effects beforehand through proper training, his first attempt would have been entirely successful.

This is a "low end" example. Imagine the result had this been a "high end" operation producing a specific structural component for an aircraft. Replacing an advanced composite wing or tail component on a commercial passenger aircraft can cost hundreds of thousands of dollars. Imagine the cost in each of the three above scenarios had the errors gone unnoticed. Lost money... lost lives.

The fields of advanced composite materials and the associated technologies are some of the fastest growing. Fiber and resin materials are becoming more and more sophisticated each day, as new materials and new applications are developed. Yet, no matter how advanced these fields become, the basic principles of ACMs remain the same. The principles are easily learned, and the knowledge can pay for itself many times over, regardless of wheth er the person who employs that knowledge is working in automotive, watercraft, or other industries. Aerospace applications are in a category of their own, and the value of proper training with ACMs is much higher.

Certifications for Aerospace Applications:

Aerospace applications are covered by very strict regulations. Aircraft maintenance engineers and technicians in Canada, the United States, and around the world, are required to obtain accredited training from government-approved training facilities. Such training is a requirement of qualification that is reflected in the license rating that authorizes an AME or AMT to carry out maintenance and repairs to advanced composites structures in aerospace applications. There is a line of accountability in industries that make use of advanced composites structures. Nowhere is this more apparent than in the aerospace industry, in which meticulous histories are maintained for every single component of commercial aircraft, including the name of every person who has provided repair and maintenance service. The same regulations that specify approved training for AMEs and AMTs also specify how materials used in aerospace ACM applications must be handled. Such materials must be certified to a level of performance, with registered dates of expiration. Factors such as storage temperature and humidity, "out time", and limits of exposure to light are covered by regulations, and documentation of all regulated factors is required.

Approved training in advanced composites methodologies and techniques is provided at only a few locations in North America, but may be had anywhere in the world. It is usually advantageous for ACM workers from foreign countries to travel to Canada or the United States in order to obtain quality training for working with ACMs.

In Canada, approved training is offered at certain colleges as part of their regular AME and AMT programs, open to both Canadian and foreign students (who will pay a significantly higher tuition for these programs than will a Canadian citizen).  Shorter programs of intensive training may also be undertaken at privately owned facilities that also reach out to the world-wide market with non-preferential tuition rates. The foremost privately-owned Canadian facility for ACM training is Renaissance Aeronautics Associates Incorporated (RAA), with headquarters in London, Ontario, Canada. This company became the first privately owned training facility in North America to be approved by both the Canadian federal transport ministry (Transport Canada) and by the Canadian Aviation Maintenance Council (CAMC). Training programs delivered by RAA are geared specifically to the practical aspects of working with ACMs. They are offered both on-site in London, Toronto, Montreal, and Vancouver facilities, and off-site anywhere in the world.

In the United States of America, training for work with ACMs is also provided by both academic institutions and by private training facilities. Several colleges and universities offer advanced composites training programs, notably University of Missouri - Rolla and Cerritos College. Abaris Training is the leading private training provider in the United States, offering a selection of courses designed to provide an in-depth understanding of theoretical and engineering aspects of ACMs. Abaris Training has its headquarters in Reno, Nevada, and operates a second campus at Griffin, Georgia. The company now also offers off-site training world-wide.

There are a number of other training facilities and companies in North America and elsewhere, specializing in various aspects of advanc ed composites training. With apologies, a comprehensive description of all of these fine institutions and their respective services is well beyond the scope of this article.

In general, courses of study offered by private and academic institutions like RAA and Canadore College (in Canada) and Abaris Training and University of Missouri - Rolla (in the United States), must meet the standards of any particular country in order to satisfy the requirements for qualification of AMEs and AMTs to work with composite materials in aerospace industries within that country. Additionally, air carriers will require foreign AMEs and AMTs to be trained to the standards that exist in the carrier's home nation. Thus, for example, training for an AMT who will be licensed by the government of Argentina  must be consistent with the AMT licensing standards of Argentina, and work carried out in Argentina on , say, a Boeing 747 belonging to Air France must conform to the specifications  and standards employed by Air France.

Conclusion:

It has been the object of this series of articles to open the reader's eyes to the vast potential of advanced composite materials, and to careers working with these amazing materials. The potential for the world of ACMs is one that has no bounds, as new materials and applications are discovered and developed literally every day. Where those materials and careers may take us in reality can only be glimpsed in our imaginations, and this series of articles has barely even scratched the surface of this huge topic. But there are rules ands principles that must be strictly followed when designing and applying ACMs and ACM structures. These can only be learned effectively through proper training.

Useful Links:

For further information you may view the following useful links:

Renaissance Aeronautics Associates Inc.
http://www.raacomposites.com

Abaris Training
http://www.abaristraining.com

Canadore College
http://www.canadorec.on.ca

University of Missouri – Rolla
http://www.umt.edu

Cerritos College
http://www.cerritos.edu

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