This is an article about an incredible material that we are starting to distribute. It represents a huge chemical engineering breakthrough: the chemists of Henkel have managed to create a glue that is a mix of CA and structural epoxy. The name of the product is Loctite 4090.
This is an impressive product for the following reason: it provides the advantages of both CA glue and epoxy:
It sets to a medium hard compound within about 3 minutes and provides decent fixture in that frame of time..
It can be accelerated with CA kicker for instant fixture and sets to 50% strength in 24 hours.
Once fully cured ( one week ) it almost has the strength of Hysol epoxies and displays very good shock resistance properties.
It sustains 300F temperature continuously and does provide excellent aging properties in these conditions.
It resists to most chemicals, including hydrocarbons and gains in strength when exposed to these chemicals up to 1000 hours.
It is shock resistant very much like Hysol 9462.
The glue comes in a 50 ml cartridge that can be put in the usual Hysol glue dispenser gun with 1:1 plungers.
Part A contains CA glue for 70% and the epoxy accelerator for 30%.
Part B contains mostly epoxy resin and a small quantity of CA accelerator.
The two parts are very reactive which each other. On that matter it is very important that they do not come in contact with each other at the cartridge tip.
For this reason the cartridge tip is very different from other Hysol products. The tip has two tubes quite largely spaced from each other that come into each cartridge compartment. The dispensing tip slots into the cartridge throat and can only be inserted one way.
For this reason the Loctite 4090 tips cannot be swapped with other Hysol tips. They are also much thinner and provide very precise dispensing in a thin glue string.
It is not recommended to try mixing the glue without dispensing tips because there is a very high risk of tubes cross-contamination that would render the whole cartridge unusable within minutes.
CA accelerator can be used on a part after assembly to boost the fixture time. Once set, the part has to be left alone for 24 hours before manipulating, and one week if full strength is required.
Storage is recommended in the fridge between 35 and 46 F
The properties of the glue are a fairly good bond to most material with a drop of shear strength compared to Hysol glues of about 15 to 20% except on hard wood.
Shear lap strength on steel is 2420 PSI vs 3000 PSI for Hysol products on average.
Shear lap strength on epoxy is 1320 PSI vs 3300 PSI for Hysol products on average.
Shear lap strength on hard wood is 700 PSI vs 1700 PSI for Hysol products on average.
I found this glue very interesting to assemble scale components like gluing fairings, scoops on the surface of a fuselage. It is also very handy for gear door hinges gluing. For bulkheads gluing in the fuselage, I would still recommend Hysol 9462. However a few dots of 4090 can be placed along the bulkhead to tack glue it in position together with CA accelerator.
This glue is also winner when you need to assemble plywood structures like component trays or gear mount assemblies. For servo brackets, I would still recommend the use of E-20NS or 9462.
Note that full curing property is achieved after one week and 50% after 24 hours. This is clearly not a glue one wants to bring to the field for structural repairs.
This is an article about the latest ( although not new ) generation of fabrics used in the aerospace industry.
These are called non crimp fabrics and are available in uni directional or multi axial combinations.
These fabrics are not woven in a conventional way. They are made of several layers of uni-directional fibers ( glass, carbon, kevlar and other ) stitched together in several directions.
The process used is to take flat ribbons of uni directional fibers that are enzymed together and carefully stitch/ glue them in flat panels.
These panels are then laid up on top of each other in 2, 3, 4 stacks or more ( up to 8 layers for some manufacturers ) to create the final product. This enables the manufacturer to create fabrics that have stiffness in the following directions: 0, 90, +45 and -45 degrees ( as well as any other direction for custom fabrics ) on a 2D plan.
The benefits of such a technology is multiple. One will understand this much better after having seen a 3 D representation and description of a standard weaving process.
The waving process, by design, forces the fibers to go above and under each other alternatively. Below is a pleated ribbon illustration of a standard plain weave pattern.
Once isolated, the fiber pattern looks like this:
One can clearly see that the fiber is not only going in the wanted horizontal direction but also quite dramatically in the vertical direction.
Additionally, applying pressure during layup increases the vertical deflection of the fibers. Altogether, this reduces the stiffness on the horizontal plan and creates small bending radii ( ribbon pleating here ) that also tend to introduce stress fracture application points in the laminate.
When a load is applied to a woven fabric a stress concentration occurs at every point where one fiber bundle passes over or under another. This causes unwanted stresses in the resin, which is much weaker than the fibers. Repeated loading and unloading, or cycle fatigue, will cause a breakdown of the resin leaving the fibers unsupported and free to buckle in compression loading. Fibers in stitch-bonded fabrics are straight and directly aligned with the load path.
Finally this up/ down pattern creates voids that will be filled by the resin, thus slightly increasing the weight of the laminate ( ie decreasing the fiber reinforcement rate ).
Non crimp fabrics.
Non crimp fabric on the other hand are mostly flat ( stitching introduces minimal vertical deflection locally as the yarn used is a very thin and soft polyester), thus offer a true horizontal alignment with minimum void between the fibers. The tows are spreads into flat ribbons.
A weaved fabric generally offer two reinforcement directions. That is 90 degrees and 0 degrees.
Non crimp fabrics can be assembled in any directions 0, 90 degrees and from 30 degrees to 70 degrees. Generally, it is considered that quadriaxial fabrics at 0, 90, +45 and -45 degrees offer quasi-uniform stiffness plates. Thus it is the product we use the most.
However, the best manufacturers offer the possibility to create any combination of angle and material for up to 7 layers at the customer convenience.
Overall, non crimp fabrics offer the following benefits compared to traditional weaving:
Better mechanical properties are obtained due to higher Fibre rate compared to traditional fabrics (lower resin consumption).
Less fiber stress concentration when load applied, thus better fatigue resistance.
Less resin usage.
Zero crimp provides better interply strength.
Due to its flat structure, the stitch-bonded fabric reduces the print-through of conventional fabrics.
Modern CAD software like Dassault Catia often include composite design modules that will guide the engineer in laying up the uni-directional fabrics in the best possible directions. Finite analysis can then provide a good feedback on achieved results.
Finally note that NCF are not new. The technique was studied in the 80s with the first assembly plants created in the USA and Italy in the 90s. However these were originally highly specialized products created for the space industry. This technique slowly spread and became available at a wider scale about 10 years ago. However carbon fiber quadriaxial NCF are still difficult to find on the retail market.
This is a short post to talk about a product that I am about to place on our web site. It is a series of plates in different thickness and density made from a 3D honeycomb fabric.
I have used that fabric for about 3 years now with great success on quite a few projects. The 3D fabric is woven in honeycomb pattern. The 2 mm thickness is given by a glass micro sphere structure embedded in the waving and enzymed in position. The fabric has got some specific advantages compared to Aramid honeycomb and Airex.
1. It is respectively 2 time and 4 times cheaper to process. 2. It bends better than both core materials above.\ and thus complies easily in molds 3. It has a higher absolute tensile strength than above core materials if used with the same fabric
The cons is mostly:
1. It is respectively 20% and 50% heavier than Airex/ Honeycomb ( impregnated product ). 2. The tensile strength reported to density is lower ( that is because the resin that it drinks binds the skin stronger but makes the plate heavier )
The reason is that the fabric, although specifically enzymed, still absorbs more resin than a non woven core material.
Anyway, we are offering a series of high tech plates at a much lower price than our Airex and Nomex plates for the same stiffness ( but higher weight ).
The plates are:
2.5 mm 6/2/6 plate at 2 kgs/ sq.m ( 6 oz/ sq.yd carbon/ 2 mm core/ 6 oz/ sq.yd carbon )
5 mm 200/2/200/2/200 plate at 3.4 kgs/ sq.m ( 6 oz/ sq.yd carbon/ 2 mm core/ 6 oz/ sq.yd carbon/ 2 mm core/ 6 oz/ sq.yd carbon )
2.5 mm 100/2/100 plate at 1.6 kgs/ sq.m ( 3 oz/ sq.yd carbon/ 2 mm core/ 3 oz/ sq.yd carbon )
5 mm 100/2/100/2/100 plate at 2.8 kgs/ sq.m ( 3 oz/ sq.yd carbon/ 2 mm core/ 3 oz/ sq.yd carbon/ 2 mm core/ 3 oz/ sq.yd carbon )
The plates are infused from our aero grade epoxy and carbon fabric.
One face is covered with peel ply for superior bonding capacity. Here is the 200/2/200/2/200 plate:
I have been developing a new material I called NEFCAR ( Novolac Epoxy Filament with CARbon ) that has been specifically designed to my requirements. Tests have been successfully ongoing for several weeks now.
The filament is a blend of Epoxy Phenol Novolac ( EPN ) and poly-DL-lactide resin developed in Japan.
The resin acts as a latent hardener and combines to EPN at high temperature.
The biggest challenge was to find the right printing bed and nozzle temperature that would allow the material to cool down slowly enough to allow the nano carbon fibers to align along each other and create continuous filaments bonded by the hybrid resin.
This is pretty much a first time in the world and I am very happy with the material characteristics. The part is about 30% lighter than with PYCABS and 75% stiffer. The high level of nano carbon fibers reinforcement makes the part incredibly easy to glue with epoxy resins.
After lots of tweaking and printing head modifications, I can now print 3D honeycomb reinforced epoxy/ carbon fiber parts.
I have reached a point where I can say that this is the most incredible material I have ever been able to work with.
Here is a video of a part printing as you can see, the head travel speed is quite fast:
Here are a couple of pictures of the part finished. The honeycomb filling is almost visible through the 0.2 mm carbon fiber layer.
Note the hinge recess and control horn already included in the printing from the CAD stage. Zero fiddling with door geometry on this part!
Here is the back of the part. the carbon fiber nature of the material is immediately evident when you get the part in your hands.
This is similar to what the Harvard University have managed to achieve but with a different technique. They use an Epoxy printing ink on a 100% custom printer where I use a thermofused hybrid epoxy/ polylactic resin/ nano fiber mix that is dispensed through a 75% modified Stratasys printer.
PCH is a new generation of material that I've been working on for several months now. It is a hybrid material made of glass fiber or carbon fiber laid up on a 3D printed honeycomb structure. What makes the strength of the material is actually the printing material. It is what I call PYCABS: a mix of ballistic grade Polycarbonate and ABS.
The result is a bullet proof material that is both very stiff and shock absorbing. I am quite proud of this as it is the first time that I come up with something as original and high performance as this. As far as I am aware of, this is unique in the industry.
The advantages of this material are the following:
3D printing allows for extremely complex shapes to be created.
The resulting composite structure is light, stiff and shock absorbing.
The full digital production chain enables a fitting tolerance of 0.2 mm.
The production time is short, and material cost reasonable.
The limitations are the fact that the part size cannot be bigger than the printing bed. In my case: 20 cm by 30 cm.
Here is a video of an AD Diamond door structure printing:
An example of a fairly complex door structure designed by CAD:
And the printed result. The glass fiber layup is on the other side of the door and makes the part quite white:
The door attaches to the main strut with CAD designed clips that conform to both the strut shape and match the door reinforcements. The full digital process allows for a fitting tolerance of 02 mm.
I am finishing the Diamond doors kit with this technique first, then I will carry on to the Scorpion, Super Scorpion and Phoenix
The materials used on the pictures above is PYCABS. I am also working on other materials like:
The honeycomb pattern is controlled and viewed in 3D before printing. A layer-by-layer view of every part is generated for this purpose.
On the picture above, one can see the first two layers ( in blue ) being offset from the next ones ( in red ) to improve gluing performance of the part.
I am also working with mathematicians whohave implemented new 3D honeycomb generation patterns. These exhibit compressibility resistance in 3 directions instead of 1 direction for classical nomex/ paper honeycomb.
The algorithm used can be tweaked to generate a larger thickness ondulation and thus create 3D honeycomb cells exactly similar on x, y and z axis.
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