Composite Materials and Best Practices
CalSTAR Composites Best Practices
Composites (Fin Specific) Workshop
Overview
This technical note condenses practical knowledge about producing composite parts from the CalSTAR team and alumni. Focus is on materials and best practices: what to use, where to get it, and how to use it. This document is not a replacement for hands-on practice and self-driven learning, but it should give newer team members a good head start.
Unlike a typical engineering note, this document is a living article with no restricted author list and no formal revision structure. Therefore, when editing, please be concise, neutral, and specific. This document is a forum for imparting hard-won composites knowledge, rather than hard-won personal philosophy. With the exception of diatribes against Bondo. These are fair game.
Comments on safety
Use good safety practices (gloves, goggles, avoid skin contact, ingestion, inhalation, etc) with all resins and materials described below. Read the MSDS and be aware of safe disposal methods as well as safe use. This document makes no attempt at a complete description of safe handling or risks of the materials described. Some particular examples of the safety precautions to be aware of are:
Again, it is essential to properly research for yourself the risks and best safety practices for each material and process before use. If you are unsure, it is always better to contact a lead and ask for assistance than to endanger yourself.
Resins
Resins are usually used with a reinforcing fiber or filler. Common resins fall into the categories of epoxies, polyesters, vinyl esters, and cyanate esters. Most layups generally use:
Cyanate esters behave similarly to epoxies, and are the most common resin system for prepreg.
Understand that all vinyl esters and polyesters require fitted working respirators, to avoid breathing in the solvents, this should be done with zero ex
Also understand that vinyl esters and polyesters should only be used in conditions with good ventilation and no spark / fire hazard, as the aerosols are flammable.
Many dusts and fillers are bad to breathe -- when in doubt wear a dust mask.
If material like a resin gets on the skin, it is usually incorrect to attempt to “wash” it off with a solvent. The reasoning is that the solvent will simply dissolve the material and make it easier to penetrate the skin! Use soap and water with manual scrubbing instead.
epoxy as the matrix for fiber-reinforced laminates
vinyl ester as the matrix for fiberglass molds
polyester (e.g. gel coat) as the hard surface coat for molds – if molds are used.
These resins are all thermosets. In other words, the curing process is a 3D chemical cross-linking, where the mers (short CH molecules of which the resin is composed) grow strong links to one another. The process is both heat-driven and exothermic, so it accelerates itself. This means two things:
You can speed up a cure by heating the resin.
Thinly spread resin (volume / surface area = low) will cure much more slowly than a mass of resin in a container (volume / surface area = high).
With regard to point (2), a large mass of curing resin left in a cup will often turn brown, smoke, and put off foul smells and lots of heat. (The self-accelerating effect is compounded by the fact that polymers have low thermal conductivities, so the heat cannot escape the curing resin easily.) Therefore always dispose of excess resin by spreading it over a large area of paper or plastic, and letting it cure in that spread-out state.
West System 105/209 epoxy
The 105 epoxy system is the default for laminated parts. Various hardeners can be combined with 105 resin to adjust cure time and cured part properties. Usually the 209 hardener is chosen, which gives a long pot life, so that the layup will not be rushed. The 105 system features a low viscosity, making it a good laminating resin. The main downside of the 105 system is its low Tg (~120°F).
Hysol 9396 epoxy
9396 is one of the stiffest and most temperature-resilient (service temperature up to 350°F) structural epoxies. It is more difficult to use in laminations due to having a higher viscosity and shorter pot life than West System 105/209. (However, the team has made many successful laminations with 9396.) It can be used as a good adhesive, and is the best option for laminates or bonds in close proximity to intense heat sources (like the exhaust). 9396 is effective as a potting and repair resin. Expect working life on the order of 1.5 hours, and at room temperature, 70% cure in 24 hours, with full cure in several days. At elevated temperature (~135°F), cure time can be significantly reduced to ~1.5 hours.
Tap 4:1 Super Hard epoxy
Tap’s 4:1 epoxy is moderately stiff and strong. It has the benefit of being readily purchased on short notice, and can be used for general purpose potting and lamination. However, as a general purpose resin it makes significant compromises: it has a higher viscosity than 105 and a shorter pot life than both 105 and 9396. Expect a working life of less than 15 minutes.
Polyester resin
The team has usually used Tap’s polyester resin, and found it serviceable. Polyester alone can be used as a matrix for fiberglass molds, and finds few other applications. In fact, other Berkeley teams have frequently used vinyl ester instead of polyester for fiberglass molds, since the vinyl ester is more thermally stable and bonds better to epoxy than polyester.
Gel coat
A polyester product called “gel coat” comes pre-filled with talc, CaCO₃, and other mineral oxides so that it can produce a thin, hard surface layer in molds. Tap’s gel coat has most frequently been used by the team for fiberglass molds. For surfacing of urethane foam plugs, a similar product called Duratec is probably superior in hardness and in holding a smooth surface during sanding; in a pinch gel coat on urethane may suffice.
Vinyl ester
Vinyl ester is very similar to polyester in processing behavior. It is somewhat more expensive than polyester, but deforms less under temperature and bonds well to both polyester and epoxy. Vinyl ester is the usual choice of matrix for fiberglass molds – this because fiberglass can be more demanding of a perfect medium for a usable quality layup. Tap’s vinyl ester product has generally been used.
Cyanate Ester
Cyanate ester is the most common resin system for prepregs (frozen fiber tapes pre-impregnated with resin). Once cured, it is mechanically similar to epoxy, but has better resistance to hot-wet conditions. In the uncured state it is very sensitive to moisture. When removing prepreg from the freezer, where it should be stored prior, it must be allowed to come to room temperature before opening the bag. Otherwise condensation on the material will ruin it. When repacking prepreg for putting back into the freezer, include a dessicant pack and seal the bag well. Cyanate ester systems require heat to properly cure. Most of the prepreg we will likely use is RS3, and cures when held at 350°F for several hours. There are published schedules of heat and pressure to define good cure cycles for various resin systems.
Fibers
Carbon Fabrics
For the most part, the team has used high-strength carbon fibers such as AS4 and IM7. These have relatively low modulus and fall into the “black aluminum” design regime. A key decision when acquiring fiber is the form of the fabric: whether to get unidirectional or woven, and if woven, what type of weave. It has been useful to get a moderate amount of unidirectional material for making strength-controlled shear panels, but for the majority of parts that are not filament wound, we will use woven cloth.
Satin or twill weaves are much easier to control during layup than plain weave. Plain weave is very difficult to use in any part with bi-directional curvature or uni-directional curvature tighter than ~200 mm radius. Therefore it is advisable to always insist on 5 harness satin or twill. Fiber areal weight of ~6 oz/yd² is generally useful. In special applications, lighter fabrics may be desirable.
Carbon fiber composites have good electrical conductivity in the plane of the laminate, but if using the carbon for example as a grounding body, it is necessary to drill into it and install a metal stud which will bypass the current past the surface epoxy (which is non-conductive) and into the center of the laminate, where contact can be made with the exposed carbon fibers. Carbon fabrics are easily cut with good, sharp shears.
By experimentation, we have found that plain weave final product should be around 0.35-0.36 g per square inch.
Glass Fabrics
The usual glass in fiberglass fabrics is E-glass, which is strong and moderately stiff. Fiberglass is good as a thermal and electrical insulator and is reasonably strong, but significantly heavier and less stiff than carbon. Many weights of cloth are available depending on the application. Usually a fiberglass mold is made using glass mat and vinyl ester resin; however, in the case of an epoxy-glass mold, one would use a woven glass fabric. Glass fabrics are easily cut with good shears.
Aramid Fabrics
Aramids (commonly referred to by the brand name “Kevlar”) are strong in tension and moderately stiff. They have extremely poor strength in compression, but extremely high strength in shear. They are therefore used where skid-protection or shrapnel containment is necessary. They find some use in the lining of section of rocket airframe where catastrophic failure which may result in shrapnel may be present. Aramids are difficult to cut in the dry state and difficult to cleanly trim or machine when cured in a matrix. In the dry state, the best method of cutting is with well-sharpened high-quality shears, and patience.
Carbon-Aramid Hybrid Fabrics
The team has experimented before with fabrics that combine both carbon and aramid fibers in the weave. Generally this hasn’t been found particularly useful, as the aramids reduce the overall stiffness and compressive strength without adding any benefit that couldn’t be otherwise more efficiently achieved by including a separate aramid layer in the stackup.
Mats
Glass fibers and carbon fibers are also produced in mat form, where the fibers are randomly oriented and loosely packed together. The fibers are lightly bound to each other by a “size” adhesive, which dissolves in the resin upon lamination. Glass mat fibers typically have a size which is soluble in polyester and vinyl ester, but has poor solubility in epoxy. Carbon mats usually get a size which has better solubility in epoxy. But the type of size can only be definitely ascertained by contacting the manufacturer. Glass mat in heavier weights (1.5+ oz/yd²) is predominantly used in combination with vinyl ester when making fiberglass molds. In low weights, glass and carbon mats are usually called “tissues” or “surfacing veils”, and are useful when a very smooth surface is required on a part without the use of gel coat. As an example, an 0.7 oz/yd² glass surfacing veil has been used for the interior surface of the restrictor; weights down to 0.3 oz/yd² are readily available.
Weaves
There is not much "theory" to selection of weave in typical rocketry usage. One usually wants twill or satin weave, and not plain. Plain weave is difficult to use on anything other than flat plates or large cylinders. Twill or satin will conform to bi-directional curves much better. Satin is most generally useful, especially in harnesses 5HS to 8HS. The tow count -- 1k, 3k, etc -- often seen associated with a weave is the number of fiber strands in each tow of the weave (a tow is a single fiber bundle -- multiple tows are woven to form a weave). So the tow count is directly related to the fiber areal weight. (Fiber areal weight -- FAW -- is the mass of fiber per unit area, usually quoted in oz/yd² or g/m². The unit g/m² is often written “gsm”.)
Fillers
Fumed Silica (cab-o-sil)
Fumed silica (also known by brand name “cab-o-sil”) is a filler powder used to thicken epoxy resins. It is lightweight and confers thixotropic (shear thickening) properties on the resin, making it very useful in all potting, filling, and surfacing applications. Epoxy filled with fumed silica creates a hard, sandable surface. Sometimes microballoons are added to either reduce weight or weaken the surface (to make sanding a little easier).
Glass Microballoons
Glass microballoons are a powder consisting of small hollow glass spheres. The hollowness makes them extremely lightweight. They are useful in potting applications where weight minimization is important. Microballoons are not as strong as fumed silica, and do not thicken the resin as effectively, therefore they are often used in combination with fumed silica.
Talc Powder
Talc powder (a magnesium silicate) can be used as an epoxy filler. It is heavier than fumed silica and makes a surface which can be very difficult to sand. Therefore, it is not commonly used in applications where a surface finish is desired. However, it does improve smoothness of the filled resin, so sometimes a small amount of talc may be added in a surfacing application.
Milled/Chopped Glass Fiber
Milled or chopped glass fibers are readily available. They are simply E-glass fibers which have been cut to very short lengths. Milled fibers are short enough to look like powder, but will significantly strengthen the resin when used as a filler (at a cost of more weight). Chopped fibers are usually ⅛” to ¼” long, and greatly strengthen the resin, but it is difficult to spread a resin smoothly when filled with chopped fibers. Therefore, milled fibers are more often useful, particularly as an additive in mold surfacing when high strength is required (at the cost of more sanding time). The CalSTAR team has utilized this in the past by impregnating JB weld adhesive with Carbon Fiber shavings.
Chopped Carbon Fiber
Chopped carbon fibers are usually produced by the team, simply by repeatedly cutting scrap carbon fabric. They are useful for rapid repair in potting and filling applications. When onsite during a test or launch day, it is useful to have on hand a quantity of chopped carbon and fast-curing epoxy, to rapidly mix up a high-strength potting compound to apply to fill damaged areas which will cure within a short time period. Resin filled with chopped carbon can be difficult and messy to control, as the fibers tend to clump together and not flow.
Bondo
Bondo is a well-known material among hobbyists and amateurs. It is notable for being weak, brittle, and difficult to control. In particular, its cure time and hardness is highly sensitive to mix ratio with the catalyst. When applied as a filler to a mold surface, the Bondo is much weaker than the rest of the surface; this discontinuity in strengths makes it difficult to achieve a smooth and continuous surface during sanding. Bondo is composed of a polyester resin with a weak filler powder, and will dissolve styrene foams. No one knows precisely why Bondo remains popular, but year after year its ill-advised usage has punished the production schedule of many rocketry and other competition teams alike. It is strongly recommended that Bondo not be used.
Bondo Professional Glazing & Spot Putty
Special dispensation is made for a particular Bondo product called “Professional Glazing & Spot Putty”. It has a finer grained filler than general Bondo, and can be useful in the single specific case where one wants to fill tiny pinholes in mold surfaces -- in this case the goal is explicitly to have a weak filling agent, so that any excess filler remaining on the surface surrounding the hole can be easily sanded off later with a fine paper, and not risk damaging or mis-shaping the rest of the surface. A common mistake is to forget that the filler is a two-part system: it must be mixed with a hardening catalyst in order to cure. UV-curing putty is available, but it can be difficult to achieve full and consistent cure; therefore, the UV-curing material is also not recommended.
Foams
Urethane Modeling Foams
Urethane foam is the standard for mold making. In general, the higher the density, the better will be the mold. Cost scales directly with density; there are trade-offs to be made. Typical densities availale are 6, 10, 20 lb/ft^3. High quality parts have been made with 6 lb/ft^3 foam, but 10 or greater is preferred, as it will improve fidelity and reduce the coating/sanding effort considerably.
Urethane foam sands well and is reasonably strong. In lower density (6 lb/ft^3) take care not to puncture the foam, as its compressive strength isn’t too high. The foam is somewhat brittle and should not be dropped from too high or danced upon too enthusiastically. Urethane foam is compatible with both epoxy and ester resins. Slabs may be bonded together with either of these agents, or urethane Liquid Nails, or Gorilla Glue. When bonding slabs, make the adhesive layer as thin as possible -- otherwise it will be a hardness discontinuity that interferes with machining/sanding.
Styrene Modeling Foams
Polystyrene foams are cheap and readily available. They usually come in 1” thick boards meant for building insulation, but can be sometimes purchased thicker. There are two basic types:
● Expanded polystyrene (EPS)
● Extruded polystyrene (XPS)
EPS is composed of many beads fused together, and is horrible to sand / mill / shape. It is usually white, and often used in molded shipping boxes or packing peanuts. XPS is much better for sanding and shaping, and comes in colors blue or pink (there is no significant difference between XPS in the two different colors). Both typically come in 1-2 lb/ft^3 density: very light and very low hardness.
Over the years, polystyrene has been used to make a number of molds for FSAE and CalSol, two other competition teams on campus. These generally have been of low quality and time-consuming to produce. Polystyrene has the twin disadvantages of being very difficult to sand smooth, while also being incompatible with all polyester resins / fillers (these resins include styrene monomers in their formulation -- clearly, then they will dissolve styrene foam).
Urethane Expanding Foams
TO-DO
Adhesives
For the most part, one uses special epoxy formulations for adhering composite parts.
Hysol 9309
9309 is a high-strength structural epoxy adhesive. It is similar in many respects to 9396, but has a special filler allowing it to bridge gaps up to 0.030” and create good fillets with honeycomb core. It has a lower glass transition temperature than 9396, therefore it can be debonded with a heated blade when necessary. One generally does not add extra fillers to 9309. It has a Tg = 130°F and service temperature up to 160°F.
3M DP4X0
DP4X0 is a high-strength epoxy adhesive with a minute pot life indicated by the value of x and 24 hrs to full cure. Pot life options include 20 minutes, 60 minutes and 90 minutes. Recommended for all general purpose bonding when fast cure time is desired. Excellent for trackside repairs. While it can be filled with milled or chopped fibers to increase strength of a repair patch, this may make it brittle and thus more prone to failure. It also comes in a "NS" or "non-sag" variant which is good for applications such as creating fin fillets.
Hysol 9396
9396 is discussed earlier in this document as a laminating and potting resin, but is repeated here. It is specifically useful as an adhesive in high-temperature locations (service temperature up to 350°F). It can be moderately filled with fumed silica to bridge bond gaps between 0.020” - 0.030”, and needs no filler at gaps less than 0.015”. Because 9396 is quite linearly rigid, a good bond joint design becomes more important wherever peel failure is a concern. As one of the stiffest resins available, with reasonably low viscosity, 9396 is particularly good as an adhesive whenever the primary design requirement is stiffness and a definite 0.005” - 0.008” bond gap can be obtained.
Hardware store 5 minute epoxies
Decent results can be achieved with adhesive epoxies available from hardware stores. Devcon brand epoxies have been used successfully and are recommended. However, 9309 or DP420 will still be superior in strength, stiffness, and repeatability.
Vacuum Bags / Tapes / Plumbing / Pumps
TO-DO
Release Agents
TO-DO
Polishing Compounds
TO-DO
Solvents and Cleaners
TO-DO
Masking Tapes
TO-DO
Tools
Shears
Shears are not scissors. Shears look like big scissors, but they’re better. Good shears are sometimes marketed as carpet and upholstery shears. They have an adjustable pivot screw to control pressure between the two blades. The blades are of alloy steel and hold an edge. Shears need to be sharpened from time to time. Correct sharpening technique is essential to maintain close contact between the two shearing edges. An example of good shears is shown from the MSC catalog below.
Saws
The most effective saws for cutting fiber composites tend to be toothless steel disks impregnated with diamond powder. These are commonly available, marketed as tile-cutting saws. They can be purchased in sizes which fit Dremels, grinders, tables, etc.
Drills
High-speed steel drill bits will go dull fairly quickly when cutting fiber composites. Cheap ones can be sacrificed for simply punching holes. Machinists will not thank you for using their good precision drills to cut composites. Carbide bits are preferred, as they will last longer and cut cleaner. High precision (diameter tolerance < 0.001”) holes are readily achievable in composites with carbide reamers.
Cutters
If a composite part is to be cut or shaped in a mill or router, the cutter should preferably be carbide, with a titanium nitride coating. Again, machinists will not thank you for dulling down their general-purpose high-speed steel cutters on composites. Sacrificial bits may be used to ease their pain with prior request to the team.
Sand Paper
A standard stock of sand paper includes 60, 100, and 200 grits in dry sanding paper; 100, 200, 400, 600, 800, 1200 in wet sanding paper. Higher grits go dull quickly; in any grit, the paper must be replaced with some frequency as it goes dull. Discard dull paper -- this is not the place to be miserly.
Scotch-Brite
Scotch-brite pads come color-coded in different levels of aggressiveness of abrasion. It is usual to keep a stock of green pads (aggressive) and light gray pads (very soft). Note that some other colors of scotch brite are “tan”, “gray”, and “dark gray” -- not to be confused with “light gray”, which is almost white in color. Like sand paper, scotch-brite goes dull with continued use, and should be discarded.
Razor blades
Single edge razor blades find innumerable uses in composites manufacture. They are cheap and disposable. It is usually worth the extra money to get precision edge stainless blades, which will hold an edge sharper and longer than the standard blades. Blades should be disposed of frequently as they go dull. Proper disposal requires a sharps box of some sort.
Fasteners
TO-DO
Bond Surface Prep
Before bonding two surfaces together, it is critical that they be properly prepared. The goal is to achieve three qualities:
Cleanness -- no interfering grit or organic particles
High surface area -- increase surface area with texture
High surface energy -- increase the molecular adhesion between the surface and the glue
Mechanical abrasion
When bonding a fiber composite surface, the goal is to achieve scratches in all directions in the plastic matrix only. Carbon fibers, in particular, are poor bond surfaces, therefore one does not want to sand into the fiber. (If you see black grit, you’ve gone too deep.) Green scotch-brite pads are an effective abrasive to achieve scratches in the matrix without attacking the fibers underneath. Scratch the surface thoroughly in all directions, either with swirling motions ~1” in diameter, or by scratching at 0°, 90°, +45°, -45° in succession.
When bonding a metal surface, sand paper may be necessary to achieve good scratching. 200 grit dry sanding is effective, again moving either in 1” swirls or a 0°, 90°, +45°, -45° succession of sanding directions.
Cleaning
Clean the surface well with degreaser and water, then isopropyl alcohol. For stubborn surfaces, acetone may be necessary, always check to ensure that the surface is acetone safe before using acetone.
Water-break test
Prior to bonding, the quality of the surfaces can be tested by putting a few droplets of water on them. If the water spreads out into a thin film, then the surface energy of the part well exceeds the surface tension of the water. This is a good sign, indicating that high surface energy has been achieved, and the bond will be good. If the water balls up, repelled from the surface, then the surface prep steps must be repeated.
Etching of aluminum
Bare aluminum in air rapidly forms an oxide layer which bonds poorly. However, if this natural oxide layer is replaced with a special chromate one, the aluminum-to-epoxy bonds is one of the strongest you can get. Therefore, after mechanical abrasion and cleaning, the aluminum is to be etched with West System 860. While still wet after etching, the second part of the 860 system is applied, which puts down a chromate layer. This protects the aluminum surface from oxidation for several hours. In this time window, the bond should be made. A respirator with good filters is recommended while applying the chromate.
Note that anodized aluminum is a very poor bonding surface, and should be completely removed. This can be time consuming.
Also note that there is a more permanent alternative to West System 860, called “iridite” or “alodine”. This surface coating makes for excellent bonds, and does not have the same restriction on time frame for bonding. (The alodined surface is good for adhering to paint as well as epoxies.)
Release Surface Prep
When the goal is to have a material not stick to a surface (i.e. a plug or mold), it is again critical that the surface be properly prepared. The goal is to achieve three qualities:
Cleanness -- no interfering grit or sticky particles
Low surface area -- keep the surface as smooth as possible, i.e. a mirror-finish
Low surface energy -- decrease the molecular adhesion to the surface
Cleaning
Flash from previous uses of the mold should they be present, should be mechanically removed. A soft scotch-brite pad (light gray) is helpful. Be sure not to scratch the mold. If aggressive cleaning is necessary, use a degreaser with water, then acetone. Otherwise use isopropyl alcohol with a towel. Blow off dust and repeat wipe-down until thoroughly cleaned.
In situations where a mold is not used, but you are interfacing a carbon fiber layup with a surface which eventually you do not want the carbon to be bonded to, following the same steps as above but replacing the mold with your surface. Remember that it is always better to be sure of what you’re doing but slower than to work quickly and risk damaging or destroying the surface.
Mold release wax
Use Meguiar’s mold release wax or Part-all paste wax. Apply a thin light layer over the whole surface with a microfiber towel. Let the solvents flash off 5 minutes, then buff in the wax until shiny with a clean microfiber. (Buffing well is important -- a shiny waxed surface will release well, whereas a hazy texture of wax can actually act as a mild adhesive!) Repeat a minimum of 3 coats. The mold release wax provides a strong, low surface energy barrier between the mold and the part. It fills and smooths pinholes and tiny scratches. Often, mold release wax only needs to be applied the first few times a mold is used -- after that, the mold becomes “seasoned”, with plenty of wax permanently impregnated into the surface.
Water-break test
Before applying mold release film, but after waxing, the quality of the release surface can be roughly observed by putting a few droplets of water on the surface. If the water balls up, then the surface tension of the water exceeds the surface energy of the mold. This is a good sign, indicating low surface energy has been achieved on the mold, and it should release well. If the water spreads out in a thin film, this means the surface must be improved, either by better waxing or (more likely) by stripping off the wax (with acetone) and sanding the surface smoother, then clean it again and re-wax.
Mold release film
Mold release film is applied every time a mold is used. It is applied as a thin liquid layer which hardens into a polymer film no more than a few microns thick. It provides a breakable layer and a geometric offset between the mold surface and the part, allowing for easier release. Dampen a towel with mold release and wipe on a single layer covering the full surface. Rewiping over an area will only dissolve the previous release and is therefore unnecessary, but not harmful. Again, understand that the mold release film is a very thin coat.
Making a Plug
In a typical application, where a male plug is to be made, and then a female mold produced off of the plug, the essential steps are:
Urethane foam slabs are bonded together into a larger block
The foam is machined by a CNC routing shop off of CAD geometry
The machined plug is sprayed with a polyester-based hard surface coat (e.g. Duratec or Gel-Coat)
The coated plug is sanded smooth and polished
The female fiberglass mold is laid up on the plug
For a nosecone of size, say, 13” in diameter, expect step (1) to take two person-days, step (3) to take two person-days, and step (4) to take six person-days. The schedule for step (2) depends on how quickly you can get the CNC shop to mill the foam and send it back. Making the female mold (step 5) is discussed separately in this document. The bottom line to be very aware of is to start early! The time estimates above are deceiving, because:
● These estimates are for experienced workers. Students new to the process will be slower, with greater risk of damaging plugs and then needing to repair them.
● All curing processes have inherent downtime while you wait for resins to harden. This compounds the time cost of any unexpected repairs.
● The other time constraints on student schedules -- you really need full workdays to be most effective, and these only happen twice a week.
It is worth checking the mass of a given foam plug in CAD, to understand how many people will be needed to move it around as it goes through the various processing steps.
MORE DETAIL TO-DO
Making a Mold
The following outlines the process for making a 2-part fiberglass mold
Necessary Supplies:
● ⅛” Particle Board
● Thick Fiberglass Mat
● Vinyl Ester Resin / MEKP Catalyst
● Oil Based Clay
● Hot glue gun
● 2-3” paint brushes
● Plastic hemispheres
● Gel coat
Outline of steps:
Build dam separating the two halves of the mold
Gel goat first side
Lay-up fiberglass on first side
Tear down dam
Gel coat second side
Lay-up fiberglass on second side
Pull mold off plug
Layup
Outline of steps:
Prepare mold
Prepare materials: carbon plies, peel ply, breather, dropcloth, vacuum bag
Wet the carbon
SafeLease the mold
Lay up on mold surface
Vacuum seal part and vacuum part
Cure
Remove part from mold
Trimming
TO-DO
Launchsite Repair
TO-DO
Bond Joint Design Rules of Thumb
TO-DO
Mold Design Rules of Thumb
TO-DO
Reading List
Some useful books and articles are compiled in the table below.
Title | Author | Where to find | Comments |
ME127 reader: Design and Manufacture with Composite Materials | Multiple, compiled by Prof. Dharan | Needs to be Sourced | Concisely combines information from various textbooks and guides into one composites bible |
Fiberglass and Composite Materials: an enthusiast’s guide | Forbes Aird | Purchase if need be – pdf is being sourced | Straightforward, covers all the basics in resins, fabrics, layups, tools, processes |
Surface preparations for ensuring that the glue will stick in bonded composite structures | L.J. Hart-Smith | Search engineering articles database | Essential reading on bond prep of surfaces |
Adhesively bonded joints for fibrous composite structures | L.J. Hart-Smith | Search engineering articles database | Essential reading on bond joint design and why bonds fail |
Mil Handbook 17-2: POLYMER MATRIX COMPOSITES MATERIALS PROPERTIES | US Dept of Defense | Extensive list of tested material properties for various fibers and resins | |
Mil Handbook 17-3: POLYMER MATRIX COMPOSITES MATERIALS USAGE, DESIGN, AND ANALYSIS | US Dept of Defense | Overview of most practical composites matters. Most common standard reference in composites world | |
Handbook of Composites | edited by S.T. Peters | Good combination of theory and practical knowledge | |
Principles of Composite Material Mechanics | Ronald F. Gibson | at engineering library | Current ME 127 textbook, lots of theory |
Tensile Properties of Glass Microballoon- Epoxy Resin Syntactic Foams | Nikhil Gupta and Ruslan Nagorny | Properties of epoxy-glass microballoon potting compounds |
Suppliers List
This is a rough and incomplete list of composites-specific suppliers that may be used.
Supplier | Location | Link | Comments |
Tap Plastics | Stores throughout Bay Area, one close to garage | Close to RFS, fairly limited selection | |
The Composites Store | Southern California | ||
ACP Composites | Livermore | ||
Douglas & Sturgess | Richmond, close to garage | ||
Last updated