OEM101#1 Helmet Material

Q1. WHAT IS FABRIC?

The term fabric can be defined as a planner structure produced by interlaced/interlooped yarns or fibers and felts made by interlocking fibers. It is a manufactured assembly of fibers and /or yarns that has substantial surface area in relation to its thickness and sufficient mechanical strength to give the assembly inherent cohesion. Basically, there are three methods by which fabrics are made. They are:
Fabric construction
Fig: Fabric construction
Weaving Process: 
Weaving is the intersection of two sets of straight yarns, warp and weft, which cross and interlace at right angles to each other. The lengthwise yarns are known as warp yarns and width wise yarns are known as weft or filling yarns and the fabric produced is known as woven fabric.
 
Knitting Process: 
Knitting consists of forming yarns into loops, each of which is typically only released after a succeeding loop has been formed and intermeshed with it so that a secure ground loop structure is achieved.
 
Non- woven Process: 
In this method, fabrics (known as non-wovens) are made of fibres held together by an applied bonding agent or by the fusing of self-contained thermoplastic fibres. Here, nothing is processed on conventional spindles, looms or knitting machines.
 
Warp & Weft:
The word warp is used as a noun to refer-
Threads length ways in a fabric as woven.
A number of threads in long lengths and approximately parallel, in various forms intended for weaving, knitting, doubling, sizing, dyeing, or lace-making.
The word weft refers to -
Threads width wise in a fabric as woven.
Yarn intended for use as in (1).
Fabric Construction:
Fabric construction refers to the fabric specification. The general format of fabric construction is given below:
 
Warp count X Weft count / Ends per inch X Picks per inch
Example: 20 X 16 / 128 X 60
Some times fabric construction is also written in the other way round i.e.
Ends per inch X Picks per inch / Warp count X Weft count 
Q2. WHAT IS FOAM?
Foam is an object formed by trapping pockets of gas in a liquid or solid. A bath sponge and the head on a glass of beer are examples of foams. In most foams, the volume of gas is large, with thin films of liquid or solid separating the regions of gas. Soap foams are also known as suds.
 
Solid foams can be closed-cell or open-cell. In closed-cell foam, the gas forms discrete pockets, each completely surrounded by the solid material. In open-cell foam, gas pockets connect to each other. A bath sponge is an example of an open-cell foam: water easily flows through the entire structure, displacing the air. A camping mat is an example of a closed-cell foam: gas pockets are sealed from each other so the mat cannot soak up water.
 
Foams are examples of dispersed media. In general, gas is present, so it divides into gas bubbles of different sizes (i.e., the material is polydisperse)—separated by liquid regions that may form films, thinner and thinner when the liquid phase drains out of the system films. When the principal scale is small, i.e., for a very fine foam, this dispersed medium can be considered a type of colloid.
 
Foam can also refer to something that is analogous to foam, such as quantum foam, polyurethane foam (foam rubber), XPS foam, polystyrene, phenolic, or many other manufactured foams.

Structure
A foam is, in many cases, a multi-scale system.
One scale is the bubble: material foams are typically disordered and have a variety of bubble sizes. At larger sizes, the study of idealized foams is closely linked to the mathematical problems of minimal surfaces and three-dimensional tessellations, also called honeycombs. The Weaire–Phelan structure is considered the best possible (optimal) unit cell of a perfectly ordered foam, while Plateau's laws describe how soap-films form structures in foams.
 
At lower scale than the bubble is the thickness of the film for metastable foams, which can be considered a network of interconnected films called lamellae. Ideally, the lamellae connect in triads and radiate 120° outward from the connection points, known as Plateau borders.
 
An even lower scale is the liquid–air interface at the surface of the film. Most of the time this interface is stabilized by a layer of amphiphilic structure, often made of surfactants, particles (Pickering emulsion), or more complex associations.

Solid foams
Further information: Polymeric foam
Solid foams are a class of lightweight cellular engineering materials. These foams are typically classified into two types based on their pore structure: open-cell-structured foams (also known as reticulated foams) and closed-cell foams. At high enough cell resolutions, any type can be treated as continuous or "continuum" materials and are referred to as cellular solids  with predictable mechanical properties.
 
Open-cell-structured foams contain pores that are connected to each other and form an interconnected network that is relatively soft. Open-cell foams fill with whatever gas surrounds them. If filled with air, a relatively good insulator results, but, if the open cells fill with water, insulation properties would be reduced. Recent studies have put the focus on studying the properties of open-cell foams as an insulator material. Wheat gluten/TEOS bio-foams have been produced, showing similar insulator properties as for those foams obtained from oil-based resources. Foam rubber is a type of open-cell foam.
 
Closed-cell foams do not have interconnected pores. The closed-cell foams normally have higher compressive strength due to their structures. However, closed-cell foams are also, in general more dense, require more material, and as a consequence are more expensive to produce. The closed cells can be filled with a specialized gas to provide improved insulation. The closed-cell structure foams have higher dimensional stability, low moisture absorption coefficients, and higher strength compared to open-cell-structured foams. All types of foam are widely used as core material in sandwich-structured composite materials.
 
The earliest known engineering use of cellular solids is with wood, which in its dry form is a closed-cell foam composed of lignin, cellulose, and air. From the early 20th century, various types of specially manufactured solid foams came into use. The low density of these foams makes them excellent as thermal insulators and flotation devices and their lightness and compressibility make them ideal as packing materials and stuffings.
 
An example of the use of azodicarbonamide as a blowing agent is found in the manufacture of vinyl (PVC) and EVA-PE foams, where it plays a role in the formation of air bubbles by breaking down into gas at high temperature.
 
The random or "stochastic" geometry of these foams makes them good for energy absorption, as well. In the late 20th century to early 21st century, new manufacturing techniques have allowed for geometry that results in excellent strength and stiffness per weight. These new materials are typically referred to as engineered cellular solids.
Q3. WHAT IS POLYCARBONATE?
Polycarbonate (PC) plastics are a naturally transparent amorphous thermoplastic. Although they are made commercially available in a variety of colors (perhaps translucent and perhaps not), the raw material allows for the internal transmission of light nearly in the same capacity as glass. Polycarbonate polymers are used to produce a variety of materials and are particularly useful when impact resistance and/or transparency are a product requirement (e.g. in bullet-proof glass). PC is commonly used for plastic lenses in eyewear, in medical devices, automotive components, protective gear, greenhouses, Digital Disks (CDs, DVDs, and Blu-ray), and sport helmets. Polycarbonate also has very good heat resistance and can be combined with flame retardant materials without significant material degradation. Polycarbonate plastics are engineering plastics in that they are typically used for more capable, robust materials such as in impact resistant “glass-like” surfaces.
 
The following diagram shows the relative impact strength of Polycarbonate when compared to the impact strength of other commonly used plastics such as ABS, Polystyrene (PS), or Nylon.
 
Another feature of polycarbonate is that it is very pliable. It can typically be formed at room temperature without cracking or breaking, similar to aluminum sheet metal. Although deformation may be simpler with the application of heat, even small angle bends are possible without it. This characteristic makes polycarbonate sheet stock particularly useful in prototyping applications where sheet metal lacks viability (e.g. when transparency is required or when a non-conductive material with good electrical insulation properties is required).

What are the Characteristics of Polycarbonate?
 
Now that we know what it is used for, let’s examine some of the key properties of Polycarbonate. PC is classified as a “thermoplastic” (as opposed to “thermoset”), and the name has to do with the way the plastic responds to heat. Thermoplastic materials become liquid at their melting point (155 degrees Celsius in the case of Polycarbonat). A major useful attribute about thermoplastics is that they can be heated to their melting point, cooled, and reheated again without significant degradation. Instead of burning, thermoplastics like Polycarbonate liquefy, which allows them to be easily injection molded and then subsequently recycled.
 
By contrast, thermoset plastics can only be heated once (typically during the injection molding process). The first heating causes thermoset materials to set (similar to a 2-part epoxy) resulting in a chemical change that cannot be reversed. If you tried to heat a thermoset plastic to a high temperature a second time it would simply burn. This characteristic makes thermoset materials poor candidates for recycling.
 
Polycarbonate is also an amorphous material, meaning that it does not exhibit the ordered characteristics of crystalline solids. Typically amorphous plastics demonstrate a tendency to gradually soften (i.e. they have a wider range between their glass transition temperature and their melting point) rather than to exhibit a sharp transition from solid to liquid as is the case in crystalline polymers.Lastly, Polycarbonate is a copolymer in that it is composed of several different monomer types in combination with one another.
Q4. WHAT IS EVA?
EVA Feature: Soft, flexible plastic with low-temperature toughness and stress-crack resistance
Flexible EVA (ethylene vinyl acetate) is the copolymer of ethylene and vinyl acetate. It’s an extremely elastic material that can be processed like other thermoplastics. The material has low-temperature toughness, stress-crack and UV radiation resistance. 
 
EVA IS WIDELY USED FOR:
Soft inner liners for rigid socket frames
Inner boots for pediatric AFOs
Orthotics for hand and wrist
Upper and lower extremity prostheses
 
PERFORMANCE CHARACTERISTICS:
 
Excellent moldability
Lightweight
Impact resistant
 
FLEXIBLE (EVA) MATERIAL OPTIONS - OP-TEK® Flex, Duraflex®, Proflex, Orfitrans™ Excel
 
OP-TEK® Flex– is a soft, flexible EVA copolymer that provides for outstanding patient comfort (helmet) when used as a liner for rigid socket frames. OP-TEK® Flex is specially formulated to maintain more consistent walls during forming compared with many other flexible plastics.
 
OP-TEK® Flex Comfort– is a soft, flexible EVA copolymer with a proprietary additive that gives the material a softer feel. This enhanced surface provides superior patient comfort when used as a liner for rigid socket frames. The additive greatly reduces friction when patients don and doff prosthetic devices. Unlike EVAs with silicone, OP-TEK® Flex Comfort exhibits excellent seaming characteristics during drape forming and more consistent walls during blister/bubble forming compared with many other EVA copolymer materials.
 
OP-TEK® Flex BiLam– provides added comfort and improves aesthetics for patients wearing carbon socket frames. The inner layer contains a hypoallergenic, FDA compliant additive that reduces friction, and the outer layer helps hide trim lines and window cut-outs of carbon socket frames.
 
Duraflex®– is a soft, flexible EVA copolymer that provides patient comfort when used as a liner for rigid socket frames. Duraflex® is harder and a little more rigid than OP-TEK® Flex and Proflex. It is available in natural (semi-transparent) and black.
 
Proflex– is a soft, flexible EVA copolymer that provides a superior level of patient comfort when used as a liner for rigid socket frames. 
 
Proflex with Silicone (Proflex-S)– is a soft, flexible EVA copolymer with a silicone lubricant. Like Proflex it provides a superior level of patient comfort when used as a liner for rigid socket frames. The silicone reduces friction when patients don and doff prosthetic devices.
 
Orfitrans™ Excel– is available in semi-transparent and black. The material pulls very easily and offers outstanding comfort for the patient.
 
Tech Tip– Be aware that certain solvents can cause cracks to propagate with EVA materials.
Q5. WHAT IS EPP?

EPP( Expanded Polypropylene) is an advanced protective system that's significantly lighter than the traditional foam inside most batters helmets. In fact. EPP is one of the lightest protective materials on the market. Yet, it doesn't sacrifice performance. Our EPP impact absorption liner is part of a three layer protection system in the helmets. It distributes the load and energy of impacts across the entirety of the helmet shell, effectively dissipating that energy away from the play The EPP impact absorption liner is uniquely formed and ventilated to maximize performance and air flow throughout the helmet.

Expanded polypropylene (EPP) is an engineered plastic foam material. By combining polypropylene resin with magic dust, and applying heat, pressure and CO2 in an autoclave, the material is formed into small plastic beads. These small, closed-cell foam beads are injected into a steam chest to create parts custom molded into complex shapes using steam heat & pressure.

EPP materials provide competitive advantages for designers and engineers looking to enhance custom molded parts.

• A variety of specialty grades & density ranging from 1.25lb. to 5.6lb. per cubic foot

• Available in a range of colors

• Unsurpassed quality / Material properties that outperform other comparable foam materials

• Lightweight with very high strength to weight ratio / highly durable

• Resistant to water, chemicals and most oils

• Resistant to temperature extremes from -35

EPP Helmet feature: Light; strong sturcture; Resistant to water; Resistant to temperature; Unsurpassed quality.

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