Crash helmets

In many applications, we exert forces on polymer products for extended periods of time. In such cases it is important that they do not deform beyond acceptable limits. We address this concern through creep testing, which may take days, weeks, or even months to perform. We can also change the rate at which we perform certain tests. Thus we might test the polymer resin to be used in a crash helmet at high speed to mimic an impact. In contrast, the film used in a plastic bag would be better tested at slower speeds, which are more representative of what it would experience during use. 

Fogging of plastic films used for packaging or agriculture, spectacle lenses, crash helmets, etc., is caused by water droplets. This decreases the transparency and is aesthetically not desirable. 

Polycarbonates and Polyurethanes The chemistry of carbonic acid derivatives is particularly important because two large classes of polymers are bonded by linkages containing these functional groups the polycarbonates and the polyurethanes. Polycarbonates are polymers bonded by the carbonate ester linkage, and polyurethanes are polymers bonded by the carbamate ester linkage. Lexan polycarbonate is a strong, clear polymer used in bulletproof windows and crash helmets. The diol used to make Lexan is a phenol called bisphenol A, a common intermediate in polyester and polyurethane synthesis. 

Three or more monomers may combine to give polymers with desired properties. For example, acrylonitrile, butadiene, and styrene are polymerized to give ABS plastic, a strong, tough, and resilient material used for bumpers, crash helmets, and other articles that must withstand heavy impacts. 

Dyneema, the strongest fabric known, is made of ultra high-density polyethylene, and is used for ropes, nets, bulletproof vests, and crash helmets. 

ABS, a widely produced copolymer used for high-impact applications like car bumpers and crash helmets, is formed from... 

Developments in plastics sports equipment are mainly aimed at improving player performance and increasing player safety. Items that fall into the first category include balls, bicycles, tennis rackets, and windsurfing boards. Crash helmets belong in the second category. 

An item of sports equipment that has been improved greatly with regard to player safety is the crash helmet. American football helmets are polycarbonate or ABS shelled, while impact nylons are often used on motorbike crash helmets. Another item of sports equipment in the United States where safety has been improved is a Reduced Injury Factor baseball that has a novel polyurethane core material. 

Percentage of crash helmet use Medium Acceptable Objective... 

Yetham, L. A., Godfreg, P. M., Chinn, P. B. Materials for Motorcycle Crash Helmets a Finite Element Parametric Study. Plastics. Rubber and Composite Processing and Applications 1994 22 215-21. 

The polyester resins can be chemically modified to suit the particular environment in which the product will function. For example, different resin systems are used for chemical storage tanks and motor-cycle crash helmets. 

The first stage was considered to be a slow environmental stress crack (ESC), produced by slight chemical attack in the weld. ESC may be defined as a reduction in the tolerance of mechanical stress caused by special chemical environments, or, alternatively, as a reduction in the time to fracture under a fixed strain. Other examples have been the failure of blow-moulded polyethylene bottles when filled with detergent, and the weakening of crash helmets made of polycarbonate when affected by petrol or adhesive badges. 

There is a multitude of polymers with widely differing properties, making them suitable for different applications like rubber tyres, crash helmets, food packagings, or plastic bags. This multitude is due to the fact that polymers consist of organic chain molecules whose structure can be controlled within wide margins (see also chapter 1). 

T-type photochromic thermoplastic systems are also finding non-opthahnic specialty applications in areas such as colouring drinks bottles, toys (including dolls which develop suntans) and crash helmet visors for motorcyclists. Photo-chromic systems are also used in formulations for surface coatings, and have been used for security printing, such as in passports. In addition, they show potential for personal care use, such as in cosmetics and hair dyes. A good description of these applications is given in Ref. [58]. 

Deterioration of mechanical properties in solvent contact has considerable technological implications. A well known example is the rapid failure of polycarbonate in crash helmets on exposure to petrol, or to the plasticizers from adhesives. Polyethylene household utensils fail at points of stress, under the influence of detergents. It has also been common where plastic moving parts in machinery are improperly lubricated and can result from improper use of solvent-based cleaning agents and polishes. 

Crash speeds must remain below a certain value in order to prevent serious injury. How a safe speed is defined is partly determined by the characteristics of a potential crash and the protection against injury that may be present when a crash occurs (e.g., seatbelts, child restraint seats, crash helmets, side underrun protection on trucks). Furthermore, the age of potential casualties should be considered when defining a safe crash speed. For example, at equal levels of crash energy, the consequences are more severe for elderly road users than for younger ones due to their greater vulnerability. 

PPE usd for protection while travelling on a road, such as cycle helmets, crash helmets and motorbike leathers worn by employees on the highway, is not covered by the Regulations. However, the requirements do apply in circumstances where this type of equipment is worn... 

Lexan has very high impact strength and is strong enough to be used in crash helmets. It is also used to manufacture telephone housings. Because Lexan can be produced as a clear colorless polymer, it is used in bulletproof windshields and in the visors of astronauts helmets. 

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