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Polyurethane Urea Elastomer
The polyurethane urea elastomer (PUU), or poly(urethane urea) elastomer, is a flexible polymeric material that is composed of linkages made out of polyurethane and polyurea compounds. Due to its hyperelastic properties, it is capable of bouncing back high-speed ballistic projectiles as if the material had “hardened” upon impact. PUUs were developed by researchers from the U.S. Army Research Laboratory (ARL) and the Army’s Institute for Soldier Nanotechnology at the Massachusetts Institute of Technology (MIT) to potentially replace polyethylene materials in body armor and other protective gear, such as combat helmets, face shields, and ballistic vests. Composition In general, PUUs are composed of both hard and soft segments that each play a role in the material’s physical properties. The soft segments consist of two types of chemical compounds, long-chain polyols and diisocyanates, that react and connect together with urethane linkages. On the other hand, the short-chain ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Polymeric Material
Polymer engineering is generally an engineering field that designs, analyses, and modifies polymer materials. Polymer engineering covers aspects of the petrochemical industry, polymerization, structure and characterization of polymers, properties of polymers, compounding and processing of polymers and description of major polymers, structure property relations and applications. History The word “polymer” was introduced by the Swedish chemist J. J. Berzelius. He considered, for example, benzene (C6H6) to be a polymer of ethyne (C2H2). Later, this definition underwent a subtle modification. The history of human use of polymers has been long since the mid-19th century, when it entered the chemical modification of natural polymers. In 1839, C. Goodyear has found a critical advance in the research of rubber vulcanization, which has turned natural rubber into a practical engineering material. In 1870, J. W. Hyatt uses camphor to plasticize nitrocellulose to make nitrocellulose plas ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Diethyltoluenediamine
Diethyl toluene diamine (DETDA) is a liquid aromatic organic molecule with formula C11H18N2. It is chemically an aromatic diamine and has the CAS Registry number of 68479-98-1. It has more than one isomer and the mixture of the two main isomers is given a different CAS number of 75389-89-8. It is often marketed as a less toxic version of 4,4'-methylenedianiline (MDA). It is also used to replace the more toxic 4,4'-methylenebis(2-chloroaniline) (MOCA). The toxicology is reasonably well understood. Uses DETDA is an industrial chemical used in the injection molding industry. One of the reasons it is used in RIM is because it gives very short demold times. It is also used extensively in polyurethanes and in both spray polyureas and elastomers. When used in elastomer production these can be used as an energy absorbing system in automobiles. It is a diamine and thus in polymer science terms is a Chain extender rather than a chain terminator. Chain extenders (''f'' = 2) and c ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Plastics
Plastics are a wide range of synthetic polymers, synthetic or semi-synthetic materials that use polymers as a main ingredient. Their Plasticity (physics), plasticity makes it possible for plastics to be Injection moulding, moulded, Extrusion, extruded or Compression molding, pressed into solid objects of various shapes. This adaptability, plus a wide range of other properties, such as being lightweight, durable, flexible, and inexpensive to produce, has led to its widespread use. Plastics typically are made through human industrial systems. Most modern plastics are derived from petrochemical, fossil fuel-based chemicals like natural gas or petroleum; however, recent industrial methods use variants made from renewable materials, such as corn or cotton derivatives. 9.2 billion tonnes of plastic are estimated to have been made between 1950 and 2017. More than half this plastic has been produced since 2004. In 2020, 400 million tonnes of plastic were produced. If global trends on pl ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Polyurethanes
Polyurethane (; often abbreviated PUR and PU) refers to a class of polymers composed of organic units joined by carbamate (urethane) links. In contrast to other common polymers such as polyethylene and polystyrene, polyurethane is produced from a wide range of starting materials. This chemical variety produces polyurethanes with different chemical structures leading to many different applications. These include rigid and flexible foams, varnishes and coatings, adhesives, electrical potting compounds, and fibers such as spandex and PUL. Foams are the largest application accounting for 67% of all polyurethane produced in 2016. A polyurethane is typically produced by reacting an isocyanate with a polyol. Since a polyurethane contains two types of monomers, which polymerize one after the other, they are classed as alternating copolymers. Both the isocyanates and polyols used to make a polyurethane contain two or more functional groups per molecule. Global production in 2019 wa ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Military Technology
Military technology is the application of technology for use in warfare. It comprises the kinds of technology that are distinctly military in nature and not civilian in application, usually because they lack useful or legal civilian applications, or are dangerous to use without appropriate military training. The line is porous; military inventions have been brought into civilian use throughout history, with sometimes minor modification if any, and civilian innovations have similarly been put to military use. Military technology is usually researched and developed by scientists and engineers specifically for use in battle by the armed forces. Many new technologies came as a result of the military funding of science. Armament engineering is the design, development, testing and lifecycle management of military weapons and systems. It draws on the knowledge of several traditional engineering disciplines, including mechanical engineering, electrical engineering, mechatronics, el ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Relaxation (physics)
In the physical sciences, relaxation usually means the return of a perturbed system into equilibrium. Each relaxation process can be categorized by a relaxation time τ. The simplest theoretical description of relaxation as function of time ''t'' is an exponential law (exponential decay A quantity is subject to exponential decay if it decreases at a rate proportional to its current value. Symbolically, this process can be expressed by the following differential equation, where is the quantity and (lambda) is a positive rate ...). In simple linear systems Mechanics: Damped unforced oscillator Let the homogeneous differential equation: :m\frac+\gamma\frac+ky=0 model damped harmonic oscillator, damped unforced oscillations of a weight on a spring. The displacement will then be of the form y(t) = A e^ \cos(\mu t - \delta). The constant T (=2m/\gamma) is called the relaxation time of the system and the constant μ is the quasi-frequency. Electronics: RC circuit In an RC ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Mail (armour)
Chain mail (properly called mail or maille but usually called chain mail or chainmail) is a type of armour consisting of small metal rings linked together in a pattern to form a mesh. It was in common military use between the 3rd century BC and the 16th century AD in Europe, and longer in Asia and North Africa. A coat of this armour is often called a hauberk, and sometimes a byrnie. History The earliest examples of surviving mail were found in the Carpathian Basin at a burial in Horný Jatov, Slovakia dated at 3rd century BC, and in a chieftain's burial located in Ciumești, Romania. Its invention is commonly credited to the Celts, [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Fracture Toughness
In materials science, fracture toughness is the critical stress intensity factor of a sharp crack where propagation of the crack suddenly becomes rapid and unlimited. A component's thickness affects the constraint conditions at the tip of a crack with thin components having plane stress conditions and thick components having plane strain conditions. Plane strain conditions give the lowest fracture toughness value which is a material property. The critical value of stress intensity factor in mode I loading measured under plane strain conditions is known as the plane strain fracture toughness, denoted K_\text. When a test fails to meet the thickness and other test requirements that are in place to ensure plane strain conditions, the fracture toughness value produced is given the designation K_\text. Fracture toughness is a quantitative way of expressing a material's resistance to crack propagation and standard values for a given material are generally available. Slow self-sust ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Polycarbonate
Polycarbonates (PC) are a group of thermoplastic polymers containing carbonate groups in their chemical structures. Polycarbonates used in engineering are strong, tough materials, and some grades are optically transparent. They are easily worked, molded, and thermoformed. Because of these properties, polycarbonates find many applications. Polycarbonates do not have a unique resin identification code (RIC) and are identified as "Other", 7 on the RIC list. Products made from polycarbonate can contain the precursor monomer bisphenol A (BPA). Structure Carbonate esters have planar OC(OC)2 cores, which confers rigidity. The unique O=C bond is short (1.173 Å in the depicted example), while the C-O bonds are more ether-like (the bond distances of 1.326 Å for the example depicted). Polycarbonates received their name because they are polymers containing carbonate groups (−O−(C=O)−O−). A balance of useful features, including temperature resistance, impact resistance and o ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Strain Rate Imaging
Strain rate imaging is a method in echocardiography (medical ultrasound) for measuring regional or global deformation of the myocardium (heart muscle). The term "deformation" refers to the myocardium changing shape and dimensions during the cardiac cycle. If there is myocardial ischemia, or there has been a myocardial infarction, in part of the heart muscle, this part is weakened and shows reduced and altered systolic function. Also in regional asynchrony, as in bundle branch block, there is regional heterogeneity of systolic function. By strain rate imaging, the simultaneous function of different regions can be displayed and measured. The method was first based on colour tissue Doppler.Heimdal A, Stoylen A, Torp H, Skjaerpe T. Real-time strain rate imaging of the left ventricle by ultrasound. J Am Soc Echocardiogr 1998 Nov;11(11):1013-19 by using the longitudinal myocardial velocity gradient, already in use transmurally. Later, the regional deformation has also been available b ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Silicate
In chemistry, a silicate is any member of a family of polyatomic anions consisting of silicon and oxygen, usually with the general formula , where . The family includes orthosilicate (), metasilicate (), and pyrosilicate (, ). The name is also used for any salt of such anions, such as sodium metasilicate; or any ester containing the corresponding chemical group, such as tetramethyl orthosilicate. The name "silicate" is sometimes extended to any anions containing silicon, even if they do not fit the general formula or contain other atoms besides oxygen; such as hexafluorosilicate .Most commonly, silicates are encountered as silicate minerals. For diverse manufacturing, technological, and artistic needs, silicates are versatile materials, both natural (such as granite, gravel, and garnet) and artificial (such as Portland cement, ceramics, glass, and waterglass). Structural principles In all silicates, silicon atom occupies the center of an idealized tetrahedron whose corner ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Microparticle
Microparticles are particles between 0.1 and 100 μm in size. Commercially available microparticles are available in a wide variety of materials, including ceramics, glass, polymers, and metals. Microparticles encountered in daily life include pollen, sand, dust, flour, and powdered sugar. Microparticles have a much larger surface-to-volume ratio than at the macroscale, and thus their behavior can be quite different. For example, metal microparticles can be explosive in air. Microspheres are spherical microparticles, and are used where consistent and predictable particle surface area is important. In biological systems, a microparticle is synonymous with a microvesicle, a type of extracellular vesicle (EV). Alternative definitions for size Mathematical: as the term "micro" refers to 10^, the range for micro would then be 10^ to 10^, or roughly 31.6 nm to 31.6 micrometers. However, general acceptance considers particles smaller than 100 nm nanoparticles. Roundi ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
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