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57-459: Gore-Tex is W. L. Gore & Associates 's trade name for waterproof, breathable fabric membrane. It was invented in 1969. Gore-Tex blocks liquid water while allowing water vapor to pass through and is designed to be a lightweight, waterproof fabric for all-weather use. It is composed of expanded PTFE (ePTFE), a stretched out form of the PFAS compound polytetrafluoroethylene (PTFE). Gore-Tex

114-642: A Poisson's ratio of exactly 0.5. Most steels and rigid polymers when used within their design limits (before yield ) exhibit values of about 0.3, increasing to 0.5 for post-yield deformation which occurs largely at constant volume. Rubber has a Poisson ratio of nearly 0.5. Cork's Poisson ratio is close to 0, showing very little lateral expansion when compressed and glass is between 0.18 and 0.30. Some materials, e.g. some polymer foams, origami folds, and certain cells can exhibit negative Poisson's ratio, and are referred to as auxetic materials . If these auxetic materials are stretched in one direction, they become thicker in

171-478: A closely held trade secret and as such, it had remained unpublished. In the 1970s Garlock, Inc. allegedly infringed Gore's patents by using Cropper's machine and was sued by Gore in the Federal District Court of Ohio . The District Court held Gore's product and process patents to be invalid after a "bitterly contested case" that "involved over two years of discovery , five weeks of trial,

228-437: A compression creep test. Initially, the compression creep test shows positive Poisson's ratios, but gradually decreases until it reaches negative values. Consequently, this also shows that Poisson's ratio for wood is time-dependent during constant loading, meaning that the strain in the axial and transverse direction do not increase in the same rate. Media with engineered microstructure may exhibit negative Poisson's ratio. In

285-403: A cork into a bottle arises only from the friction between the cork and the bottle due to the radial compression of the cork. If the stopper were made of rubber, for example, (with a Poisson's ratio of about +0.5), there would be a relatively large additional force required to overcome the radial expansion of the upper part of the rubber stopper. Most car mechanics are aware that it is hard to pull

342-427: A cube stretched in the x -direction (see Figure 1) with a length increase of Δ L in the x -direction, and a length decrease of Δ L ′ in the y - and z -directions, the infinitesimal diagonal strains are given by If Poisson's ratio is constant through deformation, integrating these expressions and using the definition of Poisson's ratio gives Solving and exponentiating, the relationship between Δ L and Δ L ′

399-440: A geological timescale, excessive erosion or sedimentation of Earth's crust can either create or remove large vertical stresses upon the underlying rock. This rock will expand or contract in the vertical direction as a direct result of the applied stress, and it will also deform in the horizontal direction as a result of Poisson's effect. This change in strain in the horizontal direction can affect or form joints and dormant stresses in

456-479: A linear isotropic material subjected only to compressive (i.e. normal) forces, the deformation of a material in the direction of one axis will produce a deformation of the material along the other axis in three dimensions. Thus it is possible to generalize Hooke's Law (for compressive forces) into three dimensions: where: these equations can be all synthesized in the following: In the most general case, also shear stresses will hold as well as normal stresses, and

513-599: A material will actually shrink in the transverse direction when compressed (or expand when stretched) which will yield a negative value of the Poisson ratio. The Poisson's ratio of a stable, isotropic , linear elastic material must be between −1.0 and +0.5 because of the requirement for Young's modulus , the shear modulus and bulk modulus to have positive values. Most materials have Poisson's ratio values ranging between 0.0 and 0.5. A perfectly incompressible isotropic material deformed elastically at small strains would have

570-422: A microporous structure that was about 70% air. It was introduced to the public under the trademark Gore-Tex. Gore promptly applied for and obtained the following patents: Another form of stretched PTFE tape was produced prior to Gore-Tex in 1966, by John W. Cropper of New Zealand . Cropper had developed and constructed a machine for this use. However, Cropper chose to keep the process of creating expanded PTFE as

627-502: A negative Poisson's ratio due to the expansion of ePTFE along all directions, contrasting the more expected reduction in the directions perpendicular to the stress in cases with volume conservation. ePTFE has tunable porosity based on the processing conditions and can be made permeable to certain vapors and gases. However, it is impermeable to most liquids, including water, a property that is exploited in certain applications such as raincoats. These additional properties in combination with

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684-472: A public patent had not been filed, the new form of the material could not be legally recognised. Gore was thereby established as the legal inventor of ePTFE. Following the Gore v. Garlock decision, Gore sued C. R. Bard for allegedly infringing its patent by making ePTFE vascular grafts. Bard promptly settled and agreed to exit the market. Gore next sued IMPRA, Inc., a smaller maker of ePTFE vascular grafts, in

741-428: A simple case auxeticity is obtained removing material and creating a periodic porous media. Lattices can reach lower values of Poisson's ratio, which can be indefinitely close to the limiting value −1 in the isotropic case. More than three hundred crystalline materials have negative Poisson's ratio. For example, Li, Na, K, Cu, Rb, Ag, Fe, Ni, Co, Cs, Au, Be, Ca, Zn Sr, Sb, MoS 2 and others. At finite strains ,

798-473: A small airspace. When there is cold bridging, vapour on the dry side can condense on the cold surface, making it appear that the thin waterproof breathable fabric has leaked. Poisson%27s ratio In materials science and solid mechanics , Poisson's ratio (symbol: ν ( nu )) is a measure of the Poisson effect , the deformation (expansion or contraction) of a material in directions perpendicular to

855-449: Is bulk modulus and E is Young's modulus . If a rod with diameter (or width, or thickness) d and length L is subject to tension so that its length will change by Δ L then its diameter d will change by: The above formula is true only in the case of small deformations; if deformations are large then the following (more precise) formula can be used: where The value is negative because it decreases with increase of length For

912-501: Is a unit vector directed perpendicular to the direction of extension. Poisson's ratio has a different number of special directions depending on the type of anisotropy. Orthotropic materials have three mutually perpendicular planes of symmetry in their material properties. An example is wood, which is most stiff (and strong) along the grain, and less so in the other directions. Then Hooke's law can be expressed in matrix form as where The Poisson ratio of an orthotropic material

969-455: Is bonded to a fabric. This membrane had about 9 billion pores per square inch (around 1.4 billion pores per square centimeter). Each pore is approximately 1 ⁄ 20,000 the size of a water droplet, making it impenetrable to liquid water while still allowing the more volatile water vapor molecules to pass through. The outer layer of Gore-Tex fabric is coated on the outside with a Durable Water Repellent (DWR) treatment. The DWR prevents

1026-414: Is called the major Poisson ratio while the smaller one (in this case ν yx ) is called the minor Poisson ratio . We can find similar relations between the other Poisson ratios. Transversely isotropic materials have a plane of isotropy in which the elastic properties are isotropic. If we assume that this plane of isotropy is the yz -plane, then Hooke's law takes the form where we have used

1083-541: Is different in each direction ( x , y and z ). However, the symmetry of the stress and strain tensors implies that not all the six Poisson's ratios in the equation are independent. There are only nine independent material properties: three elastic moduli, three shear moduli, and three Poisson's ratios. The remaining three Poisson's ratios can be obtained from the relations From the above relations we can see that if E x > E y then ν xy > ν yx . The larger ratio (in this case ν xy )

1140-402: Is enabled by the unwinding of PTFE molecules to create large pores within the structure. This favors highly ordered, crystalline PTFE that allows the molecules to disentangle more easily and uniformly when stretched. The porosity is largely determined by the stretching temperature and rate. Changing the stretching rate from 4.8 m/min to 8m/min can increase the porosity from 60.4% to 70.8%. Due to

1197-470: Is leaking when it is not. Wear and cleaning will reduce the performance of Gore-Tex fabric by wearing away this Durable Water Repellent (DWR) treatment. The DWR can be reinvigorated by tumble drying the garment or ironing on a low setting. Gore requires that all garments made from their material have taping over the seams, to eliminate leaks. Gore's sister product, Windstopper , is similar to Gore-Tex in being windproof and breathable, and it can stretch, but it

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1254-410: Is nearly inert inside the body. Specifically, expanded polytetrafluoroethylene (E-PTFE) can take the form of a fabric-like mesh. Implementing and applying the mesh form in the medical field is a promising type of technological material feature. In addition, the porosity of Gore-Tex permits the body's own tissue to grow through the material, integrating grafted material into the circulation system. Gore-Tex

1311-410: Is not waterproof. The Gore naming system does not imply any specific technology or material but instead implies a specific set of performance characteristics. Expanded polytetrafluoroethylene is used in clothing due to its breathability and water protection capabilities. Besides use in rainwear ePTFE can now be found in space suits . Gore-Tex is also used internally in medical applications, because it

1368-488: Is then For very small values of Δ L and Δ L ′ , the first-order approximation yields: The relative change of volume ⁠ Δ V / V ⁠ of a cube due to the stretch of the material can now be calculated. Since V = L and one can derive Using the above derived relationship between Δ L and Δ L ′ : and for very small values of Δ L and Δ L ′ , the first-order approximation yields: For isotropic materials we can use Lamé's relation where K

1425-531: Is used in a wide variety of medical applications, including sutures, vascular grafts, heart patches, and synthetic knee ligaments, which have saved thousands of lives. In the form of expanded polytetrafluoroethylene (E-PTFE), Gore-Tex has been shown to be a reliable synthetic, medical material in treating patients with nasal dorsal interruptions. In more recent observations, expanded polytetrafluoroethylene (E-PTFE) has recently been used as membrane implants for glaucoma surgery . Gore-Tex has been used for many years in

1482-445: Is usually due to uniquely oriented, hinged molecular bonds. In order for these bonds to stretch in the longitudinal direction, the hinges must ‘open’ in the transverse direction, effectively exhibiting a positive strain. This can also be done in a structured way and lead to new aspects in material design as for mechanical metamaterials . Studies have shown that certain solid wood types display negative Poisson's ratio exclusively during

1539-463: Is very dependent upon weather conditions, especially temperature, humidity, and wind. Fabric construction which directs water away from the body, rather than membranes, coatings, or laminates, can be used to keep the wearer dry. This means that perspiration can be moved away from the body more effectively, as both liquid water and water vapour can be directed. These are directional fabrics such as Nikwax Analogy and FurTech, which are also breathable in

1596-516: The Leeds University Rain Room show no signs of leakage after 4 hours of simulated rain five times heavier than heavy rain. However, some garments made from fabrics that exceed 20 000 mm have leaked through zips, hoods, and seams. Fabric head ratings do not totally specify water resistance of a garment, as it does not test closures such as zips. In addition, the breathability of nearly all waterproof/breathable fabrics

1653-503: The yz -plane of isotropy to reduce the number of constants, that is, The symmetry of the stress and strain tensors implies that This leaves us with six independent constants E x , E y , G xy , G yz , ν xy , ν yz . However, transverse isotropy gives rise to a further constraint between G yz and E y , ν yz which is Therefore, there are five independent elastic material properties two of which are Poisson's ratios. For

1710-436: The assumed plane of symmetry, the larger of ν xy and ν yx is the major Poisson ratio. The other major and minor Poisson ratios are equal. Some materials known as auxetic materials display a negative Poisson's ratio. When subjected to positive strain in a longitudinal axis, the transverse strain in the material will actually be positive (i.e. it would increase the cross sectional area). For these materials, it

1767-494: The best materials have 20,000 mm and 20,000 g. One specific definition of "waterproof/breathable" requires the fabric to withstand a pressure of over 1,000 millimetres of water (9.8  kPa ) pressure without leaking (see hydrostatic head ). These values should be taken with some caveats. Rain room tests show that some fabrics with less than 1,000 mm of water resistance keep water out sufficiently for practical purposes. Garments made from these fabrics tested in

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1824-459: The company knew about the dangers of PFOA/PFAS since the 1990s. Gore-Tex materials are typically based on thermo-mechanically expanded PTFE and other fluoropolymer products. They are used in a wide variety of applications such as high-performance fabrics, medical implants , filter media, insulation for wires and cables, gaskets , and sealants. However, Gore-Tex fabric is best known for its use in protective, yet breathable, rainwear . Before

1881-405: The conservation of illuminated manuscripts . Explosive sensors have been printed on Gore-Tex clothing leading to the sensitive voltametric detection of nitroaromatic compounds. The "Gore-Tex" brand name was formerly used for industrial and medical products. Gore-Tex has been used since the 1980s to make bagpipe (woodwind instrument) bags as an alternative to bags made of animal hides as it

1938-599: The conventional sense (although these examples are actually a combination of two different fabrics, a directional "pump" layer underneath a distinct windproof and water-resistant outer layer; while effectively completely waterproof against rain, they would fail a strict hydrostatic head test as given in the definition above). Garments that combine waterproofing with some thermal insulation , such as those manufactured by FurTech and Nikwax Analogy , resist cold bridging , heat transferred through layers of poorly-thermally-insulating materials in close contact that would be prevented by

1995-537: The core technology will continue to be based on PTFE, which is a PFAS compound. Many Gore-Tex products have a durable water repellent coating and the version that do not contain PFCs of environmental concerns are marketed as "Gore PFC EC Free DWR". Unlike the "Gore DWR", it lacks any form of oil repellency. The company intends to replace ePTFE membrane with expanded polyethylene membrane by 2025 in consumer fabrics. The new material, while intended to perform comparably to

2052-426: The direction of compression. Conversely, if the material is stretched rather than compressed, it usually tends to contract in the directions transverse to the direction of stretching. It is a common observation when a rubber band is stretched, it becomes noticeably thinner. Again, the Poisson ratio will be the ratio of relative contraction to relative expansion and will have the same value as above. In certain rare cases,

2109-545: The existing ePTFE material, will cost more, and require more frequent washing. in 2023, two lawsuits have been filed against Gore on the matter of PFAS related water pollution around its Cecil County, Maryland manufacturing plant and the Maryland Department of the Environment has ordered an investigation and residents in the monitoring area have been offered bottled water. One of the lawsuits alleges that

2166-468: The federal district court in Arizona. IMPRA had a competing patent application for the ePTFE vascular graft. In a nearly decade-long patent/antitrust battle (1984–1993), IMPRA proved that Gore-Tex was identical to prior art disclosed in a Japanese process patent by duplicating the prior art process and through statistical analysis, and also proved that Gore had withheld the best mode for using its patent, and

2223-473: The full generalization of Hooke's law is given by: where δ ij is the Kronecker delta . The Einstein notation is usually adopted: to write the equation simply as: For anisotropic materials, the Poisson ratio depends on the direction of extension and transverse deformation Here ν is Poisson's ratio, E is Young's modulus , n is a unit vector directed along the direction of extension, m

2280-460: The high work hardening rate of PTFE, ePTFE is significantly stronger than the unstretched material. On a microscopic level, this work hardening corresponds to the increasing crystallinity of PTFE as the fibrils untangle and orient upon the application of an external stress. ePTFE has a strikingly high ultimate tensile strength (50-800 MPa) relative to its full-density counterpart (20-30 MPa) as a result of its high crystallinity. This behavior also yields

2337-420: The inherent properties of PTFE-based materials more generally (chemical inertness, thermal stability) make ePTFE a versatile material for a range of applications. The most common process used to produce large sheets of ePTFE at scale is a tape stretching process through the following steps: Factors such as strain rate, oven temperature, sintering time, and sintering duration can affect the specific properties of

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2394-443: The introduction of Gore-Tex, the simplest sort of rainwear would consist of a two-layer sandwich, where the outer layer would typically be woven nylon or polyester to provide strength. The inner one would be polyurethane (abbreviated: PU) to provide water resistance, at the cost of breathability. Early Gore-Tex fabric replaced the inner layer of non-breathable PU with a thin, porous fluoropolymer membrane ( Teflon ) coating that

2451-480: The main claim of Gore's product patent was declared invalid in 1990. In 1996, IMPRA was purchased by Bard and Bard was thereby able to reenter the market. After IMPRA's vascular graft patent was issued, Bard sued Gore for infringing it. Gore-Tex is used in products manufactured by many different companies. Gore's patents on ePTFE based fabric expired in 1997 and ePTFE membrane waterproof fabrics have become available from other brands. For his invention, Robert W. Gore

2508-514: The main outer layer from becoming wet, which would reduce the breathability of the whole fabric. However, the DWR is not responsible for the jacket being waterproof. Without the DWR, the Gore-Tex layer would become soaked, thus preventing any breathability, and the wearer's sweat being produced on the inside would fail to evaporate, leading to dampness there. This might give the appearance that the fabric

2565-635: The performance of these fabrics. Water resistance is measured by the amount of water, in mm, which can be suspended above the fabric before water seeps through. Breathability or moisture vapor transmission rate is measured by the rate at which water vapor passes through, in grams of water vapour per square meter of fabric per 24-hour period (g/m /d), often abbreviated to just "g". In recent years some, but not all, sporting goods manufacturers have begun including this information on their product labels. Typical mid-range fabrics tend to have values of 5,000 mm of water resistance and 5,000 g of breathability;

2622-478: The perpendicular direction. In contrast, some anisotropic materials, such as carbon nanotubes , zigzag-based folded sheet materials, and honeycomb auxetic metamaterials to name a few, can exhibit one or more Poisson's ratios above 0.5 in certain directions. Assuming that the material is stretched or compressed in only one direction (the x axis in the diagram below): where and positive strain indicates extension and negative strain indicates contraction. For

2679-474: The pipe to increase in diameter and slightly decrease in length. The decrease in length, in particular, can have a noticeable effect upon the pipe joints, as the effect will accumulate for each section of pipe joined in series. A restrained joint may be pulled apart or otherwise prone to failure. Another area of application for Poisson's effect is in the realm of structural geology . Rocks, like most materials, are subject to Poisson's effect while under stress. In

2736-504: The relationship between the transverse and axial strains ε trans and ε axial is typically not well described by the Poisson ratio. In fact, the Poisson ratio is often considered a function of the applied strain in the large strain regime. In such instances, the Poisson ratio is replaced by the Poisson function, for which there are several competing definitions. Defining the transverse stretch λ trans = ε trans + 1 and axial stretch λ axial = ε axial + 1 , where

2793-413: The resulting ePTFE sheet which can be tailored to match particular applications. PTFE is a fluoropolymer made using an emulsion polymerization process that utilizes the fluorosurfactant PFOA , a persistent environmental contaminant. The International Agency for Research on Cancer has classified PFOA as carcinogenic to humans. Gore pledged in 2017 to eliminate PFCs such as PFOA by 2023, although

2850-408: The rock. Although cork was historically chosen to seal wine bottle for other reasons (including its inert nature, impermeability, flexibility, sealing ability, and resilience), cork's Poisson's ratio of zero provides another advantage. As the cork is inserted into the bottle, the upper part which is not yet inserted does not expand in diameter as it is compressed axially. The force needed to insert

2907-496: The shear modulus, Poisson's ratio is near 0.5. For open-cell polymer foams, Poisson's ratio is near zero, since the cells tend to collapse in compression. Many typical solids have Poisson's ratios in the range of 0.2 to 0.3. The ratio is named after the French mathematician and physicist Siméon Poisson . Poisson's ratio is a measure of the Poisson effect, the phenomenon in which a material tends to expand in directions perpendicular to

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2964-415: The specific direction of loading . The value of Poisson's ratio is the negative of the ratio of transverse strain to axial strain . For small values of these changes, ν is the amount of transversal elongation divided by the amount of axial compression . Most materials have Poisson's ratio values ranging between 0.0 and 0.5. For soft materials, such as rubber, where the bulk modulus is much higher than

3021-542: The testimony of 35 witnesses (19 live, 16 by deposition), and over 300 exhibits" (quoting the Federal Circuit). On appeal, however, the Federal Circuit disagreed in the famous case of Gore v. Garlock , reversing the lower court's decision on the ground, as well as others, that Cropper forfeited any superior claim to the invention by virtue of having concealed the process for making ePTFE from the public. As

3078-495: The transverse stretch is a function of the axial stretch, the most common are the Hencky, Biot, Green, and Almansi functions: One area in which Poisson's effect has a considerable influence is in pressurized pipe flow. When the air or liquid inside a pipe is highly pressurized it exerts a uniform force on the inside of the pipe, resulting in a hoop stress within the pipe material. Due to Poisson's effect, this hoop stress will cause

3135-472: Was able to hold air while allowing moisture to escape, and did not degrade with exposure to water. Waterproof fabric Waterproof/breathable fabrics resist liquid water passing through, but allow water vapour to pass through. Their ability to block out rain and snow while allowing vapour from sweat to evaporate leads to their use in rainwear, waterproof outdoor sports clothing, tents, and other applications. Standard laboratory testing protocols define

3192-456: Was co-invented by Wilbert L. Gore and Gore's son, Robert W. Gore . In 1969, Bob Gore stretched heated rods of polytetrafluoroethylene (PTFE) and created expanded polytetrafluoroethylene (ePTFE). His discovery of the right conditions for stretching PTFE was a happy accident, born partly of frustration. Instead of slowly stretching the heated material, he applied a sudden, accelerating yank. The solid PTFE unexpectedly stretched about 800%, forming

3249-617: Was inducted into the U.S. National Inventors Hall of Fame in 2006. In 2015, Gore was ordered by the Federal Circuit Court of Appeals to pay Bard $ 1 billion in damages. The U.S. Supreme Court declined to review the Federal Circuit's decision. ePTFE has a porous microstructure composed of long, narrow fibrils that intersect at nodes. Increasing the processing temperature or increasing the strain rate leads to more homogenous expansion with more spherically symmetric pores and more intersections between fibrils. The formation of ePTFE

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