Auxetics+Materials+(1)


 * 5. Auxetic Materials: **

- Auxetics are [|materials] that have a negative [|Poisson's ratio].
 * 5.1 ** : **Characteristics**:

- Since Poisson’s ration is the ratio between the contractile lateral strain and the tensile axial strain “for a material stretched axially”, So it is normally + ve. But in Auxtics, it is - ve as during stretching the material from one dimension, the other perpendicular dimension becomes thicker.



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- The term auxetic derives from the [|Greek] word α ὐ ξητικός  (auxetikos) which means "that which tends to increase" and has its root in the word α ὔ ξησις , or auxesis, meaning "increase" (noun). This terminology was coined by Professor Ken Evans of the [|University of Exeter]. - Scientists have known about auxetic materials for over 100 years, but have only recently given them special attention. The earliest published example of a synthetic auxetic material was in Science in 1987, entitled "Foam structures with a Negative Poisson's Ratio" by R.S. Lakes from the [|University of Iowa]. The use of the word auxetic to refer to this property probably began in 1991.
 * 5.2 ** : **History**:

Apart from the scientific value of having materials with a negative Poisson`s ration, auxetic materials show enhanced mechanical properties such as: Which make them superior to classical materials for many practical applications.
 * <span style="font-family: 'Baskerville Old Face','serif'; font-size: 18.6667px;">5.3 ** **<span style="font-family: 'Baskerville Old Face','serif'; font-size: 18.6667px;">:Advantages of Auxetic materials: **
 * <span style="font-family: 'Baskerville Old Face','serif'; font-size: 18.6667px;">increased shear stiffness
 * <span style="font-family: 'Baskerville Old Face','serif'; font-size: 18.6667px;">increased plane strain fracture toughness
 * <span style="font-family: 'Baskerville Old Face','serif'; font-size: 18.6667px;">increased indentation resistance

<span style="font-family: 'Baskerville Old Face','serif'; font-size: 18.6667px;">Key areas of application are seen in the biomedical field. Prosthetic materials, surgical implants, suture/muscle/ligament anchors and a dilator to open up blood vessels during heart surgery are all possible. Another area relates to the use of auxetic materials in piezoelectric sensors and actuators. <span style="font-family: 'Baskerville Old Face','serif'; font-size: 18.6667px;">Auxetic foam and honeycomb filters offer enhanced potential for cleaning fouled filters, for tuning the filter effective pore size and shape, and for compensating for the effects of pressure build-up due to fouling. These benefits rely on the pores opening up both along and transverse to the direction of a tensile load applied to an auxetic filter. The pores of a non-auxetic filter open up in the stretching direction but close up in the lateral direction, leading to poorer filter performance. The effect of stretching on the de-fouling of an auxetic polymeric honeycomb fouled with glass beads has been investigated. For the particular honeycomb studied the value of Poisson’s ratio is dependent on the stretching direction. The studies clearly demonstrate that de-fouling is enhanced when the filter is loaded in the direction with the largest negative Poisson’s ratio. <span style="font-family: 'Baskerville Old Face','serif'; font-size: 18.6667px;">The breakthrough development of a continuous process to produce auxetic materials in fibrous form has created the opportunity to apply their unique characteristics in a wide range of applications previously not possible. Fibers can be used in single or multiple filament structures and can be used to produce a woven structure. Typical performance characteristics expected of auxetic fibers and structures are detailed in the table of applications, together with a list of the applications in which these characteristics could offer significant benefits. **Table 1 (Part A).** Application-performance characteristic matrix for auxetic fibers and auxetic fiber based structures. || Application
 * <span style="font-family: 'Baskerville Old Face','serif'; font-size: 18.6667px;">5.4 ** **<span style="font-family: 'Baskerville Old Face','serif'; font-size: 18.6667px;">: Applications: **
 * <span style="font-family: 'Baskerville Old Face','serif'; font-size: 18.6667px;">5.4.1: Biomedical Industry: **
 * <span style="font-family: 'Baskerville Old Face','serif'; font-size: 18.6667px;">5.4.2: Filters: **
 * <span style="font-family: 'Baskerville Old Face','serif'; font-size: 18.6667px;">5.4.3:Auxetic Fibers: **
 * Fiber

Pull-Out

Resist. || Fiber

Fracture

Tough || Energy

Absorp. || Densif.

& Indent.

Resist || Impact

Resist ||
 * ** Composite Materials **

Auxetic fibre reinforcement in composites || ====X==== || ** X ** || ** X ** || ** X ** || ** X ** ||
 * ** Personal Protection Clothing **

Crash helmets, body armour, sports clothing ||  ||   || ** X ** || ** X ** || ** X ** ||
 * ** Fitration **

Woven structures using auxetic fibres ||  ||   ||   ||   ||   ||
 * ** Mechanical Lungs **

Microporous hollow auxetic structures ||  ||   ||   ||   ||   ||
 * ** Ropes, Cords & Fishnets **

High strength, lower weight ||  || ** X ** ||   ||   ||   ||
 * ** Upholstery Fabrics **

Enhanced abrasion properties & entrapment of fire retardant components ||  ||   || ** X ** || ** X ** ||   ||
 * ** Biomedical **

Controlled release of drugs ||  ||   ||   ||   ||   ||
 * **Medical Bandages**

Prevents swelling of wound by application of wound healing agent ||  ||   ||   ||   ||   || **Table 1 (Part B).** Application-performance characteristic matrix for auxetic fibers and auxetic fiber based structures. || Application
 * ** Fibrous Seals ** ||  ||   || ** X ** || ** X ** || ** X ** ||
 * Release

Entrapped

Particles || Wear

Resist. || Microporous

Breathable

Structure || Constant

Pressure

Structure ||
 * ** Composite Materials **

Auxetic fibre reinforcement in composites ||  ||   ||   ||   ||
 * ** Personal Protection Clothing **

Crash helmets, body armour, sports clothing ||  ||   || ** X ** || ** X ** ||
 * ** Fitration **

Woven structures using auxetic fibres || ** X ** ||  || ** X ** || ** X ** ||
 * ** Mechanical Lungs **

Microporous hollow auxetic structures || ** X ** ||  || ** X ** ||   ||
 * ** Ropes, Cords & Fishnets **

High strength, lower weight ||  || ** X ** ||   ||   ||
 * ** Upholstery Fabrics **

Enhanced abrasion properties & entrapment of fire retardant components || ** X ** || ** X ** ||  ||   ||
 * ** Biomedical **

Controlled release of drugs || ** X ** ||  || ** X ** ||   ||
 * **Medical Bandages**

Prevents swelling of wound by application of wound healing agent || ** X ** ||  || ** X ** || ====X==== ||
 * =====Fibrous Seals===== ||  || ** X ** ||   || ** X ** ||

<span style="font-family: 'Baskerville Old Face','serif'; font-size: 18.6667px;">5.5: Links to external material for further reading:

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<span style="font-family: 'Baskerville Old Face','serif'; font-size: 18.6667px;">Video Link:

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