Auxetic composite materials can be produced either from conventional components via specially designed configurations or from auxetic components. This paper reviews manufacturing methods for both these scenarios. It then looks at the possibility of property enhancements in both low velocity impact and fibre pull out due to the negative Poisson's ratio. Tests revealed that auxetic carbon fibre composites made from commercially available prepreg show evidence of increased resistance to low velocity impact and static indentation with a smaller area of damage. Also, using auxetic fibres in composite materials is shown to produce a higher resistance to fibre pullout.

The design, manufacturing and characterization of warp knit textile structures with enhanced drapeability and energy absorption is reported in this paper. Four textile structures were produced, all based on a triangular or double arrowhead structure, which is known to lead to a negative Poisson's ratio ν. Mechanical testing has confirmed that textile structures can be produced which are auxetic at ± 45° to the warp direction, with ν of up to −0.22 ± 0.03.

The term 'auxetic' is applied to materials that possess a negative Poisson's ratio n. The use of auxetic polymers has been limited because of problems with deploying them in their fabricated forms, i.e. as 10 mm diameter cylinders. This paper reports the successful development of a processing route to produce a more useful and usable form of auxetic polymeric material, namely bres. A conventional polymer processing technique (melt spinning) is the basis of this technique, with novel modi cations. Video extensometry was used to measure the Poisson's ratio and a value of n = 0•60±0•05 was obtained.

Auxetic materials when stretched axially expand instead of contracting laterally. Following Lakes's [1] successful production of auxetic foams, a variety of auxetic products have been fabricated including honeycombs [2], polymeric and metallic foams [1] and microporous polymers [3,4]. An interesting feature of auxetic materials is that they are predicted [5], and have been found, to have enhanced properties. For example, it has been shown experimentally that the indentation resistance [6] of auxetic materials has been enhanced by up to four times when compared with the conventional equivalent. Other enhanced properties include plane strain fracture toughness [7], energy absorption [8], and shear modulus [9].The first synthetic auxetic microporous polymer was a particular form of polytetrafluoroethylene (PTFE) [10]. It was found that the auxeticity in this case was solely because of its complex microstructure [10]. This consisted of nodules interconnected by fibrils that react co-operatively to produce a negative Poisson's ratio. Similar microstructures have also been engineered in polymers such as ultra-high-molecular-weight polyethylene (UHMWPE) [3], polypropylene [4] and nylon [11], which were all produced by a novel thermal processing route consisting of three distinct stages; compaction [12], sintering [13] and ram extrusion [14]. The entire process takes place in a specially designed extrusion rig with extrudates produced in the form of cylindrical rods. Although having this special property, there were found to be limitations on the production of auxetic materials in the form of cylinders. In particular, the cylinders (having diameters varying between 9 and 15 mm) were found to be unsuitable for application-based research and were restricted to laboratory-based testing. Moreover, the process involved was not continuous and problems were envisaged in producing them on a large scale. 1 2 More recently, a novel thermal processing techniqueinvolving melt spinning has been employed to produce an auxetic product in a more useful and usable form, namely as a fiber [15]. This has led to auxetic polypropylene (PP) fibers being fabricated in a continuous process. Videoextensometry analysis was used to show the auxetic nature of the PP fiber. The processing route developed for auxetic polypropylene fibers is, in principle, flexible enough to be adapted to produce other polymeric fibers [15] and films [16] in auxetic form.This paper reports in detail the production of auxetic polyester fiber, including the characterization by videoextensometry.Abstract Auxetic materials are referred to as those having negative Poisson's ratio (ν). Initial work at Bolton successfully fabricated auxetic polypropylene fiber using a novel thermal meltspinning technique. This paper reports in detail both the methods and principles involved in screening polyester powder and also the manufacturing method for successful production of auxetic polyester fibers. Videoextensometry along with micro-tensile testing were used to measure the Poisson's...

A series of gold(I) isonitrile complexes were prepared and converted to the corresponding diaminocarbene gold(I) complexes by reactions with primary and symmetrical secondary amines. Twelve crystal structure analyses of the gold(I) complexes could be obtained, in addition NMR studies allowed an analysis of the different diastereomers present in solution. In the gold‐catalyzed phenol synthesis these complexes were very successful as pre‐catalysts, reaching an unprecedented 3050 turnovers with a problematic substrate. Good conversions in the hydration of phenylacetylene could also be achieved.