Modelling the seam architectures for textile performing
Sewing of textile preforms offers a lot of opportunities for the future production of FRP parts. Although out of plane properties and damage tolerance abilities of the preform improve by stitching, stitching degrades the in plane properties of the preform. The choice of material and process parameters is crucial to realise the benefits of stitching. This demands modelling and simulation of stitched textile structures. Currently simple textile structures like multi layer woven fabrics and multi layer non-crimp fabrics can be modelled. This paper shows a concept for a mathematical modelling of stitching architectures including the generation of the thread surfaces. The model can help in realising two functions. On the one hand different material and process parameters can be taken into account and on the other hand the computed surface description including geometrical dependencies can be transferred into a structural mechanic model (e.g. WiseTex).
Mechanical performance of carbon fibre-reinforced composites based on stitched preforms
A comparative assessment of the influence of pure assembly seams based on a thin (11 tex) polyester yarn in a zigzag geometry on the resulting mechanical performance of a non-crimped fabric (NCF) carbon fibre-reinforced epoxy composite manufactured by vacuum-assisted resin transfer moulding is presented. This study was aimed at generating a solid foundation regarding the overall performance level of stitched NCF composites and at identifying critical property changes. The comprehensive evaluation of the mechanical composite properties includes static as well as dynamic tests of the in-plane properties as well as a characterisation of the interlaminar properties such as apparent interlaminar shear strength (ILSS) and compression after impact (CAI). It is demonstrated that mechanical properties such as the tensile and compression stiffness and CAI strength are not degraded by the chosen stitching parameters, whereas the tensile and compression strength, ILSS as well as the tensile fatigue behaviour are reduced as a result of pronounced localised fibre ondulations. A direct comparison to properties of a commonly used 5H satin woven fabric composite verifies that the overall performance of these particular stitched NCF composites must be enhanced with regard to the identified key criteria to meet the level required for aircraft applications and in order to maintain the performance advantage of NCF composites as compared to standard woven fabrics in general. Promising approaches include the use of different yarn materials based on soluble thermoplastics and/or modified stitching parameters.
Developmental aphasia: The perception of brief vowels and extended stop consonants
Abstract Developmental dysphasics and matched controls were examined for their ability to discriminate (a) two synthesized vowel-vowel syllables and (b) two synthesized consonant- vowel syllables. For both vowels and consonants, dysphasics were impaired when the discriminable components of the two stimuli were brief (43 msec) but unimpaired when these components were 95 msec or longer. It is concluded that developmental dysphasics have no difficulty in discriminating transitional auditory information as such and that their impaired discrimination of synthesized stop consonants is attributable solely to the brief duration of the discriminable components.