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).
Carbon composites based on multiaxial multiply stitched preforms. Part 1. Geometry of the preform
Experimental investigation of the internal geometry of a multiaxial multiply carbon reinforcement, stitched by warp-knitting, reveals the general features of this promising class of textile reinforcements. The uniform placement of the fibres is disturbed by the stitching, which creates resin-rich zones in the composite. The shape of the stitching loops, change of the stitching yarn thickness along the loop and statistical characteristics of spacing of the stitching has been studied. These features are covered by a descriptive empirical model of the internal geometry of multiaxial multiply fabrics. The model is implemented in the textile modelling software WiseTex, which serves as a preprocessor for meso-mechanics and permeability modelling.
Submicron polymer structures with X-ray lithography and hot embossing
This article describes the process chain for replication of submicron structures with varying aspect ratios (AR) up to 6 in polymethylmethacrylate (PMMA) by hot embossing to show the capability of the entire LIGA process to fabricate structures with these dimensions. Therefore a 4.7 μm thick layer of MicroChem 950k PMMA A11 resist was spin-coated on a 2.3 μm Ti/TiOx membrane. It was patterned with X-ray lithography at the electron storage ring ANKA (2.5 GeV and λc ≈ 0.4 nm) at a dose of 4 kJ/cm3 using a Si3N4 membrane mask with 2 μm thick gold-absorbers. The samples were developed in GG/BDG and resulted in AR of 6–14. Subsequent nickel plating at 52°C resulted in a 200 μm thick nickel tool of 100 mm diameter, which was used to replicate slit-nozzles and columns in PMMA. Closely packed submicron cavities with AR 6 in the nickel shim were filled to 60% during hot embossing.