This paper provides an overview of the recent definition, technologies and current trends regarding 3D fabrics. In this paper a definition of 3D fabrics, including spacer fabrics, is given and the recent technologies regarding weaving, braiding, weft and warp knitting and tailored fiber placement are presented. Furthermore, an overview of the latest developments in 3D fabrics at the Institut für Textiltechnik of RWTH Aachen University is presented including: large circular 3D knitting, braided and woven structures for medical purposes, newest testing methods and equipment for spacer fabrics, multiaxial fabrics for composites, warp knitted spacer fabrics for space and construction applications, ceramic matrix composite 3D braiding and 4D textiles.

Abstract3D-knits are typically produced on flat knitting or special circular knitting machines in a time-consuming process. The utilisation of a sewing-like pattern opens up the potential of a 10–50 times faster production on common large circular knitting machines as compared to conventional flat knitting machines. Since common large circular knitting machines are not designed for this technology, the limitations and the stability of process conditions have been rarely studied. To further proof the feasibility and increase technological maturity, agile product development is conducted. As a concept product, a sports bra with customised cups is developed and demonstrated, which is knitted in a single step in approx. 5 min using the sewing-like pattern on a large circular knitting machine. The agile process is utilised to build process knowledge, develop a methodology for product design and to defined a descriptive process terminology. In order to further accelerate and digitize the production process, an algorithm is developed and implemented to convert CAD-data into machine readable knitting structures. The paper presents the basics of the 3D-Knit one large circular knitting machines and a defined terminology. Furthermore, process knowledge is built up and from this a sequence of development steps is derived. The development of a 3D-knitted sports bra is presented as a proof of concept of the technology. Further, the first steps for digitalising the product development process are given. The results open up application possibilities in sportswear, upholstery and aerospace with increased productivity and hence cost reduction.

Spacer fabrics are three-dimensional textile structures consisting of two textile cover surfaces and a spacer thread. Up to now, spacer fabrics have been tested according to standards for flat textiles or other non-textile materials. However, these standards do not take into account the special requirements for testing spacer fabrics. Some sample holders of the testing devices are not designed for the thickness of the spacer fabrics, so that the tests cannot be carried out. In other tests, the samples can be mounted, but the test results are falsified by the methodology, e.g. strong compression of the sample before testing. Therefore, objective comparisons among spacer fabrics or between spacer fabrics and conventional flat textiles or non-textile materials cannot be made in all areas of application. The focus of this paper is in the developing of testing devices for seven test setups (1. sample preparation, 2. maximum force, 3. thickness, 4. compression, 5. mass per unit area, 6. permeability to air, 7. abrasion resistance). The new testing devices and methods were designed and manufactured using the method of an iterative development process. The following steps were carried out identically for all seven test setups: deficit analysis, development of concepts, construction of test benches, evaluation, transfer into standards. As part of this research work the developed devices where both tested and evaluated by industrial partners as well as later translated into a standard by the German Institute for Standardization (DIN e.V.). As a central result, a first standard for the testing of spacer fabrics was created and published: DIN 60022–1 “Spacer textiles – Terms and definitions, sample preparation” [4]. For testing textiles, it is important that geometrically identical and structurally intact samples are prepared. Therefore, this standard provides measurement tools and methods for the evaluation of sample quality (e.g. roundness of circular samples, maximum offset and shearing of the surfaces). Two further test methods (determination of thickness and air permeability) were developed and are now being transferred to standards. Within the new test standards, the special properties of spacer fabrics are given special consideration. In addition to the test methods developed within this work, further research is necessary. In particular, the tilting stability (linked to the in-plane and out-of-plane shear measurement) as well as the compression behaviour of spacer fabrics are important tests that need to be analysed and further developed. Therefore, further research is planned for six test methods (1. compression hardness, 2. compression set, 3. tilting stability, 4. pressure point distribution, 5. abrasion resistance, 6. maximum force). This work enables standardized testing of spacer fabrics and thus objective comparisons not only between various spacer fabric constructions but also with conventional flat textiles and with non-textile materials.