For about 10 years we have been dealing with the modeling and calculation of mechanical properties of textiles. In the picture: distance fabric at bending.

Simulation of Mechanical Textile Properties

The focus is on simulation methods that enable efficient predictions of the behavior of woven and knit textiles. Important parameters to be considered are

  • the mechanical attributes of the individual weaving yarns
  • and a suitable description of the mesh geometry.

 

Challenge Coefficients of Friction between Yarn Types

While the elongation properties of the individual fibers can be quite easily determined experimentally, determining the coefficients of friction between the various fiber types requires a much greater effort. The necessary fiber parameters are usually defined by suitably equipped experimental textile institutes and then provided to ITWM.

In this case, the main application area is especially in technical and medical textiles, which must strictly adhere to certain performance specifications. Some examples include: bandages that are supposed to exert pressure when in contact with the patient’s skin or, perhaps, there is a need to find a material specifically made to provide maximum protection, for example, either for a bullet proof vest or for work clothes like cut protective trousers.

Generally, the work of the textile group does not end with a specific textile product, rather more in the advanced development of appropriate simulation tools that the customer then uses to run various simulations – with changing materials or geometric parameters. Besides the evaluation of a specific textile design by simulation, the tools also enable the optimization of the performance characteristics for different design variants.

 

Clients from Various Industries

Our clients are among others producer of:

  • compression bandages
  • auto textiles
  • protective safety systems of all kinds
  • occupational and protective clothing

Other potential customers include companies that produce textiles in the broadest sense for use in the construction industry; for example, the materials built into drainage systems that must be able to withstand a certain pressure. In addition to the current focus on mechanical attributes of fabrics, other characteristics such as fluids transport will be studied in the future.

Software FiberFEM (DFG-Project)

Multiscale modeling and simulation of woven and knitted fabrics with a special focus on the contact between individual threads or fibers, including 3D-knitwear and fi ber materials with heterogeneous microstructure, is the topic of this research area. The value adding development of a textile with optimal properties is also included in the studies. The contact leads to a nonlinearity of the problem and direct numerical simulation is very expensive. Therefore, a multiscale computational approach that permits a reduction of the problem dimension is used for effective calculations. The problem has two small parameters: The first is the relationship between periodicity or representative fabric element and the dimensions of the whole fabric.

For example, in the following project funded by the German Research Foundation:

 

Objectives

  • Correct design and simulation of spacing knits using mathematical models and algorithms
  • Mechanische und mathematische Mehrskalenmodellierung, -simulation und Strukturoptimierung unter Berücksichtigung des Kontaktes einzelner Fasern
  • Mechanical and mathematical multiscale modeling, simulation and structural optimization considering the contact of individual fibers

 

Methods

  • Geometrical characterization of the periodicity cell
  • Determination of stress scenarios
  • Generation of the virtual structure
  • Simulation of elastic properties (FiberFEM, FIFST)
  • Simulation of the flow properties of the compressed spacer structure (GEODICT)
  • Development of experimental evaluation methods for 3D spacer structures
FiberFEM-Modell
© Photo ITWM

Structure in the FiberFEM model

Kompression Abstandsgewirke
© Photo ITWM

Compression spacer knit

Strömung Abstandsgewirke
© Photo ITWM

Flow spacer knit

In considering the contact, both asymptotic approaches require an innovation that requires a new analysis, which is the subject of the DFG Project “Modeling and Simulation of Fiber Structures and Industrial Textiles”, underway in collaboration with the department of mechanical engineering at the University of Erlangen.

The results have been published in separate mathematical and mechanical journals. In the first paper, an effective elasto-plastic material behavior is derived for textiles under consideration of contact, while further papers derive the contact conditions for beams from the known three-dimensional frictional forces and fiber cross section data.

 

Software Package FiberFEM

Corresponding computational algorithms were implemented and are based on the beam Finete Element method, extended to the contact. In addition to calculating the effective mechanical material properties for a variety of existing woven and knitted fabrics in industrial and life science applications, the approach also has the potential for the optimal design of innovative textiles having a prescribed mechanical properties profile.

Furthermore, the developed approach for textiles can simulate and analyze different surface treatments. In this way, it is possible to determine in advance the quality of the resulting fabric surface in order to prevent the formation of wrinkles and other visual inhomogeneous features.