For about 10 years we have been researching on the modeling and the computation of mechanical properties of textiles. In the picture: bending of a warp knitted spacer fabric.
© Fraunhofer ITWM
The focus is on simulation methods that enable efficient predictions of the behavior of woven and knit textiles. Important parameters to be considered are
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.
Our clients are among others producer of:
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.
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.
The finite element method is used as a tool for the simulation of a textile. It is implemented with truss and beam elements (after application) and has been extended and implemented for the treatment of thread contact problems with sliding and friction in the software package TexMath developed at the Fraunhofer ITWM.
As input variables TexMath requires, besides the microstructure description of the considered textile, the fiber cross section geometry as well as mechanical fiber parameters, such as tensile stiffness, strength, durability and friction. As output the effective mechanical textile parameters are returned.
Besides the simulation of the effective mechanical material properties for a large number of already existing woven and knitted textiles from technical and medical applications, the approach also offers the potential for the targeted design of new textiles with a given mechanical property profile.
In addition to the evaluation of a specific textile design, the tools also allow the optimization of performance characteristics for different design variants. Corresponding calculation algorithms are implemented based on the beam finite element method, extended to the contact and friction of fibers. In addition to the calculation of effective mechanical material properties for a large number of existing woven and knitted fabrics, the approach enables the optimal design of innovative textiles with a given mechanical property profile.
Furthermore, the developed approach can simulate and analyze different surface treatments for textiles. In this way, it is possible to determine the quality of the resulting fabric surface in advance to prevent the formation of wrinkles and other visually inhomogeneous features.
Knitting pattern optimization to achieve a given desired stress profile (left curve). The right curve shows the simulation deviation (the error) in each optimization step, the pattern evolution is shown in the middle.
Fraunhofer Institute for Industrial Mathematics ITWM