Test Method Development


Luciano Avila Gray, M.Sc.

Research Team Leader

Tel.: +49 (89) 289 - 15203
E-Mail: avilagray@lcc.mw.tum.de

The production of composite components is expanding beyond traditional hand-layup methods to a wide range of advanced processes like fiber placement or RTM technologies. Standardized testing doesn’t exist for many of these processes, so current methods must be adapted and new technologies developed. The main research with respect to development of test methods at the LCC is presented hereinafter.

Resin infiltration technologies

Permeability and compaction of dry textiles mainly influence resin infiltration technologies like e.g. vacuum infusion (VARI, VAP, etc.) and RTM. At the LCC different permeability test setups are developed (1D, 2D setup and through-thickness) which have complimenting benefits. These facilities give the LCC a unique position in the study of material characterization with regard to the permeability of dry textile preforms.

Figure 1: a.) Setup for 2D-permeability and compaction tests b.) Flow front fitting and c.) Evolution of flow front during analysis of a 2D-permeability test

Draping behavior of textile composites

The draping behavior of textile composites is an important characteristic in order to manufacture composite structures with complex shapes and geometries. For manufacturing and process-simulation, the resulting in-plane shear deformation needs to be understood and may be characterized by means of the picture-frame test. This test yields draping properties such as shear modulus, fiber locking angle and the viscous behavior of the respective material system.

Figure 2: Picture-frame test a.) initial state of specimen b.) sheared state of specimen c.) universal testing machine with installed temperature chamber

Thermoplastics

Thermoplastic composites differ strongly from thermoset composites conditioned by their different molecular structure which can be also observed during testing. Furthermore, different manufacturing processes (e.g. thermoforming, induction welding or fiber placement technologies) influence the mechanical performance of thermoplastic composites strongly.

Figure 3: Micrographs of thermoplastic composites processed with different manufacturing technologies

In addition to mechanical and thermo-analytical tests, micrographs may also be used to analyse thermoplastic material. These micrographs enable the visual evaluation of the influences that the different processing methods and parameters have on the materials.

Tape material characterization upon processing with Fiber Placement

Many manufacturing technologies use extensive semi-finished products like fabrics or NCFs which are layered to form a laminate. Considering uni-directionally reinforced tape materials used for Fiber Placement, Tow Placement or Tape Laying additionally each laminate layer consists of tapes placed next to each other. Hence, inhomogeneities resulting from gaps and overlaps of single tapes and their influence on the material properties of fiber placed tapes are investigated at the LCC. Furthermore, testing methods for the laser-assisted thermoplastic Fiber Placement process are developed to define both material- and process-related parameters.

Figure 4: T peel test of thermoplastic UD prepregs a.) universal testing machine b.) initial state of specimen c.) specimen during testing