Page 17 - ILK Research Report 2020

Doctorate Dr.-Ing. Thomas Behnisch

On the influence of transverse pressure-induced damage

on the mechanical properties of textile reinforced ceramics
matrix composites

Supervising Professor: Prof. Dr.-Ing. habil. Maik Gude

Textile composite ceramics have very high density-specific
stiffnesses and strengths that remain almost constant well
into the high-temperature range. The direction-dependent
properties of these fracture-tolerant ceramic composites
can be tailored and advantageously adapted to specific
application characteristics. Therefore, textile composite
ceramics offer enormous potential for applications in
high-temperature lightweight engineering.
The understanding of materials for these composite mate-
rials with predominantly planar textile structures has been
steadily improved in recent years, so that a description
of the material behaviour in the plane of the textile rein-
forcement structure is possible with the existing mathe-
matical models. However, there are reservations about
unrestricted use, primarily for safety-relevant components, Fig. 1: PhD Commission (from left to right): Prof. Modler, Prof. Kästner,
as uncertainties remain regarding the complex material Dr. Behnisch, Prof. Michaelis, Prof. Gude, Prof. Ullrich
behaviour under stresses in the direction of the compos-
ite thickness (out-of-plane). In particular, there is currently gained on damage phenomenology and failure behaviour
limited experience with so-called transverse compressive thus contributes to a significantly improved understanding
stresses and their effects on the in-plane behaviour. of the material. Based on this, a damage and failure model
Within the scope of this work, a comprehensive, scale-span- validated for in-plane loading was extended to predict
ning in-situ structure investigation (fig. 2) as well as an anal- the transverse pressure-induced property degradation,
ysis of the damage and failure behaviour under transverse so that in addition to the mathematical description of
compressive stress, which is still pending for textile com- the influence of transverse pressure-induced damage on
posite ceramics, could be carried out. For the first time, the the mechanical properties of textile composite ceramics,
correlation between the textile composite ceramic mate- an improved prediction of the deformation, damage and
rial structure and the material behaviour under transverse failure behaviour is possible.
compressive stress was demonstrated. The knowledge

Fig. 2: Experimental procedure
for cross-scale in-situ structure
investigation under transverse
pressure loading

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