PSI - Issue 23

Zdeněk Chlup et al. / Procedia Structural Integrity 23 (2019) 505 – 510 Zdenek Chlup/ Structural Integrity Procedia 00 (2019) 000 – 000

506

2

1. Introduction

Generally, brittle matrix composite materials utilising long fibres as reinforcement are the most effective in term of toughening synergism effect. The brittle matrix combined with the brittle reinforcement results in a tougher composite than are its individual components (Low, 2006). Ceramics matrix composites are rather expensive due to the demanding processing as well as costly raw materials. Also, modification of the fibres surface prior embedding in a matrix is the most common and effective but expensive technique to maximise toughness of CMCs (Chawla, 2012). The prospective cost reliable method can be also a modification of a matrix as was demonstrated for SiOC based matrix reinforced by basalt fibres elsewhere (Cerny et al., 2013; Fiore, Scalici, Di Bella, & Valenza, 2015). On the other hand, polymer matrix fibre reinforced composites are a good alternative with the drawback in the application range restrictions (Dhand, Mittal, Rhee, Park, & Hui, 2015). The partially pyrolysed polysiloxane based matrix composites can be a compromise between ceramic and polymeric matrix (Weichand & Gadow, 2015). Such composite pyrolysed at 650°C can exhibit the fracture toughness values on the level of 20 MPa.m1/2 together with flexural strength reaching 1 GPa when microstructure and manufacturing parameters are optimised (Černý et al., 2015). This work aims at the fibre chemical composition effect on the mechanical properties when the matrix and processing are kept unchanged.

Nomenclature D f,avg average fibres diameter v f

fibre volume fraction in the composite geometrical (bulk) composite density

 c  m

matrix density fibre density

 f E

dynamic Young’s modulus

 f,m flexural strength K Ic,cnb fracture toughness

2. Experimental The identical matrix precursor Lukosil M130 (Lučební závody a.s., Czech Republic) a polymethylsiloxane resin was used for the preparation of all composite materials under investigation. Fibres varying in their chemical composition, diameter and surface quality, namely, Basalt fibres (Kamennyj vek), E-Glass and R-Glass (Saint Gobain Vetrotex, Germany) fibres and Carbon fibres (Toray, Japan) were employed as a reinforcement see Table 1 for details about the chemical composition.

Table 1 Typical chemical composition of used fibres in composites (in wt.%).

Al 2 O 3 17 14 24

Fe 2 O 3 <1 <1 5

B 2 O 3

SiO 2

Na 2 O

C

FeO

CaO

MgO

Basalt

54 54 58

-

8

4

4 1 6

3

- - -

E-Glass R-Glass Carbon

5

21

<1 <1

<1 <1

- -

9

-

-

-

-

-

-

-

>99

Roving immersed in a dilute resin bath was used for prepreg preparation. After drying for 48 hours at 20°C were prepregs stacked and embedded into a mould. The pressure of 0.3 MPa was applied during curing at 250°C. The partial pyrolysis took consequently place at 650°C with 10 hours dwell under a nitrogen atmosphere.