CARBON PERGAMON Carbon4l(2003)563-570 Elastic moduli of nanocrystallites in carbon fibers measured by in-situ X-ray microbeam diffraction Dieter Loidl, Herwig Peterlik,, Martin Muller, Christian Riekel, Oskar Paris Institute of Materials Physics, University of vienna, Boltmanngasse 5, A-1090 vienna, Austria Institute of Experimental and Applied Physics, University of Kiel, LeibniestraBe 19, D-24098 Kiel, Germany ESRF. BP 220. F-38043 Grenoble Cedex. Fro Erich Schmid Institute of Materials Science, Austrian Academy of Sciences and Metal Physics Institute, University of Leoben, Jahnstrasse 12.4-8700 Leoben. Austria Received 13 September 2002: received in revised form 14 October 2002; accepted 15 October 2002 Abstract The in-plane Youngs modulus and the shear modulus of carbon nanocrystallites were investigated during in-situ tension tests of single carbon fibers by X-ray diffraction using the shift of the 10 band in the meridional direction and the change in the azimuthal width of the 002 reflection. The limiting value for the young s modulus was found to be 1 140 GPa, which is higher than the value for graphite obtained from macroscopic specimens, but coincides with recent measurements on nanotubes. Furthermore, the shear modulus was evaluated using a uniform stress approach and was found to increase with increasing misorientation of the crystallites. It turns out that both the in-plane Youngs modulus and the shear modulus are not constant, but dependent on the orientation parameter o 2002 Elsevier Science Ltd. All rights reserved Keywords: A. Carbon fibers; C. X-ray diffraction; D. Elastic properties, Microstructure, Lattice constant 1. Introduction dimensional structures and exhibit only a weak cross- sectional texture with differences in skin and core. A Carbon fibers combine high tensile strength and high number of structural models, such as ribbon-shaped and tensile modulus with low weight. They are an ideal elongated layers [13], a basket-weave structure [8or a reinforcing material for lightweight structures, e.g. in model consisting of crumpled and folded sheets of layer aerospace applications. In these applications, either high planes, have been proposed [11]. The interlinking of the tenacity or high Youngs modulus is required layers may be responsible for the (usually) high strength of The structure and morphology of carbon fibers have PAN-based carbon fibers [ 19). On the other hand, for MPP been investigated in detail by electron microscopic meth- (mesophase-pitch-based fibers a wide variety of different ods, i.e. SEM [1-7 TEM and HRTEM [8-12, and by structures is observed, e.g. a three-dimensional arrange- X-ray scattering [13-18]. Carbon fibers consist of stacked ment of crystallites and cross-sectional textures such exagonal carbon layers forming small coherently scatter- onion-like, or radial and radially folded structures [17, 20 ing units of only a few nanometers in size [12]. The high Whereas for PAN-based fibers the heat treatment tempera degree of preferential orientation along the fiber axis of the ture(HTT) is the main parameter used to control the layer planes is mainly responsible for the extraordinarily degree of orientation and thus the mechanical properties. high Young s modulus of the fibers [17]. On the one hand, for MPP fibers there are additional ways to influence the PAn (polyacrylnitrilej-based fibers are usually almost one structure arising from the pitch precursor and from the process used to convert it into a fiber form. Edie [20]gives an overview of the effect of different processing parame- orresponding author. Tel :+43-1-4277-51350 fax: +43.1- ters on the structure. In most cases the fibers obtained are 4277-9513 turbostratic,, i.e. the fibers exhibit no regular stacking E-mail address: herwig. peterlik( @univie. ac at(H. Peterlik order of the layer planes and the distance of the planes is 0008-6223/02/S-see front matter 2002 Elsevier Science Ltd. All rights reserved PII:S0008-6223(02)00359-7Carbon 41 (2003) 563–570 E lastic moduli of nanocrystallites in carbon fibers measured by in-situ X-ray microbeam diffraction a a, b c d Dieter Loidl , Herwig Peterlik , Martin Muller , Christian Riekel , Oskar Paris * ¨ a Institute of Materials Physics, University of Vienna, Boltzmanngasse 5, A-1090 Vienna, Austria b Institute of Experimental and Applied Physics, University of Kiel, Leibnizstraße 19, D-24098 Kiel, Germany c ESRF, BP 220, F-38043 Grenoble Cedex, France d Erich Schmid Institute of Materials Science, Austrian Academy of Sciences and Metal Physics Institute, University of Leoben, Jahnstrasse 12, A-8700 Leoben, Austria Received 13 September 2002; received in revised form 14 October 2002; accepted 15 October 2002 Abstract The in-plane Young’s modulus and the shear modulus of carbon nanocrystallites were investigated during in-situ tension tests of single carbon fibers by X-ray diffraction using the shift of the 10 band in the meridional direction and the change in the azimuthal width of the 002 reflection. The limiting value for the Young’s modulus was found to be 1140 GPa, which is higher than the value for graphite obtained from macroscopic specimens, but coincides with recent measurements on nanotubes. Furthermore, the shear modulus was evaluated using a uniform stress approach and was found to increase with increasing misorientation of the crystallites. It turns out that both the in-plane Young’s modulus and the shear modulus are not constant, but dependent on the orientation parameter.  2002 Elsevier Science Ltd. All rights reserved. Keywords: A. Carbon fibers; C. X-ray diffraction; D. Elastic properties, Microstructure, Lattice constant 1. Introduction dimensional structures and exhibit only a weak cross￾sectional texture with differences in skin and core. A Carbon fibers combine high tensile strength and high number of structural models, such as ribbon-shaped and tensile modulus with low weight. They are an ideal elongated layers [13], a basket-weave structure [8] or a reinforcing material for lightweight structures, e.g. in model consisting of crumpled and folded sheets of layer aerospace applications. In these applications, either high planes, have been proposed [11]. The interlinking of the tenacity or high Young’s modulus is required. layers may be responsible for the (usually) high strength of The structure and morphology of carbon fibers have PAN-based carbon fibers [19]. On the other hand, for MPP been investigated in detail by electron microscopic meth- (mesophase-pitch)-based fibers a wide variety of different ods, i.e. SEM [1–7], TEM and HRTEM [8–12], and by structures is observed, e.g. a three-dimensional arrange￾X-ray scattering [13–18]. Carbon fibers consist of stacked ment of crystallites and cross-sectional textures such as hexagonal carbon layers forming small coherently scatter- onion-like, or radial and radially folded structures [17,20]. ing units of only a few nanometers in size [12]. The high Whereas for PAN-based fibers the heat treatment tempera￾degree of preferential orientation along the fiber axis of the ture (HTT) is the main parameter used to control the layer planes is mainly responsible for the extraordinarily degree of orientation and thus the mechanical properties, high Young’s modulus of the fibers [17]. On the one hand, for MPP fibers there are additional ways to influence the PAN (polyacrylnitrile)-based fibers are usually almost one- structure arising from the pitch precursor and from the process used to convert it into a fiber form. Edie [20] gives an overview of the effect of different processing parame- *Corresponding author. Tel.: 143-1-4277-51350; fax: 143-1- ters on the structure. In most cases, the fibers obtained are 4277-9513. ‘turbostratic’, i.e. the fibers exhibit no regular stacking E-mail address: herwig.peterlik@univie.ac.at (H. Peterlik). order of the layer planes and the distance of the planes is 0008-6223/02/$ – see front matter  2002 Elsevier Science Ltd. All rights reserved. PII: S0008-6223(02)00359-7