Analysis of Strain and Stress in Ceramic, Polymer and Metal Matrix Composites by Raman Spectroscopy

Abstract

Raman scattering is a unique tool providing information on the structure and short‐range order of matter. Stress‐induced Raman shifts can be used to determine the stress/strain in films, fibres, particulate composites and, more generally, in any phase a few microns or more in scale. Quantitative results follow from a wavenumber calibration as a function of tensile strains or pressures applied to reference fibres or crystals. Furthermore, if the material is coloured, (near) resonant Raman scattering occurs, which enhances the scattered light intensity and simplifies the spectra – especially for harmonics – but drastically reduces the analysed volume (in‐depth penetration ∼10–100 nm). This paper discusses the effective and potential advantages/drawbacks of Raman micro‐spectrometry technique. The procedures to improve the sensitivity, the legibility and the reliability will be addressed. Examples will be chosen among (aramid, C, SiC) fibre‐ reinforced ceramic (CMCs), polymer (PMCs) or metal matrix (MMCs) composites.

SiC, from Amorphous to Nanosized Materials, the Exemple of SiC Fibres Issued of Polymer Precursors

“…Each Raman peak corresponds to a specific vibration (bending, stretching, librational, rotational and lattice modes) of a given chemical bond, and provides information (even on heterogeneous materials, e.g. composites) such as the phase nature and symmetry, distribution, residual stress,… (Colomban, 2002;Gouadec & Colomban, 2007). Since the Raman scattering efficiency depends on the polarisability of the electronic cloud, it can be very sensitive to light elements involved in covalent bonds (C, H, N, B, O, …), which is a valuable advantage, when compared to X-ray/electron-based techniques (EDS, micro-probe,…).…”

“…This band presents a strong resonant character, evidenced by a high dependence of the intensity and position on wavelength. Additional components below 1300 cm -1 arise from hydrogenated carbons and those intermediate between D and G bands have been assigned to oxidised and special carbon phases (Karlin & Colomban, 1997;idem, 1998;Colomban et al, 2002). The wavenumber of the sp 3 carbon bond (D peak) measures the aromaticity degree (aromaticity is a function of the "strength and extension size" of the π electronic clouds and thus also function of the crystal order) and hence is directly related to the electric properties of the material (Mouchon & Colomban, 1996).…”

“…Another important point is that for coloured materials, the interaction between laser light and matter must be very strong and hence the light absorption. This may have detrimental effect (local heatingand thermal induced wavenumber shift - (Colomban, 2002), oxidation and phase transition ) in the lack of attention but this also controls the penetration depth of the laser light: the penetration can be limited to a few (tenths of) nanometers (Gouadec & Colomban, 2007).…”

Types, structure and mechanical properties of silk

“…Experimental confirmation has been provided by nanomechanics, i.e. the quantitative study of the bond change under controlled tensile/compressive stress-strain, measured by Raman scattering (Marcellan et al, 2003;Colomban, 2002;Colomban et al, 2006;Gouadec and Colomban, 2007). These studies confirm that mechanical properties are driven by the main phase, the amorphous one, and in most of the cases, even in polymers with a high crystalline content, the crystalline phase does not play a significant role in determining the form of the tensile curve.…”

Residual Stress Investigation in SiC/MoSi2(p) Composites

“…[10,11] Recently, Raman piezo-spectroscopy has been largely used to investigate the residual stress field inside ceramic material, including particulate-reinforced composites [12][13][14][15] and fiber-reinforced composites. [16][17][18] In this contribution, residual thermal stresses arising in SiC-based materials containing 10 and 30 vol% MoSi 2 particles were investigated by Raman piezo-spectroscopy, measuring the stress-induced wavenumber shift of the 796 cm -1 b-SiC peak in the MoSi 2 -reinforced composites in respect with a zero-stress reference un-reinforced SiC material. A preliminary calibration procedure was carried out for determining the piezo-spectroscopic coefficient pertinent to the b-SiC phase in the materials of the present work, as it is well known that this coefficient strongly depends on many factors specific of the material, such as grain size, presence of secondary phases, porosity, etc, and on the processing parameters.…”