EXPERIMENTAL DETERMINATION OF STRESS STATE IN DAMAGED COMPOSITE LAMINATES. MACROSCOPIC PROPERTIES ALTERATION AND DAMAGE MODES IDENTIFICATION by Dionysios T. G. Katerelos Sound Technology and Musical Instruments Department Ionian Islands Technological Educational Institute St. Typaldou ave., Lixouri GR GREECE

Raman scattering C. V Raman 1928 Incident light hv

Kevlar 49 fibre spectrum in air and the origin of the used Raman bands Tension Compression Mainly C-C stretching Mainly C = O stretching 1611 cm cm -1 O C H N

Calibration Curves α σ = cm -1 / GPa α ε = -4.1 cm -1 / % Tensile Stress / GPa Tensile Strain / % Wavenumber Shift / cm -1 Kevlar ® 49

Raman Apparatus

Stress Transfer – Interfacial Shear Stress Galiotis et al.

Damage Recording due to Broken Fibers Galiotis et al.

Positions of the fibres - sensors End tabs Transverse Cracking – Specimen Geometry Fully saturated specimen. The Raman “window” is indicated

Transverse Cracking – Poor Glass Raman signal: The use of appropriate sensors of the order of the magnitude of the reinforcing fibres to measure the developing strain

Transverse Cracking Cross-Ply Laminate [0/90] s

Transverse Cracking Angle-Ply Laminate [0/45] s

Transverse Cracking Secondary Damage Modes

Young’s Modulus Reduction due to Cracking in Cross – Ply Laminates

Young’s Modulus Reduction due to Cracking in Angle – Ply [0/+45] s Laminates

Stress Concentration in Notched Composites

Thermal Sensing Galiotis et al.

Transverse Cracking Secondary Damage Modes Modeling