Through-the-Thickness Mechanical Properties of Smart Composite Laminates Gang Zhou, L.M. Sim, P.A. Brewster and A.R. Giles Department of Aeronautical and Automotive Engineering, Loughborough University, Loughborough, Leicestershire LE11 3TU, UK International Conference on Composites Testing and Model Identification 28 th January 2003

Background and Motivation Smart composite structures:sensory and adaptive – – Sensory smart structures can monitor structural environment or detect and assess damage – – Adaptive smart structures can modify/control the host structural behaviour Embedded optical fibres/SMA wires affect short-term through-the-thickness mechanical properties? Facilitate the design of smart structures 2

3 EFPI sensor Micrograph showing embedded OF

4 Whether or not defects associated with embedded if OFs/SMA wires affect ttt mechanical properties if? Under what conditions will these properties thresholds be affected thresholds? how much How are these properties be affected how much? Objectives

5 Focal Points of Current Investigation: Optical fibres: Orientation Number/volume fraction Through-the-depth location Stress concentration effect SMA wires: Number/volume fraction

6 Through-the-thickness mechanical properties and experimental techniques Interlaminar shear (ILS) properties Short beam shear (SBS) method Iosipescu shear method Flexure Three-point bending Four-point bending

7 Specimen Manufacturing Beam specimens Acrylate-coated single mode OF of 0.25 mm dia. (OC) Nitinol wire of 0.5 mm dia. (M-M) T700/LTM45-EL carbon/epoxy prepreg (ACG) Autoclave with a single-cycle cure at 60 0 C – EFPI sensors are cured at 65 0 C – Austenitic completion temperature of SMA wires is about 70 0 C Iosipescu ILS specimens Iosipescu ILS specimens:two 90 0 notches

8 Micrographs showing embedded OFs

9 Micrograph showing embedded OFs

10 Micrograph showing embedded nitinol wires

11 Orientation and through-the-depth location

12 Arrangement of OFs in the transverse direction

13 Through-the-depth location of OFs in Iosipescu shear specimens

14 ILS shear strength via SBS method OFs in the longitudinal directionOFs in the transverse direction Table 4 Table 5

15 ILS shear properties via Iosipescu method with OFs in the transverse direction Table 6

16 Flexure properties via 3-point bending method with OFs in the longitudinal direction Table 7

17 Flexure properties via 3-point bending method with OFs in the transverse direction Table 8 -20%

18 3-point bending flexure properties with OFs in the longitudinal direction Table 9

19 3-point bending flexure properties with OFs in the transverse direction Table % -32%

20 4-point bending flexure properties with 3OFs in the longitudinal direction Table 11

21 4-point bending flexure properties with 5 OFs in the transverse direction Table % -26%

22 Micrograph showing 5 embedded OFs

23 SBS ILSS with SMA wires in the longitudinal direction Table 13

24 3-point bending flexure properties with SMA wires in the longitudinal direction Table 14

25 Conclusions Specimens containing OFsSpecimens containing OFs –Short-term ILS and flexural moduli: –Short-term ILS and flexural moduli: no effect –Short-term flexural strength –Short-term flexural strength with OFs at any TTT location in the longitudinal direction no effect –Short-term flexural strength degradation: Transverse / Sym-Q / 3 OFs / 3-point Moderate (20%) Transverse / Single-out Q / 5 OFs / 3-point Significant (25%) Transverse / Sym-out Q / 5 OFs / 3-point Significant (32%) Transverse / Single-out Q / 5 OFs / 4-point Moderate (14%) Transverse / Sym-out Q / 5 OFs / 4-point Significant (26%) Specimens containing up to 5 SMA wiresSpecimens containing up to 5 SMA wires –Short-term ILS strength and modulus –Short-term ILS strength and modulus: no effect –Short-term flexural strength and modulus –Short-term flexural strength and modulus: no effect