Experimental and numerical studies on the deformation behavior of polymer based composite plates subjected to bending F. Bosia, J. Botsis, T. Gmür, M.A.Mustafa & L. Humbert Laboratory of Applied Mechanics & Reliability Analysis (LMAF) Swiss Federal Institute of Technology Lausanne Switzerland Presented at: CompTest 2003 ENSAM Châlons en Champagne, France

outline background experimental results numerical simulations m optical fiber sensors m issues in laminated composites experimental results m strain measurements through the thickness using FBG m strain measurements on the surface using strain gauges and full field ESPI & strain gauges numerical simulations m 2-dimensional of equivalent single layer models m 3-dimensional of the actual lay-up

use of FBG sensors 1. Basic experiments in mechanics of materials m measure forces on fibers in a bridging zone study the interface : matrix – fiber study residual stresses in polymeric materials measure deformation behavior through the thickness on composite laminated plates 1. Basic experiments in mechanics of materials 2. On structural monitoring and control

fiber Bragg grating (FBG) sensors silica doped with germanium & hydrogen I R T   core FBG B expose fiber to UV over a certain length change n0 FBG length : 0.1 - 10mm

FBG sensor - principles of operation - compact - lightweight - minimally invasive (ø125 mm) - immune to e-magnetic interference - great resistance to corrosion - high temperature capacity  3000C FBG are: UNIFORM STRAIN FIELD Non-UNIFORM STRAIN FIELD

FBG sensors - principles of operation opto-mechanical relation axial stress transversal stresses

composite materials: relevant length scales @

CLASSICAL LAMINATE THEORY equivalent 2D single layer theories CLASSICAL LAMINATE THEORY FIRST ORDER THEORY HIGHER ORDER THEORY (CLPT) Analytical / numerical results lack experimental validation &

materials and specimens 4/1 Glass fibre / Polypropylene matrix prepregs 8-ply (90°/0°)2s , 250mmx300mm, thickness 4.9mm FBG sensors (125m polyimide-coated monomode fibres) λB 1530 nm; Grating length: 3 or 6 mm. UPPER PLATE Preparation: 1) Compression moulding 2) Autoclave PREPREG STACK EMBEDDED SENSOR(S) LOWER PLATE 10 Bar, 190° C.

locations of FBG sensors 4ème couche (0°) 3ème couche (90°) 2ème couche (0°) 1ère couche (90°) Fibres à 90° dans la 2ème couche (0°) Fibres à 90° dans la 4ème couche (0°)

materials and specimens 4/1 Glass/PP Twintex (Vetrotex Int.) PLATE 8-ply (90°/0°)2s , 250mm x 290mm, thickness 5mm 16-ply (90°/0°)4s , 250mm x 290mm, thickness 10mm 50 <Span/Depth <10 x O L b l Fibre optique b/2 L/2 y z h FBG sensor specimen quality checks - void content - thickness variation mechanical characterization - single layer and laminate properties - influence of embedded FBG

experimental methods specimen “shift’’ y y z z O x O x s L L/2+D L/2 b l O. Fibre b/2 L/2 y z h FBG SG s x O L/2+D y z FBG SG D

locations of FBG sensors length of FBG = 6mm FBG embedded centrally in the specimens Location through the thickness Through-the-thickness (8-ply specimens): a) b) c) 1/2 2/3 3/4 8-ply specimens: Z Y 16-ply specimens: a) 1/2, b) 2/3, c) 3/4, d) 4/5, e) 6/7

8 finite element simulations Plate specimen, 3-point bending configuration 8 Important problem is that of the boundary conditions due to the variations in the thickness of the plates. ABAQUS - CLPT and First Order laminate theories tested - 3D simulations have been carried out

Electronic Speckle Pattern Interferometer

loading configuration specimens strain gauges FBG sensor loading arm

Electronic Speckle Pattern Interferometer in-plane measurements in the presence of large out-of-plane component Discrepancies between ESPI-measured displacements (u,v,w) and actual object displacements (u’,v’,w’) due to Misalignment of the surface normal and the viewing direction; Varying surface normal direction on a curved surface. u = u’cosa +w’sina,

Three- point bending with line loads experimental-numerical comparison Three- point bending with line loads (span/depth=10) SHIFT : 0 mm SHIFT : 10 mm

Three-point bending with concentrated loads experimental-numerical comparison Three-point bending with concentrated loads (span/depth=10) SHIFT : 0 mm SHIFT : 10 mm SHIFT 20 mm

SUMMARY e A non-linearity appears when s/d is about 10 and depends on the type of load (line or point load) and the location of the FBG with respect to the load. e The single layer CLT and 1st order shear theories seem to work for s/d more than 25. e Optical Fibre Bragg Gratings offer an indispensable tool to study, in a non invasive manner, deformation behaviour of layered composites.

references additional results using FBR at LMAF/EPFL - F. Bosia, J. Botsis, M. Facchini & P. Giaccari, Composite Science and Technology, Vol. 62, 2002, p. 41. - F. Bosia, T. Gmür, & J. Botsis, Composite Science and Technology, Vol. 62, 2002, p. 55. - M. Studer, K. Peters & J. Botsis,, Composites B, to appear. - K. Peters, P. Pattis & J. Botsis, Journal of Materials Science Letters, Vol. 21, 2002, p. 887. - M. Studer, J. Pietrzyk, K. Peters, J. Botsis, & P. Giaccari, International Journal of Fracture, Vol. 114, 2002, p. 379. Sources used in the view graphs @ From: I. M. Daniel & O. Ishai, ‘engineering mechanics of composite materials’, 1994 & From: J.N.Redy, ‘mechanics of laminated composites’, 1997 Work sponsored by the Swiss National Science Foundation