Micro-Scale Experiments and Models for Composite Materials. PhD-student : Sanita Zike Supervisor s : Lars P. Mikkelsen , DTU Wind Energy, Section of Composites and Materials Mechanics Bent F. Sørensen , DTU Wind Energy, Section of Composites and Materials Mechanics
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PhDproject duration: 1. January 2012 - 31. December 2014
Project type & funding: PhD-A project, DCCSM Core (DSF)
The targetof the PhD project is to establish coupled modelling-experimental approaches for bridging the understanding of compositematerial properties from micro to macro scalelength.
Wang, G.F. & Van der Giessen, E., 2004. Fields and fracture of the interface between a glassy polymer and a rigid substrate. European Journal of Mechanics - A/Solids, 23(3), pp.395-409.
Jeong, H.Y. et al., 1994. Slip lines in front of a round notch tip in a pressure-sensitive material. Mechanics of materials, 19(1), pp.29–38.
Modelling and experimental determination of plasticity zone by formation of shear bands in polymer material around notches, single and multiple fibre/matrix interfaces.
Glass – Polymer- Glass
Sørensen, B.F. et al., 1998. Fracture resistance measurement method for in situ observation of crack mechanisms. Journal of the American Ceramic Society, 81(3), pp.661–669.
Sørensen, B.F. et al., 2010. Cohesivelawsforassessmentofmaterialsfailure: Theory, ezperimentalmethodsandapplication. DoctorofTechnicesthesis, DTU.
.Goutianos, S., Frandsen, H.L. & Sørensen, B.F., 2010. Fracture properties of nickel-based anodes for solid oxide fuel cells. Journal of the European Ceramic Society, 30(15), pp.3173-3179.
Interface studybetween glass and polymer introducing DCB testing method in optical microscope and ESEM
The ending of research project involves understanding the correlation between the observed micro- and macro-scale properties of composite materials.
In micro-scale materials can sustain higher loads, therefore show better strength properties than the same materials in macro-scale.
The project intention is to develop approaches, which can be used to predict macroscopic behaviour knowing the micro-scale properties.
Strain gauge electrical resistance is changed with small deformations of inner grids.
Calibration of strain gauges has to be done to obtain gauge factor:
Obtain correction methods for strain gauge measurements
Purpose is to determine the measurements accuracy of strain gauges used in soft materials testing.
development of numerical model in FEM program ABAQUS;
in situ micromechanical measurements under optical microscope incorporating digital image correlation (DIC) system
Experimentally observed discrepancy between different strain measurement methods:
Why SG, clip on and laser extensometer measurements show different strain values?
Elastic modulus of specimen
Elastic and plastic deformation
Strain gauge dimension
(elongation of end-loops)
1.5 - 10 mm
3.8 - 5.0 µm
1 – 30 mm
25 – 150 mm
10 – 25 mm
2 D model & fibre/matrix interface
SG: uniform foil with ½ thickness (2D), elastic-plastic, back-to-back SGs
Specimen: ¼ symmetry (3D), elastic, elastic-plastic
Parts: solid, homogeneous, deformable
Elements: plane stress & 3D stress
Load: displacement boundary
3 D model
Manufacturers provided strain gauges are calibrated on stiff material - steel.
Usage of strain gauges on softer material than constantan, requires new calibration or gauge factor correction.
Gauge factor (GF)
Gauge factor correction:
Correction coefficient (C) – ratio between actual and SG determined strain:
Specimen thickness & fibre/matrix interface
Strain gauge length & stiffnessParameter study results