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  4. Probing the Strength and Fracture Toughness of Hard Second Phases at the Micron Scale
 
conference presentation

Probing the Strength and Fracture Toughness of Hard Second Phases at the Micron Scale

Mueller, Martin Guillermo  
•
Pejchal, Václav  
•
Michelet, Lionel  
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2015
17th International Conference on the Strength of Materials (ICSMA-17)

It is known that the mechanical properties of composite materials and alloys are influenced by the intrinsic mechanical properties of their reinforcements or second phases. It is however challenging to determine such local properties, given their small size and irregular shape. Here we present two newly developed methods to probe the local strength and fracture toughness combining focused ion beam (FIB) milling with microtesting techniques and finite element (FE) simulation. To probe local strength Nextel™ 610 nanocrystalline alumina fibers are used as a test bench material. Deep-etching is carried out to expose the fibres over lengths of a few tens of μm from an aluminium matrix. FIB milling is then used on selected fibres to machine a wide notch oriented perpendicular to the axis of the fibre. A nanoindenter with a flat tip is then used to apply a compressive force along the notched fibre's axis, which produces a bending moment in the ligament opposite to the notch leading to failure. The measured response coupled with the FE model of each notched fibre is used to calculate the stress state in the ligament prior to failure. The strength distribution across a series of such tests is statistically analyzed and fractographic analysis with a SEM is performed. To probe local fracture toughness we produce thin chevron-notched cantilever beams by FIB micromachining. These beams are then loaded using a nanoindenter. The method is successfully applied once the procedure to generate sufficiently thin triangular ligaments with the FIB is mastered, which is crucial to ensure that instability occurs after some stable crack growth, leading to meaningful toughness measurements which are minimally influenced by FIB-induced defects. Test data are interpreted using compliance calibration curves determined by FE simulation of each beam. The method is demonstrated on small volumes of fused quartz and alumina fibres and produces reproducible results consistent with expected values.

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Type
conference presentation
Author(s)
Mueller, Martin Guillermo  
Pejchal, Václav  
Michelet, Lionel  
Zagar, Goran  
Fornabaio, Marta  
Rossoll, Andreas  
Cantoni, Marco  
Mortensen, Andreas  
Date Issued

2015

Written at

OTHER

EPFL units
LMM  
CIME  
Event nameEvent placeEvent date
17th International Conference on the Strength of Materials (ICSMA-17)

Brno, Czech Republic

9-14 August 2015

Available on Infoscience
July 16, 2015
Use this identifier to reference this record
https://infoscience.epfl.ch/handle/20.500.14299/116303
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