Interface fracture surface energy of sol-gel bonded silicon wafers by three-point bending

International audienceTo probe the interface of silicon sol-gel bonded wafers we developed in-situ micromechanical bending test coupled with optical microscopy. The silicon wafers were bonded together at room temperature using sol-gel silica and dried at 60 oC and sintered at 600 oC. Beam specimens were cut from the bonded wafers, then notched and tested in three-point bending. During bending the crack opening from a notch and the deviation along the interface was observed with an optical microscope. To quantify the interfacial debonding from considering the experimental results, a simple energy balance allows an apparent inter- facial fracture surface energy to be determined. Experi ments and the determined interfacial surface energies show that the bonding of the silicon wafers depends on the silica sol-gel chemistry and on the temperature of the thermal treatment during the bonding process

Mechanical and fracture properties of cellulose-fibre-reinforced epoxy laminates

Epoxy laminates reinforced with cellulose-fibre mats (CFM) have been synthesized and characterized. The influence of CFM dispersion on the mechanical and fracture properties of these laminates have been characterized in terms of elastic modulus, hardness, flexural strength, fracture toughness, indentation responses, impact-fracture, crack-growth resistance and in situ fracture. The reinforcement by the CFM resulted in a significant increase in the strain at break, indentation creep, fracture toughness and impact toughness but moderate increase in flexural strength and flexural modulus. A pronounced R-curve behaviour is exhibited by the CFNI-reinforced epoxy sample, which failed in a graceful manner with slow and stable crack-growth. The micromechanisms of toughening and crack-tip failure processes are identified and discussed in the light of observed microstructures from in situ and ex situ fracture. The implications for new approaches in the 'eco-design' of environmentally friendly composite materials are addressed. (c) 2006 Elsevier Ltd. All rights reserved