Specimen size and geometry effects on fracture toughness of Al2O3 measured with short rod and short bar chevron-notch specimens

Plane strain fracture toughness measurements were made on Al2O3 using short rod and short bar chevron notch specimens previously calibrated by the authors for their dimensionless stress intensity factor coefficients. The measured toughness varied systematically with variations in specimen size, proportions, and chevron notch angle apparently due to their influence on the amount of crack extension to maximum load (the measurement point). The toughness variations are explained in terms of a suspected rising R curve for the material tested, along with a discussion of an unavoidable imprecision in the calculation of K sub Ic for materials with rising R curves when tested with chevron notch specimens

A low cost coarse/fine piezoelectrically actuated microgripper with force measurement.

International audienceThe last decade was characterized by an important increase in the request concerning miniature products. Nowadays, the miniaturization of the products represents major strategic and economic stakes. Economic surveys expect an important increase in the needs for MEMS (Micro Electro Mechanical Systems) and MOEMS (Micro Opto Electro Mechanical Systems) in various fields. Components used in MEMS are different from those used in microelectronics technology. Micromanipulation of flat SMD (Surface Mounted Devices) electronic components has been successfully done using vacuum handling systems. However, components used in MEMS have electrical, mechanical, optical or fluidic functions. These components have complex 3D shapes. This is why new micromanipulation technologies must be developed taking into account the specificities of these new components. One of the most important functions is the gripping of microcomponents. In order to fulfil the demands concerning microhandling, various laboratories have developed prototypes of microgrippers. Most of them are able to handle micro-objects in a narrow range of sizes. Moreover, these grippers are rarely equipped with precise sensors for force measurement. However, measuring the force applied by the gripper on the manipulated object is very important in order to avoid damaging or destroying the object. In this paper we present the design and the control of a microgripper dedicated to very high precision tasks. This microgripper is able to handle small components in a wide range of sizes (from 100 µm to several mm). The object handled can be moved laterally on several cm with force control

Comparing carriers as a support media of white-rot fungi in natural tannins removal

In the last decades, White-rot Fungi bioremediation potential has been widely investigated, providing remarkable results toward several recalcitrant molecules. However, full-scale applications based on fungi are not employed yet and little is known about their optimal operating conditions, such as (i) their ability to grow without sterile conditions, (ii) co-substrate requirements and (iii) the accurate carrier design for fungal growth. In this study, several batch tests were performed as preliminary steps to evaluate the possible design of a pilot-scale reactor based on fungal biomass to be operated under not-sterile conditions in the removal of Quebracho natural tannin. The tests were performed to verify fungal affinity, including Basidiomycetes and Ascomycetes for innovative cellulose-containing carriers compared to commonly employed PolyUrethane Foam Cubes. In particular, four fungi, including three Basidiomycetes White-rot Fungi, Bjerkandera adusta, Phanerochaete chrysosporium and Tyromyces chioneus and the Ascomycota strain Aspergillus tubingensis, were employed. As a first step, fungi were tested to evaluate their ability to attach and grow onto 12 types of innovative carriers made by High-Density PolyEthylene and containing cellulose in different percentages. Other tests were performed without sterile conditions. In particular, fungal abilities (i) to attach and grow onto two different types of support, including cellulose-containing carrier and polyurethane foam cubes and (ii) to biotransform recalcitrant molecules (Quebracho natural tannin) (iii) to grow and operate synergistically in a consortium of two fungi, were evaluated. The main parameters evaluated were soluble Chemical Oxygen Demand (sCOD) reduction and dry weight increase. Basidiomycetes showed high affinity for cellulose-containing carrierswith the highest cellulose percentage (7%) achieving full colonization and 60% coverage, in sterile conditions and not- sterile conditions, respectively. These results were associated with a Quebracho sCOD removal of 25 ± 4%, without sterility. When combined, the two selected strains, Bjerkandera adusta and Aspergillus tubingensis were able to grow on carriers and to remove up to 15 ± 4% of tannins recalcitrant sCOD. This study provides evidence of (i) Basidiomycetes high affinity for cellulose-containing carriers that could favour fungi attachment in sterile and not-sterile conditions and (ii) the feasibility of a combined use of Ascomycetes and Basidiomycetes in bioremediation