Toughening the Macro Defect Free (MDF) Cements

Abstract

Thermal stability and sealing performance of perfluoroelastomer seals as a function of crosslinking chemistry Abstract. High performance polymer based-cements (i.e. cements having a water to cement ratio, w/a , close to 0.1) almost totally free of defect, have been developed in recent years claiming a great interest for their very high tensile strength compared with traditional cements. These materials can be produced utilizing very simple unit operations and further formed in complex shapes with high surface quality. Indeed these materials have the disadvantage of being too much brittle and for this main reason they are rarely utilized in practice. Toughening the Macro Defect Free Cements (MDF) implies the strict control of the structure. The structure is governed by the process-induced paste modifications. In this paper we show that toughening can be achieved with elastomeric particles having well defined size distribution and physico-chemical characteristics in relation with both the binder polymer and the cement chemistry.

Viscoelastic Properties of Soft Adhesives

“…The same circumstances hold for the structural adhesives even if they lay in their glassy state where non-equilibrium conditions are in order. [5][6][7][8][9][10][11][12] Indeed, in soft adhesives, the intensity of the threedimensional state of stress during peeling is strongly dependent on the flexural stiffness of the tape, once the surface properties of the backing and the tape (namely, the roughness and the surface tension) and the adhesive thickness are fixed. The presence of voids allows the fibril formation due to the rapid transformation of the three-dimensional state of stress into unidirectional stress states within the adhesives parts confined by voids.…”

Algorithms for Flaw Detection by SHM with Static Sensors Approach

“…The damage detection can be performed with two different types of sensors; dynamic sensors (i.e., piezo) and static sensors (like strain gages or sensor optic fibers). [ 1–6 ] Dynamic sensors work by transmitting waves through the structures; the waves are deviated and/or reflected by damages; the use of a suitable software could allow a correlation of the wave deviation with the types and sizes of defects and damages contained in the structure. Some concerns exist utilizing of dynamic sensors during the flight, due to the superposition of the waves with the flight vibrations.…”

“…The presence of damages causes a change of the strain field that can be correlated with the damages’ type, location, and sizes. [ 6–8 ] The major difficulty of this approach is given by the need to know the load level, which is always known during a lab test but whose knowledge in service is not obvious. Two different algorithms finalized to overcome this difficulty have been developed and patented in Leonardo aircraft; they are based on a reverse finite element method (F.E.M.)…”

Polymer-Modified Calcium-Aluminate Macro Defect Free (MDF) Cements

“…MDF cements are a particular example of composite materials, they are characterized by high elastic properties (E≈ 35 GPa) and strength (σr ≈ 150 MPa). Thanks to their potential, these materials have been the subject of numerous studies after being developed in the early 1980s [1][2][3].…”