Issue 16

G. Pesquet et alii, Frattura ed Integrità Strutturale, 16 (2011) 18-27; DOI: 10.3221/IGF-ESIS.16.02 20 brittle, adhesive 2015 is ductile and adhesive AW106 is very ductile. The several mass fractions that were used are summarized in Tab. 3.Up to 25% of TEMs were added to the adhesives. Particle size 10-20 µm Shell thickness 3-4 µm Density 1.13 g/cm 3 Chemical composition of shell Vinylidene-chloride-copolymer Chemical composition of core Isobutane Table 1 : Characteristic of the TEMs (F-30D) used in the present study. Adhesive w/ hardener Glass transition temperature (°C) Araldite AV138M/HV998 80 Araldite 2015 67 Araldite AW106/HV953U 45 Table 2 : Adhesives selected with indication of T g . Figure 1 : Tensile stress-strain curves of the epoxy adhesives without particles. AV138M/HV998 0 wt% 10 wt% 20 wt% Araldite 2015 0 wt% 10 wt% 20 wt% AW106/HV953U 0 wt% 25 wt% Table 3 : Mass fractions studied for the three adhesives. Specimens manufacture A critical point in this study is the mixing of TEMs in the adhesive. For that purpose, a mixer relying on centrifugal force was used (DAC 150.1 FVZ Speedmixer, Hauschild, Germany). This allows an efficient and homogeneous dispersion, creating visibly bubble-free mixing. The mixture was checked through a scanning electron microscope (SEM) analysis. Small samples were immersed in liquid nitrogen before being fractured. At this temperature, the materials were very brittle and the fracture surfaces were very neat. The particles were always well dispersed. The mixture was poured in a mould consisting in a silicone rubber and a metallic frame [9]. A pressure of 2 MPa was applied in a hot press to the mould. All specimens were cured at 40ºC at varying times (16h for AV138M, 4h for 2015 and 6h for AW106) to ensure complete cure. The specimens were machined afterwards from the bulk plates.