Mechanical Properties

The bulk material properties, reported in Table 2, were obtained on the 2.2 ± 0.2 mm thick film adhesive after curing it between two sheets of PTFE release liners in an autoclave for 30 min at a temperature of 130° C and a pres­sure of 0.8 MPa, except for indentation hardness, as noted below. Tensile tests were conducted according to JIS K 6251 standard [22] on adhesive dumbbells with a procedure similar to the one set out in ISO 527 Parts 1 and 2 [23,24]. In­dentation hardness (durometer) was measured in accordance with JIS K 6253 [25] by stacking three layers of the cured film adhesive on top of each other to achieve a specimen thickness of approximately 6.6 mm. Tear strength was meas­ured according to JIS K6252 [26].

Furthermore, as has been reported earlier, the physical properties of the sil­icone film adhesive show a low dependency on temperature [15].

Figure 5 shows the tensile stress-strain curve of the cured silicone film adhe­sive at room temperature as averaged over a separate set of 50 uniaxial tensile extension measurements [obtained with a strain rate of 500 mm/min on ASTM D 412 [27] type (dumbbell) specimens], as well as the corresponding graphs for secant modulus (stress-strain ratio) and tangent modulus (slope of the stress – strain curve). The graphs for the tangent and secant moduli of elasticity con­verge towards a Young’s modulus of about 9.3 MPa. For this set of data, an ulti­mate tensile strength of 8.6 MPa is reached at 250 % (95 % fractile Ru5 = 7.85 MPa). Additionally, the form of the graph indicates that the material data can be characterized by an incompressible neo-Hookean material model with a shear modulus of 2.5 MPa [28].