Tensile Tests on the Materials
Type-1A material specimens to DIN EN ISO 527-2  were used to analyze the material behavior at various temperatures and determine the material parameters under tensile loads. The specimens were loaded according to DIN EN ISO 527-1  with displacement control at a rate of 1 mm/min. Between five and ten specimens per adhesive were tested at temperatures of —25, + 25, and + 75°C. Each specimen was preconditioned at the respective temperature for 24 h prior to the test. A video extensometer was used to ensure noncontact measurement of the deformation. The stress-strain diagrams (stress and strain in these diagrams are technical data referring to the original section) show just how much the behavior of each adhesive depends on the temperature. By way of example, only the two most interesting adhesives of each type are described here.
The epoxy resins (Fig. 4) exhibit a very stiff material behavior at low temperatures with brittle material failure, and a very resilient behavior at high temperatures. The stiffness of EP4 only drops after room temperature has been exceeded, but then very distinctly. The polyurethanes (Fig. 5), too, were found to be very resilient at high temperatures. At low temperatures they are almost as stiff as the epoxy resins, but exhibit a plastic behavior after reaching the
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aFirst Glas, Rhinstrafie 132, 12681 Berlin, Germany.
bDELO Industrie Klebstoffe, Delo-Allee 1, 86949 Windach, Germany.
cPanaeol-Elosol, Daimlerstrafie 8, 61449 Steinbach, Germany.
dHuntsman Advanced Materials, Klybeckstrafie 200, 4057 Basel, Switzerland.
eHenkel AG & Co. KGaA, Henkelstrafie 67, 40191 Diisseldorf, Germany.
f3M Deutschland, Carl-Schurz-Strafie 1, 41453 Neuss, Germany.
FIG. 4—Stress-strain diagram for epoxy resins EP1 and EP4 at various temperatures.
maximum stress. The acrylate adhesives (Fig. 6) also exhibit a temperature – dependent behavior, which is typical of this group of adhesives . However, this behavior is not as pronounced as it is with the epoxy resins. The rise in the stiffness as the temperature drops is less pronounced. The material behavior at low temperatures has proved to be particularly advantageous for the acrylic adhesives investigated; the adhesives exhibit good flexibility at low temperatures and only fail after a distinct yield range.