Characterizing acrylic foam pressure sensitive adhesive tapes for structural glazing applications—Part II: Creep rupture results

This is a second part of a paper on measurements of mechanical characteristics of high-performance acrylic pressure sensitive adhesive (PSA) tapes, an alternate fastening method for structural glazing. The acrylic PSA used in the study was 3M™ VHB™ G23F Tape. For comparison, parallel creep tests were also conducted on 3 silicones: two one-part and one two-part compositions. Mechanical characteristics determined for the acrylic foam PSA include the viscoelastic properties over a range of temperatures and test rates. Creep rupture results are summarized here as the Part II paper while ramp-to-fail strength and DMA (dynamic mechanical analysis) results were summarized in an accompanying paper (Part I paper). Using the time–temperature superposition principle, master curves of VHB™ Tape storage and loss moduli in shear and tension were developed with data from a dynamic mechanical analyzer. The thermal shift factors obtained from these constitutive tests were successfully applied to the creep rupture and ramp-to-fail data collected at 23, 40, and 60 °C, resulting in master curves of ramp-to-fail strength (Part I paper) and creep rupture durability (in Part II) measured in both shear and tension. The creep results revealed some of the design tradeoffs inherent in the application of VHB™ Structural Glazing Tapes versus structural silicones. VHB™ Tape has more time and temperature dependence than the silicones. VHB™ Tape has lower strength than most structural silicones over the time ranges studied, a fact that is addressed by lower design stresses for VHB™ Structural Glazing Tape and larger tape widths for equivalent creep performance to structural silicone sealants. On the other hand, the short-term strength of VHB™ Tape approaches and even exceed that of structural silicones, a feature that may be advantageous in applications like wind loading and protective glazing. While both bonded VHB™ Tape and structural silicone specimens exhibited some voids, there was less sensitivity of time to failure to the voids and defects seen in the VHB™ Tape specimens tested and significantly less scatter in the time to failure data than specimens made with the structural silicones.