Toughened adhesives shear properties

Table III. T-Peel and Lap-Shear Properties of Adhesive Joints of Adhesive A Formulations at Various Levels of ME Ac Toughener...

Adhesives based solely on epoxy resins and amine curing agents give cross-linked materials that have high modulus but are very brittle and have no resistance to peel forces. Epoxy resins became much more useful when it was found that rubber flexibilizers could be added to increase crack resistance. Further, it was found that under appropriate reaction conditions, these rubbers could act to "toughen" the epoxy system. That is, addition of rubber flexibilizers tends to reduce the Tg and shear properties of an epoxy. When an epoxy is "toughened" little or no change occurs in the Tg and shear properties while a substantial increase in... 

Backing the adhesive, the choice of room temperature vulcanized silicon has more to do with the thermal resistance of that particular adhesive family than shear strength. In such an application, a minimum of 0.5 MPa out of plane resistance is currently specified. In applications at such high temperatures, the choice of a silicon adhesive combines the mechanical resistance with a thermal insulation. No toughening properties are required since there is no creeping against the mechanical load. The material, the ablative thermal protection and the bonding system, has more to do with Vulcan, the God of fire than Hercules. 

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