(Courtesy 3M)
Selecting a structural strength adhesive for a specific application requires performance criteria of several characteristics. First are bond-making properties that determine ease of use and in-place manufacturing cost:
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Degree of surface preparation necessary
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Time to handling strength
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Cure conditions of heat or room temperature, the degree of pressure, and the fixturing to maintain that pressure
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Viscosity for pumping and staying in place after application. Pseudoplastic and thixotropic qualities are desireable so that the adhesive thins during the shearing action of delivery and thickens in place without further shearing.
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Application with automated bulk systems or hand-held applicator to meet varying production requirements.
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Then there are the following cured bond properties:
Physical Properties
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Adhesion to a variety of substrates allows bonding of dissimilar materials if necessary
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High cohesive strength is desirable
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Flexibility improves peel strength by flexing with peel stress
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High elastic modulus of substrate and adhesive resists stress at the bond line
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High damping capacity of the adhesive dissipates dynamic stresses of vibration, motion, & impact throughout the bond & peel stresses at the bond line
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Flexibility and damping resistance resists thermal expansion stresses when the coefficients of thermal expansion are different between adhesive and substrates
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Environmental Resistance
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Resists end-use or post-processing temperatures to maintain adhesive chemistry and the physical bond
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Withstands physical shock at a range of temperatures
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Maintains adhesive performance despite exposure to UV light, rain, salt water, and other weathering conditions
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Chemical Resistance
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Ability to withstand degradation from diesel fuel, solvents and other chemicals
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