Mechanisms of degradation in adhesive joint strength: Glassy polymer thermoset bond in a humid environment

Journal Article · Thu Aug 06 00:00:00 EDT 2015 · International Journal of Adhesion and Adhesives

DOI: https://doi.org/10.1016/j.ijadhadh.2015.07.014 · OSTI ID:1236247

Kropka, Jamie Michael ^[1]; Adolf, Douglas Brian ^[1]; Spangler, Scott Wilmer ^[1]; Austin, Kevin N. ^[1]; Chambers, Robert S. ^[1]

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1. Sandia National Lab. (SNL-NM), Albuquerque, NM (United States)

The degradation in the strength of napkin-ring (NR) joints bonded with an epoxy thermoset is evaluated in a humid environment. While adherend composition (stainless steel and aluminum) and surface preparation (polished, grit blasted, primed, coupling agent coated) do not affect virgin (time=0) joint strength, they can significantly affect the role of moisture on the strength of the joint. Adherend surface abrasion and corrosion processes are found to be key factors in determining the reliability of joint strength in humid environments. In cases where surface specific joint strength degradation processes are not active, decreases in joint strength can be accounted for by the glass transition temperature, T_g, depression of the adhesive associated with water sorption. Under these conditions, joint strength can be rejuvenated to virgin strength by drying. In addition, the decrease in joint strength associated with water sorption can be predicted by the Simplified Potential Energy Clock (SPEC) model by shifting the adhesive reference temperature, T_ref, by the same amount as the T_g depression. When surface specific degradation mechanisms are active, they can reduce joint strength below that associated with adhesive T_g depression, and joint strength is not recoverable by drying. Furthermore, a critical relative humidity (or, potentially, critical water sorption concentration), below which the surface specific degradation does not occur, appears to exist for the polished stainless steel joints.

• Research Organization: Sandia National Laboratories (SNL-NM), Albuquerque, NM (United States)
• Sponsoring Organization: USDOE
• Grant/Contract Number: AC04-94AL85000
• OSTI ID: 1236247
• Report Number(s): SAND--2014-16234J; 533734
• Journal Information: International Journal of Adhesion and Adhesives, Journal Name: International Journal of Adhesion and Adhesives Journal Issue: C Vol. 63; ISSN 0143-7496
• Publisher: ElsevierCopyright Statement
• Country of Publication: United States
• Language: English