Session: 02-05-01: Session #1: 7th Symposium on Fastening and Joining Research and Advanced Technology

Paper Number: 94434

94434 - Effect of Autoclave Cure Temperature, Pressure, and Time on the Glass Transition Temperature and the Degree of Cure of Epoxy Film Adhesive Joints 

 

This experimental study investigates the effect of autoclave cure temperature and pressure, their respective build-up ramp rate, and the cure time duration of curing, on the glass transition temperature, degree of cure of epoxy film adhesive joints.  A fully programmable commercially available mini-bonder autoclave is used for bonding Aluminum alloy substrates using epoxy film adhesive (AF163-2k).  Five cure variables are studied for their effect on the adhesive glass transition temperature T_g and the degree of cure , and the strength of baseline, as well as subsequently heat-cycled, film adhesive single lap joints (SLJs).  Cure variables include two arbitrarily chosen levels of cure time t, cure temperature T and its ramp rate R_t, cure pressure P and its ramp rate R_p.  A commercially available Dynamic Mechanical Analysis DMA system is used (Q800) for measuring the adhesive viscoelastic properties that quantify the adhesive glass transition temperature T_g, which is used for determining the corresponding degree of cure of the film adhesive.  

 

The study shows a significant effect of the autoclave curing variables and variable-interaction on the glass transition temperature, degree of cure, joint strength, and failure mode of test epoxy film adhesive joints.  

 

The study demonstrates the correlation between glass transition temperature T_g changes and the corresponding changes in adhesive degree of cure  and joint strength as a function of the level of cure temperature T.  For the duration of cure time t is set to a shorter value of t₁=40 minutes, which is still within the range specified by the adhesive manufacturer, joint bonding at a higher cure temperature of T₂ =126.67 would increase the adhesive glass transition temperature T_g and the degree of cure , which would accordingly increase joint strength.  This is as compared to curing for 40 minutes at a lower cure temperature of T₁= 93.33, which reduced the glass transition temperature and the degree of cure, resulting in a reduced strength of test joints.

 

Data shows that using a lower temperature ramp rate R_t1 = 1.11º C/min, to reach the cure temperature level, would increase the adhesive degree of cure and joint strength, by allowing more time for curing that would allow more mobility of monomers that increases the cross linking in the adhesive polymer.  A higher level of cure pressure P₂= 0.689 MPa resulted in higher glass transition temperature and degree of cure, as to a lower cure pressure P₁=0.345 MPa.  The higher cure pressure resulted in the formation of intermolecular hydrogen bonding between the hydroxy groups and carbonyl groups and increased the interaction of the polymer chains.  That would improve the cross-linking densities and increase the mechanical strength of the cured epoxy film adhesive.  More results, data analysis, and conclusions are provided.

 

Keywords: Film adhesives, Autoclave bonding, Glass transition temperature, Degree of cur

Presenting Author: Sayed Nassar Oakland University

Presenting Author Biography: Dr. Sayed A. Nassar is currently a Distinguished Professor of Mechanical Engineering, and founding director of the Fastening and Joining Research Institute (FAJRI) at Oakland University (OU) in Rochester, Michigan-USA. He is the co-editor and co-author of the Handbook of Bolts and Bolted Joints, Taylor & Francis, 1998. At Oakland University, he developed a graduate level fastening and joining curriculum and an externally funded research program with more than 30 Ph.D. and MS Dissertations and MS theses on fastening and joining topics, which led to 200 peer reviewed publications on the subject. In addition to his academic teaching and research, Dr. Nassar is regularly engaged with industry through applied fasteners and bolted joint research projects, short courses, tutorials, and hand-on workshops for over 30 years at: GM (US, Mexico), Ford, FCA (US, Egypt), Hyundai Research Center (S. Korea), John Deere (US, Spain, India), First and Second Auto (China), and NASA. Nassar is also a frequent presenter and tutorial developer/instructor on Bolted Joints at international technical conferences and fastener trade shows (e.g. ASME/SAE, FF USA, FF Mexico,...etc.). Dr. Nassar is the CEO and Chief Technology Officer of University Research and Engineering Consultants (UREC, LLC), which is the home of BoltVibe software for vibration loosening analysis (BoltVibe.org). He received his M.S. and Ph.D. degrees in Aerospace Engineering from the University of Cincinnati, Cincinnati, Ohio-USA.

Authors:

Sayed Nassar Oakland University
Shraddha Jagatap Oakland University
Nitesh Hirulkar Oakland University