Mode I Rigid Double Cantilever Beam Test and Analysis Applied to Structural Adhesives

Abstract

Computational modeling and design using structural adhesives in dynamic events, such as vehicle collisions, requires material properties across a range of deformation rates. In this study, the analysis of the rigid double cantilever beam (RDCB) geometry [7, 8] has been evaluated to measure the critical mode I energy release rate (G _IC ) and the traction-separation response of a structural adhesive at quasi-static rates. Standardized test geometries such as the tapered double cantilever beam (TDCB) are used to measure G _IC ; however the large specimen size is not conducive to measuring properties at high deformation rates and requires additional tests to determine the full traction-separation curve for an adhesive. In contrast, the low mass and size of the RDCB enables use of this geometry for dynamic testing, which will be the focus of future research. Importantly, the RDCB test can provide the entire traction-separation curve of the adhesive from one test. A first series of experimental tests at quasi-static deformation rates identified high variability in the measured response. This variability was reduced by using a new fixture to improve alignment and maintain constant bond-line thickness, highlighting the sensitivity of this method to small variations in sample geometry. In addition, the surface preparation method was crucial to reducing variability in the measured response and achieving primarily cohesive failure in the bond. In this study, the RDCB analysis method was applied to a toughened epoxy structural adhesive. The average measured maximum traction and separation-to-failure of the structural adhesive were 35.3 MPa and 0.214 mm respectively. The average critical energy release rate of the tested adhesive was 3497 J/m². Future investigations will consider optical measurement of displacement on the sample, enhanced data analysis methods, and dynamic testing of adhesive using the RDCB geometry.