On the Use of a Driven Wedge Test to Acquire Dynamic Fracture Energies of Bonded Beam Specimens

Abstract

A driven wedge test is used to characterize the mode I fracture resistance of adhesively bonded composite beam specimens over a range of crosshead rates up to 1 m=s. The shorter moment arms (between wedge contact and crack tip) significantly reduce inertial effects and stored energy in the debonded adherends, when compared with conventional means of testing double cantilever beam (DCB) specimens. This permitted collecting an order of magnitude more crack initiation events per specimen than could be obtained with end-loaded DCB specimens bonded with an epoxy exhibiting significant stick-slip behavior. The localized contact of the wedge with the adherends limits the amount of both elastic and kinetic energy, significantly reduces crack advance during slip events, and facilitates higher resolution imaging of the fracture zone with high speed imaging. The method appears to work well under both quasi-static and high rate loading, consistently providing substantially more discrete fracture events for specimens exhibiting pronounced stick-slip failures. Deflections associated with beam transverse shear and root rotation for the shorter beams were not negligible, so simple beam theory was inadequate for obtaining qualitative fracture energies. Finite element analysis of the specimens, however, showed that fracture energies were in good agreement with values obtained from traditional DCB tests. The method holds promise for use in dynamic testing and for characterizing bonded or laminated materials exhibiting significant stick slip behavior, reducing the number of specimens required to characterize a sufficient number of fracture events.

Understanding Surface Adhesion in Nature: A Peeling Model

“…The second method is the wedge peel test (Figure b) to evaluate the adhesive strength in mechanical manufacturing field. During the test, a wedge, in touch with two adhesive surfaces, is drawn along the length direction of the specimen . The values of peel strength measured using wedge peel tests, corresponded with the results by fracture mechanics methods …”

On the dynamic response of adhesively bonded structures

“…The double cantilever beam (DCB) is generally used to investigate the mechanical performance of the adhesive interface normal to its surface [22,23,26,27,28,29,30], while the end notched flexure (ENF) resolves the adhesive's response tangential to its surface [24,26,31,32,33]. The single leg beam (SLB) is usually employed to reveal the adhesive's mechanical performance under more complex stress states [25,26].…”

Higher Rate and Impact Tests

“…For the DCB, this becomes an important factor when the loading rate exceeds about 10 m s −1 . This can be overcome by the use of dual actuator loading, or by the use of a driven wedge, as reported in [14].…”