14 - Acoustic Emission monitoring of adhesively bonded wood joints under quasistatic and cyclic fatigue mode II fexure loads using end-notch-fexure specimens

• Published in: Journal of acoustic emission 2018-01, Vol.35, p.S31
• Main Authors: Brunner, A.J, Clerc, G, Niemz, P
• Format: Article
• Language: English
• Subjects: Acoustic emission testing; Adhesives; Fatigue; Fatigue testing machines; Laminated materials; Materials; Rankings
• ISSN: 0730-0050

Adhesive bonding is becoming more and more important for manufacturing structures or structural elements made from wood. For designing such structures, the performance of adhesives has to be evaluated under quasi-static and cyclic fatigue loading as well as under corresponding fracture loads. The performance of wood glued beams under quasi-static loading is fairly well understood, but their cyclic fracture behavior remains still largely unknown. There are indications from standard tensile shear tests with several types of adhesive that the performance ranking of adhesives under cyclic fatigue loading may differ compared with that observed in the same test under quasi-static loads. Hence, it is of interest whether this is also the case for quasi-static and cyclic fatigue mode II shear fracture. For the mode II shear fracture tests, adhesively bonded joints with wood adherends are prepared with two different adhesives, one a rather brittle (phenol resorcinol formaldehyde) system and one a rather ductile (one component polyurethane) system. These are then compared for their performance under quasi-static and cyclic fatigue mode II in-plane shear fracture loads. Those adhesives are presenting different failure mechanism, for the ductile adhesive the failure will propagate in the interface between wood and adhesive and for the brittle one the crack will mainly run in the wood. For the fracture tests a set-up with four-point end notched flexure specimens is being used, analogous to testing of adhesively bonded polymer composites joints and polymer composite laminates. Selected fracture tests were monitored by acoustic emission for assessing damage evolution due to the mode II in-plane shear fracture loads. The acoustic emission monitoring initially also contributed to identifying shortcomings of a first test set-up that was subsequently modified. The discussion will focus on the comparison between two different types of adhesive and between quasistatic and cyclic fatigue fracture loads.