Interfacial adhesion and fracture behaviour of laminated engineered wood products

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Adhesive laminating technology is no doubt one of the driving forces keeping Canada's wood products producers more competitive, and it relies on the production of high-performance and durable engineered wood products (EWPs). Canadian wood scientists and industry have identified technical reasons for adopting such an emphasis on EWPs, such as: (1) Diameters of available softwood and hardwood logs have been dramatically decreased; and (2) High potential exists for early entry to high-value EWP markets with products like cross laminated timber for construction and laminated wood crossties for railway lines. The bond strength and life span of adhesive laminated wood products must be accurately evaluated and estimated. Currently, the most widely-adopted method for evaluating the bond strength of a laminated product is a so-called “block shear test,” which is specified in Canadian and American Standards. However, research has revealed that such a method is not reliable since a failure in bond strength usually occurs in the wood, rather than along a bondline, which fails to provide proper adhesive bond strength information. A close look at the specimen configuration and experimental setup of a block shear specimen reveals that there exists a complex combination of shear and normal stresses at the corner of a specimen notch, and that bending stresses along the shear plane are a result of misalignment(s) in loading. This calls for a new evaluation method. The overall theme of this proposed program is the study of interfacial adhesion and fracture behaviour of laminated engineered wood products, thereby contributing to a fundamental understanding of their bonding characteristics, as well as a further substantial contribution to creation of value-added wood products. The specific objective is to develop a proper method for the evaluation of bond quality of laminated wood products. Four graduate students and four undergraduate students will be recruited and will apply mechanics theories to conduct crack analysis along the bondlines of laminated specimens under short-span bending and will compare the results with those from conventional block shear test approaches. Considerations will be given to both symmetric and asymmetric configurations, which both exist in parallel and cross laminated wood products. The expected outcomes of this proposed program are:(1) a fundamental understanding of the bond characteristics of laminated engineered wood products through the development of suitable near-reality test methods, and (2) a proposal on new test methods for measuring the bond strength of laminated wood products to the Canadian Standards Association and the American Society for Testing and Materials.