Interfacial adhesion and fracture behaviour of laminated engineered wood products

胶粘复合技术无疑是保持加拿大木制品生产商更具竞争力的驱动力之一，它依赖于生产高性能和耐用的工程木制品（ewp）。加拿大木材科学家和工业界已经确定了采用这种强调EWPs的技术原因，例如：(1)可用软木和硬木原木的直径急剧减少；(2)建筑用交叉层压板和铁路用交叉层压板等产品早期进入高价值EWP市场的潜力很大。必须对胶合层合木制品的粘接强度和寿命进行准确的评估和估计。目前，最广泛采用的评估层压产品粘结强度的方法是所谓的“块剪切试验”，这在加拿大和美国标准中有规定。然而，研究表明，这种方法是不可靠的，因为粘结强度的破坏通常发生在木材中，而不是沿着粘结线，这不能提供适当的粘结强度信息。仔细观察块体剪切试件的结构和实验设置，可以发现在试件缺口角处存在复杂的剪应力和法向应力组合，并且沿剪切平面的弯曲应力是加载错位的结果。这就需要一种新的评价方法。该计划的总体主题是研究层压工程木制品的界面粘附和断裂行为，从而有助于对其粘合特性的基本理解，以及对创造增值木制品的进一步实质性贡献。具体目的是开发一种评价复合木制品粘结质量的合适方法。招募4名研究生和4名本科生，运用力学理论对层合试件在短跨弯曲作用下的粘结线进行裂纹分析，并将结果与常规块体剪切试验方法进行比较。将考虑对称和不对称配置，这两者都存在于平行和交叉层压木制品。该计划的预期成果是：(1)通过开发合适的接近现实的测试方法，对层压工程木制品的粘合特性有基本的了解；(2)向加拿大标准协会和美国测试与材料协会提出测量层压木制品粘合强度的新测试方法。

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.