Interfacial adhesion and fracture behaviour of laminated engineered wood products

胶层压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，它依赖于高性能和耐用的工程木制品(Ewps)的生产。加拿大木材科学家和工业界已经确定了采用Ewps的技术原因，例如： (1)可利用的针叶木和阔叶木的直径已大幅减少； (2)早期进入高价值EWP市场的潜力很大，建筑用交叉层压木材和铁路线用层压木材交叉等产品。 胶合木制品的粘合强度和使用寿命必须得到准确的评估和估计。目前，最广泛采用的评估层压产品粘结强度的方法是加拿大和美国标准中规定的所谓的“块剪切试验”。然而，研究表明，这种方法是不可靠的，因为粘合强度的失效通常发生在木材中，而不是沿着粘合线，这无法提供正确的粘接强度信息。仔细观察块状剪切试件的试件构型和试验装置，发现试件缺口拐角处存在复杂的剪应力和正应力组合，沿剪切面的弯曲应力是加载不对中的结果(S)。这就需要一种新的评价方法。 这一计划的总体主题是研究层压工程木制品的界面粘合和断裂行为，从而有助于从根本上了解它们的粘合特性，并进一步为创造高附加值的木制品做出重大贡献。本研究的具体目的是建立一种适用于层压木制品粘接质量评价的方法。将招收4名研究生和4名本科生，他们将应用力学理论对短跨度弯曲层合试件的接合线进行裂缝分析，并将结果与传统的块体剪切试验方法进行比较。将考虑对称和非对称配置，这些配置既存在于平行木制品中，也存在于交叉层压木制品中。这一拟议方案的预期结果是： (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结特性有一个基本的了解，以及 (2)向加拿大标准协会和美国测试和材料学会提出一项关于测量层压板产品粘合强度的新测试方法的建议。

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.