Wood adhesive joints

Advances in the chemistry and technology of wood adhesives, the rheology of wood adhesive joints, and details of specific industrial gluing processes are all important, but they must be left for others to review. Even within the subject of adhesion to wood, I will limit comment primarily to research since 1970. Marian and Stumbo (JL, 2), Jurecic ( 3), Halligan (4), Patton (5), and Collett (6) have carefully reviewed the earlier contributions to adhesion to wood. Their efforts will not be duplicated except where necessary to provide perspective. 

D 4502 Test Method for Heat and Moisture Resistance of Wood Adhesives Joints... 

COHESIVE FAILURE CHARACTERISATION OF WOOD ADHESIVE JOINTS... 

Fracture Mechanics, Wood adhesive joints, shear loading, cohesive failure. 

Cohesive Failure Characterisation of Wood Adhesive Joints... 

Fig. 11 Non linear deformations in the wood adhesive joint loaded in shear at the critical experimental conditions.

Sheppard, A., Kelly, D., Tong, L., (1998), Int. J. of Adhesion and Adhesives 18, 385. Wemersson, H., (1994), Fracture characterization of wood adhesive joints. Report TVSM-1006, Lund University, Division of Structural Mechanics, Lund, Sweden, Simon, F., Morel, S., Valentin, G. (1997). In Proceedings of the Euromech Colloquium 358, Mechanical behaviour of adhesive joints, analysis, testing and design, Pluralis, Paris, pp. 341-351. 

ASTM D-4502, Standard Test Method for Heat and Moisture Resistance of Wood-Adhesive Joints. Rather than using an expensive autoclave as in D-1101 and D-2559, moisture aging in this test is accomplished in moist aging jars. The samples are exposed to prescribed temperature-humidity cycles in the jars heated in ovens. The strength of the aged samples is measured by standard methods and compared to similar virgin samples. 

The crack initiation energy can readily be determined from a mode I cleavage test using a double cantilever beam specimen [1,2]. This method has been applied to wood-adhesive joints by many researchers [3 17]. The test requires the beam compliance (C), load at crack initiation (P ), crack length at initiation (a), specimen thickness (/), and change in beam compliance = change in displacement of load points/change in... 

Anatomical features such as the SI, S2, and S3 layers of the cell wall (Fig. 2) are especially important in the fracture of wood and wood-adhesive joints. There are three general types of fracture at the microscopic level [20] transwall, intrawall, and intercellular... 

Very high fracture toughness values for wood adhesive joints can be attributed to a combination of adhesive plastic deformation and reduction of microcracking of the wood around the crack tip. A flexible adhesive layer, especially a thick layer, distributes the... 

Figure 12 Characteristic crack growth behavior and fracture toughness of wood adhesive joints (a) strong/unstable (b) strong/stable (c) strong/moderately unstable (d) weak/stable.

The use of phenolic resins for wood bonding has been reviewed by Pizzi, Dinwoodie, Kollmann and coworkers, " the U.S. Department of Agriculture, and Barth. Tapered double cantilever beam specimens have been recently used to test the effect of bondline thickness and cure time on the fracture energy of phenolic-wood adhesive joints. ... 

Moisture Resistance of Wood-Adhesive Joints. This recent standard defines procedures where the degrading effects of heat and moisture on bond quality are measured in such a way that the data can be analyzed by means of classical rate process equations. Results have shown that usefal, long-term extrapolations of environmental effects can be made. 

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