Лако-красочные материалы — производство

Julio F. Davalos West Virginia University, Morgantown, West Virginia, U. S.A. Pizhong Qiao The University of Akron, Akron, Ohio, U. S.A. I. INTRODUCTION There is a worldwide need to rehabilitate and improve civil infrastructure, and to this end, new construction materials and methods are being intensely investigated to alleviate current problems and provide better and […]

Understanding the causes and mechanisms of fracture in adhesive-bonded joints and mate­rials is important to improving their performance, developing products based on new com­binations of materials and adhesives, predicting the performance of new materials, and developing design methods for structural joints. In this chapter I have briefly discussed some aspects of wood and adhesive fracture, […]

Lei and Wilson [35,67] developed a model for the fracture toughness (KIc) of flakeboards bonded with PF resin adhesive. The model is based on the initial crack length (a) in the specimen, the average size of the inherent flaw (O) in the solid wood, the expected increase in crack length resulting from nonbonded interflake cracks […]

A. Structural Joints There are no standard design methods for adhesive-bonded wood joints, let alone design methods based on fracture mechanics. This is obviously due in part to the complexity of the fracture behavior of wood joints and materials. The lack of adequate design methods has obviously been a hindrance in furthering the use of […]

External loads are imposed on a bonded joint or structure by the dead weight of the structure and its contents, accumulated snow, wind, and people. The average stresses in a joint created by these loads can be calculated from structural analysis, but the maximum stress at joint edges is more difficult to determine. These stresses […]

The moisture content of both the wood and the adhesive affect the fracture behavior of adhesive bonded joints. Wood joints are especially sensitive to moisture effects as a result of the porosity and permeability of wood, which allows ready access by water to both the interior of the wood member and the adhesive layer. Irle […]

Structural joints are purposely not designed with the fibers intersecting the plane of the bondline as a result of the weakness of this design. However, this relationship can be of Figure 14 Effect of adherend grain angle to the bondline on the fracture toughness of bonded wood joints in cleavage. (From Ref. 3.) great importance […]

A natural crack initiated in the center of the adhesive layer in a symmetric joint between symmetric isotropic (metal) adherends will tend to propagate through the center of the adhesive layer. However, in wood joints, there is a strong tendency for the crack to travel in the wood near the joint. This condition should be […]

Once it initiates, a crack may propagate in one of several ways. It may fracture completely and catastrophically as glass (unstable) (Fig. 12a), it may fracture in several moderate 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. increments of growth with […]

1. Crack Initiation Fracture of wood and bonded joints and materials begins at a geometric or material discontinuity where displacement of the adherends (due to external or internal stress) creates the greatest stress concentration and where either the adherend or the adhesive is the weakest. Examples of geometric discontinuities in adhesive-bonded wood joints are the […]