Joints fracture mechanics

Fig. 4.14. Some adhesive joint fracture mechanics specimens, (a) Tapered double cantilever beam (TDCB). (b) Thick double cantilever beam (DCB). (c) Thin double cantilever beam or wedge cleavage specimen, (d) Independently loaded mixed-mode specimen (ILMMS). (e) Scarf joint.

Kinloch, A. J., Interfacial Fracture Mechanical Aspects of Adhesion Bonded Joints, Review Article, Journal of Adhesion, vol. 10, 1979, p. 193. 

Fractionation of chain molecules according to their chain length, 727 Fracture mechanics, 472 Free enthalpy of formation, 753, 754 Freely jointed chain model, 247 Free-rotation model, 246 Free surface energy, 229 Free volume fraction, 537 Freeze-off time, 806 Freezing-in process, 151 Frequency doubling, 349 factor, 751... 

A first aim in the present study was to establish whether the approach proposed by Femlund Spelt, which will be described in more detail below, could be applied to bonded composite joints. A second objective was to evaluate the benefits to be gained from a fracture mechanics characterisation when industrial structural assemblies are considered, both qualitatively in material selection, and quantitatively when failure predictions are required. 

Another aspect to be considered is the difficulty in producing curved structures with the same fibre content as flat laboratory panels. This effect is shown in Figure 16, at the comer the laminate thickness is larger than at the flat section and fibre content is rather lower. This will affect the bending stiffness of the arm and the predicted failure load. This figure also shows the fillet, which is critical to initiation in the specimens without implanted defects. It is well known that fillets can significantly alter the load path in lap shear joints and increase the failure loads (see [1] and Figure 3 for example). If a fracture mechanics approach is to be applied this effect must be considered. Some recent studies on stress intensity factors for such cases may allow this to be addressed [22]. 

Paraschi, M., A fracture mechanics approach to the failure of adhesive joints, PhD thesis. Department of Mechanical Engineering. 2002, Imperial College, University of London London. 

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

It is my great pleasure to introduce the proceedings of the ESIS TC4 conference, Fracture of Polymers, Composites and Adhesives , which was held in the mountain resort of Les Diablerets, Switzerland between 15-18 September 2002. This was the third conference organised by TC4 and, as on the two previous occasions, it reflects the main activities of the committee which are focussed on developing fracture mechanics test methods for polymers, adhesive joints and composites. 

Because the fracture toughness depends both on cure time and temperature, the arbitrary selection of time and temperature for accelerated tests may not be appropriate for reliable prediction of longterm service life of joints (J7). In order to reduce test variability and improve the durability prediction of adhesive joints, it would be necessary first to control the cure temperature and time required to produce a level of fracture toughness that does not change further (14). The study is thus an excellent example of a multidisciplinary approach combining chemistry, fracture mechanics, and wood science in the investigation of the adhesive bonding of wood. 

Ebewele, R. O. The Fracture Mechanics Approach to the Assessment of Adhesive Joint Performance in Bonded Wood Products, Ph.D. thesis, Univ. of Wisconsin Madison, WI, 1980. 

The pain of OA is not related to the destruction of cartilage, but arises from the activation of nociceptive nerve endings within the joint by mechanical and chemical irritants. OA pain may result from distention of the synovial capsule by increased joint fluid, micro fracture, periosteal irritation, or damage to ligaments, synovium, or the... 

Adherend fracture Failure of a bonded joint under mechanical stress in the adherend material, thus, outside the adhesive layer. Indicates that the bond strength is higher than the adherend strength. 

The fracture-based approach derives from continuum fracture mechanics theory, which claims the strength of most real solids is governed by flaws within the material [2]. To help predict this type of behavior, many test methods have been developed to determine fracture properties of adhesives. These tests are used to characterize the mode I, II, and III fracture properties of many types of material systems. In this study, the focus will be on the mode I and II characteristics of bonded joints for automotive applications. 

Blackman, B. R. K. and Kinloch, A. J., "Fracture Tests for Structural Adhesive Joints, in Fracture Mechanics Testing Methods for Polymers," Adhesives and Composites, A. Pavan, D. R. Moore, and J. G. Williams, Eds., Elsevier, Amsterdam, 2001, pp. 225-267. 

As previously mentioned, the single lap joint is the most common test used to evaluate adhesives because of its practical resemblance to many real-world joint designs. The adhesive lap joint has proven useful over the years and will likely continue to be widely used in the future. This paper discusses some of the complexities of the lap joint. The discussion will now concentrate on using finite element analysis to aid in a fracture mechanics approach to aid in understanding the mechanics of a lap joint. It will, to some extent, explore the validity of the design rules discussed above and look at the affect of some of the joint features that are not considered in these rules. 

Finally, it will be demonstrated that fracture mechanics provides insight into the preferred path of crack growth, A perplexing problem that, despite considerable speculation over the last 50 years, has remained unsolved is why do cracks follow a particular path For example, for many practical joints, it has been observed that cracks typically proceed in the adhesive rather than along the interface. This phenomenon is so common that, in his classical text on adhesives, Kinloch states [11] ... 

The failure of an adhesive joint can be considered to involve the initiation and propagation of naturally occurring (intrinsic) flaws or defects. Fracture mechanics is the field of mechanics concerned with the study of the formation and propagation of cracks in materials. The objective of using fracture mechanics is to determine the bond durability of a specific adhesive and provide a basis for estimating the fracture, fatigue, and service life of the adhesive joints. It uses methods of analytical solid mechanics to calculate the driving force on a crack and those of experimental solid mechanics to characterize the resistance of a material to fracture. 

The failure of adhesive joints depends on the combination of peel and shear loading. In fracture mechanics, three basic modes of loading (Fig. 6.10) are the following ... 

As a final note in this section, a few examples taken from the research of the authors and their associates, on the utility of fracture mechanics in conjunction with numerical analysis, might be informative. Some of the research in the authors laboratory has centered on identifying the loci of failure initiation and the paths followed by cracks as they proceed through the adhesive in a joint. 

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