Axially loaded butt joint

Fig. 2. An example of the stress distribution in an axially loaded butt joint (after Adams et al.y (ao = applied average axial stress a = 2.5 GPa Eg = 69 GPa aspect ratio = 20)...

The axial-loaded butt joint is the simplest geometry for stress distributions arising from the application of tensile loads. Several investigators have addressed the stress analysis of this geometry using both analytical and finite element methods. ... 

A number of different loading methods and specimen configurations have been devised and reported in the literature. For example, both the axially loaded butt joint [5] and the single overlap-shear joint loaded in tension [6] have been employed. These test geometries were described in Chapter 6 and the latter is used in the ASTM standard test for assessing the fatigue strength of... 

Kuenzi and Stevens (1963) analysed the axially loaded butt joint allowing for the radial strain in the adherends but ignoring any necking in the adhesive. They obtained the following equation for the Poisson s ratio of the adhesive ... 

However, if purely elastic behaviour is considered, the axially-loaded butt joint can be used to provide useful data on the elastic properties of structural adhesives. The loading can be static or dynamic. In the former case, the problem is to measure the strains and displacements across a thin glue-line. Usually, extensometers will be attached to the adherends and a suitable correction made for the adherend strains as shown in Fig. 81(d). Then... 

Thus, the complex strain distributions in axially loaded butt joints make it difficult quantitatively to predict their stress-strain behaviour and ultimate tensile strength from the bulk properties of the adhesive without the use of a non-linear stress analysis and a detailed understanding of the response of the adhesive to the local stress concentrations around the perimeter of the joint. Conversely, it would be very difiicult to use the stress-strain data obtained from axially loaded butt... 

Gauge length and displacements in the axially loaded butt joint... 

In tension, the recommended test is the bulk tensile test. The axially loaded butt joint has poor repeatability and suffers from constraining effects. 

Adams RD, Coppendale J (1977) The elastic moduli of structural adhesives. In AUen KW (ed) Adhesion 1. Applied Science, London, pp 1—17 Adams RD, Coppendale J (1979) The stress-strain behaviour of axially-loaded butt joints. J Adhesion 10 49 Adams RD, Peppiatt NA (1974) Stress analysis of adhesive-bonded lap joints. J Strain Anal 9 185... 

Despite the fact that adhesive joints are rarely designed to be loaded directly in tensile mode, tensile tests are eommon for evaluating adhesives. The axially-loaded butt (or poker chip ) joint geometry, as recommended by ASTM D897(52), is depicted in Fig. 4.11. 

Axially loaded butt or poker-chip joints... 

The ASTM D 897 tensile button test is widely used to measure the tensile strength of a butt joint made with cylindrical specimens (Fig. 20.3). The tensile strength of this bond is defined as the maximum tensile load per unit area required to break the bond (measured in pounds per squre inch). The cross-sectional bond area is usually specified to be equal to 1 in.2. The specimen is loaded by means of two grips that are designed to keep the loads axially in line. The tensile test specimen requires considerable machining to ensure parallel surfaces. 

This problem involves moisture diffusion in a butt joint with a viscoelastic adhesive layer. The geometry and loading are shown in Figure 17. Due to the symmetry of the problem, only a quarter of the Joint is modeled. The material properties and the diffusion parameters for the adhesive are given in Table 7. Since the adhesive has very high compliance, the adherend is assumed to behave as a perfectly rigid body relative to the adhesive. Hence, the adherend is replaced by a specified uniform displacement of 0.004 mm (2% strain in the adhesive) in the axial direction. 

Figure 6.7 Stress distribution in a butt joint loaded in tension [10].

Non-axial loading of a butt joint leads directly to cleavage stress this differs from direct tension only in the concentration of stress at one side of the specimen. All joint configurations can be regarded as elaborations of these two types of joint and they are dealt with in detail later in this book. 

Regarding the measurement of the impact strength in terms of force or stress, a first case is represented by the simple butt joint of hollow cylinders, loaded axially in tension. A thorough... 

In the case of axial loading, the square end can be substituted by a taper, as shown in O Fig. 27.23. O Figure 27.24 presents some cylindrical joints that are commonly used in bars and tubes. These solutions are advantageous in relation to the butt joints because a larger bonded area is obtained and the peel stresses are reduced. However, most of the solutions presented in O Fig. 27.24 require heavy machining, which obviously renders the process expensive. 

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