Scarf butt joint

Tongue-and-groove joints are self-aligning and provide a reservoir for the adhesive. Scarf butt joints keep the axis of loading in line with the joint and require no extensive machining [6]. 

P(6) If the scarf angle 0 > 20°, the joint shall be considered to be a butt joint and Ueated accordingly. 

P(2) Instead of butt joints a strap, scarf or lap joint configuration shall be used (see Figure 5.41). The joint design is then undertaken according to the procedures for strap or scarf joints respectively. When using strap configurations the adherend ends shall also be bonded. 

A V-joint or rounded butt joint are generally preferred for making a solvent butt joint. Scarf joints and flat butt joints are difficult to position and to apply pressure to during the solvent evaporation phase of the process. Surfaces must also be clean. Any residual mold release agents or mold polishing compounds can inhibit solvent bonding. 

Joint jomt [ME jointe, fr. OF, fr. joindre] (13c) n. The location where two separately made parts are joined with each other by adhesive bonding, welding, or fastening. Skeist I (ed) (1990) Handbook of adhesives. Van Nostrand Reinhold, New York. See also butt joint, lap joint, and scarf joint. 

Lap joint (1823) n. A joint made by placing one surface to be joined partly over another surface and bonding or fastening the overlapping portions. Compare butt joint and scarf joint. 

See also butt joint, lap joint, and joint scarf. 

Although the joggle lap joint allows shear stresses to be in the same plane as the bonded parts, it does not combine tensile and shear stresses in line with adherends. The double-butt lap joint, the recessed and landed-scarf joint, and the tongue-and-groove butt joint combine both types of stresses in line and, therefore, are recom-mended ... 

Tapered butt joints and double scarf-lap joints also permit bonding and provide maximum tensile and shear strength. Overlap joints are recommended for bonding cylindrical parts ... 

Typical Joint designs using brazing lap and scarf in thin Joints with large contact areas or a combination of lap and fillet. Fillets can help to distribute stresses at the Joint. Butt Joints are possible but can cause stress concentrators in bending. 

Most common joint is the lap or variations on the lap, for example, the tapered lap and scarf (preferred). Can also incorporate straps and self-locating mechanisms. Butt joints are not recommended on thin sections. 

Scarf (or bevel) butt joint Good - generally practical... 

Fig. 4.1. Elastic stress distributions in various kinds of bonded joints, (a) Lap shear, (b) Butt-tensile and scarf, (c) Cleavage, (d) Peel.

A scarf joint reaches its maximum strength when the scarf tip is sharp. However, in actual applications this kind of a sharp tip is difficult to manufacture. Also the bondline thickness becomes extremely difficult to control close to the tip. Therefore, it is required that the tip should have a butt end with a finite thickness of at least 1.0 mm. 

The section on design of structural adhesive joints will describe and cite advantages and disadvantages of joint geometries, such as butt, lap, scarf, strap, and combined versions of these. A general design criterion will also be included. Another section of the chapter will pertain to fracture mechanics. General theories on fracture mechanics and test techniques used to characterize structural adhesives fracture behavior will be discussed. 

Figure 50 shows the adhesive shear stress distributions for a doublescarf joint and a double butt-strap joint and compares them with ordinary single- and double-lap joints. The double butt-strap joint gives the lowest stress concentration at its middle, but is then identical to the ordinary, parallel double-lap joint at the other end. For this reason, it is suggested that the straps should be bevelled or scarfed so that the stress concentration might approach that of the double-scarf joint. 

Mechanical adhesion depends on surface topography, which can be considered a collection of many geometrical forms. Therefore, mechanical adhesion depends on the stress states of different adhesive joint geometries on the scale of the surface topography, which may include many lap, butt, and scarf joints in the interphase region. To address this issue, Ma et al. (2001) compared the stress distributions in adhesive joints as functions ofvarying geometrical interfaces described mathematically in polynomial or other functional forms, as well as the material properties of the adhesive and the adherend or two different substrates joined by an... 

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