Common joint designs

Finally, the above are concerned with the design and destructive testing of adhesive joints but non-destructive testing is also an important aspect of adhesives technology and will be discussed in the present chapter. 

There are four types of stresses which are commonly referred to when considering adhesive bonded joints. These are normal (or direct) stresses, shear stresses, cleavage stresses and peel stresses and they are illustrated in Fig. 6.1. As the name suggests, normal or direct stresses are normal to the plane on which they act and may be tensile or compressive whilst shear stresses are parallel to the plane on which they act. These two types of stresses represent the two sorts of components into which the total stress on any arbitrary plane can be divided. However, it is convenient to identify two further types of stress cleavage stresses which typically arise as the result of an offset tensile force or bending moment and peel stresses which arise if one or both of the substrates are flexible. (These last two terms are frequently used interchangeably by authors.) 

as discussed by Lees [1], practical joint designs must take other factors into consideration. They must allow cost-effective assembly and the design must allow the adhesive to be applied in an appropriate pattern stripes and crosses are preferred so that upon placing the substrates together air entrapment does not occur, which is possible with a closed-loop pattern. Liquid or paste form adhesives may be more accurately placed if they are deposited in a 

This design is far stronger as cleavage/peel stresses are greaNy reduced 

Based upon spof -welding designs where access is needed l o bo h sides 

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A common joint design for clay pipe, one which the pipe manufacturer will probably try to sell, is a "pressure joint." For this kind of joint an elastomeric or flexible collar is set into, and usually cemented to, the inside of the bell. The inside dimension of the collar is smaller than the outside dimension of the spigot, so when the spigot is seated in the bell the collar squeezes tightly against... 

A series of common joint designs and their modifications are shown in Appendix K. 

In adhesive bonding, shear is a major type of stress when one substrate is forced to move parallel and relative to the other substrate. The entire bonded area is efficiently used when joints are stressed in shear. Thus tensile-shear overlap design is a common joint design used in adhesive bonding. (See adhesives tests. Fig. A.6.)... 

First, common joint designs to be found in many industrial applications will be discussed and some basic design considerations reviewed. 

A simple lap joint consists of two sheets joined together with an overlap and is a very common joint design in industry. The joints were manufactured using an alignment jig that ensured... 

This chapter discusses the overall concepts for designing adhesively bonded joints and some guidelines for some of the more common joint designs are discussed. 

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. 

In any case, both the FEA/ERR analysis from this study and the experimental results cited from the literature clearly demonstrate the importance of considering adherend thickness in the design of Joints. Test results and commonly used design rules that ignore this aspect of adhesive joints should be used with great caution. 

Joint Design Allowables and Service Life Assessments. Friction stir welding has been demonstrated in a variety of joint designs (Fig. 13.15). The most commonly used joints are the full-penetration butt joints and the parfial-penetration lap joints, followed by the edge joint, capture joint, and fillet joint, listed in order of ease of manufacture. Friction stir welding is not a dropin process, and existing riv-... 

A joint is defined by its type, parameters, and auxiliary entities. The type of joint determines the degrees of freedom. Auxiliary entities are the reference points and lines needed for the definition of movements allowed by the degrees of freedom. Figure 5-20 introduces common joints from the everyday design of mechanisms by their motions, degrees of freedom, and auxiliary entities. 

Fig. 4.2. Common engineering joints and joint designs, (a) The lap joint and its variants, b) Containment joints for plates, extrusions and pultrusions. (c) Ways of minimising peel in laps, doublers and stiffeners.

Lap joints are the most commonly used adhesive joint, because they are simple to make, are applicable to thin adherends, and stress the adhesive to be stressed in shear. However, the simple lap joint causes the adhesive to be stressed in shear. In this design, the adherends are offset, and the shear forces are not in-line, as was illustrated in Figure 7.15. This factor results in cleavage stress at the ends of the joint, which seriously impairs its efficiency. Modifications of lap-joint design (Figure 7.17) include ... 

Other thermal welding processes that are less common than those described above but still used in industry are infrared welding and laser welding. These are generally used in specialty processes or with applications that require unique methods of heating because of the joint design or nature of the final product. 

Semidovetail joint. The sernidovetail joint is probably the most common joint used for position and contour control in plastic parts. The semidovetail joint is used in place of a full dovetail joint because the latter is not required since location in the inside direction is controlled by the joint on the other side of the part. More importantly, the semidovetail joint requires two-thirds the wall thickness of a fiill dovetail joint. A semidovetail joint around the entire perimeter of the part provides location, tends to mask minor warpage and debris from joining devices (surplus adhesive, solvent, welding flash, etc.), and is reasonably tolerant of dimensional variations. In addition, if designed steel-safe, it can be readily adjusted if the molded parts turn out to have too... 

Figure J.l Common flat adhesive joint designs butt, plain lap, and single strap. (See Appendix K for joint design improvements on these.)...

A wide variety of adhesively bonded joint configurations are available to the designer based on the application and scope of use [7]. Commonly, joint configurations that have been analyzed in the literature are single-lap joints, double-lap joints, scarf joints, and step joints (Figure 1). 

It is necessary, therefore, to test an adhesive by many techniques to simulate the conditions that it may be subjected to in service. The three types of tests to be discussed are tensile, shear, and peel. These tests are the most common and result in information which is useful for reliable joint design. Response to dynamic testing such as fatigue, creep, and impact will also be introduced. 

The single-lap joint is the simplest and most common joint used today for several reasons (1) it is easy to fabricate (2) many designs used in... 

The most common adhesive bond is the overlap or lap type. There are many variations of the overlap joint but the simplest type is the single-lap joint. This configuration has been the subject of much work (see Section III) so the geometric factors which effect joint design, such as bond area or overlap length and adherend thickness are well known. 

Silent chain manufacturers have developed several joint designs to reduce chordal action and joint wear. These different designs can be classified into two broad categories. They may be single-pin or two-pin joints. Silent chains with two-pin joints are much more popular for power transmission. Silent chains with single-pin joints are more common for conveying and will be covered here briefly. Silent chains with two-pin joints will and be discussed more extensively. 

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