Glue line thickness

Adhesives of this type were developed for repair and maintenance in transport facilities, plants, pipelines, ships, etc. in the open air. In-situ conditions require development of adhesives usable at all ambient air temperatures, in wet weather, in deep waters, and in oil product media and other liquids. Smfaces to be glued together may be covered with corrosion layers, and glue line thickness cannot be limited. There is no need for any additional alteration of the joints. 

Results of experiments on S/I/S free films and on S/I/S bonded joints with thermoplastic glue line thickness of 0.3, 0.5 and 0.7 mm appear together in Fig. 4, previously published (3) All preparations were made with the 50% styrene content polymer. The preparation temperature was... 

Provides uniform, controlled glue line thickness. 

Keywords Adhesive modulus Adhesys expert system Co-axial joints Compression Concealed joints Creep Elastic limit Epoxy Epoxy composite Einite element analysis Glue line thickness Goland and Reissner Hart-Smith Heat exchanger Hooke s Law Joint designs Joint thickness Lap shear strength Peel Plastic behaviour Polyurethane Pipe bonding Shear stresses Shear modulus Stress distribution Thick adherend shear test Tubular joints Volkersen equation Young s modulus... 

Consider a lap joint with an overlap of 25 mm and a length for the purposes of stress calculation of only 25 mm. For the initial assessment two pieces of mild steel of thickness 1.5 mm are bonded together using an adhesive of modulus 0.4 GPa, an elastic limit of 19 MPa and a glue line thickness of 0.05 mm. When a high load of 3000 N is applied, the distribution of stress is calculated to be as follows (Fig. 11). 

A third option is to control the glue line thickness. A glue line of 50 microns (0.05 mm) is normally considered quite generous for a small joint. If we control the gap so that the glue line is increased to 100 microns, then the stress is handled in a more acceptable manner (see Fig. 17). 

If we increase the glue line thickness fiarther, the stress levels become even more uniform, as shown in Fig. 18. 

If we increase the glue line thickness in addition to increasing the aluminium thickness, then we have a condition which meets the need to design within the elastic region (Fig. 23). 

The stress situation is not acceptable. However, if the glue line thickness is increased from 0.05 mm to 0.25 mm, not only is the stressed joint satisfactory, but it is still satisfactory with a 50% load increase from 100 Nm to 150 Nm (see Fig. 31). 

Figure 3i An increase in glue line thickness to 0.25 mm is satisfactory even with a 50%...

Figure 38 The joint ends have improved design if the glue line thickness increases in...

A normal glue line thickness, without glue line control, is often less than 0.025 mm. In order to cope with high stresses, the glue line should be much thicker, in the region of 0.2 to 0.3 mm. Some adhesives are available today, which automatically control the glue line to a specific thickness. However, the use of dimples can have benefits in situations where electro-deposition of paint is important. Adhesives generally provide electrical insulation between components which would prevent the deposition of paint. 

Inspection of the equation also shows that the adhesive stress increases as the glue line thickness decreases. This is potentially negative, since squeeze-out at the edge of the doubler... 

GLUE-LINE thickness Thickness of the fully dried adhesive layer. 

But what of the adhesive Are its properties the same in the thin film form (OT mm or so thick) as they are in bulk For many years, it was believed that the elastic moduli increased with reducing glue-line thickness. Unfortunately, this was based on an inadequate interpretation of a careful experiment Recent work has shown that the film and... 

Benson (1969) has indicated more fundamental limitations in the Goland and Reissner theory in that the derivation of the bending moment factor, fc, allows for the rotation of the overlap region, but the internal stresses in the joint are derived assuming no rotation. The solution for the adhesive shear and the tensile stresses are only strictly accurate for fc = 1-0, i.e. for very low loads. It should be pointed out that the derivations relating the bending moment factor to the load assume that the joint is monolithic, i.e. that the glue-line thickness is... 

It should be noted that complete removal of the spew by machining would be difficult without machining either of the adherends, so that some spew, similar in size to the glue-line thickness, is likely to be left at the end of any joint. Moreover, machining may initiate cracks in the adhesive, especially if it is one of the more brittle, high-temperature adhesives. Thus an adhesive layer with a square edge is not only undesirable but is unlikely, and even difficult to obtain in practice. 

Using typical values for such a joint, we have that Ii = l3 = 3mm, l2 = 0-3 mm (= glue-line thickness), Gadherends = 26 GPa and Gadhesive = 1-3 GPa. Then ... 

Joints made using 3532 and AV119 both exhibited an increase in SDC with increase in glue line thickness. This trend is illustrated in O Figs. 30.12 and O 30.13. The trend is clearly more significant in the case of the 3532 joints, where quadrupling the glue line thickness leads to... 

Furthermore, the fact that increasing the glue line thickness of the A VI19 by almost a factor of 10 results in only a negligible damping increase suggests that joint geometry is not... 

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