Bond line thickness plastics

Unstable damage development of thick bond-lines (lower plastic strain development) resulted in adhesive cracking in multiple locations with a cohesive-type failure and lower failure strengths. 

The adhesives shown in Figs. 41.15 and 41.16include plastics fillers as spacers to keep the bond-line thickness constant. The use of such adhesives is very helpful to control the thickness without particular attentiveness. 

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... 

The gap between the parts and therefore the thickness of the adhesive film has an important bearing on the characteristics of the joint [4], A thick bond line (>0.25 mm) will generally be a weakening feature for cyanoacrylates as the mechanical strength of the cured cyanoacrylate film is likely to be less than the plastic or other substrate... 

Typically, the yardstick for qualitatively measuring the internal resistance of an adhesive bond to an external load has been the determination of the strain distribution in the adhesive and adherends. This is a difficult task. Even in simple lap joints, the actual stress—strain distributions under load are extremely complex combinations of shear and tensile stresses, and are very prone to disturbance by nonuniform material characteristics, stress concentrations or localized partial failures, creep and plastic yielding, etc. It is extremely difficult to accurately measure the strains in adhesive joints with such small glue line thicknesses and such relatively inaccessible adhesive. Extensometers, strain gauges, and photoelasticity are being used with limited success [12]. 

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