Butt joints mechanical properties

Adhesion between the polymeric film and substrate is a major concern. Poor adhesion could result in flaking or peeling of the coating from the substrate core. Moisture could accmnulate at the film-substrate interface and compromise the mechanical protection provided by the coating. Polymer adhesion is related to both film-substrate interfacial interactions and internal stresses within the film. Polymer adhesion can be evaluated by peel tests or butt joint tests. Apart from the specific properties of the polymers, excipients used in tablet formulations can influence film-tablet adhesion. Since adhesion between a polymer and the tablet smface is due primarily to hydrogen bond formation, hydrophobic agents may decrease adhesion by... 

In a similar study, Brewis et al observed the same type of reductions in the mechanical properties of the adhesive. They demonstrated that the reduction in strength of single lap joints on exposure to moisture was linearly related to the fractional water content of the joints. On saturation with water the joints were weakened by 44%, whereas films of the adhesive were weakened by as much as 74%. It was pointed out that the lack of correlation between the bulk and adhesive joint strength was due to the different stress distributions in the two situations. They concluded that the principal mechanism of loss of adhesive joint strength was by diffusion-controlled water plasticization of the adhesive. There is an apparent discrepency between this work, in which water has a reversible effect on joint strength, and that of Butt and Cotter, in which the effect is irreversible. This will be discussed further in Section III.B. 

Escher, G. A., and W. B. MacDonald Chemical and Mechanical Properties of Butt and Strap Joints, Proceedings of the 1975 Conference on Managing Corrosion with Plastics, National Association of Corrosion Engineers, Houston. 

In the investigation reported herein, the mechanical properties of type 301 stainless steel were studied at 70, -320 and -423 F in samples of steel that had been cold-worked 42, 62, and 78. Toughness was studied by means of notched tensile tests at the same temperatures, and a notch-to-unnotch tensile ratio was calculated. The latter was taken as a criterion of resistance to brittle fracture. In addition, the tensile properties of heliarc butt-welded joints of the same materials were determined. The welded joint data were included because low-temperature properties of welded joints are of practical importance in pressurized cryogenic propellant tanks. 

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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