Flexible adhesives
Adhesive bonded joints are capable of withstanding a substantial degree of movement. Due to the elastic properties of the adhesives, tension is distributed over large surface areas, which means that local overstraining of both the substrate and the adhesive is avoided. The required stability and rigidity required in constructions are achieved by adjusting the thickness, surface area and cut of the adhesive, as well as the adhesive used. A minimum layer thickness is necessary in order to absorb movement. Another advantage of flexible adhesives is the absorption of vibrations. This enables sound transmission to be considerably reduced.
The rigidity of a bond is determined on one hand by the modulus of the adhesive used, and on the other hand by geometric dimensions. The greater the modulus of the adhesive and the greater the surface area, the higher the rigidity. The smaller the modulus and the greater the layer thickness, the lesser the rigidity. Constructions that prevent lateral contraction of the adhesive when under a tensile load increase rigidity, but reduce stability.
The stability of an adhesive bond also depends on properties of the adhesive and the dimensions. Alongside internal stability (cohesion), the bond to the substrates (adhesion) is a decisive factor in the overall stability of an adhesive bond. Both the rigidity and stability of an adhesive depend on environmental and age factors. For this reason, aside from the ascertained characteristic values of an adhesive, reduction factors, i.e. safety factors, are necessary. Here, as well as the temperature range in which the system is to be used, other factors such as changing loads and chemical and physical influences come into play.