Adhesion macro-bonding

On the other hand, in the case of cellulose dinitrate or 2i-nitrate, the structure is generally irregular, hence no adhesion between the chains exists. With a small number of irregularly distributed hydroxyl groups there exists little probability that the macro-molecules could be joined together by means of hydrogen bonds (Fig. 89b, see also Figs. 86 and 88). 

Again, mechanical retention, either macro or micro, is the predominant mechanism. The metal structure can be perforated and the bonding system, a structural adhesive, flows through the holes to provide the retention, for example Rochette Bridge. The metal can be etched either chemically or elecirochemically to produce a surface suitable for micro-mechanical retention. 

Block copol3nners form a new class of molecular composite materials by the phase separation of incompatible hard and soft segments which form their macro-molecular structure. Thermoplastic elastomers where the soft segments form the continuous phase have been extensively investigated by means of an adsorption-interdiffusion (A-I) model for the interfacial phase which bonds the hard and soft phases. The molecular structure and rheological activity of the interfacial phase in thermoplastic elastomer block copolymers is shown to play a dominant role in nonlinear viscoelastic response, mechanical hysteresis and energy absorption. Creation of elastomeric microphases in epoxy structural adhesives has been recently identified with in situ block copol3nnerization between carboxy terminated nitrile (CTBN) rubber and the diepoxide. 

Tbe adhesive does not yield in the classic. sense of ductile metals. Instead, a series of fractures (hackles) at 45 to the bond surface develop as the adhesive is strained beyond its elastic limit, reducing the once-continuous adhesive layer to a series of discrete ligaments that are bent under what remains a shear load at the macro level. When the load is removed, the ligaments recover elastically, almost back to the original configuration, with virtually no offset. However, the cracks remain, the adhesive is permanently softened , and the density of the hackles increases as the... 

At the macro level, at which most bonded joint analyses are made, the mechanical data needed are complete stress-strain curves in shear for a range in temperatures covering the operating environment. Typical structural adhesives are stronger and more brittle at low temperatures and weaker and more ductile at high temperatures than at room temperature, as shown in O Fig. 44.1. 

The solid friction is calculated by an energetic approach which is described in [1] and in more depth by Bartel [10]. The components of the solid friction are deformation and adhesion. The first one can be calculated from the elastic-, plastic deformations of the macro and micro geometry. To calculate the adhesion force, some assumptions have to be taken into account at the moment Adhesive bonding can only occur if plastic deformation of the material takes place and secondly if local temperatures exceed a critical value which lead to a desorption of the fluid film. Since the simulation program is not able to determine local temperatures yet, the second assumption cannot be tested. But it seems reasonable that the plastically deformed micro asperity also experience local temperature peaks. Since it is quite sophisticated to get reliable values for the shear strength in adhesive bonding, in this work one sixth of the universal hardness or plastic pressure limit of 100Cr6 (SAE 52100), respectively, is used ... 

---