Autohesion

Note that for autohesion of viscoelastic layers in contact above To, that the above equations can be utilized by substituting for I with the molecular structure factor H t) (and appropriate ratios) from Table 1 such that... 

Voyutskii, S.S., Autohesion and Adhesion of High Polymers. John Wiley and Sons, New York, 1963. 

The mechanism by which a thermoplastic matrix composite consolidates to form a laminate was attributed to autohesive bond formation between plies [13,18]. Autohesion, however, can... 

The mechanism governing the formation of interply bonds has been established as autohesion or self-diffusion [28], Autohesive bonding is controlled by two mechanisms (1) intimate contact between the interfacial surfaces, and (2) diffusion of the macromolecules across the interface. Figure 7.22 shows the phenomenon of autohesion for an amorphous thermoplastic polymer. At time zero, the two surfaces are pressed together. Providing the temperature is... 

Figure 7.22 Schematic diagram of autohesive bond strength development across an interface...

Destructive mechanical tests commonly are used to characterize autohesion of polymers. In the mechanical tests, two polymer surfaces normally are pressed together at a given temperature for a specified length of time. The fracture stress or fracture energy of the interface then is measured using the appropriate test. 

If wetting is instantaneous and the instantaneous wetting load at initial time is negligible, then the autohesive bond fracture stress, cr, is proportional to the fourth root of contact time and the fracture energy, GIC, is proportional to the square root of contact time as shown in the following equations ... 

The interply bond strength for thermoplastic matrix composites has been shown to be dependent upon the processing parameters, pressure, temperature, and contact time. If the temperature distribution in the composite is nonuniform during processing, the ply interfaces will bond (or heal) at different rates. Thus, for a specified processing cycle, it is important to know precisely the temperature and degree of autohesive bonding at every point in the composite laminate in order to estimate the required process time. 

The process by which a thermoplastic matrix composite consolidates to form a laminated structure has been attributed to autohesive bond formation at the ply interfaces. Autohesive bond formation is controlled by two mechanisms (1) intimate contact at the ply interfaces, and (2) diffusion of the polymer chains across the interface (healing). The rate of autohesive bond formation and hence the speed of the composite consolidation process is directly related to the temperature-pressure-time processing cycle. 

Consolidation and development of interlaminar bond strength for thermoplastic matrix composites have been modeled by two mechanisms intimate contact and autohesion. Intimate contact describes the process by which two irregular ply surfaces become smooth (Fig. 13.10). In areas in which the ply surfaces are in contact, autohesion occurs, and the long thermoplastic polymer chains diffuse across the ply boundaries. Filament winding with thermoplastic matrix materials is considered an on-line consolidation process in that local... 

The autohesion process starts after intimate contact has been established at any point on the interface. The degree of autohesion Dau can be approximated by the expression (Eq. 13.16)... 

As is the case for Dic, complete autohesion and complete bonding correspond to Dau = 1 and Db = 1, respectively. To account for nonisothermal autohesion, which occurs in on-line consolidation processes such as filament winding, the degree of bonding must be calculated at discrete time steps and summed [21]. 

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