Interface debond criterion

The interface debond criterion used in this analysis is based on the concept of fracture mechanics where the strain energy release rate against the incremental debond length is equated to the interface fracture toughness, Gk, which is considered to be a material constant... 

Substituting the solutions for the three major stress components determined in the bonded and debonded regions, a fiber-matrix interface debond criterion is derived as... 

Interface debond criterion and partial debond stress... 

The material behavior for debonding, based on the strain energy approach as an interface debonding criterion, is shown by the dotted line in Figure 22c,... 

Based on the shear strength criterion for the interface debonding, the condition for the fully bonded interface requires that the maximum IFSS be obtained at the... 

The basic requirement necessary to satisfy the partially debonded interface is that the crack tip debond stress, cr, (and the debond length, ) must be greater than zero. From the debond criterion given by Eq. (4.68)... 

To show clearly how and to what extent the parameter, Zmax. varies with the properties of the interface and the composite constituents, a simple fiber pull-out model by Karbhari and Wilkins (1990) is chosen here. This model is developed based on the assumption of a constant friction shear stress, Tfr, in the context of the shear strength criterion for interface debonding. In this model, the partial debond stress may be written as... 

It is envisaged that the degradation of the frictional interface properties and the corresponding increase in the relative displacements eventually lead to debond crack growth once the debond criterion is satisfied. The debond criterion based on the energy balance theory given by Eq. (4,35) under monotonic loading can be rewritten as... 

The earliest works of trying to model different length scales of damage in composites were probably those of Halpin [235, 236] and Hahn and Tsai [237]. In these models, they tried to deal with polymer cracking, fiber breakage, and interface debonding between the fiber and polymer matrix, and delamination between ply layers. Each of these different failure modes was represented by a length scale failure criterion formulated within a continuum. As such, this was an early form of a hierarchical multiscale method. Later, Halpin and Kardos [238] described the relations of the Halpin-Tsai equations with that of self-consistent methods and the micromechanics of Hill [29],... 

Based on the same average fiber tensile strength model as that employed in Section 4.2.3, the fiber fragmentation criterion is derived in terms of the external stress, ffa(= (h = o er, for the partially debonded interface ... 

Another important result from the atomistic simulations was that the stress-strain response of a region of material around an interface that debonded could be represented by an elastic fracture analysis at the next higher size scale if the interface was assumed to be larger than 40 A. Hence, an elastic fracture criterion was used in the microscale finite element analysis, which focused on void-crack... 

The failure behavior of composite propellants, which are filled elastomers, is complicated by the presence of filler particles. Under loading, phenomena such as cavitation and debonding can arise at or near the filler-matrix interface. (1, 2) Identification of a practical failure criterion for such... 

The first case is related to the arguments given in Section 6.1 if the interfacial gc (static, but also dynamic) is too low, once cavities are nucleated at the interface, they can easily propagate, coalesce and debonding occurs without any fibril formation. The second case is discussed in Section 6.2 and occurs when the elastic modulus of the PSA is too high (Dahlquist s criterion is not met) or when the surface is too rough for the adhesive to conform to it during the short contact time. 

In a recent publication, the authors proposed a new test set-up to measure the interfacial strength between polymer joints. The joint is loaded parallel to the interface. Uniform stresses normal to the interface are caused indirectly by notches. There are no stress singularities in the whole sample and there are only normal interface stresses in the debonding region. Consequently, a simple strength criterion could be applied. 

This stress distribution is the basis for the determination of the adhesion strength at the interface. In such a case, the maximum stress criterion can be applied to determine the debonding strength ... 

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