Interlaminar region

A detailed numerical study (Bond 2005) has shown that for the same overall fiber volume fraction, the diffusion coefficient D is rather insensitive to the spacing or distribution of circular fibers, although, in the case of composite laminates, the presence of a resin-rich interlaminar region would affect the overall value of the transverse component of D. 

Another important aspect of testing the adhesive as part of an adhesive-joint system is that the joint presents a number of options for the location of the failure path. Failure may be cohesive in approximately the center of the adhesive layer. It may be cohesive but near the interface as is often seen in peel testing. It may be interfacial along the adhesive-substrate interface or it may run entirely within an interphase, for example, within a metal oxide/ adhesive interphase region. The failure path could run cohesively through the substrate, for example, the crack could run in the interlaminar region of a fiber-reinforced polymer composite substrate (Kinloch et al. 1992). Finally, some combination of the above could occur. Each of these options for the failure path may lead to a different fi-acture resistance being measured and thus adhesive-joint tests and their interpretation are necessarily more complex than bulk adhesive studies. 

At the free edges of a laminate (sides of a laminate or holes), the interlaminar shearing stresses and/or interlaminar normal stress are very high (perhaps even singular) and would therefore cause the debonding that has been observed in such regions. 

MPa. At the stress maximum or in the region where the stresses remain nearly constant a strong delamination occurred, which probably reduces the interlaminar shear strength dramatically. Therefore the high strain-values cannot really be used for design. 

In the present chapter, different uses of nanocomposites in structural composites are presented. They can be used in the polymer matrix as nano-reinforcements or in the interfadal region in conventional composites in order to mainly improve interlaminar strength, and hence to avoid delamination. They can also exist in the form of nanocomposite fibers as reinforcement in all-polymer composites or directly as self-reiifforced nanocomposites. 

A more comprehensive investigation was undertaken by Herrera-Franco and Drzal [53] and the authors suggested that the differences observed in the tests were due to the manner in which each test reacted to the conditions that prevailed at the interface region. The short beam shear is only an estimate of the interlaminar shear, whereas the losipescu does produce a state of pure shear (Table 20.20). 

Hodzic A, Kim J K, Lowe A E and Stachurski Z H (2004) The effects of water aging on the interphase region and interlaminar fracture toughness in polymer-glass composites, Compos Sd Technol 64 2185-2195. 

Delamination, particularly between plies, has been observed as a major failure source, [l],[2],[3]. It is caused by interlaminar stresses in the region of the free edge [4],[5], arising by the mismatch of material properties [6]. 

For small 0 values (0 = 5° - 10°), failure is dominated by the surface-ply failure at the free edge. Both Tsai-Hill and interlaminar failure criteria predict much higher strengths in this region. 

In the region 0=15°- 30°, free edge (interlaminar or surface-ply) failure dominates. 

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