Interlaminar deformation

Polyethylenes undergo interlaminar deformation during tensile elongation. This can give rise to a double yield phenomenon. At the onset of the hrst tensile yield, chain slip and lamella rotation occur and this process is reversible. The second tensile yield is irreversible and coinsides with lamella fragmentation (36). These mechanically induced morphological changes and the observation of any double yield phenomena are dependent on several structural factors that can be controlled by... 

TP powders can be also be used for mode Il-interlaminar fracture improvement of laminates (Zeng et al., 1993). TP particles spread between layers largely improve the plastic deformation. GIIc varies linearly with the TP volume fraction (Zeng et al., 1993). 

Susceptibility to interlaminar failure is a major weakness of advanced laminated composite materials. It can occur by in-plane shearing (i.e., sliding) (mode II). and out-of-plane shearing (i.e.. tearing) (mode III) as well as by tensile (mode I) deformation. Mode II loading is of particular interest, as values have been shown to correlate with compression after impact data [142.143]. which is required for such purposes as civil aircraft certification. 

In contradistinction, Ti2AlCo.5No.5, is harder, more brittle and significantly stronger, than the end members Ti2AlC and Ti2AlN, which can be deformed plastically up to 5% strain, even at room temperature [98]. At a temperature of 1200 °C, a solid solution softening effect is observed, the reasons for which are still unclear, although they may be related to the aforementioned interlaminar decohesions. 

Generally a span/thickness ratio of 16 is used but, for materials which tend to fail in an interlaminar shear mode (such as unidirectionally reinforced composites), a ratio of 20 is to be preferred. Flexural strength is a convenient method for comparing properties, because it involves a stress/deformation mode that is often encountered under service conditions, and the test specimens are relatively small. 

The actual contribution of this microfailure mechanisms to the interlaminar fracture energy of the composites tested under particular conditions are a function of the number of events taking place, the real area of fracture surface formed, and the size (length and width) of the damage zone (DZS) around the main crack. The larger the latter becomes the more side cracks have to be expected, and the more energy is consumed by plastic deformation of the polymer matrix material. 

The significant factor for having low perforation energy was also identified from postindentation dye penetration tests (Figure 19.12). The dye penetration tests revealed minimum delamination around the hole and an extended narrow cross-pattern in the cases of pristine and 5 wt% GB-modified laminates. On the other hand, 1 and 3 wt% GB laminates showed excessive delamination. This implies that the energy absorption mechanisms in 1 and 3 wt% GB laminates were not only due to deformation but also to mainly interlaminar delamination. 

Luo Q, Tong L (2008) Analytical solutions for adhesive composite joints considering large deflection and transverse shear deformation in adherends. Int J Solids Struct 45(22-23) 5914-5935 Luo Q, Tong L (2009a) Calculation of energy release rates for cohesive and interlaminar delamination based on the classical beam-adhesive model. J Compos Mater 43(4) 331-348... 

In laminated, i.e. highly anisotropic beams, in which the ratio of the axial Young s modulus to the interlaminar shear modulus can be high (>20), transverse shear deformation can become significant at low modes of vibration even for beams of t/L<0.01 [5]. 

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