Composite failure mechanism

The seismic effects are generally considered as pseudo-static forces to be added to the other static forces. A detailed review ofthe literature regarding the computation of passive earth pressure using planar failure, composite failure mechanism and experimental investigations are presented in the following sections. In addition, the review of the literature for the computation of earthquake-induced displacements is also presented. 

Planar Failure Mechanism versus Composite Failure Mechanism... 

It can be noted from Table 2 that the values of K,. predicted by employing the composite failure mechanism are lower than the planar failure mechanism reported in Kramer (2003) for the case of <5 > 0.4 and the difference increases for higher values o 8 / 4>. Similar observations can... 

For example, it can be found in Figure 8 that the assumption of planar failure surface overestimates the critical acceleration values (k g ) to the extent of 11.52% for = 30°. In addition, for a constant value of k = 0.46 and

planar failure mechanism predicts the magnitude of sliding displacement (-9) value as 10 cm, whereas composite failure mechanism predicts S value as 70 cm, the difference reaches as high as 85.71%. It may be noted in Figure 9 that the assumption of planar failure surface overestimates the value of k and difference reaches as high as 34.48% for 4> = 30°, and further for a constant value of = 0.40, planar failure mechanism predicts a rotational displacement (6) of 2.0°, whereas compos-... 

Figure 8. Comparison of sliding displacements (S) estimated using planar and composite failure mechanisms for different k and (j) values.

Basha, B. M., Babu, G. L. S. (2008). Seismic passive earth pressure coefficients by pseudo-dynamic method using composite failure mechanism. 

A decrease in radius of filler particles in the composite will result in an increased value of stresses needed to initiate the composite failure. Mechanisms of failure in a composite could take place in the polymer matrix by shear yielding and/or crazing, inside the aggregates of filler particles and/or at the interface matrix/filler by mechanism of dewetting. In particulate-filled composites, yielding and crazing do not depend on the work of adhesion between matrix and filler, VFmf, or thermal stresses, but these influence the dewetting phenomenon, considerably, (Eqn. 5) ... 

Minor morphological differences, as between MR and NATSYN show up by their thermomechanical responses. Work on polymer chain conformations in bulk, 1968-to date, especially on fluorinated acrylics with B. McGarvay and W. Lee, on elastomeric dienes with H. Mark and K. Sato, and of entanglements in GRS witn R. Meyers, followed. These experiences were reviewed, with emphasis on the structural factors in rubber-like behavior at all phases of extension, in a chapter coauthored by T. L. Smith, on the Rupture of Elastomers in Liebowitz s treatise "Fracture , while later analyses focused on the effect of fillers in elastomers, the role of interfaces in composites, failure mechanisms in plastics as a function of morphology, and on resulting lessons for polymer engineering. 

Roulin-Moloney A C 1989 Fractography and failure mechanisms of polymers and composites (London Elsevier)... 

The possible fatigue failure mechanisms of SWCNT in the composite were also reported (Ren et al., 2004). Possible failure modes mainly include three stages, that is, splitting of SWCNT bundles, kink formation, and subsequent failure in SWCNTs, and the fracture of SWCNT bundles. As shown in Fig. 9.12, for zigzag SWCNT, failure of defect-free tube and tubes with Stone-Wales defect of either A or B mode all resulted in brittle-like, flat fracture surface. A kinetic model for time-dependent fracture of CNTs is also reported (Satapathy et al., 2005). These simulation results are almost consistent with the observed fracture surfaces, which can be reproduced reasonably well, suggesting the possible mechanism should exist in CNT-polymer composites. 

Microcomposite tests have been used successfully to compare composites containing fibers with different prior surface treatment and to distinguish the interface-related failure mechanisms. However, all of these tests can hardly be regarded as providing absolute values for these interface properties even after more than 30 years of development of these testing techniques. This is in part supported by the incredibly large data scatter that is discussed in Section 3.2.6. 

Birger, S., Moshonov, A. and Kenig, S. (1989). Failure mechanisms of graphite fabric epoxy composites subjected to flexural loading. Composites 20, 136-144. 

Drzal, L.T., Rich, M.J., Camping, J.D. and Park, W.J. (1980). Interfacial shear strength and failure mechanisms in graphite fiber composites. In 35th Annual Tech. Conf., Reinforced Plast. Compo.sites Inst., SPI, Paper 20C. 

The term fracture toughness or toughness with a symbol, R or Gc, used throughout this chapter refers to the work dissipated in creating new fracture surfaces of a unit nominal cross-sectional area, or the critical potential energy release rate, of a composite specimen with a unit kJ/m. Fracture toughness is also often measured in terms of the critical stress intensity factor, with a unit MPay/m, based on linear elastic fracture mechanics (LEFM) principle. The various micro-failure mechanisms that make up the total specific work of fracture or fracture toughness are discussed in this section. 

Summary of the failure mechanisms in fiber reinforced composites "... 

In using Eq. (6.10) to predict / , of a given composite system it is important that the said failure mechanisms all exist. If any one mechanism is apparently absent the corresponding toughness term must be excluded from the / t equation. It is also worth emphasizing that / , varies linearly with reciprocal of the frictional shear strength of the interface, i.e. l/tf, with the lower limit of (1 — Ff)/fm when if approaches infinity. This relationship has been shown to apply to many carbon fiber polymer matrix composites (CFRPs) (Harris et al., 1971 Beaumont and Phillips,... 

Fig. 6.12. Toughness maps depicting contours of predicted fracture toughness (solid lines in kJ/m ) for (a) glass-epoxy composites as a function of fiber strength, Uf, and frictional shear stress, tf and (b) Kevlar-cpoxy composites as a function of at and clastic modulus of fiber, Ef. The dashed line and arrows in (a) indicate a change in dominant failure mechanisms from post-debonding friction, Rif, to interfacial debonding, Sj, and the effect of moisture on the changes of Of and Tf, respectively. Bundle debond length...

Friedrich, K. and Karger-Kocsis, J. (1989). Unfilled and short fiber reinforced semi-crystalline thermoplastics. In Fractography and Failure Mechanisms of Polymers and Composites, (A.C. Roulin-Moloney ed.), Elsevier Appl. Science, London, pp. 437-494. 

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