Pullout mechanism

Silicon nitride has been reinforced by carbon [159] and Suzuki et al [160] have investigated fiber pullout mechanisms of carbon fiber reinforced SisN4 ceramic composites. Carbon fiber composites are stable in N2 at high temperatures [161,162]. At present, interest has been generated in SiC-SiC composites. Lundberg et al [163,164] successfully HIPed carbon fiber reinforced Si3N4 composites and Guo et al [165] used carbon fiber to reinforce Si3N4. Silicon nitride will react with carbon ... 

The aspect of the flow curves in Fig. 9.6 indicates the predominant condition of the test. For instance. Fig. 9.6a shows uniform serrations (stick-shp) associated with a continuous, step-by-step process of fiber slipping away off the polymeric block. This exclusive pullout mechanism occurred only in the first part of the curve depicted in Fig. 9.5c. In this case, the fiber was intact after the test and, in some cases, covered with a layer of polyester. By contrast. Fig. 9.6d shows a smooth curve up to fracture. In this case, no pullout process occurred, and the fiber had undergone tensile rupture in association with the last horizontal part of the curve. The intermediate condition of both pullout and fiber rupture are shown in Fig. 9.6b, c. 

M.R. Krishnadev, S. Berrada, N. Banthia and J.F. Fortier, Deformed steel fiber pullout mechanics influence of steel properties , in R.N. Swamy (ed.) Fibre Reinforced Cement and Concrete, Proc. RILEM Symp., E FN SPON, 1992, London and New York, 390-399. 

Toughening for whisker-reinforced composites has been shown to arise from two separate mechanisms frictional bridging of intact whiskers, and pullout of fractured whiskers, both of which are crack-wake phenomena. These bridging processes are shown schematically in Figure 13. The mechanics of whisker bridging have been addressed (52). The appHed stress intensity factor is given by ... 

Experimentally it has been shown that both frictional bridging and whisker pullout play an important role in toughening industrially manufactured composites. Such investigations confirm that to maximize toughness via both mechanisms requires a high volume fraction of whiskers and a high composite modulus to whisker modulus ratio. For example, consider the effect of 20 vol % SiC whisker E = 500 GPa) reinforcement of various matrices on the toughness as presented in Table 7 (53). 

Schnell, R., Stamm, M. and Creton, C, Mechanical properties of homopolymer interfaces transition from simple pullout to crazing with increasing interfacial width. Macromolecules, 32(10), 3420-3425 (1999). 

Blast loaded structures produce high reaction loads at column supports. This usually requires substantial base plates as well as high capacity anchor bolts. Achieving full anchorage of these bolts is of primary importance and will usually require headed bolts or plates at the embedded end of the bolts to prevent pullout. When anchor bolts are securely anchored into concrete, the failure mechanism is a ductile, tensile failure of the bolt steel. Insufficient edge distance or insufficient spacing between bolts results in a lower anchorage capacity and a brittle failure mode. 

Miller, B., Gaur, U- and Hirt, D.E. (1991). Measurement of mechanical aspects of the microdebond pullout technique for obtaining fiber/resin interfacial shear strength. Composites Sci. Technol. 42,207-219. 

The reduced hardness and improved machinability are attributed primarily to the crack deflection process. It can be seen in Fig. 13.8 that the composite showed obvious particle pullout and significant crack deflection along interphase boundaries due to the weak interface bonding. The crack deflection mechanism (absorbing fracture energy and blunting crack tip) could lead to an increase in machinability. As described above, the thermal expansion... 

Short fibre composites, fibre orientation, fracture toughness, fracture mechanisms, fibre pullout, fibre debonding, critical fibre angle. 

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