Rupturing reinforcements

The Sizewell B model provided by then CEGB was overpressurised. Figure 7.33(a) gives the displacement pattern. The vessel model failed at 3.15 times the design pressure by rupturing reinforcements crossing the developed eraeks. The model is of the type indicated in Figs. 7.30 and 7.31. The post-mortem of the Sizewell B containment model with crack patterns is shown in Fig. 7.31. 

Even plastics with fairly linear stress-strain curves to failure, for example short-fiber reinforced TSs (RPs), usually display moduli of rupture values that are higher than the tensile strength obtained in uniaxial tests wood behaves much the same. Qualitatively, this can be explained from statistically considering flaws and fractures and the fracture energy available in flexural samples under a constant rate of deflection as compared to tensile samples under the same load conditions. These differences become less as the... 

Crazing. This develops in such amorphous plastics as acrylics, PVCs, PS, and PCs as creep deformation enters the rupture phase. Crazes start sooner under high stress levels. Crazing occurs in crystalline plastics, but in those its onset is not readily visible. It also occurs in most fiber-reinforced plastics, at the time-dependent knee in the stress-strain curve. 

Figure 4.68. SN curves of reinforced semi-aromatic PA, examples of maximum stress S (MPa) versus number of cycles at rupture (N)...

Example 12.4 Influence of the Environment on D i. Nitromethane is interesting to some people because it explodes. The reason is, of course, in the cleavage of the carbon-nitrogen bond. The monomer, compared to its trimer (taken as a model for the crystal), reveals that the C and N net charges change by A c — 8.7 and A n—1-1 me. respectively, on crystallization. Our bond energy formula and the appropriate parameters thus indicate that the crystalline environment reinforces the CN bond by 4.7 kcal/mol, which is significant at the local point of rupture, responsible for the reaction [251]. 

Steel fiber has been used to reinforce concrete. When 10-mil square bar 2 inches long is incorporated into concrete to the extent of 2% by volume, the modulus of rupture (flexural strength) increases by a factor of 2. When impregnated with polymer the fiber reinforced concrete-polymer increases the modulus of rupture by another factor of 2.5. Thus, an over-all increase by a factor of 5 in the flexural strength is achieved... 

In principle any isotropic material can be reinforced the combination of the materials has to meet the requirement that the reinforcing material has to be stiffer, stronger or tougher than the matrix furthermore there has to be a very good adhesion between the components. In a composite the reinforcement has to carry the stresses to which the composite material is subjected the matrix has to distribute the stresses. By means of a good distribution of the reinforcement the latter blocks the propagation of cracks, which mostly start at the outer surface, and would lead to rupture of the whole object if no blockade were present. By optimum reinforcement the strength of a matrix material can be improved to the tenfold, albeit in one direction. 

In this paper, the importance of particle and whisker reinforcement to creep and creep rupture behavior of ceramics is discussed. Particle and whisker additions generally increase both the fracture toughness and creep resistance of structural ceramics. These additions also act as nucleation sites for cavities. Cavities form preferentially in tensile specimens. This results in a creep asymmetry, in which composites creep faster in tension than in compression. As a consequence of cavitation, the stress exponent for creep in tension 6-10,... 

Above the threshold, deformation occurs as a consequence of direct particle interaction. Several mechanisms of interaction have been suggested solution-precipitation flow of fluid between particles and cavity formation at the particle matrix interface. These theories of creep suggest several rules to improve creep behavior (1) increase the viscosity of the matrix phase in multiphase materials (2) decrease the volume fraction of the intergranular phase (3) increase the grain size (4) use fiber or whisker reinforcement when possible. As the creep rupture life is inversely proportional to creep rate, lifetime can be improved by improving creep resistance. 

Fig. 8.15 Changes in interface microstructure in SiC fiber-reinforced BMAS glass-ceramic composites induced by exposure to high temperature oxidizing environments, (a) After tensile stress-rupture experiment at 1100°C, the 90° fibers show a distinct dual layer at the BN coating-fiber interface, (b) After thermal aging for 500 h at 1200°C, a subtle double layer appears at the same site, (c) Near the composite surface, the effects of thermal aging (and oxidation) are more pronounced.24...

K. M. Prewo, Fatigue and Stress Rupture of Silicon Carbide Fiber-Reinforced Glass-Ceramics, J. Mater. Sci., 22, 2695-2701 (1987). 

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