Brittle separation

Brittle separation of an adhering system, under loading perpendicular to the interface, normally occurs in a crack-opening mode. 

The force requirement for separation, in a mode in which rigid facing surfaces remain exactly parallel, would be enormous (25). Brittle separation at an interface, in the absence of a dissipation mechanism resembling the mechanism that controls bulk fracture, would occur at a much lower level of force. So it will be necessary to postulate a dissipation mechanism, such as an interfacial craze, for those cases in which a polymer that has a high Tg does not separate easily from a hard solid. 

It is clear that if the criterion (la) or (3a) holds for interfacial separation before fibril drawing (whether on account of AG being small or Oy being large) then there will not be a large dissipation of energy,, per unit advance of the macroscopic separation front, and there will be very little work for the applied force to do. So the force required to open up an interfacial crack, in brittle separation, will be small ... 

Next, we may make an estimate with respect to brittle separation by a craze mechanism. We can assume a fibril radius of the order of... 

Dichloramine-T. Dilute 80 ml, of freshly prepared 2N sodium hypochlorite soluticMi (preparation, p. 525) with 80 ml. of w ter, and then add with stirring 5 g. of finely powdered toluene-p-sulphonamide, a clear solution being rapidly obtained. Cool in ice-water, and then add about 50 ml. of a mixture of equal volumes of glacial acetic acid and water slowly with stirring until precipitation is complete the dichloro-amide separates at first as a fine emulsion, which rapidly forms brittle colourless crystals. Filter off the latter at the pump, wash well with... 

The fundamental goal in the production and appHcation of composite materials is to achieve a performance from the composite that is not available from the separate constituents or from other materials. The concept of improved performance is broad and includes increased strength or reinforcement of one material by the addition of another material. This is the well-known purpose in the alloying of metals and in the incorporation of chopped straw into clay for bricks by the ancient Egyptians and plant fibers into pottery by the Incas and Mayans. These ancient productions of composite materials consisted of reinforcing britde materials with fibrous substances. In both cases the mechanics of the reinforcement was such as to reduce and control the production of cracks in the brittle material during fabrication or drying (2). 

There are two basic types of cast iron white, and grey. The phases in white iron are a and FejC, and it is the large volume fraction of FejC that makes the metal brittle. The name comes from the silvery appearance of the fracture surface, due to light being reflected from cleavage planes in the FejC. In grey iron much of the carbon separates... 

Some manufacturers have experienced die above mentioned Ni3S2 scale formation phenomenon under certain gas conditions, which led to die failure of a rotating blade. One such experience involved a fracture dial was distinctly intergranular with evidence of secondary intergranular cracks or grain separation across die fracture. Intergranular facets of die fracture were sharp and distinct with little evidence of any ductile mode. The fracture appeared to have occurred in a brittle intergranular mode. 

Parts of the tank were projected to distances up to 360 m (1200 ft). Twenty-two pieces of the tank were recovered, constituting approximately 80% of the original tank. Debris was found clustered in two separate areas, namely, within the radii of 5° to 20° and 65° to 95° from the car s direction of movement. Three empty tank cars located up to a distance of three railroad tracks from the exploded car were blown from the rails. The undercarriage of the car was bent into a V-shape (see Figure 2.1). One person was killed in the explosion. Analysis of a recovered piece of the tank car showed that failure was due to brittle fracture. 

Agitation was stopped and the contents of the flask were removed to a Separatory funnel. The aqueous and resinous layers were separated and the solvent was removed from the resinous layer by vacuum distillation. After the removal of the solvent, heating at a reduced pressure of 1.5 to 2.5 mm and at a temperature of 245° to 250°C was continued for 4 /2 hours. The condensate then had a viscosity of 4.0 poises when measured as a 60% solution in toluene and, on cooling, solidified to a brittle mass. 

This example of aluminium illustrates the importance of the protective him, and hlms that are hard, dense and adherent will provide better protection than those that are loosely adherent or that are brittle and therefore crack and spall when the metal is subjected to stress. The ability of the metal to reform a protective him is highly important and metals like titanium and tantalum that are readily passivated are more resistant to erosion-corrosion than copper, brass, lead and some of the stainless steels. There is some evidence that the hardness of a metal is a signihcant factor in resistance to erosion-corrosion, but since alloying to increase hardness will also affect the chemical properties of the alloy it is difficult to separate these two factors. Thus althou copper is highly susceptible to impingement attack its resistance increases with increase in zinc content, with a corresponding increase in hardness. However, the increase in resistance to attack is due to the formation of a more protective him rather than to an increase in hardness. 

Rubber separators have a relatively low porosity ( 50 - 55 percent) and thus high acid displacement and electrical resistance. Furthermore, they are brittle and for this reason difficult to handle in larger sizes. In order to balance this disadvantage, an adjustment to a lower degree of crosslinking has been attempted the result was a corresponding increase in susceptibility to oxidative attack. 

A mixture of powdered poly(vinyl chloride), cyclohexanone as solvent, silica, and water is extruded and rolled in a calender into a profiled separator material. The solvent is extracted by hot water, which is evaporated in an oven, and a semiflexible, microporous sheet of very high porosity ( 70 percent) is formed [19]. Further developments up to the 75 percent porosity have been reported [85,86], but these materials suffer increasingly from brittleness. The high porosity results in excellent values for acid displacement and electrical resistance. For profiles, the usual vertical or diagonal ribs on the positive side, and as an option low ribs on the negative side, are available [86],... 

Sintered PVC separators for open stationary batteries are produced in the same way as the corresponding starter battery version (Sec. 9.2.2.2). Their brittleness and thus difficult processability are disadvantages, as is their relatively low porosity the concerns about release of chloride ions and subsequent increased corrosion are to be considered here as well. On the other hand,... 

---