Brittle Brittleness

Failure mode Ductile Ductile Ductile Ductile Brittle Brittle Brittle Brittle... 

Flexibility Brittle Brittle Brittle Excellent Good... 

Low Temperature Brittleness. Brittleness temperature is the temperature at which polyethylene becomes sufficiently brittle to break when subjected to a sudden blow. Because some polyethylene end products are used under particularly cold climates, they must be made of a polymer that has good impact resistance at low temperatures namely, polymers with high viscosity, lower density, and narrow molecular weight distribution. ASTM D746 is used for this test. 

Brittleness Brittle materials exhibit tensile stress-strain behavior different from that illustrated in Fig. 2-13. Specimens of such materials fracture without appreciable material yielding. Thus, the tensile stress-strain curves of brittle materials often show relatively little deviation from the initial linearity, relatively low strain at failure, and no point of zero slope. Different materials may exhibit significantly different tensile stress-strain behavior when exposed to different factors such as the same temperature and strain rate or at different temperatures. Tensile stress-strain data obtained per ASTM for several plastics at room temperature are shown in Table 2-3. 

Notched Izod impact D256 at —40°C (J/m) 7500 Brittle Brittle... 

Cohesive to brittle. Brittleness increases with increasing Ca2+ and decreasing sugar. Thermoreversible... 

The brittle-ductile transition temperature depends on the characteristics of the sample such as thickness, surface defects, and the presence of flaws or notches. Increasing the thickness of the sample favors brittle fracture a typical example is polycarbonate at room temperature. The presence of surface defects (scratches) or the introduction of flaws and notches in the sample increases Tg. A polymer that displays ductile behavior at a particular temperature can break in the brittle mode if a notch is made in it examples are PVC and nylon. This type of behavior is explained by analyzing the distribution of stresses in the zone of the notch. When a sample is subjected to a uniaxial tension, a complex state of stresses is created at the tip of the notch and the yield stress brittle behavior known as notch brittleness. Brittle behavior is favored by sharp notches and thick samples where plane strain deformation prevails over plane stress deformation. 

All materials tend to fracture if stressed severely enough. Some materials fracture more easily than others, and are thereby said to be brittle . Brittleness is the property of a material manifested by fracture without appreciable prior plastic deformation. In ductile fracture significant plastic flow occurs before fracture. Strain at fracture is more than a few per cent, unlike brittle fracture, and may be several hundred per cent. However, a sharp distinction cannot be made between brittle and ductile fracture since even in glassy materials some deformations take place. Further, a given material will fail in a brittle manner under some conditions and a ductile manner under other conditions. Thus, brittle fracture is favored by the low temperature, fast loading and when the state of stress approaches a uniform, i.e., triaxial or dUatational, state. Materials with low T are more... 

In brittle micas, the interlayer cations are divalent (e.g., Ca " ). The bond is stronger and although the layered structure still imparts basal cleavage they are more brittle. Brittle micas are uncommon minerals and not of any real interest. 

Matched coefficient of thermal expansion (a). In cases in which the film and substrate are different it will be almost impossible to achieve an exact match in a. A sigiuficant difference in a should be avoided because it can cause poor adhesion and cracking of the film. The latter problem is particularly relevant to ceramics, which are often brittle. Brittle materials are particularly weak in tension and therefore it is better if ocaim < oCsubstrate this will put the film in compression. 

Boyle s law Boyle s law states that for a fixed amoimt of gas kept at a fixed temperature, pressure and volume are inversely proportional, brainstorming Brainstorming is a method of shared problem solving in which all members of a group engage in unrestrained discussion and spontaneously generate ideas, brittleness Brittleness is the opposite of plasticity brittle material is not flexible and is easily broken. 

Plastics generally increase in strength and become more rigid at low temperature. However, many plastics will become brittle. Brittleness results when a material loses its yield. Brittleness can result from crystallization, although many linear polymers become brittle without crystallizing. Rubber-type materials exhibit brittle behavior similar to that of thermoplastics. It also should be noted that some plastics have useful properties below their brittle points (e.g., polystyrene and polymethyl methacrylate). 

A brittle material will break easily when given a sudden blow. This property is associated with hardness, since hard materials will often be brittle. Brittle materials cannot be used in the working parts of power presses, which are subjected to sudden blows. 

Failure mode Brittle Brittle Ductile Ductile... 

For obvious reasons, all structures should be designed to avoid brittle fracture of any kind however, under particular conditions, such fracture may occur in practically all materials. For metals or plastics, if brittle fracture is conditioned by low temperature, fatigue, rate of loading, etc., it is a natural and common way of fracture for several kinds of matrices used in building and civil engineering materials. Matrices based on various cements and all kinds of ceramic materials are considered as brittle. Brittleness is the principal disadvantage, which should be controlled in all structural and even non-structural applications of these materials. 

Ductility of one of the constituent powders is not a requirement for mechanical alloying to occur. A number of brittle/brittle systems have been shown to form solid solutions of intermetallic compounds during milling (Davis et al. 1988, Davis and Koch 1987). In contrast to the layered morphology exhibited by ductile systems, brittle/brittle systems develop a granular morphology. While the alloying mechanism is not well understood with brittle systems it is evident that material transfer between the components plays an important role (Davis et al. 1988). 

Brittle Brittle Bulk chipping, through thickness fracture, brittle interfacial fracture, microfracture in coating, microfracture in substrate... 

Finally we discuss in this section the special problem of assessing compatibility in amorphous binary mixtures in which the T s of the individual constituents happen to lie comparitively close. A possible solution to this problem lies in observations, now confirmed in both PPO-PS and PPO-pClS/PS copolymers, regarding large deformation properties of such blends. It has been found that these properties, particularly the tensile strength, offer a sensitive additional criterion. Thus for compatible systems a pronounced maximum is observed in measurements of tensile strength as a function of blend composition. In incompatible systems, conversely, a minimum is found, (10,13). Additional tests of the general applicability of this suggested criterion particularly with respect to brittle-brittle polymer systems is under way. 

Sulfuric Acid (Cone.) +57.9 Brittle Brittle +36 Cracked... 

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