Strength and Toughness

5 MPam / could be attributed entirely to crack wake effects, including frictional sliding, SiC particle bridging and plastic deformation of alloy bridges, rather than to changes in the crack-tip profile. Anderson [96] measured Kic in four-point bending for both a base composite and a SiC-reinforced composite and obtained 7.8 and 

6 MPam /, respectively. The decrease observed after growth into the particulate preform is inconsistent with the results of Pickard et al. but it is unlikely that the alloys used for the two composites were the same. 

In additional results [97] for the fracture toughness, Kic, determined from a single edge-notched beam test, values of 3.6 MPa m (for a 100 pm SiC particulate preform) up to 6.2MPam (13 pm SiC) were reported. This trend is the opposite of that reported by Pickard et al. [91]. Values of the elastic modulus reported in this later work ranged from 261 to 328 GPa. 

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Toughening Mechanisms. The mechanics of tetragonal-to-monoclonic transformation can effect the strength and toughness of the... 

Fiber-Reinforced Plastics. PVA fiber, with its high strength and toughness, has become widely used as reinforcement fiber for FRP. Strength as high as 1.8 N/tex (18 gf/dtex) has been reported (32,41). Penetration in this field will therefore become more active. 

Steels develop exceUent combinations of strength and toughness if heat-treated by quenching to martensite, foUowed by tempering (see Steel). 

Nickel—Iron. A large amount of nickel is used in alloy and stainless steels and in cast irons. Nickel is added to ferritic alloy steels to increase the hardenabihty and to modify ferrite and cementite properties and morphologies, and thus to improve the strength, toughness, and ductihty of the steel. In austenitic stainless steels, the nickel content is 7—35 wt %. Its primary roles are to stabilize the ductile austenite stmcture and to provide, in conjunction with chromium, good corrosion resistance. Nickel is added to cast irons to improve strength and toughness. 

Soft-drink bottles made from poly(ethylene terephthalate) (PET) are usuady made by stretch-blow mol ding in a two-step process. Eirst, a test-tube-shaped preform is molded, which is then reheated to just above its glass-transition temperature, stretched, and blown. Stretching the PET produces biaxial orientation, which improves transparency, strength, and toughness of the botde (54,56). A one-step process is used for many custom containers that are injection stretch-blow molded. 

Because of its high strength and toughness, spun nylon yams tend to form unsightiy pihs, ie, balls of fiber on the fabric surface containing some short lengths of fiber, in flat woven and apparel fabrics. This is also why bulked continuous-filament yam (BCE) is preferred over spun yams for loop pile carpets. 

Silicon. Sihcon [7740-21-3] added to copper forms alloys of high strength and toughness along with improved corrosion resistance, particularly in acidic media. Sihcon in small amounts can improve fluidity. Sihcon is a very harmful impurity in leaded tin bron2e alloys, however, because it contributes to lead sweat and unsoundness. 

The yield strength and toughness of Dural differ enormously in these three conditions (slow-cooled, quenched, and quenched and aged) the last gives the highest yield and lowest toughness because the tiny particles obstruct dislocations very effectively. 

Chain scission—resulting in a loss in strength and toughness. 

Mechanical properties. Properties commonly of importance here are rigidity, creep resistance, strength and toughness. For some applications resistance to repeated flexing or abrasion may be critical. 

Small amounts (usually <10%) of plasticizer could be used in the blending system to improve the processing properties of the material by lowering the melting and glass-transition temperatures. The addition of liquid plasticizer also makes the material soft but at the same time, the strength and toughness of the material decreases. 

H. Worth, UK, An Excellent Historical Perspective on Structural Materials and Fine on Stiffness, Strength and Toughness (1976). 

It produces a topping with good tensile strength and toughness. 

Tenacity. Whilst some plastics are rigid and others flexible, all commercial materials show a degree of strength and toughness superior to simple crystals and common glass when rapidly stressed. 

Throughout this book all the different types of mechanical properties are presented and reviewed. These mechanical properties include a tremendous range of different types that can usually be characterized by their stiffness, strength, and toughness. 

Molecular orientation results in increased stiffness, strength, and toughness (Table 8-12) as well as resistance to liquid and gas permeation, crazing, microcracks, and others in the direction or plane of the orientation. The orientation of fibers in reinforced plastics causes similar positive influences. Orientation in effect provides a means of tailoring and improving the properties of plastics. 

Other ceramic cutting-tool materials include alumina, Si-Al-0-N, alumina-carbide composites and, more recently, a composite of silicon nitride reinforced with silicon carbide whiskers. This last material can be produced by chemical-vapor infiltration (CVI) and has high strength and toughness as shown in Table 18.3.Cl... 

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