Ductile fiber

The descriptions presented in the foregoing sections are concerned mainly with composites containing brittle fibers and brittle matrices. If the composite contains ductile fibers or matrix material, the work of plastic deformation of the composite constituents must also be taken into account in the total fracture toughness equation. If a composite contains a brittle matrix reinforced with ductile libers, such as steel wire-cement matrix systems, the fracture toughness of the composite is derived significantly from the work done in plastically shearing the fiber as it is extracted from the cracked matrix. The work done due to the plastic flow of fiber over a distance on either side of the matrix fracture plane, which is of the order of the fiber diameter d, is given by (Tetelman, 1969)... 

Morton J. and Groves G.W. (1974). The cracking of composites consisting of discontinuous ductile fibers in a brittle matrix-effect of fibre orientation. J. Mater. Sci. 9, 1436-1445. 

Figure 5.91 Schematic illustration of tensile strength versus fiber volume fraction for continuous, unidirectional ductile fibers in a brittle matrix. Adapted from N. G. McCrum, C. P. Buckley, and C. B. Bucknall, Principles of Polymer Engineering, 2nd ed., p. 269. Copyright 1997 by Oxford University Press.

Figure 15.13 Dependence of tensile strength cr on fiber volume fraction for aligned fiber composite containing ductile fibers and brittle matrix.

Wetherhold R C, Corjori M and Das P K (2007) Multiscale considerations for interface engineering to improve fracture toughness of ductile fiber/therinoset matrix composites, Compos Sci Technol 67 2428-2437. 

C.K.Y Leung and J. Chi, Crack bridging force in random ductile fiber reinforced brittle matrix composites , J. Eng. Mech. ASCE. 121,1995,1315-1324. 

C. K.Y. Leung, Design criteria for pseudo-ductile fiber reinforced composites , ASCE J. Engineering Mechanics. 122,1996,10-18. 

Figure 8.7. Types of microstructures producing R-curve effect a) dispersion of hard particles b) microstructure causing multicracking c) phase transformation inducing compressive stresses at crack tip (case of partially stabilized zirconia) d) reinforcement of the matrix by ductile fibers and e) reinforcement of the matrix by high resistance fibers [MEN 92]...

Jets for continuous filament textile yam are typically 1 cm diameter gold—platinum ahoy stmctures with 20—500 holes of 50—200 p.m diameter. Tire yam jets are also 1 cm in diameter but typicahy use 1000—2000 holes to give the required balance of filament and yam denier. Staple fiber jets can have as many as 70,000 holes and can be made from a single dome of ahoy or from clusters of the smaller textile or tire yam jets. The precious metal ahoy is one of the few materials that can resist the harsh chemical environment of a rayon machine and yet be ductile enough to be perforated with precision. Glass jets have been used for filament production, and tantalum metal is a low cost but less durable alternative to gold—platinum. 

Composite Strengthening. An alternative strengthening method which holds great promise for producing advanced high temperature aUoys involves the incorporation of fibers or lamellae of a strong, often brittle phase, in a relatively weak, ductile, metallic matrix. This technique has been... 

Table 13 is a representative Hst of nickel and cobalt-base eutectics for which mechanical properties data are available. In most eutectics the matrix phase is ductile and the reinforcement is britde or semibritde, but this is not invariably so. The strongest of the aHoys Hsted in Table 13 exhibit ultimate tensile strengths of 1300—1550 MPa. Appreciable ductiHty can be attained in many fibrous eutectics even when the fibers themselves are quite britde. However, some lamellar eutectics, notably y/y —5, reveal Htde plastic deformation prior to fracture. 

A series of events can take place in response to the thermal stresses (/) plastic deformation of the ductile metal matrix (sHp, twinning, cavitation, grain boundary sliding, and/or migration) (2) cracking and failure of the brittle fiber (5) an adverse reaction at the interface and (4) failure of the fiber—matrix interface (17—20). 

Cemented carbides belong to a class of hard, wear-resistant, refractory materials ia which the hard carbides of Group 4—6 (IVB—VIB) metals are bound together or cemented by a soft and ductile metal biader, usually cobalt or nickel. Although the term cemented carbide is widely used ia the United States, these materials are better known iatemationally as hard metals (see also Refractories Refractory coatings Refractory fibers). 

A unidirectional fiber-reinforced composite material deforms as the load increases in the following four stages, more or less, depending on the relative brittleness or ductility of the fibers and the matrix ... 

Net-tension failures can be avoided or delayed by increased joint flexibility to spread the load transfer over several lines of bolts. Composite materials are generally more brittle than conventional metals, so loads are not easily redistributed around a stress concentration such as a bolt hole. Simultaneously, shear-lag effects caused by discontinuous fibers lead to difficult design problems around bolt holes. A possible solution is to put a relatively ductile composite material such as S-glass-epoxy in a strip of several times the bolt diameter in line with the bolt rows. This approach is called the softening-strip concept, and was addressed in Section 6.4. 

The single filament pull out test, sometimes called the microdebond test, has received attention for some years as a way to assess the adhesion between fibers and matrices in fiber composite [90,91]. It provides a direct measure of interfacial adhesion and can be used with both brittle and ductile matrix resins. 

Increased Glass fibers Ductility, cost Ductility, cost Glass fibers are the most... 

Strength Fibrous minerals Ductility gaining tensile strength. Carbon fibers are more expensive fibrous minerals are least expensive but only slightly reinforcing. Reinforcement makes brittle resins tougher and embrittles tough resins. Fibrous minerals are not commonly used in amorphous resins. 

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