Brittle fibers

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). 

Destruction of the fiber filler may occur during compression of a composite. It is evident that the destroying process is more pronounced for high-modulus, brittle fibers such as glass or carbon. For the materials containing organic fibers the destruction rate is considerably lower. 

There is increasing evidence in recent years in the fragmentation test of some brittle fiber-brittle matrix composites that a matrix crack is developed at the position of the fiber break. The presence of the matrix crack and its physical size are shown to alter the stress distributions at the fiber-matrix interface. As the applied strain... 

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)... 

If a ductile matrix is reinforced with brittle fibers as in most thermoplastic and metal matrix composites, the matrix forms bridges in the plane of the broken fibers and the work of matrix shearing / ms is given by (Cooper and Kelly, 1967 Tetelman, 1969 Cooper, 1970)... 

Apart from the above three major engineered interface concepts, the ductile coating material may also heal up the surface flaws that are often generated during the fiber manufacturing processes, and protect the brittle fiber surface during subsequent processing. 

Johannsenite, Ca(Mn,Fe )Si206, is a species in whieh p = 0. There is little additional trivalent ion (Al, Fe, or Cr ) substitution. The mineral is most commonly found as spherulitic aggregates of brittle fibers or prisms. Another pyroxene, acmite (NaFe Si206), has been found as large (100 X 35 X 20 cm) single crystals of prismatic shape, as needles, as felted aggregates of fine fibers, and as capillary crystals. 

Figure 5.89 Schematic illustration of stress-strain curves for continuous, unidirectional fiber-reinforced composites containing brittle fibers in a ductile matrix. Contributions from fibers and matrix are shown as dashed lines at (a) low fiber volume fractions and (b) high fiber volume fractions. Adapted from N. G. McCrum, C. P. Buckley, and C. B. Bucknall, Principles of Polymer Engineering, 2nd ed., p. 267. Copyright 1997 by Oxford University Press.

Cannabis indica Lamarck, classified by Lamarck in 1783, is a shorter plant that s more densely branched. Seldom over eight feet tall, it has short, brittle fibers and thus is not very useful for fiber but generally contains the greatest amount by weight of Cannabis resin. Until recently, it s cultivation has been mainly restricted to India, Persia and the Arab countries, where its leaves are often made into a milkshake and its resin is pressed into hashish. 

As early as in 1958, Rich and Blow showed that NaDC forms a helical complex of macromolecular dimensions [72]. They observed that unusual changes occurred in NaDC (0.1 m) in the presence of glycylglycine (0.1 m). There was a large initial increase in the viscosity of the medium, and they were able to draw glassy and brittle fibers, which showed a regular structure by X-ray diffraction. With time the solution reached a gelatinous state and they could lift the cohesive mass, which was more like a gelly. 

Uniaxial Reinforcement with Long Brittle Fibers... 

Figure 15.10 Tensile stress versus tensile strain curves for brittle fibers in a ductile matrix.

Figure 15.11 Tensile stress versus tensile strain curves for aligned fiber composite containing brittle fibers and ductile matrix, (a) Low fiber volume fraction (b) high ( )y. (From Ref. 7.)...

Depending on x, Gf, and g, two failure modes are possible for aligned short brittle fiber composites fiber pullout and fiber fracture. Let us consider a composite in which > e. If / < 4, the average stress in the fiber will be given by Eq. (15.47), so the strength in the composite can be written... 

It is assumed that the tube is made of a composite material which is composed of stiff duetile fibers arranged in a parallel uniform array in a ductile matrix. The eomposites of metal-metal type are eonsidered, first of all. However, the combination of a ductile matrix with brittle fibers can be easily accounted for, as well. As an example of the latter ease serves the aluminium alloy reinforced with boron fibers. 

PHYSICAL PROPERTIES a group of six different minerals occurring naturally in the environment most common type is white others are blue, gray, or brown long thin fibers similar to fiberglass not volatile not soluble serpentine asbestos chrysotile mineral, strong, resistant to chemicals and heat amphibole asbestos brittle fibers, resistant to chemicals and heat... 

Crack tip shielding by Second-phase brittle fibers with partial... 

The ceramic matrix composites (CMCs) contain brittle fibers and a brittle matrix. This combination ends up in a damage tolerant material. CMCs are of interest to thermostmctural applications. They consist of ceramics or carbon reinforced with continuous ceramic or carbon fibers. Their mechanical behavior displays several typical features that differentiate them from the other composites (such as polymer matrix composites, metal matrix composites, etc. .. ) and from the homogeneous (monolithic) materials. 

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