Ductile matrix

Many metals are naturally brittle at room temperature, so must be machined when hot. However, particles of these metals, such as tungsten, chromium, molybdenum, etc., can be suspended in a ductile matrix. The resulting composite material is ductile, yet has the elevated-temperature properties of the brittle constituents. The actual process used to suspend the brittle particles is called liquid sintering and involves infiltration of the matrix material around the brittle particles. Fortunately, In the liquid sintering process, the brittle particles become rounded and therefore naturally more ductile. 

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. 

Phosphorus appears to have a beneficial effect on the growth rate. At sub-critical temperatures it helps to stabilise the carbide, while at temperatures up to about 900°C the presence of the hard phosphide eutectic network restricts the deformation to which the much more ductile matrix would otherwise be subject. Since the phosphide eutectic melts at about 950°C, irons containing appreciable amounts of this constituent should clearly not be exposed to this temperature. 

Kikuchi Y., Eukui T., Okada T., and Inoue T. Origin of rubber elasticity in thermoplastic elastomers consisting of crossUnked rubber particles and ductile matrix, J. Appl. Polym. Sci., Appl. Polym. Symp., 50, 261, 1992. 

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)... 

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.

Cast magnesium alloys used for structural applications comprise a highly heterogeneous ductile matrix with several dominant types of inclusions that dictate fatigue resistance. We use the term inclusion as distinctly different from a crack, as the former occurs naturally as products of the casting process, while the latter is... 

S. Groh et al Fatigue crack growth from a cracked elastic particle into a ductile matrix. Phil. Mag. 88, 3565-3583 (2008)... 

Film-induced cleavage models. It has been suggested that dealloying and/or vacancy injection could induce brittle fracture. The model assumes that a brittle crack initiates in a surface film or layer and this crosses the film/matrix without loss of speed. The brittle crack will continue in the ductile matrix until it eventually blunts and arrests. Verification of this model needs better understanding of the surface films and brittle fracture. (Jones)5... 

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.)...

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. 

Much thinner metal fibers are manufactured by the so-called bundle pulling process, in which wires are embedded in a ductile matrix (e.g. copper) and are jointly subjected to a continuous filament process. The fibers remaining, after removal of the matrix, have diameters down to 12 pm, but diameters down to 0.5 pm can be obtained with this process. 

The composite systems studied by Takayanagi et al. (1980) used the polyaramides poly(p-phenylene terephthamide), PPDT, or pol.y-p-benzamide (PBA) as the reinforcing component with nylon 6 or nylon 66 as the ductile matrix polymer. Block copolymers of one of the aromatic polyamides with one of the nylon polymers were also evaluated. The blends were prepared by extruding the sulfuric acid solutions of polymers into a... 

The decohesion of the particles from the matrix was frequently observed in blends with ductile matrix and poorly adherent particles. Typical cases for such a... 

Certain types of laminate are susceptible to creep, as discussed in Chapter 1. The use of 0° plies greatly reduces the creep rate and the problem is not usually severe with long fibre composites, although laminates consisting entirely of 45° plies can show a scissor-closing motion, that is, a reduction in the angle to 43° or thereabouts if held under a sustained load with a sufficiently ductile matrix. 

Trachte and DiBenedetto, 1971 Wambach et ai, 1968). Since PPO is much more ductile at 25 C than the epoxy resins mentioned, the effects of filler and adhesion promoter on PPO should tend to resemble the effects on an epoxy resin in a ductile state (e.g., at 130°C). Indeed this is the case. The point is that a filler tends to increase surface roughness and hence y in an otherwise brittle matrix, especially if the filler-matrix adhesion is poor, but tends to inhibit plastic deformation (by constraints or by simple volume replacement) in an otherwise ductile matrix. Such effects are not accounted for in Nielsen s simple treatment (Section 12.1.2.3) and conceivably may occur as competitive mechanisms (see Figure 12.20). A useful summary of such competitive factors is given in Table 12.3 for the glass-bead-epoxy systems (DiBenedetto and Wambach, 1972) the discussion should be relevant to other cases as well. 

Schematic sketch of tensile stress-strain curves for fibres and matrix (a) brittle fibres in ductile matrix and (b) ductile fibres in brittle matrix. 

Schematic sketch graph of tensile strength i for aligned fibre composite containing brittle fibres in a ductile matrix (case I). 

Schematic sketch graph o( tensile strength o-, versus fibre volume fraction lor an aligned fibre composite containing dfaconlinuous brittle fibres in a ductile matrix (dotted lines show the case of continuous fibres, for comparison). 

Therefore, in this moulded bar, the fibre length exceeds /,. The carbon fibre-nylon case corresponds to brittle fibres in a more ductile matrix ... 

To explain the mechanism of transgranular S.C.C. in a brass, Newman and Sieradzki have proposed the film-induced cleavage model, according to which a brittle crack that initiates in a thin surface film propagates into the ductile matrix and eventually blunts and arrests, after which the process repeats itself [39, 44, 45]. 

Adding to this, there may be alternative polymer combinations - the matrix does not have to be PLLA. In fact, there may even be biodegradable polymer combinations for MFC in which, for example, PLLA is the reinforcing component surrounded by a ductile matrix. Furthermore, additional drawing steps could be added to maximize the orientation of the reinforcing polymer as well as decrease fibril diameters. A very interesting overlap of MFCs and particulate composites provides even more potential for Improvement and scope for future work because, as mentioned before, nanoparticles could be used to modify the reinforcing polymer s thermal properties to enhance creep resistance. 

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