A physically-based abrasive wear model for composite materials Page: 4 of 22
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DUCTILE- AND BRITTLE-MATRIX COMPOSITES
The sliding of abrasives on a solid surface results in volume removal. The mechanism of
wear depends on the mechanical properties of the solid [19,20]. In a ductile solid, the primary
wear mechanism is related to plastic deformation and the hardness of the material is a key
parameter in governing the amount of material removal. However, the dominant mechanism in a
brittle solid depends on fracture at or near the surface and the governing property is the toughness
of the material.
To improve wear resistance, additional phase(s) can be introduced to either a ductile or a
brittle material. However, the required mechanical properties of the reinforcement and the role of
the reinforcement will be different in ductile vs. brittle matricies. For a ductile matrix, a hard
secondary phase is needed to reduce wear, such that the presence of the hard reinforcement
increases the effective hardness of the matrix, thereby reducing the penetration of the abrasive
medium. Consequently, increasing the effective hardness acts to reduce the amount of material
removed. Here, we term such a multiphase system composed of a ductile matrix and a hard
reinforcement as a hard-reinforcement or hardened composite. On the other hand, a tough
reinforcement phase is needed for a brittle matrix to increase wear resistance. The presence of a
tough secondary phase reduces the tendency for fracture at or near the surface, and therefore
tends to decrease the wear rate. In certain ceramic matrix composites, i.e., brittle matrix
materials, the addition of a relatively ductile second phase can result in synergistically favorable
wear behavior in which the composite wear rate can be less than the wear rates of the individual
constituents. This is denoted by region B in Fig. 1 and has been observed in ceramic composites
[2,3]. A multiphase system composed of a brittle matrix and a tough reinforcement may be
termed a ductile-reinforcement or toughened composite.
The present study is focused on hard-reinforcement particulate composites, which have been
the object of most modeling studies of the wear of composites in the past [e.g., 6,7]. We will
consider reinforcement volume fractions in the range 0 to 0.5, since at higher volume fractions
one can expect significant particle-particle interactions. From a practical standpoint, it is difficult
to manufacture particulate composites at volume fractions greater than 0.5 due to void formation
ABRASIVE WEAR MODEL
A model has been developed with simplified geometry in two dimensions, namely a
triangular abrasive medium particle acting on a composite containing idealized rectangular
reinforcements. The model is based on the "equal wear rate assumption"; this postulates that the
different components of a composite wear at steady state at an equal rate through the
redistribution of the specific loads [7,21]. A general schematic drawing of a two-phase composite
with a ductile matrix and a hard reinforcement in abrasion is shown in Fig. 2. The characteristic
size of the reinforcement is represented by the parameter DR.
If the fracture toughness of the matrix/reinforcement interface exceeds the minimum
toughness of either constituent (a "strong" interface), then plowing will be the predominant wear
mechanism; consequently, the resulting wear debris will be small in relation to the reinforcement
size. With such strong interfacial bonding, the entire reinforcement particle will contribute to
improving wear resistance. Both rules of mixtures are commonly based on this assumption. In
practice, however, the interfacial bonding between the constituent materials may not be this
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Lee, Gun Y.; Dharan, C.K.H. & Ritchie, Robert O. A physically-based abrasive wear model for composite materials, article, May 1, 2001; Berkeley, California. (https://digital.library.unt.edu/ark:/67531/metadc780737/m1/4/: accessed April 20, 2019), University of North Texas Libraries, Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.