Құрама материалдардағы толтырғыштардың ролі

Term used for composite materials

Aggregate is the component of a composite material that resists compressive stress and provides bulk to the composite material. For efficient filling, aggregate should be much smaller than the finished item, but have a wide variety of sizes. Aggregates are generally added to increase the strength of composite materials. For example, the particles of stone used to make concrete typically include both sand and gravel. Many construction cement add in aggregates to increase its mechanical strength. Aggregates make up 60 80% of the volume of concrete and 70 85% of the mass of concrete.

Aggregate composites tend to be much easier to fabricate, and much more predictable in their finished properties, than fiber composites. Fiber orientation and continuity can have an overwhelming effect, but can be difficult to control and assess. Fabrication aside, aggregate materials themselves also tend to be less expensive; the most common aggregates mentioned above are found in nature and can often be used with only minimal processing. Not all composite materials include aggregate. Aggregate particles tend to have about the same dimensions in every direction (that is, an aspect ratio of about one), so that aggregate composites do not display the level of synergy that fiber composites often do. A strong aggregate held together by a weak matrix will be weak in tension, whereas fibers can be less sensitive to matrix properties, especially if they are properly oriented and run the entire length of the part (i. e., a continuous filament). Most composites are filled with particles whose aspect ratio lies somewhere between oriented filaments and spherical aggregates. A good compromise is chopped fiber, where the performance of filament or cloth is traded off in favor of more aggregate like processing techniques. Ellipsoid and plate shaped aggregates are also used.

In most cases, the ideal finished piece would be 100% aggregate. A given application's most desirable quality (be it high strength, low cost, high dielectric constant, or low density) is usually most prominent in the aggregate itself; all the aggregate lacks is the ability to flow on a small scale, and form attachments between particles. The matrix is specifically chosen to serve this role, but its abilities should not be abused.

Toughness is a compromise between the (often contradictory) requirements of strength and plasticity. In many cases, the aggregate will have one of these properties, and will benefit if the matrix can add what it lacks. Perhaps the most accessible examples of this are composites with an organic matrix and ceramic aggregate, such as asphalt concrete ("tarmac") and filled plastic (i. e., Nylon mixed with powdered glass), although most metal matrix composites also benefit from this effect. In this case, the correct balance of hard and soft components is necessary or the material will become either too weak or too brittle.