Aggregate Composites
There are 2 catagories of aggregate composites:

1. Large Particulate Composites
   The particulates are relatively large and are present in large concentrations. (>25% and typically between 60-90%) 
   The mechanism of strengthening is the (equiaxed) particulates restrain the matrix movement in the vicinity of the particulate. i.e. the matrix transfers some of the stress to the particulates. This needs strong interfacial bonding between matrix and particulate. The most effective reinforcement is obtained by relatively small particulates, uniformly dispersed.                               
                                                    
   Examples include:
   
   • polymers with fillers
   • portland concrete
   • asphaltic concrete
   • cermets
     ceramic particles in a metal matrix
     such as WC in Co (used for a cutting tool) or SiC in Al
   • vulcanized rubber with carbon black
     carbon black in a rubber matrix - used for tires
   • W in Cu
   • Mo in Cu
   • W in NiFe
   • thermoplastic elastomer
     elastomer in thermoplastic polymer
                                    
     
2. Dispersion Strengthened Composites
   The particulates are small in size and are present in small concentrations. (<15%) 
   The strength comes from the particulates impeding dislocation motion. This mechanism of reinforcement is like precipitation hardening, but not as pronounced.  If several volume percent of a hard and inert particulate material is added to a matrix material, the particulates impede dislocation motion. Unlike the mechanism for Large Particulate Composites, this mechanism is on the atomic order. Unlike precipitation hardening, the strength is retained at high temperatures.
                            
   Examples include:
   
• TD Nickel
  Thoria (TO2) dispersed in a Ni matrix
• Sintered Aluminum Powder (SAP)
  Alumina (Al₂O₃) coated Al particles dispersed in an Al matrix
• Al₂O₃ in Cu
  Alumina particles dispersed in a copper matrix
• Al₂O₃ in Fe
  Alumina particles dispersed in an iron matrix
  
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