Accession Number : ADA302084

Title :   Process Defects in Composites.

Descriptive Note : Final rept. 25 Feb 91-30 Nov 94,

Corporate Author : ARIZONA STATE UNIV TEMPE

Personal Author(s) : Krajcinovic, Dusan ; Mignolet, Marc

PDF Url : ADA302084

Report Date : 30 JAN 1995

Pagination or Media Count : 202

Abstract : The principal objective of the present research was to study the causes of the damage and structural disorder in polymers and fiber reinforced polymers attributed to the curing process. It was first demonstrated that the rate at which the molecular chains rupture and damage evolves is at its maximum immediately after the sol to gel transition, i.e. just after gel molecule is formed. This observation implies that the duration of the stage during which the autoclave temperature is lowered can be shortened if so desired but also that a rational model must span at least two scales (micro and macro) and must couple the heat transfer, collision theory (rate of chemical reactions of association and dissociation) and balance of mechanical momentum. Moreover, the material parameters change with time as a result of the evolving order, increased connectivity (progressive crosslinking of molecular links) and attendant viscosity. None of these effects can be described by the traditional tools of the continuum mechanics. A second aspect of the present investigation focused on the clustering of fibers that arises during the curing process. It was shown that this phenomenon is initiated during the transition of the melted matrix from an approximately Newtonian fluid to a non-Newtonian one and that its growth rate increases sharply with the fiber concentration at that time. Thus, to minimize the formation of clusters of fiber, the curing process should minimize both the transition time but also the corresponding fiber concentration. Estimates of the cluster growth rates were provided to provide a quantitative assessment of the fiber clustering potential.

Descriptors :   *FIBERS, *COMPOSITE MATERIALS, *CROSSLINKING(CHEMISTRY), *CHEMICAL REACTIONS, *FIBER REINFORCEMENT, HEAT TRANSFER, TEMPERATURE, MECHANICAL PROPERTIES, MODELS, MOLECULES, PARAMETERS, STRUCTURAL PROPERTIES, POLYMERS, GROWTH(GENERAL), THEORY, RATES, ORDER DISORDER TRANSFORMATIONS, CONTINUUM MECHANICS, RUPTURE, TIME, CLUSTERING, SCALE, CHAINS, BALANCE, FLUIDS, TRANSITIONS, CURING, VISCOSITY, DISSOCIATION, GELS, MOMENTUM, COLLISIONS, AUTOCLAVES.

Subject Categories : Laminates and Composite Materials
      Refractory Fibers

Distribution Statement : APPROVED FOR PUBLIC RELEASE