Automatic monitoring of composite prepregs

An on-line method using a processor for non-destructively determining fiber volume fraction and resin porosity of a composite material wherein the following parameters of the composite material or prepreg are known:

• density and layup sequence, the method comprising:
• supporting a transducer assembly above the composite material or prepreg;
• moving the composite material or prepreg under the transducer assembly and periodically stopping the moving the composite material;
• determining the elastic modulii of the composite material;
• propagating two independent acoustic waves via the transducer assembly via the transducer assembly through the composite material each time the moving the composite material under the transducer assembly is stopped;
• receiving the acoustic waves propagated through the composite material in the processor;
• determining in the processor the velocity of each of the two acoustic waves propagated through the composite material from the received acoustic waves propagated through the composite material, the respective velocity being V.sub.1 and V.sub.2 ;
• determining the thickness of the composite material and inputting the thickness into the processor;
• and
• determining in the processor the fiber volume fraction and resin porosity of the composite material using the velocities, V.sub.1 and V.sub.2, the thickness, the elastic modulii of the constituent materials and the known parameters of density and layup sequence.

An apparatus for non-destructively determining fiber volume fraction and resin porosity of composite material comprising:

• a roller having an outer peripheral surface;
• a roller-transducer housing having an outer peripheral surface;
• a support for rotatingly supporting the roller and the roller-transducer housing with outer peripheral surface of the roller being spaced a predetermined distance from the outer peripheral surface of the roller-transducer housing, the composite material being disposed between the outer peripheral surface of the roller and the outer peripheral surface of the roller-transducer housing whereby rotation of the roller and the roller-transducer housing moves the material in an advanced direction between the roller and the roller-transducer housing when the roller and the roller-transducer housing are rotating;
• motor means for drivingly rotating at least one of the roller and the roller-transducer housing to move the composite material in the advanced direction;
• a transducer assembly supported in the roller-transducer housing for propagating two acoustic waves through the composite material;
• means for receiving the acoustic waves propagated through the composite material and
• outputting the received acoustic waves in a digital format;
• and
• a processor for receiving the two acoustic waves in a digital format and determining the velocity of each of the acoustic waves, V.sub.1 and V.sub.2, the processor having inputted therein a thickness of the composite material, a density, an elastic modulii of the constituents materials and a layup sequence, the processor determining the fiber volume fraction and the resin porosity of the composite material using the velocities, V.sub.1 and V.sub.2, the thickness of the composite material, the density, the elastic modulii of the constituent materials and the layup sequence.