Nondestructive test for flexible composites
View Patent ↗A method for testing internal differences in reinforced flexible composites including placing a flexible composite on a rigid support structure, tapping the composite with a tapper of predetermined mass, determining a value representative of the impact duration of the tap and/or computing a value representative of the local stiffness of the composite. The composite may be a power transmission belt or portion thereof with tensile cord reinforcement. The method is useful for comparing the degree of penetration of elastomer into the tensile cord, for example in a cast polyurethane toothed belt.
1. A method of testing internal structural variations within a flexible, elastomeric-matrix, composite article comprising an elastomeric matrix and a reinforcing fiber structure embedded therein, said method comprising the steps of:
mounting said composite article in a fixed position;
tapping the article;
determining the impact duration of the tap; and
comparing the impact duration to a reference value.
2. The method of claim 1 further comprising computing a value representative of the local stiffness of the article from the impact duration to be used in said comparison.
3. The method of claim 1 wherein said comparison indicates degree of penetration of said elastomeric matrix material into said reinforcing fiber structure.
4. The method of claim 1 wherein said composite article is a power transmission belt reinforced with tensile cord embedded in said belt.
5. The method of claim 1 wherein said mounting includes pre-stressing the article.
6. The method of claim 5 wherein said pre-stressing is a bending stress.
7. The method of claim 1 wherein said mounting includes placing a portion of the article to be tested on a rigid support structure for support in a substantially unstressed state.
8. A method of testing internal structural variations comprising:
placing a flexible, elastomeric-matrix, composite article on a rigid support structure,
tapping the composite with a tapper of predetermined mass,
determining a value representative of the impact duration or contact time of the tap, and
comparing the impact duration or contact time to a reference value;
wherein the composite article comprises an elastomeric matrix and a reinforcing fiber structure embedded therein.
9. The method of claim 8 further comprising computing a value representative of the local stiffness of the composite.
10. The method of claim 8 wherein the tapper comprises an accelerometer.
11. The method of claim 8 further comprising repeating the tapping at various points over a predetermined area and producing a graphical representation of the stiffness over that area.
12. The method of claim 8 wherein the flexible, elastomeric-matrix, composite article is a power transmission belt or a portion thereof.
13. The method of claim 12 wherein the support structure is a pulley.
14. The method of claim 8 wherein the flexible, elastomeric-matrix, composite article is a belt slab or a portion thereof.
15. The method of claim 8 wherein the flexible, elastomeric-matrix, composite article is a toothed power transmission belt, and the support structure provides support in a land region between two belt teeth, and the tap is directed over the supported land region.