Monitoring a structure for damage

2:

• The structure according to claim 1, in which the variation in surface characteristics comprises cracking of the surface to an extent dependent upon the degree and/or type of damage to the structure.

3:

• The structure according to claim 1, in which the coating is a glassy polymer.

4:

• The structure according to claim 1, in which the coating is a thermoset polymer.

5:

• The structure according to claim 1, in which the coating is a mixture of polymers and fillers.

6:

• The structure according to claim 1, in which the coating is a cementitious ceramic.

7:

• The structure according to claim 1, in which the characteristics of the surface of the coating vary with damage to the structure which includes impact damage, damage due to compressive or tensile loading above a certain threshold or damage due to repeated loading below the said threshold.

8:

• The structure according to claim 1, in which a said conductive track is formed on the surface of the coating by a direct write process.

9:

• The structure according to claim 1, comprising a protective helmet in which the coating is applied to an interior surface of the helmet.

10:

• The structure according to claim 1, comprising an aircraft structural component.

11:

• The structure according to claim 1, in which the coating includes crack initiation means.

12:

• The structure according to claim 11, in which the crack initiation means comprises particulates in the coating.

13:

• The structure according to claim 11, in which the crack initiation means comprises voids in the coating.

14:

• The structure according to claim 11, in which the crack initiation means comprises micro-cracking in the coating.

15:

• The structure according to claim 1, in which the coating is calibrated whereby to display the said variation in characteristics in response to a defined state of damage.

16:

• The structure according to claim 1, in which the series of conductive tracks comprises a grid array disposed across the structure.

17:

• The structure according to claim 16, including a series of electrical connections positioned around a periphery of the grid array and monitoring means connected via said connections to the grid array, the monitoring means being adapted to interrogate the grid array whereby to determine a location on the structure of any said damage.

18:

• The structure according to claim 17, in which the monitoring means is arranged to interrogate the grid array during use of the structure.

19:

• A method of testing a structure for damage, the method including the steps of providing the structure with a coating defining a surface and having a series of conductive tracks applied to the surface in intimate contact therewith, the surface having specific failure characteristics tailored to the structure which vary in a predetermined manner with damage to the structure and the resistance of the series of conductive tracks being made variable in known relationship with the variation in surface characteristics of the surface, including measuring an electrical parameter of the series of tracks and comparing the measured parameter with the same parameter of the tracks when measured for the undamaged structure.

20-22. (canceled)

23:

• The method according to claim 19 in which the parameter measured is resistance.

24:

• The method according to claim 19, in which the series of conductive tracks comprises a grid array having a series of electrical connections positioned around a periphery of the grid array and the method includes the step of operating monitoring means connected via said connections to the grid array to interrogate different combinations of connections whereby to determine a said electrical parameter for each combination followed by analysis of said parameters to determine a location on the structure of any said damage.

25:

• The method according to claim 24, in which determination of the location on the structure of any damage by analysis of the parameters includes making reference to results of previous calibration data for the structure.