MONITORING DEVICE FOR DETECTING STRESS STRAIN AND METHOD FOR USING SAME

• US 20090310120A1
• Filed: 06/10/2009
• Published: 12/17/2009
• Est. Priority Date: 06/16/2008
• Status: Active Grant

• Current Assignee: Simpson Strong-Tie Company Incorporated (Simpson Manufacturing Company Incorporated)
• Original Assignee: Duhane Lam, Mark Ellens
• Inventors: Lam, Duhane, Ellens, Mark
• Granted Patent: US 8,525,979 B2
• Time in Patent Office: Days
• US Class Current: 356/35
• CPC Class Codes: G01B 11/168 by means of polarisation

Abstract

The present invention provides a monitoring device for detecting stresses and strains in structural components and a method of using the monitoring device. The monitoring device comprises a base material, one or more attachment points for attaching the monitoring device to a structure to be monitored, a detection zone on the monitoring device, and a means for detecting the presence of stress and strain in the detection zone. The dimensions and material of the monitoring device are chosen such that a predetermined level of strain transmitted to the monitoring device from the structure will result in a known level of stress and strain in the detection zone. Detection of stress and strain in the detection zone can be correlated to a level of stress and strain experienced by the structure at the point of attachment of the monitoring device.

Claims

1. A monitoring device for detecting stress and strain in a structure, said monitoring device comprising a base material, one or more attachment points for attaching said monitoring device to said structure, a detection zone, and a means for detecting the presence of stress and strain in said detection zone;

said base material and the dimensions of said monitoring device chosen so that a predetermined level of strain transmitted to said monitoring device by said structure through said attachment points results in a known level of stress and strain in said detection zone.

2. The monitoring device according to claim 1, wherein said base material and said dimensions are chosen so that a predetermined level of strain transmitted to said monitoring device by said structure through said attachment points causes plastic deformation in said detection zone.

3. The monitoring device according to claim 1, wherein said means for detecting stress and strain in said monitoring device comprises a photoelastic layer applied to said detection zone.

4. The monitoring device according to claim 3, wherein said photoelastic layer comprises a coating applied as a dry powder and fused together with heat to form a continuous coating.

5. The monitoring device according to claim 1, wherein said base material comprises a material with photoelastic properties, said material providing said means for detecting stress and strain in said monitoring device.

6. The monitoring device according to claim 3, wherein said monitoring device comprises an integrated polarizer attached on top of at least a portion of said photoelastic layer.

7. The monitoring device according to claim 1, wherein said means for detecting stress and strain comprises a strain gauge applied to said detection zone.

8. A monitoring device for detecting vibration or shock loads in a structure, said monitoring device comprising a base material, one or more attachment points for attaching said monitoring device to said structure at one end of said device, a free end, a detection zone, and a means for detecting the presence of stress and strain in said detection zone;

said base material and the dimensions of said monitoring device chosen so that a predetermined level of vibration transmitted to said monitoring device by said structure through said attachment points results in plastic deformation in said detection zone.

9. The monitoring device according to claim 8, wherein said means for detecting stress and strain in said monitoring device comprises a photoelastic layer applied to said detection zone.

10. The monitoring device according to claim 9, wherein said photoelastic layer comprises a coating applied as a dry powder and fused together with heat to form a continuous coating.

11. The monitoring device according to claim 8, wherein said base material comprises a material with photoelastic properties, said material providing said means for detecting stress and strain in said monitoring device.

12. The monitoring device according to claim 9, wherein said monitoring device comprises an integrated polarizer attached on top of at least a portion of said photoelastic layer.

13. A method for monitoring stress and strain in a structure or part comprising:

a. Providing a monitoring device for detecting stresses and strains comprising one or more attachment points for attaching to a structure, said monitoring device designed to exhibit a certain level of strain or to deform plastically when said monitoring device is subjected to a predetermined amount of strain through said attachment parts,

b. Providing a means for detecting strain in or on said monitoring device,

c. Attaching said monitoring device to said structure to be monitored,

d. Inspecting said structure by observing or measuring said monitoring device to determine whether said monitoring device is experiencing a certain level of strain or has deformed plastically in said detection zone,

Whereby strain or plastic deformation in said detection zone on said monitoring device indicates that said structure has experienced a stress strain level in excess of said predetermined amount.

14. The method according to claim 13, further comprising forming said monitoring device out of a photoelastic material.

15. The method according to claim 13, further comprising providing a photoelastic layer on top of at least a portion of said detection zone on said monitoring device.

16. The method according to claim 15, wherein the step of providing a photoelastic layer on top of at least a portion of said detection zone on said monitoring device comprises the step of applying a dry powder to said monitoring device and fusing said powder using heat to form a continuous coating.

17. The method according to claim 14, wherein the step of providing a means for detecting plastic deformation in said monitoring device comprises the step of providing an integrated polarizer attached permanently on top of at least a portion of said detection zone.

18. The method according to claim 14, wherein the step of detecting strain in said monitoring device comprises the steps of:

a. Illuminating the device with polarized light

b. Viewing the device through a polarizing filter

c. Observing for the absence or presence of fringe patterns in the reflected light

Whereby the presence of fringe patterns indicates that elastic strain or plastic deformation is present, and that the stresses and strains in said structure to be monitored have exceeded said predetermined amount.