Detection of thermal damage of composites using molecular probes

Abstract

Improved methods of detecting thermal exposure are provided herein. The provided methods utilize initially dormant luminescent probes incorporated into a matrix to form a composite. When exposed to heat over a period of time, the luminescent probes are “activated” through a molecular transformation initiated by thermal energy. The activated probes exhibit a luminescent profile based on the extent of thermal exposure, thereby providing an indicator of the thermal exposure experienced by the matrix. When the composite is used to produce a structural component of a vehicle (e.g., an aircraft), the methods provide a convenient, large-area indicator of thermal damage experienced by the structural component.

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows: 
     
         1 . A method of monitoring thermal exposure of a composite, comprising:
 (a) providing a composite, comprising:
 (i) a matrix; and 
 (ii) a first probe, wherein the first probe is not luminescent until activated by heat to a temperature above 200° C., after which it becomes luminescent and has a first luminescence profile; 
   (b) exposing the composite to a time-temperature profile that includes a portion of time at a temperature above 200° C.; and   (c) measuring an optical property of the composite.   
     
     
         2 . The method of  claim 1 , wherein the matrix is selected from the group consisting of a thermoset polymer, a thermoplastic polymer, and a sol-gel. 
     
     
         3 . The method of  claim 1 , wherein the optical property is stimulated emission of the first probe. 
     
     
         4 . The method of  claim 1 , wherein the first probe is fluorescent or phosphorescent. 
     
     
         5 . The method of  claim 1 , wherein the matrix is transparent at wavelengths within the first luminescence profile. 
     
     
         6 . The method of  claim 1 , wherein the first probe is incorporated within the matrix. 
     
     
         7 . The method of  claim 1 , wherein a coating on the matrix comprises the first probe. 
     
     
         8 . The method of  claim 1 , wherein the time-temperature profile comprises a rise in temperature from a first temperature to a second temperature between a first time and a second time. 
     
     
         9 . The method of  claim 8 , wherein the time-temperature profile comprises temperature variations. 
     
     
         10 . The method of  claim 8 , wherein the time-temperature profile comprises repeated temperature cycles. 
     
     
         11 . The method of  claim 1 , wherein the composite further comprises a second probe. 
     
     
         12 . The method of  claim 11 , wherein the first probe and the second probe combine to be a time-temperature indicator of thermal damage. 
     
     
         13 . The method of  claim 11 , wherein the optical property is the combined stimulated emission of the first probe and the second probe. 
     
     
         14 . The method of  claim 1 , further comprising a step of analyzing the optical property to determine thermal exposure of the composite. 
     
     
         15 . The method of  claim 14 , wherein the step of analyzing the optical property comprises comparing the optical property to a calibration data set. 
     
     
         16 . The method of  claim 1 , wherein the matrix further comprises carbon fibers. 
     
     
         17 . The method of  claim 16 , wherein the matrix is a carbon-fiber reinforced plastic composite. 
     
     
         18 . The method of  claim 1 , wherein the composite is a structural component of a vehicle. 
     
     
         19 . The method of  claim 18 , wherein the composite is a structural component of an aircraft.