Mechanoluminescence paint sensor for stress and crack visualizations

Abstract

A method of using a paint sensor to observe stress distributions of a stressed substrate includes the steps of applying a composition including a paintable medium and a mechanoluminescence material to a substrate, allowing the composition to form a solid film on the substrate, allowing the substrate to be stressed following the formation of the solid film, and measuring the stress the substrate has undergone by determining the mechanoluminescence of the solid film. A composition for visualizing stress or crack distributions includes a paintable medium and a mechanoluminescence material dispersed therein.

Claims

1. A method of using a paint sensor to observe stress distributions of a stressed substrate comprising providing a composition comprising a paintable medium and a mechanoluminescence material; applying the composition to a substrate having one or more curved surfaces; allowing the composition to form a flexible solid film on the substrate, wherein the flexible solid film is optically transparent at wavelengths from 400 nm to 1000 nm; and allowing the flexible solid film on the substrate to be stressed, thereby allowing the flexible solid film to visualize crack distributions within the substrate by mechanoluminescence of the flexible solid film.

2. The method of claim 1, wherein the step of allowing the substrate to be stressed includes applying a mechanical force to the substrate.

3. The method of claim 1, wherein the step of allowing the substrate to be stressed includes allowing the stress to occur over a predetermined interval, and wherein the crack distributions are observed over the predetermined interval.

4. The method of claim 1, wherein the solid film does not crack or become brittle following said step of allowing the substrate to be stressed.

Description

EXAMPLE

Example 1

(1) As one example for demonstrating the present invention, commercial SAOED powder materials (LumiNova G-300M, United Mineral & Chemical Corporation) were used to manufacture thin ML sensing film. The SAOED powder was mixed with a commercial optical epoxy resin (West System 105 Epoxy Resin and West System 206 Slow Hardener) and thin ML sensing film with a thickness of 0.02 inches was manufactured by the doctor blade method. The mass ratio of the epoxy resin to the SAOED powder was 3:1, and the powder was dispersed uniformly in the epoxy using a magnetic stirrer. Standard dog-bone shaped aluminum (Al) specimens were coated with the cut ML sensing film by using a commercial adhesive (M-Bond 200 from Micro-Measurements). During tension tests of the coated Al specimens, images were obtained at a fixed frame per second by using a charge-coupled device (CCD) camera (AVT Manta G-033B) with a consistent gain level setting, and Vision Builder AI software (National Instruments) was used for capturing the images. The camera was positioned approximately 26 cm from the specimen with an exposure time of 0.1 ms and 10 fps. Using an Instron digital input/output board, the CCD camera and controller of the Instron testing machine (220 kips) were synchronized to achieve a perfect coincidence between the captured images and the load step data.

(2) Once the images and the load step data were obtained, MATLAB software was used to carry out the image processing. In the first step of the image processing, all images were sorted by time. The gray level images were then read and converted to pixel values. An area on the ML film image was selected, and the average value of light intensities in the area was used for calculations. The area integration of the gray level value on the specimen divided by the region of interest yields an average value of the ML light intensity corresponding to the stresses acting on the ML film. Since the frame rate was fixed at 10 fps, light intensity versus time could be drawn for each time step (0.1 s). This data was synchronized with the load step data to obtain the light intensity-force (i.e. stress) curves.

(3) The ambient light from the environment was completely blocked to minimize errors and inconsistencies of the ML light intensity during the test. The ML sensing film was consistently excited with a 40-watt commercial lamp; two minutes was sufficient for acquiring fully photoexcited ML light intensity. However, even if it is not fully photoexcited (i.e. charged), the ML sensing film can still emit light under mechanical stresses because the mechanical stress is one of the excitations that generate separated charges (i.e. electrons-holes) similar to photoexcitation. If it was not fully photoexcited, changes of the ML light intensity may not be consistent due to different initial ML light intensity and effects of stress-free PL decay. Therefore, before any tests were carried out, the ML sensor was fully photoexcited. The wavelength of the excitation light source was between 400 and 1000 nm and the wavelength peak was around 600 nm. After full excitation, stress-free persistent luminescence (PL) light was emitted that displayed a naturally decaying intensity with respect to time. The maximum load was limited to 15 kN (230 MPa on an aluminum specimen) so that the aluminum specimen was within the linear elastic range. The maximum load was applied at different strain rates and different stress-free PL decay time intervals. For example, after full photoexcitation of the ML sensing film, the different time intervals were elapsed until the onset of the loadings.

(4) In light of the foregoing, it should be appreciated that the present invention significantly advances the art by providing an improved compositions comprising a paintable medium and a mechanoluminescence material and associated methods of use. While particular embodiments of the invention have been disclosed in detail herein, it should be appreciated that the invention is not limited thereto or thereby inasmuch as variations on the invention herein will be readily appreciated by those of ordinary skill in the art. The scope of the invention shall be appreciated from the claims that follow.