Engineering
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Mechanoluminescent Visualization of Crack Propagation for Joint Evaluation
Chapters
Summary January 6th, 2023
In this study, a protocol is presented that describes the use of mechanoluminescent (ML) visualization for monitoring crack propagation and mechanical behavior during adhesive joint evaluation testing.
Transcript
To utilize mechanoluminescent sensing result errors, this protocol shows that preparation of the mechanoluminescent sensor, the kinds of measurement environment, and the recording conditions that should be adopted for repeatabilities. The advantage of this method is direct visualization of the crack tip and strength, stress distribution, and concentration in mechanical stimuli which are originally difficult to quantify directly. This protocol focuses on visualizing mechanical information during adhesive evaluation test.
It can also be utilized for structural health monitoring, design, and mechanical stimulation of structure, structural material, and joints. Demonstrating the procedure for spraying ML paint will be Yumi Nogami. And for DCB and Lap-Shear test will be Wakana Sugawa, Chieko Hirakawa, Maiko Iseki, and Yoko Sakamoto, technical stuff of my laboratory.
To begin, prepare the test specimen by applying the mechanoluminescent paint on the pretreated surface of the Double Cantilever Beam, or DCB, with an air spray or spray can. Next, make the experimental setup for the mechanoluminescent measurement by mounting the mechanoluminescent paint sprayed specimen onto the mechanical testing machine using a special zig. Place the cameras in front of each test specimen surface facing the position of the crack tip to be monitored.
Then check the camera conditions to ensure that it can record the afterglow during the estimated measurement time of the mechanical testing. To perform mechanoluminescent observation in the DCB test, set the camera's recording rate to one or two frames per second, exposure time to 0.5 or one second, and gain to the maximum. Next, irradiate the mechanoluminescent paint sprayed DCB specimen with 470 nanometer blue light for excitation using a blue LED from every camera direction for one minute.
Start the camera recording five seconds before finishing the blue light irradiation. Let the specimen remain in the dark for one minute to ensure that the afterglow settles down. Then apply a mechanical load using a mechanical testing machine with a loading rate of one millimeter per minute to obtain the mechanoluminescent image.
Calculate the crack length by using the information on the crack tip position which is determined from the mechanoluminescent point during crack propagation in the mechanoluminescent paint sprayed specimen to obtain the fracture toughness G1C expressed in kilojoules per square meter using the equation. To perform the mechanoluminescent observation in the Lap-Shear test, set the camera recording rate to 10 to 50 frames per second, Exposure time to 0.02 or 0.1 seconds, and gain to the maximum. Then irradiate the mechanoluminescent paint sprayed DCB specimen with 470 nanometer blue light, start the camera recording, and wait in the dark condition as demonstrated earlier.
Apply a mechanical load with a loading rate of one to five millimeters per minute to obtain the mechanoluminescent image. The recorded mechanoluminescent behavior during the DCB test showed intense mechanoluminescence at the position of the initial crack due to the strain concentration. The recorded mechanoluminescent behavior during the Lap-Shear test showed intense mechanoluminescence first at the edges of the adhesively bonded in lapped areas and then the mechanoluminescent points moved from the adhesive edges to the center with intense mechanoluminescence seen at the center point.
The most important things to remember should be balance of the performance of mechanoluminescent sensor film. Waiting time until mechanical eroding and the recording conditions. Joint and composite material in light weighting structure are known as difficult part to simulate mechanical behavior.
The mechanoluminescent visual sensing method provide a real and right answer to read appropriate design and prediction.
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