On the application of liquid‐crystal thermography for the nondestructive detection of delamination in composite structures

Abstract

To prevent the catastrophic failure of composite structures, several nondestructive testing methods have been developed. In this study, a new technique to evaluate these structures by using thermochromic liquid crystal (TLC) thermography is presented. Temperature gradients produced by sensitive liquid-crystals are used to detect delamination in composite specimens. The effects of constituent materials and delamination size/location are investigated. The results from TLC thermography are compared to those from infrared thermography. Finally, advantages/disadvantages of the new method are discussed. On the basis of the results from this study, it could be concluded that the TLC thermography can be used as an inexpensive nondestructive testing method in inspection of composite structures. POLYM. COMPOS.,

A Survey of Scrutinizing Delaminated Composites via Various Categories of Sensing Apparatus

“…Results obtained from the application of different thermography techniques on composite structures are here provided. Starting from the upper leaves of thermography in Figure 3, LC thermography technique has been applied for artificial delamination detection within CFRP and GFRP laminates in comparison to IR thermography [15]. Liquid-crystal was applied on the black-painted side of the specimen while heat flow occurs through the thickness.…”

“…Visible liquid-crystal (LC) thermography acts based on the fact that LCs having a dynamic phase between solid and liquid exhibit phase transitions against temperature changes, reflecting visible colors [15]. In [15], LC is sprayed on one side of the sample coated with paint and the other side is heated. Temperature maps appeared in the form of visible lights are captured by a color camera.…”

“…Thermographic inspection is applied for detection of composite structures by measuring thermal (electromagnetic) radiation patterns emitted through the object's surface [18]. Arrangements of data acquisition system and excitation source in the thermography process are organized into (a) reflection mode, in which both infrared camera and excitation source are placed on one side of the specimen [15,34], and (b) transmission mode, in which infrared camera and excitation source are on the opposite sides [20,24]. Due to lacking direct access to both sides of a specimen in most applications, reflection mode has extensively been investigated in the literature.…”

Strength prediction and experimental damage investigations of plain woven CFRPs with interacting holes using multi‐instrument measurements

“…IRT is a non‐destructive test method which detects infrared energy emitted from an object, changes it to temperature, [ 36,37 ] and shows an image of temperature distribution. [ 38 ] Passive IRT is used in this study to record the temperature of the sample during the mechanical testing.…”

Detection of flaws in a two-dimensional body through measurement of surface temperatures and use of conjugate gradient method

“…In this method, heat load is applied to a test case and the temperature distribution is visualized using special infrared cameras. By analyzing the temperature distribution in the test case, existence of flaws can be identified [3]. The main advantage of this method is the fact that no damage can be inflicted to the material during testing; however the method is unable to determine the exact location and the size of the flaw in 3D domain.…”