Detection of Delamination in Carbon-Fibre-Reinforced Polymers with Lock-In Thermography

Abstract

Attention of this paper is devoted to testing and evaluation of carbon-fibre-reinforced polymer specimens with lock-in thermography. Several specimens were prepared by a vacuum infusion technique using a low-viscosity epoxy system; delaminated areas were simulated by the insertion of thin Kapton® diskettes at a given depth through the thickness. Artificial defects had different shapes (circular or elliptical) and dimensions. Inserts were located at different depths and, in some cases, by overlapping more than one Kapton®-shaped layer (i.e. two or more concentric discs, each of different diameter). A preliminary test campaign was performed by differential scanning calorimetry and rheometry to find optimal processing parameters to achieve fully cured state of matrix and to avoid the formation of defects in accordance with aerospace standards for composites manufacturing. Specimens were non-destructively inspected with optical lock-in thermography; results were presented in terms of phase images. All inserts were discovered and also well outlined under difficult conditions such as in the case of thin overlapped foils.

The design of infrared non-destructive testing for investigation multi-layer materials

“…(3) implies that the transfer function depends on the excitation frequency through 1 . In other words, the parameter 1 is the nondimensional equivalent of .…”

“…Material, civil and aerospace engineering are some of the application areas of infrared thermography [1], [2], [3]. The inspection becomes more challenging for composite and multi-layer materials especially in the field of aerospace [4].…”

Determination of the modulation frequency for thermographic non-destructive testing

“…Nondestructive testing techniques based on infrared thermography find application in several fields such as structural and civil engineering [1,2], with application to restoration and maintenance of historical structures [3,4]; material and aerospace engineering [5][6][7]; and evaluation of safety and reliability (quality control) in manufacturing [8]. Detecting the characteristics of a possible defect in a reasonably short time can be crucial for processes cost effectiveness and minimization of human life threats in working environments [9].…”

“…Specifically, infrared thermography is an inspection method in nondestructive testing to detect a defect on the surface and the subsurface of a material body [17]. Active infrared thermography [6,[18][19][20] refers to a class of detection techniques in which an infrared camera captures images of the surface of a material body rendering the temperature distribution corresponding to a periodic boundary excitation, and identifies possible anomalies by detecting patterns associated with reflected thermal spatial transients. Detection techniques depend on several parameters such as thermal conductivity, heat capacity, and defect depth as internal factors and convection heat transfer, variation on surface emissivity, and ambient radiation reflectivity as external factors [17].…”

Analytical and simulation investigation of the experimental design for infrared non destructive testing

“…Nondestructive testing techniques based on infrared thermography find application in several fields such as structural and civil engineering [3], [4] also applied to restoration and maintenance of historical structures [5], [6], material and aerospace engineering [7], [8], [9], and evaluation of safety and reliability in manufacturing (quality control) [10]. Detecting the characteristics of a possible defect in a reasonably short time can be crucial for processes cost effectiveness and minimization of human life threats in working environments [11].…”