Infrared Thermography for Inline Monitoring of Glass/Epoxy under Impact and Quasi-Static Bending

Abstract

Featured Application: The scope of this work is to show the potential of infrared thermography to collect important information to be exploited for the characterization of new composite materials. An infrared imaging device can be included in most mechanical test setups for the in-line monitoring of samples undergoing either impact or quasi-static bending, or else fatigue tests. As an important assertion, the use of infrared thermography allows for fast inspection of relatively large surfaces in a remote way without any alteration of the inspected part and without safety-at-work concerns.Abstract: In this work, glass/epoxy has been chosen as case study as it represents the most-used composite material, being appropriate for a vast variety of applications and a reasonable performance/cost compromise. This material has already been inline impact-monitored with infrared thermography, mostly for feasibility tests. Now, impact tests are repeated by changing some parameters and by inline monitoring simultaneously with two different infrared cameras to share a high frame rate and spatial resolution at the same time. In addition, glass/epoxy is monitored also while it is under quasi-static bending tests. The aim of this paper is to show what it is possible to learn from thermal signatures developing in the same material when it is either impacted or under quasi-static bending.

The Contribution of Infrared Thermography to Impact Testing of Composite Materials†

“…As an example, some ∆T images, taken with the SC6800 infrared camera at a frame rate of 960 Hz, are shown in Figure 2. These images are relative to a glass/epoxy (GFRP) specimen impacted at energy E = 8.3 J [6]. As expected, the first image (Figure 2a), taken before impact, displays a surface at an almost uniform ΔT = 0 value.…”

“…Finally, the dark zone is replaced by a warm zone (Figure 2f) which accounts for the whole extension of the damage. The ∆T images can be further post-processed and analysed to get valuable information about: initiation, propagation and extension of impact damage and about the characteristic times of the material's reaction to the impact [3,6]. In particular, the characteristic times when the hammer gets in touch with the specimen surface and when it leaves that surface can be evaluated by focusing the attention on cooling phenomena.…”

“…Of relevance is the possibility to detect the impact damage [3][4][5] since composites, especially the thermoset matrix-based ones, could be severely damaged without any visible sign. In addition, as demonstrated by Meola et al [3,6], monitoring specimens under mechanical tests with infrared thermography allows to get information which can help understanding the material behavior under load. As an important result, from the surface temperature map, it has been possible to distinguish between the impact coupled effects and secondary effects induced by the fixture, which could contribute to the whole damage extension and which are difficult to be recognized and excluded a posteriori after impact [7].…”

The Contribution of Infrared Thermography in the Characterization of Glass/Epoxy Laminates through Remote Sensing of Thermal-Stress Coupled Effects

“…A glass fiber reinforced polymer (GFRP) including unidirectional E-glass fibers and low viscosity epoxy resin is herein considered [3]. More specifically, 8 epoxy impregnated E-glass plies are hand lay-up stacked at [0°2, 90°2]s to obtain an overall sample thickness of 2.9 mm; curing is performed under press at ambient temperature.…”

Special Issue on ‘Novel Ideas for Infrared Thermography and Its Application to Integrated Approaches’

“…Meola et al selected glass/epoxy for impact tests by changing, with respect to previous analyses, some parameters and by inline monitoring simultaneously with two different infrared cameras to share a high frame rate and spatial resolution at the same time. In addition, the same material was monitored during quasi-static bending tests, by showing that it is possible to learn from thermal signatures when glass/epoxy is either impacted or under quasi-static bending [18].…”