Abstract
The thermoelastic response obtained from an infra-red (IR) detector contains two components: the magnitude of the small stress induced temperature change caused by the thermoelastic effect and the phase angle of the temperature change relative to a reference signal generated by an application of a stress change. The phase angle is related to nonlinearity in the thermoelastic response and departures from the simple linear relationship that underpins thermoelastic stress analysis (TSA). The phase data could be used to make an assessment of temperature evolutions caused by viscoelastic behaviour resulting from damage and provide a basis for its evaluation. In the current paper the physics of other infra-red techniques used for non-destructive evaluation is used to better understand the nature of the thermoelastic response. The objective is to provide better exploitation of TSA by alternative processing of the IR measurements. Three case studies are presented that demonstrate the potential of the alternative processing for evaluating damage.
Highlights
The detection and qualification of damage in engineering materials and structures presents an ongoing challenge
Placed in the wider context of infra-red (IR) thermography techniques currently used in non-destructive evaluation (NDE), the ultimate aim is to combine pulsed phase thermography (PPT) and acoustic or vibro-thermography (VT) with thermoelastic stress analysis (TSA) to enhance NDE procedures
In the TSA data it can be seen that the weft yarns have the larger thermoelastic response, despite the majority of the stress being carried by the warp yarns [13]
Summary
The detection and qualification of damage in engineering materials and structures presents an ongoing challenge. There are many tools and many different approaches for assessing damage evolution One such technique is thermoelastic stress analysis (TSA). One reason for the lack of applications in the field is the challenge of applying the technique without the application of a cyclic load This topic has been examined in [5] and more recently in [1]. As the most notable cause of nonlinearity in the thermoelastic response results from heat transfer, a means of separating the adiabatic and non-adiabatic processes is necessary. This may be achieved by utilising the phase. The third example examines the absolute temperature field as damage evolves under low cycle fatigue
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