Assessment of fatigue damage evolution in woven composite materials using infra-red techniques

Abstract

Please cite this article as: Fruehmann, R.K., Dulieu-Barton, J.M., Quinn, S., Assessment of fatigue damage evolution in woven composite materials using infra-red techniques, Composites Science and Technology (2010), doi: 10.1016/ j.compscitech.2010 This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain. ACCEPTED MANUSCRIPT 1 ASSESSMENT OF FATIGUE DAMAGE EVOLUTION IN WOVEN COMPOSITE MATERIALS USING INFRA-RED TECHNIQUES ABSTRACTThermoelastic stress analysis (TSA) is used to study the growth of fatigue damage in single and two ply, 2 x 2 twill woven composite materials. Test specimens were subjected to a uniaxial tensile cyclic loading with maximum stresses of 10, 15 and 20% of the ultimate failure stress. The development of fatigue damage locally within the weft yarns is monitored using high resolution TSA. The specimens were subsequently inspected using optical microscopy to evaluate the location and extent of cracks.Cracks were found in the weft fibres, running transverse to the loading direction. It is demonstrated that the lighter weight fabric is more resilient to damage progression. A signature pattern is identified in the TSA phase data that indicates the onset and presence of fatigue damage in the composite material.

Data-rich characterisation of damage propagation in composite materials

“…ΔT values were divided by the mean temperature T0 at each pixel location to give a normalised thermoelastic response (ΔT/T0). Expressing the thermoelastic response in the form ΔT/T0 is useful as it makes account of any changes due changes in room temperature or because of localised heating at damage sites [9], but not heat transfer. K1 and K2 were not evaluated as they are coupled with the stresses (see equation (1)) and it is not possible to extract these directly from the ΔT/T0 data.…”

“…[10,11], where the images captured were under sampled and correlated with the cyclic load to reconstruct the overall strain change necessary to perform the DIC over a number of cycles. Likewise [9] is an example of where TSA has been used to evaluate fatigue damage progression. However, in the present work the aim is to capture both the IR data used for the TSA and the DIC data from a cyclically loaded specimen in a synchronised fashion without the need to pause the data collection.…”

Fatigue Limit Evaluation of Composite Materials by Means of TSA

“…Whilst phase can slightly change through analysed area due to nonperfect homogeneity of the surface conditions, it remains locally constant in presence of linear elastic behaviour of material and thus, if adiabatic conditions are achieved. If damage occurs, non-linearity of thermoelastic signal and phase variations can be observed [14].…”

“…Fruehmann et al [14] discuss the use of the phase signal for detecting fatigue damage at low stress amplitude, as well, is highlighted.…”

“…Infrared Thermography Technique (IRT) has been exploited to better understand fatigue damage on different type of materials: such as metals and composites [8][9][10]. Moreover several methods and data analysis have been developed to obtain the information about the fatigue behaviour by studying heat sources generated during tests [11][12][13][14][15]. Graphical method to assess fatigue limit in metals has been proposed by Luong [16] and Risitano [17], by adopting the surface temperature detection in samples during a stepwise loading procedure.…”