Abstract

A Digital Image Correlation (DIC) based method is proposed to characterize Mode I fatigue delamination onset and propagation in laminated composites. With the help of DIC, the displacement field around a delamination crack is obtained and further processed to determine the position of the crack tip. With this method the delamination length can be measured automatically in each cycle with a precision on the order of few hundreds of micrometers. The fatigue delamination onset life is then determined by detecting the increase of the delamination length, and the fatigue delamination propagation rate is calculated. The proposed method produces more conservative fatigue life measurements in comparison with the compliance increase method in ASTM D6115.

Highlights

  • Digital image correlation (DIC) is a popular tool to measure deformation on the surface of a material

  • The crack tip detection with Digital Image Correlation (DIC) was applied to nine different tests, and the initial crack tip position measured from the first cycles, a0(DIC), was recorded

  • The fitted initial crack length, a0(Fitting), was used to verify the accuracy of Equation (1). It indicates that DIC detection and fitted initial crack length both exhibit a good accuracy, which differs from microscope observation by less than 0.36 mm

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Summary

Introduction

Digital image correlation (DIC) is a popular tool to measure deformation on the surface of a material. One of its appealing features is the capability to detect highly heterogeneous displacement fields and strain maps. This advantage makes DIC interesting for characterization of materials that involve discontinuities, for example, for estimation of stress intensity factors [1], detection of the crack path [2] and general observation of failure in composites [3,4]. Fatigue delamination onset and propagation tests are commonly adopted to measure the number of cycles to onset the delamination (N) and the rate of its propagation under certain levels of load. The fatigue delamination onset test for Mode I is commonly performed according to ASTM D6115 standard [5], which is the only standard available to characterize fatigue delamination in composites

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