Abstract
Measuring small-magnitude strain fields using a digital image correlation (DIC) technique is challenging, due to the noise-signal ratio in strain maps. Here, we determined the level of accuracy achievable in measuring small-magnitude (<0.1%) homogeneous strain fields. We investigated different sets of parameters for image processing and imaging pre-selection, based on single-image noise level. The trueness of DIC was assessed by comparison of Young’s modulus (E) and Poisson’s ratio (ν) with values obtained from strain gauge measurements. Repeatability was improved, on average, by 20–25% with experimentally-determined optimal parameters and image pre-selection. Despite this, the intra- and inter-specimen repeatability of strain gauge measurements was 5 and 2.5 times better than DIC, respectively. Moreover, although trueness was also improved, on average, by 30–45%, DIC consistently overestimated the two material parameters by 1.8% and 3.2% for E and ν, respectively. DIC is a suitable option to measure small-magnitude homogeneous strain fields, bearing in mind the limitations in achievable accuracy.
Highlights
IntroductionCalcium phosphate cements (CPCs) are bone substitute materials used for tissue defects filling [1]
Calcium phosphate cements (CPCs) are bone substitute materials used for tissue defects filling [1]. they should mimic the mechanical behavior of bone tissue, their mechanical properties are still far from optimal
The present studywith investigated the suitability for measuring small-magnitude, The present study investigated the suitability of for measuring small-magnitude, homogeneous strain field, by experimentally determining the accuracy achievable using digital image correlation (DIC) to homogeneous strain field, by experimentally determining the accuracy achievable using
Summary
Calcium phosphate cements (CPCs) are bone substitute materials used for tissue defects filling [1]. They should mimic the mechanical behavior of bone tissue, their mechanical properties are still far from optimal. CPCs are brittle [2,3,4], and the limited data available in the literature suggests that this material can only withstand small strain levels (range 0.1–0.2%) before failure [5,6]. CPC testing is performed on small specimens (typically up to 20 mm in their largest dimension) [8,9,10]. Measuring strain values the material undergoes to during testing is useful to compare different formulations of CPCs regarding elastic response and toughness enhancement. Contact-type extensometers cannot be used, because the knife edges would damage the specimen surface
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