Evaluation of the advanced artificial athlete and Hall effect sensors for measuring strain in multi-layer sports surfaces

Computer models are a useful means to explore the loading behaviour of third generation (3G) artificial turf sports surfaces; however, measuring the material stress–strain behaviour under realistic high loading rates is challenging. Therefore, the purpose of this study was two-fold: to evaluate the advanced artificial athlete (AAA) for measuring strain behaviour of polymeric sports surfaces under high loading rates typical of player interactions; and to evaluate Hall effect sensors (HES) for measuring strain behaviour of an individual layer within multi-layer sports surfaces. An independent optical measurement system (GOM) provided gold standard sample deformation and strain. Forty-five impacts onto three test samples were measured simultaneously using the three systems. Poor agreement was found between AAA and GOM peak sample deformations and strain (systematic bias 2.4 mm, 95% confidence intervals ± 1.3 mm, strain RMSD 29%), largely attributable to errors in the AAA time of initial contact. Using a regression equation to correct this time led to much better agreement in AAA peak deformations and strain (systematic bias 0.1 mm, 95% confidence intervals ± 0.7 mm, strain RMSD 8%). Good agreement was found between the HES and GOM (systematic bias 0.2 mm, 95% confidence intervals ± 0.4 mm, strain RMSD 11%). The corrected AAA and HES methods can measure deformation of polymeric sports surfaces under realistic loading rates to an accuracy of < 1 mm. In terms of strain, errors increase with decreasing peak sample deformation indicating that both systems should be used with caution for peak deformations < ~ 4–5 mm