Skin friction related behaviour of artificial turf systems

The occurrence of skin friction related injuries is an issue for artificial turf sports pitches and remains a barrier to their acceptance. The purpose of this study was to evaluate the current industry standard Securisport® Sports Surface Tester that measures skin surface related frictional behaviour of artificial turf. Little research has been published about the device and its efficacy, despite its widespread use as a standard FIFA test instrument. To achieve a range of frictional behaviours, several “third generation” (3G) carpet and infill combinations were investigated; friction time profiles throughout the Securisport rotations were assessed in combination with independent measurements of skin roughness before and after friction testing via 3D surface scanning. The results indicated that carpets without infill had greatest friction (coefficients of friction 0.97–1.20) while those completely filled with sand or rubber had similar and lower values independent of carpet type (coefficient of friction (COF) ≈0.57). Surface roughness of a silicone skin (s-skin) decreased after friction testing, with the largest change on sand infilled surfaces, indicating an “abrasive” polishing effect. The combined data show that the s-skin is damaged in a surface-specific manner, thus the Securisport COF values appear to be a poor measure of the potential for skin abrasion. It is proposed that the change in s-skin roughness improves assessment of the potential for skin damage when players slide on artificial turf

Measurement of strain and strain rate during the impact of tennis ball cores

The aim of this investigation was to establish the strains and strain rates experienced by tennis ball cores during impact to inform material characterisation testing and finite element modelling. Three-dimensional surface strains and strain rates were measured using two high-speed video cameras and corresponding digital image correlation software (GOM Correlate Professional). The results suggest that material characterisation testing to a maximum strain of 0.4 and a maximum rate of 500 s-1 in tension and to a maximum strain of -0.4 and a maximum rate of -800 s-1 in compression would encapsulate the demands placed on the material during impact and, in turn, define the range of properties required to encapsulate the behavior of the material during impact, enabling testing to be application-specific and strain-rate-dependent properties to be established and incorporated in finite element models

Strategy towards next generation artificial turf surfaces with lower risk of skin abrasion injury

One of the main concerns with artificial turf is the increased incidents of skin abrasions compared to natural grass. The aim of this study is to modify the main component material of the artificial turf yarns with grafted-from sulfobetaine methacrylate (SBMA) brushes so as to reduce skin-abrasion of these surfaces; and to investigate the significance of tribo-pairs in determining skin-friendliness of a surface. Standard stainless steel tribometer tips were not able to discern the effect of surface grafting whereas frictional measurements carried out using FIFA-recommended skin surrogates showed a decrease in the coefficient of friction (μ) of up to 77% from 1.33 to 0.30 for hydrated SBMA-modified substrates. This study introduced the use of an appropriate tribo-pair for skin-surface friction measurement that can potentially be used for quantifying the skin-friendliness of artificial sports surfaces. It has also provided a strategy that could lead to next generation artificial turfs with significantly reduced risk of abrasion injury

Characterisation of ball degradation events in professional tennis

Tennis balls are acknowledged to degrade with use and are replaced at regular intervals during professional matches to maintain consistency and uniformity in performance, such that the game is not adversely affected. Balls are subject to the international tennis federation’s (ITF) ball approval process, which includes a degradation test to ensure a minimum standard of performance. The aim of this investigation was to establish if the ITF degradation test can assess ball longevity and rate of degradation and determine if there is a need for a new degradation test that is more representative of in-play conditions. Ball tracking data from four different professional events, spanning the three major court surfaces, including both men’s and women’s matches were analysed. The frequency of first serves, second serves, racket impacts and surface impacts were assessed and the corresponding distribution of ball speed and (for surface impacts) impact angle was determined. Comparison of ball impact frequency and conditions between in-play data and the ITF degradation test indicated the development of a new test, more representative of in-play data, would be advantageous in determining ball longevity and rate of degradation with use. Assessment of data from different surfaces highlighted that grass court subjected the ball to fewer racket and surface impacts than hard court or clay. In turn, this appears to influence the distribution of ball speed on impact with the surface or racket, suggesting a surface-specific degradation test may be beneficial. As a result of these findings a new test protocol has been proposed, utilising the in-play data, to define the frequency of impacts and impact conditions to equate to nine games of professional tennis across the different surfaces

Characterisation of ball impact conditions in professional tennis: matches played on hard court

To assess ball performance for research and development purposes requires greater understanding of the impact conditions a tennis ball experiences in professional tournament play. Ball tracking information taken from three consecutive years of an ATP 250 tour event played on hard court were analysed. The frequency of first serves, second serves, racket impacts and surface impacts were assessed per game and extrapolated to show how many impacts a single ball is subjected to. Where applicable the pre- and post-impact velocity and angle were found and the distribution of each analysed. In total, data from 65 matches comprising 1,505 games were analysed. On average, each game contained 70.26 (± 16.23) impacts, of which 9.23%, 3.16%, 37.78% and 49.83% were first serves, second serves, racket impacts and surface impacts respectively. As a result, assuming all balls in play are used evenly, a single ball is expected to be subjected to 105 (± 24) impacts over the course of the nine games that it is in play. The results of the investigation could be used to design a wear protocol capable of artificially wearing tennis balls in a way that is representative of professional play

Tribological investigation into achieving skin-friendly artificial turf surfaces

A main concern with artificial turfs is the increased incidences of skin abrasions compared to playing on natural grass. The proliferation of these surfaces draws attention to the skin-friendliness and related test methods of the products. This study focuses on the yarn component and explores the significance of tribopairs in identifying the skin-friendly property of hydrophilically-modified polypropylene. The frictional behaviour of poly(sulfobetaine methacrylate)-grafted substrates were studied under dry and hydrated conditions with standard steel tribotips, commonly used in frictional assessments. The measurements were repeated with tribotips made from silicone skin, used in large-scale artificial turf testing. Results showed that when hydrated, hydrophilic polymer brushes were successful in reducing silicone skin-sample friction by 75.8%. Interestingly, when extended trials were conducted, a step-jump in the frictional values of highly-modified samples was observed, attributed to the diminishing hydrated layer with prolonged testing. In contrast, the standard steel tribotips were unable to discern the effects of surface grafting or hydration, measuring consistently low frictional values across all samples. This study highlights the importance of tribotip selection and introduces a bench-top test method that can potentially be used for the quantification of skin-friendliness of artificial turf yarns during product development stages

Addressing skin abrasions on artificial turfs with zwitterionic polymer brushes

To address the skin-friendliness of synthetic surfaces intended for sports applications, the frictional properties of hydrated zwitterionic polymer brushes are investigated outside of the common aqueous environment where an excess of lubricating water molecules is absent. Photo-grafted poly(sulfobetaine methacrylate) (pSBMA) brushes of various irradiation durations are prepared on polypropylene substrates and the improvement in frictional properties of the pSBMA-modified surfaces against a silicone skin counter-surface is studied. Frictional measurements under both dry and hydrated surface conditions shows that the applied surface modification was capable of forming a stable lubrication layer in the absence of excess water, significantly reducing the coefficient of friction by up to 78.8%. The pSBMA brushes also provide the additional advantage of antifouling – exhibiting resistance towards pathogenic Staphylococcus aureus with almost zero surface colonization for samples irradiated for 1200 s. The low skin-sample friction under ambient conditions and desirable fouling-resistance highlights the potential of pSBMA brushes as a modification strategy for achieving skin-friendly surfaces targeted at reducing the risk of skin abrasions

Insights to skin-turf friction as investigated using the Securisport

© 2015 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license.The objective of this study was to investigate the effect of the infill and fibers of an artificial turf surface to the overall frictional behavior of the surface. The assessment was conducted using the Securisport test device in accordance to the FIFA Test Method so as to evaluate the effectiveness of the standard test in describing the frictional property of an artificial turf surface. Experiments showed that surfaces of varying infill depths and infill types produced characteristic features in their friction profiles that were a result of the fiber-infill interactions. The surface without infill exhibited the highest frictional values, with distinct peak and trough features. Surfaces completely filled with sand or rubber displayed similar profiles with relatively low frictional values. Test results showed that turf fibers influenced the frictional behaviour of partially-filled systems to a great extent. The results from the Securisport were useful in providing insights to how various turf components affect the skin-turf interaction and may be beneficial in the development of more skin-friendly turf products

Multiparameter and Parallel Optimization of ReaxFF Reactive Force Field for Modeling the Atomic Layer Deposition of Copper

In this study, we aim to develop a ReaxFF reactive force field for simulating the reaction mechanism of copper atomic layer deposition (ALD). To achieve this, we optimized the Cu/C, Cu/H, and Cu/N parameters of ReaxFF and extended the existing Cu potential to describe Cu/C/H/O/N interactions involved in Cu ALD. The parametrization procedure was implemented through an efficient multiparameter and parallel optimization scheme based on the Taguchi method. Using the newly developed Cu potential, we performed reactive molecular dynamics (RMD) simulations on an “abbreviated” ALD cycle using a [Cu­(^<i>i</i>Pr-amd)]₂ (^<i>i</i>Pr-amd = <i>N</i>,<i>N</i>′-diisopropylacetamidinate) or Cu­(dmap)₂ (dmap = dimethylamino-2-propoxide) precursor with the H radical as a coreactant. In the first half-cycle, the [Cu­(^<i>i</i>Pr-amd)]₂ precursor is found to adsorb dissociatively on the Cu surface as Cu­(^<i>i</i>Pr-amd) monomers. During the second half-cycle, H radicals partly eliminate precursor fragments to the gas phase, but some intermediates such as C₅H₁₂N₂ and C₂H₄N remain on the surface and may become a source of contamination. On the other hand, the Cu­(dmap)₂ precursor dissociates into Cu­(dmap) and dmap on the Cu surface. The second half-cycle is initiated through a hydrogen transfer reaction, which completely eliminates the dmap ligands to the gas phase. In general, our RMD simulations suggest that the surface chemistry of Cu­(dmap)₂ during the ALD is simpler and cleaner than that of [Cu­(^<i>i</i>Pr-amd)]₂