Effects of loading rate on the deformation and cracking of dental multilayers: Experiments and models
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The paper presents the results of combined experimental, analytical, and computational studies of contact-induced deformation and cracking in dental multilayers. These include studies of individual layers and composite structures that consist of tri-layers of glass bonded to ceramic-filled polymer foundation with an acrylate-based join material. Loading-rate-dependent Young’s moduli of the join and foundation materials were obtained from monotonic compression tests. Critical loads were also determined for the tri-layers from Hertzian contact tests at different loading rates. The fracture onset (sub-surface radial cracking) was detected using an in situ telescope. The measured rate-dependent Young’s moduli were then incorporated into a finite element model that was used to predict the rate-dependent critical loads in the tri-layer system. Finally, the paper shows that the observed loading rate-dependence of the critical load (for radial cracking) is due to the combined effects of slow crack growth in glass and rate-dependent Young’s moduli in the join and foundation layers.
I. INTRODUCTION
Occlusal contact in the oral cavity often occurs over a range of loading rates that may induce viscoelastic deformation in the dentin-like ceramic-filled polymer foundations and join materials.1,2 However, most of the existing mechanics models of occlusal contact do not account for the viscoelastic deformation that can occur in dental multilayers. This can lead to errors in the predictions of failure conditions or deformation characteristics of dental restorations.1,2 One example of this is in the recent studies of loading rates on the failure of tri-layers consisting of glass bonded to polycarbonate with epoxy joins.1 In these studies, failure was assumed to occur as a result of slow crack growth (SCG) in the top glass layers. However, the predictions of the critical loads required for failure due to radial cracking were somewhat different from the experimental results obtained at slow loading rates. In the discussion of Ref. 1, the authors suggested that these differences might be due to possible viscoelastic deformation in their multilayered structures. In an effort to explain these differences, Huang et al.2 considered the combined effects of SCG and viscous deformation (creep) of the polycarbonate foundation and
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Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/JMR.2006.0114 970
J. Mater. Res., Vol. 21, No. 4, Apr 2006 http://journals.cambridge.org Downloaded: 17 Mar 2015
join materials. Their mechanics prediction of the failure loads suggested that the differences between the measured and predicted loads can be explained by the additional effects of viscous deformation. However, their viscous models were fitted to creep test data that were obtained under static loading conditions that do not mimic the clinically relevant loading rates. This paper presents the results of a combined experimental, theoretical, and computational study of the effects of loading rate on the failure of mult
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