Abstract
(1) Background: Open-cell polyurethane foam mechanical behavior is highly influenced by microstructure. The determination of the failure mechanisms and the characterization of the deformation modes involved at the micro scale is relevant for accurate failure modeling. (2) Methods: We use digital image correlation (DIC) to investigate strain fields of open-cell polyurethane foams of three different densities submitted to compression testing. We analyze the effect of some DIC parameters on the failure pattern definition and the equivalent strain magnification at the apparent ultimate point. Moreover, we explore speckle versus non-speckle approaches and discuss the importance of determining the pattern quality to perform the displacement correlation. (3) Results: DIC accurately characterizes the failure patterns. A variation in the subset size has a relevant effect on the strain magnification values. Step size effect magnitude depends on the subset size. The pattern matching criterion presented little influence (3.5%) on the strain magnification. (4) Conclusion: The current work provides a comprehensive analysis of the influence of some DIC parameters on compression failure characterization of foamed structures. It highlights that changes of subset and step sizes have a significant effect on the failure pattern definition and the strain magnification values, while the pattern matching criterion and the use of speckle have a minor influence on the results. Moreover, this work stands out that the determination of the pattern quality has a major importance for texture analysis. The in-depth, detailed study carried out with samples of three different apparent densities is a useful guide for DIC users as regards texture correlation and foamed structures.
Highlights
Open-cell rigid polyurethane (PUR) foam is considered a reliable cancellous bone surrogate because of its similarities with regards to morphometry and mechanical behavior [1,2,3,4,5]
The compression response of open-cell polyurethane foams can be divided into a linear stage where the cells deform reversibly, a yielding region up to the ultimate point and a post-yielding non-linear region characterized by a softening region followed by a densification stage at high nominal strains, shown in Figure 6 for three samples of different apparent densities
Compression failure in foamed structures is more localized rather than spread and it is highly influenced by microstructure
Summary
Open-cell rigid polyurethane (PUR) foam is considered a reliable cancellous bone surrogate because of its similarities with regards to morphometry and mechanical behavior [1,2,3,4,5]. Its increasing relevance in the biomechanical field has motivated several investigations aiming at characterizing this foamed structures, either commercial [1,2,3,4,6,7] or self-produced [5,6]. This material presents some advantages with respect to real bone specimens, such as it does not suffer from dehydration or biodegradation and has a lower cost [1]. The determination and characterization of the deformation modes in open-cell foams is necessary to a more accurate mechanical behavior assessment, which is useful for many biomedical and engineering applications
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