Warped finite element models predict whole shell failure in turtle shells

Abstract

Finite element (FE) models have become increasingly popular in comparative biomechanical studies, with researchers continually developing methods such as 'warping' preexisting models to facilitate analyses. However, few studies have investigated how well FE models can predict biologically crucial whole-structure performance or whether 'warped' models can provide useful information about the mechanical behavior of actual specimens. This study addresses both of these issues through a validation of warped FE models of turtle shells. FE models for 40 turtle specimens were built using 3D landmark coordinates and thin-plate spline interpolations to warp preexisting turtle shell models. Each actual turtle specimen was loaded to failure, and the load at failure and mode of fracture were then compared with the behavior predicted by the models. Overall, the models performed very well, despite the fact that many simplifying assumptions were made for analysis. Regressions of observed on predicted loads were significant for the dataset as a whole, as well as in separate analyses within two turtle species, and the direction of fracture was generally consistent with the patterns of stresses observed in the models. This was true even when size (an important factor in determining strength) was removed from analyses - the models were also able to predict which shells would be relatively stronger or weaker. Although some residual variation remains unexplained, this study supports the idea that warped FE models run with simplifying assumptions at least can provide useful information for comparative biomechanical studies.

Performance in three shell functions predicts the phenotypic distribution of hard‐shelled turtles

“…Here, the method was used to transform a model of a bog turtle ( Glyptemys muhlenbergii ) shell into all of the theoretical shapes evenly dispersed throughout shape space (Supporting Information File ). Details are in Stayton (). As a species close to the mean shape for extant shells, this individual represents a reasonable base.…”

“…). Maximum stresses represent a biologically relevant measure that can predict failure in turtle shells (Stayton ).…”

“…) and turtles possess modest species richness (∼320 species; Turtle Taxonomy Working Group 2017), so evolutionary analyses remain manageable while presenting a sufficient sample size for powerful statistical tests. Relationships between shell shape and performance have been demonstrated for multiple functions (Boyer ; Domokos and Várkonyi ; Rivera ; Stayton , ) and ecomorphological patterns in shell shape have been documented (Claude et al. ; Stayton et al.…”

Functional performance of turtle humerus shape across an ecological adaptive landscape

“…Attempts to include cortical thickness into the analysis introduced uncertainty due to poor correlation with the morphospace. Although it would be ideal in future analyses to develop methods to include the complex distributions of cortical thickness into our models, it has also been demonstrated that surface meshes without internal geometry can accurately predict the biomechanical behavior of shape (Stayton ).…”

Finite Element and deformation analyses predict pattern of bone failure in loaded zebrafish spines

“…This technique digitally models an object of known material properties using a series of linked nodes of known number and geometry, that can be subjected to a wide variety of forces outputting the predicted geometry, strain and deformation. Results can be validated by comparison with the results of loading experiments in which a sample is loaded ex vivo (10,11). FEA has been used in zebrafish to identify regions of high strain and test contributions of shape and material properties in joint morphogenesis (12,13) and to study strain patterns in a single vertebra (14).…”