New Double Indentation Technique for Measurement of the Elasticity Modulus of Thin Objects

Herrel

Genbrugge

et al. 2012

Bird beaks are layered structures, which contain a bony core and an outer keratin layer. The elastic moduli of this bone and keratin were obtained in a previous study. However, the mechanical role and interaction of both materials in stress dissipation during seed crushing remain unknown. In this paper, a multi-layered finite-element (FE) model of the Java finch's upper beak (Padda oryzivora) is established. Validation measurements are conducted using in vivo bite forces and by comparing the displacements with those obtained by digital speckle pattern interferometry. Next, the Young modulus of bone and keratin in this FE model was optimized in order to obtain the smallest peak von Mises stress in the upper beak. To do so, we created a surrogate model, which also allows us to study the impact of changing material properties of both tissues on the peak stresses. The theoretically best values for both moduli in the Java finch are retrieved and correspond well with previous experimentally obtained values, suggesting that material properties are tuned to the mechanical demands imposed during seed crushing.

Section: Physiological Finite-element Modelmentioning

confidence: 99%

Multi-layered bird beaks: a finite-element approach towards the role of keratin in stress dissipation

Herrel

Genbrugge

et al. 2012

“…This was done in three regions of the mandibles: at the tip, in the middle and at the base. The elasticity modulus (Young's modulus) was measured with a custom-built double indentation set-up, a technique especially designed for small, thin samples (for a detailed description, see [26,27]). To evaluate the potential difference in Young's modulus between the cuticle layers, the measurements were repeated after scraping away approximately 20% of the thickness of the samples of one individual.…”

Section: Materials Properties: Young's Modulus and Poisson Ratiomentioning

confidence: 99%

Finite-element modelling reveals force modulation of jaw adductors in stag beetles

Goyens

Aerts

et al. 2014

Male stag beetles carry large and heavy mandibles that arose through sexual selection over mating rights. Although the mandibles of Cyclommatus metallifer males are used in pugnacious fights, they are surprisingly slender. Our bite force measurements show a muscle force reduction of 18% for tip biting when compared with bites with the teeth located halfway along the mandibles. This suggests a behavioural adaptation to prevent failure. We confirmed this by constructing finite-element (FE) models that mimic both natural bite situations as well as the hypothetical situation of tip biting without muscle force modulation. These models, based on micro-CT images, investigate the material stresses in the mandibles for different combinations of bite location and muscle force. Young's modulus of the cuticle was experimentally determined to be 5.1 GPa with the double indentation method, and the model was validated by digital image correlation on living beetles. FE analysis proves to be a valuable tool in the investigation of the trade-offs of (animal) weapon morphology and usage. Furthermore, the demonstrated bite force modulation in male stag beetles suggests the presence of mechanosensors inside the armature.

“…Here, we propose two techniques to quantify the Young moduli in bone and keratin of the beak of the Java finch. First, a double-indentation technique designed to measure thin biological samples [14,15] is used. Second, an inverse analysis is performed: in an FE model, we adjust the material properties to obtain the best fit between a model and an experimental measurement quantifying actual beak deformation using digital speckle pattern interferometry (DSPI).…”

Section: Introductionmentioning

confidence: 99%

Determination and validation of the elastic moduli of small and complex biological samples: bone and keratin in bird beaks

Herrel

Aerts

et al. 2011

In recent years, there has been a surge in the development of finite-element (FE) models aimed at testing biological hypotheses. For example, recent modelling efforts suggested that the beak in Darwin's finches probably evolved in response to fracture avoidance. However, knowledge of the material properties of the structures involved is crucial for any model. For many biological structures, these data are not available and may be difficult to obtain experimentally given the complex nature of biological structures. Beaks are interesting as they appear to be highly optimized in some cases. In order to understand the biomechanics of this small and complex structure, we have been developing FE models that take into account the bilayered structure of the beak consisting of bone and keratin. Here, we present the results of efforts related to the determination and validation of the elastic modulus of bone and keratin in bird beaks. The elastic moduli of fresh and dried samples were obtained using a novel double-indentation technique and through an inverse analysis. A bending experiment is used for the inverse analysis and the validation of the measurements. The out-of-plane displacements during loading are measured using digital speckle pattern interferometry.