Center for Advanced Vehicular Systems

Objective: To determine the structure-property relationships of both soft biological tissues and animal outer armor. Use the relationships to develop material models for implementation into finite element codes.

Background
Human Tissue: Establishing a sound understanding of the material properties in soft tissue is important. This understanding may enable more effective design and manufacturing of tissue engineered constructs as well as assist in the development of soft tissue finite element models that have a mechanical response close to that of human tissues. Numerous models have been established to evaluate the complex nature of soft skeletal connective tissues and internal organs with their main purpose being to enhance the understanding of the fundamental bases of the material (Setton et al. 1992; Ateshian et al. 1997; Yin et al. 2004). Most of the current soft tissue continuum scale models can be grouped into two major categories: microstructural and phenomenological. None of which have been successful in elucidating the underlying structural mechanism that determines the tissue behavior. Also, the models have not included the formation of tissue defects and their dependence on strain level, strain rate and initial status of tissues. Thus, this study purports to evaluate such responses for the future development of a human body finite element mesh to accurately predict injury risks.

Animal Armor: The notion is to study the microstructure-property relations of the animal world and assess the similarities/differences to penetration in helping developing a design methodology for man-made armor designs. The natural world includes armor systems that are essentially composites, e.g., abalone shell, turtle shell, or ram horn. They have occupied the attention of many researchers in the recent years due to their novel hierarchical structures and remarkable mechanical properties that are far beyond their component materials as well as synthetic counterparts (Meyers et al. 2006). Such distinctive mechanical properties of biological composite materials are the consequences of their organization in terms of composition and structure. Several studies on the structures and mechanical responses of different biological composite materials have been extensively reported in the literature. In this research, we are exclusively focusing on the structures, materials properties, and mechanical behavior of the turtle shell.


Approach
Human Tissue: The accurate constitutive models of different tissues/organs are important for robust computational modeling, which would help assess the safety of individual in events of vehicle crash, organ tolerance in a narrow compartment full of harsh shocks and vibrations. Current dummy models based on steel and rubber components cannot provide fidelity assessment. We plan to determine the structure-based constitutive models that best describe the viscoelastic behavior of these tissues. We will perform multiscale modeling on the skin,and liver, and implement our results into a finite element environment.
Animal Armor: Although the turtle shell possesses superior armor behavior against environmental threats, their structure and mechanical responses surprisingly have not been studied. The main objective of this research is to quantify the impact capability of the turtle shell based on the materials and geometric characteristics, and the multiscale microstructure-property relations. Since no structure-property relations have been analyzed on the turtle shell, there exists a lack of experimental database of such biological structural material. Moreover, there is no systematic research on this biological structure to understand structure-property phenomena and biological pathways to create bio-inspired synthetic materials. Therefore, a contrast-comparison study of the structure-property relations between the turtle shell and other biological structural materials could provide understanding for novel bio-inspired safety system design methodologies. Multiscale structure and mechanical properties will be quantified under nano-, micro-, meso-, and macro-scales by using the turtle shell obtained from the natural death of a box turtle. Mechanical tests in this research will include nano-indentation, micro-indentation, bending, and quasi-static as well as high-rate compression tests.


Team Members: L. Williams (MSU), J. Liao, S.J. Park, H.J. Rhee, M.F. Horstemeyer


Subtasks
Human Tissue
Task 1.1 – Conduct macroscale skin experiments
Task 1.2 – Quantify the internal microstructural change of the skin under high impact
Task 1.3 – Conduct macroscale liver experiments
Task 1.4 – Quantify the internal microstructural change of the liver under high impact
Task 1.5 – Implement the structure-property relationships into a multiscale internal state variable model

Animal Armor
Task 2.1 – Carry out geometric characteristics to develop global model of the turtle shell by FEM and mechanical tests on the entire turtle shell to validate the model
Task 2.2 – Analyze multiscale structure and chemical composition of the turtle shell
Task 2.3 – Characterize materials/mechanical properties of the turtle shell
Task 2.4 – Contrast/Compare the structure-property relations between the turtle shell and other biological structural materials