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Macrodamage Accumulation Model for a Human Femur 时间:2017-09-09 22:48 来源:未知作者:admin 点击: 次 Abstract:The objective of this study was to more fully understand the mechanical behavior of bone tissue that is important to find an alternative material to be used as an implant and to develop an accurate model to predict the fracture of the bone. Predicting and preventing bone failure is an important area in orthopaedics. In this paper, the macrodamage accumulation models in the bone tissue have been investigated. Phenomenological models for bone damage have been discussed in detail. In addition, 3D finite element model of the femur prepared from imaging data with both cortical and trabecular structures is delineated using MIMICS and ANSYS® and simulated as a composite structure. The damage accumulation occurring during cyclic loading was analyzed for fatigue scenario. We found that the damage accumulates sooner in the multiaxial than in the uniaxial loading condition for the same number of cycles, and the failure starts in the cortical bone. The damage accumulation behavior seems to follow a three-stage growth: a primary phase, a secondary phase of damage growth marked by linear damage growth, and a tertiary phase that leads to failure. Finally, the stiffness of the composite bone comprising the cortical and trabecular bone was significantly different as expected.
1. Introduction
In order to understand the bone fracture, it is very important to study the macrodamage of the bone with respect to mechanical and physiological loads. Bone tissue is a complex, multiphasic, heterogeneous, anisotropic, and highly hierarchized material structure. Predicting and preventing bone fracture is a very important area in orthopaedics given the volume of fractures that occurs annually. From a macroscopic point of view, bone tissue is divided into two types: the trabecular bone with 50–95% porosity [1] and the cortical bone with 5–10% porosity [1]. Bone tissue can be divided into five levels [2], which are macro, meso, micros, submicro, and nanostructure. The macrostructure level is the whole bone, which ranges from several millimeters to several centimeters, as shown in Figure 1. In this paper, an attempt has been made to establish a detailed understanding of the bone tissue mechanical behavior as it is important in the device design and to derive implant life. Correspondingly, an accurate damage prediction model for a bone tissue is needed in order to predict the fracture of the bone or the reliability of a bone-implant structure.
Numerous damage models were proposed using the macrostructure of the bone. However, each model has made an assumption regarding the mechanical properties, loading conditions, or the structure of the bone. These assumptions have not given realistic predictions for the damage accumulation in a bone. Depending on the mechanical properties of bone tissue, bone damage models can be divided into elastic-viscoplastic, elastoplastic, and plastic damage models. In addition, depending on the damage type, bone damage models can be divided into electromagnetic, fracture, bending, and fatigue damage models. The elastic-viscoplastic damage models take into consideration that the bone has elastic, plastic, and viscus material properties.
Recently, several models have been proposed that describe the damage model of the bone as an elastic viscoplastic model such as Keyak and Rossi [3]. They proposed fracture load by using finite element models and several failure theories [3]. However, they used isotropic material properties for bone tissue. Some studies proposed elastoplastic damage modes as well. These models take into account elastic and plastic material properties such as in the Garcia et al. study [4] and the Fondrk et al. study [5]. They proposed elastic plastic damage models for bone tissue and developed a model for cortical bone tissue only. Other studies proposed plastic damage models, which take into consideration that the bone has plastic material properties only. In addition to the mechanical properties, the loading conditions have a significant effect on the macrodamage accumulation of the bone. Some studies analyzed only tension, compression, or three-point bending [6].