Human Material Mechanics

Author: Zhao Fang / et al.
Editor-in-Chief: Dong Yingshuang
Publisher:
Publish Date: 2004-11-20
Features:
Fragment: Chapter 1 Introduction
1. The Task and Research Methods of Human Material Mechanics
Biomechanics is the application of mechanics to biology, a discipline that studies the laws of biological life activities using mechanical principles. It is an interdisciplinary field that emerges from the integration of mechanics, anatomy, physiology, and biochemistry. As an independent discipline, it rapidly developed after the 1960s. In recent years, biomechanics has played an extremely important role in human movement analysis, the study of disease causes, the design of various prostheses and artificial organs, and the advancement of sports science, anthropology, astronautics, and other fields.
Biomechanics is a discipline with a broad research scope and very rich content. From the study of the relationship between the structure and mechanical properties of cells, tissues, and biological fibers in micro-biomechanics to the study of the interactions between various animals, plants, humans, and the external environment of biological systems, all fall within the research scope of biomechanics.
Biological quantum mechanics, biological thermodynamics, and other branches of biomechanics are highly theoretical. Trauma mechanics, medical biomechanics, and sports biomechanics are some of the more practically oriented branches.
As a part of biomechanics, human material mechanics primarily studies the mechanical properties of solid human materials. Human solid materials include bones, muscles, tendons, ligaments, skin, and blood vessels. They are not ideal elastic, plastic, or viscoelastic materials, each having its own unique mechanical characteristics. The mechanical properties of bones are similar to those of mechanical and building materials and are relatively easy to understand. Currently, our understanding of bones is also quite comprehensive and accurate.
In contrast, soft tissues such as muscles, tendons, ligaments, skin, and blood vessels in the human body exhibit viscoelastic properties and are diverse and complex, with varying mechanical properties. Therefore, when studying them, it is essential to combine material testing results with theoretical analysis.
Following the general research methods of mechanics, the study of human material mechanical properties involves the following steps:
(1) Investigating the structure of human materials. Anatomy allows us to understand the geometric structure of the research subject.
(2) Measuring the mechanical properties of materials such as bones, muscles, and tendons to establish material constitutive equations. This is one of the central issues in studying the mechanical properties of human materials. In biomechanics research, it is often very difficult to test materials such as bones, muscles, and tendons by separating them, especially maintaining their living state. Additionally, biological materials often undergo large deformations, and their stress-strain relationships are generally nonlinear and history-dependent, making it challenging to establish nonlinear constitutive equations. The solution is to first establish the mathematical form of the material constitutive equation, then verify it through experiments, modify the mathematical formulas, and determine the mathematical parameters.
(3) Establishing differential equations that describe material properties based on the constitutive equation and fundamental laws of physics.
(4) Solving the established differential equations with certain boundary conditions using analytical or numerical methods.
(5) Conducting physiological experiments to verify the solutions of the boundary value problems, modifying the theoretical results to ensure consistency between theory and experiment.
Through a series of iterative studies, both qualitative and quantitative aspects of the problem are addressed, with the aim of inferring changes in organ function from changes in material mechanical properties. Currently, many problems cannot be satisfactorily resolved following the above steps, primarily due to the difficulty of meeting the experimental conditions required to establish constitutive equations for living tissues. If human tissues and organs are separated from their natural environment, it is impossible to obtain the boundary conditions needed to describe the mechanical properties of living tissues, and thus, the solution to the boundary value problem cannot be obtained.