ABSTRACT
Indentation, when used as a mechanical testing method, can be dened as a general method to measure the mechanical properties of materials by inducing a notch or recess in the tested object and then analysing the force-deformation relationship. e size of the indenter is smaller than the compressed object, which is the most important dierence between indentation and compression. In traditional mechanical engineering,
indentation has been widely used to measure the stiness of various materials including metals, plastic, rubber, foam and elastomers. Some international standards have been dened for testing hardness and other material properties of metallic materials using indentation methods, such as ISO14577-1: Metallic materials-Instrumented indentation test for hardness and materials parameters-Part I: Test method. Commonly used stiness parameters include the Vickers hardness, Rockwell hardness and the Brinell hardness. In recent years, the instrument-based indentation techniques, including nanoindentation, have been developed (Oliver and Pharr 1992; VanLandingham 2003; Fischer-Cripps 2006). Because the requirement for preparing a specimen for an indentation test is simpler than that for a traditional standard test such as compression, it is useful not only in vitro but also in vivo using a noninvasive test, and this test has been broadly applied for the measurement of so tissue elasticity. e earliest application of indentation for tissue assessment, which was used for the test of skin elasticity, was proposed in the 1910s (Schade 1912). At that time, the indentation system was bulky with manual operation, and the method for recording data was also very primitive, which made its applications very limited. However, with the fast development of modern techniques in electronics, computers, sensing, automatic control and signal processing, the indentation techniques for biological so tissues also have developed rapidly. Until now, quite a number of indentation systems have been developed that are applicable in various testing conditions. In the following section, the development of indentation techniques used for so tissue elasticity measurement is reviewed.
