Masahiro Todoh

The frictional coefficient of the temporomandibular joint and its dependency on the magnitude and duration of joint loading.

In synovial joints, friction between articular surfaces leads to shear stress within the cartilaginous tissue, which might result in tissue rupture and failure. Joint friction depends on synovial lubrication of the articular surfaces, which can be altered due to compressive loading. Therefore, we hypothesized that the frictional coefficient of the temporomandibular joint (TMJ) is affected by the magnitude and duration of loading. We tested this by measuring the frictional coefficient in 20 intact porcine TMJs using a pendulum-type friction tester. The mean frictional coefficient was 0.0145 (SD 0.0027) after a constant loading of 50 N during 5 sec. The frictional coefficient increased with the length of the preceding loading duration and exceeded 0.0220 (SD 0.0014) after 1 hr. Application of larger loading (80 N) resulted in significantly larger frictional coefficients. In conclusion, the frictional coefficient in the TMJ was proportional to the magnitude and duration of joint loading.

Adaptive Stiffness Design for Multimaterial Structural System

Stiffness is one of the basic characteristics of structural system, and is an important feature for structural design problems. Although it has been often recruited as the design objective or constraints, the structural optimality attained has guarantee only for the mechanical conditions considered at the design stage. The adaptive stiffness design for force-dependent stiffness is a concept to tailor the structural stiffness in accordance with the external load applied. The passive adaptive stiffness has been realized by usingsingle conventional material only. In this article, it is evolved to the active one that enables us to switch the force-dependent stiffness actively in part in the context of the multimaterial structural system. The topology design problem is formulated for the distribution of conventional and functional materials under the constraints of mean compliance and its switchingpoint as the structure. The effectiveness of the proposed structural design concept is examined through numerical case studies solved by the SIMP method of topology design.

Material Structure Design of Stress-Dependent Adaptive Stiffness

Use of functional material is a primitive and most promising approach to the functional structural system, e.g. adaptive/smart structures. It, however, is not always necessary for a certain aspect of such structural function. This study proposes a material structure design approach to the stress-dependent anisotropic adaptive stiffness by using the conventional linear elastic material of isotropy. The structural design problem has been formulated for the material structure consisting of mesoscopic unit cells and solved by using the simple isotropic material with penalization (SIMP) method for the topology design and the traction method for the geometry design for microstructure of the unit cell. The effectiveness of the proposed idea has been examined through numerical studies in two-dimensional cases.