Bone specimens used for evaluating the mechanical properties of bone may not have been necessarily preserved by the same method before they become available. To this end, the mechanical properties of bone may be affected by freezing, a common preservation method, as well as by formalin and other preservation solutions. In this study, bone specimens were preserved by different methods (i.e., freezing, preservation in saline, preservation in ethanol, and preservation in formalin) to examine the effects of each preservation method on the fracture characteristics of bovine femoral cortical bone. Regarding the crack extension behavior in the fracture toughness test, microcracks accumulated at the top of the slit in the low-load region before the maximum load was reached. When such accumulated microcracks grew to a visible size, a crack was formed from the top of the slit, and then grew with subsequent expansion of the processing zone. The fracture toughness values of the bone groups preserved in formalin and neutral buffered formalin were significantly lower than those of the bone groups preserved by other methods. As the fracture surface by scanning electron microscopic observations was smoother with a loading rate of 20 mm/min than with 1 mm/min, cracks were considered to develop easily, resulting in a lower fracture toughness value. Scanning electron microscopic observations of a test section subjected to a low loading rate showed that the fracture surface of the bone groups preserved in formalin or neutral buffered formalin was flat and smooth. In the other preservation groups, the lamellae adjacent to the top of the slit had undulating contours with plastic deformation. [

Bone fracture toughness has been well studied, however, it is also important to investigate the effect of preservative treatment on the mechanical properties of bones. It is necessary to evaluate crack initiation and propagation after fracture because this process may be different in the case of injured bone tissues. In this study, we attempted to analyze the strain distribution on bone tissue surface by using image correlation techniques in order to elucidate the relationship between microscopic bone damage and strain distribution. Bovine femoral cortical bone was employed as the bone specimen and the three-point bend test method was used to determine the fracture toughness, in accordance with the ASTM E399 guidelines. An Instron type machine was used in the fracture toughness test and the loading rate was set to 1 mm/min. Black and white spray paint was applied in a random pattern to the surface of the specimens, and the specimens were loaded until they were ruptured. Bone surface strain analysis was performed using image correlation techniques and the changes were recorded in a digital image. In order to evaluate the effects of preservative treatment on the mechanical properties of bone, we categorized the specimens into 4 groups: the control group included the specimens that were submitted for testing immediately after machining and the preservation group comprised specimens that were analyzed after preservative treatment with different method (formalin, ethanol and physiological saline solution). A strain analysis performed using image correlation techniques allowed the visualization of the increased strain at the forward end of the slit of the specimens. The strain value at the forward end of the slit (the longitudinal direction of specimens) measured at the time of rupture in the control group was approximately 4 times larger than that in the formalin preservation group, thereby suggesting the embrittlement of bone organic constituents due to preservative treatment.

Advanced fiber reinforced composite materials are used as structural members in various fields because of their high strength and high stiffness to weight ratios, and hence analysis of thin laminated structures is important. Post buckling behaviors of thin laminated plates under uniaxial compression have been discussed by many researchers. However, little research has been performed on the secondary buckling phenomenon for thin laminated plate which occurs with further increase of load. In this paper, the stability condition of carbon epoxy symmetrically laminated plates with initial deflections under uniaxial compression which are simply supported along four edges is determined, using the second variation of total potential energy. The necessity of secondary buckling is proven analytically, and the effects of various factors, such as initial deflection, lamination constitution, and number of layers, are clarified.

Advanced fiber-reinforced laminated plates have been used for structural members in various fields, by virtue of their high specific strength and stiffness. This paper considers, by use of Galerkin's methods, the postbuckling behaviors of angle-ply laminated plates with initial deflection under biaxial compression that is simply supported along four edges. The inevitability of postbuckling behaviors is proved analytically, and the effects of various factors, such as initial imperfection, lamination angle, biaxial compressive load ratio, and postbuckling deflection pattern, are clarified.

Advanced ber-reinforced composite materials are being used as structural members in various elds because of their high strength and high stiffness-to-weight ratios. Hence, analysis of thin laminated structures is important. The post-buckling behaviors of thin laminated plates under uniaxial compression have been discussed by many researchers. However, little research has been performed on the secondary buckling phenomenon for thin laminated plates, which occurs with further increase of load. In this paper, the stability conditions of carbon-epoxy symmetrically laminated plates with initial de ections under uniaxial compression that are simply supported along four edges are determined using the second variation of total potential energy. The necessity of secondary buckling is proven analytically, and the effects of various factors, such as initial de ection, lamination constitution, and number of layers, are elucidated.