Impact extractive fracture of jointed steel plates of a bolted joint

This study is concerned with the development of a fracture criterion for the impact fracture of jointed steel plates of a bolted joint used in a car body. For the accurate prediction of crash characteristics of car bodies by computer-aided engineering (CAE), it is also necessary to examine the behavior and fracture of jointed steel plates subjected to impact loads. Although the actual impact fracture of jointed steel plates of a bolted joint used in cars is complicated, for simplifying the problem it might be classified into the shear fracture and the extractive fracture of jointed steel plates. Attention is given to the extractive fracture of jointed steel plates in this study. The extractive behavior and fracture of three kinds of steel plates used for cars are examined in experiments and numerical simulations. The impact extraction test of steel plates jointed by a bolt is performed using the one-bar method, together with the static test. In order to understand the mechanism of extractive fracture process of jointed steel plates, numerical simulations by a FEM code LS-DYNA are also carried out. The obtained results suggest that a stress-based fracture criterion may be developed for the impact extractive fracture of jointed steel plates of a bolted joint used in a car body

Thermoelastic Damping in Micro- and Nano-Mechanical Systems

The importance of thermoelastic damping as a fundamental dissipation mechanism for small-scale mechanical resonators is evaluated in light of recent efforts to design high-Q micrometer- and nanometer-scale electro-mechanical systems (MEMS and NEMS). The equations of linear thermoelasticity are used to give a simple derivation for thermoelastic damping of small flexural vibrations in thin beams. It is shown that Zener's well-known approximation by a Lorentzian with a single thermal relaxation time slightly deviates from the exact expression.Comment: 10 pages. Submitted to Phys. Rev.

Numerical Study on Characteristics of Stress in Ω-Shaped Tubular Bellows

Tubular bellows is a mechanical device for absorbing energy or displacement in structures. It is widely used to deal with vibrations, thermal expansion, and the angular, radial, and axial displacements of components. In the present study, the characteristics of stress in Ω-shaped tubular bellows are studied numerically. An Ω-shaped of tubular bellows available in market is subjected to internal pressure and deflection loads. The stresses are compared with the conventional U-shaped bellows. Elastic analyses of a two-dimensional, axisymmetric model with structural solid elements were carried out. A full convolution of each bellow was modeled. The dimensions of the bellows are as follows: ri_i = 64mm, r_0 = 77mm, q = 11.5 mm, and thickness t = 0.45mm. The bellows are made of SUS321 with properties of E = 193 GPa and υ = 0.3. The numerical results show good agrement with analytical results. The distributions of axial stresses are plotted for each bellows. It was concluded that the most destructive stress in bellows was meridional bending stress. The meridional bending stress in Ω-shaped of tubular bellows are lower than the U-shaped ones but higher than in toroidal bellows.特集 : Special Section for the Papers Presented at the Symposium on Mechanical Engineering, Industrial Engineering, and Robotics held at Noboribetsu, Hokkaido, Japan on 11 - 12 January 201

Decreased alveolar bone turnover is related to the occurrence of root resorption during experimental tooth movement in dogs

Objective:  To investigate the relationship between root resorption (RR) and bone turnover in two different types of tooth movement in dogs. Materials and Methods:  A total of 16 dogs in two different groups were used. Tooth movement of dog premolars resulted from approximately 200 g of force. Histomorphometric analysis of premolar roots was assessed after 4 and 12 weeks of tooth movement by comparing nonresorptive to resorptive surfaces. Results:  Histomorphometric analysis indicated a significant decrease in the bone formation rate in the root resorptive areas, which resulted in decreased bone volume after 12 weeks. The threshold to detect RR in periapical radiographs was about 1.0 mm2. Conclusions:  A sustained mechanical load, due to the prolonged stress and strain of continuous mechanics, induces elevated bone metabolic activity, such as the bone turnover (remodeling) and change in bone volume (modeling). Therefore, our data support the hypothesis that increased RR is related to decreased bone formation (turnover) in high stress areas exposed to prolonged orthodontic tooth movement

ステンレス・フレキシブルチューブの健全性評価

平成23年度 プレ共同研究成

Behaviour of Crack-Rate Sensitive Brittle Materials in Dynamic Lateral Compression

In order to investigate the behaviour of brittle tubular materials in static and dynamic lateral compression tests (LC tests), an analytical technique including crack-rate sensitivity of brittle materials was applied. From the analysis, it was found that the maximum load, Pmax, in LC tests increases with the increase of the loading rate and this tendency is more remarkable when the crack-rate sensitivity of a brittle material is large. The results from dynamic and static experiments using a mullite ceramic tubes support reasonably the results obtained from the analysis.Dans le but d'étudier le comportement des matériaux fragiles en forme de tube, en essais de compression latérale (essais CL) en estimation statique et dynamique, une technique analytique incluse la sensibilité de la vélocité de la fissure des matériaux fragiles a été appliquée. Du point de vue de l'analyse, il a été observé que la charge maximale, Pmax, en essais CL croît avec l'augmentation de la vitesse du chargement. Cette tendance est plus remarquable quand la sensibilité de la vitesse de la fissure des matériaux fragiles est grande. Les résultats expérimentaux obtenus à partir de l'estimation statique et dynamique en utilisant les tubes en céramique-mullite, supportent bien les résultats obtenus à partir de l'analyse

Dynamic and quasi-static lateral compression tests of ceramics tubes

Dans le but d'étudier la déformation des tubes céramiques en compression latérale, une série d'expérience a été conduite en velocité dynamique et statique. Il a été constaté que la charge et la deflection quand la fracture s'est produite en essais dynamiques sont plus grandes que celles obtenues en essais statiques. Cependant, aucune différence dans le module d'Young n'est apparue dans les deux cas. En utilisant la theorie des poutres en coubes primaires, la pression de fracture des tubes ceramiques pourraient être dérivée des resultats expérimentaux. Le module d'Young a montré une bonne concordance avec les resultats obtenus à partir des essais de tension. La pression de fracture a aussi montré la valeur proche de la resistance au fléchissement des tubes céramiques.In order to investigate the deformation of ceramics tube in lateral compression, a series of experiments was carried out at dynamic and static rates. It was observed that the load and deflection when fracture occurred in dynamic tests were greater than those obtained in static tests. However, a difference between Young's moduli obtained dynamically and statically was not found. By using a primary curved beam theory, Young's modulus and the fracture stress of ceramics tube could be derived from the results of experiments. The Young's modulus showed reasonable agreement with that obtained from tensile tests. The fracture stress also showed the value close to the bending strength of the ceramics tube