Study on vibration and stability of functionally graded cylindrical shells subjected to hydrostatic pressure

Based on the Flügge’s shell theory, the vibration characteristics and stability of submerged functionally graded (FG) cylindrical shell under hydrostatic pressure is examined. By means of conversion switch on axial wave number, the coupled frequency of submerged FG cylindrical shell with various boundary conditions is obtained, using wave propagation method and Newton method. Then the critical pressure of FG cylindrical shells is given by applying linear fitting method. Results are compared to known solutions, where these solutions exist. The natural frequency and critical pressure of FG cylindrical shell are illustrated. The effects of constituent materials, volume fraction, boundary condition and dimensions on the natural frequencies and critical pressures of submerged FG cylindrical shell are illustrated by examples

Stress intensity factors for cusp-type crack problem under mechanical and thermal loading

The general solutions of the stress intensity factors (SIFs) for a cusp-type crack problem under remote uniform mechanical and thermal loads are presented in this work. According to the complex variable theory and the method of conformal mapping, a symmetric airfoil crack is mapped onto a unit circle, and both the temperature and stress potentials are used to solve the relevant boundary-value problems. By introducing the auxiliary function and applying the analytical continuation theorem, the SIFs at the cusp-type crack tip can be analytically determined. The obtained SIF results are dependent on the geometric configurations of the cusp-type crack components and the magnitudes of the mechanical and thermal loads. For some combinations of combined loads, the SIF is maximized, and the system has a high risk of damage

Study on vibration and stability of functionally graded cylindrical shells subjected to hydrostatic pressure

Based on the Flügge’s shell theory, the vibration characteristics and stability of submergedfunctionally graded (FG) cylindrical shell under hydrostatic pressure is examined. By means of conversionswitch on axial wave number, the coupled frequency of submerged FG cylindrical shell with variousboundary conditions is obtained, using wave propagation method and Newton method. Then the criticalpressure of FG cylindrical shells is given by applying linear fitting method. Results are compared to knownsolutions, where these solutions exist. The natural frequency and critical pressure of FG cylindrical shell are illustrated. The effects of constituent materials, volume fraction, boundary condition and dimensions on the natural frequencies and critical pressures of submerged FG cylindrical shell are illustrated by examples.2nd International Symposium on Engineering Mechanics and its Applications, Kitakyushu, Japan, 30 – 31 August 201

Convenient Devonding Strength Evaluatiom for Spray Coating Based on Intensity of Singular Stress

Hearth rolls are used in continuous annealing furnace to produce thin steel sheet. The roll surface is usually coated by using thermal spraying, which has high adhesive strength and wears resistance. However, in the ceramics coating, thermal stress caused during heating and cooling process in the furnace may lead to debonding due to the low toughness of ceramics. In order to improve the heat resistance of the thermally sprayed coating, it is essential to evaluate the debonding strength. Generally, heat resistance of thermal spray coating is evaluated by thermal shock test prescribed by JIS H8304 and it has been discussed in terms of singular stress at the end of the interface for JIS specimen under thermal shock. However there is no research considering the real axial-symmetric geometry condition of the multilayer structure. Thus this paper will focus on the intensity of the singular stress at the end of interface for a 2D axial-symmetric model. Then, the most suitable conditions are discussed with varying the coating thickness and compared with our previous study.Proceedings of 5th International Conference on Fracture Fatigue and Wear, FFW 2016, 24-26 August 2016, Kitakyushu, Japa

Evaluation of Adhesive Strength Based on the Intensity of Singular Stress Field of Single Lap Joint

In this study, the adhesive strength for single lap joint is investigated based on the intensity of singular stress field. First, the critical intensity of singular stress at the adhesive dissimilar joint is calculated by using finite element method (FEM) based on the experimental result. It is found that the adhesive strength can be expressed as the critical intensity of singular stress field. Then, a suitable evaluation method of adhesive strength is investigated focusing on the intensity of singular stress field. The effect of specimen geometry on the intensity of singular stress is considered. The results show that the intensity of singular stress field decreases with increasing the adherend thickness, the minimum intensity of singular stress can be obtained when the adherend thickness is large enough. The results of the deformation angle at the interface corner edge show a similar trend as in intensity of singular stress field, and the minimum deformation angle can be obtained when the adherend thickness is large enough. The usefulness of the method is investigated focusing on the deformation angle at the interface corner edge.Proceedings of 5th International Conference on Fracture Fatigue and Wear, FFW 2016, 24-26 August 2016, Kitakyushu, Japa

The strain rate concentration factor for round and flat test specimens

In this study, the strain rate concentration is considered for high speed tensile test, which is now being recognized as a standard testing method. To evaluate the impact strength of engineering materials, Izod and Charpy tests are unsuitable since they cannot control the impact speeds and therefore the testing results do not coincide with the real failure of real products. For smooth specimens, the strain rate can be determined from the tensile speed u/t and specimen length l as ε̇smooth=u/tl. For notched specimens, however, the strain rate at the notch root ε̇notch should be analyzed accurately. In this study, therefore, the strain rate concentration factor defined as Kt ε̇ = ε̇notch/ε̇smooth is studied with varying the notch geometry and specimen length for round and flat test specimens. In particular, the relationship between the strain rate concentration factor and the stress concentration factor is investigated by varying the notch geometry and specimen length

Several solutions of intensity of singular stress useful for evaluating bonded strength

Proceedings of 4th International Conference on Fracture Fatigue and Wear, FFW 2015, Ghent University, Belgium, 27-28 August 2015Adhesive joints are widely used in many industrial sectors since the numerous advantages over other traditional joints. However the mismatch of different materials may cause debonding of the joints. Since few studies are available for evaluating the bonded strength, this study will focuses on the solutions for the intensity of the singular stress for several typical adhesive joints, such as bonded plate and butt joint in plane stress state, bonded cylinder/pipe under axial-symmetric state. In this research, an effective numerical method combined with FEM results is used to obtain the SIFs at corner of adhesive joints in arbitrary material combinations. Here the simple bonded plate, which has already been solved accurately in our previous study, is used as the reference problem. We will discuss the effect of the adhesive thickness in a butt joint, and defined a new parameter for semi-infinite structure; and for the bonded joints in axial-symmetric, the nonsingular terms are derived so that the SIFs can be obtained, and it is found that the axial-symmetric problem are quite different since the SIFs cannot be dominated by the Dunders’ parameters. And at last, the SIFs for several problems are discussed and compared with each other

Several solutions of intensity of singular stress useful for evaluating bonded strength

Adhesive joints are widely used in many industrial sectors since the numerous advantages over other traditional joints. However the mismatch of different materials may cause debonding of the joints. Since few studies are available for evaluating the bonded strength, this study will focuses on the solutions for the intensity of the singular stress for several typical adhesive joints, such as bonded plate and butt joint in plane stress state, bonded cylinder/pipe under axial-symmetric state. In this research, an effective numerical method combined with FEM results is used to obtain the SIFs at corner of adhesive joints in arbitrary material combinations. Here the simple bonded plate, which has already been solved accurately in our previous study, is used as the reference problem. We will discuss the effect of the adhesive thickness in a butt joint, and defined a new parameter for semi-infinite structure; and for the bonded joints in axial-symmetric, the nonsingular terms are derived so that the SIFs can be obtained, and it is found that the axial-symmetric problem are quite different since the SIFs cannot be dominated by the Dunders’ parameters. And at last, the SIFs for several problems are discussed and compared with each other.Proceedings of 4th International Conference on Fracture Fatigue and Wear, FFW 2015, Ghent University, Belgium, 27-28 August 201

Vibrio parahaemolyticus, enterotoxigenic Escherichia coli, enterohemorrhagic Escherichia coli and Vibrio cholerae

This review highlighted the following: (i) pathogenic mechanism of the thermostable direct hemolysin produced by Vibrio parahaemolyticus, especially on its cardiotoxicity, (ii) heat-labile and heat-stable enterotoxins produced by enterotoxigenic Escherichia coli, especially structure–activity relationship of heat-stable enterotoxin, (iii) RNA N-glycosidase activity of Vero toxins (VT1 and VT2) produced by enterohemorrhagic Escherichia coli O157:H7, (iv) discovery of Vibrio cholerae O139, (v) isolation of new variant of Vibrio cholerae O1 El Tor that carries classical ctxB, and production of high concentration of cholera toxin by these strains, and (vi) conversion of viable but nonculturable (VBNC) Vibrio cholerae to culturable state by co-culture with eukaryotic cells