Materials Science Forum Vol. 813

Abstract: For all the concrete structures in marine environment, the durability of concrete structures is focus of the concern for the serious corrosion of reinforcement in concrete caused by chloride penetration. The core issues of chloride penetration are chloride transportation mechanics in marine concrete. So it is important to study chloride transportation mechanics in marine concrete under coupling action of multi-mechanistic. The variational principle of coupling dynamics of chloride transportation is established by work and energy transfer principle and energy conservation law. Complete basic equations are obtained by deriving stationary value conditions of variational principle of coupling dynamics of chloride transportation. It is shown in this paper that it is a suitable way to study coupling dynamics of chloride transportation by variational principles.

Abstract: Geometric configurations such as hull shape, shell thickness, stiffener layout, and type of materials are the key factors influencing the structural performance of pressure hulls. The aim of this study is to maximize the structural efficiency of elliptical deep-submerged pressure hull under hydrostatic pressure. Minimize the buoyancy factor of a submarine pressure hull under hydrostatic pressure was proposed as an objective function for both composite and steel models. The thickness and the orientation angle of each layer, the radii of the ellipse and the operating depth are taken as design variables. Also, the shell buckling strength and the angle-ply laminated failure strength are considered in the case of composite model. In the other hand, the shell thickness, the radii of the ellipse, the stiffeners offsets, the stiffeners dimensions, and the operating depth, are selected as design variables for steel model with shell buckling and materials yielding constraints. The analysis is performed using commercial finite element analysis software ANSYS. Additionally, a sensitivity analysis is performed to study the influence of the design variables on the structural optimum design. Results of this study provide a valuable reference for designers of underwater vehicles.

Abstract: In this work, a computational method dedicates to realize the residual stress calculation for multi depths with incremental hole-drilling method. An optimized finite element model is determined with proper size compared to the experiment. By invaliding the mechanical properties of the drilled section in the model, the step-by-step drilling procedure is simulated for incremental hole-drilling method. As the practical application of such computational method, a bulk metallic glass (BMG) sample being mechanically treated by severe plastic process is used to demonstrate the distribution of residual stresses along thickness direction.

Abstract: The foam core sandwich composite ship is a new kind ship using special materials. The advantages include easy molding, short construction period and so on. However, due to the specialty of the material property as well as the complexity of structures, there are element applicability and calculation efficiency problems when conducting FEA (Finite Element Analysis) calculations of the whole ship. Based on experiment and simulation result, a sandwich shell element is found which is equivalent to the solid element of beam and plate. An efficient and practical way is developed using this equivalent shell element to calculate a catamaran including the analysis of the structure responses in different working conditions. This methodology has a great reference value when conducting computer simulation calculation of foam core sandwich composite ships and marine structures.

Abstract: It is widely believed that large composite materials are difficult to build a ship which is longer than 40 meters because of lack of structural stiffness. Up to now, the ships, 72-meter in length, made of glass fiber reinforced composite have been in serve abroad, while 35 meters in China. Therefore, it’s absolutely necessary to study the problem about the stiffness of the 70-metre composite materials hulls. Start from integration design and finite element analysis of composite materials and structure, the influences of material component, laminated angle and laminated sequences of composite materials’ hull on the dynamic stiffness and static stiffness of the ship are studied to explore the method of improving stiffness. The result show that, in the conditions of having the same molded surface, ship's weight and applied stress, it can improve the ship’s longitudinal stiffness to reach standard requirements by using the part of the high modulus fiber as well as the high modulus fiber laying on the outboard of the hull.

Abstract: Fatigue is a major cause of failure in marine structures resulting from random wave and wind loading. A nonlinear ultrasound method for fatigue evaluation which uses interaction of two non-collinear nonlinear ultrasonic waves with quadratic nonlinearity is investigated in this paper. A hyperbolic system of conservation laws is applied here and a semi-discrete central scheme is used to solve the numerical problem. The numerical results prove that a resonant wave can be generated by two primary waves with certain resonant conditions. Features of the resonant wave are analyzed both in the time and frequency domains, and several regularities are found on intensity distribution of the resonant wave in two-dimensional domain.

Abstract: Interfacial creep fracture behavior of sandwich composites consisting of E-glass/ unsaturated polyester (UPE) resin and E-glass/vinyl ester (VE) resin facings over PMI foam core has been experimentally investigated. Digital image correlation (DIC) method was employed in the double cantilever beam (DCB) test to measure the creep displacement field surrounding the crack tip. Crack opening displacements (COD) at various creep time were extracted from the creep displacement field and mode I stress intensity factors were determined using the small region COD-based linear extrapolation method. Significant increments of COD and nominal stress intensity factor are found in specimen with UPE resin and specimen with VE resin after 24 hours creep test. It is also found that specimen with UPE resin has a better interfacial creep fracture resistance than that of specimen with VE resin.

Abstract: In the present paper, pCBT casts and pCBT/E-glass fiber composites were prepared. In order to study the mechanical performance of the thermoplastic material in the aging environment, the specimens were exposed to salt spray, hygrothermal as well as immersion conditions. The hygroscopicity and mechanisation of the material were studied. From this research work, it is found that, in corrosion tests, the water absorb rate increases at the beginning of the test and decreases with the increase of time. Chloride ion concentrationb and a higher corrosion time have some influence on the moisture absorption kinetics. The results also show that the mechanical properties such as modulus and strength of pCBT and its glass fiber composites change with the trendency of moisture absorption curves.

Abstract: In order to study on mechanical performance as the target of environmental corrosion resistance property, three kinds of glass fiber fabrics like biaxial warp knitted fabric, biaxial stitch-bonded felt and three axial warp knitted fabric were used to prepare textile reinforced composites in five layers laminated structure, which were soaked in seawater environment for 180 days. The result showed that, the surface appearance of textile reinforced composite became muddy and the color became darker, the tensile strength and bending strength of composites decline of the whole with the extension of soak time, the average loss rate of tensile and bending performance are respectively 24.8% and 56.5%, all of these provide the theoretical basis for researching and developing high-quality composite materials.

Abstract: In natural medium, engineering materials and structures, it can be found that there are cavities everywhere. Sometimes the surface of the structure is fixed, and it could be seen as a rigid line. When structure is impacted by dynamic load, the scattering field will be produced because of the cavities and the fixed surface, and it could cause dynamic stress concentration at the edge of the cavities. In this paper, the solution of displacement field for elastic semi-space with fixed surface and multiple cylindrical cavities by anti-plane SH-wave is constructed. In complex plane, considering the displacement boundary condition of the fixed surface, the displacement field aroused by the anti-plane SH-wave and the scattering displacement field impacted by the cylindrical cavities comprised of Fourier-Bessel series with undetermined coefficients are constructed. Through applying the method of multi-polar coordinate system, the equations with unknown coefficients can be obtained by using the stress free condition of the cylindrical cavities in the radial direction. According to orthogonality condition for trigonometric function, these equations can be reduced to a series of algebraic equations. Then the value of the unknown coefficients can be obtained by solving these algebraic equations. The total wave displacement field is the superposition of the displacement field aroused by the anti-plane SH-wave and the scattering displacement field. By using the expressions, an example is provided to show the effect of the change of relative location of the cylindrical cavities. Based on this solution, the problem of interaction of multiple cylindrical cavities and a linear crack in semi-space with fixed surface can be investigated further.