CRIEPI has developed a highly accurate, low cost flaw depth sizing technique in ultrasonic nondestructive inspection, which is easy-to-use in comparison to standard techniques such as crack tip diffraction and TOFD techniques. This technique is called the short path of diffraction (SPOD) technique. This paper deals with essential parameter such as vibration mode, refracted angle and probe separation for back surface breaking flaws.

View full abstract

CRIEPI has developed a high accurate, low cost, efficient flaw depth sizing technique in ultrasonic nondestructive inspection, which is easy to use in comparison to standard techniques such as crack tip diffraction and TOFD techniques. This technique is called the short path of diffraction (SPOD) technique. This paper deals with applicability of SPOD to front surface flaws. In this paper is has shown that SPOD can be applied to depth sizing of front surface flaws as well as back surface flaws

View full abstract

An efficient homogenization method for nonlinear problems is introduced. In order to avoid prohibitive computational cost, we have already developed a homogenization technique using characteristic deformation mode superposition. However, in the mode superposition technique, the approximation error is caused depending on the analysis case. In this paper a new method is proposed, in which the same accuracy as the exact method is preserved by solving the microscopic equilibrium equation while the tangential matrix of the multiscale equilibrium equation is approximated using the mode superposition method. The performance of the proposed method is examined together with the block LU factorization algorithm, and satisfactory results are obtained.

View full abstract

Adaptive mesh refinement and local/non-local transition in our quasicontinuum method (Phys. Rev. B, Vol.69, No.21 (2004), pp. 214104 (1-10).) are studied in this paper. Although deformation gradients have been used to determine the mechanical state of an element in the original quasicontinuum method, we adopt elastic stiffness coefficients which govern stress-strain relations at finite deformation. Elastic stiffness coefficients are calculated using the interatomic potential function, so we do not need to prepare reference node (atomic) positions. Confirming its availability, we perform nano-indentation simulations in the two dimension, and it is found that the criterion values estimated using deformation gradients or elastic stiffness coefficients show a positive correlation.

View full abstract

This paper deals with one-dimensional generalized thermoelasticity in a composite thin film constructed of a piezoceramic layer and a structural layer, when damping effect is taken into account. The film is initially at reference temperature and subjected to a ramp heating on the free surface of the piezoceramic layer. By applying Lord and Shulman's theory, the governing equations for the temperature changes, heat fluxes, particle velocities, axial stresses and electric field intensity are reduced to a system of nine first-order partial differential equations. This problem has been numerically analyzed by employing the method of characteristics. Finally, the effect of a damping coefficient on time histories of the temperature changes, axial stresses and electric field intensity are illustrated graphically.

View full abstract

This paper investigates the thermoelectromechanical interaction between two parallel cracks in a piezoelectric strip under thermoelectric loadings. The crack faces are supposed to be insulated thermally and electrically. By using the Fourier transform, the thermal and electromechanical problems are reduced to a system of singular integral equations, respectively, which are solved numerically. Numerical calculations are carried out, and detailed results are presented to illustrate the influence of the crack length, the crack location, the crack spacing and the magnitude of the electric loading on the stress and electric displacement intensity factors.

View full abstract

In the assessment of structural integrity and remaining life of a power component operated at high temperatures, creep-fatigue damage evaluation is frequently required. When evaluating creep-fatigue damage, peak strain range and relaxation history of peak stress in the component are needed to estimate. These stresses and strains are, in many cases, generated by secondary stresses. Fully inelastic finite element stress analysis may provide the necessary information on these. Performance of and preparations for this kind of analysis are, however, usually laboring and costly. This paper investigates elastic follow-up behaviors in components subjected to displacement-controlled loading, and proposes simplified methods to assess peak strain and relaxation history of peak stress basically from elastic stress analysis. The methods are based on the nature of elastic follow-up factors of power law type inelastic bodies.

View full abstract

The extended finite element method (X-FEM), which can model the domain without explicitly meshing crack surface, can perform stress analyses for solving fracture mechanics problems efficiently. In this study the principle of superposition is utilized to solve crack problems in conjunction with X-FEM. In the proposed method, the surface load distributed on the crack surface, which is modeled implicitly by the interpolation functions with enrichment terms, is introduced to X-FEM analysis. Moreover the energy release rate at the crack front is evaluated by the domain integral method with boundary integral terms for the surface load. The proposed method is verified through numerical analyses of two-and three-dimensional crack problems in the linear fracture mechanics.

View full abstract

A new numerical method was presented for stress intensity factors (SIFs) analyses of a three-dimensional interface crack between dissimilar anisotropic materials subjected to thermal stress. The M-integral method was applied to the thermoelastic interfacial crack in three-dimensional anisotropic bimaterials. The moving least square method was used to calculate the value of the M-integral. The M-integral in conjunction with the moving least square method can calculate the SIFs from only nodal displacements obtained by the finite element analysis. We analyzed the SIFs of external circular interfacial cracks in jointed dissimilar anisotropic solids subjected to thermal load and showed the distributions of SIFs along the crack front. The distribution of stress and the crack opening displacement obtained by the asymptotic solution with the SIFs are compared with those obtained by the FEM with fine mesh. They are almost identical each other.

View full abstract

In our laboratory, cavitation erosion experiments have been carried out on various materials for about 40 years since 1970. The database was constructed and carbon steel data was analyzed in 2004. In this study, erosion resistance of cast irons, aluminum alloys, copper alloys and titanium alloys are compared with the regular carbon steels. The resistance is 1/3 to 1/5 lower for gray cast iron and 2/3 to 1/3 for ductile cast iron as compared with carbon steel of the same hardness. When cast irons are exposed to cavitation, graphite was removed first and the region acts as a stress raiser, and therefore the erosion resistance of cast iron is much lower than that of carbon steel with the same hardness. The resistance is 1/3 to 1/5 for aluminum alloy as compared with carbon steel. Erosion resistance of aluminum alloys are lower than carbon steel, because the fatigue strength of aluminum alloys is as low as one half of the fatigue strength of carbon steel. The resistance of copper alloy and titanium alloy is almost the same as that of carbon steel.

View full abstract

Cavitation erosion often causes the leakage of water in piping systems of industrial plants. In this study, cavitation erosion tests were carried out for the pipe steel specimens fabricated from carbon steel pipes for pressure service, alloy steel pipes and stainless steel pipes. Total 15 pipe materials were tested in a stationary specimen test method using a vibratory apparatus specified by ASTM G32-03 and cavitation erosion were evaluated for each material. It was found that the erosion resistance could be estimated precisely by material hardness.

View full abstract

This study deals with the deformation and mechanical response of a shape-control plate which consists of an aluminum alloy plate and a pre-strained NiTi shape memory alloy (SMA) wire. The shape-control plate exhibits reciprocating bending deformation by heating and cooling. Bending deformation tests of the plate are carried out by electric heating and natural cooling of the SMA wire, and then mechanical response of the bent plate under electric heating is examined by three-point-bending. The experimental results exhibit that the bending deformation of the plate is considerably stable over more than two thousand heating-cooling cycles, and that the load-deflection relation of the bent plate is almost linear. Furthermore, the bending deformation and mechanical response of the plate are analyzed by a simple beam theory for the aluminum alloy plate and Brinson's one-dimensional constitutive model for the SMA wire. The numerical results describe well the deformation behavior and mechanical response of the shape-control plate observed in the experiments. The proposed numerical model can be useful in the design and estimation of the shape-control plate.

View full abstract

The effect of tool geometry on microstructure and tensile shear strength in friction stir spot welds of 6061 aluminium alloy sheets was studied. Tools with three different shoulder diameters were evaluated. The shape parameters d_n and t_u were defined from the weld structure observed on the cross section of the weld centre, which represent the actual nugget size and the thickness of the upper sheet under tool shoulder circumference, respectively. These parameters and the shape of the boundary between the upper and lower sheets varied depending on shoulder diameter, tool rotational speed and tool holding time. The tensile shear strengths at the fixed tool rotational speed were dependent on tool holding time and shoulder diameter. Two fracture modes were recognized under tensile shear loading at the shoulder diameters of 10 and 15 mm. The dependence of static strength on shoulder diameter was discussed based on the shape parameters and fracture modes.

View full abstract

Electromagnetic acoustic transducers (EMATs) are applied to detection of resin flow front in manufacturing process of fiber reinforced plastics by resin transfer molding (RTM) method. In order to improve the quality of RTM products, real-time monitoring of resin flow is required. Dielectric sensors have been used for such purposes, although they should be embedded in the products. In this study, we propose to detect the resin flow front by measuring the amplitude of multiple echoes in the mold. Reflection coefficient of ultrasonic wave depends on the boundary condition. During the passage of flow front across the measuring area, echo amplitude decreases. Multi-point EMAT, which dispenses with the sensor scan, is also developed. It was ensured that the resin flow front passage can be detected as stepdown of echo amplitude using the EMAT set on the outer surface of the mold.

View full abstract

Both surface hardness and subsurface depth of hardening in carbon steel parts after induction hardening could be nondestructively predicted by measuring a diffraction peak broadening, because the shape of X-ray diffraction peak broadened in proportion to martensitic transformation quantity in our previous study. However, this nondestructive method had a serious problem that the prediction accuracy lowered when thick martensite layer remained on the surface of parts. In this study, peak broadening of plural points including the inspection point were measured, and then the subsurface hardened zone depth was spatially estimated. As the result, the prediction error was about 2.6 mm by measuring peak broadening at the only inspection point, while the prediction error could be improved to 0.2mm by the adoption of multipoint evaluation method. The improved prediction error of 0.2mm was comparable to that by measuring hardness distribution on the cut surface of parts.

View full abstract

Carbon nanotubes (CNTs) are potentially useful for developing functional nanodevices such as thermal probes, flow sensor arrays, and AFM probes. Controlling the growth position of CNTs grown by chemical vapor deposition (CVD) is crucial to fabrication of these nanodevices. We propose an easy, non-lithographic process of making CNT sensor probes using CVD. Growth positions of CNTs were precisely controlled by depositing a patterned barrier layer above the catalyst layer. Then, the CNTs were grown from the exposed catalyst layer using CVD. This method is easily applied to assembling bridged CNTs. We used focused ion beam etching to remove the barrier layer and expose the catalyst membrane. Through the proposed method, we made a bridge of CNTs at the tip of a Si edge. This type of bridge can be used as the nanoprobes for local sensing of physical properties.

View full abstract

Various studies have been conducted on using magnesium alloy instead of conventional iron or aluminum in automobile components, office equipment, home electric appliance, due to the light weight and superior specific strength of magnesium alloy. However, even stronger alloys are needed for structural material. One common way to enhance the strength of magnesium alloy is to increase the Al content. Compacted and solidified billets (preforming) were manufactured using chips (powder) of an AZ91 alloy, and a satisfactory extruding material was obtained by extruding the billets. The report describes the manufacturing of billets from AZ91 chips, extruding of the billets, and studies on the extrusion properties and mechanical characteristics of the extruded material.

View full abstract