Insu Jeon

The role of higher order eigenfields in elastic–plastic cracks

Abstract The two-state conservation law is utilized, in conjunction with finite element analysis, to obtain the complete Williams eigenfunction series for elastic–plastic cracks, including the intensities not only for the inverse square root singularity and the T-stress but for the higher order singular and nonsingular terms as well. It is shown that the J-integral comprises only the contributions from the mutual interaction between all complementary pairs of the eigenfields. The same applies to the M-integral with a slightly different definition for the complementary pair. Particularly, it is found that the higher order singularities interact with the nonsingular higher order eigenfields to generate the extra configurational force, in addition to the energy release rate resulting from the inverse square root singularity. This additional J-value is associated with the translation of the plastic zone alone, with the crack tip being fixed. Numerical examples show that the effect of the higher order terms is negligible in terms of J when the plastic zone size is small, but that the higher order terms make a difference in the plastic zone configuration through the interaction between the singular and the nonsingular terms in the case of the large scale yielding.

Rayleigh surface wave in a piezoelectric wafer with subsurface damage

An analytical study is carried out on the propagation of Rayleigh surface waves in a piezoelectric wafer with subsurface damage. The region of subsurface damage is considered to be a functionally graded piezoelectric thin film. The findings show the influence of the gradient parameter, thickness of the region of subsurface damage, and three different types of damage on the properties of surface-wave propagation, including the phase velocity and electromechanical coupling factor. They can provide theoretical guidance in nondestructive evaluation for the analysis of the reliability and durability of electronic devices made of piezoelectric wafers.

Higher order eigenfields in mode II cracks under elastic-plastic deformation

The explicit formulation of theJ-integral and theM-integral is constructed in terms of the stress intensity factor and the higher order stress coefficients for Mode II cracks under small or large scale yielding. Furthermore, the stress intensity factor and the higher order stress coefficients as well are computed with the aid of the two-stateJ- and theM - integral, which is found to be accurate and efficient. It is found that the contribution from the higher order singularities to theJ - integral is closely related to the configuration of the plastic zone.

Edge delamination in a laminated composite strip under generalized plane deformations

Edge delamination cracks in an elastic laminated composite strip are considered within the range of generalized plane deformations. By way of a simple regular finite element method, the method of mutual integral, wherein generalized plane strain solutions are employed as auxiliary fields, is applied to edge delamination cracks to obtain the complex stress intensities. The proposed numerical scheme is found to be very efficient and accurate. Moreover, the crack growth stability is examined for various loadings, including compression, bending and torsion, in terms of the energy release rate and mode mixity.

Enriched finite element analysis for a delamination crack in a laminated composite strip

Edge delamination cracks in laminated composite strips are analyzed with the aid of the enriched finite element method, wherein the asymptotic singular solution for a delamination crack is incorporated into finite elements. The strip is assumed to be in the state of generalized plane deformations including extension (compression), bending or torsion. Comparison of the numerical results with those from other methods is made to confirm the solution. The crack growth stability is examined for a couple of ply orientations in terms of the energy release rate and mode mixity.

3D Analysis of Crack Growth in Metal Using Tension Tests and XFEM

To prevent the occurrence of fractures in metal structures, it is very important to evaluate the 3D crack growth process in those structures and any related parts. In this study, tension tests and two simulations, namely, Simulation-I and Simulation-II, were performed using XFEM to evaluate crack growth in three dimensions. In the tension test, Mode I crack growth was observed for a notched metal specimen. In Simulation-I, a 3D reconstructed model of the specimen was created using CT images of the specimen. Using this model, an FE model was constructed, and crack growth was simulated using XFEM. In Simulation-II, an ideal notch FE model of the same geometric size as the actual specimen was created and then used for simulation. Obtained crack growth simulation results were then compared. Crack growth in the metal specimen was evaluated in three dimensions. It was shown that modeling the real shape of a structure with a crack may be essential for accurately evaluating 3D crack growth.

Nondestructive Structural Analysis on Deformation Properties of Highly Porous Aluminum Material

The cell-structure of highly porous aluminum material prepared by melt foaming technology was investigated under deformation with fine-focus X-ray 3D-CT to make clear the development target porous material for automobile industries with improved reliability. It was confirmed that structures with more fine, more uniform and exclusion peculiar anisotropic pores would make improved mechanical properties of the material.

Evaluating the material properties of underfill for a reliable 3D TSV integration package using numerical analysis

Abstract The effects of the material properties of the underfill layer on thermal stress and deformation in 3D through silicon via (TSV) integration packages were evaluated through numerical analysis. Sample TSV packages with underfill composed of different silica volume ratios were fabricated. The sample packages were used to measure thermal deformation using a Moire interferometer. Also, a cross-section from these samples was used for 2D finite element modeling and numerical analysis to obtain its thermal deformation. The experimental and numerical results were compared to confirm the suitability of the numerical technique in this research. A four-chip-stacked TSV integration package, which includes underfill layers of four different silica volume ratios, was proposed and designed. The diagonal part of the TSV integration packages were three dimensionally modeled and adopted for numerical analysis. Among the underfill with different silica volume ratios in the designed packages, a silica volume ratio of around 20% shows the best performance for a reliable flip chip bonding process, effectively minimizing thermal stress and deformation in the package.

Development of Hip Joint Mechanical Stem for Minimally Invasive Surgery

Conventional total hip joint replacement(THR) surgery requires a long incision and long rehabilitation time. The stem used in THR is inserted into the cancellous bone of the femur where it plays the role of the artificial joint. Minimally invasive surgery(MIS) has been devised to reduce muscle damage to patients. In this study, a mechanical stem was developed on the basis of MISto reduce the incision length through the principle of the gear. The mechanical stem consists of six components. A prototypical model for a mechanical stem was fabricated using an acryl-based polymer, and its workability was confirmed. To actualize the mechanical stem, a three-dimensional Bio-CAD modeling technique was applied. The hip joint area based on computed tomography(CT) was reconstructed. The safety of the mechanical stem by applying more load than the weight of a man under virtual surgery environment conditions was confirmed by finite element analysis.

Structural analysis on anisotropic deformation properties of highly porous aluminum material

The cell-structure of highly porous aluminum material prepared by foaming of aluminum alloy melt with titanium hydride was investigated nondestructively with fine-focus X-ray 3D-CT at several interrupt steps during slow compressive deformation. The foamed highly porous aluminum has anisotropic shape of each cell inevitably because of gravity force during solidification of foamed material and mechanical properties especially the dependence on the deformation direction of highly porous aluminum is analyzed well from the size and shape of each void composing the porous material. The statistic anisotropic distribution of these form factors such as three axial lengths and directions at the time of ellipsoidal approximation of each cell was found to be less important to improve the mechanical properties of this type of material.