Asynchronous electrical activation, as induced by myocardial infarction, causes various abnormalities in left ventricle function. The influence of the electrical asynchrony on regional mechanics of the left ventricle is simulated using a mechanical heart model and an electrical heart model. The mechanical model accounts for the ventricular geometry, the fiber nature of the myocardial tissue, and the dependency of the activation sequence of the ventricular wall. The electrical model is based on a heart-torso model with realistic geometry, and different action potential waveforms with variables in duration are used to simulate the abnormal electrical activation after myocardial infarction. Regional deformation, strain and stress are calculated during systole phase. The preliminary results show that asynchronous electrical activation, as an important factor, significantly affects regional mechanical performance of the infarcted left ventricle, it indicates heterogeneous contraction pattern and elevated systolic stresses near the injured region. The simulated results are compared with solutions obtained in the literature. This simulation suggests that such coupled heart models can be used to assess the mechanical function of the left ventricle with diseases such as myocardial infarction, and more realistic models of cardiac function are essential for clinical evaluation of heart disease.
This study examines the axisymmeteric problem on an elastic layer with a penny-shaped crack situated in its middle plane. The crack surfaces are subjected to uniform pressures. The layer surfaces are free from stresses for case I while smooth-clamp conditions are prescribed on the layer surfaces for case II. By assuming series expansions for the normal displacement on the crack surfaces, both cases are reduced to analytical and exact solutions through infinite system of simultaneous equations. An expression for the stress intensity factor at the penny-shaped crack is evaluated in a simple form of a series which involves coefficients of the solutions of the simultaneous equations. Numerical results are obtained to examine the effects of the layer thickness and boundary conditions of the layer surfaces on normal stress and displacement distributions and on the stress intensity factors.
When stress corrosion cracking or corrosion fatigue occurs, multiple cracks are frequently initiated in the same area. According to section XI of the ASME Boiler and Pressure Vessel Code, multiple cracks are considered as a single combined crack in crack growth analysis, if the specified conditions are satisfied. In crack growth processes, however, no prescription for the interference between multiple cracks is given in this code. The JSME Post-Construction Code, issued in May 2000, prescribes the conditions of crack coalescence in the crack growth process. This study aimed to extend this prescription to more general cases. A simulation model was applied, to simulate the crack growth process, taking into account the interference between two cracks. This model made it possible to analyze multiple crack growth behaviors for many cases (e. g. different relative position and length) that could not be studied by experiment only. Based on these analyses, a new crack growth analysis method was suggested for taking into account the interference between multiple cracks.
This paper discusses the generation of micro-fractures in a granite under super critical water environment. In order to create an artificial pathway of water in geothermal reservoir with limited permeability, hydraulic stimulation technology is commonly employed. In this study, simulated hydraulic stimulation tests were performed using thick-walled cylindrical specimens of 45mm outer diameter, under temperatures up to 600°C and confining pressures up to 100MPa. The experimental results of simulated hydraulic stimulations showed that no macroscopic fracturing took place and predominant fluid flow occurred at high temperature regime. The permeability of the granite was also measured using the same cylindrical specimen configuration as used in the simulated hydraulic stimulation tests. The permeability test results showed that the permeability of the granite was enhanced drastically when the temperature exceeded the critical point of water, whilst no significant increase in the permeability was observed under the subcritical water condition. Optical microscopy of the micro-structural change revealed that the enhanced permeability was due to the formation of micro-fractures under the supercritical water environment. This laboratory-scale test result suggests that it may be possible to generate a micro-fracture network by injecting water into a high temperature rock mass whose conditions exceed the critical point of water and to extract the heat energy through the generated fracture network from the supercritical rock mass.
The indentation fracture (IF) method, the single-edge precracked beam (SEPB) method, and the single-edge V-notched beam (SEVNB) method were applied to evaluate the fracture toughness of four kinds of porous ceramics of SiC, Al2O3 and Mg2Al4Si5O18 with porosity ranging from 37 to 43%. The microstructures of these materials were composed of ceramics grains, glassy grain boundaries and pores. Each grain was joined together with the glassy grain boundary phase. The IF and SEPB methods were not applicable because both precracks and indenter traces were not visible. On the other hand, the SEVNB method was applicable because the V-notch could be easily machined by grinding. In the case of the SEVNB method, the applied load versus back-face strain plots under four-point bending showed nonlinearity prior to the maximum load. The R-curve behavior was estimated from the compliance change of specimens. The fracture toughness of porous ceramics was smaller than that of dense ceramics, and increased with increasing crack extension. Since the stable crack predominantly propagated along glassy grain boundaries, the R-curve behavior depended on the loading rate and matrix grain size. The increment of the R-curve by grain bridging became larger for coarser-grain sized ceramics.
By employing the Stroh formalism, a general solution satisfying the basic laws of two-dimensional linear anisotropic elasticity has been written in a complex variable formulation. To study the stress singularity, suitable stress functions have been assumed in the exponential form. The singular order near the anisotropic elastic composite wedge apex can then be found by satisfying the boundary conditions. Since there are many material constants and boundary conditions involved, the characteristic equation for the singular order usually becomes cumbersome or leaves in the form of a system of simultaneous algebraic equations. It is therefore difficult to get any important parameters to study the failure initiation of the composite wedges. Through a careful mathematical manipulation, a key matrix N^ that contains the information of material properties and wedge geometries has been found to be a dominant matrix for the determination of the singular order. A closed-form solution for the order of stress singularity is thus written in a simple form. Special cases such as the wedge corners, cracks, interfacial joints or cracks, a crack terminating at the interface, etc. can all be studied in a unified manner.
Within the framework of a phenomenological approach a set of multi-axial creep damage constitutive equations for 0.5Cr0.5Mo0.25V ferritic steel at 590°C is developed in which a new formulation is employed. The deficiency of the previous formulation and the need for improvement became apparent after a critical review of the development of creep damage constitutive equations for 316 stainless steel(1). The need for improvement was further underpinned by a call for modification of the constitutive equations(36). Recently, a specific formulation was proposed and validated(2)-(4). This paper reports the latest developments of the multi-axial creep constitutive equations for 0.5Cr0.5Mo0.25V ferritic steel at 590°C including: 1) the fundamental requirement; 2) formulation; 3) validation; and 4) conclusion. It systematically shows the suitability of this new set of constitutive equations and the incapability of the previous ones. Furthermore, it contributes knowledge to the methodology.
The research described in this paper grew from the serendipitous discovery of the TD (Twinning Deformation) effect, which was discovered by the first author. The experiment involved a Shape Memory Alloy (SMA) column that was plastically deformed into a cosine wave. The column was then compressed from either end. As the compressive force was increased, the column became straighter. The curved column-buckling load is the same as that of the straight one. In this research, numerical analysis was performed on the distributions of stress and deformation of the SMA beams under compression. Analysis of the anti-buckling capability involves a theoretical treatment of Non-Euler buckling. One way of explaining the buckling mechanism is to consider the moment-deflection ratio as a spring constant. The result of this calculation is in good agreement with those obtained for experimental buckling loads. And based on the same analysis, the neutral fiber (or structural center) of the curved column was also calculated.
Press-formed sheet metal parts are usually adhesively bonded together at the final stage of assembly. Instead of such a conventional process, a new technique of press-forming of adhesively bonded sheet metals was investigated. In this process, first flat sheets are adhesively bonded, and then press-formed into final shapes. From V-bending experiments on adhesively bonded aluminium alloy sheets, it was found that large shear deformation occurred in the adhesive layer during the bending, which in some cases lead to the delamination. Both from the experimental observations and numerical simulation, it is concluded that the large shear deformation of the adhesive layers can be suppressed when performing air-bending of enough long span, rather than die-contact V-bending.
The ultrasonic wave velocities in a polycrystalline aggregate are sensitively influenced by texture changes due to plastic deformation, and their relationship was systematically analyzed by Sayers [J. Phys. D: Appl. Phys. 15 (1982)]. According to Sayers's proposed model, it is possible to construct ultrasonic pole figures via the crystallite orientation distribution function (CODF), which can be derived by using ultrasonic wave velocity changes. In the previous paper, the theoretical modeling to simulate ultrasonic wave velocities propagating in solid materials under plastic deformation has been proposed by the authors and proved to be in good agreement with experimental results. In the present paper, the proposed theoretical modeling is applied to construct the ultrasonic pole figures based upon Sayers's model under various loading conditions of uniaxial tension, pure torsion, equi-biaxial tension-compression, biaxial compression and biaxial tension, respectively. To examine the accuracy and reliability of the ultrasonic pole figures simulated by the proposed theoretical modeling, the ultrasonic pole figures are compared with those analyzed by the finite element polycrystal model (FEPM). The results show a remarkable qualitative similarity among the two methods.
The thin films of titanium nitride(TiN)with the thickness of 0.5, 1.0, 2.0, 4.0µm were coated on a steel substrate by the ion beam mixing method. The film had a strong fiber texture with <110> axis perpendicular to the film surface. The initial residual stress was equi-biaxial compression between -4.4 to -5.6GPa. For all thickness cases, the initial part of the changes of the in-plane stresses in the film due to external tensile loading agreed well with the prediction based on elasticity. While the substrate was under an uniaxial stress, the film was in the biaxial state of stress because of the mismatch of Poisson's ratio. When the measured stress in the film exceeded a certain value, the stress departed from the linear relation and leveled off. The onset of nonlinearity was nearly coincident with the first appearance of cracks. The stresses at the onset of nonlinearity and leveling-off decreased with increasing film thickness. The ratio of Young's modulus between loading and unloading decreased as the film thickness increased.
A new noninvasive diagnosis method based on the pulse heating thermographic NDT was proposed for incipient caries of human teeth. Experiments were conducted to study the applicability of the proposed method to the quantitative evaluation of location and shape of the incipient caries as well as the quantitative diagnosis of the degree of incipient caries. The incipient caries were artificially introduced to the extracted human teeth with various severities. Impulse heat flux by the xenon flash lamp was applied to the surface of the tooth and sequential thermal images were taken by the high-speed infrared thermography. It was found that the caries were clearly identified as the localized high temperature region in the sequential thermal images. A coefficient of the temperature descent was obtained from sequential thermal images. It was found that the degree of the demineralization, i. e. the degree of incipient caries was evaluated from the temperature descent coefficient. Further the proposed technique was applied to the detection of natural incipient caries in an extracted human molar tooth. It was found that natural incipient caries was also clearly identified in the thermal images.