Analysis of crack propagation in brittle materials is reviewed. Some examples are introduced in crack path prediction under triaxial stress state, dynamic crack propagation and crack growth in nonhomogeneous materials.

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In continuum mechanics it is not clear what principle is equivalent to the principle of material frame indifference (PMFI). In the present paper, it is first shown that not only mechanical conservation laws but also frame transformation laws of constitutive quantities and source (quantities are simultaneously derived for a changing frame under the assumption that the forms of the first and second laws of thermodynamics are invariant for changes of frame. Next, considering whether the reverse proposition is true or false, an explanation of the relationship between the PMFI and the invariance of the laws of thermodynamics for changes of frame is given. Then the bases of the PMFI are determined, clarifying the relationship between the PMFI and the frame invariance of the Clausius-Duhem inequality. Moreover, it is indicated that this method, which enables derivation of conservation laws using changes of frame, is equivalent to both the principle of virtual power and the method of Green and Rivlin.

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In linear fracture mechanics, stress intensity factors which control the fracture behavior of materials are calculated from stress distributions acting on crack surfaces, with the aid of superposition even for remote applied stresses. A method of evaluating such stress distributions from each mode of discontinuous displacement along a crack with mode I and II components has been proposed by the authors. In this study, the calculation method, which was restricted to constant stress fields, has been developed for use in nonuniform stress fields so that it can be applied to fatigue cracks with residual stresses in the wake of the propagation. Using this method, local stress distributions which control the crack deformation and stress intensity factors K_Ι and K_II for the fatigue crack were predicted under a mixed-mode stress condition, and effects of residual stresses near the fatigue crack on mode II crack deformation were discussed.

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A higher-order theory of caustics for mixed-mode running cracks is developed by using the general asymptotic solutions for a dynamically propagating crack tip. The analytical expressions are obtained for the Jacobian equation that determines the initial curve, and for the image equations on a screen. With the use of the higher-order coefficients determined by the finite-element simulations of actual dynamic fracture experiments, the effects of the higher-order terms on the caustic curve are investigated on the basis of the present theory. It was found that the r^1/2 stress field plays an important role in the formation of caustic patterns. A higher-order theory of caustics for stationary cracks is also derived in this paper.

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In this paper, the effect of environmental conditions, especially humidity, on the fatigue strength of polymers is discussed. Acrylonitrile butadiene styrene (ABS) and acetal homopolymer (POM), which are utilized in industrial applications, were used. The fracture surface was observed by means of scanning electron microscopy (SEM)and the fatigue specimen was quantitatively analyzed with a scanning acoustic microscope (SAM) to clarify the influence of environmental conditions. As a result, it was found that (1) ABS and POM in high-humidity conditions exhibit a shorter fatigue life than in low- and medium-humidity conditions, and (2) the fatigue strength of polymer is considered to be influenced by the elastic properties of the specimen surface. With the measurement of leaky surface skimming compressional wave (LSSCW) velocity, elastic properties in microareas of the polymer became clear.

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In order to study the relationship between cavitation bubble collapse pressures and deformations on materials, a new technique was developed using a pressure sensor which can measure bubble collapse pressures and surface damage at the detecting area simultaneously. Impact loads occurring in a vibratory device were measured and compared with pit or crater sizes observed with a microscope at an early stage on the surfaces of pure Al, Cu, Fe and Ni. A linear relationship was obtained between impact load and the area of pit or crater. The hardnesses of various metals under impact loads at collapse in cavitation bubbles are about one order larger than those under static loads. Critical impact load necessary to form a pit or crater was found to differ among the materials.

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A method for determination of the complex shear modulus of damping materials is presented, which involves a torsional vibration test of an elastic rectangular rod bonded to layered damping materials on both sides. The value determined by means of this method must take into account the effect of the thin adhesive layers bonding the elastic and the damping material. This effect is evaluated by means of the five-layer theory accounting for the adhesive layers. The reliability of the determined values is considered in conjunction with the adhesive layer thickness and the material properties of both the adhesive and the damping material. Furthermore, instability of the determined values in the high-temperature range is discussed.

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This paper provides an exact analysis for shear stress of a symmetrical five-layered rectangular rod with damping viscoelastic core layers, and presents the torsional rigidity and loss factor in a closed form. Numerical evaluations of maximum shear stress in both elastic and core layers are carried out and the points of occurrence of the maximum stress are discussed. The layered composition which maximizes the loss factor of the rod clearly exists in accordance with the thickness of each layer and its material constant, and an optimum damping design by means of the rod composition is considered. The temperature having peak value of loss factor shifts with varying core layer thicknesses. The damping design of the rod for the environmental temperature is determined by the optimal adjustment of core layer thicknesses.

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The high-pressure phase diagram of an Al-rich Al-Li alloy at a 5.4-GPa pressure was investigated. To determine the equilibrium state under high-pressure and high-temperature conditions, the quenching method was applied and a phase analysis of the sample was performed using X-ray diffraction and microscopic observations. The resultant solid solubility of lithium in aluminum was subsequently increased up to 20 at% and the eutectic temperature increased to 800°C. Then the material properties (mainly elastic moduli) for supersaturated solid solutions treated under high pressure were also investigated. The shear modulus of the solid solutions increased at the rate of 0.28 GPa/at%Li ; in contrast, the bulk modulus decreased 0.52 GPa/at%Li.

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A numerical simulation system for the estimation of mechanical properties and functions of the human left ventricle has been constructed in an interdisciplinary research project spanning the medical and engineering fields. The numerical simulation system can be expected to improve the diagnostic techniques for heart diseases from empirical, subjective, and qualitative ones to scientific, objective and quantitative ones. The system is integrated by four fundamental models : (1) a mechanical model of myocardial muscle fiber which produces the active force, (2) a mechanical model of the left ventricle which is composed of the model muscle fiber, (3) a transmission model of electric stimulus, and (4) a circulatory system model which gives the after-and pre-loads to the left ventricular model. In this paper, the fundamental system of the simulator is explained, and some typical examples of computational results obtained by this system are shown and discussed.

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o investigate the causes of self-excited oscillations of collapsible tube flow, measurements of dynamic tube deformation were conducted using a laser displacement meter supported on a pulse-motor stage together with an electromagnetic flow meter. The results have clarified that fluid velocity approaches pressure wave velocity, which is estimated from the tube law, at the throat around the stability boundaries and that a supercritical flow and subcritical flow occur alternately during oscillations. By contrast, a linearized lumped parameter model has been developed. The model demonstrates that slight supercritical flow leads to instability of the negative stiffness type and also suggests that negative dynamic resistance induces instability of the negative damping type. Although causes such as unsteady flow separation were not examined here, a self-excited oscillation caused by supercritical flow close to choking has been verified experimentally and theoretically.

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Effects of cholesterol feeding periods on the mechanical properties of the excised thoracic and abdominal aortae of rabbits fed a diet containing a high concentration of cholesterol and saturated fat were investigated by means of a tensile testing machine. The mechanical parameters, such as tensile strength, incremental elastic modulus, tensile stress, and an elastic parameter of the thoracic and abdominal aortae, decreased during the development of atherosclerosis. However, their ultimate strain increased. The abdominal aortae were stiffer compared with the thoracic aortae during the feeding periods studied. Cholesterol concentration in blood plasma increased with the period of feeding. Although the cholesterol level significantly correlated with the decrease of tensile strength of the thoracic aortae, it was not significantly correlated with the other deformation and fracture parameters of the aorta.

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Remodeling is a critical feature of living tissue such as bone. From the mechanical viewpoint, remodeling is recognized as a regulation process of stress due to tissue growth and atrophy. The volumetric change of the bone tissue causes a nonuniform natural state. Because of the statical indeterminacy, residual stress may remain in the tissue even when all external forces are removed. Permitting the existence of the residual stress, a rate-type model is proposed for mechanical bone remodeling by means of volumetric growth/atrophy of the tissue. The rate of remodeling is expressed as a function of the local stress and its derivatives, seeking the equistress state. This does not refer to any goal stress specified a priori. The basic features of the proposed model are examined using a simple model of the diaphysial bone. A case study is conducted for a simplified tibia-fibula system, and it is demonstrated that the proposed model has the capability to describe the bone remodeling process qualitatively.

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