Stress-strain curves of polycarbonate (PC) are determined in a wide range of strain rates under conditions of uniaxial strain. The effect of strain rate on the stress is investigated under these conditions. A plate impact testing apparatus, a drop hammer testing machine and a universal testing machine are used for the high strain rate (10^6 to 10^7 s^<-1>), medium strain rate (10^2 s^<-1>) and low strain rate (10^<-3>s^<-1>) tests, respectively. The plate impact test is used to obtain stress-strain curves for PC undergoing uniaxial strain. Stress-time histories are obtained in PC at impact velocities of 718 and 540 m/s using polyvinylidene fluoride (PVDF) gauges. Lagrangian analysis is used to extract strain-time histories under conditions of uniaxial strain from the experimental stress data. The drop hammer testing and universal testing methods combined with an extrapolation procedure are used to determine the stress-strain behaviors of PC under conditions of uniaxial stress. The stress-strain curves at medium and low strain rates in uniaxial strain are constructed on the basis of the Wood's equation from the uniaxial stress data. The strain-rate sensitivity of the stress is found to increase when the strain rate is raised into the shock loading regime.

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The mechanical response of a bellows under impact loading and unloading was determined by the strain-gauge method and analyzed by the finite element method (FEM). It was found that the FEM simulated strain responses agree well with the experimentally measured ones, and the maximum axial stress occurs on the inner surface of the inner corrugation nearest the fixed end of the bellows. Amplitudes of the stress response increase with increasing loading or unloading speeds on the bellows.

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This paper presents the results of an investigation carried out into the plastic collapse and deformation behaviour of a rotating pipe impact on a stationary target pipe. To predict the plastic energy dissipation during the deformation of circular section pipes, a modified plastic collapse analysis adapting upper bound technique based on an existing deformation mechanism model was considered. The studies carried out show clearly that the failure mode in a pipe during impact with another pipe or with a solid rod does not only depend on relative local strength of these pipes but is due to a complex interaction of various parameters, e.g. impact velocity, span to diameter ratio of the target pipe and the supporting conditions of the target pipe and also of the impact position. The results throw good light and illustrate the influence of kinetic energy and its impact position on the energy absorption characteristic of the target pipe.

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This paper deals with the attenuation of impact load through patella-patellar tendon-tibial tuberosity (PTT) complex with respect to the progress of ossification of growing cartilage in tibial tuberosity. Materials used in this study were PTT complexes and patellar tendons taken from porcine hind legs with three different stages of ossification of tibial tuberosity. Their stages of ossification were represented by body weight (20, 100, and 200kgf). Impact tensile tests on PTT complexes and patellar tendons were performed at room temperature using the split-Hopkinson pressure bar technique. In both tests on PTT and patellar tendons, pretensile loads were applied to them just before an application of impact load. The experimental load transmission ratio of PTT complexes increased with an increase of pretension, independent of body weight. Larger body weight, or highly ossified PTT complex appeared to show lower load transmission ratio. Significant change in Young's modulus of patellar tendon with an increase of pretension as well as the progress of ossification of growing cartilage in tibial tuberosity was not found. Impact response analyses were also performed for the prediction of load transmission ratio as well as the section subjected to maximum strain in PTT complexes with different stages of ossification based on the one-dimensional wave propagation theory. The results obtained from the dynamic analyses well corresponded to the location of injuries in different stages of growing process, while static analyses could not predict such clinical situation.

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Graphite crucibles are widely used to metallurgical industries under very severe thermal stress conditions in high temperature. In this study situations of the temperature and thermal stress distributions are analyzed for a graphite crucible of an aluminum vapor deposition apparatus, using by ADINA finite element method. The analysis is carried out considering distinct difference of heat transfers on upper andlower level of the liquid aluminum inside of the crucible subjected to high frequencyinduction heating. These stress distributions of crucible were simulated to the thermalstress distributions in a circular disk subjected to local heating at the central area. Using the disk specimens of crucible materials, the thermal shock resistance and the thermal shock fracture toughness tests are carried out by means of arc discharge heating. In this study three kinds of specimen; namely (A) graphite material, (B) pitch impregnated graphite and (C) alumina impregnated material of (B) are used. Obtained results are compared and discussed on the fracture mechanical properties for thermal stress of the three crucible materials.

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Notched specimens of porous silicon carbide with porosity 37% were fatigued under four-point bending at frequencies of 30 and 0.3 Hz. The fatigue life expressed in terms of time was rather insensitive to the test frequency, while that expressed in terms of cycles was much shorter for the case of 0.3Hz than for 30 Hz. A time-dependent stress corrosion mechanism was mainly responsible for crack propagation, and stress cycling enhanced the crack propagation mechanism. The crack length was estimated from the change of the compliance of the specimen. The crack propagation curve was divided into Stages I and II. In Stage I, the crack propagation rate decreased even though the applied stress intensity factor got larger with crack extension, and turned to increase in Stage II. The transition from Stage I to II took place at the crack extension of around 0.8 mm. This anomalous behavior is caused by crack-tip shielding due to microcracking and asperity contact. Fractographic observations showed that the fracture path was along the binder phase between SiC particles, more precisely along the interface between particles and binders.

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Solidificatioin of hydroxyapatite (HAp) and its bonding with titanium (Ti) was achieved simultaneously by using a hydrothermal hot-pressing method at the low temparaure as low as 150℃. A mixture of calcium hydrogen phosphate dihydrate and calcium hydroxide was used as a starting powder material for solidifying HAp. The joining behavior of HAp and Ti depended on the surface finishing condition of the titanium. From Raman spectroscopy of the Ti surfaces, it was found that TiO_2 formed at the Ti surface affected the bonding characteristics of the HAp/Ti interface. 3-point bending tests were conducted to obtain an estimate of the fracture toughness for the HAp/Ti interface as well as for the HAp ceramics only. Core-based specimens were used for the fracture toughness tests and a pre-crack was introduced along the HAp/Ti interface of the bonded specimens. The fracture toughness tests showed that the induced crack from the pre-crack tip deviated from the HAp/Ti interface and propagated into the HAp. The fracture toughness determined on the HAp/Ti specimen was closed to that of the HAp ceramics only (〜0.30MPa).

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We measured the reduction of the elastic modulus due to material damage in Al_2O3-and SiC/TiB_2- ceramics occurring during steady and stable crack growth by exploiting so-called V(z)-curves obtained with a scanning acoustic microscope. The results support the microcrack model assuming a formation of microcracks inside a frontal process zone around a macrocrack. From the measurements the microcrack density parameter and the size of the process zone are obtained. The contribution of the microcracks to the crack resistance is deduced as well as the their shielding effect around the macrocrack. However, the calculated increase of the crack resistance is about twice smaller than the measured one. For the prediction of the crack resistance, it is shown that the influence of residual compressive stress must be taken into account and that wake effects play an important role as well.

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Geothermal energy is one of the most environment-conscious resources among the natural resources. Recently, the development of a supercritical geothermal system at great depth has been proposed to enhance the geothermal heat extraction. In order to design the supercritical geothermal reservoir whose temperature and pressure conditions exceed the critical point of water, the formation behavior of the geothermal reservoir under the great depth conditions has to be examined. In this study, we develop a new numerical analysis code for analyzing the hydraulic fracturing behavior in deep-seated rock mass. This code consists of two parts: "flow analysis" which computes the pressure distribution in the induced crack, and "crack propagation analysis". The former is based on a finite difference method. The later is based on a finite element method with embedded crack element. In the "crack propagation analysis", the mixed-mode fracture behavior with process zone formation is modeled. A shear dilation is accounted for in the fracture model. The numerical results show that the crack growth behavior, i.e. the mode of crack propagation depends on the depth. Under a typical tectonic stress condition, the crack growth mode is dominated by the opening fracture mode above the depth of 4 - 5 km, whereas the influence of the shear fracture mode increases with increasing the depth. This result may suggest that the current target of supercritical geothermal reservoirs may be formed mainly under the opening fracture mode.

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Mullite/SiC composite ceramics was sintered and subjected to three-point bending on specimens made according to the appropriate JIS standard. Semi-elliptic surface crack of 100 - 200 μm in diameter was made on each specimen. By using three kinds of specimens that was smooth, cracked and crack healed, crack-healing behavior and cyclic fatigue strength were determined systematically at room temperature. Static fatigue strengths was determined systematically at room temperature,700℃ and 1000℃. A crack was healed at 1000℃. The main conclusions obtained are following: (a) Mullite/SiC composite ceramics has an ability to heal a crack, (b) Crack healed specimens showed higher cyclic and static fatigue strengths than as-received specimens, and this fact was caused by healing of small cracks caused by polishing, (c) Crack-healed zone had enough fatigue strength and most fracture occurred outside the crack-healed zone, (d) Crack-healed specimen has sufficient strengths for cyclic and static fatigue at room temperature, (e) The static fatigue strengths of crack-healed samples at 700℃ and 1000℃ were similar to the values at room temperature, (f) The specimen subjected to crack-healing at 1000℃ had a sufficient fatigue strength even at 1000℃.

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Structural imperfections in synthetic diamond crystals prepared under high temperature-high pressure (HPHT) in the presence of Fe_<65>Ni_<35> catalyst have been examined by cross-sectional transmission electron microscopy (TEM). Etch pits on the (111) surface of the diamond, which are generated by the screw dislocations meeting the diamond (111) surface at the points of emergence of dislocations, can be revealed by chemical etching and used to study the motion of dislocations under the action of applied stress. There exist a number of hexagonal dislocation loops, twins, stacking faults and array of dislocations in the HPHT-grown diamond crystals. The hexagonal dislocation loops derive from supersaturated vacancies resulted from quenching from high temperature, the formation of vacancy disc on the (111) close-packed plane and its subsequent collapse form a dislocation loop. The twins may be formed due to the carbon atoms falling by mistake into positions where a twin crystal can form during diamond growth. Moire images reveal that the density of stacking faults is higher. The stacking faults may be generated by the condensation of supersaturated vacancies in the HPHT-grown diamonds on the (111) plane. The terminating of stacking faults on intersecting twins by moirg images suggests that the bordering partial has propagated by glide up to the twin interface during diamond growth, this may be described by the reaction of Shockley partial dislocation with a twin on the (111) plane. The array of dislocations may be related to the internal stress, which are caused by the micro-inclusions in the diamonds.

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In this paper an improved three-dimensional simulation model (FRACSIM-3D) is presented. It incorporates the mechanical rock-fluid interaction during hydraulic stimulation in more rigorous way than the existing two-dimensional model FRACSIM-2D and quantitatively predicts the 3D reservoir growth behavior. In this model the pre-existing fractures are generated stochastically. The fractal size distribution of the penny-shaped fractures with random orientation is assumed. The fluid flow through the discrete fracture network is simulated by mapping the connectivity of the fractured rock to a regular cubic grid under condition of constant injection pressure. The fluid flow is approximated by the Darcy law equation. Pressure distribution within the fractured rock is used for calculating the growth of the cracks apertures and shear displacements. This requires several iterations; solving the complete flow model simulating the fracture system anew each time and recalculating the shear displacement using the inner fracture pressure from the previous iteration. The results of this numerical solution for hydraulic stimulation are in good agreement with the existing field data collected at the Hijiori hot-dry-rock (HDR) reservoir.

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A prediction of host rock permeability in the deep seated geothermal reservoir is essential for the assessment of a potential geothermal energy extraction system. In order to test the permeability of granite under high temperature and high pressure conditions, experiments were undertaken using thick-walled cylindrical specimen of 45 mm outer diameter and 5 mm inner diameter. The permeability of the sample specimen was estimated from flow rate, and the pressure difference between borehole pressure (internal pressure) and confining pressure, based on Darcy's law. Permeability tests were conducted at temperatures of up to 600 ℃ and confining pressures of up to 100 MPa. Experimental results show that the permeability of granite increased with increasing temperature, particularly above 350 ℃. Examination of microcracks, by optical microscopy, showed that crack density in granite, after experiments at 600 ℃, and confining pressures of both 25 MPa and 100 MPa, was larger than at a confining pressure of 20 MPa. This indicates that water-rock interaction processes at supercritical conditions directly affect micro-cracking of granite. In addition, it was noted that hydrothermal cracking occurs at a temperature above 400 ℃ and a pore pressure above 25 MPa, This result indicates that it may be possible to increase granite permeability and to create a porous type reservoir in a supercritical rock mass, by hydrothermal cracking.

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A fracture of brittle solids under compression was discussed. Special attention was paid to the influence of confining stress and the presence of free boundary on a behavior of crack growth. Cracks tend to grow unstably leading a brittle splitting when they are loaded by longitudinal compression together with lateral tension. When the lateral stress is also compression, cracks always grow in a stable fashion. Presence of free boundaries near the crack tend to increase its stress intensity. This increase is mainly caused by the outward bending deformation. A possible mechanism of pseudo ductile deformation (shear rupture) experienced in the compression experiments of rocks was discussed in detail as a result of interference of an echelon of cracks.

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