From a design point of view, external force value applied to structures knowing closely is one of very important problems. Measurement of Impact Load frequently uses the strain gauge, but there are cases that correct evaluation is difficult because of diffusing stress wave in strikers or targeting at transient phenomena. In these cases the mean evaluating its value based on mechanical information in specimens is valid. In this paper, we focused attention on Coherent Gradient Sensing (C.G.S.) fringe patterns near loading point when using C.G.S. method, developed the measuring method of load value by C.G.S. method and considered its adequacy.
The impact compressive failure behavior of a unidirectional T700/2521 carbon/epoxy laminated composite in the three principal material directions or fiber (1-), in-plane transverse (2-) and through-thickness (3-) directions is investigated on the conventional split Hopkinson pressure bar (SHPB). Cubic and rectangular block specimens with the same square cross section are machined from a 42-ply unidirectional composite laminate. The uniaxial compressive stress-strain curves up to failure at quasi-static and intermediate strain rates are measured on an Instron testing machine. A pair of steel rings are attached to both ends of the rectangular block specimens to prevent premature end crushing only in the 1-direction tests on the Instron testing machine. A modified sleeved SHPB is applied to allow recovery of the failed specimen without being subjected to repeated compressive loading during the test. It is shown that the ultimate compressive strength (or failure stress) exhibits no strain-rate effect in the 1-direction, but a slight strain-rate effect in the 2- and 3- directions over a strain-rate range of 10-3 to 103/s. It is also shown that the ultimate compressive strain (or failure strain) decreases marginally with strain rate in all three directions. Dominant compressive failure mechanisms are found to significantly vary with strain rate, depending on the three principal material axes.
To design the transparent automobile interior and exterior components under crash loading, it is necessary to understand the dynamic mechanical properties as well as the transparency. This paper characterizes the tensile behavior of a thermoplastic amorphous resin, cyclo-olefine polymer (COP) and COP/clay composites, at the dynamic strain rate. Moreover, the present research attempts to study the effect of the total amount of clay content on the mechanical properties such as the apparent elastic modulus, the yield strength, the fracture strain and the strain energy up to failure. Meanwhile, the influence of the amount of clay content on the transparency of the COP/clay composites is also investigated. The studied blend ratios are COP/clay = 100/0, 99/1, 98/2 and 95/5 vol%, respectively. Dynamic tensile tests are conducted at the nominal strain rates of 0.1 s-1, 1 s-1, 10 s-1 and 100 s-1. It is found that the total light transmittance is reduced by about 13% in the case of blending 1 vol% of clay particles, compared to that of neat COP. The apparent elastic moduli of COP and COP/clay composites show the weak sensitivities of the strain rate and the clay content. However, the absorbed strain energy up to failure has the strong dependencies of the total amount of clay content as well as the strain rate. It appears that the material ductility of COP/clay = 99/1 vol% is the largest among all the blends at the nominal strain rate of 100 s-1. It is considered that such morphology, in which the small content of clay particles is blended, can nucleate the initiation of nano voids leading to the stress concentration in the adjacent matrix and then fibrillation of the matrix polymer, which results in the ductile fracture mechanism.
In the vehicle industries, collision safety and reliability of cars under impact loading become more and more important in recent years. This study is concerned with the development of a fracture criterion for the impact fracture of jointed steel plates of an overlap bolted joint used in a car body, which contributes to crash simulations by computer-aided engineering (CAE). The impact behavior and fracture of jointed steel plates of the bolted joint are examined by experiments and numerical simulations. The specimens of jointed steel plates were made of a steel plate with tensile strength of 270MPa, while the jig plate is made of high tensile strength steel of 980MPa. The impact shearing test of the specimens was performed using the split Hopkinson bar technique for tension impact, together with the static test using a universal testing machine INSTRON 5586. Numerical simulations by FEM code LS-DYNA were also carried out to compare with experimental results and to understand the mechanism of fracture process of the overlap bolted joint plate. Good quantitative agreement was observed between the experimental results and the numerical simulations with respect to the behaviors of shear stress and deformation until rupture took place in the jointed steel plates. This study suggests that a stress-based fracture criterion may be developed for the impact fracture of jointed steel plates of an overlap bolted joint used in a car body.
In order to investigate the relationship between the mechanical properties of rocks and the electromagnetic phenomena during their fracture, uni-axial compression and three-point bending tests for two kinds of rocks, granite and gabbro, with different content of quartz were carried out at quasi-static and dynamic rates. Not only the stress-strain or load-deflection curve but also the output of ferrite-core antenna located close to specimens in a shielding box made of Permalloy plates, which indicates the magnitude of electromagnetic wave, were measured through a band-pass filter. The dynamic compressive and bending strengths were larger than those in static tests and there is strain-rate dependence in their strength of both rocks. It was also found that the intensity of electromagnetic waves measured in dynamic compression tests for granite was much greater than that observed in static tests, i.e. the electromagnetic phenomenon strongly depends on loading rates, too. Even in dynamic bending tests for granite, relatively large electromagnetic waves were observed as well as in compression tests. This fact cannot be explained by the frictional electrification theory, because the bending fracture usually occurs under mode I, i. e. without rubbing of crack surfaces.
In this study, the method evaluating the interfacial strength (i.e. interfacial fracture toughness) of ceramic thermal barrier coatings (TBCs) is proposed based on the indentation test method. The obtained results are summarized as following ; (1) Lesage & Chicot model was applied to evaluate the interfacial fracture toughness of TBC, firstly. The results showed that the associated fracture toughness was varied with the indentation load condition, which means that Lesage & Chicot model is unsuitable to TBC interfacial strength evaluation. (2) The alternative complex stress intensity factor for evaluating TBC interfacial fracture toughness with the indentation test was introduced by assuming that the internal crack geometry induced by the indentation identifies the rectangle shape spread along the specimen surface. It was found to be able to apply the proposed equation to TBC interfacial fracture toughness evaluation.
A central hole of the steam turbine rotor can be degraded with creep damage during the operation. And it is important to measure the creep damage of this part to determine the replacement time. Usually the damage is measured with the hardness change, electric resistance change or the observation of the creep void (for example A parameter : damaged grain boundary parameter). However, the inspected results of the replaced rotor indicate the measured damage is overestimated and too conservative. This is caused by the change of hardness and electric resistance with heat history during the operation not only with the creep damage. And furthermore the master curves to evaluate the creep damage are obtained from the uniaxial creep test results. In this study biaxial creep tests to simulate the stress distribution of the central hole of the rotor under centrifugal force is conducted to clarify the effect of the biaxial stress on creep damage of a steam turbine rotor mterial. Micro creep cracks are proved to be initiated from a little inner location from the surface and the obtained A parameter is greater than that of uniaxial creep test under the equal creep damage ratio.
In order to establish the life assessment method for the welded hot reheat elbow of modified 9Cr-1Mo steel, an internal pressure creep test is conducted with a full size elbow component. The results are following, (1) : The elbow component finally leaked at weld metal. The rupture time was 1606 hours. The creep damage seemed to be initiated near the inside surface of the elbow and to grow towards the outside surface along to the fine-grained HAZ of the seam weld. In outside neighborhood, the crack that had initiated along the fine-grained HAZ changed the direction of initiation into the weld metal. (2) : The results obtained by the Time of Flight Diffraction (TOFD) inspection for detecting cracks under the surface at the seam weld on the intrados of the elbow show the presence of a crack near the inner surface of the elbow at the end of life. (3) : The fracture life of the full size elbow internal creep test based on the stress level at the mean diameter formula was slightly shorter than the uniaxial creep test results.
Steel and concrete composite deck, which is arranged channel shape steel members in the transverse direction on the top surface of the bottom steel plate, has been investigated by the authors. By the arrangement of channel shape steel members welded to the bottom steel plate, the steel and concrete composite deck with cellars in the concrete becomes to be more lightweight than typical types of steel and concrete composite decks. For highway bridge decks, it is very important to verify the fatigue strength of the welded joint. In this paper, fatigue tests of the welded joint between the channel shape steel and the bottom steel plate were carried out under the tensile fatigue stress.
Biocompatible piezoelectric materials are becoming increasingly important for actuators and sensors in medical devices. In this paper, we highlighted on some perovskite oxides MgSiO3, CaSiO3, CaTiO3 and CaZrO3 which are biocompatible piezoelectric materials discovered by first-principles calculation in our previous studies. In order to verify their biocompatibility, the cytotoxicity of their isomeric oxides with the same components was examined as comparing with typical perovskite oxides Pb(Zr, Ti)O3 and BaTiO3. The fibroblast (L929) cells were cultured during 7 days and the effect of materials was evaluated by the half maximal inhibitory concentration (IC50). As a result, the colony formation assay indicated that BaTiO3, CaTiO3, MgSiO3 and CaZrO3 has the higher IC50 values. On the other hand, CaSiO3 and Pb(Zr,Ti)O3 shows the strong toxicity. The obtained IC50 values had a good correlation with the proliferation ratio in our previous studies.