It is found that metallic glasses can be rejuvenated by a thermal process using experimental and simulation methods. We have reported that an increase in the potential energy, decrease in the density, and change in the local structure as well as mechanical softening were observed after the thermal rejuvenation. We proposed two parameters in the annealing condition of Ta/Tg and Vc/Vi to evaluate the rejuvenation behavior. A rejuvenation map was actually constructed using these two parameters. It is important to satisfy the condition of Ta/Tg ≥ 1.2 during annealing because of the resetting the thermal history of metallic glasses over 1.2Tg for rejuvenation. The glassy structure changes into a more disordered state by rejuvenation, resulting in the disappearance of icosahedral short-range order (SRO). We also investigated that the rejuvenation occurs partially in a Zr55Al10Ni5Cu30 bulk metallic glass (BMG) when it is annealed at Ta/Tg ~ 1.07 followed by rapid cooling. This phenomenon probably originates from disordering in the weakly bonded (loosely packed) region in the heterogeneous local structure model. Such the thermal rejuvenation provides a novel approach for improving the mechanical properties of metallic glasses by controlling their intrinsic glassy structure.
We have focused on a rejuvenation behavior of recovery annealed Pd42.5Cu30Ni7.5P20 metallic glass. Specific heat measurement results revealed that only 33%, which is lower than that (44%) of a Zr50Cu40Al10 metallic glass, was recovered by annealing. This result indicates that the recovery of a Pd42.5Cu30Ni7.5P20 metallic glass is more difficult than the Zr-based alloy. The hardness measurement results obtained from the indentation test also supported this finding. The time dependence of the normalized storage modulus E’/Eu at 0.8Tg of both metallic glasses were successfully demonstrated by the KWW (Kohlrausch-Williams-Watts) equation, which means that the relaxation/rejuvenation behavior of each sample was well described by the free volume change. It also suggested that the distribution of relaxation modes of the Pd42.5Cu30Ni7.5P20 metallic glass is much narrower in a β-relaxation region. The normalized loss modulus E”/Eu implied that two areas, one is in correlation to the free volume change and the other is not, are embedded in the intrinsic β-relaxation region and the lower rejuvenation ability in the Pd42.5Cu30Ni7.5P20 metallic glass may originate from a low volume fraction of the former area. The present study will provide the universal information for the research subject on the thermal rejuvenation in metallic glasses.
Dissimilar metallic joining was performed by resistance spot welding of SUS304/CP-Ti plates, where stacking of Zr, Cu and Al foils with Zr50Cu40Al10 supercooling alloy composition were placed between the plates as inserted materials. The microstructure in nuggets depends on the stacking sequence of the inserted foils. The size of cavity formed in the nuggets was smallest, no cracks were found in the nuggets and the welding boundary between the nugget and the SUS304 plate was undulated finely for the welded specimen exhibiting the highest tensile shear strength. No metallic glassy phase was found in the nuggets, but the composition of crystalline phase formed in the nuggets was close to high glass-forming alloy, i.e. high supercooling alloy, Zr50Cu40Al10.
The microstructure and magnetic properties of rapidly solidified in Ag52Cu23.2La4.8Fe20 (at.%) alloy, which was designed as the combination of Ag-rich Ag65Cu29La6 alloy with high glass forming ability (GFA) and Fe, was investigated. An amorphous phase formation was observed in melt-spun ribbon of ternary Ag65Cu29La6 alloy. The composite of Ag-Cu-based polycrystalline matrix and BCC-Fe globules was obtained in Ag52Cu23.2La4.8Fe20 alloy. The size of BCC-Fe globules embedded in Ag-Cu based polycrystalline matrix was the order of 50 nano-meter. The Fe addition deteriorated the GFA in Ag-rich Ag-Cu-La alloys. The combination of liquid phase separation and stabilization of thermal melt for an amorphous phase formation during rapid cooling leads to the formation of the particular solidification microstructure in Ag-rich Ag-Cu-La-Fe alloy. The melt-spun ribbon shows the typical ferromagnetic magnetic properties due to the 50 nano-meter ordered BCC-Fe globules.
The fatigue ratio [fatigue limit (σW) / tensile strength (σB)] of bulk metallic glass (BMG) was initially smaller by an order of magnitude than that of the crystalline structural alloys of 0.3 to 0.6. Then, the BMG was regarded as useless for structural members. However, the σW/σB of BMGs increased with increasing the year, and recently a large value of about 0.8 was shown for a Ti-based BMG, and the maximum cyclic stress (σmax) was about 90% of the σB. Since BMG has no dislocation, it may not show fatigue. Therefore, in this report, using high-purity elements, the Zr-based BMG with less impurities and less defects was made by arc-melt Cu mold tilt casting method, which is expected to have less impurities or defects, and fatigue strength of the BMG was examined by also paying attention to the polishing of the specimen surface. As a result, higher value of the σW/σB about 0.8 ~ 0.9, and the σmax/σB of about 0.9 ~ 1.0 were shown. In addition, the influence of increase in number of casting times with same master BMG, which raises the yield rate of the master BMG, on the σB and σW and the influence of the specimen surface polishing level on the σW are reported.
Metallic glass has both metallic (high electrical conductivity) and glassy (thermoplasticity) properties. Therefore, metallic glass is expected to be used in various applications such as precision processing products requiring metallic properties. It is implicitly considered that the mechanical creep is expressed in glassy materials as a result of transition from a glass state to a supercooled liquid state due to thermal glass transition. However, the relationship between thermal glass transition and mechanical creep has not been investigated in detail so far. In this study, creep behaviors were measured by thermomechanical analysis (TMA) in Zr55Cu30Ni5Al10 metallic glass, which is a typical alloy system, to obtain creep onset temperatures under various applied tensile stresses and heating rates. As a result, at applied tensile stress of 5 MPa, the creep onset temperature monotonously increased with increasing heating rate and exhibited a kinetic tendency. On the other hand, when the applied tensile stress was 25 MPa or more, the creep onset temperature temporarily decreased with an increase in the heating rate and turned to increase. This is a non-kinetic tendency different from that of thermal glass transition. It is presumed that in the creep process of metallic glass, in addition to the creep process due to thermal glass transition, another process suppressing creep is competing.
In Japan, even if it is seen worldwide, it has a lot of earthquakes, and it is said that Japan is an earth-quake nation. Therefore, we must think about earthquakes in situation of our lives. And the thing from which we will suffer great damage by a big earthquake the near future is expected, for example, Nankai Trough massive earthquake. However, it is very difficult to take measures at the same time to the respective regions. In this study, the earthquake risk an infrastructure in all part regions possessed are focused, and the earthquake risk is expressed quantitatively by a risk curve. Moreover, it was revealed that urban area do not have same risk by comparing earthquake risk curve in all part regions.
Initiation of cracks along PC cables is regarded as a cause of degradation of PC bridges. In the presented study the existing PC bridges with cracks along PC cables were investigated, and their visual condition and condition of PC cables and sheath were inspected by means of Non-Destructive Testing and Semi-Destructive Testing methods. The results showed, that there is a strong relationship between presence of water in the sheath and initiation of cracks. Assuming, that expansion pressure of freezing water in sheath is the cause of initiation of cracks, the experimental and analytical study was carried out. The obtained results allowed to clarify the mechanism of cracks’ initiation and to conduct risk assessment of the existing bridges with cracks along PC cables.
Due to the bcc microstructure of α-phase ferrite, low carbon steels highlight a significant effect of the strain rate on its mechanical properties, such as yield stress. Indeed, at a constant temperature, the higher the strain rate is, the higher the uniaxial yield stress becomes. Some studies also pointed out similar trend for the fatigue strength of low carbon steels in high cycle fatigue regime. An influence of the loading frequency on the dislocation arrangement of observed fatigued specimens has also been reported. Nevertheless, strain rate effect on the fatigue strength of low carbon steels has not been discussed from a viewpoint of rate process yet. Referring to this point, an analytical model based on the activation energy of dislocations was proposed to evaluate the fatigue endurance of low carbon steels. Accepting five typical data sets actually obtained by fatigue tests, analytical results based on the present model were compared with the experimental data. Thus, it was found that the analytical results are in good agreement with the experimental results. In addition, this work also includes a discussion on the activation energy of the dislocation related to the present model. Activation volume of the dislocations thus calculated showed good agreement with corresponding experimental data available in the literature.
In the field of structural identification, Kalman filter and Particle filter have been one of the most widely used tools. These are called parameter identification and data assimilation methods and are methods for updating sim-ulation models one by one while introducing measurement data to the simulation model. In the updating process, the dynamic characteristics of the observed structure such as the stiffness and damping properties are estimated. However, in order to ensure the identification accuracy, it is extremely important to set the process noise. This study attempts to develop a SHM system that can accurately evaluate the integrity for the structure that has not been destroyed due to an earthquake. The first attempt is made to detect the damage occurrence from the re-sponse data by using AR model. In evaluation of response, AR coefficients are used to detect a sudden change of structural condition caused by seismic load. The second attempt is made to identify the structural parameter for the purpose of damage quantification by using merging particle filter. Finally, the performance of the proposed system is discussed through numerical simulations and a shaking table test.
Recently, assessing the integrity of the structures accurately and reliably has become extremely important in various fields in order to increase operational lifetime and improve safety. Detecting surface damage such as cracks, spalling and so on in evaluating the soundness of the structure is particularly important as it is one of the major factors causing deterioration and destruction of the structure. In this study, we develop a real-time screening system for structural surface damage by using object detection technique and generative model based on deep learning. The accuracy of object detection depends largely on the quality and quantity of images given as training data in advance. These images are not kept even by road management companies, etc., and tend to be short. In this study, we generate images of the crack using deep generative model and introduce them into object detection technique. Finally, we investigate whether the detection accuracy of damage is improved by introducing generated images as training data.
In this study, a statistical estimation of S-N curves for high-strength steels from their static mechanical properties was attempted. First, the fatigue data of high-strength steels were extracted from the “Database on fatigue strength of metallic materials” published by the Society of Materials Science, Japan (JSMS), and the S-N curves of respective steels were determined from the JSMS standard, that is, the “Standard evaluation method of fatigue reliability for metallic materials: Standard regression method of S-N curve”. The correlations between the regression parameters obtained here and the static mechanical properties were investigated. Thus, significant correlations were found between the regression parameters and static mechanical properties (e.g., fatigue limit E and tensile strength σB). Based on these correlations, the S-N curves of high-strength steels were successfully predicted from their static mechanical properties, similar to structural carbon steels and aluminum alloys in previous studies. Moreover, from the distribution of the fatigue limit E, the percentile points for the estimated S-N curve were predicted. It was finally confirmed that 84 % of the S-N data series fall within the estimated interval of ±2s, where s represents the standard deviation of the fatigue limit.
It is believed that a workshop is an effective methodology to promote interactive risk communication. While people think about disaster prevention shortsightedly and optimistically, so such viewpoints are obstacles to communicate with various stakeholders. This paper proposes the workshop based on Future Design to overcome them and verification of effectiveness. This study reveals that introducing role of future generation promotes creating long-term ideas even if it is high cost and not for themselves. Furthermore, there are observed several trends between three groups of each age. The results confirm that the workshop integrated Future Design is effective to introduce long-sightedly and subjective opinions about making ideas such as disaster prevention.
When we formulate a recovery plan, we have to attempt consensus among organizations of community. District Impact Analysis (DIA) support system is developed for supporting consensus building among theirs. This system establishes a recovery plan based on prerequisites for disaster. Our previous research formulates a restoration schedule on a daily basis. In this study, we develop and evaluation of the restoration schedule considering time division. Several example cases demonstrate to the impact of time division of restoration schedule.
Various preparations for possible disasters should be made so as to minimize the damage in the disasters such as a fire or an earthquake. Several kinds of disaster simulations have been developed to recognize the impact of the damages. In particular, a lot of evacuation simulation methods using multi-agent system, which are considered as the useful and powerful method to deal with complex system containing a lot of elements, have been proposed for guiding evacuees safely. The Social force model is one of the evacuation simulation models that consider the influences and interaction of the other evacuees. In order to improve the precision of the simulation, the parameters included in it should be appropriately determined. In this paper the determination method of the parameters in the social force model is proposed, in which the evolutional computing method is applied for the collecting evacuees flow data.
Surface treatments involving residual stresses are an effective method to increase the fatigue strength of forged steel products. Therefore, X-ray stress measurement is important to evaluate the fatigue strength of these materials. For large forged steel products, regions where alloy elements are segregated cannot be avoided. Furthermore, because of the large size of these products, it may be difficult to measure their residual stresses in a laboratory. Nevertheless, compact and portable X-ray equipments operating based on the cosα method using a two-dimensional detector, are appropriate for the measurement of the residual stresses at the manufacturing sites. Although it is known that carbon and alloy elements concentration influence X-ray stress measurement, there is little research about the influence of segregation in X-ray stress measurement using the cosα method. This study evaluated the differences in X-ray stress results using the cosα method in segregation regions of large forged products made of CrMo steel, under tensile stress. It was confirmed that the differences between the X-ray stress and nominal stress increased with increase of carbon concentration in segregation, and crystal grains in which coarse and fine grain size coexist worsen the linearity of the cosα diagram. Because the level of carbon concentration and grain size varies at each X-ray irradiation points, we proposed an averaging method of X-ray stresses on plural measurement points as an effective way to avoid the effect of segregation.
When cohesive surface soils are treated to create cement-based ground improvements, suppressing the aggregation of the clay particles with the cement-based solidifying material particles is an important consideration. Herein we evaluated a method that reduces the variation in the soil improvement body’s strength by the generation of an electrical repulsive force between the particles due to the surfactant for aggregation suppression. The aggregation suppression mechanism was first verified by measuring the ζ-potential of the particles. The effect of reducing the variation in the soil improvement body strength was verified with an unconfined compression test using a specimen manufactured by indoor mixing. Finally, the effectiveness of the methodology was evaluated with on-site testing. Upon adding a surfactant, positively charged cement-based solidifying material particles have their potentials reduced, thereby becoming negatively charged. Therefore, electrical repulsion operates between these particles and the negatively charged clay particles, thereby preventing aggregation, increasing the fluidity of the soil-cement slurry, and reducing the variation in the strength of the soil improvement body. Finally, the effectiveness of the methodology was confirmed by on-site testing.