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The air compression of a high-speed train entering a tunnel results in micro-pressure waves (MPWs), which can cause environmental problems. To mitigate MPWs, tunnel hoods with discrete windows are installed at the tunnel entrances. By properly adjusting the window conditions, the efficiency of the tunnel hood in mitigating MPWs can be enhanced. Per Japanese convention, window conditions are optimized by changing the opening/closing pattern in the longitudinal direction (pattern optimization). The optimization pattern of the windows is fundamentally different if there is a change in the train speed, train nose length, the relative position between the train and the windows, or the train nose shape. Therefore, for extremely long tunnel hoods, the optimal state of the windows is almost impossible to detect numerically or experimentally using pattern optimization. In this study, we realized a rapid and simple optimization of the windows of the tunnel hood (i.e., area optimization) for mitigation of MPWs by field measurements. The result demonstrated that the area optimization considerably helps in mitigating the MPWs, despite the simplicity of the procedures.

We conducted a theoretical investigation of the cross-sectional aspect ratio of a rectangular channel to have sufficiently low frictional resistance under less than 150 of the Reynolds number. From the theoretical consideration, it was clarified that 3.40 or more is recommended as a criterion for determining the aspect ratio. This addresses the problem of determining the interval of rectangle channels, installed in a plate reactor. There is a concern that the real system does not follow the analytical solution, assuming laminar flow, since the higher aspect ratio leads to disturbances of the flow such as the emergence of vortices. However, in the channel’s volume range of (W × H × L) = (7.0 mm × 0.38 mm × 0.26 m), such a turbulence was not observed in the detailed numerical calculation by CFD, where both calculation results were in agreement to within 3% accuracy. Moreover, even in an experimental system with a surface roughness of ca. 7%, friction resistance took agreement within an accuracy of ±30%.

Internal friction of a Mn-11Cu (at.%) alloy was studied in the main [001], [011] and [111] crystallographic directions by applying tensile stress. Two internal friction peaks were observed in three directions. One is twin boundary-related relaxation peak (in the temperature range of 200–300 K), which is highest in the [001] direction and lowest in the [111] direction. Other is associated with reverse martensitic transformation (~430 K), and its orientation dependence is small. The orientation dependence of the twin boundary-related internal friction peak is discussed based on the Schmid factor for the movement of {011} twin boundaries.

We were successful in controlling the arrangement of Ti3Ni4 in a single-crystalline Ti-50.8Ni (at.%) alloy. Only three variants of Ti3Ni4 form when tensile stress is applied in the [111] direction during aging heat-treatment while four variants form when the stress is absent. The lack of one variant of the precipitate causes different arrangement of the R-phase variants. This results in obvious decrease in the internal friction in the R-phase state. An extremely high internal friction of 0.25 was also found in the R-phase state formed in the specimen including four variants of Ti3Ni4.

The impulsive pressure wave (micro-pressure wave) emitted from a tunnel portal is one of the environmental problems associated with high-speed railways. The principle underlying the countermeasures for this micro-pressure wave is to reduce the pressure gradient of the compression wavefront at the tunnel portal. This study investigated the influence of the ballast layer on the rate at which compression waves steepen in railway tunnels. Field measurements in an actual Shinkansen tunnel with slab tracks were recorded before and after installing ballast along most of the length of the tunnel. Previously published results on the spread of the compression wavefront in a ballasted track tunnel are also presented for comparison. A rapid method using an empirical equation is shown to accurately estimate the variation in the maximum pressure gradient of the compression wavefront in certain conditions. A more widely applicable estimation method using a numerical analysis is also demonstrated, which describes the distortion of the compression waveform. The results show that both of these methods can estimate the influence of the ballast quantity on mitigating the compression wavefront steepening in Shinkansen tunnels.

Iron-doped Ni-Ti shape memory alloys are known for their R-phase transformation. The stress-induced R-phase transformation and its reverse transformation can be utilized to create a temperature change based on elastocaloric heating and cooling. We studied the elastocaloric properties of hot rolled Ni48Ti50Fe2 and Ni46Ti50Fe4 alloys with three different approaches: 1) the calorimetry and specific heat measurements, 2) mechanical stress-strain behaviour and Maxwell relation based calculations and 3) direct measurement of adiabatic temperature change by stress application and removal. We compared the results related to different approaches and present the essential properties related to elastocaloric effect in these alloys. We show that the temperature change due to energy dissipation of the R-phase transformation is minor in comparison with the elastocaloric temperature change. The maximum adiabatic temperature change expected from the latent heat of R-B2 transformation is 12.4 K for the Ni48Ti50Fe2 alloy and 8.7 K for the Ni46Ti50Fe4 alloy. We also report an increasing tendency of the peak temperature for the elastocaloric effect when the applied stress increases.

In this paper, we report that the superelasticity and the elastocaloric effect of Ti-50.8Ni (at.%) alloy are drastically improved by a combination of precipitation and grain refinement strengthening. The process is as follows: first, aging at 773 K after solution treatment to form coherent fine precipitate of Ti3Ni4; second, cold working followed by annealing at 673 K to form nanocrystalline grain containing Ti3Ni4. The decay of the superelasticity and the elastocaloric effect by 100 stress cycles is

Significant grain growth assisted by a martensitic transformation near or below room temperature was found in a nanocrystalline Ti-50.8Ni (at.%) alloy. Significant grain growth was observed when thermally- or stress-induced B2 ↔ R ↔ B19′ (B2: parent phase, R and B19′: two types of martensite phases) martensitic transformation is repeated while not when B2 ↔ R transformation is repeated. This implies that martensitic transformation to and from the B19′ martensite phase assist the grain growth. Transmission electron microscope observations indicate that migration of grain boundaries could be the main mechanism for the grain growth.

The size effect on the mechanical behaviors of single crystalline Fe-31.2Pd (at.%) micropillars with four different pillar diameters (approximately 2 μm, 1 μm, 500 nm and 400 nm) were studied by compressing in the [001] direction. Both the Young's modulus and yield stress increase with the decrease of pillar diameter. The main defects in the plastically deformed pillars are the {111} deformation twins, which could be covered by high density of dislocations after further plastic deformation in a 400 nm pillar. A repeatable elastic-like strain ~4% was observed for more than 40,000 cycles.

We have investigated the influence of twin boundary properties on the damping behavior of single crystalline Fe-31.2Pd (at%) alloy, which exhibits a weak first-order martensitic transformation. Different static tensile stress was applied by dynamic mechanical analyzer to adjust the twin boundary density and hydrogen was doped to modify the twin boundary mobility. A high damping capacity (tan δ > 0.1) in a wide temperature range from about 140 K to 230 K was observed under a low static stress of about 0.3 MPa. Hydrogen doping further increased the maximum value of the damping capacity by introducing a relaxation tan δ peak. The damping capacity decreased with increasing static stress probably due to the decrease in twin boundary density.

Depending on Pd content, disordered Fe-Pd alloys take various crystal structures: body-centered cubic (BCC), body-centered tetragonal (BCT), face-centered tetragonal (FCT) and face-centered cubic (FCC) structures. We have measured specific heat of Fe-Pd alloys to understand the lattice stability and electronic state of the alloys. At the phase boundary between FCT and FCC phases, electronic specific heat coefficient shows a local maximum and the Debye temperature shows a local minimum. A local maximum of electronic specific heat coefficient also appears in the BCC region with Pd content of near 10 at.%.

Elastocaloric effects in shape memory alloys are usually caused by latent heat associated with the stress-induced martensitic transformation. We report here that the rubber-like behavior of the R-phase in nanocrystalline Ti-50.8Ni (at.%) wires, realized by an aging heat treatment under tensile stress, also contributes a significant elastocaloric effect. The efficiency of the elastocaloric effect caused by the rubber-like behavior is higher than that caused by the stress-induced B2 ↔ B19′ transformations because of the small energy dissipation. The usage of the rubber-like behavior is a method to extend the temperature window of the elastocaloric effect in shape memory alloys.

We have detected an inverse elastocaloric effect in a Ti-51Ni (at%) alloy which contains aligned coherent particles of Ti3Ni4 formed by aging under tensile stress. In this alloy, the temperature of the specimen decreases when stress is applied due to a stress-induced reverse martensitic transformation (from the R-phase to the B2-phase) The temperature decrease caused by this effect is about 1.1 K at 300 K. The internal stress field around the Ti3Ni4 precipitate is responsible for this effect. A further increase in the tensile stress causes a temperature rise due to a conventional elastocaloric effect.

A high-speed train entering a tunnel generates a compression wave in the tunnel and a micro-pressure wave. The magnitude of the micro-pressure wave is approximately proportional to the maximum pressure gradient of the compression wave ( ∂ p / ∂ t ) max . High-speed railway operations require the consideration of the nose shape of the train in order to reduce ( ∂ p / ∂ t ) max generated by a train entering a tunnel. In this study, the compression waves generated by axisymmetric trains running at the offset position in double-track tunnels were investigated using a train launcher facility. Paraboloids of revolution, ellipsoids of revolution, and cones were used as the simplest nose shapes. The cone-nose train generated the largest value of ( ∂ p / ∂ t ) max , and the paraboloid-nose train generated the smallest value of ( ∂ p / ∂ t ) max among the three nose shapes. Although this tendency is the same as that for center running, the ratio of ( ∂ p / ∂ t ) max for the cone-nose train to that for the paraboloid-nose train became larger for offset running than center running. Moreover, the maximum value for the generation time of the compression wave was derived from acoustic theory, and the nondimensionalization of ( ∂ p / ∂ t ) max considering the nose length was proposed using it. Since the inverse of the nondimensionalized ( ∂ p / ∂ t ) max denotes the ratio of the generation time of the compression wave to its maximum value, it was defined as the efficiency of a train nose in the range of zero to unity. The values of the efficiency were almost constant with the nose length and 0.7, 0.6, and 0.5 for paraboloid-, ellipsoid-, and cone-nose shapes, respectively.

We have constructed a time-temperature-transformation (TTT) diagram for the martensitic transformation in a Ti-51.3Ni (at%) alloy. The transformation proceeds when the specimen is held at fixed temperatures between 110 K and 140 K, but not at other temperatures. The time required for the formation of 0.1% of the martensite phase is plotted as a TTT diagram. It exhibits a C-curve with a nose temperature near 130 K. Application of a thermal activation model to the TTT diagram suggests that the size of a nucleus of the martensite phase is about (2.2 nm)3.

Micro-pressure waves (MPWs) are radiated from tunnel exits when trains enter the tunnels at high speeds. Because MPWs produce infrasound and audible noise around the tunnel portal, they should be suppressed to mitigate its environmental impact. Hood installation at the entrance portal of tunnels is a common MPW suppression method. However, an increase in train speed mandates a corresponding increase in hood length. This paper reports the development of a tunnel entrance hood that allows a decrease in the extension required at high speeds. Calculations based on the acoustic theory were used to investigate an economical hood-extension method, and model experiments were performed to validate predictions. Results revealed that increasing the cross-sectional area of the extended part of the hood over that of existing hoods can effectively shorten the overall hood length. As a result, the first optimum cross-sectional area of the hood was greater than that of the tunnel by a factor of 3.9, and the second optimum value demonstrated a corresponding factor of 3.2. Based on this finding, the proposed hood design can be more economical than existing hoods.

Iron-rich Fe–Al binary phase diagram in the composition range of 23–26 at% Al shows a complex structure partly due to magnetic properties of the disordered A2-phase, the ordered B2-phase and the ordered DO3-phase. In this study, the disorder-order transformations between the constituent phases have been investigated through magnetization measurements of Fe-xAl alloys (x = 22.0, 24.0, 24.3, 24.7, 26.5 at%). It is found that spontaneous magnetization of the B2-phase is larger than that of the DO3-phase and smaller than that of the A2-phase. The former relation disagree with previous reports but was further confirmed as the decrease of the B2-DO3 transformation temperature under magnetic field (−1.58 K/T). It is also found that the Curie temperature of the B2-phase (836 K for Fe-24.7 at%Al alloy) coincides with that of the A2-phase; furthermore, these temperatures agree with the phase boundary between B2-region and (A2+B2)-region.

A disordered Fe-31.2Pd (at.%) alloy exhibits a weak first-order martensitic transformation (MT) from a face-centered cubic structure to a face-centered tetragonal structure. We employed a Dynamic Mechanical Analysis (DMA) to understand the transformation behavior. As the temperature decreases, the storage modulus E ′ decreases in the parent phase and increases in the martensite phase. The loss tangent (tan δ ) shows a slight increase when approaching M s (=225 K), suggesting the formation of movable interfaces even above M s . The value of tan δ is nearly proportional to (1 − c/a ) 2 below M s , meaning that highly mobile twinned interfaces are essential for internal friction below M s . The so-called transitory term of tan δ is negligibly small for the MT of this alloy.

A high-speed train entering a tunnel generates a compression wave. When the compression wave reaches the exit portal of the tunnel, a micro-pressure wave radiates outward. The magnitude of the micro-pressure wave is approximately proportional to the pressure gradient of the compression wave arriving at the exit portal. As the micro-pressure wave can cause environmental problems, tunnel entrance hoods have been installed at many portals of long slab track tunnels on the Japanese high-speed railway, the Shinkansen to reduce the magnitude of the micro-pressure wave. In this study, field measurements were taken in a Shinkansen long slab track tunnel with a hood at its entrance. The compression wave distorts during its propagation through a long slab track tunnel. The dependence of the propagation characteristics on the initial compression waveform was clarified on the basis of field measurements on different trains and hood window configurations. It was shown that compression waves with a waveform of the pressure gradient that has shallow valleys tend to steepen more easily and that the optimum window pattern of the hood depends on the length of the tunnel. Furthermore, a mathematical model corresponding to the results of the field measurements was proposed to describe the distortion of the compression waves.

This paper is the second part of a two-part study on the propagation characteristics of compression waves generated by a train entering a long slab track tunnel with a tunnel entrance hood, which generates a tunnel compression wave with multiple peaks in the waveform of its pressure gradient. In Part 1, we described field measurements on the propagation characteristics of the compression waves generated by Shinkansen trains in a 9.7-km-long tunnel, and we compared the results with those of simulations. It was shown that initial waveforms whose pressure gradient waveforms have shallower valleys tend to steepen more easily, and a mathematical model of the distortion based on the field measurements using a quasi-laminar friction model was proposed. This follow-up report describes the theoretical and numerical analyses conducted on the basis of the mathematical model. Initial waveforms of the pressure gradient that have no valleys and are higher on their right-hand side grow up easily during propagation; this is due to the unsteady friction being small in the region where the magnitude of the second time derivative of the pressure is small. This results in a dependence of the propagation characteristics on the initial waveform of the compression wave.

Diffuse satellites appearing in electron diffraction pattern of shape memory Ti–(50 − x )Pd– x Fe (14, 16, 18, 19 and 20, in at.%) alloys have been investigated. The satellites appear in each alloy below T min , where its electrical resistivity shows a local minimum. The positions of satellites are g B2 + 〈 ζ ζ ¯ 0〉 * , where g B2 is a reciprocal lattice vector of the B2-phase. The value of ζ is smaller than 1/5 at T min for all the alloys; it increases with decreasing temperature and decreases with increasing iron content. The value of ζ at T min agrees with the length of the nesting vector previously calculated by the present authors. This result implies that Fermi surface nesting is the origin of diffuse satellites in Ti–(50 − x )Pd– x Fe alloys.

Magnetic behavior of equiatomic FeAl alloy is still not satisfactorily understood. In this work, we studied the magnetic properties of disordered FeAl alloy both experimentally and using first-principles theories and revisited the alloy system in perspective of the inhomogeneity present in the system. After obtaining magnetic exchange interactions from first-principles theories, we carried out Monte-Carlo simulations on special quasi-random structures (SQS) and compared the results with experimental measurements. We tried to understand the plethora of often differing results and explain them in terms of possible inhomogeneities in the system.

When a high speed train enters a tunnel, a micro-pressure wave radiates out from its exit portal. The micro-pressure wave can cause wayside environmental problems. Topography around the tunnel exit portal affects the peak value of the micro-pressure wave. In this paper, model experiments using a train model launcher were performed for investigating the effects of topography around the tunnel portal on the micro-pressure wave. Four types of topographic models, infinite flat ground, excavation on one side, excavation on both sides and elevated bridge, were used to measure the spatial distribution of the peak values of the micro-pressure waves. Furthermore, a modification of a prediction model for the peak value of the micro-pressure wave radiation was made on the basis of the experimental results.

We have investigated the relation between the negative temperature coefficient (NTC) in electrical resistivity and the formation of the athermal ω phase in Ti–xNb (26 ≤ x ≤ 29 at.%) alloys. The alloys with 26 ≤ x ≤ 28 exhibit NTC in electrical resistivity and a temperature hysteresis appears in the temperature region of NTC. In these alloys, athermal ω phase forms in the temperature range of NTC in resistivity. The alloy with x = 29 also shows NTC but no detectable temperature hysteresis appears. In this alloy, the athermal ω phase does not form, but diffuse satellites appear at g β + 1 / 2 ζ ζ ¯ 0 ∗ , where gβ is a reciprocal lattice vector of the β phase in the temperature range of NTC. These results suggest that NTC in the electrical resistivity in Ti–xNb alloys is related not only to the formation of the athermal ω phase but also to the appearance of diffuse satellites at g β + 1 / 2 ζ ζ ¯ 0 ∗ .

Time dependence of the first order magnetostructural transition in Pd doped B2-type FeRh (Fe0.45Rh0.45Pd0.1 alloy) has been investigated. This alloy exhibits a first order ferro–antiferro magnetostructural transition at 170 K in the cooling process under a low magnetic field (0.1 T). The transition also proceeds by holding at temperatures near 170 K. In addition, we also found that the transition temperature decreases with increasing magnetic field, and the transition is suppressed under a magnetic field of 5 T or higher. Removal of the magnetic field at 4.2 K induces the magnetostructural transition, but a part of the ferromagnetic phase remains at 4.2 K. In the subsequent heating process, the remaining ferromagnetic phase (high temperature phase) transforms to the antiferromagnetic phase (low temperature phase). Such an abnormal transition implies that the first order magnetostructural transition in Fe0.45Rh0.45Pd0.1 alloy is caused by a thermal activation process.

Effect of magnetic field on isothermal martensitic transformation of a sensitized SUS304 stainless steel has been investigated. The TTT diagram of 0.5 vol.% α′ martensite shows a double C-curve with two noses located at about 100 and 200 K. As the strength of magnetic field increases, the nose temperature decreases and the incubation time shortens for the upper part of the double C-curve, that is due to the γ → α′ martensitic transformation. Meanwhile, the nose temperature of the lower part of the C-curve, that is due to the γ → ɛ′ → α′ transformation, does not change under the magnetic field although the incubation time shortens by the application of magnetic field. Morphology of the α′ martensite is almost independent of the strength of magnetic field when holding is made at upper nose (200 K). On the other hand, when holding is made at the lower nose (100 K), the width of the ɛ′ martensite including α′ martensite becomes thinner as the strength of the applied magnetic field increases.

We have investigated twin-like microstructure of the martensite phase in a Ni 55.5 Mn 20.0 Ga 24.5 (at.%) alloy by using transmission electron microscope (TEM). The bright field image of the martensite phase showed striped microstructure composed of two crystals. Assuming that both crystals have orthorhombic structures, we calculated the axial ratios c / a and b / a from the 1 1 1 diffraction patterns by using angles between reflections. As a result, we found that the axial ratios of one crystal are slightly different from those of the other crystal. This result implies that the twin-like (striped) microstructure of Ni 55.5 Mn 20.0 Ga 24.5 is not true twin but is pseudo-twin.

The tetragonality c / a of FCT martensite phase in an Fe 3 Pt depends on the degree of order S of the L1 2 -type parent phase. As the degree of order increases, the tetragonality c / a changes from being less than 1 ( S = 0.75) to being larger than 1 ( S = 0.88). In this study, we have investigated a martensitic transformation behavior in a single-crystalline Fe 3 Pt with a degree of order which is in between 0.75 and 0.88, and have found the existence of orthorohombic martensite phase in the Fe 3 Pt.

Recently, we reported single variant formation in an Fe–55at.%Pd is certainly realized from a disordered fcc-phase to an ordered L1 0 -phase by heat-treatment under magnetic field. In the present study, we have investigated microstructure evolution during the process of the single variant formation by an X-ray diffraction and an electron microscopy observation. As a result, followings are obtained: size of the ordered particles at the early stage of ordering is about 2 nm and the nucleation ratio of preferable variant, whose easy axis lies in the field direction, is higher than that of other variants. Each of the ordered preferable variant grows by consuming the order variants and finally come together to become a single variant. Based on the observation, a model is proposed for the single variant formation of the ordered L1 0 -phase under magnetic field.

Martensitic transformation (MT) start temperature of the Fe–33Ni nanoparticles prepared by a Sol–gel and Reduction method was found to be higher than that of bulk specimens with the same composition, which is in contrast to the suppressing MT behaviors of nanoparticles in the previous works. Pre-existing bcc phase and polycrystalline structure were confirmed to assist MT in the Fe–33Ni nanoparticles. The mechanism associated with the promotion effect of the pre-existing bcc phase and the grain boundary on MT is discussed.

Displacement of atoms causing diffuse satellites in a Ti–32Pd–18Fe alloy (in at%) has been investigated by transmission electron microscopy (TEM). In this alloy, diffuse satellites appear at incommensurate positions given by gB2+q when the zone axis is [111] and [001], but they are missing when [110]. This results imply that the satellites appear because of a transverse wave with a propagation vector of q∼1/5〈ζζ¯0〉⁎ and displacement in 〈110〉 direction. Possibly, this transverse wave occurs as a result of phonon softening of the TA2 phonon branch, which is a common feature for B2-type Ti-based shape memory alloys.

The B2–B19′ transformation in Ti–51.2Ni (at.%) alloy exhibits a clear time dependence. The transformation starts after an incubation time when the specimen is held above M s , and proceeds while holding in the temperature range between 160 and 100 K. The nose temperature is expected to be near 130 K. The reverse transformation also shows a clear time dependence.

We have investigated the martensitic transformation in B2-type Fe 50 Rh 40 Pd 10 alloy. The B2-phase (cubic structure) of this alloy exhibits a magnetic transition on cooling from a ferromagnetic phase to an antiferromagnetic phase at 270 K. It then shows a martensitic transformation at 175 K. The martensite phase has a tetragonal structure with a tetragonality c/a = 1.17. We confirmed that the specimen deformed in the martensite phase show an imperfect shape memory effect in association with the reverse transformation. The reverse transformation (from the antiferromagnetic tetragonal phase to the ferromagnetic B2-phase) is expected to be controlled by a magnetic field.

Some shape memory alloys exhibit so-called temperature memory effect (TME) associated with their thermoelastic martensitic transformations. In this paper, we report that the same TME also appears in association with a first order magnetic transition between an antiferromagnetic phase and a ferromagnetic phase in FeRh. Although the TME in shape memory alloys appears only in the heating process, the TME in FeRh appears both in the cooling and heating processes. Presumably, the arrangement of antiferromagnetic domains and ferromagnetic domains is responsible for the TME in FeRh.