The concept “Disaster Mitigation and Sustainable Engineering” is introduced comprehensively and several examples are shown in this paper. It is emphasized that it can be effectively realized in the field “smart materials and structural systems.” As serious disasters may not occur for a long period of time, and the structures for disaster mitigation suffer from vast amount of maintenance cost etc., they are better to be used daily. Their compactness and deploying function are also very useful. In order to demonstrate the concept, two examples having been experimentally tried are introduced, that is, artificial forests and deployable structure based on honeycomb to be used against flooding. Other examples and products in the world are also introduced and future directions are discussed.
Melt-spun, rapid solidified Galfenol (Fe-Ga) ribbon sample showed large magnetostriction and good ductility as compared with conventional bulk sample because the ribbon has fine columnar grain which was formed during melt-spinning process. The large magnetostriction is caused by the release of considerable large internal stresses in as-spun ribbon as well as the remained [100] oriented strong textures after annealing. In order to obtain larger magnetostrictive force than ribbon sample, in this study, magnetostrictive bulky Fe-Ga alloy was fabricated by combining laminate of rapid-solidified ribbons (80 μm in thickness) and spark plasma sintering/joining (SPSJ). SPSJ is characterized by short time and low temperature heating and sintering process. The laminated sample made by SPSJ maintained the unique metallurgical microstructure of polycrystalline texture of columnar grains as well as almost non-equilibrium metastable phase with little existence of ordered precipitations in as-spun ribbons. The excellent sintered sample having large magnetostoriction was obtained under a condition of the compressive stress of 100 MPa at the temperature of 973 K. The magnetostriction depended on compressive pre-stress level for specimen and reached about 100 ppm which was a half of value obtained for the ribbon sample. Furthermore, by following short annealing for this specimen, the magnetostriction increased to 170-190 ppm comparable to the ribbon's value.
As a first step to develop a health monitoring system with active and embedded nondestructive evaluation devices for the machineries and structures, multi-functional SAW (surface acoustic wave) device was developed. A piezoelectric LiNbO3(x-y cut) materials were used as a SAW substrate on which IDT(20μm pitch) was produced by lithography. On the surface of a path of SAW between IDTs, environmentally active material films of shape memory Ti50Ni41Cu(at%) with non-linear hysteresis and superelastic Ti48Ni43Cu(at%) with linear deformation behavior were formed by magnetron-sputtering technique. In this study, these two kinds of shape memory alloys SMA) system were used to measure 1) loading level, 2) phase transformation and 3)stress-strain hysteresis under cyclic loading by utilizing their linearity and non-linearity deformation behaviors. Temperature and stress dependencies of SAW signal were also investigated in the non-sputtered film state. Signal amplitude and phase change of SAW were chosen to measure as the sensing parameters. As a result, temperature, stress level, phase transformation in SMA depending on temperature and mechanical damage accumulation could be measured by the proposed multi-functional SAW sensor. Moreover, the wireless SAW sensing system which has a unique feature of no supplying electric battery was constructed, and the same characteristic evaluation is confirmed in comparison with wired case.
Barkhausen noise (BHN) method seems a useful tecnique to non-destructive evaluation of martensite phase transformation of ferromagnetic shape memory alloy, which is used as the filler of our proposing "Smart Composite Board". The concept of design for "Smart Composite Board" which can combine the non-destructive magnetic inspection and shape recovery function in the material itself was formerly proposed. In the present study, we survey the possibility of Barkhausen noise (BHN) method to detect the transformation of microscopic martensite phase caused by stress-loading in Fe-30.2at%Pd thin foil, which has a stable austenite phase (fcc structure) at room temperature. The BHN voltage was measured at loading stress up to 100 MPa in temperature range of 300K to 373K. Stress-induced martensite twin was observed by laser microscope above loading stress of 25 MPa. A phase transformation caused by loading stress were analyzed also by X-ray diffraction. The signals of BHN are analyzed by the time of magnetization and the noise frequency. BHN caused by grain boundaries appears in the lower frequency range (1kHz-3kHz) and BHN by martensite twin in the higher frequency range (8kHz-10kHz). The envelope of the BHN voltage as a function of time of magnetization shows a peak due to austenite phase at weak magnetic field. The BHN envelope due to martensite twins creates additional two peaks at intermediate magnetic field. BHN method turns out to be a powerful technique for non-destructive evaluation of the phase transformation of ferromagnetic shape memory alloy.
Ti50Ni50-xCux fine fibers were successfully developed by the arc-melted rapid-solidification method.It has been very difficult to do the conventional melt-work processing from the bulk material of this alloy to very fine fiber because of the brittleness from metallic compounds especially in the range of Cu⩾8 at%. The fibers showed good shape memroy effect. As Cu content increased, the temperature hysteresis of recovery strain-temperature curves as well as DSC curves became smaller and the tensile strength showed more than 1000MPa in Ti50Ni40Cu10 at% fiber. Therefore, the developed rapid-solidified, thermoelastic fiber fiber actuator/sensor materials have high potentiality of applications for micro-machines and the fillers of smart composites.
The possibility to detect the phase transformation with martensites by heating or cooling as well as stress-loading in ferromagnetic shape memory Fe-30at percent Pd alloy thin foil by using magnetic Markhausen noise sensor was studied. MBHN is caused by the irregular interactions between magnetic domain and thermally activated martensite twins during magnetization. In general, the envelope of the MBHN voltage versus time signals in Fe-29at percent Pd ribbon showed two peaks during magnetization, where secondary peak at intermediate state of magnetization process decreased with increasing temperature, while the MBHN envelopes in pure iron did not change with increasing temperature. The variety of MBHN due to the phase transformation was apt to arise at higher frequency part of spectrum during intermediate state of magnetization process and it decreased with disappearance of martensite twins. Besides, MBHN increased monotonically with increasing loading stress and then, it decreased with unloading, however MBHN showed large hysteresis between loading and unloading passes. Based on the experimental results from MBHN measurements for both thermoelastic and stress-induced martensite phase transformations in Fe-30at percent Pd ribbon samples, MBHN method seems a useful technique to non-destructive evaluation of martensite phase transformation of ferromagnetic shape memory alloy.
Fe-Pd thin films were deposited on SiO2/Si substrates by RF magnetron sputtering. The compositions were determined by the chemical analysis to be ranged in Pd-content about 30.0 at%. The thin films were solution-treated at 1173 K for 180s in vacuum and subsequently cooled by Ar gas flow. In the Fe- 32.62 at%Pd specimens, the as-deposited thin film possesses ultra-fine grains resulting in a long-range disorder structure. After the heat treatment, ((gamma) Fe, Pd) with an fcc structure is recrystallized and the crystallized thin film shows the texture orientation with (111) and (100) planes parallel to the film surface. In the Fe-29.97 at%Pd specimens, the as-deposited thin film exhibits a bcc structure due to less Pd content. After the heat treatment, ((gamma) Fe, Pd) fcc structure is formed at higher Pd content. Magnetic properties of the thin films are affected by the composition, crystal structure and grain size. In as-deposited thin films, two- stage I-H hysteresis loops are observed on account of the fine grains. After the heat treatment the rectangularity of the hysteresis loops is improved especially in the oriented Fe- 32.62 at%Pd thin film and Curie temperature increases with the increase of Pd-content. Magnetostriction of 3.6 X 10-5 at an applied magnetic field H equals 8.0 kA/m (equals 0.1 kOe) is observed in the solution-treated Fe-32.62 at%Pd thin film.
Photoelastic model material with shape memory effect and molding processes of the material is developed in this research. Matrix and fiber of the photoelastic model material developed in this research are respectively epoxy resin and wire of Ti50Ni50 shape memory alloy. It is called Ti50Ni50 shape memory alloy fiber epoxy composite. It is assured that Ti50Ni50 SMA-FEC is satisfied with the requirements of photoelastic model material and can be used as photoelastic model material and can be used as photoelastic model material. The maximum recovering strain of Ti50Ni50 SMA-FEC is occurred at 80 degrees in any prestrain of Ti50Ni50 shape memory alloy wire fiber and in any fiber volume ratio. Recovering strain is increased with the increment of the prestrain and the fiber volume ratio.
Metal matrix composites (MMCs) have been studied intensively with expectation of applying MMCs to various structural and machine components. A recent summary of the thermomechanical behavior of MMCs has been given elsewhere.1'2 One of the important findings in the recent studies is that strengthening of MMCs is identified by two mechanisms: back stress strengthening and dislocation punching.3'4 In most MMC systems, the coefficient of thermal expansion (CTh) of reinforcement is smaller than that of metal matrix, resulting in tensile residual stress in the matrix at room temperature. This tensile residual stress in the matrix reduces the tensile flow stress (particularly yield stress) of a MMC.5 If the residual stress in the matrix in a MMC is controlled to be compressive, the tensile flow stress of the MMC is expected to be increased. A shape memory alloy (SMA) fiber, after its shape is memorized and presirained at martensitic phase, can shrink to its original length upon heating to austenitic finish temperature. If such shrinkable SMA fibers are embedded in a metal matrix to form a MMC, compressive residual stress in the matrix is induced at austenitic stage, resulting in enhanced tensile flow stress of the MMC, see the process of inducing such compressive residual stress in the matrix in Fig. 16. Motivated by the above idea depicted in Fig. 1 ,we are led to process TiNi SMA fiber/i 100 Al matrix (TiNi/Al) composite by pressure casting route, the details of which has been given elsewhere6. As-processed TiNi/Al composite was machined to tensile specimen of flat bar type and given tensile prestrain c at martensitic stage, then heated to 363K just above the austenitic finish temperature (337K), followed by tensile testing at 363K. The results of the stress-strain curves of TiNi/Al composite with and without prestrain, and unreinforced Al are shown in Fig. 2. It is obvious from Fig. 2 that the flow stress of the TiNi/Al composite with prestrain is higher than that of the composite without it, which in turn is higher than the unreinforced metal due to back stress strengthening mechanism. The strengthening due to prestrain is the main subject of this paper. The analytical model similar to the present one has been developed for the analysis of a short fiber SMA fiber MMC.7 Analytical modeling will be stated in section II and numerical results and comparison with the experimental results will be discussed in Section III, followed by the conclusion in Section IV.
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print or electronic format on
SPIE.org.
INSTITUTIONAL Select your institution to access the SPIE Digital Library.
PERSONAL Sign in with your SPIE account to access your personal subscriptions or to use specific features such as save to my library, sign up for alerts, save searches, etc.