Materials Science Forum Vol. 879

Abstract: The vertical jump is a commonly used test and widely studied in literature. Indeed, it is one of the most prevalent method of assessment on sport performance because the jump height is highly correlated with leg extensor muscles power. This paper deals with the study on a new contact mat system whose performances have been compared with a force platform. Some tests have been performed and the relative comparative results will be presented. The study shows a significant concurrent validity of Wi-JumpLe system for the flight and ground contact time measurements. In conclusion, the new contact mat structure together with the electronic measurement system is legitimate to assess vertical jump height and leg extensors muscle power.

Abstract: In spite of the potentially harmful effects of vibrations on the human body, a new path was recently opened for the use of these mechanical means in the therapeutic field. The stimulation of proprioceptive and exteroceptive sensitivity is the main target in both peripheral (diabetes type 1 and type 2) and central (stroke, Parkinson's disease multiple sclerosis) nervous system disorders, particularly for the recovery and maintenance of functional state. By the way the response to the treatment is highly variable from subject to subject. Our experimental apparatus consists of a virtual reality system "LEAP Motion" which involves the patient in the execution of visuo-manual tasks in a virtual environment while receiving vibrotactile stimulation. We also used a modular 36 channels EEG system and a vibratory stimulation system able of delivering vibratory stimuli perpendicular and tangential to the body surface area.The study evaluation of motor performance and the ability to perform the tasks of visuomotor task assigned, in the presence and absence of vibratory stimulation and in real time, evoked potentials in the cortex.The vibration frequency extended from 5 to 200 Hz and with accelerations between 0.3G and 1,5G with displacement amplitude of about 0.5 mm applied on the affected limb hand. As the frequency, the amplitude and the direction of the vibration may vary we studied the relationship between the characteristics of the stimulus and the perception in the cerebral cortex, or other levels of the nervous system, studying potential models of elicitation of the somatosensory system. In this regard, our study took into account patients with Parkinson's disease and in particular evoked potentials N18 N20 N24 N30 particularly related to tactile stimulus, and indicative of the level of perception and processing in the brain of the Parkinson's patient.

Abstract: The precision in localization of the UBISENSE Real Time Location System was assessed for evaluating the possibility of using the system in the detection of movements and position of athletes on the field during sport performance. The system was implemented in an indoor lab space measuring 11 by 7 meters. Four sensors were installed on the roof at a height of 3 meters above floor. Various sampling rates were used with a single location tag. UBISENSE is using UWB localization technology based on the triangulation of time of arrivals of UWB pulses at the different antenna sensors. Precision varied in position and speed determination being position resolution in the range of 15 to 50 cm while speed precision was in the figure of 6% at slow actual speed of 0.18 m/s up to 20% at fast speed of 1 m/s. This was mainly due to sampling frequency in the location system. In conclusion, as long as speed of the athlete is not at stake, the position can be measured with quite good resolution and sampling frequency so to permit the evaluation of sport performances of the athlete during the exercise or activity. A very attractive feature of the system is that the athlete must be tagged with a very low-weight and quite comfortable active tag which, on the contrary to video tracking systems, doesn’t need to remain in the field of view.

Abstract: Otoacoustic emissions are a by-product of the active nonlinear amplification mechanism located in the cochlear outer hair cells, which provides high sensitivity and frequency resolution to human hearing. Being intrinsically sensitive to hearing loss at a cochlear level, they represent a promising non-invasive, fast, and objective diagnostic tool. On the other hand, the complexity of their linear and nonlinear generation mechanisms and other confounding physical phenomena (e.g., interference between different otoacoustic components, acoustical resonances in the ear canal, transmission of the middle ear) introduce a large inter-subject variability in their measured levels, which makes it difficult using them as a direct measure of the hearing threshold using commercially available devices. Nonlinear cochlear modeling has been successfully used to understand the complexity of the otoacoustic generation mechanisms, and to design new acquisition and analysis techniques that help disentangling the different components of the otoacoustic response, therefore improving the correlation between measured otoacoustic levels and audiometric thresholds. In particular, nonlinear cochlear modeling was able to effectively describe the complex (amplitude and phase) response of the basilar membrane, and the generation of otoacoustic emissions by two mechanisms, nonlinear distortion and linear reflection by cochlear roughness. Different phase-frequency relations are predicted for the otoacoustic components generated by the two mechanisms, so they can be effectively separated according to their different phase-gradient delay, using an innovative time-frequency domain filtering technique based on the wavelet transform. A brief introduction to these topics and some new theoretical and experimental results are presented and discussed in this study.

Abstract: A photoplethysmographic (PPG) near infrared (850nm) system has been developed for the non-invasive assessment of superficial tissues’ (skin) swelling and redness. The PPG signal is treated to avoid ambient light and to extract the DC (direct current) and AC (alternate current) components. These components are then subtracted from the same components acquired on a reference site on the same subject. The resulting measures are used in a model able to classify different states of inflammation of the tissues. Numerical results permit to follow the inflammation state and to evaluate possible medical and physiotherapy interventions. To avoid artefacts due to compression of the skin by the instrument, a pressure sensor has been also embedded on the optical sensing head of the system, so that the measures are considered as valid only if they are taken within the same range of applied pressure on the skin. This is important to get comparable PPG measures. Heart rate and hemoglobin oxygen saturation measures are a by-product out of the system and they can be exploited for other purposes or they can be taken into account for a better evaluation of the inflammation state. Although the system is still a research prototype and no real model is available about how inflammation affects the optical properties of the skin, the very first qualitative results show a strong sensibility of the system to skin alterations due to acute inflammation.

Abstract: The evolution of recrystallization texture in commercially pure aluminum sheet cold-rolled by 90% reduction in thickness was measured by Juul Jensen et al. The cold-rolling texture consisted of the Goss {110}<001>, Brass {110}<112>, S {123}<634>, and copper {112}<111> components. When the cold-rolled aluminum sheet was annealed at temperatures between 253 and 341°C for times between 5 min and 20 h., the cube {001}<100> component evolved. The evolution of the cube texture cannot be explained by either the oriented nucleation theory by Burgers and Louwerse or the oriented growth theory by Barrett. The cube texture evolution originates from the Copper component by the strain-energy-release-maximization (SERM) theory by Lee. Once the Cube oriented, dislocation free nuclei evolve, they are in the best position to grow at the expense of neighboring deformed high energy grains of the Goss, Brass, S, and Copper orientations, and the volume fractions of the Goss, Brass, S, and copper components would decrease. However, the volume fraction of the Goss component increased a little at annealing temperatures of 253 and 278°C, at variance with expectation. Low stacking-fault-energy alloys with the brass {110}<112> rolling texture evolve the {236}<385> texture after recrystallization, whereas high stacking-fault-energy alloys with the brass rolling texture evolve the Goss texture after recrystallization by the SERM theory, resulting in the increase of the volume fraction of the Goss texture.

Abstract: Ti-29Nb-13Ta-4.6Zr (TNTZ), which is one of metastable beta-type Ti alloys, has developed as one of representative biomedical and dental Ti alloys in Japan. TNTZ subjected to solution treatment shows Young’s modulus of 60 GPa, which is close to that of cortical bone. In addition, TNTZ has very low cytotoxicity and good bone biocompatibility as well. Heat treatment like solution treatment and aging (STA) is mainly used for improving the mechanical properties of metastable beta-type Ti alloys because of alpha precipitates, while Young’s modulus also rises drastically. This study was investigated the effects of mechanical surface modifications such as fine particle bombarding (FPB) with steel and hydroxyapatite particles or friction stir processing (FSP) on the mechanical strength of TNTZ in order to maintain low Young’s modulus. The relative bone contact ratios between the cancellous bones of Japanese white rabbits and column-shaped TNTZ subjected to FPB of steel particles were also evaluated. Vickers hardness (HV) of TNTZ subjected to FPB with fine particles of steel and hydroxyapatite particles increased by HV30 to 200 at the edge of the specimen surface to around 100 to 300 mm in depth as compared with that of TNTZ subjected to solution treatment. The hydroxyapatite layer was formed on the specimen surface by FPB with fine particles of hydroxyapatite particles, although the trend was not significant by FPB with steel particles. Furthermore, the fatigue strength in high cycle fatigue region of TNTZ subjected to FPB with steel particles was improved and the fatigue limit showed around 400 MPa, although that of TNTZ subjected to FPB with fine particles of hydroxyapatite particles were around 60 MPa higher than that to TNTZ subjected to solution treatment (230 MPa). TNTZ with a rough surface texture (Ra: 0.65 μm) showed a relative bone contact ratio of more than 80% after undergoing FPB with fine particles of steel particles; this value was significantly higher than that of TNTZ with a surface texture (Ra: 0.07 μm). Lastly, the microstructure of TNTZ subjected to FSP showed the recrystallization area by the frictional heating with very fine equiaxed beta phase with an average grain diameter of 3.0 μm. The change in Vickers hardness of TNTZ subjected to FSP was almost identical to that of Young’s modulus and showed the almost same trend of FPB.

Abstract: Tensile and low cycle fatigue properties of Sn-5Sb (mass%) solder were investigated with miniature size tensile specimens. The effect of temperature and strain rate on tensile properties and the effect of temperature on low cycle fatigue properties were examined. Tensile strength increases with increasing strain rate regardless of temperature investigated. For elongation, the effect of temperature on it is negligible although it slightly increases with increasing strain rate. The low cycle fatigue life of Sn-5Sb obeys by the Manson-Coffin’s equation. The effect of temperature on the fatigue life is negligible in the temperature range from 25 ^oC to 150 ^oC. In the low cycle fatigue test with a high total strain range of 4%, cracking at phase boundary mainly occurs regardless of temperature investigated. In the case of a low total strain range of 0.4%, ductile fracture mainly occurs, and cracking at phase boundary with generation of grooves also occurs at high temperature.

Abstract: Al-Mg-Si system alloy have good strength and high ductility without heat treatment. However, the castability in this alloy is inferior to other aluminum alloy, in particular, hot-tearing is easy to occur during solidification. In our previous study, hot-tearing was not occurred in the case of 0.04%Sr addition to this alloy, because of the remarkable refinement of eutectic Mg₂Si phase. In this study, in order to clarify the mechanism of the change of the crystallized eutectic Mg₂Si morphology, the effect of Sr addition on the solidification structure in Al-6%Mg-3%Si alloy was investigated. By Sr addition to this alloy, the change of the nucleation mode from homogeneous to heterogeneous was occurred with the temperature drop at the start of eutectic reaction, and the great change of eutectic growth mode from facet to non-facet was thought to be a main reason improving of hot-tearing.

Abstract: The recrystallization behavior of hot-deformed austenite of 0.55% C low alloy steels at 900, 850 and 800°C was investigated by a conventional double-hit compression test and a new method which reconstructs the parent austenite orientation map from an EBSD (electron backscattering diffraction) orientation map of daughter lath martensite. The new method can clearly reconstruct the parent austenite structure at high temperature from the daughter lath martensite structure and we can obtain the information on crystal orientation of the work-hardened austenite. It was revealed that recrystallization of austenite at 800 °C is significantly retarded by the addition of 0.1% V. The strong texture of <110> parallel to the compression direction develops just after the hot-deformation, but this texture becomes weaker as the recrystallization progresses. By applying the reconstruction method, it becomes possible to evaluate various phenomena related to the hot-deformation of austenite