Hayato Nakatani

Acoustic source localization in anisotropic plates.

The conventional triangulation technique cannot locate the acoustic source in an anisotropic plate because this technique requires the wave speed to be independent of the propagation direction which is not the case for an anisotropic plate. All methods proposed so far for source localization in anisotropic plates require either the knowledge of the direction dependent velocity profile or a dense array of sensors. In this paper for the first time a technique is proposed to locate the acoustic source in large anisotropic plates with the help of only six sensors without knowing the direction dependent velocity profile in the plate. Experimental results show that the proposed technique works for both isotropic and anisotropic structures. For isotropic plates the required number of sensors can be reduced from 6 to 4.

Mechanical and thermal properties and water absorption of jute fiber reinforced poly(butylene succinate) biodegradable composites

The poly(butylene succinate) (PBS) biodegradable composites reinforced with jute fibers were developed. The effect of fiber content (10–60wt%) on the properties and water absorption of jute/PBS biodegradable composites was studied. The effect of alkali, silane, and combined alkali and silane surface treatment on the properties and water absorption of jute/PBS composites was investigated. The mechanical properties of surface treated jute/PBS composites were significantly higher than those of untreated ones. Compared with alkali or silane treatment, the combined alkali and silane surface treatment showed better mechanical properties of jute/PBS composites. The best mechanical properties of jute/PBS composites were achieved at 50wt% in this study, which showed an increase in tensile strength by 517.9%, tensile modulus by 3529.8%, flexural strength by 302.6%, and flexural modulus by 1949.1% compared with those of PBS resin. Fractured surface morphologies of composite specimens exhibited an improvement of interfacial fiber–matrix adhesion in the composites reinforced with surface-treated jute fibers. The surface-treated jute/PBS composites having good fiber–matrix adhesion resulted in stable composites with better thermal stability than untreated jute/PBS composites. The water absorption amount of the composites increased with increasing the fiber content. The surface-treated jute/PBS composites showed relatively lower water absorption behavior compared to untreated ones.

A two-step hybrid technique for accurately localizing acoustic source in anisotropic structures without knowing their material properties

Acoustic source localization techniques generally assume straight line propagation of waves from the acoustic source to the sensor. However, it is well-known that in anisotropic plates the acoustic energy does not always propagate in straight lines. Even for isotropic plates containing a cavity or an inclusion between the acoustic source and the sensor the straight line propagation assumption is violated. In such cases only options available in localizing acoustic source is to use relatively expensive distributed sensor systems, or to follow time reversal techniques based on the impulse response functions which is labor intensive and computationally demanding. A two-step hybrid technique is proposed in this paper for predicting acoustic source in anisotropic plates. During the first step it was assumed that the waves propagated along straight lines from the acoustic source to the sensor. The source was localized with this simplifying assumption. Then this first prediction was improved in the second step by solving an optimization problem. Experimental results showed that the second step always moved the estimates towards the actual source location. Thus it always reduced the prediction error irrespective of whether the final prediction coincided with the actual source location or not.

Improving accuracy of acoustic source localization in anisotropic plates.

The acoustic source localization technique for anisotropic plates proposed by the authors in an earlier publication ([1] Kundu et al., 2012) is improved in this paper by adopting some modifications. The improvements are experimentally verified on anisotropic flat and curved composite plates. Difficulties associated with the original technique were first investigated before making any modification. It was noted that the accuracy of this technique depends strongly on the accuracy of the measured time difference of arrivals (TDOA) at different receiving sensors placed in close proximity in a sensor cluster. The sensor cluster is needed to obtain the direction of the acoustic source without knowing the material properties of the plate. Two modifications are proposed to obtain the accurate TDOA. The first one is to replace the recorded full time histories by only their initial parts - the first dip and peak - for the subsequent signal processing. The second modification is to place the sensors in the sensor cluster as close as possible. It is shown that the predictions are improved significantly with these modifications. These modifications are then applied to another sensor cluster based technique called the beamforming technique, to see if similar improvements are achieved for that technique also with these modifications.

Locating Point of Impact on an Anisotropic Cylindrical Surface Using Acoustic Beamforming Technique

A beamforming array technique with four sensors is applied to a cylindrical geometry for detecting point of impact. A linear array of acoustic sensors attached to the plate record the waveforms of Lamb waves generated at the impact point with individual time delay. A beamforming technique in conjunction with an optimization scheme that incorporates the direction dependent guided Lamb wave speed in cylindrical plates is developed. The optimization is carried out using the experimentally obtained wave speed as a function of propagation direction. The maximum value in the beamforming plot corresponds to the predicted point of impact. The proposed technique is experimentally verified by comparing the predicted points with the exact points of impact on a cylindrical aluminum plate and a cylindrical composite shell. For randomly chosen points of impact the beamforming technique successfully predicts the location of the acoustic source.

Mechanical properties of fiber/matrix interface in polymer matrix composites

This paper reviews the mechanical properties of interface adhesion between the fiber and matrix mainly by interpreting the authors’ past articles. First, the methods for evaluating interface mechanical properties are described considering micromechanical testing using single-fiber composite specimens. In particular, the test-type dependence of the obtained interfacial strength is discussed, and this paper suggests that the cruciform specimen technique is an appropriate testing method. Then, this paper presents another way to obtain interface properties that is extracted from a bulk composite test. Moreover, the time and temperature dependence of the interface strength and the interface failure envelope under a combined stress state are described, respectively. Interface toughness is also discussed at the end of this paper, and it is implied that the value might be much lower than those presented in many conventional articles.

Impact localization on a cylindrical plate by near-field beamforming analysis

A beamforming array technique with 4 sensors is applied to a cylindrical plate for detecting point of impact. Linear array of acoustic sensors attached to the plate record the waveforms of Lamb waves generated at the impact point with individual time delay. An optimization technique with an objective function is incorporated into the beamforming technique in order to deal with the direction dependent Lamb wave speeds in a cylindrical geometry. The optimization is carried out using the experimentally obtained wave speed as a function of propagation direction. The maximum point in beamforming plot with minimized objective function corresponds to the localized point of impact. The proposed technique is experimentally verified by comparing the predicted points with the exact points of impact on a cylindrical aluminum plate. For randomly chosen points of impact the beamforming technique successfully predicts location of the exact acoustic source.

Numerical validation of split Hopkinson pressure bar technique for evaluating tensile mechanical properties of CFRP laminates

The present study proposes a simple numerical simulation technique for the split Hopkinson pressure bar (SHPB) and then investigates the experimental conditions for composite materials in a tensile-loading SHPB. The following issues were investigated through experiment and numerical simulation: (i) the effects of the cross section and acoustic mismatch between the jig with a slit and screw and the input/output bars on the loading condition and (ii) the effects of the duration time of the applied load and the acoustic impedance mismatch on the stress–strain curve obtained by SHPB testing. From the numerical simulation results, the following conclusions were found: (i) the proposed jig with a slit and screw can apply an ideal one-dimensional displacement to a specimen and (ii) the material characterization of a composite material by SHPB testing might be possible by optimizing a longer duration time if the acoustic mismatch is greater.

Detecting the point of impact on a cylindrical plate by the acoustic emission technique

An optimization based technique for detecting the impact point on isotropic and anisotropic flat plates developed by Kundu and his associates is extended here to the cylindrical geometry. An objective function is defined that uses the cylindrical coordinates of four sensors attached to the cylinder and four arrival times to locate the point of impact by minimizing the objective function that gives the least squares error. The proposed technique is experimentally verified by predicting the points of impact and comparing the predicted points with the actual points of impact.

Eye Movement Analysis of Japanese Sewing Scissors Craftsman

The purpose of this study is to elucidate the skill of a blacksmith who has an ability to produce a pair of scissors whose two blades accurately comes across in the length, width and angle of each blade, even though they were produced separately. The processing method this scissor artisan employs is known as “So-hizukuri” (total forging process). The elucidation was conducted through observing the line of sight of the artisan using an eye movement analysis camera during his forging process. There are four main stages in the So-hizukuri process, and each stage involves several steps. In this study, we asked the scissor artisan to wear an eye movement analysis camera while engaging with the “Namatogi” (grinding before quenching) step in the “rough finishing before quenching” stage, which is the second in the four main stages, and observed his eye movements. We viewed the video recorded by the eye camera, and studied which parts of the blades he focused on, and the amount of time he focused on each part, when the artisan was comparing the two blades by laying one blade on top of the other. As a result, it was clarified that the artisan works on each of the left and the right blade alternately and gradually at every step toward the final stage, as the left and right blades of the scissors come across accurately when the scissors are completed. At any point in the process, he did not focus on forging one blade intensively, use a measuring instrument to measure the length of the blades, or use one of the blades as a standard to match the other blade.