Yasushi Niitsu

Strain recovery mechanism of PBT/rubber thermoplastic elastomer

Abstract The thermoplastic elastomer (TPE) prepared by dynamic vulcanization is a two-phase material in which crosslinked rubber particles are densely dispersed in a ductile polymer matrix. The TPE shows an excellent strain recovery, even though the matrix consists of ductile plastics. This behavior was exemplified in a 50/50 poly(butylene terephthalate)(PBT)/ethylene rubber blend. Finite element method (FEM) analysis revealed that: (1) the low stress evolved in PBT matrix with bulk deformation, especially in the ligament matrix between rubber particles in stretching direction, is locally preserved within an elastic limit and it acts as an in situ formed adhesive for interconnecting the rubber particles, and (2) the volumeric strain of rubber particles with high Poissons ratio provides the contractile stress to heal the plastically deformed PBT phase outside the ligament matrix. Such strain mechanisms were supported by the polarized FT-Raman spectroscopy in terms of the peak shift caused by chain distortion, its anisotropy, and the gauche-to-trans transformation associated with plastic deformationm, in comparison with those in neat PBT.

Inelastic stress-strain response of 214Cr-1Mo steel under combined tension-torsion at 600°C☆

Abstract The results of the third-phase activity of the Subcommittee on Inelastic Analysis and Life Prediction of High Temperature Materials, JSMS, are summarized in this series of papers. As the first part, the evaluation of inelastic constitutive models under plasticity-creep interaction conditions is presented in extension of the previous report of the phase 2 activity. Seven types of experiment were performed under multiaxial loading of tension and torsion with normalized and tempered 2 1 4 Cr-1Mo steel at 600 °C: (i) step-up/down creep, (ii) uniaxial tension with strain rate change, (iii) cruciform stressing, (iv) biaxial mechanical ratcheting, (v) cyclic torsion, (vi) in-phase cyclic straining and (vii) out-of-phase cyclic straining. The experimental results of these benchmark tests are compared with the simulated results by seven types of constitutive models to evaluate their accuracy in simulating the experimental behaviour of the material.

Seismic and Wind Performance of Five-Storied Pagoda of Timber Heritage Structure

In Japan, there exist a total of 22 five-storied timber pagodas constructed before the middle of 19 centuries. All of those pagodas are registered as the important cultural heritages by Japanese Government, while some of them are listed in World Cultural Heritages such as Horyu-ji Temple’s Pagoda that was built in the end of 7th century. As those timber pagodas in seismic areas have survived against earthquakes during their long histories, their earthquake resistant capacity has been studied for a century. However, the actual dynamic behaviors of timber pagodas subjected to large earthquakes should be recorded to understand the seismic performance. Furthermore, an interesting structural issue has recently risen of wind resistant capacity of traditional five-storied timber pagodas, as such tall timber structures may be severely affected by strong wind. In order to record the actual dynamic behaviors during not only earthquakes but also typhoons, we have been conducting earthquake and wind monitoring at Hokekyou-ji Temple in Ichikawa City, next to Tokyo, which has survived for 4 centuries against not only large earthquakes but also severe typhoons. Hence, while the earthquake monitoring has been done by the conventional method utilizing accelerometers, the dynamic displacement of the structural response to wind has been directly measured by a new technique employing an image process system using LED makers and CCD camera, because the wind response includes much longer period component in general, therefore, it must be difficult to measure accurately the wind response by accelerometers. The scope of the present paper are 1) to review the past studies to understand the excellent earthquake resistance of five-storied timber pagodas, as well as, to introduce our research project of seismic and wind monitoring that has been successfully conducted since 2007, 2) to interpret those monitoring records which would be useful for understanding seismic and wind performance of the heritage timber pagodas that have survived for many centuries with describing the simulation analysis of seismic response, and 3) to show the long term monitoring records of the horizontal displacement of the heritage structure.

A New Measurement Technique of Low-Level Strain Retardation in Optoelectronic Materials

This paper introduces the principles and execution of a new technique for low-level strain retardation measurement, which requires only three phase-stepping images, with precision. It then discusses the potential of this new technique for improving automated photoelasticity. To verify the new technique experimentally, a precise crystal wave plate of having low-level retardation was used as a specimen. The tolerance in retardation was 10.0plusmn4.7 nanometers. The measurements of the retardation with standard deviation using the new technique were also found to be 10.0plusmn4.7 nanometers, which agreed well in spite of low-level amount of retardation. Moreover, the measured offsets of the angular orientation were found to be -0.05plusmn4.46 degrees with standard deviation for angular position of the rotation stage for the specimen. The instrument described in this paper includes beam splitters to measure the influence on these measurements to develop the instrument into an automated one in future research. Finally, it is suggested that an automated photoelasticity will now be possible within an error of around plusmn3nm in retardation and around plusmn5degrees in its related orientation

Development of Scanning Stress Measurement Method Using Laser Photoelasticity.

We have developed an optical equipment which possesses high detection sensitivity for measuring small optical retardation induced by stress by means of laser photoelasticity. A He-Ne laser is used as a light source to measure small stress in transparent materials. We explain the theory and process of the measurement of optical retardation in the materials. The magnitude of principal stress difference as well as the direction of the principal stress are obtained simultaneously and quantitatively using our equipment. In order to evaluate the performance of the optical retardation measurement equipment, the stress distribution of a pulled rectangular glass plate with notches at both sides was measured using the equipment. The results of stress distribution agreed with the analytical results. Stress at many points can be determined quickly using the equipment and scanning stress distribution measurement has been realized.

Effect of crystalline orientation on photoelastic constant of Si single crystal

We developed an optical birefringence measurement equipment by using a photoelastic modulator and a polarized laser. A He-Ne infrared laser is used as a light source to measure the optical birefringence in silicon wafers. We explain the theory and process of the measurement of stress in silicon wafers. The magnitude of principal stress difference and also the direction of the principal stress are obtained simultaneously and quantitatively using our experiment. The optical birefringence of (100), (111) and (110) face silicon stressed specimens were measured. From the experimental results, the photoelastic constant depends on the crystalline orientation. By the stress-strain analysis of silicon single crystal, it was found that the relation between the principal strain difference and the retardation was independent of crystalline orientation.

Effect of temperature variation on plastic behavior of S25C mild steel

Abstract Plastic behavior of S25C mild steel was investigated at constant and variable temperatures in the range from room temperature to 400°C. The combined loading tests were carried out with the thin walled tubular specimens by applying the axial and torsional loads. The initial yield condition of the material obeyed Trescas law, but the stress-strain relation after yielding followed neither Trescas nor Misess laws. Bauschingers curves in the torsional loading conditions were different from those in the axial loading conditions. The stress-strain relations subsequent to the tensile pre-strain were obtained at various temperatures. The experimental results were compared with the isothermal stress-strain relation.

Shaking Table Test of Full Scale Model of Timber Framed Brick Masonry Walls for Structural Restoration of Tomioka Silk Mill, Registered as a Tentative World Cultural Heritage in Japan

Tomioka Silk Mil is the first model silk-reeling factory that the Japanese Government established in 1872. The main building is structurally characterized by timber framed brick masonry walls. The buildings were constructed using European and Japanese traditions. Walls were built of locally produced bricks, manufactured using a technique introduced from Europe, and the buildings were roofed with traditional Kawara tiles. The scope of the paper is to present the outcomes of the shaking table tests using full-scale model of the timber framed brick masonry walls. Those tests were successfully conducted to study the seismic behaviors of such composite structures under extremely strong motions. As well as, they were performed to examine the effectiveness of the proposed strengthening technique using aramid fiber wires. In the present study, 3-dimensional dynamic displacement was directly measured by the image processing technique utilizing high-speed optical cameras. This new technology revealed both the dynamic deformation of the walls and the safety limit of the displacement in dynamic phase.

Improving light marker accuracy on camera images

The accuracy of measurement systems that use image processing is very dependent on the method used to determine the target center position on the image. The digital image correlation (DIC) method,1 which combines image matching and sub-pixel estimation using correlation interpolation, enables registration of pairs of images in many processing applications, such as camera calibration and measurement of structures or fluids. However, DIC is unable to determine the exact center position. Therefore, a light marker is installed on the surface of the object and the central point of the marker is estimated by the centroid calculation method (where the geometric center is determined).2 Although this method can be realized with the sub-pixel accuracy of DIC, there is a bias error in the measurement, depending on the threshold that separates the bright spot from the region of interest.3 Our study proposes a dynamic threshold method to reduce the bias and error of the calculated value. In addition, we evaluated the measurement accuracy of the center position of a bright spot and analyzed the error in certain imaging conditions using Monte Carlo simulation. We sought to improve the well-known technique of threshold selection for image binarization (converting to a black and white image) known as discriminant analysis.4, 5 This technique selects an optimal threshold by the discriminant criterion, which maximizes the separability of two classes in a gray-level histogram. The sub-pixel position measurement has a systematic error when used with this threshold selection method, which is caused by a higher threshold compared with the average intensity of the background (see Figure 1). Our study proposes an improved dynamic threshold method from discriminant analysis by using a threshold fth D m1 C k 1, where m1 and 1 are the average and variance, respectively, of the gray level of the background (denoted as class 1 in Figure 1) and k is a coefficient. This equation indicates that the threshold varies depending on Figure 1. Gray-level histogram of a light-marker image. The dotted line indicates the threshold value selected by the discriminant analysis method. Class 1 and class 2 denote background and object, respectively.

Real Time Displacement Measurement of Lattice Pattern Using High Speed Camera

The 2D or 3D displacement measurement is required in the vibration testing for the scenic technology because of the complex loading conditions. However, there is no convenient 2D displacement measurement. In this research, 2D displacement measurement with real time image processing is developed. The target of camera image is a lattice pattern drawn on the paper sheet.