The dependences of the elongation speed and temperature on the ultimate tensile properties in polyethylene solids such as the tensile strength and elongation at break for different temperatures were superimposed, by shifts along the elongation speed axis, to give a master curve as a function of the time to rupture. The shift factors obtained from the equation. On the other hand, the strain rate and temperature dependences of yield behavior followed a kinetic process proposed by Eyring. was investigated, in which a double-edge-notched specimen was used to avoid necking. The data on ultimate properties super-positioning of both the tensile strength and ultimate strain followed the form of the Williams–Landel–Ferry (WLF)equation. On the other hand, the strain rate and temperature dependences of yield behavior followed a kinetic process proposed by Eyring.

Polymeric materials under harsh conditions undergo appreciable degradation, such as color change, lowering of mechanical strength, crack formation and deterioration. It has been established that these obvious changes are initiated by chain scissions owing to chemical reactions, such as oxidation and hydrolysis depending on the polymer skeletal structure. The subsequent degradation phenomena propagate through the architecture in a wide length scale from nanometers to micrometers. Accordingly, the time scale of degradation phenomena ranges from picosecond of the molecular motions to tens of years of aging of plastic molds such as gas pipes. In the present review, fundamentals of polymer degradation are described, and related topics are presented.

In the present study, a matrix stress-strain relationship is calculated from the off-axis stress-strain relationship of CF/PP laminates by inverse analysis based on Eshelby model combined with Mori-Tanaka theory. Then, the stress-strain relationship and yield shear stress at various temperatures is estimated by viscoelastic characteristic. Next, the temperature dependence of strength and strength variation of unidirectional CF/PP are predicted from the matrix yield shear stress and Weibull distribution using the extended GLS model, which takes into account the existence of initial defects. Comparison of the predicted strength of CF/PP with the test results in previous studies shows the validity of the prediction method of the temperature dependence of strength by the extended GLS model.

Hiroshi SAITO and Satoshi OSAWA This study aimed to clarify the effect of the atmospheric plasma pressure treatment condition on the interfacial bonding of the carbon fiber (CF)/polypropylene (PP) composites. Here, both the CF and PP were modified using the atmospheric plasma pressure treatment. The PP surface was modified under the processing electric power of 20 W and processing time of 30 s. The CF surface was modified under the elevated processing electric power and time. The apparent interfacial bonding strength was evaluated by the tensile strength perpendicular to the fiber direction. As a result, the effect of the atmospheric plasma treatment employed in this study on the properties of PP was limited, whereas the surface of CF was damaged under the processing electric power of 20 W, resulting in the decrease of the apparent interfacial bonding strength of the CF/PP. In addition, the apparent interfacial bonding of the CF/PP tended to increase and the decrease with the increase of the processing time, indicating that the trade-off relation between the surface modification and damaging would decide the interfacial bonding of the Cf/PP. Finally, the possibility of the superposition formulation between the processing electric power and the processing time was discussed.

To determine the optimal molding conditions for thermal imprinting, it is necessary to understand the thermo-viscoelastic properties of polymer obtained by compression tests. This is because contact resistance acts at polymer/mold interface in compression tests, and this contact resistance may affect the thermo-viscoelastic properties. Furthermore, this contact resistance may depend on the specimen thickness. In this study, static compressive creep tests were performed on polycarbonate specimens (3 mm in diameter) with different thicknesses ranging from 0.5 to 5 mm to investigate the effect of contact resistance on thermo-viscoelastic properties. The results showed that specimen thickness had little effect on the shift factor. In contrast, the creep function was affected, and the stress relaxation time was slower with thinner specimen thickness. By clarifying the relationship between the shift amount on the logarithmic time axis of the creep function and the thickness of the specimen, it was possible to predict the creep function of a thin plate specimen from that of a bulk specimen.

For the Double Cantilever Beam (DCB) and End Notched Flexure (ENF) test, it is necessary to measure the crack length to calculate fracture toughness in Mode-I and Mode-II, respectively. In this research, we proposed a new method to measure the crack length in the DCB and ENF tests by using the acoustic emission (AE) method, which can detect the cracking behavior. The crack tip positions were identified by the AE arrival time difference with removing noises and using the precise analyze method as the Akaike Information Criterion. As a result, the position of the crack tip obtained by the arrival time difference of the AE during the DCB test showed equal or more precise value than the position obtained by microscope observation, therefore, the AE method can be used for measurement of the crack tip position. In the ENF test, AE could observe the internal cracking behavior before the fracture, however, microscope observation could not catch that cracking behavior. Furthermore, the damage mode can be specified from the frequency analysis of the AE waveform measured during the DCB and ENF test. Consequently, our proposed method for DCB and ENF tests with the AE techniques is valuable.

Along with the development of additive manufacturing, research on micro-lattice structures has been actively conducted because proper design of the unit cell structure can help achieve various mechanical properties, such as ultralightweight, high strength, and high energy absorption capacity. In aerospace, lattice structures made of polymer matrix composites have great potential, but their application requires an understanding of the properties of polymers. This study aims to clarify the strain rate dependence of the compressive properties of polymer lattice structures and the deformation modes of the struts forming their unit cells. Polymer lattice structures with different unit cell geometries were fabricated using a laser-based optical 3D printer, then compression tests were performed at different strain rates in the low strain rate range. Strain distributions on the side surfaces of the lattice structures were obtained by digital image correlation, revealing the principal deformation modes of the struts composing each structure. The relationship between the macroscopic compressive properties of the lattice structure and the principal deformation modes of the struts was confirmed. It was suggested that the strain rate dependence of the compressive properties depends on the principal deformation mode of the struts.

Damage modes in Carbon Fiber Reinforced Plastics (CFRP) includes matrix cracking, matrix/fiber interface debonding, interlaminar delamination, and fiber breakage. Acoustic Emission (AE) techniques are used to identify these damage modes; however, the transfer functions are generally not considered when identifying damage modes. In this study, we measured the frequency characteristics of AE sensors with Wavelet transform and considered the effect from the AE measured data during the tensile tests. Obtained data (with or without considering the effect of frequency characteristics) were clustered by k-means++ and corresponded to the damage mode as transverse cracking. As the results, the clustering results with considering the frequency characteristics become more accurate than the results without considering the functions. Furthermore, the Wavelet transferred data with linear or logarithmic scale were also clustered, and we finally suggested the most precise method for clustering for transverse cracking in this study.

This study evaluated the Mode I interlaminar delamination fracture toughness of s-CF/PA6 (short Carbon Fiber/Polyamide 6) laminates molded by FDM (Fused Deposition Molding) type 3D printer, using DCB (Double Cantilever Beam) tests on two different configurations. We also tested and compared dried and undried specimens. Fracture surface observations by scanning electron microscope revealed the mechanism of toughness development and factors affecting interlaminar delamination fracture toughness. The results showed that angle ply exhibit higher toughness than cross ply. The toughness of dried specimens was higher than that of the non-dried specimens. These results were highly variable. One reason for this is the difference in adhesion states and voids between layers. One possible cause of insufficient welding is a molding area temperature during molding. In addition, insufficient welding may occur if the filaments are printed when they are not sufficiently dry. As for voids, there is a possibility that they can be improved by adjusting the 3D printer.

The present paper addresses the performance of the λ type enforcement braking device (EBD) aimed to prevent traffic accidents in a road construction region. Our research concerns the EBD-mechanism installed in the road works area with the traffic-lane regulation. Here we contend that the employment of the discussed device leads to a significant increase of the drivers’, pedestrians’ and workers’ safety protection. The presented evaluation of breaking characteristics and further optimization of EBD structure reveals the effect of the tool’s performance improvement on the collision safety and reliability of the proposed solution. In this study, a particular attention is given to the role of the mast on the EBD’s operation, while our previous papers ^{6, 7)} elaborated the influence of the arm-shape, arm-length and the connecting height of the arm for the mast on braking properties. A simple model collision tests and theoretical calculations based on the conservation law of energy and momentum were employed in our study. The obtained results enabled us to disregard that possible effect of the arm shape and conclude that the use of the long arm and higher connecting height are effective for the shortening of the braking distance, which constitutes the significant extension of our previous studies. The collision tests carried out with three different velocities and the EBD model with extended arm lengths was employed. We arrived to a proper structure optimization by careful examinations of the influence of the mast angle in the λ-type long arm EBD on the braking characteristics.

Cavitation damage on the inner surface of the mercury target for the spallation neutron source occurs by proton bombarding in mercury. The prediction method of the cavitation damage using Monte Carlo simulations was suggested taking variability of the bubble core position and impact pressure distribution into account. The impact pressure distribution was estimated using the inverse analysis with Bayesian optimization was conducted with comparison between cavitation damage distribution obtained from experiment and the cumulative plastic strain distribution obtained from simulation. The average value and spread of maximum impact pressure estimated assuming the Gaussian distribution were 3.1GPa and 1.2μm, respectively. Simulation results reproduced experimental results and it can be said that this evaluation method is useful.