In the present study, we investigated the effects of mixing time on the dispersion and degradation behaviors and mechanical properties of high density polyethylene (HDPE) / ultra high molecular weight polyethylene (UHMWPE) blends. Optical microscopy revealed that the dispersion of UHMWPE in HDPE was improved by increasing mixing time, and the UHMWPE was almost homogeneously dispersed with HDPE at the mixing time longer than 250 s. Thermal analysis revealed that molecular dissolution of UHMWPE into HDPE occurred even in the early stage of mixing below 250 s. On the other hand, gel permeation chromatography and infrared spectroscopy suggested that as the mixing time increased, the thermal decomposition producing trans-vinylene group and the oxidation reaction producing carbonyl group proceeded simultaneously, resulting in the progress of chain scission. The chain scission was noticeable above 250 s. In the tensile test, the influence of dispersibility on the tensile properties became dominant at the initial stage of mixing, and both the strength and strain at break were improved by increasing the mixing time up to 250 s, although these properties decreased for the mixing time longer than 250 s. In addition, from the discussion of mixing parameter, it is suggested that the improvement in dispersion and the progress of degradation accompanying the increase in mixing time occurred due to an increase in total rotation number and thermal history. Therefore, it is important to select an appropriate mixing time to improve the dispersion of UHMWPE without degradation.

Hot-drawing of polystyrene (PS) films improved the fracture nature from brittle to ductile due to the chain orientation. However, the brittle-to-ductile transition mechanism has not been clearly understood. This study investigated the ductile deformation mechanism of the oriented PS films by using birefringence and polarized FT-IR measurements during tensile tests. Comparison of tensile properties for the oriented PS films with various drawing conditions revealed that the brittle-to-ductile transition occurred at around 0.05 of the degree of chain orientation. The birefringence data, which were analyzed with a modified stress-optical rule (MSOR), suggested the chain orientation beyond the yield point during the ductile deformation. The polarized FT-IR data represented that, before yield point, the main chain of PS became oriented to the tensile direction, and, after the yield point, a phenyl ring as a side-group of PS aligned. The difference in the orientation behaviors of main-chain and side-group dissipated the stress concentration in the oriented PS films, and generated the shear-yielding deformation, resulting in the ductile deformation.

We found that the addition of 1-octadecanol (OD) and octadecane (C18) to high-density polyethylene (HDPE) can modify the crystalline and amorphous phases of HDPE selectively. According to the dynamic mechanical analysis, OD was co-crystallized with the crystal phase of HDPE. It is interesting that OD promoted α-relaxation of HDPE at the higher temperatures than the melting point of OD. On the other hand, in HDPE blended with C18, it was suggested that C18 exists in the amorphous layer of HDPE and activates the relaxation of the amorphous chains of HDPE. Such selective modification of the supermolecular structure and mechanical property by the addition of olefin-like low-molecular-weight compounds becomes the fundamental knowledge of the roles of lubricants in the molding process of olefinic materials.

Tensile fracture properties of glassy poly(methyl methacrylate) (PMMA) and poly(vinyl chloride) (PVC) were observed by constant-speed stretching at a wide range of stretching rates, including very low stretching rates. When the stretching rate was decreased to very low value, despite the decrease in stress with decreasing stretching rate, both PMMA and PVC specimens no longer showed ductile deformation accompanied by necking and fractured at low strains around which the yield point appeared. This abnormal "embrittlement" observed at very low strain rates was not due to simple physical aging during stretching. Furthermore, fracture near the yield point as observed at very low strain rates was frequently observed even in the strain rate range where ductile deformation was also achieved. The tendency for fracture to occur around the yield point, which was commonly observed in both PMMA and PVC, is likely a general nature of glassy polymers. Since the yield point is a manifestation of the flow in glassy polymers due to nonlinear relaxation, the nonlinear relaxation mechanism which enables glassy polymers to deform largely probably contains a mechanism that generates nuclei for fracture.

We attempted to reproduce foamed or porous materials with inhomogeneity similar to that of functionally graded materials (FGMs) using a 3D printer, and to evaluate their mechanical properties. Using a lattice model, we evaluated the compressive properties by changing the thickness. As a result, it was found that the lattice model can sufficiently express the mechanical properties of foamed materials. Young’s modulus of the “Square model”, in which the cells are square, decreased sharply as the thickness increased, reaching about half the value of 1 layer. On the other hand, Young's modulus of the Wide model material, in which the cells are horizontally elongated, did not decrease. Furthermore, a model was created to express the internal irregularity of the holes (lattice) such as FGM, and a comparison was attempted using the same mechanical test. It was found that the Young's modulus depended on the thickness of the “Square model” layer. Furthermore, when compared to an alternating laminate model sample with an increased number of interfaces to evaluate the effect of the uneven interface of the bubbles, it was found that although the Young's modulus increased as the thickness of “Square model” layer decreased, the slope decreased slightly in the region of increased density where there was a rapid increase in stress because of the interface. This was found to be due to the presence of large voids in the uneven lattice distribution at the interface.

Particle dispersion strengthening Δσ is theoretically expressed by the following equation as functions of Taylor factor M, line tension factor of dislocation β, shear modulus G, Burgers vector b, bowing angle θ and the mean free path λ. Δσ= 2MβGb sin θ / λ The β–value is given by the following equation as functions of the radius of elastic stress field of dislocation r, the radius of dislocation core r₀ and the dislocation constant k (= 0.71-1 for bcc iron). β=ln(r/r₀)/4πk During bowing of a pinned dispersion, the r–value becomes smaller with increasing θ due to the interaction between pinned dislocations. In this paper, the r-value is expressed by the following equation as functions of θ, the initial value of elastic stress field r^* and the mean cut-off diameter of particles on a slip plane d^*. r = d^*+ (r^*- d^*) cos θ (r^*> d^*) The r^*–value depends on dislocation density ρ; r^*=(4/π)^1/2/√ρ. Theoretical calculations proved that the maximum value of　Δσ is obtained at θ≒70˚ where cos θ ≒1/3 and sin θ≒0.94. Therefore,　Δσ and β can be rewritten as follows under the condition θ≒70˚. Δσ= 1.88MβGb/λ β= ln{(r^*+2d^*)/3/r₀}/4πk Experimental results agreed well with the calculated values for Δσ, when the r₀–value was put at 2b. It was also confirmed that Δσ is over-estimated by Orowan model and under-estimated by Ashby-Orowan model, because the values of sin θ and r are put as sin θ =1 and r= r^* in Orowan model and also sin θ =0.8 and r= d^* in Ashby-Orowan model. It is concluded that particle dispersion strengthening can be accurately estimated by taking the change of r–value during dislocation bowing into consideration.

The authors previously evaluated the groundwater recharge functions of porous pavement using a tank model (JSMS, JP, Vol. 59, No. 11, pp. 861–868), and used Powell's conjugate direction method (Powell's method), which is said to be prone to local suboptimal solutions, as a method for identifying the tank model parameters. Doubts have been raised about the results of identifying the tank model parameters and the evaluation of the groundwater recharge functions of the porous pavement based on this tank model constant identification. In this paper, the tank model parameters were re-identified using the Genetic Algorithm Random Search method (GA method), and the validity of the identification results (tank model parameters) using the Powell's method and the validity of the groundwater recharge functions evaluation of the porous pavement based on these identification results were verified. As a result, it was confirmed that there was no need to revise the evaluation of the groundwater recharge functions (rainwater infiltration function and rainwater storage function) of the porous pavement, even though the identification result by the Powell's method may have resulted in a localized suboptimal solution.

Carbon fiber reinforced plastic (CFRP), which has the characteristics of lightweight, high specific strength and high specific stiffness, is applied to various structures such as aircraft and automobile. In particular, strength evaluation of woven CFRP used for structural components is still challenging. Currently, the strength evaluation using homogenization method is widely studied. However, for homogenization method, some precise dimensional measurements are needed during the modelling process, so a simpler method is desirable. In addition, strength evaluation using actual product of CFRP is the mainstream. There is also the issue of cost. Therefore, in this study, modeling and analysis using orthogonal anisotropy are conducted on twill weave CFRP specimen and structural sample by the general-purpose structural analysis software NASTRAN. Tensile and bending tests are conducted on the specimen, and loading tests using a fixture are conducted on the structural sample for comparison with the analysis. Strength evaluation is also conducted using the knee-point, which initial fracture begins to occur. As a result, the modulus of elasticity obtained from the analytical tensile test is in good qualitative agreement with the experimental value. The strength evaluation using 22.5° pitch stress from the analysis and the knee-point shows availability to predict the initial fracture behavior of the specimen and structural sample.

The effect of Al/O ratio on the development of acicular ferrite microstructure development and the toughness in weld material containing low oxygen has been studied. Three base steel plates with different aluminum contents were prepared by vacuum melting method. The addition of 0~10% CO₂ into Ar shielding gas and the Ar gas double shield technique during arc welding of base plates formed various oxygen levels from 16 to 307 ppm. The samples with different Al/O ratio were thus obtained. The optical microstructures showed that coarse grain boundary ferrite was formed along prior austenite grain boundaries in all samples. When Al/O ratio was from 0.39 to 1.13, some of the inclusions appeared to be acted as nucleation site for acicular ferrite and weld metal with acicular ferrite exhibited good toughness (vT_rs<243 K). In this case, SEM-EDX chemical composition analysis of these inclusions indicated that inclusions were rich in oxygen, manganese and sulfer with a small amount of aluminum and silicon. It was assumed that the MnS precipitated on Al₂O₃-MnO-SiO₂ inclusion and become effective nuclei of acicular ferrite.

The stress relaxation mechanism of hardwood (Magnolia obovata Thunb.) was analyzed using the Kohlrausch–Williams–Watts (KWW) function and a Cole–Cole plot to elucidate the effects of moisture content and static displacement. The relationship between relaxation modulus of elasticity and moisture content was examined in a stress relaxation test, which was performed for one week at a stress ratio of 35%. Two linear regions appeared in the double logarithmic relaxation modulus plot against logarithmic time. The stretching parameters and specific relaxation times were obtained by fitting the KWW function to the relaxation data. The specific relaxation time was the shortest at a moisture content of 6–8%. The effect of static displacement on stress relaxation was examined using dynamic mechanical analysis, which was performed for 1 h at stress ratios of 11% and 33%. At a stress ratio of 11%, the relaxation modulus ratio to logarithmic time changed after 0.1 h. Both the former and latter relaxation processes can be fitted to Cole–Cole circles. At a stress ratio of approximately 33%, the change in storage modulus ratio over logarithmic time changed in the later period, whereas it monotonously increased at a stress ratio of 11%. Only the former relaxation data could be fitted into the Cole–Cole circle; however, the latter relaxation process could not be fitted. A stress ratio of 35%, which was applied in the stress relaxation test, may be out of linear viscoelasticity.