In this study, mechanical properties and morphological change of polypropylene (PP) and polyamide 6 (PA6) blend prepared by reactive processing (RP) with addition of PP-grafted maleic anhydride (PP-g-MAH) as a compatibilizer was investigated. As RP methods, three different procedures for feeding PA6 and/or PP-g-MAH through side feeder were employed and two different types of PP-g-MAH were used. The PP/PA6 blends obtained by feeding PA6 and PP-g-MAH through side feeder (Tp.Sn.c) showed high mechanical properties: the elongation at break increased up to 700% and the domain size of PA6 phase decreased dramatically from 29μm to 1.6μm. Although the modulus and the elongation at break of PP/PA6 blend with PP-g-MAH increased with the amount of PP-g-MAH, they reached constant values up to 3 or 5 phr in both cases of KY-H and KY-L. Furthermore, it was found that the degree of crystallinity of PP decreased and PA6 in the PP/PA6 blend can be changed with the amount of PP-g MAH.
We report results of on-line wide-angle X-ray scattering (WAXS) measurements for melt spinning process of poly(ethylene terephthalate) (PET). In order to obtain good results, we have conducted experiments by paying attention as much as possible. First of all, a special experimental set-up has been developed by employing a purge box which contains the spin line and the X-ray detector (imaging plate), as well, with helium gas purge, in order to minimize noise level due to air scattering. Furthermore, a high-molecular weight PET sample prepared by solid-state polymerization was used in order to increase the spin line stress, which accommodates us with starting of orientation-induced crystallization at low take-up velocities. A special care to minimize the swaying of the spin line has been taken as well by employing a perforated metal guard inside the spinning tube which covers the spin line from the spinneret to the winder with insertion of the helium gas purge box in the middle. This worked well for suppression of the air turbulence. By such special experimental treatments, we have succeeded in conducting on-line two-dimensional WAXS measurements during the high speed melt spinning of PET fibers with the take-up velocity of 1600m/min. As a high brilliant X-ray source, we utilized SPring-8 (Japan Synchrotron Radiation Research Institute, Harima, Japan). The combination of above mentioned techniques enabled us to obtain crystalline reflections from oriented crystals with only 2min exposure. Nevertheless, we observed no appreciable change in crystallinity and orientation of crystallites along the spin line. It is because the control of positioning the neck point where the crystallization sets in was sensitively influenced by the ambient gas condition. Further special care to overcome this difficulty should be taken in our future study.
Composite materials of cross-linked poly(dimethylsiloxane) (PDMS) and gold nanoparticles were prepared from vinyl-terminated PDMS precursor using tetrakisdimethylsiloxysilane as cross-linker and hexachloroplatinic acid as catalyst. According to the direction of the electric field, the peak wavelength of absorption spectrum of the stretched sample shifted. This feature is, in principl, induced by the formation of linear arrangements of gold nanoparticles along the stretching direction and consequent resonance of localized surface plasmon. The shift of the peak wavelength changed reversibly with the strain ratio. The simultaneous measurement of stress and birefringence suggested the reversible change of the PDMS network even after large deformation to the non-Gaussian region. Transmission electron microscopy revealed that the gold nanoparticles form spherical primary aggregates with the diameter ranging from tens to one hundred nanometers. On the basis of the results of small angle X-ray scattering experiment, deformation of the primary gold aggregates was thought to be the origin of the linear arrangement of gold nanoparticles. These results suggest the possibility of tuning the resonance property of the surface plasmon by changing the degree of stretching of the material.
Stress-strain relations of poly(propylene oxide) (PPO) and polybutadiene (PB) elastomers are investigated by general biaxial strain testing where the strains in two orthogonal directions are varied independently. The data for general biaxial deformation provide an unambiguous basis to estimate the form of strain energy function (W) governing the stress-strain relations of elastomers. The function W (I1, I2) = C10(I1-3) + C01(I2-3) + C11(I1-3)(I2-3) + C20(I1-3)2 + C02(I2-3)2, where I1 and I2 are the first and second invariants of Green's deformation tensor and Cij (i, j = 0, 1, 2) are the numerical coefficients, satisfactorily describes the data in the whole range of biaxial strain for the two elastomers.
Effects of crosslinked molecular structures in glassy epoxy networks on the nonlinear viscoelastic behavior have been studied in terms of strain-induced structural change. We prepared four epoxy glasses with different crosslink densities from the same epoxy precursor by controlling fractions of chain-extender and crosslinker in curing agents. The epoxy glasses were subjected to uniaxial compression at a temperature 18K below the glass transition temperature of each sample. With increasing crosslink density, initial elastic moduli and yield stresses decreased, whereas flow stresses appearing after the strain softening almost unchanged, except for the most tightly crosslinked sample showing lower flow stresses. Results of density measurement and DSC showed that an increase in the crosslink density made the glassy structures more unstable. These results show that unstable glassy structures due to constraints on segmental mobility introduced by crosslinked molecular structures lessen the initial elastic modulus and the yield stress. On the other hand, the variation of crosslink density had almost no effect on the flow stresses of the glasses. This observation presumably indicates that molecular crosslinks have little effect on the strain-induced structural change. When the crosslink density comes to quite high, however, the crosslinks are likely to start affecting the flow stress, i.e. strain-induced unstable glassy structures.
The effects of notch geometry on the tensile strength of notched fiber-reinforced polymer (FRP) plates in dynamic tensile strength tests were investigated. A short-glass-fiber-reinforced polypropylene (GF/PP) plate containing 30% E-glass fiber by weight was prepared by injection molding. The notch-root radii were 0.5, 1, and 2mm, while the notch depth ranged from 2 to 5mm. Dynamic tensile strength tests were carried out at room temperature of 23°C and a tensile speed of 1000mm/s. The validity of the fracture criterion based on the concept of the severity near the notch root was previously confirmed for notched FRP plates under static loading. In other words, the maximum elastic stress at fracture is determined only by the notch-root radius. This is accomplished by the experimental data of the static tensile test at a constant cross-head speed of 0.5mm/min (= 0.008mm/s). When the time to a fracture was the same, the results of the dynamic tensile strength tests showed that the maximum elastic stress at fracture is determined by the notch-root radius but is independent of the notch depth. Thus, the concept of the severity near the notch root could be applicable to the fracture of notched FRP plates in dynamic tensile tests. On the other hand, the fracture strength of FRP is time-dependent, and this dependence is called viscoelastic behavior. Therefore, when the tensile speed is varied, the maximum elastic stress at fracture would be determined by the notch-root radius and time.
In this paper, one technique for reduction of stress concentration at stop hole edges by closing the crack surface between stop holes using ICR treatment was proposed. Tensile and bending test results showed the effectiveness of reduction of stress concentration until opening the closed crack. In tensile test, closed crack opened after nominal stress of 100MPa, while closed crack did not open under nominal stress of 200MPa in bending test. Finite element analysis results also showed that the stress at crack closed by ICR treatment under tensile load was higher than that under bending moment. By closing the crack surface in both sides, the second moment of inertia is recovered about 70% of that without crack. On the other hand, the cross-section area closed by ICR treatment becomes one third of that without crack. Therefore, the nominal stress when the closed crack open under bending moment was higher than that under tensile load. Additionally, it was found that the stresses at closed crack under tensile load and bending moment were higher than that estimated stress by structural mechanics. The reason of this is that the stresses in closed crack area and in ligament areas are not sufficiently distributed. In this research, to estimate the stresses introduced at closed crack under tensile load and bending moment, simple equations considering the bias of stress distribution were also proposed.
A type of triaxial apparatus equipped with a micro porous membrane at the pedestal, together with a pair of bender elements (BE) at both ends of the specimen has been newly developed for measuring the elastic shear modulus, G of soil specimen with the suction, s, as well as the mean net stress, pnet. A series of triaxial BE test on Toyoura sand was carried out. The effects of suction and mean net stress on the G-value are manifested in a manner that the relationship of normalized shear modulus ,G/ (e) (n.b., (e) : void ratio function) against (pnet+s) or (σv,net +s)・(σh,net +s) is unaffected by the magnitudes of suction.
Methods of evaluating the one-sided tolerance limit (A- and B- basis values) of combined sample sets are derived. The A- and B- basis values are statistically calculated numbers that respectively indicate that at least 99 and 90 percent of the population is expected to equal or exceed the statistically calculated value with a confidence of 95 percent, and they are used to determine strength tolerance limits in aerospace designs. The A- and B-basis values tend to be underestimated when the sample size is small and the conventional methods are used. Our novel methods improve the basis values by combining multiple sample sets from normally (Gaussian) distributed populations. We extended analysis of variance (ANOVA) to evaluate the A- and B- basis values by using non-central t-distribution under the condition of equality of variances. In addition, we derive coefficients for the basis values under the condition of non-equality of variances by using a Monte-Carlo method. Numerical examples show that both methods, i.e., equality and non-equality of variance cases, increase the A- and B-basis values.