The complex shear modulus, G*=G'+iG", of glassy poly (methyl methacrylate) (PMMA) has been measured during creep elongation and constant speed elongation where plastic flow is observed. In creep experiments, the stress level is chosen so that it agrees with that of the steady plastic flow observed by constant speed experiments. In the state of steady plastic flow, value of G* obtained by the creep elongation and the constant speed elongation agrees with each other. This agreement leads to the conclusion that molecular structures developed in steadily flowing glass do not depend on the deformation history. At the lowest strain rate or the lowest creep stress, G' gradually increases with elongation and exceeded the value for undeformed sample. This result shows that the polymer glass can be hardened during post-yield plastic flow.
Structural, thermal and mechanical properties of the blend of poly (ethylene naphtalate) [PEN] and poly (ethylene terephtalate) [PET] were investigated using 1H nuclear magnetic resonance (NMR), differential scanning calorimetry (DSC) and tensile testing machine. The PEN/PET blends were obtained by melt blending (mixing for 2min at 310°C and quenching with ice water). Structural formation in unoriented amorphous (50/50) PEN/PET blend films during drawing at 85°C, 100°C and 130°C was studied by In Situ X-ray measurements, and the results were discussed by comparing with those of PEN and PET themselves. PEN in blend films was partially miscible with PET partly due to the formation of copolymers by transesterification during blending. This miscibility is estimated from the findings, that is, the blend film exhibited a single glass transition temperature (Tg) and the Tg increased linearly with increasing PEN content. The heat of crystallization by cold-crystallization and the heat of fusion by melting were the lowest value in (50/50) PEN/PET blend film among the blends. The (50/50) blend showed the highest degree of transesterification (ca. 6%). The tensile stress at the yield point and the tensile modulus of PEN/PET blend films increased with increasing PEN content. Though PET film could not be drawn above 100°C at a lower drawing rate, PEN/PET blend films was drawable. In (50/50) PEN/PET blend film crystallization proceeded gradually with the drawing at 100°C which was under Tg (117°C) of PEN. The crystallization was evidenced by the α-form crystalline reflection of PEN which was detected by In Situ X-ray measurements.
This study is concerned with the analysis of relationship between the interfacial energy of polymer and the micro voids that are formed by stretching the composite polymer sheet having incompatible particles in the matrix. Now we tried to simulate the void formation, considering the interfacial delamination between Poly (ethylene terephthalate) (PET) and dispersed incompatible polymers, and to compare the numerical results by finite element method (FEM) with experimental one. By introducing the method in which the displacement constraints were removed at a critical value of stress near interface region, it was simulated that the void became larger with decreasing critical stress of interfacial delamination. The results are summarized as follows; (1) Enlarging the aspect ratio of void coincided with increasing the interfacial energy between PET and incompatible polymers experimentally. (2) Decreasing the critical stress of interfacial delamination coincided with increasing the interfacial energy in FEM. (3) Dependence of actual load-displacement behavior on the interfacial energy difference was qualitatively demonstrated by changing the critical stress of interfacial delamination in FEM.
Optimum strength of polyvinyl-chloride (PVC) sheet thermoformed by uniaxial stretching was studied by mechanical test, thermally stimulated deformation recovery and structural observation using polarized light. In spite of tensile stress evolution during rapid cooling of thermoformed sheets, their deformation recovery behavior at reheating showed no evidence of storage of strain energy probably lessening static strength of thermoformed sheets. Sheets thermoformed at 100°C had quite high ductility presumably due to the peculiar crystalline structure still left in PVC after thermoforming. Sheets thermoformed at 130°C showed much less ductility and was found to have no crystalline structure.
Vinylester resin having hydroxymethyl group (VEDA) was synthesized by the reaction of epoxy resin having hydroxymethyl group with acrylic acid. Effect of hydroxymethyl group on photopolymerization and after thermal curing of VEDA were studied. α-isobutyl ketone was used as phtoinitiator. Glass transition temperature (Tg) and storage modulus (E') of cured resin were increased after thermal cure. This result is considered to be due to the increase of crosslinking density of the cured resin by condensation reaction of hydroxymethyl group at higher temperature. The cured films of VEDA on glass, steel and poly (methyl methacrylate) plates were found to exhibit good adhesion to those substrates, resulting in introducing hydroxymethyl group.
Effective flow conditions for making fine structure of a model immiscible polymer blend, i.e., equiviscous immiscible polymer blend was examined by using interrupted flow and combination of step increase and decrease of shear rate. Overshoot peak of first normal stress difference, which corresponds to the existence of most elongated domains, was used as an indicator for changing shear rate. That is, shear rate was decreased (including zero shear rate) just after the overshoot peak of first normal stress difference appeared. Time needed to rupture the elongated domains and also droplet size and distributions thus obtained were compared to the data evaluated by using shear flow with step increase of shear rate. The time needed to rupture the domain with interrupted flow and combination of step increase and decrease of shear rate was shorten to be one fifth and the size of domains and their distribution were almost the same compared to corresponding data for flow with step increase of shear rate. It was concluded that decreasing of shear rate at the most elongated state of domain structure is an effective procedure to make fine structure of immiscible polymer blends.
Viscoelasticity and morphology of polycarbonates being multi block copolymers composed of bisphenol A polycarbonate, PC, and polydimethylsiloxane, PDMS, were investigated as a substitute for soft poly (vinyl chloride). Mechanical properties of the soft polycarbonates were found to be well stable for temperature compared with soft poly (vinyl chloride). Modulus of the polycarbonates could be controlled by varying PDMS content. Small angle X-ray scattering experiment and electron microscope revealed that the sort polycarbonates formed microdomain structures.
Dynamic birefringence and dynamic viscoelasticity of bisphenol A polycarbonate were simultaneously measured over a wide range of temperature from -150 to 180°C. Large γ dispersion observed for the complex Young's modulus was found to be inactive for the complex strain-optical coefficients, which is the ratio of birefringence to the strain. The present result indicates that γ dispersion cannot be attributed to the reorientation of any atomic groups, but to the relaxation of internal strain by translational motions. Dynamic birefringence was anticipated to be a new experimental method for the subrelaxation of glassy polymers.
In order to improve the wear properties of artificial joints, a slightly cross-linked ultra high molecular weight polyethylene (UHMWPE) was compressed at molten state and crystallized by cooling to room temperature. The molecular chain of the UHMWPE was orientated to the direction of deformation. Density and melting point of the mold article were increased in accordance with compression ratio. The αc peak of loss modulus was shifted to higher temperature compared with the non-compressed sample. And it was also revealed that the weight loss of the compressed UHMWPE was remarkably less than that of a non-compressed sample from the result of the pin-on-disc wear test.
One of the few methods available for creating fine grains is protium treatment, which easily produces a fine-grain size of 1 to 3μm in α+β Ti-6Al-4V alloys. However the minimum grain size obtainable by this treatment is not yet known. The purpose of present investigation is to obtain submicron grain size through improvement of the protium treatment conditions by varing the protium absorption content and lowering the protium desorption temperature. The experimental results obtained are as follows. The grain size of titanium alloy becomes ultra-fine grain (grain size: 0.3-0.5μm) through a process in which 0.5mass% of protium is absorbed and the protium desorption temperature is lowered from 973K to 873K. The β phase percentage in the α phase matrix tends to increase as a result of the protium treatment. The yield strength of ultrafine grained materials is improved by protium treatment in accordance with the Hall-Petch's law. Such materials show high elongation for high strength.
Postbuckling behaviors and load-carrying capacity of thin laminated curved plates under uniaxial compression have been discussed by many researchers. However, little research has been performed on the secondary buckling phenomenon for thin laminated curved plate which occurs with further increase of load. In this paper, CFRP laminated curved plates under uniaxial compression which are simply supported along four edges is considered as an example. By a proposed method based on the second variation of total potential energy to judge the stability of postbuckling equilibrium state, the inevitability of secondary buckling is proven analytically, and the effects of various factors, such as dimension of curved plate, assumed virtual displacement pattern, postbukling deflection pattern and average axial shortening, on the secondary buckling values are clarified.
One of the typical leaves with wide leaf shape is a leaf of butterbur (Petasites japonicus). To investigate the mechanical contribution of veins in wide leaves, the length and diameter of veins, the angle between veins and the thickness of lamina were measured by using optical devices. It was found that butterbur leaves have veins with an ellipse cross-section instead of a circle cross-section and analogous geometry irrespective of their size. To obtain the mechanical properties of veins and lamina, static tensile tests were carried out. Young's modulus of veins was about 60MPa, which was about eleven times greater than that of lamina. By using the geometrical data and mechanical properties of veins and a lamina, a number of leaf models were made for FEM analysis. It was found that the capability for supporting load of the leaf model with the most similar venation pattern to a real butterbur leaf was greater than that of other models with simplified patterns, even the total mass of a leaf was maintained to be constant.
An impact fracture test method has been developed to measure fracture toughness under mixed mode I/II loading using a center-notched disk specimen. The test is executed in such a way that diametrical impact load are applied to the specimen, which is set with the crack inclining toward the direction of loading at a definite angle. Time variation of the energy release rate is accurately evaluated by the convolution integral of the dynamic response function for the cracked disk. Dynamic and quasi-static tests were performed and fracture toughness for brittle materials was measured. The results indicated that the dynamic fracture toughness for the present brittle materials was not lower than the static one under pure mode I/II and mixed-mode loading. Comparing the results with some representative criteria, it was found that these criteria were not suited to interpret the fracture under mixed-mode loading in the present brittle materials.
The influence of Laves phase precipitation on a fracture process and creep rupture strength of W alloyed 9%Cr ferritic steel was investigated. Additionally, the change in strengthening factors during creep was examined by Vickers hardness and nano-indentation tests in order to clarify the material degradation mechanism. The main results obtained are as follows. (1) Laves phase is the preferred site for cavity to initiate. This cavity initiation at Laves phase and subsequent small crack formation cause the fracture of long-termed creep specimen. (2) The creep rupture strength at 600°C decreases with pre-aging at 650°C. Laves phase is closely associated with the decrease in the rupture strength, because the rupture time decrease as the amount of Laves phase increases. (3) Nano-indentation testing technique revealed that the matrix softening during thermal aging was caused by the decrease in the amount of W and Mo in solid solution due to Laves phase precipitation. This decrease in solidsolution strengthening due to Laves phase precipitation causes the above-mentioned decrease in the rupture strength. (4) The annihilation of dislocation is the predominant factor of the matrix softening in the transient creep region, while the matrix hardness decreases as the amount of W and Mo in solid solution decreases with Laves phase precipitation after the transient region.
Mixed gas corrosion testing is used to simulate corrosion damage of electrical contacts. As a result of the demand for lower cost while maintaining high reliability, the testing conditions should be optimized to avoid overquality. Accordingly, we have determined the optimum exposure time in testing by comparing the corrosion damage on contacts exposed to mixed gas with that of field exposure. The maximum corrosion damage on the contacts was evaluated by extreme-value statistics. The optimum exposure time in testing is determined to be 10 hours for 10 years field exposure. The gas and moisture penetrate into plastic housing in which the contacts are placed. And the diffusion analysis of moisture in the plastic housing shows that the testing must be performed without the housing. Furthermore, we have designed a method for assessing the corrosion severity of the field environment. The method has been applied at two different fields.