The stress risen in solidification process of epoxy resin is investigated experimentally and analytically. The process is divided into curing process and thermal process after curing. In the first process the resin is changed to solid state from liquid state and internal stress is risen by volumetric change in the phase transition as well as change of mechanical properties. In the sccond process solidified resin suffers heat treatment and residual stress remains due to thermal shrinkage and viscoelastic effect. The volumetric change and the elastic constant during phase transition process are experimentally measured by dilatometer and torsional blade analysis and the results are formulated by using viscoelastic models. The internal stress and the deformed state of the cured resin in hollow of plate are analyzed on the basis of the formulated results. The analyzed deformed state coincides approximately with the experimental state. The thermal deformation and the viscoelastic properties of solidified resin under various temperature conditions are experimentally investigated by thermal tests and creep tests. The formulated results are applied for the analysis of residual stress of resin block contained metal plate under various thermal histories. The analyzed results fit for the experimental values qualitatevely.

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Epoxy resins usually shrink during the curing and cooling processes. When the shrinkage in constrained by some reason, such as an adhesion with other materials, the constrained shrinkage is converted to residual stress. The magnitude of the residual stress depends on both the elastic modulus and the thermal and curing shrinkage in the glassy region of the cured resins. The effect on the chemical structure on the residual stress in epoxy networks was discussed. Namely, some epoxy resins which have lower glassy modulus and lower thermal expansion coefficient were introduced.

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The present paper describes the residual stress and deformation due to thermoviscoelastic behavior of materials and non-uniformity temperature in the cooling process during its molding. The viscoelastic model including an element for thermal expansion is proposed in order to express the viscoelastic behavior of material with temperature change. Using this model, a qualitative prediction of the residual stress and deformation of cooled viscoelastic material is done. Using the linear-viscoelastic theory, fundamental equations for the residual stress and deformation of a viscoelastic strip, where an unsteady and non-uniformity temperature distribution is assumed in the direction of thickness, are shown. The theoretical values of residual stress and deformation of the strip which is made by epoxy resin are calculated under various temperature conditions. Finally, epoxy resin strips are actually cooled, and the residual stress and deformation of strips is measured. The experimental results are compared with the theoretical ones and the relationship between the residual stress or deformation and thermoviscoelastic behavior are quantitatively explained.

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The residual stresses in a molded product can be mainly classified into two types according to the mechanism of their generation. One is what is called flow induced residual stress and the other is called thermal stress. In the present paper, the mechanism on the generation of these residual stresses and the method for predicting them in our PDC CAE system for the injection molding are explained. The flow induced residual stress is due to freezing of flow stress in its relaxation process and is concerned with molecular behavior such as an orientation. In our system the Leonov model representing viscoelastic behavior of a molten polymer is used for simulating the relaxation and freezing of flow stress. The thermal stress is caused by non-uniformity temperature distribution in a molding product. In our system, this thermal stress and creep strain and shrinkage/warpage deformation are calculated using the thermodynamic equations of equilibrium under the load of the thermal strain which arises in proportion as temperature lowers in the cooling process. By the simulation results, the flow induced residual stress is smaller than the thermal stress. The flow induced stress, however, is not able to be neglected, because it becomes the cause of anisotropy of mechanical properties and optical properties of a molded product.

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Recently, a series of injection molding process can be simulated with advanced computer. Injection molding simulation makes it possible to predict defects of products and to optimize various conditions and a shape of mold before making trial parts. Injection molding simulation consists of 3-stages, mold cooling, filling and warping analysis. Though fairly accurate results can get with mold cooling and filling analysis, warping analysis doesn't have enough precision to evaluate results quantitively. To improve the precision of warping analysis, thermo-viscoelastic model that considers distribution of material properties, values through the thickness was proposed. As a result, the residual stress calculated with this model showed better agreement to the measured residual stress.

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Optical methods for measuring stress and strain can perform whole field analysis, unlike point-wise methods such as strain gages. However, it is time-consuming to analyze the whole field data because of a huge amount of data. Therefore image processing is widely used recently to save labor. In the early stage of the image processing for fringe pattern analysis, the method detecting the fringe center lines was used. It is, however, difficult for the method to obtain accurate results and to perform automated analysis. After the stage, some new methods using the characteristics of image processing have been developed. Especially, phase analysis methods using all data of an image are widely used because of the ability of highly accurate and fully automated analysis. This paper introduces the Fourier transform moire and grid method (FTMGM) and the phase shifting method using Fourier transform (PSM/FT). The former uses a 2-D image and the latter does a 3-D image. The principle for measuring accurate stress and strain distribution, and some examples applied to composite materials, honeycomb materials, rubber tubes, rubber plates, glass plates and epoxy plates are shown.

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A simplified optical method based on photoviscoelasticity is proposed for measuring the transient stress and strain generated in a two-dimensional photoviscoelastic body. First, the fundamental equation for the simplified optical method is derived from the relationships between the stress, strain and birefringence in the two-dimensional photoviscoelastic body based on the linear photoviscoelastic theory. As examples of the application, transient principal strain and its direction in a square plate with a circular hole of polyurethane resin produced by non-proportional loading under a constant temperature are measured by using the simplified optical method. Next, residual stress in a beam of epoxy resin by rapid cooling is also measured by this method.

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Researches on the residual birefringence of injection molded substrates for optical disc are reviewed. Molding factors on the occurrence of the birefringence and the influence of the molding conditions on the three dimensional birefringences of polycarbonate substrates are discussed. Relationships between the birefringence (n₁-n₂) in the plane and (n₁-n₃) in the cross section and melt temperature, mold temperature, injection rate and cooling time, etc. are clarified quantitatively.

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This paper describes the generation mechanism of residual stress in thermoplastic resins under injection molding. First, the generation mechanism is qualitatively explained by using a thermoviscoelastic model. Second, Polypropylene (PP) resin plates are molded under various dwelling conditions, and these thermoviscoelatic properties which have a direct effect on their residual stresses are carefully measured. Finally, the residual stresses in PP resin plates are measured by a layer removal method. By comparing these residual stresses under various dwelling conditions with the numerical ones by the thermoviscoelastic model the thermoviscoelastic properties mentioned above, the generation mechanism of residual stress in thermoplastic resins under injection molding is discussed quantitatively.

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Copper clad laminates, widely used as raw materials of printed circuit boards for TVs and VTRs, are required the low warp during the production process of circuit boards due to automated process. A numerical simulation method of the warp for the copper clad laminates are explained during the heating and cooling process. A thermoviscoelastic model with either zero or infinite viscosity is proposed to simulate the bechavior of the resin material and the laminated beam theory is applied to express the warp of the laminates. The theoretical results of the warp show almost good agreement with the experimental results during the soldering process, where the warp becomes largest among the whole production processes. By analyzing the calculated results, the dominant factors of the warp are clarified and the effects of the thermoviscoelastic becavior are quantitatively determined.

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Recently, polymers widely used as machine parts and structural members, and their conditions used become severe. Therefore understand of fracture phenomena characteristic to polymers is important for making better reliability of machines and structures, and preventing any accidents caused by their fracture. Many theoretical and experimental studies have stated that local strains near the notch-root and the crack-tip strongly affect initiation and propagation of fatigue cracks, respectively. However in spite of their studies, fatigue crack initiation and propagation at the notch-root have been recognized to be very complicated. The difficulties and limitation in cvaluating the small crack propagation behaviors with continuum analysis of fracture mechanics parameter of ΔK are also pointed out. In this paper, local strain at the notch-root during process of crack initiation and local strain at the crack-tip during process of crack propagation in polymer are measured in real time under low cycle fatigue tests by the fine grid method, the relations between local strain and crack initiation and crack propagation are investigated, and a more accurate approach for fatigue life estimation is discussed. In addition, a real-time measurement system of local strain at the fatigue crack tip using image processing is described.

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It is a well known fact that cold worked thermoplastics have a tendency to change their shapes at elevated temperatures. In the case of material fabricated in the molten state, a similar deforming behaviour is found that discs sliced from the extruded round bar deform into a cone shape and also calendered sheets shrink in the longitudinal direction without any application of external force. The deformation which is called as recovery - induced thermal deformation here and is a recovery of strain memorized in thermoplastics at the time of material processing, increases with the increase of temperature and with the time duration at the subsequent reheating. Two new forming process based upon this phenomena are proposed in this paper. The above deformed cone is bulged into a complicated shaped cup with the assistance of a low comperessed air blow. A sheet is bent to various shapes with the aid of line heating. Dimensional stability of the formed parts produced by these processes is confirmed to be acceptable.

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The alumina powder added with sodium stearate as a lubricant was compressed by Cyclic-CIP and the change in relative density of the alumina compacts was investigated, Sedimentation experiments indicated that the addition of sodium stearate (≧2wt%) resulted in uniform adsorption of sodium stearate on surface of the alumina powder. By compressing the alumina powder added with sodium stearate repeatedly (Cyclic-CIP), the density of the alumina compacts reached to 63% or larger when the applied pressure was as low as 100MPa. This density coincided with the density of the alumina compacts which was compressed by ordinary CIP at 500MPa. By adding sodium stearate to the alumina powder a high density compact was obtained for a few cycles. It meant that the addition of lubricant to the powder was effective for Cyclic CIP as well as ordinary CIP. From pore size distributions of the compacts, it was suggested that the rearrangement of primary particles was promoted by compressing powder repeatedly.

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This study observes melting states of polymer in the heat barrel of the injection molding machine through a transparent window and analyzes the obtained images by a technique of the image processing. By examining several feature parameters of the images, the factors for representing melting state of polymer are considered in order to know the relation between the moloding conditions and melting process of the polymer.

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In recent paper authors proposed “void dispersion method” to control more widely thermal expansion coefficients (CTEs) of composites materials. This method introduces microvoids in the matrix of composites and utilizes an interaction effect between the reinforcement and the microvoids which yields reduction of themal expansion coefficients. However the introduction of microvoids gives rise to various drawbacks, such as weakening interfaces and becoming sensitive to humidity in the air. Thus in this paper, effect of humidity in the air on porous composites has been examined. A skeletonized 3D composites were used as a typical porous composite. It was shown that the introduction of voids in the matrix leaded to wider specific surface and resulted in higher diffusion of water in the matrix. Main phenomena manifesting the water absorption effect were shown to be higher CTE in low temperature region and low glass transition temperature. As a measure to prevent the water absorption, galss coating on the surface of the porous composite was finally examined and it is shown to be effective under the low humidity environment.

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Creep behaviors of Bulk molding compound (BMC) has been researched using a creep bending instrument and in an oven. Because the creep compliance of BMC obtained by experiments showed wide dispersion even though on the same temperature, properties of creep compliance have been studied on statistical analysis. It was found that the data showed the normal distribution. From this fact, a creep compliance curve which was drawn from the median of data on each measuring temperatures and times, were used to make a master curve of creep compliance. It was concluded that visco-elastic behavior of BMC was an Arrhenius type since a master curve was given and the relationship between shift factors and tested temperature showed two straight lines on Arrhenius plotting paper.

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Multi-layered metals are expected to be useful to prevent hydrogen embrittlement. Hydrogen permeation and embrittlement of a multi-layered dual phase stainless steel (DPS18) that is made of ferritic stainless steel (SUS444) and austenitic stainless steel (SUS316L) have been investigated. Hydrogen diffuses in a ferritic phase, where hydrogen diffusivity is large, around a austenitic phase in DPS18. Hydrogen embrittlement is occurred in DPS18 rather than SUS316L. As a result of discussion, necessary conditions to design a composite material that has high strength for hydrogen embrittlement were obtained as follows : (a) hydrogen solubilities are different between component materials ; (b) one phase has high resistance for a crack propagation under hydrogen environment ; (c) an aspect ratio is much larger than a ratio between hydrogen diffusivities in component materials.

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