The SMC has been developed as a material for the mass production system using press moulding, but some problems arise due to its heterogeneity caused by fibre orientation. The faults observed in the products, such as the appearance of brittle regions in the resin-rich parts or at the weld lines and the surface sink produced at the convex parts, may be regarded as the moulding problems. The purpose of this study was to prevent the above troubles and to construct the CAD system for SMC press moulding process. The case of the symmetrical configuration with one rib part in full charge was treated in the previous paper. In this paper, the effect of asymmetrical configuration with one or two rib parts was investigated to solve the above problems associated with the flow state through the evaluation of flexural strength determined after observation of the material flow state. The analytical method was established by using a linear incremental finite element method and considering the fibre orientation and heterogenity. It was found that the tendency to go around the rib corner increased with increasing the degree of asymmetry, resulting in the resin rich region at the rib corner and no surface sink. Although the weld line at the opposite side of the rib remained, the reduction of flexural strength became less due to curving of the weld line. The stress analysis after the observation of the flow state supports the above tendency well.
In this paper, discussion is focused on the mechanical modelling of fiber bridging which affects the resistance of opening-mode crack extension parallel to fibers in unidirectional fiber-reinforced composites. Firstly, the formation process of a bridging fiber is considered and a model of this single fiber bridging is made to characterize precisely the behavior of bridging fibers under crack opening. By using this model, the forces acting on crack surfaces through a bridging fiber are estimated and the relationship between crack opening displacement and equivalent cohesive stress due to large number of bridging fibers is obtained. An attempt is made to derive equations which describe the crack extension with the cohesive stress acting on crack surfaces. By solving numerically these equations, the crack extension behavior is simulated. The simulated result shows agreement with the experimental result of a unidirectional glass fiber-reinforced epoxy composite. It is concluded that the fiber bridging discussed here accounts for the opening-mode crack extension behavior parallel to fibers in the unidirectional fiber-reinforced composites.
Previously it has been shown that AE ring-down counts of glass-mat FRP in low-cycle fatigue loading become steady at the comparatively initial stage and their amounts are approximately linear with the fatigue life on a log-log diagram. In the present study, it was found that AE ring-down counts at each cycle during low-cycle fatigue could be evaluated from the strain response at the corresponding cycle by using the relation between strain and AE counts in static tests. It was also shown that the strain at each cycle during fatigue could be represented by the secant modulus and the modulus under unloading, and that both moduli at each cycle could be calculated from the applied stress and the secant modulus at the first cycle of the fatigue tests. Based on these concepts and then using the above-mentioned relation between AE counts and fatigue life, the prediction of low-cycle fatigue failure was made by a simulation method. A rather good agreement between the simulated and tested results was obtained.
The fracture mechanisms of three kinds of model composities, such as the unidirectional glass fiber, the 0°/90° glass fiber and the plain weave cloth reinforced composites, were studied by using the acoustic emission (AE) method in tension, and by observation with optical and electron microscopes. It was found that the fracture mechanisms were different from each other because of their different types of reinforcement, and the AE event rate and the AE total energy were the effective parameters to make them clear. The fracture mechanisms could not be explained by the AE amplitude distribution, but by the power spectrum of AE waves based on the frequency analysis. The dominant frequencies in AE signals due to the matrix cracking, the debonding, the fiber breaking and the friction between fibers could be specified, and they increased in order of such phenomena.
The aim of this study was to develop a new BMC (Bulk Molding Compound) with low molding shrinkage and high acid resistance. The resin system used in this study was a novolac type epoxy resin with low shrink additive and the reinforcements used were glass, carbon and aramid fibers. Firstly the mold shrinkage, the heat distortion temperature and the electric resistance of BMC were measured as the functional properties. The immersion test was carried out in a bath with a mixed solution of 25wt%H2SO4 and 7.5wt% HNO3 at 65°C up to 3000hr. The weight change and the reduction of mechanical properties were measured in order to examine the degradation mechanism of BMC. It is concluded that Hybrid BMC which are reinforced by glass, carbon and aramid fibers show the excellent functional properties. The acid resistance of BMC developed in this study is much higher than that of BMC in which the matrix is the epoxy resin with high acid resistance.
The failure modes of wood were outlined and their basic types were illustrated in schematic diagrams and pictures. The broken ends of cells and the fractured surfaces of cell walls in the fractured wood pieces had complicated forms and structures. Their fractured types were classified into several categories in relation to wood structure, and their technical terms were proposed. In tension parallel or perpendicular to grain, failure modes of cellular structure are divided into two main categories, namely, “intercellular (interwall)” and “transcellular (transwall)”. The intercellular failure occurs at or close to the intercellular layer (middle lamella), and the fractured surface is almost parallel to the fibers. The transcellular failure shows the following fracture types, “longitudinal split”, “cross”, “oblique” and “splintering”. As to the transwall failure of the wall layers and lamellae, there are six fracture patterns, “cross”, “oblique”, “plicate-pattern”, “split”, “splintering” and “interlayer (or interlamellar)”. The fractured surfaces of nonfibrillar type are often found on the broken ends of lingnin-rich wall. In compression parallel to grain, minute failures are detected as wrinkles on the lumen surface, or as slip planes or bendings of cell walls. They progressively develop from microscopic failure lines to macroscopic ones. In compression perpendicular to grain, a remarkable deformation occurs in the cross-sectional shape of cells.
Fracture toughness testing was carried out for Japanese beech, castor aralia, ramin, false arbor-vitae, and ramin and false arbor-vitae impregnated with polyethylene glycol (PEG). The main results obtained are summarized as follows: (1) The load-displacement curves had different patterns for different woods. (2) The fracture toughness value of the RL system was larger than those of the TR-RT and TL systems. (3) The fracture toughness value of the wood impregnated with polyethylene glycol was larger than that of the untreated wood.
In this paper, the fractography and tensile strength of “Tokkuri-byo” disease-infected-Hinoki (Chamaecyparis obtusa Sieb. et Zucc.), which had a very large growth at the root and contains a lot of abnormal cells, were investigated. The results obtained are summarized as follows: (1) The distribution of annual ring width showed the existence and degree of “Tokkuri-byo”. (2) “Tokkuri-byo” disease-infected-Hinoki had much less tensile strength than normal Hinoki. (3) The abnormal cells contained in “Tokkuri-byo” disease-infected-Hinoki showed different fracture types from those of normal Hinoki, depending on these tissue structure properties. Consequently, the macroscopic fracture type of “Tokkuri-byo” wood depends on the quantity and quality of those abnormal cells. (4) In the tensile test, “Tokkuri-byo” wood produced more radiate ray-type fractures different from the normal one.
Tactile roughness of planed wood was investigated in relation to geometrical surface roughness and growth ring structure of the wood. Specimens used were small quarter-sawn plates of eleven species shown in Table I. In order to evaluate tactile roughness of the specimens, sensory tests by human hand were executed by the method of paired comparison, and the data were analyzed by the composite standard technique. Other roughness values of the specimens were measured with the instrument of the stylus method. Furthermore, the growth ring structure of the specimens was observed with naked eyes and a magnifier, and photographed with a camera. The tactile roughness expressed as the psychological value Z did not show a significant correlation with the center line mean roughness of the specimens, but with the roughness of real profile curve Rm defined as in Fig.1 (a). The Rm had also a highly significant correlation with the waviness of real profile curve W defined as in Fig.1 (b), which in most cases indicated good correspondence to the waviness of the growth ring structure. Thus the tactile roughness of the planed wood seems to come largely from the waviness such as the growth ring structure, rather than the porous structure of cellular elements in the wood.
Abrasive charcoal for Japan lacquer ware, called Surugazumi, is made from Aleurites species and the portion with narrow annual ring width is selected based on many years experience. The physical properties of the abrasive charcoals which were made in various processing conditions and their performance evaluation for sanding were investigated. (1) DSC (Differential Scanning Calorimetry) analysis of thermal decomposition on abrasive charcoal was effective to evaluate the carbonization degree. X-ray analysis showed that the carbonizing temperature had a direct effect upon crystallites of charcoal contributing to hardness. (2) A good abrasive charcoal could be classified by hardness pencil and frequency of sound in sanding the surface of Japan lacquer ware. (3) The good abrasive charcoal, which was selected from the portion with narrow annual ring width and was chared at 800°C, had a larger coefficient of friction in sanding the surface of Japan lacquer and led the sanding depth to be deeper. (4) The good abrasive charcoal might be easier to sand even in water with sanding residue because it has a large amount of vessels.
In order to produce composite materials having dimensional stability and hygroscopicity similar to wood itself, three kinds of alcohols (propanol, propanediol and glycerine) were reacted with 4, 4'-diphenylmethane diisocyanate (MDI) in heartwood of Hinoki (Chamaecyparis obtusa SIEB. et ZUCC.). The hygroscopicity and dimensional stability were evaluated by the amounts of urethane compounds combined with wood components, urethane compounds deposited into wood cavities and free alcohols. Their amounts were determined by means of the solvent extraction method. In the reaction of alcohols and MDI in wood, the amount of products introduced into wood increased with increasing the number of hydroxyl groups and mole fraction of alcohol in the reaction system. The moisture-excluding efficiency (MEE) and the anti-swelling efficiency (ASE) decreased with increasing the amount of products. The combined urethane components which exist in cell walls contribute directly to the increase of MEE and ASE. There is no significant effect of depositing urethane components on ASE. Also, the free alcohols considerable affect the increase in hygroscopicity of the treated wood.
In this paper the piezoelectric relaxation of cellulose and wood in a low temperature region was studied in relation to the elastic and dielectric relaxations. The piezoelectric strain constant d=d'-id", the piezoelectric stress constant e=e'-ie", the elastic constant c=c'+ic" and the dielectric constant ε=ε'-iε" were measured at the frequencies of 100Hz, 50Hz and 10Hz over a temperature range from -130°C to 0°C. There were observed the piezoelectric, elastic and dielectric relaxations. The activation energies for these relaxations were about 10kcal/mole. These relaxations were ascribed to methylol rotation in cellulose. Piezoelectric relaxation is often ascribed to the elastic and dielectric relaxations in the noncrystalline phase of the two-phase system in which piezoelectric crystallites are embedded in a nonpiezoelectric matrix phase. The present observations, however, suggest that the piezoelectric relaxation takes place in the crystalline phase and that the two types of polarization with opposite signs and different relaxation time exist in the crystalline phase.
Source wave analysis technique was applied to analyze the impact forces on wood based panel floors. The peak level and contacting interval of the source wave at impact points were evaluated for the plywood floor and also for the floors finished with two different materials, a vinyl-chloride sheet and a needle point carpet. In the case of the plywood floor, the impact forces by flexible bodies, such as rubber shoes stepping and rubber ball dropping, have almost the same characteristics as those in the case of concrete slub floors. The characteristics of impact force on the plywood floor by rigid bodies, such as high-heeled shoes stepping and mini-tapping machine impact, differ from those on the concrete slub floors. The finish materials lengthen the contacting intervals for the rigid body impact in the order of vinyl-chloride sheet and needle point carpet, although they have no influence on the contacting interval for the flexible body impact.