Box-hearted square timbers are very liable to ckeck containing heartshake on the end where splits develop on the surfaces by growth stress and drying stress. In order to prevent check and split, veneers were bonded on the surfaces of square timber perpendicularly intersecting each fiber direction to reduce the shrinkage during drying. The summary of the results obtained is as follows: (1) Checking and splitting can be minimized or eliminated by decreasing the surface shrinkage of square timber. (2) Internal check partially occurred in wood at high temperature conditions during vacuum drying of timber with high frequency heating. The drying condition of eliminating check and split in wood was below 50°C wood temperature. (3) Tensile stress was distributed in the shell of timber while compressional stress was distributed in the core. Though these stresses increased or decreased during drying, there was no reversal in drying stress. (4) Impregnating the cross section with polyethylene glycol prevented checking and heartshaking of cross section. (5) The most suitable adhesive for bonding surface square timber and veneer was a resorsinol resin because of its heat resistance and its ability to bond with wet wood.
A probabilistic model was developed for predicting the bending strength of 5 ply glulam (beam depth: 10-12cm) by using the distribution of the modulus of elasticity (MOE) of laminae. A random number generation method assuming that the relationship between the MOE and the modulus of rapture (MOR) of a lamina was represented by a weighted regression line and a standard error was proportional to the square root of the MOE was used in the model. In order to validate the model, a distribution of bending strength of twenty eight kinds of 5 ply glulam (four species, seven arrangements of laminae) was predicted, and the results were compared with the actual test data. Kolmogorov-Smirnov (K-S) tests were conducted to ascertain the compatibility between the predicted and the actual bending strength of the glulam. In twenty three predictions out of the twenty eight, a null hypothesis “The actual test data could be the samples from the predicted distribution”. were rejected over the 20 percent critical value.
The temperature dispersion of the elastic modulus of Hinoki wood (Chamaecyparis obtusa Sieb. et Zucc.) occuring at about 200°C was investigated in longitudinal vibration at various frequencies. The results are summarized as follows. (1) There existed the elastic temperature dispersions in the elastic modulus across the grain ER, the elastic modulus along the grain EL and the elastic modulus in a direction 45 degree from the grain direction E45 below 250°C at low frequencies from 1Hz to 100Hz. (2) The temperature of the dispersion shifted toward higher temperature as the measuring frequency became low. The values of the enthalpy of activation ΔH≠, the free energy of activation ΔF≠, and the entropy of activation ΔS≠ for the elastic dispersion of wood were estimated (Table I). The values of the apparent activation energy of E45 was a little larger than that of ER. (3) The temperature of the dispersion shifted toward higher temperature by repeating the measurement of the elastic modulus. It may be considered that changes of wood substance took place, for example crystallization or thermal decomposition by heat treatment.
The top plate of guitar is usually made from two wood species which belong to different genus, that is, german spruce (Picea abies) and western redceder (Thuja plicata). To clarify the characteristics of these species and of the wood materials for guitar top plate, the acoustic properties of the specimens prepared from the neighbour portion of the top plate were measured by means of free-free flexural vibration method. The results were compared with the evaluation by an expert of guitar manufacture. The mean values of specific dynamic Young's modulus (E/γ) and tanδ of german spruce were higher than those of western redceder, while among various wood species these two had higher E/γ and lower tanδ in the longitudinal direction. These characteristics were particularly pronounced in the specimens which were judged by the expert to be high grade. Moreover, the standard deviations of the acoustic properties of the high grade specimens were smaller than those of the medium or low grade ones regardless of the species. The value of E/γ in the longitudinal direction, which can be obtained easily, seemed to be a convenient criterion for selecting the wood material suitable for guitar top plate. Because it correlated highly with tanδ in the longitudinal direction, and also with the ratio of tanδ in the radial direction to that in the longitudinal direction. Evaluation using both E/γ and tanδ in the longitudinal and radial directions was more appropriate, because the experimental values of E/γ and tanδ in any grain angle agreed with the values calculated based on Hankinson's equation.
Sliding of a coffee cup and a dish on table top emits the friction sound. This paper deals with the effects of the composition of table top and physical qualities of the surface on the sound level of the friction sound and the mechanism of the friction sound emission. Japanese oak veneers (0.6mm and 1.4mm in thickness) and meramine sheets were overlaid, and an ethylene-propylene rubber sheet was also sandwiched as an absorbing material between surface material and base boards (plywood and particle board). The results obtained are as follows: (1) The power spectrum of the friction sound is composed of tap tone and noise components. (2) The regression analysis shows that the sound level can be represented quantitatively by the apparent surface hardness and the interval of surface roughness. (3) Synthesizing of the friction sound from tap tone of a board shows that the friction sound originates from the collision of the projection at the bottom surface of a cup and that of a board. This is the reason why the power spectrum of the friction sound resembles that of the tap tone. (4) In order to reduce the sound level of friction sound the followings are effective: the surface is not so hard, the sandwiching of absorbing sheet reduces apparent hardness and the sound level, and the surface roughness is not so fine.
Three-layer board (OR-board) having flake-type oriented particles (average alignment angle (AAA): 10.7deg.) as the faces and strand-type random-oriented particles as the core, cross-oriented three-layer board (CO-board) in which the core consists of strand-type particles oriented (AAA: 33.9deg.) perpendicular to the direction of the oriented face layer, and three-layer board (RR-board) having random-oriented face and core particles were produced. The effects of the ratio of face layer weight to total board weight (FW) on bending properties and dimensional stability of the boards were investigated. Bending properties in the oriented direction of the OR-board increased with an increase in FW and the ratio of parallel-to-perpendicular (||/⊥) value for modulus of rupture (MOR) and modulus of elasticity (MOE) of OR-board with the FW of 60 percent was about 5 and 4, respectively. Bending properties of the CO-board with the FW of 15 percent corresponded to those of the RR-board. MOE values of the three-layer board estimated from the thickness and MOE of the individual layer were in good agreement with experimental values under MOE of about 50×103kgf/cm2. The ⊥/|| ratio for linear expansion of OR- and CO-board with the FW of 60 percent was 3.8 and 2.9, respectively.
WPC was produced from corona-pretreated wood and methyl methacrylate (MMA). To remove MMA homopolymer, WPC specimens were extracted with acetone. Dimensional stability of these WPC specimens was compared with that of WPC produced by an ordinary heat catalyzed method. The degree of apparent grafting of MMA to wood (wall polymer content) increased with an increase in corona discharging time (0-120 minutes, 15kV). The wall polymer content of the WPC exceeded that of an ordinary WPC, and it reached the maximum of 80%. Anti-swelling efficiency (ASE) and moisture excluding efficiency (MEE) of the WPC exceeded that of the ordinary WPC, and they reached the maximum of 50 and 55%, respectively. Relationship between ASE and wall polymer content was linear in both tests of moisture and water absorption. Furthermore, relationship between MEE and wall polymer content was linear. These relationships of ASE and MEE against wall polymer content were the same as those of the ordinary WPC. From the results of wall polymer content and dimensional stability, the most suitable concentration of MMA-methanol solution for the impregnation into wood was found to be 80%.
The natural frequency of longitudinal vibration due to sound emitted by hitting the cross section of lumber with hammer was measured to determine the modulus of elasticity (Et) and weight change. And its application for mechanical grading of lumber and quality control for drying in the mill was discussed. Et was recognized to be highly linear to the modulus of elasticity determined by static bending test (Es). Et was hardly affected by the length and section of lumber as compared with Es, and practically represented the average value of Et of components. Since the change of natural frequency during drying process was associated with Et and weight loss due to desorption of water, it might be used as an effective rough classification method for mechanical grading and quality control in drying. Especially, as the third lowest natural frequency of longitudinal wave was hardly affected by piling, measurements of longitudinal vibration after sawing and weight change during drying process could be considered as a reasonable quality control system.
The X-ray diffraction method was used to measure the phase stress in composite ceramics of zirconia mixed with 20 and 40 wt% alumina which were subjected to elastic bending. The phase stress in each phase was determined from the diffractions of Al2O3 (146), Al2O3 (1.0.10) and ZrO2 (133). The phase stress increased in proportion to the applied stress; the proportional constant was larger for Al2O3 than for ZrO2. The macrostress calculated from the phase stresses by using the rule of mixture was nearly equal to the applied stress. The theoretical calculation based on the self-consistent model of elastic deformation of composites gave a lower phase stress to Al2O3 and a higher phase stress to ZrO2 when compared with the experimental results. The theoretical analysis should be elaborated to include the influences of the free surface and the third phase on phase stresses.
The stress-strain curve of Ti-Ni alloy on pseudoelasticity forms a hysteresis loop, and there appear large amounts of recoverable strain energy and dissipated strain energy. The experiments on a wire under cyclic uniaxial tension were carried out and the influences of test temperature, maximum strain and shape memory processing temperature on the cyclic behaviors of these strain energies were investigated. The results obtained are summarized as follows. (1) The recoverable strain energy was large as the test temperature became high, and decreased with the number of cycles. (2) The dissipated strain energy depended little on the test temperature for small maximum strain, but decreased significantly in the early cycles at low test temperatures if the maximum strain was larger than the range of stress-induced martensitic transformation. (3) Among the attenuation rates of various strain energies under cyclic deformation, the attenuation rate of dissipated strain energy was largest. The variation of attenuation rate of every strain energy was significant in the early cycles, but became almost constant after the 20th cycle. This means that the training before the actual use is effective for the cyclic stability of each strain energy. (4) The rate of strain energy storage increased with the number of cycles, but the rate of strain energy dissipation decreased. (5) Both recoverable strain energy and dissipated strain energy were large as the maximum strain became large in the early cycles. If the maximum strain was in the range of stress-induced martensitic transformation, each strain energy for the 100th cycle became almost a constant value. (6) The recoverable strain energy was small as the shape memory processing temperature became high. The dissipated strain energy was large as the shape memory processing temperature became high in the early cycles, but became largest at 673K of shape memory processing temperature for the 100th cycle.
The 6-4 brass specimen containing α-phase and β-phase was used as an example of the two-phase alloy and compressed uniaxially. Inhomogeneous plastic deformation of grains appearing on the free surface of the specimen was observed by a scanning electron microscope. The change of the length of grain was measured on the photographs in the longitudinal and the transverse directions of the specimen. The effect of plastic strain on the surface roughness was also measured with the stylus instrument. It was found that the mean strain of α-phase was larger than that of β-phase, though there was a scatter of the strain in each phase. Both the mean strain in respective phase and the standard deviation of the strain increased in proportion to the applied strain. The surface roughness also increased linearly with the applied strain, which mainly resulted from the inhomogeneous deformation of grains of α and β phases. The deformation behaviour of the two-phase 6-4 brass was discussed by comparing with that of the single-phase polycrystalline copper.
Machining conditions giving high residual compressive stress in carbon steel were examined experimentaly in this study. The relation between dimensions/configurations of cutting edge and resisual stress was analyzed mainly. The influence of corner radius of the top of cutting edge, miner cutting edge clearance angle and feed per tooth were checked. The residual stress was measurted by using X-ray. The diffraction profiles were approximated to Gausian curves, and the peek positions were decided by using a method of nonlinear least squares. The followings became obvious as the results of analyses. When the feed per tooth was made smaller with an appropriate corner radius and small cutting edge clearance angle, high compressive residual stress occurred in the right angle direction of machining. The penetration depth of residual stress became deep when high compressive residual stress occurred.
Need for precise grooving and cutting of ferrite-based composite materials into magnetic heads is increasing recently in the field of electronic industry. As materials for magnetic heads have inherent internal stress, it influences the quality of the head processed by cutting and grooving. This study focuses its attention on the effect of internal stress on its cutting behavior. Indentation and scratching tests were carried out to know the cutting mechanism of the composite ferrite material. it was found that the crack length and chipping area increased with an increase in applied load during scratching. The mode of crack growth and chipping pattern also varied with tensile load. Especially, the chipping area was very sensitive to tensile load under small indentation load.
Since the deformation process at high strain rate is adiabatic one, the temperature rise caused by plastic work appears in the specimen during the deformation. The temperature rise is a transient phenomenon so that the measurement of the temperature rise is very difficult. On the one hand, the amorphaus polymer indicates the shape memory effect which is dependent on the test temperature of the polymer specimen. In this paper, the effect of strain rate on the shape memory effect of poly (vinyl chloride) specimen compressed at various strain rates is investigated experimentally. Eventually, the maximum temperature rise of the specimen which was impacted longitudinally at one end is deduced using the experimental results described above. The results show that the recovering ratio which is the recovering length against the deformed one, decreases with increasing strain rate and it is considered that the temperature of the poly (vinyl chroride) specimen impacted longitudinally at high strain rate of 103-104S-1 is above the glass transition temperature.
In order to compare the impact characteristics of polycarbonate (PC) and polycarbonate with acrylic films for degeneration resistance on the surfaces (PC(F)), the instrumented Charpy impact tests were carried out. The results obtained are as follows: (1) The specific absorbed energies of PC and PC(F) specimens changed little at a small notch radius in the temperature range of -110-45°C but the specimens showed the ductile-brittle transition at a larger notch radius, and the transition temperature of PC(F) specimens shifted higher than that of PC specimens. (2) The ratio of the specific absorbed energies of PC(F) nd PC decreased remarkably with an increase in notch tip radius when the notch tip radius became over 0.02mm in the temperature range of -110-0°C. (3) It was found from microfractographs that the crack initiated at the middle of thickness in PC(F) test specimen at a small notch tip radius, but it initiated near the interface between PC resin and film in the specimen at a large notch tip radius.
The tensile and fatigue properties of spheroidal graphite cast irons with ferritic matrix structure and pearlitic one, being austenitized at 1173K and austempered for either 5min or 2h at 573K, were investigated. The amount of retained austenite in ferritic matrix was more than that in pearlitic matrix. Axial fatigue tests were conducted at a stess ratio of R=0.1. The tensile strength of the both as-received materials were improved by austempering treatment. Separation at the graphite-matrix interface during tensile deformation occurred first and the initiation of cracks followed around each graphite. Finally these cracks were simultaneously linked-up. As the result of the coalescence of those cracks the fracture surface of the as-received materials exhibited brittle pattern. On the other hand, the fracture surface of the austempered specimens showed a mixed type of microvoid formation and quasi-cleavage associated with austempering structure pattern. Although the fatigue strength of the material austempered for 2h was rather improved, the strength for the 5min one was weakend as compared with that of the as-received material. The fatigue crack growth rate da /dn of both austempered materials, was higher than that of the as-received at lower ΔK values. Fatigue crack path followed a mixed type of both transgranular and intergranular fracture. Characteristic fracture surface in the vicinity of the fatigue limit was predominantly covered by intergranular fracture without straiation in the ferritic matrix, while considerable lamellar structural pattern was observed in the pearlitic matrix. Fracture surface of the austempered specimen showed no significant difference irrespective of austempering time and indicated the similar structural pattern as in the static tensile fracture.
Database for the strength of materials is desired strongly as it is a powerful tool for searching out strength data. But as for fatigue properties, it is rarely possible to get suitable data to design or maintain machines and structures for a particular material and testing conditions directly from the database. In general, its fatigue properties must be estimated from the data obtained under similar testing conditions. In this paper, a method for predicting the missing properties in fatigue database is discussed. Good correlations between the tensile property data and the exponents or coefficients of the equations for cyclic stress-strain curves and Manson-Coffin law were obtained for steels specified by JIS for machine structural use. By using these relationships, S-N curves under uniaxial tension-compression can be predicted for steels, if their tensile properties are known. A conversion method of fatigue strength is also proposed between rotating bending and uniaxial conditions or between reversed torsion and uniaxial conditions.
The strength degradation of steel adhesive joint in water environment was investigated. A model is proposed in which the process of progressive decrease in joint strength due to water uptake is considered as that of progressive growth of an apparent crack at the joint interface, and the strength degradation of adhesive joint can be analysed on the basis of fracture mechanics. It was found that in the specimens immersed in water for the same duration of time, the depth of the apparent crack increased with increasing water temperature, while the water concentration at the tip of respective crack was nearly the same. The fracture strength after immersing the joint in water at various temperatures was determined as a function of a single variable of Dt. The effect of side diffusion on the joint strength is not negligible in the case of longer immersion, especially at higher temperatures.
The susceptibility to stress corrosion cracking (SCC) and its fracture morphology of pure titanium in CH3OH/HCl solutions with various HCl concentrations at room temperature were examined fractographically. It was found from the stress-free immersion tests in CH3OH/HCl solutions that the weight loss increased gradually with the immersion time, and that the intergranular corrosion occurred scarcely. In the subsequent tensile tests in air, however, the mechanical properties deteriorated greatly due to the intergranular embrittlement, especially during the prior immersion at a concentration of 0.4% HCl. The SCC susceptibility under constant load conditions also increased in a CH3OH/0.4% HCl solution. The fracture mode was changed from an intergranular into a transgranular fracture, and finally into a ductile fracture. A similar tendency was revealed by SCC tests under slow strain rates: In the crosshead speed of 5×10-2-5μm/s, all three modes of intergranular, transgranular and ductile fracture were observed. The aging treatment after stress-free immersion improved the mechanical properties, and thus decreased the area fraction of intergranular fracture. From the evidence introduced here, a possible mechanism for SCC of pure titanium was discussed.
Waste silica with 5.6μm mean particle diameter was mixed with lime and autoclaved in alkaline solutions at 180°C for several hours under saturated vapor pressure. The observation under a scanning electron microscope (SEM), DTA and X-ray analysis were performed to determine the microstructure, phase component and crystallinity of the reaction products. The additions of sodium and potassium hydroxides accelerated the hydrothermal reaction. On the contrary, lithium hydroxide served as an inhibitor, because of the formation of Li2SiO3 on the surface of silica. Glauconite (mica group), an impurity in waste silica, retarded the crystal growth of calcium silicate hydrate, because of the formation of analcite (zeolite group) by sodium hydroxide. The use of low concentration of NaOH or KOH resulted not only in a considerable reduction in autoclaving time, but also in increasing the bending strength of calcium silicate hydrate briquettes. The addition of 1 wt% potassium titanate whisker (K2O·6TiO2) into the waste silica and lime caused the bending strength of briquettes to increase by about 40%.
The fracture surface reconstruction technique has been applied to dimple and stretch zone patterns to elucidate the quantitative relationship between three-dimensional parameters of fracture surfaces and material properties. The followings have been made clear. Testing temperature of Charpy impact tests is closely related to the averaged ratio of surface area and the averaged depth of dimples irrespective of kinds of steels; the higher the former, the greater the latter in dimple fracture surfaces. Similarly, the greater the absorbed energy is, the greater the averaged ratio of surface area and the averaged depth of dimples become. When the height of stretch zone is high, the height can be automatically and precisely deduced without human assistance.