Recently, recycling of fiber reinforced plastics (FRP) is becoming the focus of attention from the point of environmental protection. In this paper, FRP wastes were tested to utilize as a bulk molding compound (BMC) additive. FRP sample board was crushed, fractionated, and supplied for BMC preparation. The mechanical strength of BMC was measured to evaluate the resin molds and resin mortars preparation. The crushed FRP addition gave no improvement to the flexural strength of BMC. This indicated that the crushed FRP acted as the filler. The BMC prepared by waste ship FRP showed lower strength than the original FRP board. The pretreatment of FRP with silane coupling reagents improved the strength of BMC. From these results it is concluded that the crushed FRP is useful as a BMC additive, when pretreated.
Threads from spiders may be one of the best structural materials produced by nature. They are used to capture and wrap insects. Less attension has been paid to their mechanical properties of spider silk in contrast to silk fibers made by silkworm. In this paper, the mechanical properties of dragline silk produced by Nephila Clavata called Jorougumo in Japanese are investigated. It is shown for the properties of the dragline that (1) the surface is featureless without any typical mark, (2) the dragline of diameter 2 to 5μm consists of the microfibres of diameter about 0.1μm, (3) the diameter is proportional to a square of the body length of spider, (4) the glass transition temperature of dragline from the spiders collected in July is lower than that in September and (5) the dragline which has the fracture stress of about 1500MPa and the fracture strain of about 0.3 is almost equivalent to the best man-made fibres such as aramid fibers.
Cutting of brittle materials such as silicon wafer is usually made with a diamond scriber or a diamond thin blade wheel. It is said that the mechanical cutting of silicon wafer using the blade leads to lower cutting quality. A non-contacting cutting method using a CO2 laser is recently being studied enthusiastically. Precision breaking of silicon wafer, however, has not been made. Breaking of silicon wafer with a YAG laser was studied at room temperature under water cooling of lapping surface. It was found from the experiments that the breaking of silicon wafer occurred through two stages of crack initiation and propagation. Meandering of the main crack is accompanied with some branching cracks which deteriolate the breaking quality of silicon wafer. Breaking mode is dependent strongly upon laser power, table feed rate and cooling condition.
Brittle fracture behavior of medium and high density polyethylene pipes has been investigated. The drop weight tear test (DWTT) was applied as a simple evaluation method to solve the rapid crack propagation problem of polyethylene pipes. Since the critical ductility index of fracture surface of plastic pipes is needed to evaluate the crack propagation/arrest temperature, the crack propagation velocity in DWTT specimens was measured and the relation between the velocity and the ductility was investigated. As a result, velocity decreased with increasing ductility to 100m/s at about 30% ductility. Data analysis was performed by Mimura's method which takes the competing velocities of gas decompression and crack propagation into consideration. From this analysis, it was concluded that the critical ductility index for plastic pipes, such as polyethylene pipes, should be less than that for steel line pipes, because the crack propagation velocity of polyethylene is less than that of steel.
Calcium silicate briquettes were prepared from raw materials of fly ash and lime by autoclaving at 180°C. The fly ash was supplied from a fluidized bed boiler and contained 29wt% unburned carbon. The briquette with the bending strength of 15MPa and the bulk density of 1.44Mg/m3 was obtained by autoclaving for the duration of 12 to 24hrs at Ca/Si=1.0. The addition of NaOH lowered the crystallinity of hydrogarnet in the briquette and decreased the bending strength. To improve the strength, waste silica containing85wt% quartz was added to the fly ash in the ratio from 0.15 to 0.75 as SiO2. The bending strength increased to 25MPa with the addition of waste silica until the ratio of 0.5 when 1N-NaOH was added. Without NaOH, the strength was not so much increased by the addition of waste silica below the ratio of 0.3.
Experiments were carried out to study the effect of interfacial strength between matrix material and fibers on the solid particle erosion behavior of FRPs. The FRPs used were epoxy resins unidirectionally reinforced by carbon fibers. Both FRPs with treated fibers and untreated fibers were used as the test materials. According to the tensile tests, the FRP with treated fibers shows higher interfacial strength than the FRP with untreated fibers. The results of the erosion tests show that the FRP with treated fibers has higher erosion resistance than the FRP with untreated fibers due to higher interfacial strength between matrix material and fibers, though the erosion rates of both FRPs are higher than that of neat resin.
The influence of reversion austenite on the fatigue behavior of a maraging steel has been investigated by using 18%Ni-8%Co-5%Mo steel. The behaviors of age hardening and reversion from martensite to austenite were examined first under various aging conditions in the temperature range of 750-850K. These aging conditions were chosen so that a selected volume fraction of austenite (γvol%=1, 2, 3 or 24%) was formed in the age hardened maraging steel. The specimens were subjected to fatigue test, crack growth test and fractography. The results obtained are as follows: (1) The formation of reversion austenite results in a great improvement of fatigue strength. Especially, a small amount of austenite (2-3vol%) markedly increases the fatigue limit of a maraging steel without reducing the hardness so much. Due to the existence of reversion austenite, crack growth tends to be suppressed and the maximum length of non-propagating crack becomes longer. (2) The existence of reversion austenite improves the fatigue fracture toughness.
Statistical fatigue tests have been carried out using smooth specimens of a spheroidal graphite cast iron (SGI) with ferritic microstructure and the fatigue life distribution was examined. It was found that fatigue cracks initiated from casting defects and thus fatigue life could be regarded as crack growth life. The scatter of fatigue life was primarily attributed to the scatter of the size of casting defects. The prediction of fatigue life was performed using the measured growth characteristics of small fatigue cracks. The results obtained agreed well with the experimental data. From the practical viewpoint, similar prediction was conducted using the growth characteristic of large cracks. When the crack opening stress was assumed to be zero, the results obtained gave longer lives than the experimetal data at high stress, but were coincident with the experimental data at low stress. Furthermore, a Monte Carlo simulation was performed using the measured distribution function of casting defect size and the similar results were obtained. In order to discuss the universality of the proposed prediction and simulation, additional fatigue tests were conducted on two SCI's with pearlitic and bull's eye microstructures, and it was found that the fatigue strength was independent of microstructure. The distribution of casting defect size in pearlitic microstructure was examined, which agreed closely with that in ferritic microstructure. This indicated that if the distribution of the size of casting defects from which cracks initiated was the same in different SCI's, then fatigue strength would be independent of microstructure, and the validity of the prediction and simulation of fatigue life distribution was confirmed.
To investigate the effect of Si-phase on fatigue properties of Al-Si eutectic alloys in the long life fatigue range (N≅107) and extra-long life fatigue range (N>108), tension-compression fatigue tests were carried out. Fatigue test specimens were prepared from two materials produced by two different processes, continuous casting and extrusion. The results obtained are: (1) In the case of continuous casting, all the fatigue fractures were caused by shear type crack, resulting shorter fatigue life. (2) In the case of extrusion, the fatigue fracture origin in the long life fatigue range was at Si-phase, while in the extra-long life fatigue range it was at the matrix. (3) The fatigue limit defined by the cycle N=107 can be predicted by the √area parameter model, i.e. with two parameters, the maximum size of Si-phase √areamax and the Vickers hardness Hv. (4) In the case of Al-Si alloy, a crack leading to fracture initiates even after 108 cycles under very low stress. Thus, extra-long life fatigue behaviour must be taken into account to both material and structural designs.
The effect of surface modification by ion implantation on the fatigue strength of 13Cr martensitic stainless steel was first described. Then the relationship between the fatigue performance and the surface microhardness of the material was dealt with. N+ ions were implanted into the specimen surface with doses in the range of 5×1013ions/cm2∼5×1017ions/cm2 with energy level of 350keV. The results of out-of-plane bending fatigue tests revealed that the fatigue strength was improved by the ion implantation with implantation doses more than 2×1017ions/cm2, and that the further increase of fatigue strength was attained by the post heat treatment following the ion implantation. The microhardness of ultra-thin surface layer of submicron order was evaluated by the method previously proposed by the authors. The results indicated that the surface layer was hardened by the ion implantation and the hardness was increased by the post heat treatment. A remarkable increase in hardness was observed at the surface layer after the fatigue test, and this increase of the microhardness well coincides with the improvement of fatigue strength by ion implantation and post heat treatment.
Fatigue crack growth tests on an extruded Al-8wt.% Zn-2.5wt.% Mg-1.2wt.% Cu-4wt.% La alloy were carried out using CT specimens (TL orientation). Crack closure was examined by the unloading elastic compliance technique. The main results are as follows; (1) The effect of stress ratio was observed on the crack growth rate, da/dN, vs. stress intensity factor range, ΔK, diagram. A higher stress ratio gives a faster crack growth rate at same ΔK. (2) Crack closure was observed under the stress ratio=0.1, and its degree was increasing with decreasing stress intensity factor range. On the other hand, it was not at the stress ratio=0.5. (3) The effect of stress ratio on the second region of da/dNvs. ΔK diagram disappeared when the effective stress intesity factor range, ΔKeff, was used instead ofΔK. (4) The second region of da/dNvs. ΔKeff diagram for the extruded Al-8wt.% Zn-2.5wt.% Mg-1.2wt.% Cu-4wt.% La alloy was in agreement with that for the commercial 7075T6 alloy. So, the fatigue crack growth resistance of the extruded Al-8wt.% Zn-2.5wt.% Mg-1.2wt.% Cu-4wt.% La alloy is nearly equal to that of the commercial 7075T6 alloy.
Three-dimensional photovisco-elasto-plastic analysis considering strain rate effect was investigated by a scattered-light method using polyester as a model material. In order to examine the mechanical and optical properties of polyester, torsion tests were carried out on solid shafts under various twisting rates at 30°C and the effects of strain rate on the shearing stress, shearing strain, fringe gradient and increasing rate of fringe gradient were investigated. Regardless of the strain rate, it was found that the shearing stress-strain relation can be expressed by a Ramberg-Osgood equation and the fringe gradient-shearing strain relation was successfully represented by a nondimensional equation. Finally, the relation between the fringe gradient and its increasing rate was formulated as a function of strain rate. From these results, we established a method to estimate the shearing stress and the shearing strain in a three-dimensional model only by measuring the finge gradient and its increasing rate. The calculated torques from the shearing stress estimated by this photovisco-elasto-plastic analysis were consistent with the applied torques on solid and hollow shafts.
The present paper shows a highly accurate analytical method utilizing complex variable method and point matching technique for the problem of two neighboring elliptical tunnels excavated in anisotropic elastic ground under 3-dimensional loading conditions, and describes the theoretical process of back analysis using this solution. The elastic characteristics of rock mass are assumed to be orthogonal anisotropy such as existing the principal axis of elasticity in x-y plane, and five stress components (σ∞x, σ∞y, τ∞xy, τ∞yz, τ∞zx) of in-plane and out-of-plane with respect to the tunnel axis (z-axis) are treated in this analytical theory. The 3-dimensional principal stresses (σ∞1, σ∞2, σ∞3) acting from arbitrary directions in the ground are determined using the results of this back analysis and measured stress of σ∞z by in-situ flat jacking technique and so on. The usefulness of this method is additionally shown through some numerical examples in this paper.
A non-destructive testing method using ultrasonic waves for composite materials has been studied. In this paper, a computer program of three dimensional image processing was developed to evaluate the defects in composite materials. The developed computer program has two particular functions, which are smoothing of scan data and decision of defect size. The size of defect was obtained by a gradient of echo level. As the examples, this method was applied to GFRP and CFRP laminates with artificial defects, and the effect of processing on the size of defects was investigated. As a result, the shape, size and location of defects in composite materials were obtained by the three dimensional image processing. It is also revealed that the detectability of defects is improved by this method. From these results, it can be shown that the method proposed in this paper is very useful to evaluate defects in composite materials.
The direct current potential drop method for on-line monitoring of side edge cracks was studied. In a plate with a single edge crack, the measured potential difference varies with crack position. Based on the distinctive distribution of potential difference, a multi-terminal DC potential technique was proposed for detecting crack length and position. In this technique, many potential difference measuring electrodes with the same spacing are fixed on the plate side. By comparing the many potential differences, the crack length and position can be calculated. The electrical field was analyzed by FEM, and the calibration curve and sensitivity were examined. The analyzed potential differences were classified based on the position. V1 is the potential difference between the electrode pair with a crack. V2 and V3 are the potential differences between electrode pairs without a crack, and are on either side of the V1 obtained electrode pair. V2 is closer to the crack than V3. V0 is the reference potential difference obtained by averaging the potential differences except V1, V2 and V3. The analysis shows that the potential difference ratio (V1+V2-V0)/V0 gives the accurate crack length, the difference of V2 and V3 gives the accurate crack position, and the sum of V2 and V3 gives the side on which the crack exists, that is, the surface or reverse-face.
The Scanning Vibrating Electrode Technique is an effective and non-destructive technique to evaluate the amount of pitting or intergranular corrosion by measuring the electropotential field near the surface of metal sample submerged in an electrolyte. However, the accurate determination of correct electropotential field is difficult, when the sensor probe approaches the metal surface and disturbes the field by itself. In order to overcome this difficulty, an inverse problem, in which the true current density distribution along the metal surface is estimated from the data having errors due to the disturbance, was solved in this paper. The 3-D boundary element method was used to deal with the governing Laplace equation. The ill condition of the inverse problem was overcome by proposing the following procedures. (1) A form of the polarization curve is presumed and the number of unknown parameters is reduced. Then the current density distribution along the metal surface is determined. (2) In order to improve the accuracy, additional electropotential is applied to the sample by a potentiostat and various data are obtained for different electropotential fields. B using the above procedures, the numerical simulation of a sample specimen was carried out. The computed results showed a significant improvement in measuring accuracy by using the inverse analysis.
Since a thermocouple can be attached on a specimen, it is possible to measure the temperature of a moving point such as a surface of deforming body. The response of thermocouple is dependent on the junction volume of thermocouple because the usual thermocouple is a welded-bead type. It is considered that the response in a compression test is improved by use of a contact surface between a specimen and a tool as a thermocouple. However, since the diameter of specimen or tool is much larger than a usual thermocouple diameter, it is also important to examine the influence of heat loss on the accuracy of measurement. This paper describes the influence of heat loss on the temperature of the contact surface during an elastic-plastic deformation. The accuracy was examined by comparing the experimental results with the numerical ones in which the heat conduction and heat transfer are taken into consideration. In the experiment a copper specimen and a stainless steel tool were used under a range of strain rate from 4×10-4s-1 to 3×10-2s-1. The experimental results obtained are in good agreement with the numerical ones and also with the experimental ones obtained using a usual thermocouple. Therefore, it is clear that the temperature measurement method utilizing the contact surface as a thermocouple is an effective one.