Elastic moduli of glass fiber that is used for reinforcement of FRP are measured in the temperature range from 20 to 300°C. In this experiment, three kinds of glass fiber samples were prepared; E-glass, C-glass and T-glass. Load was placed on a specimen in a transparent furnace controlled at predetermined temperatures. The elongation of specimen was read by a reading microscope and the diameter of specimen was measured by a micrometer. The elastic modulus of glass fiber was calculated by the gradient of load-elongation diagram, the diameter of glass fiber and the distance between the marks on the glass fiber specimen. The results obtained are as follows; (1) The elastic modulus of glass fiber obtained was 60-80GPa at room temperature, and depended on composition and diameter of glass fibers. (2) The elastic modulus of E-glass decreased with increasing temperature, while that of C-glass did not change very much with temperature and that of T-glass increased with temperature. (3) In any case, the elastic moduli of small size fibers were larger than those of large size fibers.
Injection moulding is an established production technology for the forming of thermo-plastics resins. Recently, it has been applied to fibre reinforced thermoplastics (FRTP), and developments in this field are continuing. However, this method has still many problems, such as brittle weakness along weld-line, warping, incomplete filling and so on, especially for the fibre reinforced plastics dealt with here. In this paper, a simulation was carried out for a box product with thin wall by considering the velocity distribution resulting from the velocity difference in flow between the upper and lower skin layers. A box was unfolded onto one plane to convert a three-dimensional structure to a two-dimensional model. After the flow analysis, the fibre orientation analysis was carried out by assuming that fibres rotate according to the velocity gradient tensor obtained for each element by the flow analysis. Finally, an attempt was made to established the deformation analysis for determining the out-of-plane deflections based on the results of the fibre orientation analysis. In the experiments, the shape of flow front, fibre orientation and out-of-plane deflection were determined by the observation of short shot mouldings, soft X-ray photographs and moire-image interrence fringes, respectively. The numerical results were compared with the experimental observation. They showed a good agreement.
Mechanical properties of injection moldings of incompatible binary polymer blends are strongly affected by morphology in the moldings. In this study, structure and mechanical properties of injection moldings of liquid crystalline polymer (LCP)/polyphenylene sulfide (PPS) binary polymer blends were investigated. The two polymers are incompatible and form separate phases in the molding. The structure of separate phases is affected very much by the blending ratio. At the low LCP concentration, the LCP forms spherical domains in the core and fibrillar structures in the skin layer. At the high concentration, the layer-structure like LCP is formed. The modulus of moldings increases with increasing LCP concentration whereas the strength decreases because of low interface strength of moldings.
FRP is widely used because of its superior characteristics as a structural material. But such characteristics of FRP as anisotropy, heterogeneity and non-weldability sometimes become weak points. Namely, when FRP is used for a structure, the joint parts become a trigger of fracture, and the strength of structure is decided by these joint parts in the majority of cases. Therefore, the development of a new joint method for FRP is strongly needed. In this paper, the tensile creep behavior of a conical shaped joint system is investigated, which has been developed recently. The creep deformation and creep rupture of the tensiled joint system were measured at various temperatures. It is reveal that these creep deformation and creep rupture during long term can be predicted by using a reciprocation law between time and temperature, which holds for the viscoelastic behavior of the bonding resin and matrix resin of FRP.
This paper presents the effect of load sequence on fatigue damage of FRP reinforced by plain woven glass fabric. Two stage pulse loading was applied to the specimen. The specimen was subjected to the first pulse load up to 1000 cycles, and then the second pulse load having a different wave profile from the previous pulse was applied to the specimen until it failed. The following conclusions were obtained from this study. (1) The fatigue life under the two stage loading can be roughly estimated by the Miner's rule although the experimental fatigue life is about 30% shorter than the predicted one. (2) The inherent characteristics in stiffness reduction under the second pulse loading cannot be identified due to the large stiffness reduction caused by the first pulse, while the specimen shows the inherent stiffness reduction given only by the second pulse even at the second stage in the case that the pulse load at the first stage does not cause the large stiffness reduction. The similar result is obtainable on the AE records. (3) It is found that the stiffness reduction is not the appropriate parameter for the degree of fatigue damage. Namely, it is hard to predict the fatigue life from the observation of the stiffness under pulse loadings.
The effects of frequency and temperature on the delamination crack growth under cyclic loading were investigated with unidirectional CF/epoxy laminates. Tests were conducted at room temperature, 50°C, and 80°C in air with double cantilever beam (DCB) specimens. At room temperature, the growth rate in terms of number of cycles, da/dN, was given by a power function of the stress intensity range, ΔK, when da/dN was larger than 5×10-9(m/cycle). The relation was almost independent of the loading frequency. At 50°C and 80°C, the growth rate in terms of number of cycles, da/dN, was given by a power function of the stress intensity range, ΔK, when da/dN was larger than 5×10-11(m/cycle). When compared at the same value of ΔK, the growth rate, da/dN, was higher for higher temperature and for lower frequency. However, the growth rate expressed in terms of time, da/dt, was found to be controlled by the maximum stress intensity factor, Kmax, independent of the loading frequency at the same temperature, i.e., the delamination crack was considered to have grown by time dependent mechanisms under cyclic loading. The da/dt-Kmax relation also depended on temperature. For higher temperature, the growth rate, da/dt, was higher at the same value of Kmax.
An investigation has been carried out concerning the influences of water absorption on the tensile and fatigue properties of two kinds of (0°/±45°/90°)2s aramid fiber/epoxy composites, i.e., Kevlar 49 and HM50 composites. The delamination growth behavior was quantitatively evaluated with a scanning acoustic microscope. The specimens used were dry and wet ones, which were respectively preconditioned in air and in water at 80°C for two months. Under a static tensile loading, for both wet and dry specimens, resin cracking and interfacial debonding in the weakest 90° ply were followed by the lowering of load carrying capacity of 90° and 45° plies, and the final fracture was caused through an increase in 0° ply stress. Resin cracking in wet specimens was observed at a lower stress level than in dry ones, because water absorption lowered the interfacial strength between fiber and matrix, i.e., lowering of the interlaminar strength of laminates. Under a fatigue loading, compliance changes were divided into three regions, i.e., Region I, II and II'. In the cases of dry specimens in air and wet specimens in air, compliance was kept constant in Region I and was increased in Region II. In the case of wet specimens in water, however, Region I was diminished and Region II started from the beginning of the fatigue test owing to the water absorption through the 90° ply cracking. The influence of water absorption on delamination growth behavior was also discussed based upon the observation of ply-to-ply delamination with a scanning acoustic microscope.
FRP (Fiber Reinforced Plastics) are most popular and widely used materials among various kinds of composites. In many kinds of FRP composites, SMC materials are frequently used as materials for various equipments. Most SMC materials are also used in various environmental conditions, such as water, ultraviolet rays, oxgen and so on. Among these conditions, water environment is a usually surrounding one around these materials and it strongly influences SMC materials' properties. Therefore, in this paper, the effects of water absorption on the fatigue properties and inner structural changes of SMC materials were investigated. In this study, SMC material composed of bis phenol A unsaturated polyester resin and E-glass chopped strand mat was used. Voids which were generated during molding process were recognized to exist in the central layer of SMC material. SMC specimens absorbed 3.0% water after 10800 hours immersion into deionized water at 30°C, and the water absorption process is shown to follow Fick's law. Fatigue life in water environment of SMC material becomes extremely short comparing to that obtained in air. As the results of SEM observation and EPMA (Electron Probe Micro Analyzer) analysis on the fracture surface, it was made clear that the absorbed water in SMC material reacted with calcium carbonate which was distributed in the matrix resin as filler. Then, the absorbed water penetrating through the dissolution regions. into inner sites caused the degradation of interfacical bonding between fiber and matrix in SMC material.
Rotating bending fatigue tests have been conducted in a 3%NaCl solution using under-aged, peak-aged and over-aged materials of two aluminum-lithium alloys, 2090 and 8090. Detailed observations on corrosion pit, fatigue crack initiation and growth have been made, and the results obtained were compared with those of conventional aluminum alloys, 2024 and 7075. The corrosion fatigue strength of Al-Li alloys significantly reduced when compared with the fatigue strength in laboratory air, but was independent of aging condition. However, the peak-aged material showed relatively higher sensitivity to corrosion environment than the other aged materials. In comparison with 2024 and 7075 alloys, Al-Li alloys exhibited better corrosion fatigue strength. It was found that the corrosion fatigue process in Al-Li alloys consisted of corrosion pit initiation and growth, and fatigue crack initiation and subsequent growth. The density and size of corrosion pits in Al-Li alloys were much higher and smaller, respectively, than those in 2024 and 7075 alloys, and the configuration was extremely irregular. Corrosion fatigue cracks initiated from such corrossion pits and then grew. The crack growth of Al-Li alloy was enhanced in 3%NaCl solution at both low and high Kmax regions, due to corrosion dissolution and crack coalescence, respectively. Furthermore, the crack growth resistance of Al-Li alloys was almost the same as that of 7075 alloy, but was higher than that of 2024 alloy.
Fracture toughness values of engineering ceramics are often obtained by conventional three point bending tests. In these tests, an initial crack usually extends unstably, and therefore it is quite difficult and also labourious to determine R-curves on ceramics. In order to perform stable crack extension tests, the stable condition for the crack extension was studied in three point bending tests. The stable condition was depicted on EBΛ*-x diagram (E; Youngs modulus of the specimen, B; the thickness of the specimen, Λ*; the compliance of the testing machine and x; the non-dimensional crack length). The diagram shows that the stable crack extension test can be performed when the value of EBΛ* is small. On the basis of the study, a crack stabilizer was newly designed to achieve the small value of EBΛ*. By using the stabilizer, the stable crack extension tests were successfully performed in an alumina ceramic.
This paper deals with the analytical approach to the depth of remaining surface cracks in ceramics ground by an orthogonal single grain. The analysis consists of the sequential treatment of the grain-work interference repeated during the grinding, the elastic/plastic stress fields in the work formed by the interference and the crack extension under the stress fields. The cracks extending from various interference positions above the surface being finished were evaluated by the depth of crack tip below the surface, considering their influence on the surface quality of the work. The maximum depth of the remaining cracks calculated was shown to be approximately consistent with those from grinding experiments for alumina ceramics and soda-lime glass over a wide range of grinding conditions (wheel depth of cut, work speed and radius of the grain tip). The maximum depth of remaining surface cracks increased with increasing wheel depth of cut until a certain value, beyond which it became constant. Increase in work speed and radius of the grain tip elongated the maximum remaining depth monotonically. These changes in the maximum depth of surface cracks with grinding conditions are due to their complex effects on the dimension of crack extension and the position of the grain-work interference.
MgO and MgO-ZrO2 sintered bodies with different grain sizes were prepared by pressureless sintering, and an artificial crack was introduced on the specimen surface by Vickers indentation method. Then the strength was measured by 3-point bending tests to examine the effects of grain size and artificial crack length on the bending strength of MgO sintered body. In the case of a crack shorter than the critical length, the bending strength was constant, irrespective of the crack length and equal to the strength of the smooth-faced specimen. Above the critical crack length, the bending strength decreased with an increase in crack length, which follows the rule of the linear elastic fracture mechanics, LEFM. The equivalent critical crack length, ac, calculated by means of LEFM, was not proportional to grain size, D, but it increased with an increase in D. The relationship between ac and D is expressed as ac=6.39+0.36D-2.89×10-3D2. Consequently, the bending strength, σ was apparently expressed by an equation, σ=262.2+402.3D-1/2.
Below the fibre saturation point, both Young's modulus and the compressive strength increase with decreasing moisture content. Consequently, most wood-handbooks show an approximate variation in mechanical properties with a change in moisture content below the fibre saturation point. On the contrary, there are some growing apprehensions for the characteristic rate of mechanical changes associated with a 1% change in moisture content. Therefore, this study aimed to confirm the effect of moisture content on Young's modulus and the compressive strength. The nine softwood species and the eleven sugi-cultivars tested in the study are given in Tables I and IV. Static compressive tests for small clear specimens gave Young's modulus E and the strength σ parallel to the grain. Both Ea/Eg and σa/σg were calculated to evaluate the effect of moisture content on the mechanical properties. Ea and Eg are Young's modulus in air-dry state and in water absorbed state. σa and σg are the strength in air-dry state and in water absorbed state. The result from the experiments is summarized as follows: (1) The Ea/Eg values for softwood species obtained in this experimental study are almost the same as shown in Table I, and the mean value calculated is 1.2. (2) The σa/σg values for softwood species are given in Tables II and III, and the values for sugicultivars in Table IV. The tables show some difference in the σa/σg values, but the difference is smaller among cultivars than among softwood species. (3) There is a tendency for nine softwood species that is apparently related to the cell wall percentage of latewood as shown in Fig. 5.
A back analysis system has been proposed for the structural design and temperature control of mass concrete structures. The system employs a nonlinear programming to heat transfer analysis using the finite element method. An effort was made to improve the efficiency of search, specifically in the case of the simplex method. Improvements were made on the following items: •Determination of the effective domain. •The shape of the initial simplex. •Judgement on convergence of the simplex in search. By using the proposed back analysis system, the inner heat generation of concrete is readily identified from the measurement results in a specimen made near a culvert box. Interior concrete temperatures are then calculated in the side wall of culvert box by using the identified results. The applicability of the back analysis scheme to estimate thermal characteristics from the field measurement results can be verified through a comparison of the calculated and measured temperatures in the culvert box.
This study has two major subjects, the use of a new material to the concrete structure, and the application of health monitoring system on the concrete structure. A glass fiber reinforced plastic (GFRP) rod was used for the concrete structure as tension reinforcement. The flexural loading test was carried out for the beam specimens both of GFRP reinforced concrete and conventional reinforced concrete. The health monitoring system which uses an optical fiber as a sensor of crack detection was manufactured by way of trial for this study and was discussed about the availability to detect the cracks. The followings were obtained from this experimental study; (1) The failure mode of the GFRP reinforced concrete beam was by shear failure combined with bending stress, though the conventional reinforced concrete beam failed in bending mode. The crack initiating load could be calculated precisely for both reinforced concrete beams, but the ultimate shear capacity could not be calculated accurately. (2) The cracks generated in the GFRP reinforced concrete beam propagated straightly upward even if in shear span, and then the beam suddenly failed by shear after the cracks began to decline obliquely. The developing rate of cracks was not uniform in bending span. (3) The crack detection system using the optical fiber, was effective to monitor developed cracks, though the flexural behavior was different between the GFRP reinforced concrete beam and the conventional reinforced concrete beam. Therefore, it was indicated that the health monitoring system using the optical fiber might be applied to the concrete beam structure.
In order to develop a nondestructive method of evaluating embrittlement for turbine casing steels, a study was conducted using lab-charged P-doped steels. P-doped steels showed evident embrittlement due to segregation of P at grain boundaries. The chemical etching test used was found to be a very good measure of embrittlement for casing steels. There was a good correlation between the width W of the etched grain boundary measured by the penetration of replicas and FATT. The correlation between W and FATT was also recognized for the samples taken from long-term-serviced casings. Multiple regression analysis was conducted in order to express FATT using W and other variables which are known or nondestructively measurable. The regression equation obtained gave an estimate of the actual FATT with the scatter of ±20°C. On the basis of this result a nondestructive evaluation method of temper embrittlement for turbine casing is proposed.