An attempt was made to disperse stably RTV-silicone as fine particles in bisphenil-A type epoxy resin by the addition of silicone-methyl methacrylate graft copolymer. The size of the silicone phase decreased to lower than 1μm with the addition of the graft copolymer. The toughness of the modified resin increased with a decrease in the diameter of silicone phase. In the region where the diameter of the dispersed phase was less than 1μm, the fracture toughness of the modified system became higher than that of the unmodified system. It is suggested that the toughening of the modified system is mainly caused by the cavitation of the fine rubber phases.
Films of poly-l-lactic acid were stretched under a novel dry-process. In the case of uniaxial stretching with free width, the stretching attained a stretch ratio up to MD×TD=3.5×1', in the case of uniaxial stretching with constant width, up to 3.0×1.0, and in the case of simultaneous-biaxial stretching, up to 2.5×2.5. The crystalline phase of uniaxially stretched films with free width had uniaxial orientation, like a fiber. For the uniaxially stretched films with constant width, however, the crystalline phase had uniplanar-axial orientation, And, the crystalline phase of simultaneous-biaxially stretched films, showed uniplanar orientation at all stretch ratios. The mechanical properties, transparency, crystallinity and degree of molecular orientation of the films were improved by this novel dry stretching process. Particularly, tensile strength and Young's modulus to machine direction increased for all the stretched films.
The fatigue properties of short fiber reinforced polycarbonate fabricated with injection molding were discussed. As the results, it appeared that the fatigue properties are affected by surface treatment of fibers, fiber content, frequency of testing, etc.. The effect of surface treatment was same as that in tensile test. It indicated that the optimization of surface treatment can be executed by comparing the tensile strength of products. The specimen treatment with an aminosilane coupling agent and a urethane binder showed the best fatigue property in this study. By this treatment, the fatigue limit increased with increasing fatigue frequency. It can be attributed to the decrease of AE energy during testing. The frequency dependence, however, changed to quite the opposite under the elastic limit when the fiber content was 10wt%. It was caused by the thermal failure occurring at the surface of specimen.
Pitch-based carbon short fibers (PCF) treated with five kinds of coupling agents(CA), were added by 22.2wt% to fill three kinds of multi-functional epoxy resins cured with three kinds of acid anhydrides as hardener. Several mechanical properties of the composite materials were studied by using a Rheovibron in the temperature range from -150 to 300°C, and by using an Instron tester. The glass transition temperature(Tg) of the composites filled with CA-treated PCF (CA) was higher than that of the composites filled with untreated PCF (UT). The storage modulus (E')of the composites filled with CA-treated PCF increased also in a wide temperature range, including the glassy region at low temperature (-140°C) and room temperature (25°C), up to high temperature (200°C). However, the increase in both Tg and E' depended on the combination of epoxy resin and hardener. The values of E' of the composites at 25°C were larger than those estimated from the rule of mixture or Halpin-Tsai equation modified by Nielsen et al.. It was also found that the effect of CA-treatment on the flexural strength of composite materials was small. In the case that the matrix of composites became brittle, the effect of CA-treatment on the flexural strength appeared remarkably large. Consequently, the multi-functional epoxy resins can be made a composite material having higher heat resistant and higher modulus by filling it with CA-treated PCF.
Hydrophilic segmented polyurethane was prepared from hydroxyl terminated poly (ethylene oxide)-poly(tetramethylene oxide)-poly(ethylene oxide) triblock copolymer (HT-ETE), 4, 4'-diphenylmethane diisocyanate (MDI) and ethylene glycol (EG). HT-ETE consists of poly (tetramethylene oxide) (PTMO) segment of molar mass 2000 at the center and poly(ethylene oxide) (PEO) segment of molar mass 1020 at both ends. The hard segment content of the polyurethane is 18wt%. The polyurethane elastomer showed low modulus up to ca. 600% elongation. Tensile strength at break (TB) of dry film was ca. 13MPa, and that of wet film with water content of 98% went up to ca. 5MPa. The introduction of PEO to the end of PTMO brought about the characteristic morphology, i.e., the microphase separation was clearly observed and the distance of hard segment domains was smaller than that of segmented polyurethanes prepared from PTMO, MDI and EG. This morphology, together with the length of soft segment and the properties of hard segment domain, was considered to make the mechanical properties of the hydrophilic polyurethane closer to a soft tissue.
The complex Young's modulus, E*(ω), and the complex strain-optical coefficient, O*(ω), of a polystyrene (PS)/bisphenol A polycarbonate (PC) blend and a graft copolymer were studied in the glass-to-rubber transition zone at frequencies ranging from 1 to 130Hz at various temperatures between 102°C and 182°C. The relaxation behaviors in E*(ω) and O*(ω) of two alloys were compared with each other in relation to the relaxation behaviors of constituents, PS and PC. It was clarified that for the blend in the mechanical spectrum two isolated relaxation peaks are detected at frequencies apart from each other, which means that the consitituents relax independently. For the copolymer two relaxation peaks of constituents were almost merged giving rise to about a single peak which indicates cooperating relaxation of the two components. The optical relaxation spectra, O*(ω), of two alloys showed distinct difference in quality and it also made us predict their compatibility to some extent. For both alloys, the stress-optical coefficient, CR, in the rubbery zone was reduced to 1/4-1/6 of the absolute value of components polymer as a result of compensation of the opposite-signed birefringences of constituent polymers. The photoelastic coefficient, Cd, for two alloys and the component polymers, PS and PC, exhibited a strong correlation with the stress-optical coefficient, CR.
Deterioration of corrosion resistance surface is attributed to the penetration of solution in environment. Therefore, the investigation on its penetration behavior is an important factor in studying lining deterioration. In this paper, the performance of organic lining made of vinyl ester resin was discussed based on the results of the following three determinations: (I) Moisture contents in the substrate and organic lining (interfacial area) by using a moisture sensor. (II) Weight increase and hardness change of the resin itself after immersion in the environmental solutions. (III) Residual adhesive strength of the lining in contact with the environments. The main results are summarized as follows: (1) For the environmental solutions with low osmotic pressure, the penetration of moisture into the interfacial area was relatively fast. On the other hand, for those with high osmotic pressure, the penetration was slow and the amount of moisture in the lining was likely to saturate in a shorter time. (2) At the initial stage, the penetration of solutions in resin was influenced by osmotic pressure strongly and the weight increase is less for those with high osmotic pressure. However, chemical substances such as HNO3, NaOH and KOH caused more weight increase in a prolonged immersion. (3) During the initial stage, the decrease of adhesive strength is caused by penetration of moisture. After that, the chemical property of the environmental solutions governs the adhesive strength and the effect depends on their constituent and concentration. (4) Though the changes in weight and hardness of the resin itself are relatively small, a drastic adhesion failure may take place and the lining resin may not serve its purpose. So, it is necessary to take the above-mentioned results into consideration.
This paper presents some experimental results carried out to investigate dynamic constitutive relationship of material from a view point of dynamic plasticity. Three kinds of experiments were executed on annealed pure copper; the jump test in which the strain rate is suddenly changed from quasi-static to dynamic, the dynamic test in which dynamic load is applied to the specimen and the dynamic reloading test in which a dynamic load is applied to the specimen previously strain-hardened to some extent. The experimental procedure is based on the torsional stress bar method, where the dynamic stress and the corresponding strain are measured at one point of the specimen in purely dynamic manner. It has been revealed that in the jump test the over-stress is uniquely related to the instantaneous plastic strain rate all through the dynamic deformation process. On the other hand, in the dynamic and dynamic reloading tests the behavior was different from the jump test such that in the initial stage of increasing strain rate the over-stress lies above the curve determined from the jump test but tend to coincide in the decreasing stage. These results are interpreted from microscopic viewpoint of dislocation motion and it is concluded that the mechanism of the rate sensitivity is same in all the cases, but the mobile dislocation density is different at the start of the dynamic plastic deformation in each test.
A bi-material problem is analyzed for bonded dissimilar two half-planes using a rational mapping function and complex stress functions. The half-planes are bonded in the finite length with cracks and subjected to coupling force and external force applied at infinity. The cracks have the same length at an end of the interface and perpendicular to the interface in each material. This analytical model can be used for the investigation of the crack initiation from the interface debonding tip. The stress analysis is carried out and the stress distribution and stress intensity factors are obtained. By focusing on an interface debonding tip, it is possible to decide analytically the fracture phenomena. The conditions of occurrence of debonding extension and crack branching are examined under different coupling and external forces for various material constants.
Extruded Al-8wt.% Zn-1-2.5wt.% Mg-1.2wt.% Cu-4wt.% La alloys with high tensile strength and good stress corrosion cracking resistance were developed and their fracture toughness was investigated. The effect of metallurgical parameter on the fracture toughness value was examined. The main results are as follows; (1) The fracture toughness values of the extruded Al-8wt.% Zn-1-2.5wt.% Mg-1.2wt.% Cu-4wt.% La, which were about 20MPa√m without anisotropy, were not influenced by Mg content. (2) The second phase particles in the extruded alloys, which consisted of Zn and La, were estimated quantitatively. The mean diameter was about 4.7μm and the volume fraction of the particles was 1.6-2.3vol.%. (3) The second phase particles consisting of Zn and La in the extruded alloys cracked easily, and became the nucleus of voids when the matrix fractured. The fracture toughness of the extruded alloys was affected by the particles. The fracture toughness value, KIc, was related to the volume fraction of the second phase particles, fv, and the mean diameter of the particles, D, as follows: KIc≈[ζσ0.2E(π/6)1/3D]1/2·fv-1/6∝(DEσ0.2)1/2·fv-1/6 where ζ is constant, σ0.2 is 0.2% proof stress and E is Young's modulus.
Fracture toughness tests were conducted by using compact specimens of a sialon in the temperature range from room temperature to 1500°C. At elevated temperatures, a fracture initiation and a fracture resistance curve (R-curve) were evaluated by the multiple specimen method. The fracture toughness, Kc, at unstable fracture by cleavage becomes constant up to 1200°C. Then, it increases up to 1400°C. At 1500°C, the fracture occurred in a stable manner. Above 1200°C, a stable fracture by grain pull out (intergranular fracture) proceeded before unstable fracture. An area percentage of grain pull out increases with temperature rise which brings an increase in slope of R-curve. However, the fracture toghness, Kin, at the initiation of stable crack growth takes maximum at 1400°C and it decreases drastically at 1500°C. So, the viscous flow of glassy phase along grain boundary has a beneficial role on the toughness between 1200°C and 1400°C.
X-ray fractography is a method of analysing the causes of accidental fracture of machine components or structures. Almost all of the previous research on this problem has been carried out using constant amplitude fatigue tests. However, the actual loads on components and structures are usually of variable amplitudes. In this study, X-ray fractography was applied to fatigue fractured surfaces produced by variable amplitude loading. Fatigue tests were carried out on Ni-Cr-Mo steel CT specimens under the conditions of repeated, two-step and multiple-step loading. Residual stresses were measured on the fatigue fractured surface by an X-ray diffraction method. The relationships between residual stress and stress intensity factor or crack propagation rate were studied. They were discussed in terms of the quantitative expressions under constant amplitude loading, proposed by the authors in previous papers. The main results obtained were as follows: (1) It was possible to estimate the crack propagation rate of the fatigue fractured surface under variable amplitude loading by using the relationship between residual stress and stress intensity factor under constant amplitude loading. (2) The compressive residual stress components on the fatigue fractured surface correspond with cyclic softening of the material rather than with compressive plastic deformation at the crack tip.
As a part of the development of a rational structural design method and in order to formulate a strength evaluation method for high-cycle thermal shock (thermal striping) in the high temperature structure, we have developed an original experimental facility which can provide cyclic thermal load with liquid sodium at a frequency of ω=0.01 to 2.0Hz between a maximum temperature Tmax of 550°C and a minimum temperature Tmin of 250°C. The following results are obtained. (1) The thermal behavior test using this facility for Type 304 S.S. has revealed that the temperature fluctuating region is limited near the surface and within 0.8mm from the metallic surface under a cycling rate of ω=0.5Hz or greater. (2) With the thermal striping condition of Tmax=550°C, Tmin=250°C, and ω=0.5Hz, the spaces of the dry clay-like cracks vary from 1 to 2mm, and the cracks are arrested at a depth of approximately 1.6mm after 2.0×106 cycles. (3) The above mentioned test verifies that the depth of the arrested crack can be roughly estimated by the linear elastic fracture mechanics of edge cracks distributed by a certain pitch.
Fretting fatigue tests of HIP-sintered silicon nitride were carried out to discuss the dominant mechanical factors influencing fretting fatigue behavior. The fretting fatigue strength of silicon nitride was not necessarily decreased with increasing the contact load (contact pressure), which is in contrast with the case of metallic materials. This contrary behavior of ceramics results from that the relative slip amplitude between specimen and contact pad increases with decreasing contact load. Furthermore, even under a constant relative slip amplitude, the ratio of the relative slip amplitude to the contact radius varied with contact load, which has an influence on fretting wear behavior and consequently on fretting fatigue behavior. These results suggest that the fretting fatigue strength of silicon nitride is affected not only by frictional force but also by the condition of partial slip in the contact region, that is fretting wear behavior.
A large number of high tension bolts are used in highway and railway bridges. High tension bolts are known to be susceptible to delayed fracture in humid environments. In order to assure the safety of bridges, these bolts are subjected to in-service inspection by sampling. In the present paper, a reliability analysis is carried out for inspection by random sampling at a constant interval. First, a theoretical equation of the reliability of a bolt subjected to inspection and replacement is derived as a function of n and q, where n is the number of inspections during the design life and q is sampling fraction. Then, by using this equation, numerical examinations are conducted for several cases to find possible combinations of n and q which satisfy a given reliability requirement. The time to failure of a bolt is assumed to follow a two-parameter Weibull distribution. The results show that the reliability of a bolt subjected to inspection and replacement is almost determined by the product of n and q.
A technique for controlling primary particle diameter, secondary particle length and magnetic properties of ultrafine iron particles prepared by pyrolysis of Fe(CO)5 has been studied. A relation between fractal dimension as a parameter of shape of the secondary particles and magnetic properties has been also studied. The length of secondary particles is closely related in the primary particle diameter; the larger the diameter, the longer the length. It is affected by the feed concentration, residence time and pre-decomposition ratio of Fe(CO)5. The coercive force of the iron particle powder reaches its maximum value of 120kAm-1 at the primary diameter of 20-25nm. The squareness Br/Bm of video tapes is improved by using longer secondary particles. It is also improved by using particles with smaller fractal dimension. The shape of secondary particles can be characterized by using fractal dimension; the smaller the dimension, the larger the squareness of video tapes.
Cyclic thermal stress tests were carried out by using aluminum chip embedded resin specimens as the model of an insulating epoxy material for semiconductor packaging or electrode molding in large scale apparatus, and the morphology of fracture pattern and the reliability were discussed. The tests showed four types of fracture patterns, and the life distribution of each fracture pattern obeyed Weibull distribution. Thus, in the case where the specimen fractured with several patterns, the statistical study has to be carried out for each pattern by determining the life distribution for each one in detail. The experiments made in different heating baths at various temperature conditions showed that the effects of these variables on lives depended on fracture patterns. The test results of the experiments with constant temperature difference showed that the mean life decreased with decreasing temperature range above the glass transition temperature (Tg). On the other hand, the test results with constant cooling temperature indicated that the temperature difference above Tg had an influence on the mean life, though the effect was less than that in the glassy state range.
An interference method is applied to the measurement of stress field in the vicinity of a fast propagating crack tip. A parallel light beam impinges upon a transparent plate specimen perpendicularly to the surface. A crack is being propagated through the specimen at a speed of five hundred m/s or more. The incident light is partly reflected either by the front surface of the specimen or by the back surface of it. The two reflected light waves interfere each other and interference fringes appear on the specimen. The interference fringes indicate the equi-thickness lines along which the sum of the principal stresses is kept constant. In the directions of 0, ±36 and ±72 degrees from the propagation direction of the crack, the orders of the interference fringes are measured as a function of distance r from the crack tip. And the dynamic stress intensity factor is obtained in each direction, respectively.
A new effective three-dimensional boundary element method of analyzing electric field produced by localized corrosions has been developed to estimate the accuracy of SVET (Scanning Vibrating Electrode Technique). With decreasing height of the electrode probe from the surface of a sample in an attempt to improve the resolution of SVET, the electrode probe disturbs the electric field and the measuring error of the current distribution increases. It is, therefore, desirable that this error is corrected by numerical analysis considering the disturbance of the electrode probe. However the scale ratio of the whole vessel of the instrument to the measurement area is larger than a factor of 105, so that the conventional BEM has a difficulty in treating such a huge number of elements. In this study, at first the distribution of current density on the slender surface of a sample where current flows out was analyzed with the two-dimensional BEM and then a three-dimensional Boundary Element analysis was performed by considering the slender surface as a simple line-shape element which has the characteristics obtained by the first 2-D analysis. By using the proposed method, the number of elements and repetitive calculations due to scanning of electrode probe can be decreased. A few numerical examples are presented to demonstrate the practical applicability of the proposed method.