It is well known that the structures of the organisms give some important hints for the material development. To obtain a new idea on the optimum design of the material structures, the fore-wing of Allomyrina dichotoma was used and its mechanical properties and micro structures were investigated. As a result, the non-equiangular laminated structure and mechanical anisotropy of A. dichotoma fore-wing were made clear. The fracture processes of the fore-wing could be classified into two types, and their fracture mechanisms depended on the average lamination angle of chitin fiber layers. The bridging chitin fibers could not be observed in type I, while they were observed in type II. It was found that the fore-wing had the anisotropic tensile behavior, and using a parameter, η, the anisotropic tensile behavior could be represented. The results obtained here should be helpful for the optimum material design.
A novel computational method for deep-drawing simulation of composite materials has been proposed with taking a three-dimensional continuum mechanics approach. The most notable feature is the consideration of micromacro coupling effects by the mathematical homogenization theory. The homogenized properties and the constitutive law are evaluated carefully using the three-dimensional microstructure model under the large deformation and biaxial loading conditions. In this paper, the knit reinforcement of aramid fiber is studied, which has very complex microstructure architecture. The polypropylene is used as the matrix. The newly developed deep-drawing simulation provides us the macroscopic deformation, strain, stress and stiffness distribution as well as the largely deformed microstructures in the deep-drawn product. The high-speed computing technique which has been developed in the previous report enables us to carry out the micro-macro coupled nonlinear analysis easily on the personal computer. The experimental work has also been conducted, and the largely deformed microstructures are compared between experiment and simulation. A good coincident was obtained, which implies the validity and reliability of the proposed computational method.
SMC (Sheet Molding Compound) is suitable for mass-production of FRP. It is usually formed in compression molding. But this molding has some problems. Therefore we propose the application of the roll forming to SMC, expecting the decrease of forming energy, short production time and controllability of fiber orientation. These studies have been carried out about the influence of parameters, such as reduction, tension between roll stands and so on. But this study has not been carried out about the influence of other parameters, such as roll velocity, roll diameter and so on. And also, the forming conditions contributing to short production time have not been found out yet. In this paper, for investigating the forming conditions contributing to lateral spread and short production time, we carried out the experiments about the influence of important parameters on load and deformation characteristics. Secondary, I estimated a optimum condition made from the results acquired by the above experiments. As the results, we obtained that lateral spread increases with increasing roll velocity and roll diameter. And also, we found out production time decreases with increasing reduction and roll velocity. Finally, we suggested the forming condition contributing to the formability of flange part and short production time. And we could make forming cycle decrease by 58.3 percent and flange height increase by 15.9 percent.
Hollow particle filled epoxy composites are fabricated by an ordinary molding technique. Young's modulus, tensile strength, fracture toughness and dielectric constant are measured as a function of density of the composites (i.e. wall thickness of the hollow particles). Specific strength is almost flat irrespective of the density, while specific modulus and the dielectric constant increase, and the fracture toughness simultaneously decreases with the decrease in the density. Fracture path varies from fractured particles in the case of particles with thinner shell to interfacial debonding in the case of thicker shell in the fracture toughness tests, while particle fracture is predominant in the tensile tests. In-situ observation of the material tests and finite element analyses are utilized to interpret the deformation and fracture behaviors and also to estimate the in-situ strength of silica. It is clarified by the observation that particles larger than 30μm in diameter are predominantly damaged and smaller particles less than 15μm are never fractured. Premature fracture of such coarse particles in early stage of loading is attributable to the strength properties. The in-situ strength of silica increases with the decrease in the particle diameter. According to the result of the finite element analysis, stress concentrates near inner surface along an equator under uni-axial loading, and this tendency becomes remarkable with the decrease in the wall thickness. On the other hand, interfacial stress decreases rapidly with the decrease in the wall thickness. The stress concentration along the equator is relaxed under multiaxial loading which is possible in the fracture toughness tests. All of these results indicate that elimination of the coarse particles is essential to improve the tensile properties, and that interfacial modification is effective only for toughness enhancement. SiCp reinforced Al2O3 and SiCp reinforced aluminum composites are also analyzed numerically to evaluate the efficiency of introducing hollow particles into ceramics and polymer materials.
Mixed mode (I+II) fracture toughness of the Interlayer-toughened composite laminates, T800H/3900-2 (Toray), which is a newly developed composite material having a tough ‘interlayer’ containing fine polyamide particles, was investigated over a very wide range of loading rate from static to impact. The MMF (Mixed Mode Flexure) specimen and SHPB (Split Hopkinson Pressure Bar) system were employed for measuring the mixed mode fracture toughness under impact loading. The strain rate dependence of fracture behavior was also studied from both macro- and microscopic aspects to clarify the mesoscopic fracture mechanism of the material. The experimental results showed the crack path was inside the toughened interlayer during the initial stage of crack growth, however, it moved from the toughened interlayer to the carbon/epoxy base lamina during the propagation stage of crack growth. The mixed mode fracture toughness was sensitive to loading rate; the impact fracture toughness for the toughened interlayer was about 23% lower than the maximum value under static loading, and the impact fracture toughness for the carbon/epoxy base lamina was about 11% lower than the maximum value under static loading. The effects of mode mixture varied with loading rate for interlayer fracture, though they did not varied for base-lamina fracture. Microscopic observation showed that the fracture morphology was sensitive to loading rate.
This paper proposes a novel computational method for the evaluation of the permeability of fiber reinforced composite materials with complex microstructures. The homogenization theory for solid-fluid mixture is employed to characterize the micro-macro coupling effects. A characteristic function associated with the flow velocity is derived, whose average is defined as the permeability tensor. The derived relation between the macroscopic velocity and pressure gradient coincides with the conventional Darcy's law. Therefore, the proposed method enables us to predict the permeability tensor numerically without any experimental work. Furthermore, the characteristic function provides useful information to understand the correlation between the microscopic architecture and the macroscopic permeability tensor. Once the permeablity tensor is given, we can use a conventional process simulator under the realistic process conditions. The macroscopic pressure gradient is obtained, which leads to the analysis of the actual microscopic flow field in the microstructure. The proposed microstructure-based evaluation can be used as the pre/post-processing of the conventional macroscopic process simulation. Three-dimensional modeling and analysis are shown for textile composites with the help of finite element method.
In the present study, an electric resistance change method is adopted for the identifications of location and size of the embedded delaminations. Indentation tests are conducted to create embedded delamination cracks in CFRP plates. Two lines and eight columns of electrodes are mounted on the plate surface for measurements of electric resistance changes due to delamination creations. Response surface methodologies are applied to obtain the relation between the delaminations and measured electric resistance changes. The effect of temperature change is experimentally measured using the plate specimen. As a result, the method can successfully estimate the location and size of embedded delaminations, and the effect of the temperature change is neglectable by using compensation for temperature change.
In order to develop a methodology for creep damage evaluation of W alloyed 9%Cr ferritic steel KA-STBA29/KA-STPA29 (ASME T92/P92), which is the candidate material for an ultra-super-critical fossil power plant, changes in electrochemical property of the steel caused by creep have been investigated. Experimental results on electrochemical polarization measurements revealed that the peak current density “Ip”, which appeared at a specific potential during potentiodynamic polarization measurement in 1N-KOH solution, increased with thermal aging and creep damage and reflected not only the thermal effect but also the stress effect on creep damage. The Ip value corresponded to the selective dissolution volume of precipitates (M23C6 and Laves phase) and the increase in the Ip due to creep damage reflected the increase in amount of chromium precipitated as Laves phase. It was also found that the difference in the Ip value between the as-tempered material and the creep damaged materials (ΔIp) were uniquely correlated with a newly proposed parameter “t·F(T)·exp(-Q(σ)/RT)” irrespective of test conditions, which is the parameter based on Laves phase precipitation kinetics. On the basis of such correlation between ΔIp and t·F(T)·exp(-Q(σ)/RT), the test temperature or the applied stress of the creep damaged materials can be nondestructively estimated by electrochemical polarization measurements.
High temperature fatigue life assessment is one of the important issues in Ni-based superalloys for a gas turbine blade. Generally speaking, however, a superalloy with higher strength has larger scatter in fatigue life at a given cyclic loading condition in comparison with conventional steels and alloys. In this study, focusing on the behaviors of fatigue crack initiation and propagation at the internal defects of eutectic γ'phase in a Ni-based single crystal superalloy (MDSC-7M), a cause of the scatter in the fatigue life of the superalloy was discussed by conducting a series of fatigue tests at 1173K. In particular, the propagation of fatigue cracks initiating at the internal defects was characterized quantitatively by means of the beach-mark method. As a result, the fatigue crack propagation rate could be correlated well with the stress intensity factor range, including a small crack of 100-150μm. It was also found that the crack propagation life (i.e., the number of cycles to failure after crack initiation) was more than 40% of the total life (i.e., the number of cycles to failure). The scatter in the fatigue life of the material tested seemed to be mainly caused by the scatter in the crack initiation life. Finally, the lower limit of the scatter could be successfully predicted with the crack growth simulation conducted for the maximum eutectic γ' phase which should be in a fatigue test specimen.
Cantilever-type rotating bending fatigue tests were carried out on high carbon chromium bearing steel in air at room temperature. Concerned with the subsurface fracture type specimens, the fatigue lives were related to three factors which are the stress amplitude at nonmetallic inclusion, the inclusion size and the granular fracture surface size around inclusion. That is, these factors can be connected to the parameters in the equation of Paris' law. Thus, crack propagation lives at flat fracture surface in fish-eye region were analyzed using fracture mechanics. It was found that the period forming granular fracture surface occupied more than 90% of the total fatigue life. It was another finding that effective factors to expand the fatigue life of this steel were smallness of the inclusion size and high value of the matrix fracture toughness.
Elastic-plastic analysis was carried out for a Mode I interlamellar crack embedded in unidirectionally-fiber-reinforced composites by means of the finite element method. The stress distribution in the vicinity of a crack tip was calculated for various crack lengths and various combinations of elastic constants for fiber and matrix. When both fiber and matrix are elastic, the stress intensified region ahead of the crack tip was divided into three regions. In the region nearest the crack tip (Region I), the distribution of stress, σy, which is the normal stress perpendicular to the crack plane, was given by the stress intensity factor, Kcom. Kcom is obtained assuming that the composite is actually composed of two parts which have different elastic constants. On the other hand, the stress distribution in the farthermost part in the stress intensified region was given by the stress intensity factor, Khomo (Region III). Khomo is obtained regarding the composite as homogeneously orthotropic. Between these regions, the stress distribution was undulated (Region II). As Kcom and Khomo can be evaluated analytically using elastic constants of fiber and matrix and Region II always appears at a distance from the crack tip equal to the thickness of matrix, the stress distribution can be predicted without carrying out numerical analyses such as a finite element analysis. When the matrix is assumed to be elastic-perfectly plastic, the length of yield region and the stress outside the yield region can be estimated from the yield stress of the matrix and the stress distribution predicted for the case where the matrix does not yield.
In order to evaluate the delamination strength of Y2O3-ZrO2 ceramics coating deposited on Co-based superalloy with CoNiCrAlY bond coat, the tensile test and the edge-indent test were carried out. When the tensile load is applied to the specimen, the ceramic coating is divided by parallel cracks, and the cracks propagate not only along the interface but also into the bond coat layer until the delamination of top coat. With an additional load, the bond coat layer also delaminates. The equation to obtain the critical strain energy release rate GCi/i+1 or the interfacial fracture toughness between i and i+1-th layers for the coating of (n-1) layers on a substrate is introduced fracture-mechanically, and the experimentally measured GC1/23 between the ceramic coating layer and the bond coat layer is lower than that between the CoNiCrAlY bond coat layer and the substrate. The delamination energy of ceramic coatings measured by the edge-indent tests almost correspond to GC1/23. Both the tensile and the edge-indent methods are applicable to evaluate the delamination strength of double layer coating specimen as well as the single layer coating specimen.
Corrosion behavior of AlN ceramics in water at 100°C and corrosion resistance of those pre-oxidized or metallized were investigated. The weight of AlN parabolically gained by reaction with water. Al2O3 layer formed by high temperature oxidation reduced the corrosion of AlN and weight gain of the specimens with 2μm thick Al2O3 layer was 1/10 or less after corrosion for 10d. Weight change of the specimens with AlOOH layer formed by hydrothermal treatment was not found after corrosion. In the case of the specimens metallized 3μm thick Ni or Cu film by sputtering method, the film was oxidized but the corrosion of AlN substrate was not found. Al2O3 and AlOOH layer prepared by oxidation of AlN and sputtered Ni or Cu film improved remarkably the corrosion resistance of AlN substrate.
The influence of limestone powder content on setting, strength and autogenous shrinkage of high-flow concrete were discussed. Ordinary Portland Cements were used with additions of 0, 10, 20 and 30wt% limestone powder. Setting of concrete was accelerated by additions of limestone powder. Strength decreased with the additions of limestone powder, but a slight decrease of compressive strength was found with addition of 10wt%. Compressive strength of concrete increased linearly with decreasing the porosity with or without additions of limestone powder. Autogenous shrinkage decreased with increasing the additions of limestone powder in the early stage, but kept increasing for long time with limestone powder. It was suggested that the increase of autogenous shrinkage due to additions of limestone powder in the long stage related to Monocarbonate.