Basics of acoustic emission (AE) detection and the theory of AE waveforms are summarized. Measuring systems and AE parameters are discussed with a brief review of historical developments. Theoretical treatment leads to kinetics of crack motion by the deconvolution analysis and kinematics on crack type and crack orientation by the moment tensor analysis (SiGMA). With increasing need for maintenance, the nondestructive evaluation of in-service structures is being actively investigated. AE techniques look promising as a means of inspecting concrete structures and evaluating their structural integrity. Applications to construction monitoring are also receiving fresh attention. These practical applications are updated, along with fracture mechanics by SiGMA.
The 6Na2O·31B2O3·63SiO2 (in mol%) glass was chosen. The photoluminescence (PL) characteristics of Eu3+ doped in the glass, which was subjected to different phase separated heat treatments, were investigated systematically. It was found that PL intensity of 5D0→7F2 transition of Eu3+ increased with phase separation developing. Furthermore, the maximum PL intensities obtained by the different heat treatment processes seem to depend on the morphology induced by phase separation, the droplet morphology having the advantage over the interconnected one with the PL intensities of 6.4 and 5.5 times as high as that in the as-cast sample, respectively. The mechanism of enhancement of the PL intensity was then discussed on the basis of the derived expression of the PL intensity. It was concluded that the induced interface after phase separation, engendering significant increase in light scattering intensity and thereby notable increase in the population of Eu3+ on the 5D0 energy level, accounted for considerable increase in the PL intensity. On the other hand, from the emission intensity ratio of the 5D0→7F2 to 5D0→7F1 transitions (R) of Eu3+, the phases into which Eu3+ segregated after various phase separation processes were estimated.
Ni-PTFE composite films with water repellency have been prepared by the electrodeposition in the nickel sulfamate plating bath in which PTFE fine particles are suspended by using a cationic surfactant. The maximum content of PTFE in the composite film was 17wt%. Above the contents of 12wt%, the contact angle of a water drop on the surface reached 156° in maximum. The surfactant was co-deposited with PTFE particles in the electrodeposited Ni-PTFE composite film. This causes that the water repellency on the surface of the film falls after the neutral salt spray test (NSS) and the thermal cycle tests. The heat-treatments above 300°C were effective to maintain the water repellent surface even after the weathering tests, while the surface morphology changed by the heat-treatment.
In this paper, a design procedure of the microstructure of composite materials is proposed for the emergence of desired macroscopic function. The homogenization method is used for the expression of the correlativity between micro- and macroscopic properties, and genetic algorithms (GA) is used to solve the optimization problem. Using the micro-macro correlative database of material properties constructed by the homogenization method, the design problem is separated into micro- and macroscopic sub-problems. Thus, the proposed procedure is quite efficient and extendable to various design problems of new advanced materials such as functionally gradient materials. As an example, a plate of graded micro-porous materials, that is free of warp and/or twist under the environment with temperature gradient from the upper to lower surfaces, is shown.
This paper presents the vibration damping of a sandwich plate fabricated by the sandwich injection moldings. The sandwich plates used in this work consist of polystyrene (PS), or polycarbonate (PC) as a skin layer and two different kinds of elastomer (FL or TH) as a core layer. FL is the elastmer in polyester group, and TH is the elastmer in olefin group. FL has more excellent adhesive property for the two skin materials, as compared with TH. Vibration tests were performed to obtain the logarithmic damping factor, by applying an impulse with a hammer on the central portion of the plate under the perfect free boundary condition. Also the relationship between core volume fractions and the damping properties were measured. It was found that PS/FL had the highest vibration damping in the plates with PS skin layers, whereas TH has higher damping property than FL. The rate of increasing in vibration damping was larger in PS/FL than in PS/TH, with increasing volume fraction of core material. The above results indicate that the adhesive property between core and skin layers makes a great influence on the damping property of the sandwich plate.
In this paper the stress-strain behavior of concrete confined by various types of FRP in the form of spiral or sheet is discussed. An experimental investigation is described, in which the main parameters are fiber volume fraction, fiber stiffness modules, fiber tensile strength and concrete strength. On the basis of the experimental results a model for stress-strain relation of concrete confined by FRP is developed which takes into account the linear elastic behavior of the FRP. The model, which will be useful in deformation analysis of FRP-concrete flexural members, utilizes an exponential equation for the ascending branch and a linear equation for the descending part. The confinement effect is expressed as a simple function of fiber volume fraction of confining FRP, its modulus of elasticity and compressive strength of unconfined concrete. A good agreement with experimental results is obtained.
The method of the analysis of a crack with bridging fibers in an infinite orthotropic elastic plate under remote uniform tensile stress is utilized to evaluate the mechanical properties of a hybrid composite with plual kinds of reinforcement fibers. Based on the evaluation of the tensile stress of the bridging fibers, the increment of the tensile stress loaded on the plate of the hybrid composite is confirmed by comparing the tensile stress calculated for the plate of composite reinforced by only one kind of fiber, which is the parent composite of the hybrid composite. The increment is affected by the interfacial shear strength of fiber and matrix, the length of crack and the number of bridging fibers.
Under conditions specified in this work, mechanical properties of commercial alumina, silicon carbide, silicon nitride and zirconia ceramics were selected from published manufacturers' catalogs. Numerical data of the selected properties for materials of 254 kinds in total were finally compiled in a computer-readable database. Interrelations among these properties were analyzed by using the database, and analyzed results were discussed. The selected properties of Young's modulus, linear thermal expansion coefficient, bending strength, Vickers hardness and fracture toughness were correlated with an apparent porosity derived from the theoretical and bulk density. Relationships of the selected properties to the porosity were fitted to exponential functions, and a good fitness was confirmed in most of the cases with a few exceptions. In general, every mechanical property tended to decrease with increasing the porosity. Although the hardness variation with respect to the bending strength was expressed by a proportional relationship for alumina and silicon carbide, a power relation was more adequate for silicon nitride and zirconia. The relation between the fracture toughness and the bending strength was fitted to a power function. In this case, a good fitness was identified for silicon carbide and zirconia, though a poor correlation was found for alumina and silicon carbide. A specific crack length, which was used to modify a fracture mechanics criterion for small cracks, was well correlated with the bending strength by a power function.
Using the X-ray method of stress measurement for Ti-6Al-4V alloys, the residual stress near the crack was measured for annealed (AN) and solution treated and aged (STA) titanium alloys, under the condition that the measured X-ray stress was in satisfactory agreement with the applied stress under tension. The residual stress measured in the wake of the propagating fatigue crack, σr, was compressive, resulting in a smaller crack opening displacement, COD, than theorized. The measured σr and COD-values let us understand the fatigue crack propagation rate da/dN in terms of the effective stress intensity factor Keff. As a result, the da/dN under the same Keff-value was smaller in the AN specimen with zigzag crack growth than in the STA specimen with straight crack growth, although the da/dN-Keff relationship under various stress amplitudes was represented by a straight line in a log-log scale separately for the AN and STA specimens.
Fatigue crack propagation tests with compact type (CT) specimens were carried out using three kinds of cast aluminum alloys designated AC4CH, AC1B and AC7A, which were subjected to hot isostatic pressing (HIP) treatment to reduce microshrinkage. Although the HIP-treated AC4CH showed a significant improvement of high-cycle fatigue strength under a rotating bending load, the crack propagation rate was the highest and the crack propagation threshold was the lowest among the materials included with a conventionally produced AC4CH. Since AC4CH has a eutectic microstructure, and since many fine eutectic silicon particles exist, fatigue cracks propagate easily along the eutectic part of the microstructure. The difference in crack propagation behavior represented by da/dN-ΔK relationship was well evaluated in terms of ΔKeff. Microshrinkage was found to cause a considerable rough fracture surface and secondary cracks, and appeared to conduce the crack closure.
The rotating bending fatigue properties of normal shot-peened (SP) and hard shot-peened (HSP) 316L austenitic stainless steels were investigated from the viewpoints of the changes of hardness distribution and compressive residual stress distribution during the high-cycle fatigue test. The investigation of the crack growth behavior was also carried out using a replication technique. It was found that the fatigue strength was improved by shot-peeving treatments, and the fatigue crack propagation mechanisms were clarified in the SP and HSP specimens. The fatigue crack growth behavior in the SP and HSP specimens was completely different from that of the non-peened specimens. The differences were caused by the change of the hardness distributions and the residual stress distributions during the fatigue test.
The effect of microstructure on creep and creep-fatigue behavior at 773K was studied in the Ti-6Al-4V alloy having three different microstructures. The three types of microstructures prepared using different heat treatment conditions included the equiaxed α structure, lenticular α structure and bimodal (composed of equiaxed α and lenticular α) structure. Creep tests were carried out under constant load conditions at 773K in air. Creep-fatigue tests were carried out under total strain controlled conditions using a trapezoidal waveform with hold times of 2min and 10min at 773K in air. Creep rupture strength of the alloy with equiaxed α structure was similar to that of the alloy with lenticular α structure and was higher than that of the alloy with bimodal structure. The number of cycles to failure under creep-fatigue condition of the alloy with lenticular α structure was lower than that of the other two structures. The effect of microstructure on crack propagation life was small as compared with crack initiation life under creep-fatigue conditions. The fracture mode of the alloy with equiaxed α and the bimodal structures was transgranular under creep-fatigue condition. On the other hand, the crack of the alloy with lenticular α structure was initiated and propagated at the interface between the α layer precipitated at the grain boundary and the lenticular α structure.
In order to investigate the effects of water vapor in air and high temperature on the strength behavior of alumina ceramics, fracture tests, static and cyclic fatigue tests were carried out under four-point bending condition at high temperature and in vacuum. Simple probabilistic evaluation on the fracture strengths in air and in vacuum indicates that though the scatters of the fracture strengths under both conditions are almost the same the strength in vacuum is higher than that in air by about 20%. This suggests that, in air, increment of defect size by water vapor must be taken into account. Results of static and cyclic fatigue tests at room temperature in air indicate that cyclic fatigue degradation is a superposition of time-dependent degradation and cycle-dependent one and both types of degradations are promoted by water vapor, because they are not observed in vacuum. The results of high temperature cyclic fatigue tests indicate that the cyclic fatigue degradation also disappears at high temperature over 800°C similar to the case in vacuum.
Hydrogen content in SUS329J1 duplex stainless steel SUS329J4L (DP3) weld metal and SUS329J3L (DP8) weld metal has been evaluated by using internal friction measurement at a frequency of about 1.5Hz and for the temperature range from liquid nitrogen temperature to 310K. The internal friction peak by hydrogen was recognized at 260K in steels fully or partially composed of austenite such as SUS304, duplex stainless steel and the weld metal, but no peak occurred in ferritic stainless steel such as SUS444. This fact means that the peak is originated from hydrogen in austenite. The linear relationship between the peak height and hydrogen content in austenite, which is independent of the microstructure, is applicable to evaluate hydrogen occlusion behavior in base metal as well as weld metal.
We succeeded to measure Poisson's ratio of polymeric materials under high pressure and high temperature. We measured Young's modulus and Poisson's ratio of polymethylmethacryrate and polycarbonate under various pressure up to 70MPa with varying temperature. For the measurement, we developed a novel apparatus; we combined a PVT test system with a ultrasonic velocity measurement system. We measured sound velocities of longitudinal and transverse wave propagated through the materials, and we obtained Young's modulus and Poisson's ratio from the velocities. The results under normal pressure were consistent with those obtained by conventional methods.