Study on joining between piezoelectric ceramics and aluminum was performed by Spark Plasma Sintered (SPS) joining method. An insert material for a joining between lead zirconate titanate (PZT) and aluminum used the Sn-3.5Ag alloy powder. The joining samples are produced by SPS at 473K for 300s to 7.2ks. The shearing test was carried out to investigate the mechanical property of the joining samples. The maximum shearing stress of 25MPa was able to be obtained. Any joining samples are ruptured at Sn-3.5Ag/Aluminum interface. The sintering time increased with increasing shearing stress and decreasing insert materials thickness and electric resistivity.
Generally, epoxy resin will be softened and its bond capacity will decrease remarkably under a high temperature environment near to or higher than the glass transition temperature (Tg) or deflection temperature under load (HDT) of epoxy resin. This paper summarizes a series of investigations for confirming the temperature effect on bonding behavior between fiber reinforced polymers (FRP) sheets and concrete. An experimental program is designed by using prism specimens subjected to a direct tensile load. The temperature around the concrete prism and the types of epoxy resin are considered as the experimental parameters. The experimental results are exploited to determine the debonding fracture energy (Gf), failure mode, and effective bonding length (Le) of the test specimens. It is observed from results that the value of Gf decreases and Le increases largely at temperatures near to or higher than Tg or HDT. Moreover, the newly developed epoxy resin presents higher temperature-resistance behavior than ordinary epoxy resin.
Materials with both of high modulus and high damping properties are necessary in many industrial fields. Super damping rubber (SDR) has high damping properties, but it has some disadvantages in mechanical properties. In this paper, a series of glass fabric reinforced polyurethane super damping rubber materials (GFRR) were developed with high strength and high damping properties for the wide use of vibration reduction. The mechanical properties, such as tension, peeling and shearing of bonding interface, were investigated, which are much superior than SDR. For the application in vibration reduction, the composite loss factor was measured by the mechanical impedance method with a free-layer damping system, while the damping properties of viscoelastic layers were conducted by the dynamic mechanical analysis (DMA). Using the RKU model, the dependences of temperature and thickness ratio of composite loss factor were analyzed. The agreement between the experiment and the analysis suggests that the composite loss factor can be predicted with a good accuracy by RKU model.
Carbon fiber reinforced Plastics (CFRP) has been well developed for many engineering structural components in the aircraft, automotive and modern space industries with its light-weight and excellent mechanical properties in the last few decades. But it is poor in vibration and noise reduction as same as metal materials. In this paper, the innovative CFRP/SDR sandwich laminates with damping rubber sheet were developed and their damping behavior was investigated by the dynamic mechanical analysis (DMA) under tensile, shear and bending vibration mode, respectively. As a result, it is shown that the damping properties of the developed 8 types of CFRP/SDR sandwich laminates depend deeply on the fiber orientation of lamina, the property of rubber sheet and its layer number and sequence. The dependence of damping property on temperature and frequency is discussed in detail. The loss factors for the developed materials are over 0.2 under shear vibration mode and over 0.3 under bending vibration mode, even reaching 0.45 for [02/SDR/904/SDR/02] laminates. It is also clear that the damping parameters depend on the vibration mode in the test. This is especially important for the CFRP based damping materials.
In this paper, damage progression process of plain-woven carbon/epoxy composites was investigated under cyclic loading. Damage state, damage degree and its location were observed in the flat-wise direction of the specimen by using thermo-elastic stress analysis (TSA). The results of TSA showed that transverse cracks initiated and accumulated in the wefts at early fatigue stage. The each location, where the damage occurred, had different damage degree at any fatigue cycles. In order to obtain accurate damage information, thermo-elastic damage analysis (TDA) was conducted. A quantitative evaluation of damage accumulation level in plain-woven carbon/epoxy composites was proposed based on the concept of damage parameters (such as damage level, damage area ratio and damage value) given by TDA results.
The requirement for the massage chairs as a medical instrument has been increasing. So, it is necessary to improve some of the machine elements of the massage chairs so that they have a higher level of the massage comfort. It is especially expected that the mechanical properties of the massage chair arms will effect the massage comfort. In this paper, CFRP was used as a material for the arm part in order to make massage comfort higher and lighten the arm weight of the massage chair. And also, the massage comfort evaluation was investigated by using the fuzzy membership function. As a result, it was shown that the bending properties of arm material and the principal strain direction on the arm produced an effect on the evaluation for the massage comfort. In addition, it was determined that it was possible to predict massage comfort by using the multiple regression analysis.
Recently real-time monitoring technique by using built-in sensors of FRP is expected to reduce the cost and enhance the reliability. In the present paper, built-in FBG fiber optic sensors were applied to cure and health monitoring of filament winding (FW) glass/epoxy pipes. FW pipes were wound by ± 45° helical ± 5° parallel winding methods. The FBG sensors were embedded between helical and parallel layers along axis direction of the pipes. Internal strain monitoring of the FW pipes was conducted during cure and fatigue tests. From the results of the cure monitoring, it was found that FBG sensors could be used for measurement of the curing shrink as well as the thermal residual strain. The results of the fatigue tests showed that strain from the FBG sensors had very good agreement with that from the attached strain gauges. Young's modulus of the pipes measured by the FBG sensor was almost constant during the fatigue tests although transverse cracks occurred in the parallel layers. However, the spectral shape reflected from the FBG sensor was affected by existence of the fatigue cracks. In order to evaluate degree of damages near the sensor, correlation coefficient calculated from the spectral shape was introduced. The experimental results showed that the correlation coefficient was useful for evaluation of damages.
SMC products generally have some ribs in order to improve stiffness of structures. However, material flow in the molding process becomes very complicated by establishing the rib in the structure. As the result, glass fiber distribution and fiber orientation in rib part change, and it often happens that required stiffness of products does not obtained. In these cases, while it is needed to change mold design, a great amount of time and cost are required. The mold for compression molding of SMC is very expensive because the mold must be able to endure the molding in high temperature and pressure. Then, the development of CAE system, which estimates the stiffness of the SMC structure with the rib from the molding condition and the mold shape is being needed and tried in order to design the mold efficiently. Each material constant was calculated in the way that Young's modulus of flat plate part was expressed by Fiber orientation, and that of rib part by B/ts. Here, B/ts is the ratio between rib width “B” and material thickness “ts” as the material passes the rib in molding process. When the rib was perpendicularly attached for the SMC material flow direction, these CAE systems were studied, but when the rib is obliquely attached, the systems are not yet studied. So, in this paper we try to estimate the Young's modulus in rib part in consideration of heterogeneity as Fiber orientation and its distribution and resin-rich, when the rib has obliquely been made for the flow direction. The factor (Fiber weight content, Orientation factor and Fiber orientation angle) that influenced Young's modulus in rib part was able to be arranged by B/ts. As the results, we get good agreement with theoretical Young's modulus and experimental Young's modulus in rib part.
A single-point mooring buoy used for shipment facility of a floating crude oil base, which some universal joints are built in, shows complicated behaviors, and gets very big tension and generates a noise based on sliding in some cases when the ocean wave is very high. It is important to evaluate the static friction coefficient μs between bracket and bearing pin in order to improve durability and reliability of the universal joints. Then, static friction tests were carried out in air, in the wet of seawater and corrosive solutions using measuring system of a model simplified specimens of bracket and bearing pin. If the specimen did not corrode, the static friction coefficient μs was, μs = 0.24 ∼ 0.28, but specimen corroded, it rose to 0.46 ∼ 0.55. It is considered that the corrosion product on the surface of specimen is one of the rise causes of static friction coefficient, and the existence of corrosion product may increase sliding resistance of the universal joint.
The effects of low-temperature aging of up to 313K on quenched Fe-30%Cr ferrite stainless steel alloys were investigated. Static strain-aging tests were performed on Fe-30%Cr alloy polycrystals containing 28ppm and 130ppm carbon in order to clarify the static strain-aging phenomenon at temperatures ranging between 313K and 473K. The 0.2%-proof stress decreased with increasing deformation temperature, but a hump of 0.2%-proof stress was evident from 373K to 473K. Activation energies obtained from the strain-aging tests measured about 71kJ/mol for the specimens containing 130ppm carbon and about 78kJ/mol for those containing 28ppm carbon. These values are in agreement with the activation energies for the diffusion of carbon and nitrogen in α-Fe. In our previous studies, we demonstrated that only carbon was concentrated at the front of Lüders bands after aging. Through some chemical interaction, the nitrogen may be unable to move to a dislocation due to the nitrogen having been combined with the chromium atoms. In addition, the hump of 0.2% proof stress could not be observed in specimens containing 28ppm carbon. Based on our findings, the static strain-aging phenomenon is considered to be associated with the diffusion of carbon in Fe-30%Cr. Using the activation energy, the number of jumps, dislocation density and mean dislocation distance were calculated. The calculated result for the dislocation density is in agreement with that obtained for the dislocation density at the front of Lüders band as reported in our previous paper.
Many types of ferrite stainless alloys have deformation that is accompanied by serration. However, in many such cases, the actual cause of the serration still remains uncertain. Observations on Fe-30%Cr alloys revealed that 0.2%-proof stress increases at two different ranges of the deformation temperature. When the 0.2%-proof stress increased at the lower temperature range, two different types of serration could be observed. The strain hardening coefficient was calculated from the stress-strain curves. The strain hardening coefficient increased in the low temperature range but did not so in the high temperature range. The critical conditions for serration were determined by measuring the changes in the temperature and strain rate. When the critical conditions are determined, then the migration activation energy of moving solute atoms can be calculated. The solute atom that plays a role in causing the serration was determined from the activation energy of the solute atoms. Calculated activation energies were found to be 79.1kJ/mol and 216kJ/mol, respectively. Based on these results, we consider the cause of the serration observed in the low temperature range to be associated with the interaction of carbon and moving dislocations, while the serration evident in the higher temperature range is regarded as being due to the interaction between chromium and interstitial solute atom pairs with moving dislocations. Similar analyses were made for the pre-strain required to cause serration. The required pre-strain was observed for serration both in the low temperature range and that in the high temperature range. We also discuss the pre-strain required for causing serration.
Buildings and infrastructure in earthquake-prone areas need to be designed and constructed with enough strength and ductility to absorb a large amount of seismic energy during earthquakes. Effective energy absorption can be achieved by placing hysteretic damper in the structures to meet the damage limitation requirements for those structures. Ultra-low carbon steel having low 0.2% proof stress (σ0.2 : 100MPa) has been used in practice for dampers to improve the damping and inelastic cyclic performance of structures. This investigation aims to obtain more ductile materials for the dampers, with a greater capacity to absorb seismic energy. The development of such ductile materials involves three steps : (1) Set 0.2% proof stress to about 100MPa, tensile stress to 400MPa, and elongation to 30% or greater as target values for the material. (2) Select a crystal lattice type capable of achieving these values. (3) Search for optimal systems based on the result of this selection. Tensile tests were carried out on several tens of Fe-Ni and Fe-Ni-Cr alloys produced for this investigation, and an austenitic system having a face-centered cubic lattice and ultra-low carbon content were found to be favorable for meeting the above requirements. Fe-15Ni-15Cr alloy was selected as a suitable candidate. A semi-production heat of this steel was made. Hot-rolled and annealed steel plate exhibited 0.2% proof stress of 76MPa, tensile strength of 421MPa and elongation of 78%.
The discrete dislocation (DD) method is one of the mesoscopic scale computer simulation procedures, which can deal with each dislocation movement in a cracked body. In this paper, the fatigue crack growing under mixed Mode I and II condition with kinking was analyzed by the 2-dimensional DD method. The material analyzed was iron with bcc structure, which has two preferred slip directions inclined ± 54.7° to the direction perpendicular to the loading axis. The fatigue crack was assumed to grow along one of two slip directions in order to simulate the crack growth behavior under mixed mode condition, observed microscopically by an atomic force microscope (AFM). The effect of a grain boundary was also introduced to figure out crack kinking behavior. The crack tip displacement along the crack growth direction, which was defined by the number of dislocations annihilated at the crack tip, was found to become smaller as crack grew due to the constraint of slip deformation by the grain boundary. The crack kinking was assumed to take place when the crack tip displacement along the crack growth direction was exceeded by that along the other slip direction.
In recent automobiles, tailor welded blanks using high strength steel sheets with various combinations of thicknesses and laser welded butt joints are being widely used to reduce weight of vehicle bodies without any decrease of their stiffness and crash performance. It is well known that underfilled weld beads are formed in such butt joints due to large gaps between steel sheets in laser welding process and the underfilled weld beads deteriorate mechanical properties and metal formability. However, the influence of the underfilled weld beads on fatigue properties of the weld butt joints is not sufficiently revealed, even though the fatigue properties are practically important for actual service of automobiles. In addition, the fatigue properties of butt joints with a step cross-section are necessary to build the design standard for tailor welded blanks. Therefore, in this paper, tensile tests and fatigue tests have been conducted for the laser welded butt joints of different thickness steel sheets with various underfilled weld beads in order to clarify their fatigue properties. Also FEM analyses have been performed to study the stress distribution, especially the stress concentration, around the weld metal in the butt joints. It is observed that the butt joints with underfilled weld beads and a step cross-section significantly deteriorate the fatigue strength, although their effects on tensile strength are small.