This paper describes the microstructural change of a Ti/Al friction weld interface during heat treatment at 673K, 773K, and 873K. TEM/EDS observations of a commercially pure Al/Ti weld confirmed that only the Al3Ti phase formed at the weld interface during heat treatment at 773K or 873K, while no intermetallic compound formed during heat treatment at 673K. The Al3Ti phase was composed of fine equiaxed grains nucleated at the interface boundary and grown up to a few microns in diameter during the heat treatment. Although the Si content was less than 0.12at% in the commercial Al/Ti weld, approximately 5at% Si was solved into the Al3Ti phase and a large amount of Si segregation, almost 20at%, was detected at the Ti/Al3Ti interface. No silicide formed during the heat treatment and the sugregation of Si was always observed. The observation of the specimen heat treated at 673K confirmed that Si segregation took place before the formation of the Al3Ti phase. The faster growth rate of the Al3Ti phase in the highly pure Al/Ti weld at 873K strongly suggested that the Si segregation retarded growth of the Al3Ti phase. The growth rate of the Al3Ti phase heat treated at 873K was in proportion to the square root of the holding time in the early stage of the heat treatment up to 3.6ksec, while it was linearly proportional to the holding time in the latter stage of the heat treatment.
Textile composites are becoming more and more important in engineering field. Need for computational simulations of their mechanical behaviors is also growing. In this study, a nonlinear homogenization method has been developed for the analysis of fracture behaviors of woven fabric composite materials. First, the mechanical behaviors of flat plates made from woven fabric composite materials were analyzed under various loading conditions, and then the reduction of modulus of elasticity by microscopic fracture was calculated precisely. Next, the nonlinear fracture analysis of a plate with an open hole was carried out. It is revealed that the knee points and notched strength are able to be predicted.
The relation between initial hydration and strength development of rapid hardening portland cement was studied. The mineral compositions of industrial cements used and their small particle portions were calculated by an improved Bouge's equation. The M1/M3 ratio and amounts of alite reacted for 12 and 24 houres were measuerd by XRD. The microstrucre of cement paste was also observed using a transmission electron microscope (TEM). Alite having a large amount of M1 phase hydrated more quickly up to 24 hours. TEM observations showed that ettringite crystals filled up space between cement particles after 12 hours. The strength of cement pastes increased with increasing amount of alite reached. The volume of ettringite formed after 12 hours may also influence the strength of cement paste for 24 hours curing.
A new grain boundary damage parameter, D-parameter, is proposed to evaluate grain boundaries damaged and to estimate the remaining life of components under creep loading at high temperature. This method is significantly different from the others firstly by specifying the grain boundaries normal to the principal stress direction in the area and secondly by defining the grain boundary damage by coalescence of voids. As the damage is analyzed from the surface structure of components, the replica is inspected by a SEM. The D-parameter method was practiced in in-situ observation of creep deformation for Ni based super alloy by SEM, and found useful for structural materials in which fine voids nucleate, grow and coalesce at the grain boundaries and cause an intergranular fracture.
Polystyrene (PS) was blended with linear low density polyethylene (LLDPE) and with elastomer styrene-ethylene-butylene-styrene (SEBS) terpolymer. The effects of the difference of dispersed phase on mechanical properties of the blends were investigated. The breaking elongation of the PS/SEBS blends was increased with increasing SEBS content. However, the breaking elongation of PS/LLDPE blends was not increased with increasing LLDPE content. This reason was studied by using the stress analysis of Finite Element Method. Little difference was found between the dilatational stress distribution in PS around SEBS particles and that around viods. This means that the craze initiation is not an important factor to control the breaking elongation of the blends. Therefore, the propagation mechanism of the craze in PS is considered to be influenced by the kind of dispersed phase. This is responsible for an increase in breaking elongation of PS/SEBS blends.
Vibration control is investigated for the 1st flexural mode of a cantilevered composite beam. A closed control loop system is designed with a non-contacting laser displacement pickup as a sensor, a pair of embedded piezoelectric ceramics as an actuator and a personal computer as a controller in order to control the vibration of the beam. The transfer function of the beam with an embedded actuator is obtained experimentally by using the vibration testing facility. An optimal control system using a linear quadratic regulator with an observer is constructed to minimize a performance index by adopting a quadratic form of the control input and controlled variables such as the deflection at the free end of the beam. The effectiveness of the controller is evaluated by simulation and by experiments.
This paper treats construction of the constitutive equation for inelastic behavior of CFRP, in which the damage effect is incorporated. At first, the authors propose an inelastic constitutive equation for CFRP subjected to cyclic loading. The constitutive equation is based on the constitutive model for cyclic plasticity proposed by the authors previously. Namely, the constitutive equation employs a damaged loading function that is similar to the loading function for metal alloys, the Ziegler type assumption to represent the movement of the damaged loading surface, and the Ramberg-Osgood stress-strain relation. To verify the applicability of the constitutive equation to the inelastic behavior of CFRP, a series of experiments, such as the cyclic tension-compression loading tests with several constant strain amplitudes, are carried out using laminated graphite/epoxy tubular specimens. The specimens have ±45 degree of fibers measured from the axial direction of the specimens. The predictions of the constitutive equation are compared with the experiments. As a result, it is found that the proposed constitutive equation can exactly predict the characteristic inelastic behavior of CFRP subjected to the cyclic loading, and that the damage variables are related to the strain amplitude of loading.
Tensile tests have been carried out using the smooth specimens of long-carbon-fiber reinforced plastic. The distribution of tensile strength was examined and the cause of the scatter was studied based on the macroscopic appearance of fractured specimens and the SEM observation of fracture surfaces. Tensile strength showed a considerable scatter which was due to the difference in fiber content and morphology of fiber distribution among specimens. Based on the experimental results, a simple model in which the scatter of fiber content and the fiber distribution were considered was developed and a simulation of the distribution of tensile strength was performed by using a modified law of mixture. It was shown that the experimental distribution could be expressed reasonably by the simulation.
Carbon fiber reinforced facing/aramid honeycomb core sandwich composite materials were studied through three point bending test. In order to clarify the influences of water on the stiffness and strength, the dry and wet specimens were used. At the same time, the fractured specimens were inspected by a scanning electron microscope (SEM) and a scanning acoustic microscope (SAM) to observe the superficial and interior fractures of the specimens, respectively, and the fracture mechanism was analyzed. The experimental results showed the following. (1) Sandwich material increased the bending stiffness a little after its absorption of 6wt.% water, but decreased the shearing stiffness by about 10%. (2) Water absorption affected the core shearing strength more than the facing strength. (3) The strength of interface between the facing layer and core of sandwich materials was larger than that of the matrix resin. (4) The buckling axis was observed on the compressive fracture surface of the wet specimens more than that of the dry specimens, which shows that most fibers in the wet specimens are fractured by compressive stress. (5) In case of short span beams whose length was shorter than 200mm, the wet specimens flexed more than the dry specimens. It is thought to be caused by the degradation of cell wall of the core.
The effect of room temperature proof testing on high temperature static fatigue life was studied on sintered silicon nitride. The tests were conducted under four point bending. Two types of specimens were used; one was ground with a #800 diamond wheel in the longitudinal direction and the other was ground with a #200 in the perpendicular direction. The proof testing effect was clearly observed on the specimens ground with a #200 as the degradation in fatigue life arose during proof testing due to residual stress induced by grinding. On the specimens ground with a #800, however, the proof testing effect was not observed at all. This seems to result from the difference in fracture mechanism between fast fracture and static fatigue fracture at high temperature.
A new technique to evaluate the thermal fracture toughness of ceramics was proposed by using the precracked slab specimens. Three kinds of mullite ceramics were used in the experiment. An initial precrack was introduced by the water quenching method, and was propagated by the three-point loading. The precracked slab specimen was held firmly by theree points and was heated from one side by a ruthenium thin film heater. The repulsive load at the restricted point was continuously measured by a load cell to monitor the thermal stress. The numerical analysis of stress intensity factor of the single edge precracked slab was conducted to determine the thermal fracture toughness from the generated repulsive load at fracture. A slight difference in thermal fracture toughness among three kinds of mullite could be detected by this technique. This experimental method is applicable to determine the thermal fracture toughness of ceramics under actual thermal shock conditions.
Recently geotechnical and environmental geophysics has become contributing toward solving problems in groundwater delineation, evaluation and protection, landfills, earth and water contamination, chemical waste disposal, nuclear waste disposal, earthquake risk evaluation, radon emanations, landslides, land subsidence, crop-land salinization, and general geoengineering. In this paper, geoelectrical information measurements including computerized subsurface visualization mainly by electrical sensitivity analysis methods are discussed.