Fatigue threshold and low-rate crack propagation properties for structural steels in 3 Pct sodium chloride aqueous solution

The fatigue threshold and low-rate crack propagation properties for a carbon steel, two high-strength steels, and two stainless steels were investigated in a 3 pct sodium chloride aqueous solution at frequencies between 0.03 and 30 Hz. Tests were conducted in a manner designed to avoid crack closure. Under freely corroding conditions, the effective values of the threshold stress intensity factor range, ΔK_th,eff, were lower than in air for all of the steels. In particular, the ΔK_th,eff values for the carbon and high-strength steels were almost equal to the theoretical ΔKth value of about 1 MPa m^1/2 calculated on the basis of the dislocation emission from the crack tip. At a given ΔK level higher than the threshold, the fatigue crack propagation rates accelerated with decreasing frequency for all of the steels. Under cathodic protection, the threshold and fatigue crack propagation properties were coincident with those in air regardless of material and frequency. The observed fatigue crack propagation behavior in a 3 pct NaCl solution was closely related to the corrosion reaction of the bare surface formed at the crack tip during each loading cycle.     

Nanoindentation as a strength probe—a study on the hardness dependence of indent size for fine-grained and coarse-grained ferritic steel

A nanoindentation hardness testing system, including an atomic-force microscope (AFM)-based nanoindentation tester and a calibration method using electrolytically polished single-crystal metals as references, was proposed. This was applied to a study of the mechanical properties of fine-grained ferritic steel (grain size of 1.2 μm) and coarse-grained ferritic steel (30 μm). An empirical function giving the macroscopic hardness for all four reference metals from the nanoindentation force curves was established. The converted Vickers hardness (HV*) of the coarse-grained steel is almost independent of the indent size. The fine-grained steel shows only HV* 130 with an indent of only 100 nm, compared with a macroscopic hardness of HV 210. The difference, HV 80, is considered to reflect the amount of grain-boundary strengthening. The critical indent size for the hardness transition seems to be around 1 μm, comparable to the grain size of the specimen. This result supports the explanation of grainboundary strengthening. It is also consistent with Pickering’s work on low-carbon steel, as the estimated locking parameter (k of 2.6×10⁵ N/m^3/2) in the Hall-Petch relationship is in good agreement with his value of 2.4×10⁵ N/m^3/2.     

Consideration of Energy Dissipation for the Strength of Adhesive Joints

For some adhesive joints where the main difference is the degree of contact at the interface, failure occurs not at the interface, but some distance away in the polymer itself. This cohesive mode of failure in the polymer was always found to be the case in our studies of cupric oxide to branched polyethylene interfaces, even where the joint was so weak that the peeled surface seemed clean of the polymer to the naked eye. It was observed that the strength of the joint was associated with the coarseness of the texture of the peeled surface of the polymer. With a differential scanning calorimetry technique we have shown that the coarseness of the surface texture and therefore the strength of the joint, is a direct function of the amount of polymer involved in plastic deformation. The strength criteria for the adhesive joint of this kind is thus the energy of deformation and not the maximum tensile stress that the material can withstand.     

Optical interconnection subsystem used in the RWC-1 massivelyparallel computer

Optical interconnection between the nodes of the RWC-1 massively parallel computer has been implemented. A one-node testbed system and an eight-node parallel processing system have been produced to demonstrate large-throughput small-skew low-latency and highly reliable optical internode connection. Each node was interconnected through dc-coupled 24-bit synchronized parallel optical interconnection at 100 MHz using 50-m-long single-mode ribboned fibers. The skew in a 24-bit data signal was suppressed to within 650 to -380 ps, and the OE/EO conversion delay time was 15.2 ns. We ran a parallel-processing program on the eight-node system as an evaluation, and the 50-m-long optically interconnected system performed as well as a 10-m-long electrically interconnected system. This clearly shows that optical interconnection will overcome the communication bottleneck in multinode computer systems     

Experience with IEC 1109 1000 h salt fog ageing test for compositeinsulators

This paper covers some examples of the STRI and NGK experience with the standard IEC 1109 salt fog test and some modifications of this test for different types of test objects     

FFTA: A fast fault tree analysis program

This paper presents a computer program for fault tree analysis. The algorithm is a bottom-up algorithm and the detailed procedure of the program is explained. The analyses are performed for six sample fault trees and the results are compared with those obtained by the BAM and CUT codes. This program has a ten to thousand times faster calculation speed compared with the BAM and CUT codes.     

Niobium–aluminum oxynitride prepared by ammonolysis of oxide precursor obtained through the citrate route

Oxynitrides in the (Nb_1−xAl_x)(O,N) quaternary system were prepared by ammonolysis of oxide precursor obtained through the citrate route. The products at 1000 °C were a mixture of Nb(N,O) and NbN_0.95 at the niobium end (x = 0) and amorphous Al(O,N) at the aluminum end (x = 1). A new cubic compound (A) appeared mixed with Nb(N,O) in the compositional range 0.1 ≤ x ≤ 0.4. Its almost pure product was obtained at x = 0.5. The X-ray diffraction pattern was rock salt type (Nb_0.56Al_0.44)(O_0.38N_0.37□₀₂₅) in F_m−3m with a = 0.43481(1) nm. The product showed superconductivity with T_c = 15 K. Its crystallinity was much improved and its superconducting volume fraction increased to 32% after its thermal annealing at 1100 °C in evacuated sealed tube. A second cubic compound (B), rock salt type Nb[(O,N)_0.85□_0.15] with a = 0.434 nm, was observed mixed with amorphous Al(O,N) in the as-prepared products of the range 0.6 ≤ x ≤ 0.9.     

Difference in the detection limits of flaws in the depths of multi-layered and continuous aluminum plates using low-frequency eddy current testing

We examined the difference in the detection limits of flaws in the depths of multi-layered and continuous aluminum plates using low-frequency eddy current testing. The detection limits were measured by using a magneto-resistive sensor. Comparing the frequency of an applied magnetic field, the detection limit at 50 Hz is deeper than that at 1 kHz. Comparing the sample structure, the detection limit in the multi-layered samples is deeper than that in the continuous samples. These results are likely due to the differences in the skin depth and conductivity of the sample.     

Eutrophication process recorded in dinoflagellate cyst assemblages--a case of Yokohama Port, Tokyo Bay, Japan.

To investigate temporal changes of water quality, a role of dinoflagellate cysts preserved in surface sediments was examined in Yokohama Port in Tokyo Bay, Japan. Two cores were collected, and sedimentation rates and ages of both were dated as approximately 1900 years or slightly older on the basis of 210Pb and 137Cs concentrations. The temporal change in dinoflagellate cyst assemblages in the two cores reflects eutrophication in Yokohama Port in the 1960s. Abrupt increases in the cysts of Gyrodinium instriatum cysts strongly suggests that a red tide was caused by this species around 1985. Dinoflagellate cyst assemblages in surface sediments appear to be good biomarkers of changes in the water quality of enclosed seas.