Axial fatigue testing of Ti–6Al–4V using an alternative specimen geometry fabricated by metal injection moulding

The hourglass-shaped specimen, which is commonly used for axial fatigue testing, cannot be easily fabricated by metal injection moulding. Consequently, this work aimed at evaluating the performance of an alternative specimen (dog bone geometry) for fatigue characterisation. Additionally, an effort towards the assessment of the fatigue damage with specimens fatigued until halflife was made. The alloy used in this study, serving as an example for the test validation, was Ti–6Al–4V. The feasibility of using the specimens for fatigue testing was confirmed with a narrow scatterband, however, only in the range of 10⁵ cycles. The crack initiation sites were always found on the surface associated with quasi cleavage facets. Specimens fatigued until halflife showed a decrease in ductility in conventional tensile testing; nonetheless, the ultimate tensile strength remained unchanged.     

Development of a nanostructural microwave probe based on GaAs

In order to develop a new structural microwave probe, we studied the fabrication of an AFM probe on a GaAs wafer. A waveguide was introduced by evaporating Au film on the top and bottom surfaces of the GaAs AFM probe where a tip 7 μm high with a 2.0 aspect ratio was formed and the dimensions of the cantilever were 250 × 30 × 15 μm. The open structure of the waveguide at the tip of the probe was obtained by FIB fabrication. An AFM image and profile analysis for a standard sample, obtained by the fabricated GaAs microwave probe and a commercial Si AFM probe, indicate that the fabricated probe has a similar capability for measurement of material topography as compared to the commercial probe.     

Two-step method to evaluate equibiaxial residual stress of metal surface based on micro-indentation tests

The present study proposed a method to evaluate the equibiaxial compressive residual stress of a metal surface by means of a depth-sensing indentation method using a spherical indenter. Inverse analysis using the elastic–plastic finite-element model for an indentation test was established to evaluate residual stress from the indentation load–depth curve. The proposed inverse analysis utilizes two indentation test results for a reference specimen whose residual stress is already known and for a target specimen whose residual stress is unknown, in order to exclude the effect of other unknown mechanical properties, such as Young’s modulus and yield stress. Residual stress estimated by using the indentation method is almost identical to that measured by X-ray diffraction for indentation loads of 0.49–0.98 N. Therefore, it can be concluded that the proposed method can effectively evaluate residual stress on metal surface.     

Modeling of a buried conductor for an electromagnetic transient simulation

The paper has proposed a distributed‐line model of a buried bare conductor with horizontal and vertical configuration by assuming an artificial insulator outside of the bare conductor so that the characteristic impedance and the propagation velocity of the buried conductor is evaluated as an insulated conductor (cable) by the cable constants/parameters of the EMTP. A shunt admittance is added to the conductor at every short distance to represent currents flowing into the earth from the original bare conductor. The admittance circuit and the parameters are evaluated either by experimental results or by published references of grounding electrodes. The model circuit has been applied to simulate transient currents and voltages on horizontal and vertical buried conductors, and the simulation results are compared with the measured results. It has been observed that the simulation results of the currents agree satisfactorily with the measured results, but the results of the voltages do not seem satisfactory. The reason for this has been discussed based on the measured results. © 2006 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.     

Fretting Fatigue Behavior of Cavitation Shotless Peened Ti–6Al–4V

Fretting fatigue behavior of cavitation shotless peened (CSP) titanium alloy, Ti–6Al–4V was investigated. Constant amplitude fretting fatigue tests were conducted at several maximum stress levels, σ_max, ranging from 400 to 555 MPa with a stress ratio of 0.1. Test results showed that the fretting fatigue life was enhanced by CSP treatment as compared to the unpeened specimen, but the enhancement was not as large as that from the shot-peening treatment. Residual stress measurements by X-ray diffraction method before and after fretting test showed that residual compressive stress was relaxed during fretting fatigue. Before fretting, CSP specimen had higher compressive residual stress on the surface than the shot-peened specimen. However, greater residual stress relaxation occurred in CSP specimen such that the relaxed compressive residual stress profile near the contact surface of CSP specimen was lower than that of shot-peened specimen. This lower compressive residual stress from fretting fatigue was the reason for shorter fretting fatigue life of CSP specimen as compared to shot-peened specimen at the applied stress level.     

Sludge Ozonation and its Application to a New Advanced Wastewater Treatment Process with Sludge Disintegration

The applicability of sludge ozonation on wastewater treatment processes was investigated to reduce the amount of excess sludge without losing phosphorus removal efficiency. Solubilization degree per ozone consumption for general sludge was in the range from 2.4 to 5.8 gSS/O₃ and from 4.1 to 7.7 gCOD/gO₃. Around 80 to 90% of solubilized organics was biodegradable at a solubilization degree of 0.3. Based on the experimental results, a lab-scale plant with sludge ozonation and phosphorus crystallization was constructed to investigate the treatment performance. Amount of excess sludge was reduced by 93% with almost complete removal of soluble BOD and phosphorus removal efficiency of more than 80%. The percentage of the effluent COD_Cr discharge increased from 10% to 14–17% after installing ozonation and crystallization because of the formation of non-biodegradable organic substances in ozonation process. Energy consumption of the innovative advanced process is comparable or can be even smaller than that of the conventional anaerobic/oxic (A/O) process in spite of the installation of ozonation and crystallization.     

Estimation of the depth of surface modification layer induced by cavitation peening

In this paper we propose an experimental method for estimating the depth to which the surface of a material is modified after being treated by cavitation peening. The estimate is made on the basis of two theories: plate theory and beam theory, in which the plastic strain in the modified layer is considered. As the depth of the compressive residual stress is an important factor for the fatigue strength and for stress corrosion cracking, a simple and straight-forward method to estimate the depth of the modified layer is needed. In the proposed method, measurements of the surface residual stress and the radius of curvature generated as a result of the plastic deformation introduced by cavitation peening are combined with either plate theory or beam theory. The most appropriate theory depends on the thickness of the specimen. The plate theory is more accurate than beam theory in the case of both a thin and thick specimens. The beam theory should be applied only in the case of a thick specimen.     

Effect of the impact energy of various peening techniques on the induced plastic deformation region

In order to clarify the relationship between the depth of dimples and the plastically deformed region beneath the surface induced by shot peening and compare the characteristics of various peening methods in terms of single impact energy, the plastic deformation regions induced by single impact at various peening techniques were visualized using Fry's etching method. The relationships between impact energy and both the dimple size and plastic deformation region in the high shot speed range (～50 m/s) were clarified, and the relationships were found to be different from those in the low speed range (～25 m/s). The plastic deformation zones induced by cavitation and laser peening were also studied in order to understand their features. The results showed that the ratio of the plastic deformation region to dimple depth induced by cavitation peening and laser peening was more than 3 times larger than that induced by conventional shot peening, though the plastic deformation volumes induced by cavitation and laser peening were smaller than that induced by conventional shot peening.     

Evaluation of the surface of alloy tool steel treated by cavitation shotless peening using an eddy current method

Cavitation shotless peening (CSP) of hot forging die made of alloy tool steel is an effective peening method because it increases the fatigue strength of the material, and both introduces compressive residual stress into the material and also work hardens it. In order to evaluate the peening intensity of the die, a quick non destructive method is needed. In this paper, the dependence of the electromagnetic properties of an alloy tool steel, Japanese Industrial Standard (JIS) SKD61, on CSP processing time was investigated using an eddy current method. The induced stress and changes in the microstructure depend on CSP processing time, and these affect the electromagnetic properties of the material, such as the electrical conductivity and the permeability. The peening intensity was evaluated by measuring these electromagnetic properties using the eddy current method.