Seiichi Nishino

The Influence of Applied Stress Ratio on Fatigue Strength of TiN-coated Carbon Steel

ABSTRACT The influence of applied stress ratio on the fatigue strength of carbon steel coated with TiN was studied on the bases of measurement of crack initiation with D. C. potential method. Fatigue tests were performed under the stress ratio of R=0 and -1 in air using the round notched specimens of 0. 37%C steel normalized, JIS S35C, coated with TiN by PVD and CVD. From the experimental results, increase of fatigue strength was observed in TiN coated specimens under the tests of R=-l, as compared with that of uncoated specimen. However, the fatigue life of coated specimens by PVD was decreased under the tests of R=0, except for the region of low stress amplitude. Also the fatigue life of coated specimens by CVD under R=0 was smaller than that of the uncoated one. The difference of fatigue life with applied stress ratio is explained by the fracture behavior of coating film on the specimen surface.

The Influence of Thickness of Intermetallic Compound Layer on Strength of Nickel-Foam Reinforced Aluminum Alloy.

This paper deals with the strength of nickel-foam reinforced aluminum Alloy (NFRA) and clarifies the influence of the thickness of intermetallic compound layer of NFRA. NFRA has two kinds of intermetallic compound layer between nickel-foam and base metal formed by artificial aging. In order to vary the thickness of intermetallic compound layer, three different heat treatment conditions were performed on three types of NFRA with different size of Ni skeletons and on AC8A aluminum alloy. Fatigue tests and tensile tests were carried out on NFRA and AC8A aluminum alloy. The fatigue life and tensile strength of NFRA decreased significantly as compared with those of AC8A. The thickness of intermetallic compound layer affects both the fatigue strength and tensile strength, since the intermetallic compound layer changes the bonding strength of the interface between nickel-foam and base metal.

WS7b4 – CORROSION FATIGUE CRACK PROPAGATION IN SQUEEZE CAST Al-Si-Mg-Cu ALLOY

ABSTRACT Behavior of corrosion fatigue crack propagation in squeeze cast Al-Si-Mg-Cu aluminum alloy, AC8A-T6, was investigated under the stress ratio of 0. 1, triangular waveform and testing frequency of 10Hz in 3. 0% saline solution using the compact tension specimens with side grooves. Corrosion fatigue crack propagation is affected by the initial stress intensity factor range, ΔKi, as the experiment was started. Path of crack propagation during corrosion fatigue showed the dependency on the microstructure consisted of the dendrite and eutectic spheroidal silicon. Corrosion fatigue crack propagated mainly along the eutectic structure and deviations in the path were larger than those under the test in air.

Fatigue Crack Propagation Behavior of Nickel-Foam Reinforced Aluminum Alloy.

Nickel-foam reinforced aluminum alloy (NFRA) has recently attracted special interest as one of the metal matrix composites. Nickel-foam is easily integrated with aluminum alloy because of high porosity, and its specific surface area is large enough to improve the wetability and adhesion and to form a Ni-Al intermetallic compound which is helpful in improving wear resistance.The aim of this investigation is to clarify the fatigue behavior of this new material. Fatigue crack propagation behavior of NFRA was studied using compact tension specimens under a testing frequency of 10Hz in air and stress ratio of 0.05, 0.5 and 0.7. Three types of NFRA with Ni-form squeeze casted with AC8A aluminum alloy were prepared and were heat treated with T6 processing.Fatigue crack propagation rate of NFRA decreased significantly as compared with that of AC8A-T6 aluminum alloy for low values of ΔK. The crack propagation rate was affected by the shape and size of nickel-foam. Acceleration and retardation of propagation rate was observed around the Ni-skelton because of propagation along the Ni-foam/matrix interface and in Ni-foam. The mechanism of crack propagation for NFRA was indicated by the equation of da/dN=A(Kmax)α(ΔK)β, where A, α and β are constant.

Prediction for high-temperature low-cycle fatigue life of austenitic stainless steel by X-ray fractography.

This paper describes an X-ray fractography for low-cycle fatigue of SUS 304 stainless steel at 873K in air under two test conditions. The first was the total strain range controlled test using triangular waves at a frequency of 0.1Hz and the second was the stress range controlled test using triangular and trapezoid waves at frequencies from 10-4Hz to 1Hz.(1) The half-value breadth obtained from X-ray diffraction on the fracture surfaces of low-cycle fatigue at high temperature was well correlated with the strain range but not with frequency. The half-value breadth was also correlated well with the failure life of the material fractured transgranularly, but was not in the case of intergranular fracture.(2) The particle size and microstrain obtained by Fourier analysis for X-ray profiles could be the good parameters for predicting low cycle fatigue life in both of the transgranular and intergranular fracture regimes.