Norihiko Hasegawa

Research on the wear characteristics of hypereutectoid steel

Abstract In this research, the wear behavior of hyper-eutectoid steel was examined at ambient temperature ranging from room temperature to a high temperature of 400 °C. A common asymmetric test rig was used, where a pin specimen of hyper-eutectoid steel is pressed against a disk of carbon steel for machine structure use. Two types of pin specimen were prepared: an as-received specimen and a quenched specimen.. As a result, the following was clarified. The protective surface film of iron oxide is not a main factor in determining the wear behavior of the hyper-eutectoid steel of as-received pin specimens. The wear behavior is closely related to the separation of the oxide film from bulk material when the sliding conditions are severe. The wear behavior of a quenched pin specimen is strongly influenced by a microstructural transition and a reduction in hardness of the pin specimen at elevated temperature.

Prototype fretting-wear testing machine and some experimental results

Abstract A new prototype fretting-wear testing machine is developed, and its performance is evaluated. In this testing machine, a spherical specimen is oscillated by a lead-zirconate-titanate semiconductor (PZT) actuator, driven by means of computer control. Thus, an arbitratry input waveform, such as sinusoidal wave, triangular wave and so on, can be easily operated to a spherical specimen. This is the special feature of our testing machine. As an example, a fretting experiment is carried out, using a steel flat specimen and a bearing steel sphere specimen. A sinusoidal input wave is added by a PZT actuator. It is clarified that there is a boundary fretting amplitude, beyond which fretting wear mass or volume increases abruptly.

In-plane deformation observation of indentation along indenter surface

In this paper, the in-plane plastic deformation, which is perpendicular to the contacting load, of soft metal in contact with a hard spherical indenter is observed on a rolled aluminum surface. By measuring a displacement due to indentation of lattice points described on the aluminum surface, the in-plain deformation is obtained. Many small ferrous impurities are scattered on and in this aluminum specimen. When a hard spherical indenter is pressed onto this aluminum surface, the distance between impurities is changed by the surface plastic deformation. The change in distance between impurities is obtained using the image processing method, and it is demonstrated that the in-plane plastic deformation of surfaces caused by indentation can be observed. Results by both the lattice point method and the image processing method are compared quantitatively.

Transient rolling behaviour of a slider supported by two rollers

A rolling element has a spring characteristic in the transient displacement region from the stationary state to a continuous rolling motion. For this reason, a bearing having a rolling element is useful for constructing an ultra-precision positioning device. In this paper, a mechanism for the damping capacity generation of a rolling element is investigated, to improve the dynamic characteristic of this positioning device. A stage supported by two rollers is constructed, and its tangential displacement is measured accurately when the driving force is acting. As a result, it is confirmed that the rolling element has a nonlinear spring characteristic. Energy loss is generated by the reciprocating motion of the stage in the transient displacement region. This is the main cause of the damping capacity. Furthermore, this energy loss or damping capacity of the stage can be improved by using two rollers with different diameters.

Effects of Lubrication Upon Plastic-Metal Contact

It is important to examine the contact mechanics between metal surfaces for greater accuracy of guideway motion and for pre-estimates of contact rigidity and damping capacity of mechanical systems. In the present study, the contact of a hard steel ball and a soft duralumin surface is examined, and the effect of lubrication on the plastic contact mechanics is discussed

Fatigue Crack Thresholds .DELTA.Kth Value of Ferritic Nodular Cast Iron at Elevated Temperatures.

The in-plane bending fatigue tests were carried out on FCD 450 at elevated temperatures up to 723 K. The threshold stress intensity range ΔKth and its effective values ΔKeffth were observed as a function of the temperature T. Plots of ΔKeffth and T revealed that ΔKeffth remained constant up to 623 K and then decreased to a value about 28% lower at 723 K. The ΔKth-T relations showed that ΔKth remained constant in the range of 473 K to 723 K, its value being about l0% lower than that at room temperature. While the ΔKeffth value at 723 K decreased by 28% lower than that at 623 K, there were no significant differences between the ΔKth value at 723 K and that at 623 K. It appears that the rise of closure level Kcl induced by the high-temperature oxide on fracture surface results in the apparent increase in ΔKth value at high temperature such as 723 K.

Statistical Fatigue Properties of Ductile Cast Irons.

Rotating bending fatigue tests of smooth specimens were carried out at room temperature on a pearlitic ductile cast iron (PDI) and austempered ductile cast iron (ADI). No significant difference due to sampling position from cast blocks in both materials was found in fatigue limit and fatigue life distribution. Then, the statistical fatigue properties of ferritic (FDI), ferritic/pearlitic (FPDI), pearlitic and austemperd ductile cast irons were investigated. The fatigue life distributions of all ductile irons were well represented by the three parameter Weibull distribution modified by the saturated probability of failure. The shape parameters of FDI, FPDI and PDI were in proportion to σ/σw independent on microstructure, while the shape parameters of both stress levels in ADI were smaller than unity. The fatigue strength of ADI was highest, but the scatter of fatigue life was largest among the all cast irons.

Correlation among static strength parameters.

The data of static mechanical properties of many kinds of ferrous metals were sampled from the database on the fatigue stength of metallic materials in JSMS. The correlations among various mechanical properties were investigated. When brinell hardness and Rockwell hardness were converted into the corresponding Vikers hardness, the relation between Vikers hardness and tensile strength can be expressed as linear. The relation between yield strength (yield stress or 0.2% proof stress) and tensile strength can be classified into two groups, each of which has a linear relationship. The first group contains low strength steels such as annealed carbon steels, normalize carbon steels and quenched and tempered carbon steels ( 0.30%C) etc.. The relationship between elongation and tensile strength in all irons and steels can be expressed as an exponential function. The data of austenitic steels and cast irons deviate from the relationship. The relation between reduction of area and tensile strength is expressed as three groups with linear relationship. The first group contains normalized and annealed carbon steels and quenched and tempered carbon steels ( 0.30%C). The third group contains alloy steels.

The Effect of Low Temperature Quenching and Quench Ageing on the Fatigue Strength of Notched Specimens of Low Carbon Steels

The fatigue limits, σw1 and σw2, which are critical stresses for initiation and propagation of stage 2 cracks respectively, were compared among annealed, quenched and quench aged steels. To examine the effect of heat treatment on the fatigue life, crack propagation rate, d(2a)/dN, was measured at a stress above σw2. The contribution of quenching and quench ageing to the increase in the fatigue limits is greater for σw2 than for σw1, and the relationship, ασw1sσw0, is kept independent of the heat treatments, where σw0 is the fatigue limit of unnotched specimens. Therefore, the notch sensitivity factor, ( σw0/σw2-1)/(α-1), is reduced by both treatments. The strengthening effect is more remarkable with quench aged steel than with quenched steel. At higher ΔK level, d(2 )/dN is independent of the heat treatment, and is correlated with the streas intensity factor ΔK. The increase in the fatigue life by quenching and quench ageing is due to the decrease in d(2a)/dN at lower ΔK level.