Mechanical properties of Si-added middle carbon martensitic steels are strongly affected by the tempering temperature and carbides precipitation. In this work, relationships between Si contents, mechanical properties and carbides precipitation are investigated using Fe-0.55C-(0.3-2.0)Si-0.7Mn-0.7Cr steels. Carbides precipitates and microstructures are evaluated by Differential Scanning Carolimetry and Scanning Electron Microscope observation, respectively. As a result, every steel with various Si content showed temper brittleness, and temperatures of embrittlement are increased with Si content increment. DSC data indicated that condition of carbides precipitate changed at the temperature of embrittlement and the temperature of recovery from embrittlement. It is observed that carbides precipitate and grow with the shape of platelet inside the martensite blocks at the temperature of embrittlement. And it is also observed that granular carbides precipitate at the grain boundaries of the martensite blocks at the temperature of recovery from embrittlement. Based on these results, the mechanism of temper brittleness is estimated as follows; platelet carbide precipitated inside martensite blocks interacts with dislocation movement and inhibits plastic deformation, so that steel easily fractures from grain boundaries and indicates low charpy impact value.

The shape memory effect (SME) in Fe-Mn-Si based alloy is associated with γ ⇄ ε martensitic transformation. It is necessary to suppress the sliding deformation and promote preferential generation of the martensitic transformation in order to improve the SME. In this study, each specimen was rolled and/or annealed and then the elastic and shape recovery ratios of them were checked by means of the bending mechanical test. Crystal structures also were inspected by electron backscatter diffraction (EBSD) for obtaining the phase distribution maps and then pole figures were drawn. On the specimens rolled as 20% and 40% reduction rate the axis of some crystals oriented to one of [001], [2 0 1], [ 1], [ 1] and the other of [001], [0 1], [ 1], [ 1]. The elastic recovery ratio improved from 27% to 36% at the reduction ratio (RR) at 20% , and to 40% at the RR 40% , however the shape recovery ratio was not improved. After the 600℃ annealing the shape recovery ratio improved from 20% to 33% in the RR 40% specimens. The cause of the elastic recovery ratio improvement is presumed that the cold rolling raised yield stress, and the expansion of martensite phase after bending test enhanced pseudoelastic effect. On the other hand, there are two reasons for improving the SME, one is the texture formation which promotes the martensitic transformation, and the other is the generation of austenite phase which easily transforms into martensite phase.

In recent years, leisure activities, such as tennis, golf, skiing, fishing, etc. are very popular. The performance of various instruments used in such leisure activities is also greatly improved. Scientific analysis on the function of such instruments is essential in order to develop practical instruments in the field of sports-leisure. Various experiential studies that clarify the characteristics of fishing rods have been published. However, there are very few scientific studies about fishing rods in the field of the so-called sports-leisure. This study deals with large deformation of fishing rods that would be useful in the development of the characteristic design of fishing rods. In this report, based on the nonlinear large deformation theory, new fundamental equations are introduced for thin, straight tapered fishing rods with a circular cross-section under concentrated loads at the free end. As a result, it is found that the large deformations of fishing rods can be described by nondimensional load parameters, the ratio of rod diameter at end and bottom, and supporting angles. Furthermore, the experimental verification of this analysis is carried out using a flexible rod acquired in the market. The theoretically predicted results are in fairly good agreement with the experimental data. Consequently, the new deformation theory is proved to be of practical use.

Traditional Japanese bows have a laminated structure made up of highly flexible bamboo and wood. Each bow is composed of multi arcs having different cross sectional areas along the length and also with different radii of curvature. Three stages setting procedure is required before shooting a Japanese bow. At first the bow is standing free, then, it is bent and constrained to have negative curvature using the bow string (chord), and finally formed into various shapes having positive curvature. Japanese bows does not have a symmetrical shape, and the position of the grip is also shifted from the center of the bow. Therefore, the deformation characteristics and the dynamics to analyze Japanese bows are very complicated. In recent years, large deformation analyses of the flexible bows have attracted attention considerably because of both analytical and technological interests in the design of bows and arrows. This study presents the details of the theoretical analysis results of Japanese bows obtained by using a simplified model consisting of multi arc segments. Each segment is treated as a large deformable nonlinear flexible beam and deformation analysis of individual arc segments is done by using the elliptic integral derived from Elastica theory. Furthermore, in order to confirm the applicability of the proposed large deformation theory, a large deformation experiment is performed. As a result, the theoretical analysis shows a very good agreement with the experimental results for the large deformed shape of the bow, which was restrained and loaded on the string. Moreover, the dynamic characteristics of Japanese bow and arrow with regard to the parameters such as the radius of curvature and bow arc ratio is evaluated.

The influence of ultrasonic shot peening (USP) on the rotating-bending fatigue life and the initiation point of the fatigue crack of shape memory alloy (SMA) wire were investigated. The effect of the compressive residual stress on the fatigue life of USP-treated SMA wire was discussed. The results obtained are summarized as follows. (1) The effect of the USP to the fatigue life of SMA is large in the small strain and slight in the large strain. (2) In the case of the USP-treated wire with coverage of 2000% and 4000%, the compressive residual stress cannot be measured around the surface. The structure on the surface may become the amorphous. (3) In the initiation point of the fatigue crack, the larger the coverage, the larger the ratio of the appearance of fatigue crack in the specimen surface is.

When the crack length is larger than a certain size, the maximum stress intensity factor (K _max) is used to explain the occurrence condition of brittle crack, and the limit condition of hydrogen assisted and stress corrosion crack propagation. Also, the fatigue crack can be explained by the stress intensity factor range (ΔK ). However, since the stress intensity factor deals with only linear elastic body, it is necessary for nonlinear range of crack tip to be small enough. It is known that in the case where this condition is not satisfied, the proposition shall be called the micro crack problem, and it is known that the crack size is smaller than the threshold value of the long crack. The purpose of this study is to unify the micro-cracking problems of various fracture modes. The crack length which is dependent on the threshold value can be explained by one concept considering the fact that the nonlinear region size of the crack tip is constant regardless of the crack length. In this paper, unified equation for micro crack problem to four kinds of cracks was proposed.

Nitriding treatment is the technology to create compound layer and diffusion layer on the surface of steel. However, compound layer has low fracture toughness, so micro cracks tend to occur on the surface of nitrided steel. Therefore, in this research, surface defects of various dimensions (20-100 μm) were artificially introduced into nitrided steel and their influence on fatigue limit was investigated. To evaluate the fatigue limit of nitrided steel with surface defect, a new evaluation equation focusing on the plastic region at the crack tip and parameter model was proposed. The relationship between defect size and fatigue limit can be predicted by this equation using the threshold stress intensity factor range of macro crack and the fatigue limit of non-defect specimen. The predicted fatigue limits were in good agreement with the experimental fatigue limit. Thus, the usefulness of this equation was demonstrated.

Although anelasticity is an important phenomenon for spring technology, affecting the size and restoring force of a spring during its operation, its time effect under stress has not been clarified yet. In this study we have evaluated the effects of compression holding time to the anelastic residual displacement of SWP-A or SUS304-WPB steel compression coil springs after unloading. Since free length variation of the coil spring is the summation of the faint twist modification in the steel wire, we can estimate pinning and unpinning phenomena of bowing-out dislocation under pure share strain. In both specimens, recovery of residual displacement showed logarithmic increase with time. The amount of residual displacement in ferrite SWP-A spring linearly increases with compression holding time from 5 to 80 s. It indicates amount of weakly-pinned bowing-out dislocations is increasing during the time of compression with certain pinning sites in ferrite. On the other hand, the amount of residual displacement in austenitic SUS304-WPB spring is small and does not increase significantly with time. It is verified that the time effect of anelastic phenomena in ferrite and austenite steel occurs in quite different way.

In the analysis of the non-contact type spiral springs, several theories about Archimedean spiral beam with limited boundary conditions have already been reported. In this paper, we introduced the theory which can freely select boundary conditions without restriction on spring shape. Then we analyzed the Archimedean spiral beam and Logarithmic spiral beam, which are typical spring shapes, and considered the effect of various boundary conditions, e.g. bending moment amount, deflection angle, etc. Since this theory is analyzed in polar coordinates, so various boundary conditions can be easily given for analysis. Additionally, we introduce applied FEM method with arc beam elements to analyze springs that are not ideal shapes. The simulation results by theorical method were in good agreement with the simulation results by FEM method. We made a spring and compared the simulation and the experiment. The simulation results were in good agreement with the experimental results. Finally, we introduce proposed methods to improve the spring performance.

The present paper has investigated the effects of wire anisotropy on the stress distributions in tensile coil springs and on their deformation behavior obtained by the finite element analyses (FEM). The types of anisotropy investigated in this paper were cylindrical and general anisotropy. The former simulates wire drawing and the latter considers the mutual influence effects of shear stresses (strains) and normal strains (stresses). The calculated deflections of tension coil springs and their spring constant agreed well with the values calculated by their well-known practical formulas for isotropic and cylindrically anisotropic springs. The values of normal stress σ_z and shear stress τ _θz on the wire cross section of these springs varied from a negative value on the outer periphery of the coil to a positive value on the inner periphery on the cross section of the isotropic springs. The distribution of the shear stress τ _θz agreed well with that of the shear stress τ _θz modified by the Wahl correction factor. In the generally anisotropic tension coil springs, however, the deflection δ showed abrupt increase, and thus the spring constant was markedly decreased for C ₁₄ ＞ 40 GPa. The distributions of σ_z and τ _θz were completely different from those in the isotropic and the cylindrically anisotropic springs. The absolute values of the normal stress σ_z in the generally anisotropic springs were more than four times higher than those in the isotropic and the cylindrically anisotropic springs. The shear stress τ _θz distribution did not agree with Wahl’s modified stress distribution. The higher absolute value of σ_z brought about sudden increase of deflection of the generally anisotropic springs for C ₁₄ ＞ 40 GPa.

In this study, 3D finite element analyses have been made on the stress intensity factors for semi-elliptic surface cracks on the inner wire surface of compression coil springs in order to investigate the effects of spring parameters on the correction factors F_i (i =I, II, and III) for the three modes of the stress intensity factors. The parameters selected for the present analyses are crack inclination angle, or the inclination angle of the cracks to the equator of the wire, θ and crack aspect ratio a/c where a is crack depth and c half crack surface length. The results are compared and discussed with those obtained by the present authors’ previous work for tension coil springs. For crack inclination angle θ, F _II was dominant over the other two factors in compression coil springs whereas F _I in tension coil springs. For crack aspect ratio a/c, F _I was dominant and the F _I－a/c relationships showed a similar tendency for eccentric angle φ in the both types of coil springs. Namely, the relationships were represented by quadratic curves of a/c projected upward and the F _I value reached its maxima for a/c =2.0 near wire surface at φ≒0° and 180°. The F _I values, however, were monotonically decreased for increasing a/c value at φ=45°, 90° and 135°.

Positron annihilation spectroscopy was applied on the spring steel SUP10 specimens which had been subjected to a certain number of fatigue loading cycles by four-point rotary bending fatigue testing to investigate the applicability for evaluating fatigue damage. First, fatigue tests were conducted to obtain the S-N diagram. The fatigue limit σ_w of the material was 550 MPa. Then additional fatigue tests were conducted at two different stress amplitude σ_a levels, σ_a = 650 MPa and σ_a = 550 MPa using specimens with a shallow notch the radius of which was 1 mm. The fatigue tests were periodically terminated, the surface of the specimen was observed to investigate whether fatigue cracks initiated and to measure the crack length, and positron annihilation spectroscopy was conducted by means of the positron lifetime analysis and the line-shape analysis to calculate the positron lifetime and the S-parameter, respectively. Before fatigue crack initiation, positron lifetime and S-parameter did not exhibit large change or even decreased in some occasions. However after fatigue crack initiation, the both parameters tend to increase monotonically, which indicates that positron annihilation spectroscopy could evaluate fatigue damage in SUP10.