0.4%C-Ti-V steel can enhance the suspension spring design stress comparing the common steel grades such as SAE 9260 or 9254 and has been increasingly applied to automobiles. Titanium and vanadium addition to this steel grade have the two significant features for improving spring corrosion fatigue property. Titanium and vanadium system precipitations lead to the fine austenite grain size with their pinning action. Furthermore tianium and vanadium system precipitations can trap the diffusible hydrogen in the steel during corrosion fatigue. Hydrogen trapping effect and austenite grain size refining can contribute to delay the fatigue crack propagation under the corrosion pit. It is cleared that titanimum has the larger effect than vanadium on the corrosion fatigue property, hydrogen embrittlement, and fracture toughness from this study and there is room for optimizing titanium and vanadium contents.
This paper presents the study on fatigue strength and fatigue life predictions of surface notched specimens of spring steel. The validity of the fatigue limit prediction and the fatigue crack growth prediction based on Haddad's equation, where the hardness of material and stress ratio were taken into considerations, were studied, compared with the experimental results. The specimens with semicircular notch by electrical discharge machining were prepared. The conditions of tests were without decarburization, with decarburization and with shot peening. The main results can be summarized below: (1) The calculated fatigue limits were slightly smaller than the experimental results for the without decarburization specimens. It can be said that the fatigue limit prediction is evaluated within the safe side in this case. (2) The calculated fatigue limits were between the experimental fracture and non-fracture results for the decarburized specimens. Therefore, the fatigue limit prediction can be said to be effective. (3) The fatigue limit prediction for the shot peeed specimens was evaluated within the safe side. It can be said that the prediction is effective. (4) The calculated fatigue crack growth behavior with da/dN-ΔK diagrams showed good agreements with experimental results. (5) The calculated fatigue life was slightly shorter than the experimental fatigue life without decarburization on the S-N curves. The calculated fatigue life showed good agreements with the experimental results with decarburization. Therefore, it can be concluded that the fatigue crack growth prediction is very effective.
The shot peening process in normal conditions produces a compressive residual stress on the surface of a material without phase transformation. But, the shot peening process produces a phase transformation (e.g., nanoferrite-phase and metal flow layer) on the surface of carbon steel under the intensified peening conditions of higher peening velocity and the use of a high-hardness shot media. Previously, we reported that the fatigue strength of springs having a nanocrystalline phase were higher than without nanocrystalline phase. This study investigates the microstructural surface layer induced by shot peening and its effect on fatigue strength. The test specimens were compressive coil springs made of oil-tempered wire. The test springs were manufactured by the same process except for the shot peening time. The shot peening time was varied as 100, 300, 500, 1000, 2000, 3000, 6000 s. Shot media was steel cut wire of diameter 0.25 mm. Surface roughness and residual stress distribution were measured. Microstructures were observed with an optical microscope and a scanning electron microscope. And, fatigue tests were carried out by using a spring fatigue test machine. The experimental values of the residual stress distribution and the surface roughness s are almost the same for 300-6000. The spring shot-peened for 300 s consists of the matrix phase and the surface metal flow phase. The spring shot-peened for 1000 s contains the white layer on a part of the surface. For the shot-peened time greater than 3000 s, the white layer almost covered full of surface. The fatigue strength increased with peening time until 1000 s. For the specimens shot-peened for more than 1000 s, the fatigue strength remained at a constant level.
Static fatigue behavior of mullite/ 15 vol% SiC whiskers/ 10 vol% SiC particles multi-composite crack-healed was investigated at room temperature and high temperatures from 1000°C to 1200°C. The multi-composite is the most candidate material as ceramic spring, because it has low Young's modulus as well as its reliability is guaranteed by excellent crack-healing ability. For estimating the usefulness of the composite as ceramic spring at high temperature, we must know the static fatigue limit at high temperature. The multi-composite having pre-crack was crack-healed at 1300°C for 2 h in air. The times to failure were investigated when the crack-healed specimens were applied the elevated tensile stress in air at room temperature and high temperatures from 1000°C to 1200°C. From the obtained results, the static fatigue limit was determined. Below 1000°C, the static fatigue limit of the composite crack-healed was found to be almost equal to the corresponding bending strength. Alternatively the static fatigue limit of the composite crack-healed was found to have lower value than the corresponding bending strength above 1100°C. Thus, the heat-resistance limit temperature for static fatigue of the multi-composite was determined to be 1000°C.
Coil springs with rectangular wire cross section, named ‘rectangular wire coil springs’, can store more strain energy than circular wire coil springs in limited space. Therefore, they have been used mainly in press dies and other special machine tools. Recently, rectangular wire coil springs come to have different uses like suspension springs in which light weight design are demanded. On the other hand, it is necessary to reduce the number of coils by adopting the large pitch angle with improved strength of wires. However, in the stress and the spring constant formulae for rectangular wire coil springs derived by Liesecke in 1930's, the effects of the pitch angle are not considered. Therefore, as pitch angle becomes larger, the difference between the calculated results and experiment becomes outstanding. Though we have design formulae for rectangular wire coil springs of large pitch angle proposed by Watanabe et al., they are the formulation of the results by FEM analysis. In other words, theoretical derivation of the design formulae for the rectangular wire coil spring has not been performed yet. In this research, new design formulae are derived theoretically. Furthermore, the validity of the new design formulae is presented in this research by comparing the results with experiment and improved FEM analysis.
Coiled wave springs (CWS) are considered as multiple layered waved washers. They are light but powerful in limited spaces. In recent years, CWS have been applied to clutches of automobiles and expected to be applied to other uses. The formulas on the spring rates and stresses of CWS have been presented by an American spring maker of Smalley Steel Ring Company, Nishio, and Japan Spring Manufacturers Association (for short, JSMA). But none of them are practical, because the accuracy is not enough. Moreover the derivations of the formulas are not clear in the case of Smalley and JSMA. It has been observed that CWS show nonlinear spring characteristics in large deflection, however, the cause has not been made clear. In this research, spring rates and stresses for CWS are analyzed theoretically. A cause of the nonlinear spring characteristics is made clear, too. Then empirical formulas on the spring rates and stresses are derived by comparing the theoretical results with experiments and FEM analysis.
The elastic performance brings an appropriate flexibility and a restoring force for installing and maintaining the routing arrangement of the control cable which is widely used as machine elements for transmitting load and displacement. On the other hand, the non-linear elastic performance has also made it difficult to design the control cable theoretically. In this study, we considered the method of the elastic analysis for the construction with non-linear stiffness property, such as a control cable and its application for the actual design. Then, we obtained following conclusions. (1) We developed the precise FEA model for the construction with various non-linear stiffness property. (2) We developed the method to predict the routing arrangement, the performance and the durability performance. (3) This developed simulation technology have been widely used in our company as the optimal and the low-cost design method in the early stage of vehicle's development.
A new spring type actuator is presented in which controls are possible by using usual control methods such as PID control. The actuator consists of a usual helical coil spring and a number of iron (ferrite) particle layers inside. The iron layers are made of silicon based adhesive material involving iron particles. The layers are pasted to the coil spring with a certain air gap between each layer. To achieve both extensive and compressive motions, a permanent magnet is attached to the top of the spring and electromagnet to the base, and the motion of the top of the actuator is controlled by electric currents in the coil of the electromagnet. In this paper, a method of forming the actuator is presented, and its characteristics are discussed experimentally. The present actuator performs well under the control. Especially, the size is small in comparison with such as moving coil actuators, the work area is large enough, and the controlled accuracy is sufficient under the position- and vibration-control.
Micro metal powder injection molding (μ-MIM) has some technical problems such as hard full-filling to narrow cavity and difficult de-molding in molding process in addition to careful operations of handling in sintering process. Sacrificial plastic mold was used to solve such several specific problems in μ-MIM process. The production method of micro plastic sacrificial mold inserted MIM (μ-SPiMIM) process was applied to manufacture advanced springs in this study. The sacrificial molds made of Polymethylmethacrylate were fabricated by injection moldings, and zigzag-type springs made of stainless steel were obtained after debinding and sintering. The dimensional accuracy and density of molded and sintered parts were evaluated with various injection molding conditions.
In recent years, light and thin-sized machines/instruments progress remarkably. Therefore, parts, e.g., mechanical springs used in those machines/instruments are more small/ thin-sized and flexible. In application of flexible parts, it is very important to check stress and deformation of materials used in those parts. And uniformity of their mechanical properties has to be guaranteed more and more. The establishment of a method of useful property evaluation test is required thereof. The research committee on evaluation of elastic property for thin plates and wires focused its activity on Young's modulus among various mechanical properties and developed a new and unique measuring method (Axial Compression Method) to evaluate Young's modulus of flexible materials by analyzing the buckling of an elastic column at large deformations. In the committee, various tests were performed to confirm the applicability of the new evaluating method by using four kinds of flexible piano wires (SWP-B) and data were accumulated. As a result, it is made clear that the new method is suitable for flexible wires. The new method proposed in this report can be applied suitably to other highly flexible materials (thin plates/sheets, composites, glass fibers, carbon fibers, optical fibers, etc.).