Recently, the demand for improved efficiency of combustion engines is rising with the strict emission constraint. Therefore the requirement for heat resistance is increasing for materials used for springs in automobile exhaust system because the exhaust gas temperature becoming higher.
Co-W-Al alloys precipitation-strengthened with the γ’ phase have good high temperature strength and considered to have potential for higher temperature application than conventional Ni base super-alloys.
However, for coil spring application, materials must have enough workability in hot and cold roll to make coil wire. In order to enhance hot workability and high temperature mechanical properties, Ni and Cr were added and the optimization was performed in the chemical composition of Co-Ni-Cr-W-Al alloy. In this article, optimization of chemical composition, and relaxation property of coil spring of the developed “COWALOY®” are reported.
In this paper, torsional fatigue tests of high strength spring steel were conducted for bar-shaped specimens with artificial small defects of various sizes at a stress ratio of R＝0.1. The shear fatigue limit decreased with the increase in defect size. The relationship between fatigue limit and the square root of the projected area of the defect was evaluated. The relationship was defined by El Haddad’s short crack correlation substituting an intrinsic defect size for an intrinsic crack depth. The relationship was characterized by the approximate formulation using the parameter; thus, the fatigue limit with a small defect can be accurately estimated by the parameter.
To investigate the influence of surface defect with arbitrary shape on fracture strength of ceramics, three-point bending tests on alumina-silicon carbide (Al2O3/SiC) ceramic composites were carried out. A standard pre-crack, a tilted pre-crack and multiple pre-cracks were introduced on the specimen surface using a Knoop indenter. The specimens without pre-cracks were also prepared to investigate the effects of natural defect. Test results showed that the fracture strength of each specimen depended on which is representative value of defect size. To evaluate the fracture strength of ceramics with arbitrary defect, a new evaluation equation was proposed based on the process zone size fracture criterion and the parameter model. The relationship between defect size and fracture strength can be predicted using this equation using the fracture toughness and the fracture strength of non-defect specimen. The predicted fracture strengths were in good agreement with the experimental fracture strengths. Thus, the usefulness of this equation was suggested.
Hydrogen in steel trapped by lattice causes hydrogen embrittlement. It is also true in vanadium (V) alloyed high strength steel. These hydrogen trapping behavior, in other words the state of in the profiles obtained by thermal desorption spectrometry (TDS). These TDS profiles effectively analyzed by Gaussian distribution function. profiles of V-alloyed steels are successfully separated into two kinds of traps concerning V alloying, whose peak temperatures are around 140 ℃ and 200 ℃. Owing to the activation energy obtained TDS profiles of different heating rates, they are defined as incoherent and coherent vanadium carbides respectively. Vanadium alloying plays another important role of suppressing the amount of hydrogen trapped along grain boundary. It the improved resistance to hydrogen embrittlement of V alloyed steel. Hydrogen trap along grain boundary is affected by stressing or straining. It to be clarified whether hydrogen trapped along grain boundary causes grain boundary type fracture in hydrogen embrittlement, or it is simply the accompanying phenomenon in hydrogen embrittlement.
The theme of this paper is the hydrogen uptake in high-strength steel mainly for spring and stabilizer of automobile, when used in actual use environment and/or corroded in laboratory-simulating accelerated corrosion environment. In addition, this report gives a new interpretation to diffusive hydrogen concentration measured with Gas-Chromatograph-based Thermo-Desorption-Spectroscopy. When hydrogen in corroded steel (bcc-based ferrite, bainite or martensite) is measured after removing corrosion layer, hydrogen signal often appears at 300 to 400℃, in addition to both diffusive hydrogen signal at below 200℃ and non-diffusive hydrogen signal at over 400℃. However, the hydrogen signal at 300 to 400℃ has not been defined correctly, and it has been regarded as a long-standing unclear problem. Through experimental data and evidence, it is shown that the hydrogen peaks at 300 to 400℃ is based on inevitably-remaining deeply-rooted rust of FeOOH which cannot be removed perfectly from corroded steel sample even with a careful hand-polishing. The hydrogen spectrum appearing at around 300 to 400℃ has no relation to both diffusive hydrogen and non-diffusive hydrogen, and it is generated inside Gas Chromatograph, and therefore, it is not involved with hydrogen embrittlement at all.
Anelasticity is an important phenomenon for spring technology, since it affects the size and restoring force of a spring during its operation. Although this property has been known more than a half-century ago, its mechanism has not been clarified yet. In this study we have evaluated the effects of magnetic treatments to the anelasticity of steel compression coil springs during elastic deformation in experiments. We measured the temporal change of recovery lengths of the specimens after unloading with or without magnetic stirring under 180mT, since free length change of the coil spring is the summation of the faint twist modification in the steel wire. Each spring of 20mm long showed about 20μm length of recovery in 2 hours from the point of 90 second after the unloading. It indicates some bowing-out dislocations during the compression were interrupted with certain disturbances. The length of recovery was increased in 10％ for the magnetic stirring specimens. Since alternatively changed external magnetic field expands the length of magnetic domain walls in steel, it suggests the walls might play the role of obstacles, such as weak pinning sites, against the recovery movement of the dislocations in anelasticity.
The record of pole-vaulting has been improving rapidly by the appearance of a flexible fiberglass. The fiberglass pole has large elasticity. In analysis of the dynamics of the pole-vaulting, it is necessary to consider a high flexibility of pole. This paper deals with a large deformation problem of pole subjected to concentrated loads by the vaulter at two supporting points near the upper end. A simple combination model consisted of a mass (vaulter) and a pole was introduced in this analysis. Several analytical formulae are derived for vertical and horizontal displacements of the vaulter and so on in terms of elliptic integrals. Furthermore, a time progress of pole deformation is investigated. From the results, it is clarified that the initial conditions (e.g., vertical and horizontal velocities of the vaulter) and the applied bending moment during the vault play important roles.
In application of thin flexible multi-layered materials, it is very important to evaluate mechanical properties of these materials in both analytical and technological interests. In this study, a new and convenient mechanical testing method (Own-weight Multi-layered Circular Ring Method) is developed for measuring Young’s modulus of each layer in a flexible multi-layered material (thin plate, or rod/wire), especially, as a useful technique to overcome the difficulty in measuring Young’s modulus of a curled/curved flexible multi-layered material. The method is based on a nonlinear theory that takes into account large deformation behaviors of flexible multi-layered materials. By just measuring a maximum horizontal displacement or a maximum vertical displacement in a flexible circular ring, Young’s modulus of each layer can be easily obtained for various thin multi-layered materials (plate and rod/wire). As an example, measurements were carried out on a thin curled/curved two-layered wire consisting of a thin steel wire (a piano wire: SWP-B) and a thin plating layer (an electrodeposited nickel layer: Ni). The results elucidate that the innovative new method could be applied to measure Young’s modulus of thin flexible multi-layered materials. In the meantime, the new method “Own-weight Multi-layered Circular Ring Method” proposed in this paper is quite a promising method and can be applied widely to measure Young’s modulus of every thin layer in a flexible multi-layered material formed by PVD, CVD, Coating, Paint, Cladding, Lamination and others besides electrodeposited thin layers.
A non-circular wire helical spring generally has a high spring constant and reduces the spring height at fully compressed condition, although the energy absorption decreases during deformation. For improving this energy absorption, we have applied Fe-Mn-Si based alloy (FMS) to the spring. FMS that is one of the shape memory alloys (SMA) have more reasonable and workable than any other type of the SMAs, e.g. Ti-Ni alloy. Its shape memory effect and super elasticity that are caused with the stress-induced γ (Austenite) ⇔ ε martensitic transformation have been studied for. The cycled tensile tests are conducted on the springs made of FMS, S45C and SUS304. The load-displacement curve of FMS obtained by the cycled tensile test indicates a reversible large hysteresis loop. This is caused by deformation in two different processes of stress-induced martensitic transformation at loading, and reverse transformation at unloading. The non-circular wire helical spring of FMS is able to absorb more energy in early stage during large deformation than of S45C and SUS304.
This committee aimed to provide technical information (commentary) that can predict high-temperature spring set (residual shearing strain “γ value”) when designing and manufacturing compact coil springs for engine valve. The committee was divided into “Literature WG (Working Group)” and “Test WG”, and Literature WG gathered and organized technical literatures related to “γ value” at higher temperature. Test WG used test springs of which the wire diameter φ 1.0, 4.0 mm of 3 steel types (SWP - A, SWOSC - V, SUS 304 - WPB), including with processing or without processing(non) of shot peening and setting. Test temperature was set from 100 to 450 ℃, clamping time was set from 24 to 312 h, and the high-temperature spring set (calculated to “γ value”) was measured after clamping test at higher temperature. Various data of “γ value” obtained with less variance, and the influence of loaded stress, temperature and time on “γ value” with reasonable tendency for each test element. We confirmed that the obtained data generally agreed with various data in past technical literatures. So, we think that the obtained data will be able to provide useful database. However, in this activity, we cannot reconsider using the obtained data about highly practical calculation formula to express the difference at the temperature range (low temperature: around 200 ℃, high temperature: around 350 ℃). In the future, it is necessary to verify the high-temperature spring set mechanism at higher temperature and re-examination of highly practical calculation formulas.