Torsional fatigue tests were conducted for spring steel SUP7 with smooth surface and artificial pits whose Vickers hardness were 430,480,550 and 620. The effect of notch, hardness and corrosive environment on the fatigue strength was studied. Following conclusions were obtained. (1) The relationship between torsional fatigue strength and hardness in the specimen with smooth surface in air environment was not linear and approximated by third function of hardness revealing the maximum value around 550Hv. (2) The notch factor of torsional fatigue strength in the specimen with artificial pits was the constant value of 1.7 with no relation to hardness and fatigue life in air environment. (3) The notch factor of torsional fatigue strength in the specimen with artificial pits was decreased with the increment of hardness approaching to the value of 1 for long-term fatigue life in corrosive environment. (4) The empirical formulas were derived indicating the fatigue strength in the specimen with artificial pits, the corrosive fatigue strength in the specimen with smooth surface, and the corrosive fatigue strength in the specimen with artificial pits by the third function of hardness.
Effects of shot peening on the bending fatigue strength of spring steel specimens (SUP9A) containing an artificial small hole were investigated. Shot peening (SP) and stress shot peening (SSP) were carried out with the specimens containing an artificial drilled hole 0.2, 0.4 and 0.8 mm diameter. Then, bending fatigue tests were carried out with the specimens. The fatigue strengths of specimens containing an artificial small hole were increased by shot peening. Stress shot peening (SSP) was effective in improving fatigue strength. The specimens containing an artificial hole 0.2 mm diameter which received shot peening fractured elsewhere the hole, and they had considerably high fatigue strengths almost equal to those of the shot peened smooth specimens. It was found that the fatigue limit of specimens having an artificial hole of under 0.2mm diameter determined by the threshold condition for non-propagation of fatigue cracks emanated outside the drilled hole. From these results, it can be concluded that an artificial drilled hole under 0.2 mm diameter could be made acceptable by shot peening.
This paper presents several finite element analyses on a dent produced by a single shot. A finite element model is discussed in order to clarify the influences of peening conditions and characteristics of material on the surface aspect. The following points are presented; (1) Dent form is influenced significantly by the yield stress of work material, but not influenced by density and Poisson's ratio. (2) Influence of Tangent modulus on the Dent form, which is work hardening coefficient, is low whenever Yield stress is high. (3) Finite element analysis method (FEM) is able to represent almost exactly dent forms.
The self crack-healing behavior of the heavily machined cracks in Si3N4/ 20 wt% SiC composite was investigate. The machined cracks were introduced in the center of specimens during making a semicircular groove by the diamond ball-drill. The machined specimens were crack-healed in various temperatures and time in air. The optimized crack-healing condition was found to be temperature of 1400℃ and time of 10 h in air. The specimen crack-healed in this condition showed the almost same strength as the smooth specimen healed. Moreover, the fracture strengths and fatigue strength of machined specimen healed at optimized condition were systematically investigated at high-temperature. The high-temperature strengths and cyclic fatigue strength of the machined specimen healed showed 700 MPa up to 1400℃, 550 MPa at 1300℃, respectively. These results demonstrate that the crack-healing could be very useful method to reduce machining cost and to increase reliability on Si3N4/ SiC composite ceramic.
An engine mount is developed which is consisting of a fluid filled rubber mount stacked with a variable spring constant absorber. In engine mounts, the transmissibility due to mass vibrations should be small, and high frequency vibration causing noise should be isolated. In the mount developed by the authors, the high frequency vibrations are isolated with a fluid filled rubber mount. It is difficult to suppress both mass vibrations and its transmissibility to the base simultaneously. For suppressing both, the authors applied an anti-resonance control system. In order to achieve the anti-resonance condition, a new type tunable absorber using conical helical spring is developed, and its control method is presented. Using our mount, both the mass vibration and transmissibility can be suppressed, and the amplitude ratio and the transmissibility can be controlled to be less than one which will be difficult to be achieved in the previous mounts. The present mount has other advantages on its compact size, small control energy and simple control system.
The newly designed springs tend to demand a steel capable of greater strength resulting in the increased possibility of delayed fracture. The study of delayed fracture, mainly on bolt steel, has been reported a good deal. However, the delayed fracture characteristics are evaluated in a variety of ways, and its evaluation method has not been established yet. In general, a spring is subject not only to static load but also to dynamic load. This makes it difficult to apply the method for bolt steel to spring steel in the practice of delayed fracture evaluation. Because of this situation, this committee, which is aimed to standardize the delayed fracture evaluation method for spring steel in future, started to implement followings: (1)Research of current delayed fracture evaluation method, (2)Survey of delayed fracture phenomena in springs, (3)Examination of charging and chemical analysis method of hydrogen. As a result of these activities, (1)understanding of delayed fracture of springs has been enhanced by the research of current delayed fracture evaluation method of bolt steel, (2)the effect of hydrogen on delayed fracture has been identified as a key study subject by the analysis of delayed fracture phenomena in springs. And (3)fundamental findings for standardizing the chemical analysis of hydrogen have been obtained through the study with a standard spring steel(JIS-SUP7).