Dynamic Material Test of Sinter-Forged Cu-Cr Alloy and Application to the Impact Characteristics of Vacuum Interrupter

Vacuum interrupters in order to be used in various switch-gear components such as circuit breakers, distribution switches, contactors, etc. spread the arc uniformly over the surface of the contacts. The electrodes of vacuum interrupters are made of sinter-forged Cu-Cr materials for good electrical and mechanical characteristics. Since the closing velocity is 1-2m/s and impact deformation of the electrode depends on the strain rate at that velocity, the dynamic behavior of the sinter-forged Cu-Cr is a key to investigate the impact characteristics of the electrodes. The dynamic response of the material at intermediate strain rate is obtained from the high speed tensile test machine test and at the high strain rate is obtained from the split Hopkinson pressure bar test. Experimental results from both quasi-static and dynamic compressive tests are interpolated to construct the Johnson-Cook model as the constitutive relation that should be applied to simulation of the dynamic behavior of the electrodes. The impact characteristics of a vacuum interrupter are investigated with computer simulations by changing the amount of chromium content

Dynamic Material Tests of Steel Sheets for an Auto-body Using the High Speed Material Testing Machine

The dynamic behavior of sheet metals must be examined to ensure the impact characteristics of auto-body by a finite element method. Since the strain-rate in the crash analysis of auto-body is under 500 Is, an appropriate experimental method to acquire the material properties at the corresponding strain-rate has to be developed. In this study, a high speed material testing machine was manufactured for tension tests of sheet metal under 500/s. Dimensions of a specimen for sheet metal need to be determined for tension test of sheet metal at intermediate strain rate because there is not a standard tension specimen for the dynamic test Numerical simulations are carried out to determine dimensions and the shape of the specimen. Tensile tests of steel sheets in auto-body are performed at several kinds of strain rates. Fast Fourier transform smoothing method is used to fit the oscillation of load caused by the ringing phenomenon of a jig

Characterization of the Material Properties of Sheet Metal for Auto-body at the High Strain Rate Considering the Pre-strain Effect

Most auto-body members fabricated by the sheet metal forming process. During this process the thickness and material properties of the sheet metal are changed with the residual stress and plastic strain. This paper deals with the material properties of the sheet metal at the high strain rate considering the pre-strain effect. Specimens are selected from sheet metals for outer panels and inner members. such as SPCEN, SPRC45E, SPRC35R and EZNCD. The specimens are prepared with the pre-strain of 2, 5 and 10% by tensile elongation in Instron 5583, which could be equivalent to the plastic strain in sheet metal forming. High speed tensile tests are then carried out with the pre-stained specimens at the strain rate of 1 to 100/sec. The experimental result informs that the material properties are noticeably influenced by the pre-strain when the yield stress of the specimens is moderate as SPECN, SPRC35R and EZNCD. The result also demonstrates that the ultimate tensile strength as well as the yield stress is increased as the amount of the pre-strain is increased

Experiment of the Formation of Adiabatic Shear band in Sheet Metal

The adiabatic shear band formation is one of the high speed deformation phenomena, in which adiabatic shear failure is physically observed as a narrow band of the continuous shear strain. In this paper, the experiment of the formation of the adiabatic shear band in sheet metal is carried out for high strength steel sheet, 60C and 60TRIP. In order to carry out experiments with a tension split Hopkinson bar, shear specimens are designed to induce large shear strains. The shear deformation of the two sheet metals of 60TRIP and 60C is quite different and the adiabatic shear band is observed with 60C only. The width of a shear band is measured by comparison of the hardness in a crack tip. The shear deformation in 60TRIP is restrained and the crack is propagated by a tensile mode since the strain hardening of 60TRIP in the high strain rate is large. The load-displacement curves show that the load with 60TRIP becomes higher than that with 60C as the displacement increases

Collapse behavior of asymmetric hat-type rectangular tube with small disturbance of loading condition

Hat-type rectangular tube is a common structural member of an auto body, usually a front side member. The front side member is an important part in absorbing the crash energy of frontal car crash. In frontal car crash the front side member should absorb the crash energy as much as possible to minimize the deformation of the passenger room. The front side member usually has a so-called hat shaped cross-section which is known to show better energy absorption efficiency than the square tube with same cross sectional area. Crashworthiness of the front side member is studied with hat-type specimens that are idealized shape of the front side member. In this research, asymmetric hat-type specimens were studied. Static and dynamic crush tests were performed with five types' of asymmetric hat-type specimen. The collapse modes show very arbitrary collapse profile even if the final energy absorptions are not so much dispersed. In this paper, finite element analysis of asymmetric hat-type specimen was performed with the small error of loading condition, describing errors in specimen specification, loading angle and experimental process. Slight error in the loading angle was considered in the finite element analysis of asymmetric hat-type specimen. The result of finite element analysis shows arbitrary collapse mode also. And this result is suggestive in estimating the efficiency of crash energy absorption during the car crash

Crashworthiness evaluation of asymmetric hat-type rectangular tube by static and dynamic crush test

The axial crush of channeled members is important in estimation of the energy absorption during the car frontal crash. In order to improve the energy absorption capacity and the velocity deceleration factor of an auto-body, the front-side members are mounted at the side of the engine room and made undergo the axial crush at the beginning of the car crash. There have been so many studies about square or rectangular boxes and hat-type specimens for the axial crush both experimentally and analytically while there are few studies about asymmetric hat-type specimens that are used for designated deformation. The axial crush of asymmetric hat-type specimens is, however, difficult to describe analytically with the kinematic crush mechanism. In this paper, asymmetric hat-type specimens are fabricated by spot welding or laser welding with different spacing between two welded spots. The specimens are then deformed for the axial crush at the various crush velocity. The experimental result shows that the specimens are not deformed in a consistent manner, but arbitrarily. In this type of axial crush, the length of the flange region is an important parameter as well as the spacing between welded spots. Experimental results also show the difference in the crush mode between the spot-welded specimens and the laser-welded ones. The difference in the first peak and average load is also demonstrated as well as the energy absorption capacity