The split Hopkinson bar (SHB) method was proposed by Kolsky in 1949 as a high strain rate compression test. Since then, the SHB method has been improved by numerous researchers in the worldwide, and has been expanded to various loading mode, such as, tension, torsion and bending. The present paper outlines the principle of the SHB method for high deformation rate testing. Recently, polymer materials have been widely used as a structural material for automobile. Thus, the present paper focuses on the evaluation technique of the compressive properties of polymer materials, with showing the flow of the data processing on the SHB method.
An accelerated testing methodology for measuring CFRP durability developed by the authors over many years is reviewed in this paper. First, the formulation for time-dependent and temperature-dependent statistical static, creep, and fatigue strengths for CFRP was done based on the matrix resin viscoelasticity. Second, these strengths of unidirectional CFRP were predicted statistically using the formulated equations. The predicted results were compared with experimentally obtained data measured from resin-impregnated CFRP strands as specimens of unidirectional CFRP. Finally, the statistical long-term tensile static, creep, and fatigue strengths are discussed in terms of the role of the matrix resin viscoelasticity.
In this study, a method for determining the viscoelastic material properties from displacement fields is proposed. Stress-strain relationship represented by the superposition integral is employed as the viscoelastic constitutive equation. Thus, the unknown properties are bulk and shear relaxation moduli. The virtual fields method based on the principle of virtual work is used as a method for the inverse analysis. The unknown material properties are determined by solving nonlinear simultaneous equations of the virtual work containing the constitutive equations. The validity of the proposed method is demonstrated by identifying the viscoelastic properties of a soft epoxy resin. Results show that the two independent viscoelastic material properties can be identified by proposed method.
In this study, the parallel plate test which is a kind of viscosity measurement technique was carried out to estimate the shift factor for optical glass. This method can reduce the measurement time in comparison to conventional creep test. First, deformation rates were calculated from histories of the displacement, which were then substituted in Gent’s equation for deriving the viscosities. The estimated viscosities indicated the temperature dependency in the viscoelastic range. Moreover, the shift factors obtained from parallel plate tests agreed well with those from static compression creep tests. Therefore, it was confirmed that the parallel plate test is an effective method for the derivation of shift factor for optical glass. In addition, the shift factors were almost same for measurement loads between 196 to 980 N.
Strain rate dependence of a low-cycle fatigue property of AZ31 magnesium alloy is investigated. Low cycle fatigue tests under low strain rate at 6.2×10-5s-1 and 6.2×10-4s-1 are performed. The stress ratio and the maximum stress are set to -1/2 and 240MPa respectively. Fatigue life, plastic strain amplitude, inelastic strain energy density per cycle and strain rate dependence are investigated. As a result, the number of cycle to fracture decrease with decreasing the strain rate. The inelastic strain energy density per cycle increase with decreasing the strain rate. The relationship between the inelastic strain energy density per cycle and the number of cycle to fracture agree with energy based model.
To extend the lifetime and enhance the safety level of aging pressurized equipment, it is vital to develop improved methods for assessing the fatigue life of austenitic stainless steel, which is a highly ductile material used for equipment and structural components in nuclear power plants. Shot peening is one of the most promising methods for increasing the lifetime of welds and other components that are subject to regular plant inspections. In this study, the effect of peening with Zr shot of varying size on fatigue crack growth and crack opening behavior in notched specimens was investigated. Large-diameter shot that could still reach the notch tip was effective at reducing both fatigue crack occurrence and the width of fatigue crack openings. This benefit was highest at low applied loads. However, once a crack had occurred, Large-diameter shot was effective at increasing the crack growth rate.
Trapeziometacarpal joint (TMC joint) of thumb is one of the joints having a complicated shape which enables to generate a wide variation of finger movements in daily life. It is important to clarify the accurate in vivo contact behavior of healthy TMC joint when evaluating post-operative joint movements. Thus, author analyzed TMC joint contact behavior in 4 different finger positions of 8 healthy adult males using magnetic resonance imaging (MRI) system. From MR images, three-dimensional bone models were constructed and a three-dimensional coordinate system was defined by the characteristic shape of each bone model. Then, three bone axial angles and three-dimensional bone motion of each 4 positions in the TMC joint were calculated: abduction-adduction, extension-flexion, pronation-supination, and Euler angles. Furthermore, contact areas of the articular cartilage in each of 4 positions were clarified from MR images. Results have shown that, the contact area changed with changing of the thumb position and it was maximum oat the thumb extension. In addition, it was clarified that the contact area moved according to the thumb position.
The λ type enforcement braking device (EBD) is a kind of an equipment designed to halt a vehicle, and in turn, prevent a potential traffic accident. The employment of EBD may considerably increase the safety protection of drivers and workers in any road construction region. For the performance improvement of EBD on the collision safety and reliability, it is necessary to evaluate the braking characteristics and optimize the structure of the device. This paper concerns the influence of the ‘arm’ which is an important EBD component on the device’s performance. In particular, the effect of the arm-shape and -length on braking characteristics is investigated by model collision test and respective theoretical calculations. The collisions with three different velocities were carried out using model of automobile and EBD with straight and bend arm shape. A general analysis of a braking distance was derived based on the conservation energy principle. In the model collision test, both straight and bend arm EBD brought us to the same braking distance result, which suggests the negligible effect of the arm shape on the braking. The output of our research was in good agreement with theoretical results. This paper demonstrates the theoretical prediction of the pertinent parameters of a collision behavior. Furthermore, the use of the long arm in the λ type EBD is effective for the shortening of the braking distance, given a proper arm structure optimization. This approach allows us to carry out the braking independent of an automobile driving system.
Spectral hemispherical transmittance of piling quartz glass plates for hemispherical irradiation was estimated by integrating directional transmitted radiant energy measured through a grated spectrometer. The transmittance was consistent with the numerical result based on ray-tracing model except periodic fluctuation (ripple) found especially in the wavelength less than 2.0μm. The ripple resulted from comprehensive polarization characteristics of the spectrometer with sapphire window and was generated for polarized radiation fundamentally. Since the spectral shape between s and p components were upside-down mutually, they could be canceled in the case of random irradiation. As the number of the plates or transmitted angle was large, irradiation into the spectrometer was more polarized and therefore the ripple in the spectral output appeared more remarkably. However, under the conditions of 8 plates the transmittance could be regarded to be reasonable. In addition, mechanism for generation of the ripple was clarified theoretically using Stokes parameter and Mueller matrices. As a result, it was cleared that the ripple didn’t appear at all if parallel ray was transmits through the sapphire vertically.