The fractography is one of the useful technique for finding the cause of breakage in the engineering parts. However, it is not easy to find an appropriate point on the fracture surface, and also the distinction of fracture surface morphology, such as dimple, river-pattern, striation and so on, needs highly skilled technique. To assist unskilled engineers, there are many studies for quantitative analysis of fracture surface morphology by means of Fractal dimension measurement. It is very interesting that fracture surface possesses fractal structure, but it is still difficult to distinguish the fracture surface morphology by using fractal dimensions measurement. On the other hand, Recurrence plots introduced by Eckmann et al. provide a way to visualize the periodic nature of events such as fracture surface’s characteristic feature. Therefore, by applying the image recognition technique to Recurrence plots obtained from fracture surface, it is expected to see the fractographical feature extraction for distinguishing fracture surface morphology.
In this study, in order to recognize the Intergranular fracture on fatigue-fractured spring specimen in a salt water environment, the image recognition technique is applied to Recurrence plots obtained from fracture surface. Since we obtained appropriate judgements for intergranular fracture, it is found that Recurrence plots and image recognition technique could be useful for a computer aided fractographical new technique.
Hydrogen entry into a high strength steel with tribocorrosion in acidic solutions was studied in the present study and it was compared with that in a neutral solution. The samples of SCM 435 high strength steel were subjected to tribocorrosion using a pin-on-disk type wear equipment and to static corrosion in neutral and acidic solutions containing Cl-. The hydrogen content entered into the steel was measured using hydrogen thermal desorption analysis. In a neutral solution, the hydrogen content in the tribocorroded sample was larger than that in the corroded sample without wear. In the acidic solution of pH 2.7, the hydrogen content in the tribocorroded sample was also larger than that in the corroded sample without wear in the case of 6 and 12 h duration time. On the other hand, the hydrogen content in the corroded sample without wear became larger than that in the tribocorroded sample after 18 h duration time. In the measurement of pH changes of the solution for the duration of 48 h tribocorrosion test and static corrosion test, it is revealed that the pH of acidic solution during tribocorrosion increased from about 2.7 to 6.0, though the pH of the acidic solution during static corrosion test revealed little variation. Because H+ consumption by hydrogen generation in cathodic reaction was enhanced with tribocorrosion in acidic solution. The concentration of H+ decreased gradually and pH became higher. As a result, corrosion of the steel and hydrogen generation were suppressed and hydrogen entry into the sample was diminished.
We investigated the characteristics of nonlinear acoustic resonant frequency shift and three-wave mixing interaction during tensile test for low-carbon steel of S25C with electromagnetic acoustic resonance (EMAR). EMAR is the application of a resonant acoustic technique with a non-contact electromagnetic acoustic transducer (EMAT). We used bulk- shear-wave EMAT, which transmits and receives shear wave propagating in thickness direction of a plate specimen. Nonlinear acoustic parameter variation has indicated incremental behavior in relation to the plastic strain, and reached to the peak value between lower yield strength strain and tensile strength strain. Those characteristics are corresponding to the dislocation densities measured by X-ray.
This paper deals with the numerical analysis of an air spring that consists of two tanks connected by a long pipe. Two resonance points may appear in the frequency response of a vibratory system supported by this type of air spring despite the fact that the system has an apparent single mass. This phenomenon is caused by the presence of a secondary mass as reported in our previous paper. It was found that the secondary mass is the mass of air which locally exists in the pipe. The magnitude of this mass is extremely small, but the acceleration of the air in the pipe ― and therefore the inertia force generated from it ― becomes very large. The generated force is further amplified by the Pascal’s principle and is transmitted to the supported mass. There are obvious nonlinear characteristics in this type of air spring; whereas the previous studies were based on linear assumptions. In this study, the governing equations for the air stream expressed by a nonlinear partial differential equation were solved by using the finite difference method. In particular, the pressure loss is evaluated due to air vortex being generated behind the orifice installed in the pipe. As a result of this study, it was found that the orifice is effective in suppressing the height of the secondary resonance point. Furthermore, this non-linear analysis provides the effective method to estimate the amplitude dependency of the dynamic characteristics of the air spring system.
In recent years, large deformation analyses of flexible spring materials have attracted attention considerably. However, there is not sufficient analysis for practical problems such as large deformation of a cable within a channel (or a pipe), or of a drill inserted in a drilling hole in rock engineering and petroleum production, or of a medical guide wire (catheter) within a blood vessel, and so on. When a thin flexible beam material is pushed through the narrow space, the beam may buckle since the leading edge of the material strikes an obstacle (or a barrier) and cannot proceed any more. The large deformation behavior will be of great concern in handling these flexible materials.
This paper deals with large deformations of a flexible elastic beam contained within a rigid channel with friction under the action of axial compressive forces at each end. Three different deformation stages in a channel are prescribed for our analysis. Using the nonlinear deformation theory, nondimensionalized analytical solutions are derived in terms of elliptic integrals. In this study, several experiments were presented and the experimental results were compared with the theoretical formulas.
As a result, the relation between the applied axial force and the pushed-in beam length is similar to that of predicted calculation by the analytical theory. Furthermore, it is made clear that the existence of friction between the beam and the wall causes a nonuniform large deformation. Incidentally, the analysis presented in this paper would be applied to the medical guide wire (catheter) and the design of machinery for handling flexible elastic materials such as sheets, tapes, films, papers, cloths and so on. In addition, designers of machines for drill , tubing strings, and sewing machines should find the results useful and easy to apply.
In this study, 3D finite element analyses have been made on the stress intensity factors for semi-elliptical surface cracks on the wire surface of a tension coil spring in order to investigate the effects of spring parameters on the correction factors, Fi (i=I, II and III) for the three modes of the stress intensity factors. The parameters selected for the present analyses are crack inclination angle θ, crack position on wire surface, normalized half crack surface length c/r, crack aspect ratio a/c and spring index s=R/r where c is the half crack surface length, r the wire radius, a the crack depth and R the coil radius of the spring. The mode I correction factor, or the normalized mode I stress intensity factor FI was found dominant over the correction factors for the other two modes in all the cases investigated. The most influential parameter for FI was the crack aspect ratio a/c, and the largest FI value was calculated as approximately 2.75 for a/c=4 near wire surface, i.e., φ=0°. The most influential parameter for the other correction factors FII and FIII was the crack inclination angle θ. The correction factors FII and FIII were revealed to take on smaller maximum values than FI: i.e., the maximum absolute value of FII was found approximately 1.3 for θ=0° and 90°near wire surface (φ=0° and 180°), and that of FIII approximately 0.59 for θ=0° and 90°at the deepest point of the crack (φ=90°).
Traditional Japanese bows are composite (clad) materials made up of bamboo and wood with very high flexibility. Each bow is composed of multi arcs with different radius of curvature and cross sectional areas along with the length. In using the Japanese bows there are three stages. At first the bow is free standing, then, it is constrained negatively using the chord. The bow is then loaded to form various shapes. Although the shape of archery is similar, Japanese bows are not symmetrical, and the grip is off center, therefore, the characteristic and dynamics of Japanese bows are very complicated. In recent years, large deformation analyses of the flexible bows have attracted attention considerably because of both analytical and technological interests in the design of bows and arrows. In this study, the details of the simulation results of Japanese bows obtained in using a simplified model treated as a nonlinear flexible beam with a large deformation are presented using the elliptic integral derived from Elastica theory. From this investigation, some interesting and valuable information are obtained. Furthermore, using a flexible thin PVC beam specimen, a large deformation experiment is performed to confirm the applicability of the large deformation theory proposed here. The experimental results closely matches that of the theoretical values. Therefore, this analysis is useful in improving the design of bows. This study would be useful to develop technique of Japanese bows in the field of the so-called sports-leisure.