Key Engineering Materials Vols. 462-463

Abstract: This paper presents a relative study on variable amplitude (VA) strain data distribution using the approach of probability density function (PDF) and power spectral density (PSD). PDF is a technique to identify the probability of the value falling within a particular interval, and a PSD is to measure the power of a signal by converting it from the time domain to the frequency domain. The objective of this study is to observe the applicability of both techniques in detecting the pattern behaviour in terms of energy and probability distribution. For this reason, a set of case study data consist of nonstationary VA pattern with a random behaviour was used. This kind of data was measured by fixing a strain gauge that connected to the strain data acquisition on the lower suspension arm of a mid-sized sedan car. The data was measured for 60 seconds at the sampling rate of 500 Hz, which gave 30,000 discrete points. The distribution of collected data was then calculated and analysed in the form of both PDF and PSD, and they were then compared for further analysis. The findings from this study are expected for determining the pattern behaviour that exists in VA strain signals.

Abstract: A stress intensity factor K was used as a fracture parameter to determine the plane strain fracture toughness KIC of AZ61 magnesium alloy using a single edge notch bend (SENB) specimen in accordance to ASTM E399 testing method. Five different specimen thicknesses of 2 to 10 mm were used in the test. A sharp fatigue pre-crack was initiated and propagated to half of specimen width at a constant crack propagation rate of about 1 x 10-8 m/cycle before the specimen was loaded in tension until the fracture stress is reached and then rapid fracture occurred. The fracture toughness KC values obtained for different thicknesses showed that KC value decreased with increasing specimen thickness. The highest KC value obtained was 16.5 MPa√m for 2 mm thickness specimen. The value of KC became relatively constant at about 13 MPa√m when the specimen thickness exceeds 8 mm. This value was then considered as the plane strain fracture toughness KIC of AZ61 magnesium alloy. Calculation of the minimum thickness requirement for plane strain condition and the size of the shear lips of the fracture surface validate the obtained KIC value.

Abstract: Vibration characteristics of partially liquid-filled or partially liquid-surrounded composite cylindrical shells are investigated in this paper. Using Rayleigh-Ritz energy method and Love’s shell theory, eigenvalue equation of the problem is derived, and the polynomial for natural frequencies of such shells is further obtained. The external work by the hydrodynamic pressure, which is introduced by liquid sloshing, is taken into account in the energy function. Hydro-elastic vibration characteristics of a composite cylindrical shell are studied by using the present method. Effects of liquid level, liquid density, fiber orientation, length-to-radius ratio, and thickness-to-radius ratio on the natural frequencies are analyzed and graphically presented.

Abstract: Theoretical investigation on incident elastic P-wave transmission across rock fracture is presented by using an optimization method. It’s assumed that the rock fracture is of nonlinear constitutive model for normal deformation, and the hyperbolic elastic model (BB model) is introduced to descript this nonlinear property. Based on the theory of momentum conservation and discontinues condition, wave propagation equation for P-wave transmission across nonlinear fracture is obtained. Parameter studies, including initial normal stiffness, the ratio of given closure to maximum allowable closure and frequency, are carried out and graphically presented.

Abstract: Cast iron and steel rolls used in the continuous pickling line must be changed frequently because the continuous acid wash equipment induces wear on the roll surface in a short period. The damage portions are usually repaired by using the flame spray coating. Recently, ceramics materials are planed to be introduced to prevent the damage because of their high abrasion and corrosion resistances. In this study new roll structure is considered where a ceramics sleeve is connected with steel shafts at both ends by shrink fitting. Here, the ceramics sleeve may provide a longer lifetime and reduces the cost for the maintenance. However, attention should be paid to the maximum tensile stresses appearing between the ceramics sleeve, spacer rings and steel shafts because the fracture toughness, plasticity and fatigue strengths of ceramics are extremely lower than the values of steel. In this study, finite element method analysis is applied to the new structure, and the maximum tensile stress and stress amplitude have been investigated with varying the dimensions of the structure. Fatigue strengths of ceramics are also considered under several geometrical conditions.

Abstract: Although a lot of interface crack problems were previously treated, few solutions are available under arbitrary material combination. This paper deals with one central interface crack and numerical interface cracks in a bonded strip. Then, the effects of material combination on the stress intensity factors are discussed. A useful method to calculate the stress intensity factor of interface crack is presented with focusing on the stress at the crack tip calculated by the finite element method. For one central interface crack, it is found that the results of bonded strip under remote uni-axial tension are always depending on the Dunders’ parameters , and different from the well-known solution of the central interface crack under internal pressure that is only depending on . Besides, it is shown that the stress intensity factor of bonded strip can be estimated from the stress of crack tip in the bonded plate when there is no crack. It is also found that when , when , and when . For numerical interface cracks , values of and with arbitrary material combination expressed by , are obtained.

Abstract: This paper presents the identification of damages and stress analysis of rail/wheel rolling contact region. The railhead surface of used rail track was investigated to identify damages and the hardness of the rail/wheel contact area was measured. Finite element method FEM code, ANSYS was used to determine the stress distribution at vicinity of rail/wheel contact area. The results showed that the hardness increased on the contact area between rail and wheel due to repeated rolling contact of rail and wheel surface. Severe damages and cracks were observed on the railhead surface and in the cross section of the rail at the contact region. The FEM simulation showed that the highest stress distribution regions were matched with the area of severely damage and high hardness obtained from the observation and experimental results.

Abstract: Bone forming phenomenon is an exquisitely genetic programmed and dynamic process that occur from early embryo skeletal development to postnatal growth and culminating in the formation of highly variable and complex but perfect optimized structures. In this study the high resolution imaging techniques such as computerized tomography (CT) is used to obtain quantitative information about the progressive changes in three-dimensional (3D) skeletal morphology and density of rabbit thighbone during early embryo skeletal development to postnatal growth. Then the changes of the thighbone volume, shape and density during the bone growth process are evaluated by using the 3D images reconstruction method, and the growing direction of the thighbone structure is also evaluated. The effects of genetic and environmental complications to optimized skeletal patterns of bone are discussed.

Abstract: In this paper, strength evaluations and reliability analysis are conducted for different types of PSSS(Periodically Symmetric Struts Supports) based on the FEA(Finite Element Analysis). The numerical models are established at first, and the PMA(Prestressed Modal Analysis) is conducted. The nodal stress value of all of the gauss points in elements are extracted out and the stress distributions are evaluated for each type of PSSS. Then using nonlinear least squares method, curve fitting is carried out, and the stress probability distribution function is obtained. The results show that although using different number of struts, the stress distribution function obeys the exponential distribution. By using nonlinear least squares method again for the distribution parameters a and b of different exponential functions, the relationship between number of struts and distribution function is obtained, and the mathematical models of the stress probability distribution functions for different supports are established. Finally, the new stress distribution model is introduced by considering the DSSI(Damaged Stress-Strength Interference), and the reliability evaluation for different types of periodically symmetric struts supports is carried out.

Abstract: In this paper, based on survey data of delays on intersections in urban highways and in accordance with theoretical capacity of each traffic lane, various reasons of delay in intersections are analyzed numerically. A discrete traffic model to simulate traffic in intersections using Gaussian mesh method is built. After modifying intersection properties, weight of each factor in terms of their effect to capacity is acquired. An optimized way to solve traffic delay is hereby recommended.