This study is devoted to the investigation of dynamic response of a curved finite beam supported by vertical supports under moving loads. For the purpose of generality, the beam is assumed to be axially loaded. Each vertical support is modeled as a linear spring and a linear damper. The analysis is based on Euler-Bernoulli beam theory. The present method utilizes the concept of distributed moving load, spring force and damping force, and avoids the use of conditions of continuity. Expressing these forces in terms of the unknown function of the problem highly simplifies obtaining an exact solution. In order to see the dominant variables involved in the problem, dimensionless equations are obtained and solved explicitly. An example is presented to illustrate the validity and accuracy of the proposed method. The results are plotted and compared for various dimensionless variables. The method can readily be extended to include an arbitrary number of supports.

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This paper deals with an inverse problem of impact-force prediction. The force is expressed in a set of expansion functions; hence, the original governing equation is reformulated to a problem of finding the weight of each expansion function. The expansion function is designed to best approximate the impact-force profile. The approach allows us to take into account more priori information of the solution; consequently, a better solution can be obtained. A numerical verification shows the estimation error of the present method is 3%, while the error of the Tikhonov solution is 18.5%.

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In this paper, first-order solutions for elastic problems with a slight-rough straight boundary shape as an arbitrary shape function y=g(x) are obtained based on a perturbation theory. The first-order solutions obtained here are valid to O(ε) order where ε=A/λ<<1; A is the amplitude and λ is the characteristic wavelength in the shape function. Firstly, a general solution for an elastic problem with a straight boundary disturbed slightly by the shape function, y=g(x), is shown. In this study, cosine as a typical periodic function and an exponential function are considered as the shape function. As an application of the general solution, the first-order solutions for semi-infinite elastic media subjected to point load and concentrated moment are shown, and these also are compared with the results obtained by finite element analysis.

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Due to a very short time span of dynamic fracture event, it is quite difficult to experimentally measure dynamic stress field near the crack tip. Node-based finite element method (NBFEM) developed by Yagawa et al was extended to solve dynamic crack propagation problems by modifying the original NBFEM and three schemes of crack tip node separation during crack propagation are examined. A dynamic stress intensity factor in mode I, K^dyn_I, is calculated for fast propagating crack at a constant speed. Three different schemes of the crack tip node separation were considered. Comparing the numerical results with those analytically obtained by Freund showed that the condition of zero initial velocity and nonzero acceleration gives the highest accuracy of three conditions with only 0.91% error.

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Composite materials have been widely applied in a variety of engineering and industrial fields over the past two decades. In order to reduce maintenance costs and to avoid potential catastrophic failure, it is essential to detect damage to these composite structures at the earliest possible stage. Evolutionary approaches, such as genetic algorithms and simulated annealing, have attracted considerable attention as a means of solving a range of combinatorial optimization problems. Accordingly, the current study applies a hybrid evolutionary approach to detect damage in a simply supported equal-sided sector of a spherical laminate shell on the basis of natural frequency and mode shape data obtained from modal testing. The simulations consider two different damage scenarios, namely single-point damage and multiple-point damage. Furthermore, to simulate the measurement errors inherent in experimental modal testing, the simulations consider three specific error conditions, i.e. no error (the ideal case), a maximum 5% error in both the natural frequency and the mode shape data, and a maximum 5% error in the natural frequency data and a maximum 10% error in the mode shape data. The simulation results indicate that the algorithm successfully detects both the location and the extent of the damage in both damage scenarios irrespective of the magnitude of the errors assigned to the natural frequency and mode shape data.

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In-situ TiB whisker reinforced, pure Ti matrix composites have been fabricated by spark plasma sintering (SPS). The microstructure and morphology of the in-situ TiB whiskers in the matrix was observed by scanning electron microscopy (SEM). Mechanical properties, such as elevated-temperature tensile strength, fatigue resistance at 600°C, and creep rupture strength at 600°C were investigated. When the composites (TiB/Ti) were sintered at 900°C with a pressure of 60 MPa for 30 min, most of TiB₂ was transformed into TiB whiskers in the matrix. The composites sintered at 900°C with a pressure of 60 MPa for 30 min had the highest tensile strength at room temperature. The tensile strength of the composites sintered by SPS is higher than those produced by vacuum arc melting. The elastic modulus of the composites increased proportionally with the TiB volume fraction. The composites show the same or higher strength of Ti-15V-3Cr-3Al-3Sn sintered by SPS at less than 600°C. The fatigue and creep resistance of the composites at 600°C are relatively higher compared to those of Ti sintered by SPS.

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It is well known that a single tensile overload applied during constant stress amplitude cycling at a positive stress ratio causes crack growth retardation. In the case of a negative stress ratio, however, the fatigue crack growth rate actually accelerated after a tensile overload. This crack growth behavior is related to the residual stress distribution and crack closure behavior. Therefore, the crack propagation rate before and after applying an overload can be evaluated by the effective stress intensity factor range. Where crack propagation was accelerated after applying an overload, blunted crack tips which occurred because of overload worked as sharp notch roots. The shape of the crack tip affected crack growth after overload in the case of negative stress ratio. In this study, it is found that acceleration of crack growth after overload is dependent on the crack opening behavior and loading conditions after overload.

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The objective is to characterize the effects of SiO₂ nanoparticles on the mechanical properties of the thermoplastic polypropylene (PP) blended with two different styrene-ethylene-butadiene-styrene tri-block copolymer (SEBS) at the intermediate and high strain rates. Tensile tests are conducted at the nominal strain rates from 3 x 10^-1 to 10² s^-1. Phase morphology is investigated by transmission electron microscopy (TEM). In addition, the fracture surfaces are observed by scanning electron microscopy (SEM) to investigate the fracture mechanisms. The elastic modulus increased only when nanoparticles were blended in the small-diameter SEBS blended PP. Decreases in the rupture strain and the strain energy up to failure were prevented for the blend system where nanoparticles were blended in the large-diameter SEBS blended PP. This is because the nanoparticles located inside rubber particles lead to the ductile fracture mechanism while the nanoparticles located outside rubber particles lead to the debonding sites between SiO₂ particles and PP matrix because of the stress concentration around them. The synergistic effect of these nanoparticles gives importance to the location of nanoparticles in PP/SEBS blend systems and the stiffness of SEBS particle.

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From a traffic safety point-of-view, there is an urgent need for intelligent tires as a warning system for road conditions, for optimized braking control on poor road surfaces and as a tire fault detection system. Intelligent tires, equipped with sensors for monitoring applied strain, are effective in improving reliability and control systems such as anti-lock braking systems (ABSs). In previous studies, we developed a direct tire deformation or strain measurement system with sufficiently low stiffness and high elongation for practical use, and a wireless communication system between tires and vehicle that operates without a battery. The present study investigates the application of strain data for an optimized braking control and road condition warning system. The relationships between strain sensor outputs and tire mechanical parameters, including braking torque, effective radius and contact patch length, are calculated using finite element analysis. Finally, we suggested the possibility of optimized braking control and road condition warning systems. Optimized braking control can be achieved by keeping the slip ratio constant. The road condition warning would be actuated if the recorded friction coefficient at a certain slip ratio is lower than a ‘safe’ reference value.

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To evaluate the fracture strength of TiN thin films deposited on the hard metal substrate WC-Co, and to investigate the influence of the deposition conditions (bias voltage V_B) on the fracture strength of TiN thin films, the sphere indentation test was carried out to determine the ring crack initiation strength σ_f,m in TiN thin films deposited on two kinds of WC-Co substrates differing in hardness using sphere indenters of varying diameter. TiN thin films 2.5 μm thick were deposited by dc magnetron sputtering under various V_B. Based on the probabilistic theory assuming a two-parameter Weibull distribution, the averages of the fracture strength σ~_f of TiN thin films without residual stress under conditions of uniform tensile stress and the residual stress σ~_R of thin films were predicted from the distribution characteristics of σ_f,m. The main results were as follows: the average σ~_f is almost independent of sphere indenter diameter and substrate hardness, and decreases with increasing V_B; the variation in σ~_f is mainly due to the grain size of thin films; the residual stress σ~_R increases with increasing V_B, and this tendency is qualitatively consistent with the measurements obtained by the X-ray diffraction method.

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