Applied Mechanics and Materials Vol. 751

Abstract: The numerical simulation is widely used, in now days, to verify the viability and to optimize structural mechanic designs. The numerical approach of elastoplastic materials can found some problems related to ill-conditioning of matrices (from FEM systems), associated to the critical points from the snap through or snap back shape of the equilibrium curve. Aiming to overcome this misfortune it is proposed a strategy via Tikhonov regularization method in association with L-curve technique to determine the regularization parameter. This strategy can be used in many numerical applications for structural analysis. The theoretical development about these Some numerical examples are presented to attest the efficiency of this proposed approach.

Abstract: The delamination growth may occur in delaminated piezoelectric shell subjected to external load and it will further cause structural failure. Based on the variational principle of moving boundary and considering the contact effect between delamination regions, in this paper, the nonlinear governing equations for the delaminated piezoelectric shell under electro-thermo-mechanical loadings are derived, and the corresponding boundary and matching conditions are given. At the same time, according to the Griffith criterion, the formulas of energy release rate along the delamination front are obtained and the delamination growth is studied. In the numerical calculation, the energy release rate and delamination growth of axisymmetrical piezoelectric cylindrical shell are analyzed, and the effects of voltage, temperature and humidity, mechanical load, delamination length and depth on delamination growth are discussed.

Abstract: Numerical simulations are widely used for forming processes optimizations nowadays. They significantly contribute to improvement of forgings quality and production costs reduction. The crucial points of the numerical simulations are material input data and implemented material models. The paper is dealing with overview of methods for the input data measurement. There are discussed tests with various options of strain measurements as well as modifications of compression tests. Part of the paper is dealing with 3D strain measurements by Digital Image Correlation (DIC) enabling local strains measurements. DIC enables direct comparison of strains experimentally measured and strains obtained by numerical simulations, which is going to be presented. Finally, possibilities of complex material description considering plastic damage are presented. The last approach is the most accurate providing the most information on material behavior for FEM simulation, the procedure includes measurements on samples of various geometries with various stress strain conditions. Examples of sample sets for these measurements are shown here together with material models describing multiaxial plastic flow and damage.

Abstract: In this paper, research on a testing method of indentation test proposed by F M Haggag is discussed first, and the experimental testing research on metallic material properties with strain aging is carried out and discussed using indentation test. The authors proposed to use indentation test to measure the properties of metallic materials with strain aging embrittlement based on experimental verification. And it provides a possibility to measure the properties of metallic materials with strain aging using nondestructive testing method.

Abstract: This research work presents the influence of Al₂O₃ nanoparticle additives on the performance characteristics of a journal bearing. Non-Newtonian fluid based on Carreau viscosity model was represented for SAE10W50 oil blended with Al₂O₃ nanoparticles in this work. Reynolds equation and energy equation have been formulated and solved numerically using finite difference method and multigrid multilevel techniques with boundary conditions. The static characteristics of the journal bearing under isothermal and adiabatic conditions were examined. The results show that the addition of Al₂O₃ nanoparticles improve load-carrying capacity of the journal but almost no change on film temperature due to good thermal property of Al₂O₃ nanoparticles.

Abstract: A new detection method for measuring weld crack of crane’s metal structure is developed.It works by combining polyvinylidene fluoride (PVDF) with curvature operational shapes (COS) algorithm. First, the theory of damage identification using the imaginary part of frequency response function was analyzed, and the extraction approach of COS was illuminated in detail. Then, the fitting method which is called gapped-smoothing method (GSM) was chosen to obtain the COS of healthy structure.Next, experiments were carried out on a steel plate with weld cracks based on PVDF. The experiment result expresses that the positions of cracks could be located precisely and the index is very sensitive to the different length of cracks. Therefore it can provide reliable information for positioning and quantitative analysis of the weld cracks.

Abstract: The present work describes an investigation into a vibro-acoustic method to check the existence of superficial flaws in composite sandwich structures, based in a technique inspired in the well known Tap Test. In this case, however, a non-impulsive excitation is provided by an especial transducer and the acoustic response is captured with a microphone. A deconvolution technique is used in order to assess the system's impulse response and generate a “failure” map after post-processing the results. Post-processed parameters evaluated are: Loudness, Sharpness and a discrepancy indicator for the transfer function (named TFDI). Results suggest that Loudness and TFDI potentially indicate the existence of a damaged core and the lack of adhesive tape.

Abstract: Nowadays, there are two socket fabrication methods in Thailand, which are resin casting and thermal vacuum method. The thermal vacuum forming method has more advantages than the resin casting method that ruins technicians' health from the volatile matter. Nevertheless, the thermal vacuum forming method can fabricate the socket with poor wall thickness distribution. The purpose of this paper is to study the effects of the feed rate of stump mould and the temperature distribution of the plastic sheet on the prosthetic socket wall thickness during the thermal vacuum forming process. The feed rates of stump mould were varied by using an industrial robot. The temperature distribution of the plastic sheet was controlled by circular and annular fiberglass insulators placed in its center. The results showed that the prosthetic socket wall thickness increases around the central area of the socket with a decreased feed rate of stump mould. The annular insulator increases the wall thickness slightly, while the circular insulator increases the thickness significantly. The wall thickness at the thinnest location increased from 1.6 mm up to 2.8 mm. In addition, wall thicknesses of areas beneath the circular insulator increased significantly between the marked positions-25 through +25.

Abstract: In order to study the relationship between the fractal dimension of rock fracture surface and temperature, uniaxial compression experiments on the granite rock and scanning electron microscopy experiments on the rock fracture surface were carried out after different temperatures. The fractal dimension was calculated by using scanning electron microscopy images. The results are as following: (1) The cracks show intergranular damage like rock candy, rivers and so on at the temperature from 25°C to 200°C. The fractal dimension are volatile, the fractal dimension reach the maximum at 200 °C, it can be inferred that the granite rock burst the most energy consumption at 200 °C; (2) From 200°C to 800°C, the cracks transform from stepped cleavage, intergranular fracture gradually to grain crushing, transgranular cracking damage with the rise of temperature. When the temperature is above 800 °C, the cracks transform from the transgranular cracks, shear slip bands gradually to dimples and microporous points. The cracks of rock surface transform from irregular crack structure to homogeneous pore structure gradually at high temperature, the weakening of rock heterogeneity is the basic reason for the decrease of fractal dimention of rupture surface, the fractal dimension is reduced from 1.634 at 200 °C to 1.595 at 1200 °C, the margin of reduction is 2.39%. At the same time, the energy consumption of rock rupture decreases with the rise of temperature, rock transforms from brittle to plastic gradually.

Abstract: The average particle sizes of the sediment deposited in deep channel of North Passage of Yangtze River estuary are different at different channel segments in the flooding and dry seasons. As a response, the critical stress for sediment incipient motion might be different, which needs to be studied systematically especially after the channel reaches a new grade with depth of 12.5m. Therefore, a series of tests on the sediment were conducted to determine the critical parameters for the sediment incipient motion with different particle sizes between 0.01mm and 0.04mmcollected from deep channel of Yangtze River. The experimental data indicate that the critical shear stresses increase exponentially with density, and the stresses are 0.2-0.7Pa for the mud with density of 1200-1600kg/m³.And the relational expression between the critical shear stress and the depth was built, which might be applied in the mathematical model to simulate the process of incipient motion for sediment in deep channel of Yangtze River and others.