Key Engineering Materials Vols. 297-300

Abstract: The effects of varying distribution type of random variables and environmental, operational, and design random variables influenced by a shock wave caused from various origins on the failure probability are systematically investigated using the first order reliability method (FORM) for buried pipeline. It is found that the failure probability of the buried pipeline increases with faster P-wave velocity and slower S-wave velocity. The failure probability is estimated to be the largest for the Weibull distribution and the smallest for the lognormal distribution. A set of similar values of the failure probability for the normal distribution and lognormal distribution are noted. The normalized margin is defined and estimated. Furthermore, the normalized margin is used to predict the failure probability simply by using the fitting lines between the failure probability and the normalized margin.

Abstract: Progressing cavity pumping technology will be extensively applied for oil exploitation because of its advantages such as lower cost, higher adaptability for oil viscosity, sand-content and oil-gas ratio. This pumping system consists of motor, reducer, coupling, progressing cavity pump, variable frequency converter and protector. Among them, oil-submerged planetary gear reducer is one of the most important transmission components, which transmits torque and adjusts the rotational speed between motor and pump. Because the reducer is required to work successively under the harsh down-hole condition of high temperature and pressure for long span, the reliability design and fatigue life become the key technical problems for research. Based on reliability theory and optimum design method, the mathematical model for reliability optimization of NWG-type gear reducer is built up and optimum geometrical parameters are found in this paper. It is testified that, with such parameters, the diameter of the reducer can be reduced, daily oil-output can be increased and life span of the pumping system can be thus lengthened.

Abstract: In the design optimization process design variables are selected in the deterministic way though those have uncertainties in nature. To consider variances in design variables reliability-based design optimization problem is formulated by introducing the probability distribution function. The concept of reliability has been applied to the topology optimization based on a reliability index approach or a performance measure approach. Since these approaches, called double-loop singlevariable approach, requires the nested optimization problem to obtain the most probable point in the probabilistic design domain, the time for the entire process makes the practical use infeasible. In this work, new reliability-based topology optimization method is proposed by utilizing single-loop singlevariable approach, which approximates searching the most probable point analytically, to reduce the time cost and dealing with several constraints to handle practical design requirements. The density method in topology optimization including SLP (Sequential Linear Programming) algorithm is implemented with object-oriented programming. To examine uncertainties in the topology design of a structure, the modulus of elasticity of the material and applied loadings are considered as probabilistic design variables. The results of a design example show that the proposed method provides efficiency curtailing the time for the optimization process and accuracy satisfying the specified reliability.

Abstract: A rubber-modified epoxy resin is widely used as adhesive and matrix materials for fiber composite material. The structural reliability of composite material depends on the fracture toughness of the matrix resin. In this study, the fracture toughness and the damage zone around a crack tip in rubber-modified epoxy resin were investigated. The volume fractures of rubber (CTBN1300×8) in the rubber-modified epoxy resin were 0%, 5% and 15% under several loading speeds. The fracture toughness(KIC) and the fracture energy(GIC) were measured by using 3-point bending specimens. The 4-point bending specimens were also used to observe damage zones at the vicinity of a crack tip in modified resins. The results show that the values of the fracture toughness and the sizes of damage zones at 5% and 15% rubber content decrease with increase in loading speed.

Abstract: The evaluation of specimen thickness effect of fatigue crack growth life by the simulation of probabilistic fatigue crack growth is presented. In this paper, the material resistance to fatigue crack growth is treated as a spatial stochastic process, which varies randomly on the crack surface. Using the previous experimental data, the non-Gaussian (eventually Weibull, in this report) random fields simulation method is applied. This method is useful to estimate the probability distribution of fatigue crack growth life and the variability due to specimen thickness by simulating material resistance to fatigue crack growth along a crack path.

Abstract: In order to investigate the effect of SP treatment on the high cycle fatigue properties such as fatigue strength, crack initiation and propagation behaviors, rotating bending fatigue tests on shot-peening (SP) treated AC4CH aluminum alloy were carried out. The fatigue properties of the SP-treated material were compared with fatigue properties of the non-peened material, the hot isostatic pressure (HIP) treated material and the semi-liquid (SL) die casting material. the main conclusions obtained were, (1) The fatigue properties of SP-treated material is most excellent in all materials. (2) The fatigue life property of AC4CH alloys is significantly affected by fatigue crack initiation behavior. The reason why the SP-treated material has longer fatigue life than those of other material is that it has no cast defects near the surface by the effect of SP treatment. (3) The reason of fatigue life improvement by SP treatment is decrease of fatigue crack propagation rate.

Abstract: This paper sums up the measures to treat cut slope in expressway and puts forward a new method to calculate the slope relability by the application of Dynamic Programming.

Abstract: A unified method is presented for the prediction of the fatigue strength of steel components containing small holes and being subjected to combined loading. Materials investigated were an annealed 0.37% carbon steel and a quenched and tempered Cr-Mo steel. Combined axial and torsional fatigue loading tests were carried out using specimens containing a small hole, which was introduced into the surface by drilling. The diameter of holes equaled the depth and was either 100µm or 500µm. The non-propagating cracks emanating in the radial direction from the holes were observed at the fatigue limit. When the loading condition is the same, they were on a plane that inclined at the same angle with respect to the specimen axis, regardless of the size of holes. This result suggested that the fatigue strength would be controlled by the Mode I threshold condition for propagation of a crack initiated on a critical plane. A criterion connecting uniaxial fatigue strength with multiaxial fatigue strength was proposed based upon the assumption that at the threshold level, the variation of the stress intensity factor of a Mode I crack initiated under combined loading equaled that under uniaxial loading. The predictive method proposed based upon this criterion is practical in that no fatigue test is necessary in making predictions. For the various conditions of in-phase and out-of-phase fatigue loadings with an imposed mean or static load, experimental results agreed well with predictions.

Abstract: The crack, which occurs because of fatigue, should often consider not only the single crack but also plural cracks occurring. In this paper, the material strength when two or more cracks occurred because of fatigue etc. was examined by calculating stress intensity factor K value by using caustics method and the photoelasticity. In general, plural cracks are known KI value decreases compared with the single crack. Therefore, the influence on K value was experimentally examined from the point of the distance between the cracks, the angle, and the crack length and the mode change. As a result, KI value influences destruction in plural in exist only mode I and the mixed mode of mode I and mode Ⅱ like this research cracks. When the crack length becomes long if the distance between the cracks narrows, the decrease of KI value grows. In addition, it has been understood that the decrease of KI value is influenced by a/w on the boundary of d/a=1 (the distance between the cracks is equal to the crack length).

Abstract: In this paper, artificial creep degradation test and ultrasonic measurement for their creep degraded specimens (Cr-Mo alloy steel) were carried out for the purpose of evaluation for creep damage. Absolute measuring method of quantitative ultrasonic measurement for material degradation was established, and long-term creep degradation tests using creep life prediction formula were carried out. As a result of ultrasonic tests for crept specimens, we conformed that both the sound velocity decreased and attenuation coefficient linearly increased in proportion to the increase of creep life fraction (fc). In frequency and noise analysis, it was conformed that the high frequency side spectra and central frequency components shift to low frequency band, and bandwidths decrease as increasing creep damage in backwall echo. And also, the ultrasonic noise linearly increased in proportion to the increase of creep degradation.