Papers by Keyword: Life Prediction

Abstract: According to the different environment characteristics of China, the environments are divided into five types. Concrete durability evaluation index system is established in connection with different influence degree of durability factors in different environment. Combining with the properties of entropy, the weight of each influence factor index in a specific environment is determined by using Extension AHP, in order to avoid the disunity and incomplete of traditional AHP and eliminate the subjectivity to a certain extent in the process of index weight calculation. On this basis, the application software of the concrete durability evaluation and the life prediction for existing structure is programmed, which is applied in the living example. The analysis result shows that the application software has some important application value and practical significance, which can evaluate the durability of concrete structure effectively.

Abstract: To predict an airborne equipment lifetime with finite element simulation method, use ANSYS and Flothem, respectively, to analysis vibration stress and temperature stress, corrected by kinetic experiment; then import the results into the failure prediction software-CALCE PWA, set the intensity and duration of stress according to its mission profile, finally get the component failure life prediction results under comprehensive temperature and vibration stress; extract the Monte-Carlo simulation data, use the single point of failure distribution fitting, fault clustering and multipoint distribution fusion method to get the board and the whole machines lifetime and reliability prediction. The design refinement suggestion of the airborne equipment is given at the end of the conclusion.

Abstract: The strain change characteristics of multiaxial fatigue are analyzed under the condition of the combined tension and torsion loading for thin-tube specimen. Based on the principle of multiaxial critical plane approach, a multiaxial fatigue damage parameter is established, which takes account of the effect of not only the maximum shear strain amplitude and normal strain amplitude on the critical plane but also the parameter of non-proportionality. The non-proportionality is the function of loading parameters which is closely contact with the strain change characteristics of multiaxial fatigue and it can indicate the whole material damage. The experiments under the tension-torsion proportional and non-proportional loading were conducted to verify the multiaxial fatigue life model proposed in this paper. The life prediction has a good correlation with the experimental results.

Abstract: This paper analysis and reviews the calculation and the predicting model of concrete carbonation depth, also discusses the influence factors of concrete carbonization and the applicability of the predicting model. In order to reduce or avoid the effect of complex factors such as material composition, humidity and temperature on the calculation of the carbonation depth and the prediction results, the predicting model of concrete carbonation depth based on the time-series changes is investigated. In this model, Box-Jenkins time series analysis is utilized to establish the regression model-AR model, which reflect the concrete carbonation depth changes over time. The research and analysis shows that the model has characteristics of simple and high precision, and with the measured data increased and updated, the prediction result is getting better and better. Using this method to evaluate the life of concrete structures which under the affection of carbonation, only need to test the carbonation depth of concrete, and the other parameters is not need consider.

Abstract: The paper introduces life prediction models and existing questions of marine concrete structures exposed to chloride environment; Theory of Box-Jenkins time series prediction method is put forward to analyze the change law of chloride concentration of reinforcemnet surface of marine concrete structures along with time; Stationary test, model identification and parameter estimate are introduced; Modeling process and best model identification are discussed by means of analyzing laws of chloride concentration changing with time, and predicts using the best model. Analysis results show that the prediction model built by Box-Jenkins method has simple form and high prediction accuracy. Whats more, future chloride concentration can be well predicted by history values without determining specific values of durability parameters.This is a new method of life prediction of marine concrete structures.

Abstract: In this paper, fatigue damage and life prediction of laser lap joints were investigated based on natural frequency as the damage variable. At each fatigue stage, damage degree of laser welded specimen was monitored by the fatigue test and dynamic response tests. The results show that in the fatigue process during the increase in the number of fatigue cycles, each order natural frequency of test specimen decreased at different rate. There was almost no damage before the number of cycles reached 60% of the fatigue life, and then cracks began to initiate. When the number of cycles reaches 80% of the life, macroscopic cracks appeared and the predicted damage degree reached to 50%. Based on relation between the change rate of the natural frequency and the fatigue damage, a new fatigue life prediction model was established. The results from experimental tests were consistent with the fatigue life prediction model.

Abstract: Based on the creep test results of T91/12Cr1MoV dissimilar welded joint at different conditions, the creep curves of this dissimilar welded joint were established by modified θ projection concept. Low stress creep life was predicted by this curve and the established creep curve shows a good agreement with the experimental data. For computation, Larson-Miller parameters method was also used in creep life forecasting of T91/12Cr1MoV dissimilar welded joint. The resu lt showed that the modified θ projection concept was more accurately in predicting the creep life than Larson-Miller parameters method in allusion to T91/12Cr1MoV dissimilar welded joint.

Abstract: Cylinder cover is an important component of the engine. It is damaged by low cycle thermal fatigue, high cycle thermal fatigue and creep in operation. Thus, the life and reliability of the cylinder cover are important criteria for engines. The temperature field and stress field of the cylinder cover are computed by the sequentially coupled analysis method: the elastic strain, plastic strain and creep strain of the dangerous point on the cylinder cover are analyzed in ten startup-working-shut down cycles; and it is proved in theory that low cycle thermal fatigue is the primary factor affecting the service life of the cylinder cover and the startup time of the engine is an appropriate parameter to estimate the life of thecylinder cover. The creep has little influence on the stress amplitude, and makes the mean stress increased. The relaxation is coexisting with creep in high temperature; it reduces the increase speed of mean stress. After finite cycles, the mean stress tends to constant gradually. Therefore, the creep-fatigue interaction can equal to thermo-mechanical fatigue whose stress amplitude and mean stress are constant. At last, the mean service life of cylinder is predicted.

Abstract: The hybrid fiber reinforced concrete containers for keeping nuclear waste (NWSC) were made by the concrete which mixed polypropylene fibers (0.9kg/m3) and 20mm basalt fiber (2.5kg/m3). The carbonation depth model was established by analyzing carbonation depth of ordinary concrete and hybrid fiber reinforced concrete that through the accelerated carbonization testing. And then two kinds of different concrete NWSC carbonation life were predict according to the similarity theory. The results show that the carbonation life of hybrid fiber reinforced concrete NWSC is 67％ higher than ordinary concrete ones, The addition of fiber can improve the resistance ability of concrete. The hybrid fiber reinforced concrete storage container can meet the requirements of the service life-300a when the thickness of the protective layer is more than 32mm.

Abstract: A series multi-axial tension and torsion low cycle fatigue life experiments of Ti-6Al-4V alloy were conducted on the MTS tension and torsion joint testing machine, in which the torsional strain control and non proportional cyclic loading method under the loading paths of circular, rectangular, square, oval and diamond were successively used. The experimental results are compared and analyzed with the results that calculated by the equivalent strain model, the energy method model and the critical plane method model. The results show that the critical plane method is the accurate prediction model to predict the multi-axial low cycle fatigue life of Ti-6Al-4V alloy.