Papers by Keyword: Curve Fitting

Abstract: The model widely used in the fatigue crack growth study in materials science and fracture mechanics is the Paris-Erdogan, which relates the stress intensity factor with the subcritical crack growth, under a fatigue regime. In this work, a seven degree polynomial is used as an alternative to model the crack propagation behavior and to be able to analyze the three regions charts of the cycles by load, in contrast to the common model that it performs at a slight approximation of the propagation phase of the trinca (region II). Finally, a comparison has been made between the proposed model and the secant method by the ASTM 647,2000 standard that adjusts the points obtained experimentally. This proposed equation is new as another alternative analytical model for which the adjustment parameter “R” are compared in relation to the classical approach in a aeronautical ABNT 4130 steel.

Abstract: In the material’s creep failure analysis, the difficulty of assessing the applied thermo-mechanical boundary conditions makes it critically important. Numerous creep laws have been established over the years to predict the creep deformation, damage evolution and rupture of the materials subjected to creep phenomena. The omega model developed by the American Petroleum Institute and Material Properties Council is one of the most commonly used creep material models for numerical analysis over the years. It is good in defining the fitness of mechanical equipment for service engineering evaluation to ensure the reliable service life of the equipment. The Omega model, however, is not readily accessible and specifically incorporated for creep evaluation in FEA software codes and creep data is always scarce for the complete analysis. Therefore, extrapolation of creep behavior was performed by fitting various types of creep models with a limited amount of creep data and then simulating them, beyond the available data points. In conjunction with the Norton Bailey model, based on API-579/ASME FFS-1 standards, a curve fitting technique was employed called regression analysis. From the MPC project omega model, different creep strain rates were obtained based on material, stress and temperature-dependent data. In addition, as the strain rates increased exponentially with the increase in stresses, regression analysis was used for predicting creep parameters, that can curve fit the data into the embedded Norton Bailey model. The uncertainties in extrapolations and material constants has highlighted to necessitate conservative safety factors for design requirement. In this case study, FEA creep assessment was performed on the material SS-304 dog bone specimen, considered as a material coupon to predict time-dependent plastic deformation along with creep behavior at elevated temperatures and under constant stresses. The results indicated that the specimen underwent secondary creep deformation for most of the period.

Abstract: The new MatPlus software supports the multi-dimensional modelling of materials properties using different data sources. Extensive mathematical functions allow curve fitting of data from different sources to any constitutive models and selectively combining models and datapoints along different dimensions. Physically consistent extrapolation of measured data within the complete multi-dimensional parametric space can be achieved. An integrated library of models can be extended by the user and already contains many popular equations like Hensel-Spittel and Zerilli-Armstrong for flow curves.

Abstract: High temperature creep properties of Al₂O₃-SiO₂ ore (65% Al₂O₃ by mass percentage, abbreviation for Al₂O₃~65) was studied. The results show that the creep rates at 1300 °C × 50h, 1400 °C × 50h and 1500 °C × 50h were-0.89% ,- 1.75%, - 5.76%,respectively. At 1300 °C, ore has good creep resistance. As the temperature increases, the high temperature creep resistance of Al₂O₃ ~ 65 bauxite ore is significantly reduced. Creep process can be divided into two stages: when the time t <30h, the sample are in the densification process; after 30 hours, the creep properties show that the relationship between time and the creep rate is linear. At 1300 °C, the absolute value which is the slope of the linear relationship is smaller, exhibited an excellent high-temperature creep resistance. The loading softening-temperature of Al₂O₃ ~ 65 bauxite ore is 1343 °C. The Sample phase and microstructure are characterized by X-ray diffraction and scanning electron microscopy (SEM). The results show that mullite reticular is formed in sample at 1300 °C; at this point, TiO₂ mostly exist as Rutile. At 1400 °C and 1500 °C, TiO₂ mostly exist as Aluminum titanate, Corundum phase portion into mullite.

Abstract: Parameter analyses in the constitutive model determine the precision of numerical results. Cam-clay model is the first elasto-plastic model in the world and widely used in the practical engineering. SYS Cam-clay model is proposed based on Cam-clay model by incorporating the concept of overconsolidation, soil structure and anisotropy. There are two groups of parameters in this model, elasto-plastic parameters that are exactly same as those in Cam-clay model and evolutional parameters that decide the variation of overconsolidation, soil structure and anisotropy. The detailed process to determine the parameters is introduced step by step.

Abstract: Stock investment is risky and beyond fixed rules to forecast precisely. In order to realize proper stocks selection from specified mathematical function model, principal component factor analysis is proposed to rebuild various stocks via its contribution rates so as to extract the principal component factors from the elimination of weak ones. According to the synthesis scoring and ranking, optimized stocks has been selected as valuable targets. Test from Genetic Algorithm to the ranking aforementioned indicates that the rationality and validity of the results.

Abstract: This paper introduces how to use the testing circuit board of measuring accuracy ofthe sensor, testing circuit board is made by the SCA100T - D01 biaxialanglesensor, ATmega8 MCU, ADS8344AD converter, MAX232 and other related components.Through the three axis turntable to rotate a precise angle, which makes thesensor in the testing circuit board has the output value, the output value indata processing, to find out the best coefficient, so as to achieve therequirements of high precision.

Abstract: This article deals with the tuning of a simplified non-linear model that represents the dynamic behavior of the manipulator arm PUMA MA2000, where excitation signals formed by a finite sum of harmonics Fourier series were used in order to obtain arm dynamical responses. Initially, non-linear mathematical model is derived by using the Euler-Lagrange notation, and then a simplified nonlinear model is obtained and tuned by using the experimental angular position measurements for waist, shoulder and elbow robot joints.

Abstract: Roscoe and Burland set the yield surface of the Cambridge model to elliptic and concluded modified Cambridge model. In this paper, the model has been improved and got the accuracy of the elastic-plastic matrix improvement model, by using the Cambridge model to calculate the volumetric strain and shear strain of soil theoreically and inculcating CU triaxial tests to measure the corresponding soil volumetric strain and shear strain and applying least squares theory to simulate the ratio of theoretical calculations and experimental results.

Abstract: This paper proposed a method for detecting fatigue detection Android smart phone system, and applied to the Android system. The system monitors the state of fatigue by smart phones photographs. Face detection method is used to localize the eyes of the driver and the eye region is extracted to monitor the movement of eyelids. An alarm rule is designed based on the PERCLOS standard to detect drowsy driving.Experiments show that the method is accurate rate, running speed, and can be used to monitor driver fatigue during the day.