Plastic deformation behavior and constitutive modeling of Cu-50Ta alloy during hot compression

This paper presents a study on plastic deformation behavior of Cu–50Ta alloy at temperatures of 286–473 K and strain-rate of 0.01–6200 s−1. The effects of temperature, strain-rate, and strain on the yield strength, flow stress, and strain-rate sensitivity coefficient were determined. A phenomenological model was established to predict variation of the strain-rate sensitivity coefficient for Cu–50Ta alloy under dynamic compression. A Johnson–Cook constitutive model was established to predict the equivalent stress–equivalent plastic strain relationship under extreme deformation (high temperature and strain-rate). The results showed that the plastic deformation behavior of Cu–50Ta alloy was affected by temperature, strain-rate, and strain. The material exhibited obvious strain-rate strengthening and thermal softening. As the strain-rate increased, the yield strength logarithmically increased. At a temperature of 286 K, the strain-rate increased from 0.01 s−1 to 6200 s−1, and the yield strength increased from 543.75 MPa to 881.13 MPa. In addition, the yield strength linearly decreased as the deformation temperature increased. Under conditions of dynamic deformation, the variation of strain-rate sensitivity coefficient could be expressed as a function of strain-rate and strain. The phenomenological model accurately described the variation of the strain-rate sensitivity coefficient of Cu–50Ta under dynamic deformation conditions. The Johnson–Cook constitutive parameters, calibrated by experimental data, described the plastic deformation behavior of the alloy under high-velocity impact.

Analysis of Nonlinear Static-Dynamic Deformation of Reinforced Concrete Frames in out-of-Limit States

Постановка задачи. Приводятся расчетная модель, алгоритм расчетного анализа и результаты расчета нелинейного статико-динамического деформирования железобетонных рам в запредельных состояниях, вызванных внезапным удалением одной из несущих конструкций. Результаты. Для создания численной модели режима статико-динамического нагружения конструктивной системы использован программный комплекс LS-DYNA с применением детальной 3Д-модели, реализующей явный метод конечных элементов. При проведении расчетного анализа были приняты физико-механические характеристики деформирования материалов в трех вариантах: полученные по опытным данным Г. А. Гениева, по опытным данным Н. В. Федоровой, М. Д. Медянкина при статико-динамическом одноосном режиме испытаний ограниченного числа стандартных образцов призм и по СП 385.1325800.2018. Выводы. Численным анализом статико-динамического деформирования железобетонной рамно-стержневой системы каркаса многоэтажного здания установлено, что дифференцированный учет количественного значения модуля вязкости бетона и соответственно времени и уровня статико-динамического догружения конструкции позволяет более строго определять критерии особого предельного состояния элементов железобетонных конструктивных систем зданий и сооружений. Statement of the problem. The article presents a computational model, an algorithm for computational analysis and the results of calculating the nonlinear static-dynamic deformation of reinforced concrete frames in out-of-limit states caused by the sudden removal of one of the supporting structures. Results. To design a numerical model of the static-dynamic loading mode of a structural system, the LS-DYNA software package was used that makes use of a detailed 3D model implementing an explicit finite element method. During the computational analysis, the physical and mechanical characteristics of the deformation of materials were taken in three variants: those obtained based on the experimental data by G. A. Geniev, the experimental data by N. V. Fedorova and M. D. Medyankin under the static-dynamic uniaxial testing mode of a limited number of standard samples of prisms and according to the Russian standards SP (СП) 385.1325800.2018. Conclusions. Numerical analysis of the static-dynamic deformation of the reinforced concrete frame-rod system of a multi-storey building has established that the differentiated accounting of the quantitative value of the concrete viscosity modulus and, accordingly, the time and level of static-dynamic loading of the structure allows one to identify the criteria for the special limit state of the elements of reinforced concrete structural systems of buildings and structures in a more rigid manner.

Monitoring Dynamic Deformation of Building Using Unmanned Aerial Vehicle

The height irregularity and complexity of steel structures bring difficulties to dynamic deformation monitoring. PDMS (photogrammetric dynamic monitoring system) can obtain the dynamic deformation of the steel structure, but the flexibility of monitoring is limited because the camera station can only be placed on the ground. In this study, UAV (unmanned aerial vehicle) -PDMS is innovatively proposed to be used in monitoring dynamic deformation of steel structures, and it is verified in the steel frame test and Jinan Olympic Sports Center Tennis Stadium test. To solve the problem that the attitude of UAV cannot be strictly maintained in the hovering process, the improved Z-MP (zero-centered motion parallax) method is used, and the monitoring results are compared with the original Z-MP method. The feasibility of UAV-PDMS applied to steel structure deformation monitoring and the feasibility of improving the Z-MP method to reduce UAV hovering error are verified. The monitoring results showed that the steel structures of the Jinan Olympic Sports Center Tennis Stadium were robust, and the deformations were elastic and within the permissible value.

ANALYSIS OF NONLINEAR STATIC-DYNAMIC DEFORMATION OF REINFORCED CONCRETE FRAMES IN OUT-OF-LIMIT STATES

Statement of the problem. The article presents a computational model, an algorithm for computational analysis and the results of calculating the nonlinear static-dynamic deformation of reinforced concrete frames in out-of-limit states caused by the sudden removal of one of the supporting structures. Results. To design a numerical model of the static-dynamic loading mode of a structural system, the LS-DYNA software package was used that makes use of a detailed 3D model implementing an explicit finite element method. During the computational analysis, the physical and mechanical characteristics of the deformation of materials were taken in three variants: those obtained based on the experimental data by G. A. Geniev, the experimental data by N. V. Fedorova and M. D. Medyankin under the static-dynamic uniaxial testing mode of a limited number of standard samples of prisms and according to the Russian standards SP (СП) 385.1325800.2018. Conclusions. Numerical analysis of the static-dynamic deformation of the reinforced concrete framerod system of a multi-storey building has established that the differentiated accounting of the quantitative value of the concrete viscosity modulus and, accordingly, the time and level of static-dynamic loading of the structure allows one to identify the criteria for the special limit state of the elements of reinforced concrete structural systems of buildings and structures in a more rigid manner.