Temperature rise in shear bands in a simulated metallic glass

Temperature rise ($\Delta T$) associated with shear-banding of metallic glasses is of great importance for their performance. However, experimental measurement of $\Delta T$ is difficult due to temporal and spatial localization of shear bands and, as a result, our understanding of the mechanism of $\Delta T$ is limited. Here, based on molecular dynamics simulations we observe a spectrum of $\Delta T$, which depends on both sample size and strain rate, in the shear bands of CuZr metallic glass under tension. More importantly, we find that the maximum sliding velocity of the shear bands correlates linearly with the corresponding $\Delta T$, ranging from $\sim$25 K up to near the melting point for the samples studied. Taking heat diffusion into account, we expect $\Delta T$ to be lower than 25 K for the lower end of sliding velocity. At high temperature, shear band bifurcation and/or multiplication can occur as a negative feedback mechanism that prevents temperature rising well above the melting point

Residual Stress Nondestructive Testing Technology Using Nonlinear Ultrasonic

The nonlinear ultrasonic theory is that ultrasonic waves interact with micro defects and the higher harmonic waves appear when the ultrasonic waves propagate in materials. The acoustic nonlinear parameters are sensitive to micro defects in the nonlinear materials. They are used to characterize the nonlinear characteristics of materials. The nonlinear ultrasonic theories and the characterization of stress in metal by the nonlinear ultrasonic are studied. The nonlinear ultrasonic testing system is built to detect the received signals which propagate in materials with stress. The variation trends of the nonlinear parameters is studied in tensile testing. This paper studies the relationship between nonlinear parameter and stress in different coupling states including contact coupling, air coupling, water coupling. Use manipulator to measure residual stress based on nonlinear ultrasonic and achieve a rapid, non-contact and non-destructive testing

Ultrasonic Tomography of Immersion Circular Array by Hyperbola Algorithm

This paper presents a development and research of a non-invasive ultrasonic tomography for imaging gas/liquid two-phase flow. Ultrasonic transmitting and receiving are implemented using a circular array model that consists of 36 transducers. COMSOL Multiphysics® software is adopted for the simulation of the ultrasonic propagation in the detecting zone. Various two-phase flows with different gas distributions are radiated by ultrasonic waves and the reflection mode approach is utilized for detecting the scattering waves after the generation of fan-shaped beam. Ultrasonic attenuation and sound speed are both taken into consideration while reconstructing the two-phase flow images under the inhomogeneous medium conditions. The inversion procedure of the image reconstruction is realized using the hyperbola algorithm, which in return demonstrates the feasibility and validity of the proposed circular array model

Inverse Kinematic Analysis and Evaluation of a Robot for Nondestructive Testing Application

The robot system has been utilized in the nondestructive testing field in recent years. However, only a few studies have focused on the application of ultrasonic testing for complex work pieces with the robot system. The inverse kinematics problem of the 6-DOF robot should be resolved before the ultrasonic testing task. A new effective solution for curved-surface scanning with a 6-DOF robot system is proposed in this study. A new arm-wrist separateness method is adopted to solve the inverse problem of the robot system. Eight solutions of the joint angles can be acquired with the proposed inverse kinematics method. The shortest distance rule is adopted to optimize the inverse kinematics solutions. The best joint-angle solution is identified. Furthermore, a 3D-application software is developed to simulate ultrasonic trajectory planning for complex-shape work pieces with a 6-DOF robot. Finally, the validity of the scanning method is verified based on the C-scan results of a work piece with a curved surface. The developed robot ultrasonic testing system is validated. The proposed method provides an effective solution to this problem and would greatly benefit the development of industrial nondestructive testing

Study on Modern Bridge Structure Health Monitoring System Based on Damage Identification

With the rapid growth of traffic, the loads\u27 design of many existing bridges can no longer meet the current vehicle load requirements, and the structural safety is seriously threatened. To ensure the structural safety of the bridge, it is necessary to monitor the bridge health and establish an early warning mechanism to prevent major accidents. The modern concrete bridge structure health monitoring based on damage identification proposed in this paper carried out principal component analysis of modern concrete bridges, and then this paper used principal component analysis (PCA) to locate the nonlinear damage source of the experimental model, which obtained the following conclusions. The maximum shear stress of the steel beam web is about 80 MPa，and the bulk stress of steel is reached at 7.5 MPa. Furthermore, to reduce the original data\u27s dimensionality, PCA effectively retains the characteristic information of the original data; empirical examples from external factor are presented. The major advantage of applying this framework is that the structural damage identification is simple and reliable with its advantages of dimensionality reduction, noise reduction, and exclusion of out-of-bounds interference factors

Simulation study of micro interface damage of particle reinforced metal matrix composites on vibration cutting

The finite element simulation of the micro interface of SiCp/Al composites under ultrasonic vibration cutting is described. The constitutive relationship of the matrix, SiC particles and interface is analyzed respectively, and a “matrix-interface-particle” dynamic physical simulation model is given. The cutting conditions of a single particle in three different cutting paths are simulated, and the removal mechanism and interface damage characteristics of SiC particles is analyzed. The reliability of the simulation results is analyzed by observing the SEM photos of the experimental samples