Flexoelectric Effect for Cracks in Piezoelectric Solids

The finite element method (FEM) is developed to analyse 2-D crack problems where the electric field and displacement gradients exhibit a size effect penomenon. This phenomenon in micro/nanoelectronic structures is described by the strain-and electric field-gradients in constitutive equations. The governing equations are derived using variational principles with the corresponding boundary conditions. The FEM formulation with C1-continuous elements is subsequently developed and implemented. An example is presented and discussed to demonstrate the effects of the strain-and electric intensity-gradients on the electro-mechanical behavior of cracked solids.

Enhanced Discrete Element Method (EDEM) and its Application to Stability Analysis of the Slope with Non-Through Joints

A new enhanced Discrete Element Method (EDEM) for modeling the system composed of cracked solids is developed by coupling the traditional Discontinuous Deformation Analysis method (DDA, a kind of implicit version of DEM) with Moving Least-Squares (MLS) meshfree approximation functions. Tracing crack growth inside fracturing blocks and other related capabilities are available in the postprocessing procedure at each iteration step. Some numerical examples are provided to verify this method, and it is prospective to solve stability problems of the slope with non-through joints and other fracture mechanics problems in a new way.

Comparative Study of Instantaneous Frequency Extraction in Nonlinear Acoustics Used for Structural Damage Detection

Nonlinear acoustics deals with various nonlinear effects that occur in ultrasonic wave propagation. The method is suitable for material characterisation, as it uses different nonlinear phenomena associated with material imperfections. The method has been used for detecting nonlinearities in cracked solids by: measuring distortions of acoustic signals, estimating resonance frequency shifts or assessing nonlinear vibro-acosutic modulations. The latter is the most widely used non-classical approach to probe material nonlinearities. The method involves vibro-acoustic interactions of ultrasonic wave and modal vibration in damaged specimens. Modulation intensity that strongly relates to damage severity - is usually assessed in the frequency domain and often leads to confusing results when large modulations are involved. The paper investigates the time domain analysis of vibro-acoustic modulated signals. Several methods for instantaneous frequency calculation used to assess the intensity of modulation - are compared. Simulated and experimental data are used in these investigations.