Effect of distributed defects on effective material properties of composites is required for the progressive failure models. Although the degradation of the effective material properties due to the presence of the lower scale damages is well investigated, how each material coefficient should be compromised in a progressive failure model is still a dilemma. Percentage of defects, the shape of the defects and their stochastic distribution may affect the individual material coefficients in a unique way and may not be uniform across the constitutive matrix. Hence, to find how the individual material coefficients in a constitutive matrix changes due to the presence of the voids and fiber breakage, all material coefficients in a constitutive matrix were studied herein. Representative volume element of a unidirectional fiber-matrix composite was studied with appropriate boundary conditions and respective material coefficients were calculated. It was found that the local gradients of the degradation curve obtained for each material coefficient are not linear with the increasing percentage of degradation and not uniform for all material coefficients. The shape and different locations of the defects with constant defect percentage were found to be inert towards affecting the material coefficients.

A high percentage of failures in sensors and devices employed in harsh industrial environments and airborne electronics is due to mechanical vibrations and shocks. Therefore, it is of paramount importance to test equipment reliability and ensure its survival in long missions in the presence of physical fluctuations. Traditional vibration testbeds employ unidirectional acoustic or mechanical excitations. However, in reality, equipment may encounter uncoupled (unidirectional) and/or coupled (multi- directional) loading conditions during operation. Hence, to systematically characterize and fully understand equipment's behavior, a testbed capable of simulating a wide variety of vibration conditions is required. The primary objective of this work is design, fabrication, and testing of AEVE 3D, an Acousto Electrodynamic three-dimensional (3-D) Vibration Exciter, which simulates coupled and decoupled (with unpowered arms) 3-D acoustic and/or 3-D mechanical vibration environments. AEVE 3D consists of three electromagnetic shakers (for mechanical excitation) and three loud speakers (for acoustic excitation) as well as a main control unit that accurately calculates and sets the actuators' input signals in order to generate optimal coupled and decoupled vibrations at desired frequencies. In this paper, the system's architecture, its mechanical structure, and electrical components are described. In addition, to verify AEVE 3D's performance, various experiments are carried out using a 3-D Piezoelectric energy harvester and a custom-made Piezoelectric beam.

Energy harvesters primarily depend on on a groups of unit cells to harvest energy at broadband frequencies so that each unit cell is responsible to harvest energy at a distinct frequency. Other design complexity, space, and financial profusion are required for transferring from unit-frequency to multi-frequency energy scavenging. Also, it is very unlikely to obtain expected power output if the available vibration source doesn’t match the designed loading condition (usually, unidirectional) of the device and requires rearrangement of the base structure to have projected output. In this paper we model the unique feature of acoustic metamaterial (AM), which is not only able to harvest energy at multiple frequencies using only a unit cell device, but also able to harvest energy under a variety of uncoupled (unidirectional) and coupled (multi-directional) vibration environments with an identical base structure arrangement.

Material properties at the vicinity of the cut-outs in composites are not entirely defect-free. The nteraction of multiple cutouts like rivet holes, the repercussion of their configuration on crack propagation, and ultimate strength were predicted using Peridynamic method and the results are reported in this article. The effect of microscale defects at the vicinity of the cutouts on macroscale damage propagation were shown to have quantifiable manifestation. This study focused on two to four holes in unidirectional composite plates with 0°, 45°, and 90° fiber directions, while the vicinity of a hole was considered degraded. Numerical results were validated using quantitative ultrasonic image correlation (QUIC) and the tensile test. Both the experimental and numerical results confirmed that the strength of the horizontal configuration is higher than the vertical in the plates with two holes. Furthermore, the square configuration was found to be stronger than the diamond configuration with four holes. When the effect of microscale defects was considered, the prediction of ultimate strength was better compared to the experimental results. The predictive model could be reliably used for progressive damage analysis.

In spite of many studies concerning the potential of auditory nerve actions, the timing of neural excitation in relation to basilar membrane motion is still not well understood. In this study, therefore, a Piezoelectric Artificial Basilar Membrane (PABM) is fabricated using Denton Explorer evaporator. The proposed dynamical system is made of polyvinylidene fluoride membrane on which 40 chromium electrodes were deposited with thickness close to 10⁴ Å. The PABM sensor was tested with variable engineering parameters that contribute to its frequency selection capabilities. To characterize the frequency selectivity of the PABM, mechanical displacements were measured using a very precise high-resolution data acquisition board. When electrical and acoustic stimuli were applied, the measured resonance frequencies were in the ranges of 600to2000. These results demonstrate that the mechanical frequency selectivity of this PABM is close to the human communication frequency range (300–3000 Hz), which is a vital feature of potential auditory prostheses.