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It is always challenging to provide appropriate material properties for a composite progressive failure model. The nonstandard percentage reduction method that is commonly used to degrade the material constants with micro-scale defects generates tremendous uncertainty in failure prediction. The constitutive matrix is composed of multiple material constants. It is not necessary that all constants degrade either equally or linearly due to a certain state of material defects. With this very concern in mind, this article presents a guideline for using a quantified perturbation for each coefficient appropriately. It also presents distribution of effective material properties (EMPs) in unidirectional composite materials with different states of defects such as voids. Irrespective of resin transfer molding (RTM) or chemical vapor infiltration (CVI) processes, manufacturers’ defects such as voids of different shapes and sizes are the most common that occur in composite materials. Hence, it is important to quantify the ‘effects of defects’ void content herein on each material coefficient and EMP. In this article, stochastically distributed void parameters such as the void content by percent, size, shape, and location are considered. Void diameters and shapes were extracted from scanning acoustic microscope (SAM) images of 300,000 cycles of a fatigued composite. The EMPs were calculated by considering unit cells, homogenization techniques, and micromechanical concepts. The periodic boundary conditions were applied to unit cells to calculate the EMPs. The result showed that EMPs were degraded even when there was a small percentage of the void content. More importantly, the constitutive coefficients did not degrade equally but had a definitive pattern.

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.

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.

The objective of this fundamental study is to provide a comprehensive insight on how the constitutive coefficients are degraded due to various common defects. These defects are such as voids and fiber breakages. Furthermore, understanding of how the degraded material properties affect the elastodynamic Green’s function in composite materials at low frequencies is investigated in detail. Traditionally, in wave propagation analysis for computational nondestructive evaluation (CNDE), except discontinuities, the test specimens are considered homogeneous and non-defective. However, how the degraded material properties affect the ultrasonic waves in the test specimen are not fully understood. In this study, the effective material properties of a composite material with various distributed damages are calculated using a proposed generalized model where all constitutive coefficients can be obtained. In General, the effect of modified constitutive material properties on Green’s function is negligible. However, in this study, it was found that it can be influential even at the lower frequencies. Thus, for accurate CNDE, it is recommended to use compromised constitutive coefficients for wave computation when material is degraded. A baseline composite material with unidirectional fibers and woven composite are considered in this study. The proposed model was verified by comparing the results with previously published models.

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 (multidirectional) 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 study is design, fabrication, and testing of an acousto electrodynamic three-dimensional (3-D) vibration exciter (AEVE 3-D), which simulates coupled and decoupled (with unpowered arms) 3-D acoustic and/or 3-D mechanical vibration environments. AEVE 3-D 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 3-D's performance, various experiments are carried out using a 3-D piezoelectric energy harvester and a custom-made piezoelectric beam.

In this study, the effect of different void sizes with different void contents are investigated on all coefficients of constitutive coefficients for unidirectional composites. The unidirectional composite can be assumed as a periodic structure. To fulfill this requirement, unit cells with different void contents and different void sizes are simulated. To capture the real effect of void sizes, the unit cells are modeled with different uniform void sizes with a fixed percentage of void content. To quantify all coefficients of material properties in presence of voids, the periodic boundary conditions are applied to the unit cells. The average stresses and strains are obtained using ANSYS interface. The results showed that in the fixed percentage of void content, constitutive coefficients degraded more with the smaller void sizes.

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 A. 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.

The objective of this study is to investigate the effect of nonlocal precursor damages through modulated constative properties on the Guided wave propagation in composite materials. To understand the effect of lower scale damage on the interaction of wave propagation in composite materials, all the constitutive coefficients need to be evaluated. Hence, a method is developed to investigate the effective material properties of damaged composite materials using the representative volume element (RVE) model. To calculate the full matrix of constitutive coefficients, periodic boundary conditions were applied on the RVE and average stresses and strains were evaluated using a finite element model. In this study, the effect of different percentages of void contents on effective material properties is presented. Further, the effect of modified material properties on the Guided wave propagation in a transversely isotropic composite plate was investigated.

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.

Primary objective of the work is to design, fabrication and testing of a 3-dimensional Mechanical vibration test bed. Vibration testing of engineering prototype devices in mechanical and industrial laboratories is essential to understand the response of the envisioned model under physical excitation conditions. Typically, two sorts of vibration sources are available in physical environment, acoustical and mechanical. Traditionally, test bed to simulate unidirectional acoustic or mechanical vibration is used in engineering laboratories. However, a device may encounter multiple uncoupled and/or coupled loading conditions. Hence, a comprehensive test bed in essential that can simulate all possible sorts of vibration conditions. In this article, an electrodynamic vibration exciter is presented which is capable of simulating 3-dimensional uncoupled (unidirectional) and coupled excitation, in mechanical environments. The proposed model consists of three electromagnetic shakers (for mechanical excitation). A robust electrical control circuit is designed to regulate the components of the test bed through a self-developed Graphical User Interface. Finally, performance of the test bed is tested and validated using commercially available piezoelectric sensors.

The differential quadrature method combined with an evolutionary optimization algorithm has been proposed for crack detection in cylindrical shell structures. The circumferential crack, which is assumed to be open, is modeled by the extended rotational spring. A crack with finite length divides the shell into four segments. The governing differential equations of motion of the shell are formulated based on Flugge's shell theory. Applying differential quadrature to the differential equations of each segment and the corresponding boundary and continuity conditions results in an algebraic system of equations. Then, an eigenvalue analysis is performed to obtain the natural frequencies of the cracked shell. To identify the crack parameters, an optimization problem is defined and minimized by Bees algorithm, a swarm-based evolutionary optimization technique. The integrity and applicability of the proposed method is confirmed by some experimental case studies. The results show that the crack statuses are predicted well.