Christian N. Della

Vibration of Delaminated Composite Laminates: A Review

Fiber reinforced composite laminates are increasingly replacing traditional metallic materials. The manufacturing process and service of the composite laminates frequently lead to delamination. Vibration analysis is an integral part of most engineering structures. In the present article we provide a relevant survey on the various analytical models and numerical analyses for the free vibration of delaminated composites. A basic understanding of the influence of the delamination on the natural frequencies and the mode shapes of composite laminates is presented. In addition, other factors affecting the vibration of the delaminated composites are discussed. Particular attention is given to composite laminates having piezoelectric sensors and actuators, and ones subjected to axial loadings.

A multi-axial fatigue model for fiber-reinforced composite laminates based on Puck’s criterion

A new multi-axial fatigue model for fiber-reinforced composite laminates based on Puck’s criterion is proposed in this article. In the fatigue model, fatigue master curves from the ATM are used to determine the uniaxial ply fatigue strengths and the multi-axial fatigue failure is then determined by Puck’s criterion with the fatigue strengths at the ply level. The fatigue master curves from ATM are generated with limited uniaxial fatigue tests and can be applied to fatigue loading conditions with various frequencies and stress ratios. Both uniaxial and multi-axial S-N curves can be derived from thefatigue model. Fatigue failure envelopes are also generated from the model to better interpret the multi-axial fatigue failure in multi-axial stress spaces. The proposed multi-axial fatigue model is based on ply-level predictions, but it can beextended to laminate-level predictions with the CLT or numerical methods such as the FEM. Multi-axial fatigue failures caused by either local or global multi-axiality can be predicted by the model. Both uniaxial and biaxial fatigue experimentswere carried out to provide test data for establishing and validating the proposed fatigue model. The application oftheproposed multi-axial fatigue model is demonstrated with predictions of S-N curves and fatigue failure envelopes of unidirectional laminates and multi-directional laminates with typical lay-up configurations. The predictions from the proposed fatigue model are also compared with various experimental results and reasonably good agreement is observed.

Mechanical Properties of Carbon Nanotubes Reinforced Ultra High Molecular Weight Polyethylene

Carbon nanotubes (CNT) have been shown to enhance the engineering properties of plastic fibers in ballistic-resistant garments enabling the garments to withstand very high impact forces while remaining to be lightweight. Previous study shows that by reinforcing ultra high molecular weight polyethylene (UHMWPE) fibers with a small amount of carbon nanotubes, the fibers are simultaneously toughened and strengthened. In this paper, we study the mechanical properties of carbon nanotube reinforced ultra high molecular weight polyethylene (UHMWPE) by using micromechanics-based Mori-Tanaka model. Results show that the addition of small amount of carbon nanotubes as reinforcement can substantially improve the mechanical properties of the UHMWPE fibers.

Vibration of beams with embedded piezoelectric sensors and actuators

This paper presents a micromechanics approach to the study of the vibration of beams with embedded piezoelectric sensors and actuators. The natural frequency of the beam is determined from the variational principle in Rayleigh quotient form. The piezoelectric sensors and actuators embedded in the beam are analysed using Eshelbys equivalent inclusion method. In addition, the Euler–Bernoulli beam theory and Rayleigh–Ritz approximation technique are used in the analysis. Results show that the size, volume fraction and location of the piezoelectric inclusions significantly influence the natural frequency of the beam. The results of the present model agree well with the theoretical results presented in the literature.

Micromechanics model for predicting effective elastic moduli of porous ceramic matrices with randomly oriented carbon nanotube reinforcements

Multi-step micromechanics-based models are developed to predict the overall effective elastic moduli of porous ceramic with randomly oriented carbon nanotube (CNT) reinforcements. The presence of porosity in the ceramic matrix that has been previously neglected in the literature is considered in present analysis. The ceramic matrix with porosity is first homogenized using a classical Mori-Tanaka model. Then, the homogenized porous ceramic matrix with randomly oriented CNTs is analysed using two micromechanics models. The results predicted by the present models are compared with experimental and analytical results that have been reported in literature. The comparison shows that the discrepancies between the present analytical results and experimental data are about 10% for 4 wt% of CNTs and about 0.5% for 8 wt% CNTs, both substantially lower than the discrepancies currently reported in the literature.

Performance of 1–3 piezoelectric composites with porous piezoelectric matrix

A micromechanics method is developed to investigate the effects of porosity in the matrix and the polarization orientations of the piezopolymer matrix and the piezoceramic fibers on the performance of 1–3 piezoelectric composites. The Mori-Tanaka (MT) method is first used to homogenize the porous piezopolymer matrix, and then the MT method for piezoelectric composites is used to analyze the porous piezopolymer matrix with embedded piezoceramic fibers. Results show that the performance of the composites is significantly enhanced by the presence of pores in the matrix and further enhanced by the opposite polarization orientation of the matrix and the fibers.

STATIC AND DYNAMIC ANALYIS OF AIR BEARING SLIDER FOR SMALL FORM FACTOR DRIVES

As the areal recording density increases in hard disk drives (HDDs), the flying physical spacing between the head and the disk decreases and the likelihood of head-disk contact during full speed rotation increases. Therefore, the simulation and modeling of the air bearing slider with ultra-low flying heights becomes an important issue for the operational shock simulation. The static/dynamic properties, including the influence of the radial position and the skew angle of the slider, the rotating speed of the disk, and the shock simulation, of the air bearing slider were analyzed. Generally speaking, for a given rotating speed of the disk, as the slider moves from the inner diameter to the outer diameter, the maximum contact pressure, the skew angle, the pitch angle, and the maximum air bearing pressure increase; while the flying height decreases. These trends are strengthened by a faster rotating speed of the disk. There are obvious oscillations in the air bearing force and the minimum spacing when contact occurs during a shock.

A Comparative Study of the Hydrostatic Performances of 1-3 Piezoelectric Composites with a Porous Matrix

In this research, a comparative study of the hydrostatic performances of 1-3 piezoelectric composites with a porous matrix is presented. The piezoelectric fibers PZT-5H and PZT-7A are considered in the present study. The micromechanics based Mori-Tanaka model is used. Results of the study show that PZT-5H/Aradite D composite have better hydrostatic performance than PZT- 7A/Aradite D composite, and this advantage of PZT-5H/Aradite D composite over PZT-7A/Aradite D composite increases with the increase of porosity in the matrix.

Effective properties of 1-3 piezoelectric composites: effect of polarization orientation

Piezoelectric ceramic/polymer composites have been widely studied because of their theoretical interest and technological applications. The 1-3 piezoelectric composites have recently received increased attention due to their potential applications in underwater acoustics and biomedical imaging. 1-3 piezoelectric composites have piezoceramic fibers, embedded in an elastically soft polymer matrix which is either piezopassive or piezoactive. Their electromechanical properties of the piezoelectric composites can be tailored to meet specific applications and their flexibility offers an additional advantage over the brittle monolithic piezoelectric. In this paper, we study the effects of the variation of the polarization orientation of the piezoelectric materials on the effective properties of 1-3 piezoelectric composites by using the micromechanics-based Mori-Tanaka method. Results for PZT/P(VDF-TrFE) composite show that the effective electromechanical properties are not significantly affected by the polarization orientation. However, the performance of the composite is significantly affected at low volume fraction of the piezoceramic fiber. These results can provide useful information for optimizing the design of 1-3 piezoelectric composites for specific applications.