Robert Y. Ting

The fracture of an epoxy polymer containing elastomeric modifiers

The fracture energies of elastomer-modified epoxy polymers have been determined over a range of strain rates from 10−2 to 103 sec−1. The modifiers included a liquid carboxyterminated butadiene acrylonitrile and a solid rubber. They were used alone and also in combination. In all cases, the modifiers increased the toughness of the base resin by orders of magnitude and one combination of liquid and solid rubber increased toughness by 60 times. There was a general decrease in fracture energy with increasing strain rate but even during impact testing the modified epoxys were 10 to 20 times tougher than the base polymer. Scanning electron microscopy revealed that, when combined with the liquid rubber, the solid rubber induced a localized shear yielding.

Evaluation of new piezoelectric composite materials for hydrophone applications

Polymer-ceramic composites with different connectivity designs have been developed. The piezoelectric d and g coefficients of these composites in hydrostatic mode were characterized as a function of pressure, temperature, and frequency. All composite samples exhibited piezoelectric properties greatly improved over those of conventional piezoelectric ceramics. However, the introduction of soft polymer matrix caused the composite properties to be highly pressure-dependent. The effect of reinforced polymer matrix on the temperature and pressure dependences of the piezoelectric coefficients was also investigated. Prototype hydrophones containing the composite samples were designed and evaluated for their free-field voltage sensitivity. The potential use of polymer-ceramic composites for underwater acoustic applications is discussed.

Unidimensional modeling of multi-layered piezoelectric transducer structures

Multi-layered transducer structures offer the potential of improved performance in terms of increased transmit sensitivity, greater bandwidth, and enhanced reception characteristics. Unfortunately, the successful design of such devices is often difficult, owing to the complex interaction between the active piezoelectric layers and passive intermediate interface layers. Furthermore, in many practical applications, the loading effects imposed by the electrical drive circuitry often limit the performance improvements that may be physically realized. This paper describes the development of a comprehensive, unidimensional modeling approach. This model may be employed to facilitate the analysis and subsequent optimization of laminated transducer assemblies. The devices currently under consideration include both piezoceramic and piezopolymer configurations, as well as alternative piezocomposite designs. The effects of varying bondline thickness and the introduction of passive interface layers are examined, as is the influence of the electrical load circuitry on overall system response. The ability to accurately predict the response of stacked piezoelectric structures is demonstrated through extensive comparison of experimental and theoretical responses. This paper concludes by highlighting the important role that modeling plays in the design, fabrication, and optimization of complex multi-layered transducer assemblies.

Modified-lead-titanate/polymer composites for hydrophone applications

Abstract Composite piezoelectrics made from Calcium-modified lead titanate rods embedded in a polymer matrix have been evaluated for hydrophone applications. These composites behave quite differently from the conventional 1–3 composites made with lead zirconate titanate ceramics. Specifically, in the modified lead-titanate case the magnitude of the d 31 coefficient is enhanced in the composite structure, and consequently the hydrostatic dh coefficient is suppressed. Nevertheless, these composites exhibit a large gh coefficient and a remark able pressure stability. An analysis shows that a substantial contribution to the composites d 31 coefficient arises from internal stresses which develop along the ceramic rods and produce a piezoelectric charge through the d 33 coefficient of the ceramic. This effect is particularly pronounced in the composite structure of the modified lead-titanate ceramic since the ratio d 33/d 31 in this ceramic is exceptionally large.

Piezoelectric properties of a porous PZT ceramic

A porous PZT material from a Japanese source was characterized for its piezoelectric properties. Initial values of 82 pC/N for the hydrostatic d constant and 0.046 Vm/N for the hydrostatic g constant were observed. The material also showed no pressure hysteresis effect upon pressure cycling. In order to improve its poor mechanical strength due to high porosity, the material was modified by an epoxy coating and by epoxy impregnation. The effect of these modifications was shown to alter the piezoelectric properties from those of the untreated samples, and, in addition, to introduce a large pressure hysteresis effect. Sample variations were found among different experimental batches, and the dependence of their piezoelectric properties on sample thickness was determined. These variations may be attributed to sample inhomogeneity resulting from powder packing and the degree of poling.

Effect of high energy electron irradiation on the electromechanical properties of poly (vinylidene fluoride-trifluorethylene) 50/50 and 65/35 copolymers

High energy electron irradiation with a broad range dosage was carried out on poly(vinylidene fluoride trifluorethylene) copolymer 65/35 mol% and 50/50 mol% films at different temperatures from room temperature to a temperature close to the melt temperature. The effect of irradiation on the properties of the films, such as electric field-induced strain, dielectric and polarisation behaviors, and mechanical modulus, is presented. The irradiated films can exhibit a very large electric field-induced strain, more than 4.5% longitudinal strain, and 3% transverse strain. The transverse strain of the stretched film can compare with the longitudinal strain; that of the unstretched film is much smaller than the longitudinal strain. With regard to the dielectric and polarization behaviors, we found that irradiation changes the copolymer from a typical ferroelectric to a relaxor ferroelectric in which the behavior of microregions under the electric field plays the key role. Between the two copolymers studied, we found that the 65/35 copolymer is preferred for both longitudinal and transverse strain generation. A model is proposed to explain the experimental results that the amplitude of the charge electrostrictive coefficient (Q) increases with decreasing crystallinity.

Characteristics of flow cavitation in dilute solutions of polyethylene oxide and polyacrylamide

The effect of high molecular weight drag‐reducing polymers on flow‐induced cavitation was studied. Cavitation was generated on the surface of a disk rotating in a test chamber. Cavitation inception was determined as a function of flow velocity, temperature, and pressure. Polymeric additives used included polyethylene oxide and polyacrylamide at various concentrations. The results showed that the inception of flow‐induced cavitation was suppressed by the high molecular weight polymers. This suppression was represented by a substantial reduction in the values of the cavitation inception parameter in polymer solutions. Polymeric additives were also found to have a strong effect in reducing the overall size of fully developed cavities. These effects were briefly discussed in terms of polymer viscoelasticity.

The hydroacoustic behavior of piezoelectric composite materials

Abstract Piezoelectric composites that contain both ceramic and polymeric phases, and non-ferroelectric glass-ceramic composites have recently been developed. These materials exhibit attractive piezoelectric properties for applications in hydrophones that operate in a hydrostatic mode. Prototype hydrophones were developed using a porous PZT ceramic, a “0–3” and a “1–3” ceramic-polymer composite and a glass-ceramic sample. The test results on the acoustical performance of these devices are presented to demonstrate the potential of these new materials for underwater acoustical applications.

Effect of polymer viscoelasticity on the initial growth of a vapor bubble from gas nuclei

The effect of polymer viscoelasticity on the initial growth of a vapor bubble from a gas nucleus is studied by analyzing such a growth in a three‐constant Oldroyd fluid. At zero polymer concentration, the result reduces to the case of a Newtonian solvent and agrees with the Plesset–Zwick theory. Numerical results show that polymer viscoelasticity retards the bubble growth, but the retardation effect is rather small.

Bubble growth in dilute polymer solutions

Under a free‐fall condition, the growth of individual gas bubbles in dilute polymer solutions was observed experimentally. A retardation in the growth rate was found as compared with the case in water.