Mechanical validation of smart structures

Abstract

TRW is developing smart structures technology for vibration control in space and automotive applications. Performance verification of composite structures with piezoceramic sensors and actuators in severe mechanical and thermal environments is a key requirement. Graphite epoxy, graphite polycyanate, and graphite thermoplastic members have been fabricated with thin lead zirconate - titanate (PZT, navy types I and II) actuator and sensor wafers embedded in the composite layup. These members were subjected to tension and compression loading, hundreds of cycles of fatigue loading at levels indicative of launch loads, and thermal cycling tests at temperatures found in the hard vacuum of space. Analytic derivations show that the product of PZT modulus and piezoelectric coefficient is a figure of merit for both actuation and sensing. Test results for embedded PZTs are promising, and show correlation with analytic predictions based on vendor material data. Static actuation performance of the type I and II PZTs was found to remain relatively unchanged following static application of tensile strains of up to 600 and 1500 , respectively. A hundred fatigue loading cycles at 60% of these static strain levels were found to cause no degradation in dynamic actuation/sensing performance, while fatigue loading at the 1500 level did cause a degradation of 13%. Twelve thermal cycles over the range C caused a further 13% average degradation in dynamic performance. Dynamic actuation and sensing characteristics were found to vary within the range of over a single temperature cycle. More testing to quantify the results on a statistical basis is indicated, especially for the temperature cycling effects, which were significant.

Uniaxial stress dependence of the dielectric properties in the Na0.5Bi0.5TiO3–NaTaO3 system

“…However, the stress sensitivity slightly increased with decreasing frequency in the samples that exhibit a frequency dispersion in the stress-free conditions, that is, samples with up to 15 mol% of NTa. 5 The main contributions to the short-term decrease come from the reorientation of domains due to the mechanical modification of the sample's domain state (mainly irreversible) and the clamping of the domain walls under pressure (reversible). A higher stress sensitivity might be connected to the nonuniform suppression of the domain dynamics with different relaxation times.…”

“…2 Historically, measurements of the stress dependence of the permittivity were widely used to determine the electrostrictive coefficients of nonpolar dielectric materials, 3 and later, the possibility of applying the permittivity-stress dependence as a way to sense pressure was proposed by Uchino. 5 Consequently, the conventional linear assumptions are insufficient and recent experimental [6][7][8] and modeling 9 efforts have therefore focused on evaluating and understanding the nonlinear behavior of ferroelectric (and ferroelastic) piezoceramics in the context of domain switching. 5 Consequently, the conventional linear assumptions are insufficient and recent experimental [6][7][8] and modeling 9 efforts have therefore focused on evaluating and understanding the nonlinear behavior of ferroelectric (and ferroelastic) piezoceramics in the context of domain switching.…”

Mechanical and vibration testing of carbon fiber composite material with embedded piezoelectric sensors

“…They also measured some reduction in strength in the test articles with the embedded chips, regardless of chip functionality. Bronowicki et al 6 tested monolithic Navy type I and II lead zirconate titanate (PZT) elements embedded in composite specimens, looking at tension, compression, temperature, and fatigue effects. They measured the piezoelectric properties throughout testing, showing the degradation with tensile strain up to 4000x10 -6 m/m, and with temperature cycling of -100 to +100 o C. Mall et al 7,8 tested monolithic piezoelectric elements embedded in composite specimens, looking at sensor voltage output under tensile and fatigue tests, and fatigue testing of the piezoelectric element when used as an actuator.…”

The integrity of piezo-composite beams under high cyclic electro-mechanical loads—experimental results

“…Surveying the published experimental studies one can found only a few relevant experimental reports where the life span of the piezoceramic patches is studied in connection to two types of stress conditions: tension/compression due to axial loads and bending stresses. Bronowicki et al [3] performed one of the first studies on the structural integrity of a smart structure with embedded active sensor/actuator. Graphite/epoxy laminates with embedded active PZT were loaded with various external tensile mechanical loads, and then completely unloaded.…”

“…Mall and Coleman [5] investigated the effect of embedded active PZT sensor/actuator on tensile strength and fatigue behavior of quasi-isotropic graphite/epoxy laminates. A commercially PZT (ACX QP15N) 3 was inserted in the two middle 90° plies. One of the first studies that tested the influence of combined electric and mechanical loads, (E/M fatigue) was presented by Mall and Hsu [6].…”