Christopher P. Henry

Static properties of crystallographically aligned Terfenol-D∕polymer composites

Crystallographically aligned [112] magnetostrictive particle (CAMP) composites were characterized quasistatically. Three volume fraction (vf) composites (26%, 37%, and 49%) were manufactured and subjected to compressive stresses ranging from −2to−24MPa, magnetic fields loading up to 400kA∕m, and thermal variations (from 0to30°C). These tests provided property measurement including maximum magnetostrictive strain (emax), elastic modulus (EH), relative permeability (μr), piezomagnetic coefficient (d33), and coupling coefficient (k33). Results show that the 49% volume fraction CAMP composite produced strains of up to 1600ppm saturation magnetostriction, which is 89% of the monolithic value (1800ppm), and a coupling coefficient of 0.65, which is approximately 75% that of the monolithic, and relative thermal stability over the range of 0–30°C.

CRYSTALLOGRAPHICALLY ALIGNED TERFENOL-D/POLYMER COMPOSITES FOR A HYBRID SONAR DEVICE

ABSTRACT Crystallographically-aligned magnetostrictive particle (CAMP) composites offer increased bandwidth and durability when compared to monolithic and laminated magnetostrictive systems. CAMP composites were evaluated under combined magnetic, thermal, and mechanical loading to determine fundamental properties used for the design of sonar transducers that incorporate these materials. Here, we examine the minor loop performance of the CAMP composites, i.e. the linear region of the strain field curve. The measurements demonstrate the benefits of the CAMP Composite technology for sonar applications, achieving strain output near that of monolithic Terfenol-D, while increasing bandwidth and durability. All volume fractions exhibited low minor loop hysteresis, and low temperature dependence.

Active material based active sealing technology: Part 1. Active seal requirements vs. active material actuator properties

Current seals used for vehicle closures/swing panels are essentially flexible, frequently hollow structures whose designs are constrained by numerous requirements, many of them competing, including door closing effort (both air bind and seal compression), sound isolation, prevention of water leaks, and accommodation of variations in vehicle build. This paper documents the first portion of a collaborative research study/exploration of the feasibility of and approaches for using active materials with shape and stiffness changing attributes to produce active seal technologies, seals with improved performance. An important design advantage of an active material approach compared to previous active seal technologies is the distribution of active material regions throughout the seal length, which would enable continued active function even with localized failure. Included as a major focus of this study was the assessment of polymeric active materials because of their potential ease of integration into the current seal manufacturing process. In Part 1 of this study, which is documented in this paper, potential materials were evaluated in terms of their cost, activation mechanisms, and mechanical and actuation properties. Based on these properties, simple designs were proposed and utilized to help determine which materials are best suited for active seals. Shape memory alloys (SMA) and electroactive polymers (EAP) were judged to be the most promising.

Broadening the Actuation Temperature Range for Acrylic Dielectric Elastomers

Dielectric elastomer actuators are an important branch of electroactive polymers with a host of applications proposed. However, the temperature range over which these elastomers are active has been limited by the glass transition temperature and thermal stability. Acrylic elastomers, VHB adhesive films from 3M Company, exhibit high actuation strain and stress at room temperature, but become too rigid to actuate below 0 °C. By lowering their glass transition temperature with the addition of a plasticizer, we show that the soft polymer actuators can be made to function at −40 °C. The plasticized films have been able to achieve >100% areal strain at −40°C. This helps extend the scope of dielectric elastomer actuators to demanding automotive applications.Copyright

Theoretical and experimental investigation of architected core materials incorporating negative stiffness elements

Structural assemblies incorporating negative stiffness elements have been shown to provide both tunable damping properties and simultaneous high stiffness and damping over prescribed displacement regions. In this paper we explore the design space for negative stiffness based assemblies using analytical modeling combined with finite element analysis. A simplified spring model demonstrates the effects of element stiffness, geometry, and preloads on the damping and stiffness performance. Simplified analytical models were validated for realistic structural implementations through finite element analysis. A series of complementary experiments was conducted to compare with modeling and determine the effects of each element on the system response. The measured damping performance follows the theoretical predictions obtained by analytical modeling. We applied these concepts to a novel sandwich core structure that exhibited combined stiffness and damping properties 8 times greater than existing foam core technologies.