Vibration damping using flexible graphite

Abstract

Vibration damping is valuable for structures, as it material for high temperature or chemically harsh environmitigates hazards (whether due to accidental loading, wind, ments. ocean waves or earthquakes), increases the comfort of Due to its resilience, in addition to its thermal resistance, people who use the structures, and enhances the reliability chemical resistance, low thermal expansion and high and performance of structures. The basic concept about thermal conductivity, flexible graphite was investigated in damping involves the absorption of external energy this work for use in vibration damping. The investigation through internal motion or friction [1,2]. A layered strucinvolved simultaneous measurement of the loss tangent ture is attractive for damping due to the large internal (tan d, i.e. damping capacity) and storage modulus (stiffsurface area involved [3,4]. The relative motion between ness) under dynamic flexure (three-point bending at a very layers produces extra shear, which means more energy small deflection amplitude) at fixed frequencies. The dissipation [5]. For instance, a viscoelastic material or a product of loss tangent and storage modulus is the loss fluid layer is sandwiched within a beam for both passive modulus. As high values of both loss tangent and storage and active damping [6–8]. However, fluid and viscoelastic modulus are desired for vibration reduction, a high value materials suffer from their poor stiffness, limited resistance of the loss modulus is desired. Rather low frequencies are to heat and chemicals, in addition to high thermal expanused in this study due to their relevance to the vibration of sion and poor thermal conductivity, which aggravate large structures and due to the fact that the loss tangent thermal stresses. decreases with increasing frequency and hence becomes Flexible graphite is a flexible sheet made by compreshard to measure at a high frequency. For the sake of sing a collection of exfoliated graphite flakes without a comparison, the loss tangent and storage modulus of binder [9–18]. Due to the exfoliation, flexible graphite has rubber were also measured. 2 21 a large specific surface area (e.g. 15 m g [19]). As a Flexible graphite sheet (Grade GTB) was provided by result, flexible graphite is used as an adsorption substrate. EGC Enterprises, Inc. (Mentor, Ohio). The specific surface 2 21 Due to the absence of a binder, flexible graphite is area was 15 m g , as determined by nitrogen adsorption essentially entirely graphite (other than the residual amount and measurement of the pressure of the gas during of intercalate in the exfoliated graphite). As a result, adsorption using the Micromeritics (Norcross, GA) ASAP flexible graphite is chemically and thermally resistant, and 2010 instrument. This specific surface area corresponds to low in coefficient of thermal expansion (CTE). Due to its a crystallite layer height of 0.18 mm within a sheet. microstructure involving graphite layers that are preferenAccording to the manufacturer, the ash content of flexible 23 tially parallel to the surface of the sheet, flexible graphite is graphite is ,5.0%; the density is 1.1 g cm ; the tensile high in electrical and thermal conductivities in the plane of strength in the plane of the sheet is 5.2 MPa; the the sheet. Due to the graphite layers being somewhat compressive strength (10% reduction) perpendicular to the connected perpendicular to the sheet (i.e. the honeycomb sheet is 3.9 MPa; the thermal conductivity at 10938C is 43 21 21 microstructure of exfoliated graphite), flexible graphite is W m K in the plane of the sheet and 3 W m K electrically and thermally conductive in the direction perpendicular to the sheet; the coefficient of thermal 26 perpendicular to the sheet (although not as conductive as expansion (CTE) (21–10938C) is 20.4310 / 8C in the the plane of the sheet). These in-plane and out-of-plane plane of the sheet. microstructures result in resilience and impermeability to Dynamic mechanical testing (ASTM D4065-94) at fluids perpendicular to the sheet. The combination of controlled frequencies (0.2, 1.0 and 5.0 Hz) and room resilience, impermeability and chemical and thermal resisttemperature (208C) was conducted under flexure using a ance makes flexible graphite attractive for use as a gasket Perkin-Elmer Corp. (Norwalk, CT) Model DMA 7E dynamic mechanical analyzer. Measurements of tan d and storage modulus were made simultaneously at various frequencies. The specimens were in the form of beams of *Corresponding author. Tel.: 11-716-645-2593; fax: 11-716length at least 25 mm under three-point bending, with the 645-3875. E-mail address: ddlchung@acsu.buffalo.edu (D.D.L. Chung). span being 20 mm. The width of the flexible graphite