1、NASA CONTRACTOR REPORT DAMPING OF STRUCTURAL COMPOSITES WITH VISCOELASTIC SHEAR-DAMPING MECHANISMS by Jerome E. Rnzickd, T15omus F. Derby, D Prepared by BARRY WRIGHT CORPORATION Watertown, Mass. ;= for Lazzgley Research Center NATIONAL AERONAUTICS AND SPACE ADMINISTRATION . WASHINGTON, D. C. . MARCH
2、 1967 f Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-TECH LIBRARY KAFB, NM IlObOLOB NASA Cl-t-14X DAMPING OF STRUCTURAL COMPOSITES WITH VISCOELASTIC SHEAR-DAMPING MECHANISMS By Jerome E. Ruzicka, Thomas F. Derby, Dale W. Schubert, and Jerome S. Pe
3、pi Distribution of this report is provided in the interest of information exchange. Responsibility for the contents resides in the author or organization that prepared it. Prepared under Contract No. NAS l-5640 by BARRY WRIGHT CORPORATION Watertown, Mass. for Langley Research Center NATIONAL AERONAU
4、TICS AND SPACE ADMINISTRATION For sale by the Clearinghouse for Federal Scientific and Tcchnicol Information Springfield, Virginia 22151 - CFSTI price $3.00 Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-Provided by IHSNot for ResaleNo reproduction
5、or networking permitted without license from IHS-,-,-DAMPING OF STRUCTURAL COMPOSITES WITH VISCOELASTIC SHEAR-DAMPING MECHANISMS By Jerome E. Ruzicka, Thomas F. Derby, Dale W. Schubert and Jerome S. Pepi ABSTRACT An investigation is conducted to evaluate the so-called geometrical parameter of struct
6、ural composites with viscoelastic shear-damping mechanisms. Design equations and graphs are developed for the geometrical parameter of a wide range of viscoelastic shear-damped structural composite designs. Using existing theory, manual and automated procedures are develo,ped for the prediction of t
7、he structure loss factor of structuralcomposites comprised of two elastic elements separated by a thin viscoelastic damping layer. Laboratory experiments are performed to verify the basic theory and design procedures developed. A comparison of theoretical predictions and experimental measurements of
8、 the structure loss factor is made for two- elastic-element structural composites fabricated from various combinations of structural materials including aluminum, steel and fibre-glass. iii Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-Provided by
9、IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-CONTENTS Page SUMMARY SECTION 1: INTRODUCTION SECTION 2: ANALYSIS AND DESIGN DATA FOR GEOMETRICAL PARAMETER Geometrical Parameter Analyses Two-elastic-element structural composites Three-elastic-element structural
10、composites Cell-insert structural composites Orthogonally symmetric cross-sections Effect of symmetrica 1 shea thing addition Formulation of Design Parameters Effect of viscoelastic damping layer thickness Equivalent modulus concept Geometrica 1 Parameter Design Data Laminated structural sheets Cons
11、trained honeycomb sheets Laminated honeycomb sheets Box-beam and I-beam constructions Structural bar designs Structural tube designs Structural shape beams Dumbbell model Geometrical Parameter Design Considerations SECTION 3: DESIGN OF TWO-ELASTIC-ELEMENT STRUCTURAL COMPOSITES Fundamellta 1 Equation
12、s for Damping Parameters Basic assumptions of theory Typical structural composite designs Development of Design Equations and Graphs Coupling parameter Z Resonant frequency ratio f/f0 Shear parameter X Generalized shear parameter equation Optimum shear parameter Xop Maximum structure loss factor qma
13、x Loss factor ratio r,/rlrnax Optimum frequency parameter 51 op Manual Design Procedure Automa ted Design Procedure Temperature Effects Other Design Considerations Static stiffness Weight Static load distribution 1 2 7 a 9 10 11 12 13 14 15 la 22 22 24 25 25 26 28 30 31 31 34 34 36 36 37 38 39 40 41
14、 41 .42 42 43 44 48 49 50 50 51 52 V Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-,., . -. - . _ -_-_ . _ - -,. . -._,- -,. _ . _ - ._ . .-. - _ Page SECTION 4: EXPERIMENTAL VERIFICATION OF DESIGN PROCEDURE FOR TWO-ELASTIC-ELEMENT STRUCTURAL COMPO
15、SITES 53 Design Procedure Application Example 53 Measurement of Structure Loss Factor 58 Theoretical and Experimental Structure Loss Factor Data 61 Sources of errors 62 Statistical analysis of experimental data 64 CONCLUSIONS 66 REFERENCES 68 FIGURES 70-176 vi Provided by IHSNot for ResaleNo reprodu
16、ction or networking permitted without license from IHS-,-,-DAMPING OF STRUCTURAL COMPOSITES WITH VISCOELASTIC SHEAR-DAMPING MECHANISMS By Jerome E. Ruzicka, Thomas F. Derby, Dale W. Schubert and Jerome S. Pepi Barry Controls Division of Barry Wright Corporation Watertown, Massachusetts SUMMARY An in
17、vestigation of parameters important in the design of structural composites with viscoelastic shear-damping mechanisms has been conducted. Design equations and graphs are developed for the so-calied geometrical parameter of a wide range of viscoelastic shear-damped structural composites, which includ
18、e: laminated beams and plates (comprised of solid and/or honeycomb structural sheets), box-beam constructions, bars of various cross-sections, square and circular tubes, structural shape beams including angle, channel, T- and I-sections, and a dumbbell model (which frequently provides a simplified r
19、epresentation of a more complex structural assembly). Using existing theory, manual and automated design procedures for the prediction of structure loss factor are developed for viscoelastic shear-damped structural composites comprised of two elastic elements separated by a thin viscoelastic damping
20、 layer. The design procedures which apply for any cross- section geometry and arbitrary structural and viscoelastic material properties, are used to predict the damping characteristics of a wide range of two-elastic- element structural composite beams employed in an experimental verification program
21、, As a design example, the details of the numerical calculations for a typical structural composite beam are presented. Laboratory experiments have been performed to verify the theoretical predictions and to provide insight into practical design considerations. A comparison of theoretical prediction
22、s and experimental measurements of the structure loss factor is made for two-elastic-element structural composites fabricated from various combinations of structural materials including aluminum, steel and fibre-glass. Structural specimens include laminated beams comprised of solid sheets, solid and
23、 honeycomb sheets, honeycomb sheets, and structural channels. A total of 118 loss factor measurements were made for various free-free bending modes of 27 different beam specimens. A statistical analysis of this data compared to the theoretical values of loss factor indicated that the difference had
24、a mean value of 0.6 per cent and a standard deviation of approximately 30 per cent. Consequently, it is concluded that the existing theory and the procedures developed for the prediction of the loss factor of two-elastic element viscoelastic shear-damped structural composites is satisfactory within
25、accepted engineering accuracy. Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-SECTION 1: INTRODUCTION The damping properties of structural fabrications can be considerably enhanced by the incorporation of viscoelastic shear-damping mechanisms in str
26、uctural members and joints Ref. 11. Special design configurations incor- porating distributed viscoelastic shear-damping mechanisms have been devised which consist of a combination of elastic beam or plate elements separated by layers of a viscoelastic damping material Ref. 2-81. The elastic element
27、s are made from common structural materials and the damping materials are generally polymers exhibiting high loss factors and relatively low values of stiffness. When structura 1 composites with constrained visco- elastic layers undergo flexural vibrations, the layers of viscoelastic damping materia
28、l are subjected to cyclic shear strains, which cause energy of mechan- ical motion to be converted into thermal energy. Because of this energy conversion process , viscoelastic shear-damped structural composites are capable of exhibiting extremely high degrees of damping. Techniques for fabricating
29、structural composites with viscoelastic shear-damping mechanisms include the use of adhesively bonded intermediate damping layers and self-bonding adhesive damping layers I Ref. 2 1. The structural composites with adhesively bonded damping layers offer the advantage of being able to provide any thic
30、kness of viscoelastic damping material in the structural composite, since the damping layer can be produced in sheet form to the desired thickness prior to bonding between the elastic structural elements. The thickness of the self-bonding adhesive visco- elastic damping layer is limited; however, it
31、s use offers an advantage with regard to the relative simplicity of production and workability of the composite structure. Edrly investigations of distributed viscoelastic shear-damping mech- anisms were concerned with the damping effectiveness of a viscoelastic damping layer constrained between two
32、 structural sheets, where one sheet was very thin relative to the other Ref. 3 I . This damped structural configura- tion was intended to represent the application of a damping tape (consisting of a thin metal foil with adhesive backing) to a structural beam requiring 2 Provided by IHSNot for Resale
33、No reproduction or networking permitted without license from IHS-,-,-additional damping. An evaluation was also made of the damping performance obtained by the application of a multiplicity of damping tapes to a structural beam Ref. 41 . It was found that multiple damping tapes offered no significan
34、t improvement in damping at high frequencies (greater than lOOOHz), but provided a substantial increase in damping for lower frequencies. Furthermore, the damping provided by multiple damping tapes was essentially equal to that of a single damping tape having a foil thickness which equals the sum of
35、 the foil thicknesses of the multiple damping tape treatment and a viscoelastic damping layer thickness equal to that of only one of the multiple damping tapes. The same maximum degree of damping was obtained whether the damping tapes were applied to one or both sides of tne structural beam being da
36、mped; however, the frequency at which the maximum damping occurred differed for these two cases. These analyses applied for the case where the total foil thickness is considerably less than the structural beam thickness. Experiments indicated that the measured and theoretically predicted damping wer
37、e in reasonably good agreement, with values of the structure loss factor being generally less than 0. 05 for practical damping tape treatments. An analysis was subsequently performed to predict tne damping properties of structural composites incorporating distributed viscoelastic shear-damping mecha
38、nisms for the case where the structural composites consisted of two elastic elements of arbitrary material and size with an intervening viscoelastic damping layer Ref. 5, 6 1. For geometrical configura- tions incorporating a thin layer of viscoelastic damping material that is soft compared to the st
39、iffness of structural materials employed in the structural composite, the structure loss factor n may be expressed in terms of three parameters, as follows: rl= 77, x, Y) (1) where fi is the loss factor of the viscoelastic G-rear-damping material, X is defined as the shear parameter, and Y is define
40、d as the geometrical parameter. 3 Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-The damping material loss factor B is the ratio of the imaginary and real components of the complex shear modulus G* = G + jG”, as follows: /3= GYG (2) where G” and G a
41、re the loss modulus and storage modulus of the visco- elastic material, respectively. The shear parameter X depends on the storage modulus and amount of viscoelastic material employed, the weight loading on the structural member, the flexural rigidity, the geometry of the cross-section, and the freq
42、uency of vibration. The geometrical parameter Y, which is a function only of the geometry of the cross-section and the modulus of elasticity of the elastic elements comprising the structural composite, may be expressed mathematically as follows Ref. 5, 7, 81: WI, - = (EI)o (3) where (EI), is the fle
43、xural rigidity of the structural composite when its elastic members are uncoupled and (EI), is the flexural rigidity of the structural composite when its elastic members are completely coupled. Theoretical and experimental evidence indicates that high values of the geometrical parameter are required
44、 for a structural composite to exhibit a high degree of damping. Based on (1) the theory of viscoelastically damped beams with two elastic elements Ref. 5 1, (2) the application of a lumped parameter model as a simplified representation of a viscoelastic shear-damped structural composite Ref. 7 1, a
45、nd (3) experimental data acquired on various structural composites Ref. 81, it is concluded that the geometrical parameter Y is a fundamental design parameter which plays a significant role in the performance of all structural composite designs which incorporate viscoelastic shear- damping mechanism
46、s. Consequently even if the equivalent of the shear parameter X is not defined for a more complex structura 1 composite, the value of the geometrical parameter in itself provides a guide for arriving at a suitable design, especially when this information is coupled with previous practical experience
47、 of designing and evaluating viscoelastic shear-damped structural composites. 4 Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-In general, the problem of designing structural composites with visco- elastic shear-damping mechanisms involves the selec
48、tion of a viscoelastic damping material having a high loss factor p and arranging the cross-section geometry of the elastic elements to produce a high value of the geometrical parameter Y. Maximization of damping at a specified frequency or temperature, however, will require the optimization of the shear parameter X for two-elastic-element structural composites or an equivalent parameter for more complex structural composite designs. Alternately, subsequent to the selection of a viscoelastic damping material having a high value of loss factor
