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Uday K. Vaidya - One of the best experts on this subject based on the ideXlab platform.

  • Affordable processing of thick section and integral multi-functional composites
    Composites - Part A: Applied Science and Manufacturing, 2001
    Co-Authors: Uday K. Vaidya, A. Abraham, Sachin Bhide
    Abstract:

    The use of multi-functional integral armor is of current interest in armored vehicles and military carriers. In the present study, thick-section laminated composites and multi-layered integrated composites have been processed/manufactured with the aim of providing multi-functionality including easy reparability, quick deployment, enhanced ballistic damage and fire protection, as well as lightweight advantages. The design of an integral armor utilizes a combination of thick-section structural composite, ceramic tiles, resilient rubber, fire retardant laminate liner and a composite durability cover. Processing techniques such as automated fiber placement and/or Autoclave Molding are traditionally used to process dissimilar multi-layered structure, but prove to be expensive. This work focuses on emerging cost-effective liquid Molding processes such as vacuum assisted resin transfer/infusion Molding (VARTM) for the production of thick-section and integral armor parts (up to 50 mm thick). While thick-section composites have applications in a variety of structures including armored vehicles, marine bodies, civil infrastructure, etc. in the present work they refer to the structural laminate within the integral armor. The processing steps of thick-section composite panels and integral armor have been presented. The integrity of the interfaces has been evaluated through scanning electron microscopy (SEM). Representative results on static and dynamic response (high strain rate, HSR and ballistic impact) of the VARTM processed thick-section composite panels are presented. Wherever applicable, comparisons are made to conventional closed-mold resin transfer Molding (CMRTM). Process sensing by way of flow and cure monitoring of the resin in the fiber perform has been conducted using embedded direct current (DC)-based sensors in the thick-section preform and integral armor interfaces. The feasibility of cost-effective VARTM for producing thick-section composites and integral armor has been demonstrated. © 2001 Elsevier Science Ltd.

  • Assessment of flow and cure monitoring using direct current and alternating current sensing in vacuum-assisted resin transfer Molding
    Smart Materials and Structures, 2000
    Co-Authors: Uday K. Vaidya, Nitesh C. Jadhav, J W Gillespie, Madhusoodan V. Hosur, Bruce K Fink
    Abstract:

    Vacuum-assisted resin transfer Molding (VARTM) is an emerging manufacturing technique that holds promise as an affordable alternative to traditional Autoclave Molding and automated fiber placement for producing large-scale structural parts. In VARTM, the fibrous preform is laid on a single-sided tool, which is then bagged along with the infusion and vacuum lines. The resin is then infused through the preform, which causes simultaneous wetting in its in-plane and transverse directions. An effective sensing technique is essential so that comprehensive information pertaining to the wetting of the preform, arrival of resin at various locations, cure gradients associated with thickness and presence of dry spots may be monitored. In the current work, direct current (dc) and alternating current sensing/monitoring techniques were adopted for developing a systematic understanding of the resin position and cure on plain weave S2-glass preforms with Dow Derakane vinyl ester VE 411-350, Shell EPON RSL 2704/2705 and Si-AN epoxy as the matrix systems. A SMARTweave dc sensing system was utilized to conduct parametric studies: (a) to compare the flow and cure of resin through the stitched and non-stitched preforms; (b) to investigate the influence of sensor positioning, i.e. top, middle and bottom layers; and (c) to investigate the influence of positioning of the process accessories, i.e. resin infusion point and vacuum point on the composite panel. The SMARTweave system was found to be sensitive to all the parametric variations introduced in the study. Furthermore, the results obtained from the SMARTweave system were compared to the cure monitoring studies conducted by using embedded interdigitated (IDEX) dielectric sensors. The results indicate that SMARTweave sensing was a viable alternative to obtaining resin position and cure, and was more superior in terms of obtaining global information, in contrast to the localized dielectric sensing approach.

  • Assessment of flow and cure monitoring using direct current and alternating current sensing in Vacuum Assisted Resin Transfer Molding
    American Society of Mechanical Engineers Manufacturing Engineering Division MED, 1999
    Co-Authors: Nitesh C. Jadhav, J W Gillespie, Madhusoodan V. Hosur, Uday K. Vaidya, Bruce K Fink
    Abstract:

    Vacuum Assisted Resin Transfer Molding (VARTM) is an emerging manufacturing technique that holds promise as an affordable alternative to traditional Autoclave Molding and automated fiber placement for producing large scale structural parts. In VARTM, the fibrous preform is laid on a single sided tool, which is then bagged along with the infusion and vacuum lines. The resin is then infused through the preform, which causes simultaneous wetting in its in-plane and transverse directions. An effective sensing technique is essential so that comprehensive information pertaining to the wetting of the preform, arrival of resin at various locations, cure gradients associated with thickness and presence of dry spots may be monitored. In the current work, direct current and alternating current sensing/monitoring techniques were adopted for developing a systematic understanding of resin position and cure on plain weave S2-Glass preforms with Dow Derakane vinyl ester VE 411-350, Shell EPON RSL 2704/2705 and Si-AN epoxy as the matrix systems. The SMARTweave DC sensing system was utilized to conduct parametric studies a) to compare the flow and cure of resin through the stitched and non-stitched preforms, b) influence of sensor positioning, i.e., top, middle and bottom layers, c) influence of positioning of the process accessories, i.e., resin infusion point and vacuum point on the composite panel. The SMARTweave system was found to be sensitive to all the parametric variations introduced in the study. Furthermore, the results obtained from the SMARTweave system were compared to the cure monitored from embedded IDEX dielectric sensors. The results indicate that SMARTweave sensing was a viable alternative to obtaining resin position and cure, and more superior in terms of obtaining global information in contrast to the localized dielectric sensing approach.

Bruce K Fink - One of the best experts on this subject based on the ideXlab platform.

  • Assessment of flow and cure monitoring using direct current and alternating current sensing in vacuum-assisted resin transfer Molding
    Smart Materials and Structures, 2000
    Co-Authors: Uday K. Vaidya, Nitesh C. Jadhav, J W Gillespie, Madhusoodan V. Hosur, Bruce K Fink
    Abstract:

    Vacuum-assisted resin transfer Molding (VARTM) is an emerging manufacturing technique that holds promise as an affordable alternative to traditional Autoclave Molding and automated fiber placement for producing large-scale structural parts. In VARTM, the fibrous preform is laid on a single-sided tool, which is then bagged along with the infusion and vacuum lines. The resin is then infused through the preform, which causes simultaneous wetting in its in-plane and transverse directions. An effective sensing technique is essential so that comprehensive information pertaining to the wetting of the preform, arrival of resin at various locations, cure gradients associated with thickness and presence of dry spots may be monitored. In the current work, direct current (dc) and alternating current sensing/monitoring techniques were adopted for developing a systematic understanding of the resin position and cure on plain weave S2-glass preforms with Dow Derakane vinyl ester VE 411-350, Shell EPON RSL 2704/2705 and Si-AN epoxy as the matrix systems. A SMARTweave dc sensing system was utilized to conduct parametric studies: (a) to compare the flow and cure of resin through the stitched and non-stitched preforms; (b) to investigate the influence of sensor positioning, i.e. top, middle and bottom layers; and (c) to investigate the influence of positioning of the process accessories, i.e. resin infusion point and vacuum point on the composite panel. The SMARTweave system was found to be sensitive to all the parametric variations introduced in the study. Furthermore, the results obtained from the SMARTweave system were compared to the cure monitoring studies conducted by using embedded interdigitated (IDEX) dielectric sensors. The results indicate that SMARTweave sensing was a viable alternative to obtaining resin position and cure, and was more superior in terms of obtaining global information, in contrast to the localized dielectric sensing approach.

  • Assessment of flow and cure monitoring using direct current and alternating current sensing in Vacuum Assisted Resin Transfer Molding
    American Society of Mechanical Engineers Manufacturing Engineering Division MED, 1999
    Co-Authors: Nitesh C. Jadhav, J W Gillespie, Madhusoodan V. Hosur, Uday K. Vaidya, Bruce K Fink
    Abstract:

    Vacuum Assisted Resin Transfer Molding (VARTM) is an emerging manufacturing technique that holds promise as an affordable alternative to traditional Autoclave Molding and automated fiber placement for producing large scale structural parts. In VARTM, the fibrous preform is laid on a single sided tool, which is then bagged along with the infusion and vacuum lines. The resin is then infused through the preform, which causes simultaneous wetting in its in-plane and transverse directions. An effective sensing technique is essential so that comprehensive information pertaining to the wetting of the preform, arrival of resin at various locations, cure gradients associated with thickness and presence of dry spots may be monitored. In the current work, direct current and alternating current sensing/monitoring techniques were adopted for developing a systematic understanding of resin position and cure on plain weave S2-Glass preforms with Dow Derakane vinyl ester VE 411-350, Shell EPON RSL 2704/2705 and Si-AN epoxy as the matrix systems. The SMARTweave DC sensing system was utilized to conduct parametric studies a) to compare the flow and cure of resin through the stitched and non-stitched preforms, b) influence of sensor positioning, i.e., top, middle and bottom layers, c) influence of positioning of the process accessories, i.e., resin infusion point and vacuum point on the composite panel. The SMARTweave system was found to be sensitive to all the parametric variations introduced in the study. Furthermore, the results obtained from the SMARTweave system were compared to the cure monitored from embedded IDEX dielectric sensors. The results indicate that SMARTweave sensing was a viable alternative to obtaining resin position and cure, and more superior in terms of obtaining global information in contrast to the localized dielectric sensing approach.

Ramesh Chandra - One of the best experts on this subject based on the ideXlab platform.

  • Active shape control of composite blades using shape memory actuation
    Smart Materials and Structures, 2001
    Co-Authors: Ramesh Chandra
    Abstract:

    This paper presents active shape control of composite beams using shape memory actuation. Shape memory alloy (SMA) bender elements trained to memorize bending shape were used to induce bending and twisting deformations in composite beams. Bending-torsion coupled graphite-epoxy and kevlar-epoxy composite beams with Teflon inserts were manufactured using an Autoclave-Molding technique. Teflon inserts were replaced by trained SMA bender elements. Composite beams with SMA bender elements were activated by heating these using electrical resistive heating and the bending and twisting deformations of the beams were measured using a mirror and laser system. The structural response of the composite beams activated by SMA elements was predicted using the Vlasov theory, where these beams were modeled as open sections with many branches. The bending moment induced by a SMA bender element was calculated from its experimentally determined memorized shape. The bending, torsion, and bending-torsion coupling stiffness coefficients of these beams were obtained using analytical formulation of an open-section composite beam with many branches (Vlasov theory).

  • Shape memory alloy actuation for active tuning of composite beams
    Smart Materials and Structures, 1997
    Co-Authors: Jeanette J. Epps, Ramesh Chandra
    Abstract:

    This paper presents an experimental - analytical study on the active tuning of composite beams using shape memory alloy (SMA) wires. Two graphite - epoxy composite beams with embedded fused silica tubes (also called sleeves) with `dummy' steel wires inserted in the sleeves were manufactured using an Autoclave Molding technique. After curing, the `dummy' wires were replaced by pre-strained SMA wires. During testing of such a beam, the beam and SMA wire are independently clamped at both ends and the SMA wires are activated using electrical resistive heating. A large tensile recovery force develops in the wires due to a phase transformation and the mechanical constraints provided by the clamps. The influence of this recovery force on the vibration behavior of the composite beams was determined by vibration testing. Analytically, these beams with SMA wires inserted in embedded sleeves were examined as beams on an elastic foundation; the spring constant of the elastic foundation depended on the axial recovery force of the SMA wire. Good correlation between analysis and experiment was achieved. A numerical parametric study of natural frequencies of composite beams with activated SMA wires was conducted. The parameters considered were the diameter and the number of SMA wires. The numerical study suggests that inserting 25 SMA wires of 20 mils diameter into a graphite - epoxy beam of 30 in length, 1 in width and 62 mils thickness increases its first frequency by 276%.

  • Torsional actuation with extension-torsion composite coupling and a magnetostrictive actuator
    AIAA Journal, 1995
    Co-Authors: Christopher M. Bothwell, Ramesh Chandra, Inderjit Chopra
    Abstract:

    This paper presents an analytical-experimental study of using magnetostrictive actuators in conjunction with an extension-torsion coupled composite tube to actuate a rotor blade trailing-edge flap to actively control helicopter vibration. Thin-walled beam analysis based on Vlasov theory was used to predict the induced twist and extension in a composite tube with magnetostrictive actuation. To validate the analysis, extension-torsion coupled Kevlar®-epoxy tubes or different ply lay-ups were fabricated using an Autoclave Molding technique. They tubes were first tested under static mechanical loads, and tip twist and axial extension were measured by means or a laser optical system and strain gages, respectively. Good correlation between theory and experiment was achieved. Subsequently, these composite tubes were tested under magnetostrictive actuation. The [11] 2 Kevlar-epoxy tube system generated the maximum twist, 0.19 deg in tension and 0.20 deg in compression. The Kevlar-epoxy systems showed good correlation between measured and predicted twist values. Finally, alternate actuator concepts for these tubes, specifically piezoelectric stacks and electrostrictive actuators, were examined, and a piezoelectric stack actuator was round to induce much larger force and twist (approximately 3 times that created by the magnetostrictive actuator/tube system)

  • Analytical-experimental investigation of free-vibration characteristics of rotating composite I-beams
    Journal of Aircraft, 1993
    Co-Authors: Ramesh Chandra, Inderjit Chopra
    Abstract:

    This article presents a free-vibration analysis of coupled composite I-beams with couplings under rotation. A linear analysis based upon Vlasov theory was developed to obtain coupled flap-lag-torsion equations of motion for I-beams made out of general composite laminates. Constrained warping and transverse shear effects were included. Free-vibration characteristics were obtained by solving these equations using Galerkin's method. In order to validate the theory, graphite-epoxy and kevlar-epoxy I-beams with bending-torsion coupling were fabricated using an Autoclave Molding technique and tested in an in vacuo rotor test facility for their vibration characteristics. Induced-strain actuation by piezoceramic elements was used to excite the I-beams in the rotating frame. Strain gauges were used to measure the response of these beams over a range of rotational speeds up to 1000 rpm. Natural frequencies and strain mode shapes were determined by carrying out signal analysis using a spectrum analyzer. Good correlation between theory and experiment was achieved. About 600% increase in torsional frequency due to constrained warping occurs for graphite-epoxy beams with a slenderness ratio of 18. Nomenclature A = cross-sectional area of blade b, h = semiwidth and semiheight of I-beam Eh Et — Young's moduli in principal directions of plies of beam Glt - shear modulus of plies in principal plane Ixx, Iyy = blade cross-sectional moment of inertia about x and y axes, respectively K] - stiffness matrix for beam Kf] = flap bending stiffness matrix Kft] — flap bending-torsion coupling stiffness matrix K] = lag bending stiffness matrix K!t] - lag bending-torsion coupling stiffness matrix [Kt] = torsion stiffness matrix KA = effective polar radius of gyration of blade cross-section V(/vv + IXX)IA

  • Structural modeling of composite beams with induced-strain actuators
    AIAA Journal, 1993
    Co-Authors: Ramesh Chandra, Inderjit Chopra
    Abstract:

    This paper presents an analytical-experimental investigation on structural modeling of coupled composite beams with distributed induced-strain actuators. Analysis based on Vlasov theory is developed to include distributed piezoelectric actuators, either surface mounted or embedded. Salient features of composite open-section beam analysis, like constrained warping and transverse shear deformation, were included. Induced-strain actuation was introduced in the constitutive relations of plate segment of the open-section composite beams. To evaluate the analytical predictions, several bending-torsion and extension-torsion coupled graphite-epoxy solid beams were fabricated using an Autoclave Molding technique. These were surface mounted with piezoelectric actuators. The actuators were excited to produce local bending moment and axial force on the beam, and the structural response was measured in terms of bending slope, induced twist, and surface strain. Good correlation between analysis and experiment was achieved. Because of the existence of a chordwise actuator moment, the induced twist of bending-torsi on coupled beams was significantly influenced by including the chordwise curvature of the plate segment of beam in the formulation. For [45]i4 solid beams, the chordwise bending of the plate segment of beam was found to increase the tip twist by about

J W Gillespie - One of the best experts on this subject based on the ideXlab platform.

  • Assessment of flow and cure monitoring using direct current and alternating current sensing in vacuum-assisted resin transfer Molding
    Smart Materials and Structures, 2000
    Co-Authors: Uday K. Vaidya, Nitesh C. Jadhav, J W Gillespie, Madhusoodan V. Hosur, Bruce K Fink
    Abstract:

    Vacuum-assisted resin transfer Molding (VARTM) is an emerging manufacturing technique that holds promise as an affordable alternative to traditional Autoclave Molding and automated fiber placement for producing large-scale structural parts. In VARTM, the fibrous preform is laid on a single-sided tool, which is then bagged along with the infusion and vacuum lines. The resin is then infused through the preform, which causes simultaneous wetting in its in-plane and transverse directions. An effective sensing technique is essential so that comprehensive information pertaining to the wetting of the preform, arrival of resin at various locations, cure gradients associated with thickness and presence of dry spots may be monitored. In the current work, direct current (dc) and alternating current sensing/monitoring techniques were adopted for developing a systematic understanding of the resin position and cure on plain weave S2-glass preforms with Dow Derakane vinyl ester VE 411-350, Shell EPON RSL 2704/2705 and Si-AN epoxy as the matrix systems. A SMARTweave dc sensing system was utilized to conduct parametric studies: (a) to compare the flow and cure of resin through the stitched and non-stitched preforms; (b) to investigate the influence of sensor positioning, i.e. top, middle and bottom layers; and (c) to investigate the influence of positioning of the process accessories, i.e. resin infusion point and vacuum point on the composite panel. The SMARTweave system was found to be sensitive to all the parametric variations introduced in the study. Furthermore, the results obtained from the SMARTweave system were compared to the cure monitoring studies conducted by using embedded interdigitated (IDEX) dielectric sensors. The results indicate that SMARTweave sensing was a viable alternative to obtaining resin position and cure, and was more superior in terms of obtaining global information, in contrast to the localized dielectric sensing approach.

  • Assessment of flow and cure monitoring using direct current and alternating current sensing in Vacuum Assisted Resin Transfer Molding
    American Society of Mechanical Engineers Manufacturing Engineering Division MED, 1999
    Co-Authors: Nitesh C. Jadhav, J W Gillespie, Madhusoodan V. Hosur, Uday K. Vaidya, Bruce K Fink
    Abstract:

    Vacuum Assisted Resin Transfer Molding (VARTM) is an emerging manufacturing technique that holds promise as an affordable alternative to traditional Autoclave Molding and automated fiber placement for producing large scale structural parts. In VARTM, the fibrous preform is laid on a single sided tool, which is then bagged along with the infusion and vacuum lines. The resin is then infused through the preform, which causes simultaneous wetting in its in-plane and transverse directions. An effective sensing technique is essential so that comprehensive information pertaining to the wetting of the preform, arrival of resin at various locations, cure gradients associated with thickness and presence of dry spots may be monitored. In the current work, direct current and alternating current sensing/monitoring techniques were adopted for developing a systematic understanding of resin position and cure on plain weave S2-Glass preforms with Dow Derakane vinyl ester VE 411-350, Shell EPON RSL 2704/2705 and Si-AN epoxy as the matrix systems. The SMARTweave DC sensing system was utilized to conduct parametric studies a) to compare the flow and cure of resin through the stitched and non-stitched preforms, b) influence of sensor positioning, i.e., top, middle and bottom layers, c) influence of positioning of the process accessories, i.e., resin infusion point and vacuum point on the composite panel. The SMARTweave system was found to be sensitive to all the parametric variations introduced in the study. Furthermore, the results obtained from the SMARTweave system were compared to the cure monitored from embedded IDEX dielectric sensors. The results indicate that SMARTweave sensing was a viable alternative to obtaining resin position and cure, and more superior in terms of obtaining global information in contrast to the localized dielectric sensing approach.

Inderjit Chopra - One of the best experts on this subject based on the ideXlab platform.

  • Torsional actuation with extension-torsion composite coupling and a magnetostrictive actuator
    AIAA Journal, 1995
    Co-Authors: Christopher M. Bothwell, Ramesh Chandra, Inderjit Chopra
    Abstract:

    This paper presents an analytical-experimental study of using magnetostrictive actuators in conjunction with an extension-torsion coupled composite tube to actuate a rotor blade trailing-edge flap to actively control helicopter vibration. Thin-walled beam analysis based on Vlasov theory was used to predict the induced twist and extension in a composite tube with magnetostrictive actuation. To validate the analysis, extension-torsion coupled Kevlar®-epoxy tubes or different ply lay-ups were fabricated using an Autoclave Molding technique. They tubes were first tested under static mechanical loads, and tip twist and axial extension were measured by means or a laser optical system and strain gages, respectively. Good correlation between theory and experiment was achieved. Subsequently, these composite tubes were tested under magnetostrictive actuation. The [11] 2 Kevlar-epoxy tube system generated the maximum twist, 0.19 deg in tension and 0.20 deg in compression. The Kevlar-epoxy systems showed good correlation between measured and predicted twist values. Finally, alternate actuator concepts for these tubes, specifically piezoelectric stacks and electrostrictive actuators, were examined, and a piezoelectric stack actuator was round to induce much larger force and twist (approximately 3 times that created by the magnetostrictive actuator/tube system)

  • Analytical-experimental investigation of free-vibration characteristics of rotating composite I-beams
    Journal of Aircraft, 1993
    Co-Authors: Ramesh Chandra, Inderjit Chopra
    Abstract:

    This article presents a free-vibration analysis of coupled composite I-beams with couplings under rotation. A linear analysis based upon Vlasov theory was developed to obtain coupled flap-lag-torsion equations of motion for I-beams made out of general composite laminates. Constrained warping and transverse shear effects were included. Free-vibration characteristics were obtained by solving these equations using Galerkin's method. In order to validate the theory, graphite-epoxy and kevlar-epoxy I-beams with bending-torsion coupling were fabricated using an Autoclave Molding technique and tested in an in vacuo rotor test facility for their vibration characteristics. Induced-strain actuation by piezoceramic elements was used to excite the I-beams in the rotating frame. Strain gauges were used to measure the response of these beams over a range of rotational speeds up to 1000 rpm. Natural frequencies and strain mode shapes were determined by carrying out signal analysis using a spectrum analyzer. Good correlation between theory and experiment was achieved. About 600% increase in torsional frequency due to constrained warping occurs for graphite-epoxy beams with a slenderness ratio of 18. Nomenclature A = cross-sectional area of blade b, h = semiwidth and semiheight of I-beam Eh Et — Young's moduli in principal directions of plies of beam Glt - shear modulus of plies in principal plane Ixx, Iyy = blade cross-sectional moment of inertia about x and y axes, respectively K] - stiffness matrix for beam Kf] = flap bending stiffness matrix Kft] — flap bending-torsion coupling stiffness matrix K] = lag bending stiffness matrix K!t] - lag bending-torsion coupling stiffness matrix [Kt] = torsion stiffness matrix KA = effective polar radius of gyration of blade cross-section V(/vv + IXX)IA

  • Structural modeling of composite beams with induced-strain actuators
    AIAA Journal, 1993
    Co-Authors: Ramesh Chandra, Inderjit Chopra
    Abstract:

    This paper presents an analytical-experimental investigation on structural modeling of coupled composite beams with distributed induced-strain actuators. Analysis based on Vlasov theory is developed to include distributed piezoelectric actuators, either surface mounted or embedded. Salient features of composite open-section beam analysis, like constrained warping and transverse shear deformation, were included. Induced-strain actuation was introduced in the constitutive relations of plate segment of the open-section composite beams. To evaluate the analytical predictions, several bending-torsion and extension-torsion coupled graphite-epoxy solid beams were fabricated using an Autoclave Molding technique. These were surface mounted with piezoelectric actuators. The actuators were excited to produce local bending moment and axial force on the beam, and the structural response was measured in terms of bending slope, induced twist, and surface strain. Good correlation between analysis and experiment was achieved. Because of the existence of a chordwise actuator moment, the induced twist of bending-torsi on coupled beams was significantly influenced by including the chordwise curvature of the plate segment of beam in the formulation. For [45]i4 solid beams, the chordwise bending of the plate segment of beam was found to increase the tip twist by about

  • Experimental-theoretical investigation of the vibration characteristics of rotating composite box beams
    Journal of Aircraft, 1992
    Co-Authors: Ramesh Chandra, Inderjit Chopra
    Abstract:

    This paper presents a theoretical-cum-experimental study of the free vibration characteristics of thin-walled composite box beams with bending-twist and extension-twist coupling under rotating conditions. The governing equations in generalized displacements were derived using a Newtonian approach. The composite structural model in the derivation used a solid-section approach and contained transverse shear-related couplings and appropriate cross-section warping. The free vibration characteristics of composite box beams were determined by the Galerkin method. In order to validate the theory, glass-epoxy, kevlar-epoxy and graphite-epoxy symmetric and antisymmetric box beams were fabricated using an Autoclave Molding technique, and tested in an in-vacuo rotor test facility for their vibration characteristics. Beam excitation in the rotating condition was effected by means of induced-strai n actuation with the help of piezoceramic bending elements. Strain gages were used to measure the response of the first three modes over a range of rotational speeds up to 1000 rpm. It was determined that the experimental frequencies and mode shapes correlated satisfactorily with the theoretical results. It is shown also that bending-shear coupling influences the flexural vibration frequencies of antisymmetric box beams significantly. Extension-shear coupling, on the other hand, does not influence the flexural-torsion vibration frequencies of symmetric box beams significantly.

  • Experimental and theoretical analysis of composite I-beams with elastic couplings
    AIAA Journal, 1991
    Co-Authors: Ramesh Chandra, Inderjit Chopra
    Abstract:

    This paper presents a theoretical-cum-experimental study on the static structural response of composite I-beams with elastic couplings. A Vlasov type linear theory is developed to analyze composite open section beams made out of general composite laminates, where the transverse shear deformation of the beam cross-section is included. In order to validate this analysis, graphite-epoxy and kevlar-epoxy symmetric I-beams were fabricated using an Autoclave Molding technique. The beams were tested under tip bending and torsional loads, and their structural response in terms of bending slope and twist measured with a laser optical system. Good correlation between theoretical and experimental results is achieved. A 630 percent increase in the torsional stiffness due to constrained warping is noticed for graphite-epoxy beams with slenderness ratio of 30. Also extension-twist coupling 'B16' of flanges of these I-beams increases the bending-torsion coupling stiffness of