This study compares the deformation characteristics of steel and carbon fiber composite (CFC) front bumper crush can (FBCC) assemblies when subjected to a full-overlap frontal impact into a rigid wall. Both the steel and composite bumper tests were conducted using a sled-on-sled testing method. Several high-speed cameras (HSCs) and accelerometers were used to gather kinematics data. The applied forces were measured using a load cell wall. For each test, the collective set of data was filtered, sorted, and analyzed to compare the performance of the steel and CFC bumpers. Similarities in Acceleration-Time plots suggested resemblance in the deformation patterns for both types of bumper systems. The difference observed in the velocity and displacement time-histories was because of the brittle nature of the composite material. The velocity-time history of the CFC FBCC had two distinct patterns, events suggesting adhesive bond failure between the bumper beam and the crush cans, which was validated through video tracking. Post-impact photographs showed a clear difference between the material behavior of composite and steel bumpers when subjected to high-velocity impact. The steel bumper beam was bent uniformly with intact, equally crushed crush cans. The composite beam was cracked in the middle and was detached from the crush cans.

A new model for determining band gaps for elastic wave propagation in a periodic composite beam structure is developed using a non-classical Timoshenko beam model that incorporates the surface energy, transverse shear and rotational inertia effects. The Bloch theorem and transfer matrix method for periodic structures are employed in the formulation. The new model reduces to the classical elasticity-based model when the surface energy effect is not considered. It is shown that the band gaps predicted by the current model depend on the surface elastic constants of each constituent material, beam thickness, unit cell size, and volume fraction. The numerical results reveal that the band gap based on the current non-classical model is always larger than that given by the classical model when the beam thickness is very small, but the difference is diminishing as the thickness becomes large. Also, it is found that the first frequency for producing the band gap and the band gap size decrease with the increase of the unit cell length according to both the current and classical models. In addition, it is observed that the volume fraction has a significant effect on the band gap size, and large band gaps can be obtained by tailoring the volume fraction and material parameters.

Composite pretwisted rotating thin walled beams (TWB) can be used as the structural model for composite helicopter and wind turbine blades for the study of aeroelastic response of the blades. In the present study, semi-analytical solution is performed for the free vibration analysis of uniform and asymmetric composite pretwisted rotating TWB. The approximation of the Green-Lagrange strain tensor is adopted to derive the strain field of the system. The Euler–Lagrange governing equations of the dynamic system and the related boundary conditions are derived via Hamilton’s principle. In order to solve the governing set of equations, the Extended Galerkin’s Method (EGM) is employed. For this purpose, the structural variables are separated in space and time and the assumed mode shapes are defined to satisfy the essential boundary conditions. For the purpose of validating the TWB model developed, the commercial finite element analysis tool, MSC Nastran is used to compare the results of modal analysis obtained by the present structural model with the finite element solution. With the results obtained in this paper, it is aimed to ascertain the effect of various coupling in circumferentially asymmetric stiffness (CAS) and circumferentially uniform stiffness CUS configurations, pretwist, angular velocity and fibre orientation, on the natural frequencies and the mode shapes of the rotating thin-walled composite beams. The results are expected to propose better predictions of the vibrational behavior of thin walled structures in general, and in the design of rotor blades of turbomachinery, rotorcraft and wind turbine systems, in particular.

Tolerance simulation’s reliability depends on the concordance between the input probability distribution and the practical situation. Pre-loading induced changes in the probability distribution should be considered in the structure’s tolerance simulation, especially for composite structures. The paper presents a tolerance simulation method for the thin-walled C-section composite beam (TC 2 B) assembling under preloading, that is prescribed clamping force. Based on FEA model of TC2B, the preloading-modified probability distribution function of the R angle spring-in deviation is proposed. Thickness variations of the TC2B are obtained from the data of the downscaled composite wingbox. These parts’ variations are input to the tolerance simulation software, and the final assembly variations are obtained. The assembly of the downscaled wingbox illustrates the effect of preloading on the probability distribution of the R angle spring-in deviation. The results have shown that tolerance simulation with the modified probability distribution is more accurate than the initial normal distribution. The tolerance simulation work presented in the paper will enhance the understanding of the composite parts assembling with spring-in deviations, and help systematically improving the precision control efficiency in civil aircraft industry.

In this study the closed-loop vibrational behavior of aircraft wing is investigated. The wing is modeled as a thin-walled composite beam with a diamond shaped cross-section. This beam model incorporates a number of non-classical effects such as material anisotropy, transverse shear deformation and warping restraint. Moreover, the directionality property of thin-walled composite beams produces a wide range of elastic couplings. In this respect, an anti-symmetric lay-up configuration i.e. Circumferentially Uniform Stiffness (CUS) is employed to generate coupled motion of transverse-lateral bending and transverse shear. The active feedback control is performed by using adaptive materials. The piezoelectric layers are symmetrically embedded in the host structure and the piezoactuator is spread over the entire beam span. As a result of this a boundary moment is induced at the beam tip and in this case, the control is achieved via the boundary moment feedback control yielding an adaptive change in the dynamical characteristics of the beam. the cases of proportional and velocity feedback control procedures are applied and the effect of ply-angle orientation on the fundamental frequencies are investigated and discussed.

This study reports dynamic aeroelastic analyses of an aircraft wing with an attached mass subjected a lateral follower force in an incompressible flow. A swept thin-walled composite beam with a biconvex cross-section is used as the structural model that incorporates a number of non-classical effects such as material anisotropy, transverse shear deformation and warping restraint. A symmetric lay-up configuration i.e. circumferentially asymmetric stiffness (CAS) is further adapted to this model to generate the coupled motion of flapwise bending-torsion-transverse shear. For this beam model, the unsteady aerodynamic loads are expressed using Wagners function in the time-domain as well as using Theodorsen function in the frequency-domain. The flutter speeds are evaluated for several ply angles and the effects of follower force, transverse shear, fiber-orientation and sweep angle on the aeroelastic instabilities are further discussed.

There are unavoidable deviations, such as shrinkage and distortions, in the composite detail parts production due to the complexity of composites fabrication. Interests in the assembly analysis of composite beams have led to a need for more accurate analysis especially in the case of fabrication deviations. This work proposes a numerical finite element model of thin-walled C-section composite beam with R-angle deviation for assembling. The rule of Hashin failure combined with cohesive element is applied to study the mechanical performance of the fiber and matrix (implemented as user subroutine UMAT in ABAQUS) while positioning and clamping. Tension and compression tests are carried out based on available standards to determine the C-section beam behavior under load. The testing data validates the proposed numerical model. The numerical model captures the experimentally obtained results with minimal error, and predicts the failure modes successfully. The proposed model allows to determine accurately the first failure location and the associated load level. It will enhance the understanding of the composite components pre-loading analysis, and help systematically improving the composites assembling efficiency in civil aircraft industry.

In this paper, dynamic and aeroelastic analysis of a wind turbine blade modeled as an anisotropic composite thin-walled box beam is carried out. The analytical formulation of the beam is derived for the flapwise bending, chordwise bending and transverse shear deformations. The derivation of both strain and kinetic energy expressions are made and the equations of motion are obtained by applying the Hamilton’s principle. The equations of motion are solved by applying the extended Galerkin method (EGM) for anti-symmetric lay-up configuration that is also referred as Circumferentially Uniform Stiffness (CUS). As a result various coupled vibration modes are exhibited. This type of beam features two sets of independent couplings: i) extension-torsion coupling, ii) flapwise/chordwise bending-flapwise/chorwise transverse shear coupling. For both cases, the natural frequencies are validated by making comparisons with the results in literature and effects of coupling, transverse shear, ply-angle orientation, and rotational speed on the natural frequencies are examined and the mode shapes of the rotating thin-walled composite beams are further obtained. Blade element momentum theory (BEMT) is utilized to model the wind turbine blade aerodynamics. After combining the structural and the aerodynamic models, the aeroelastic analysis are performed and flutter boundaries are obtained.

Depending on the type of matrix materials, composites can be broadly divided into three different major classifications: Organic-matrix composites (OMC), metal-matrix composites (MMC), and ceramic-matrix composites (CMC). OMC can be further sub-classified into polymer-matrix composites (PMC) and carbon-matrix composites or carbon-carbon composites. In this paper the main objective is to focus on polyurethane based PMC composites. Polyurethane is one of the widely used polymer matrix materials. It has diversified applications, easily available and cheap. In this computational study a composite shaft with a core made of matrix material completely wrapped around by a woven fiber cloth with a very strong bonding between core and fibers is considered. Three different types of woven fibers: fiber glass, Kevlar 49, and carbon fibers, are considered. A woven fabric is the interlocking or weaving of two unidirectional fibers. This configuration is often used to produce curve surfaces because of the ease with which it could be placed on and conform to curved surfaces. Authors had fabricated these three composites in their in-house laboratory. They had also experimentally measured the mechanical properties of these composites using 3-point bending test which already been published. In this current study finite element analyses has been performed for the modeling of the static response of these three different polyurethane based composite shafts as fiber glass reinforced polyurethane epoxy, carbon fiber reinforced polyurethane epoxy, and Kevlar fibers reinforced polyurethane epoxy for three different boundary conditions. These three boundary conditions are simply supported, cantilever, both end fixed types with bending loads applied at the middle for simply supported case and distributed load along the length of the shaft for the last two types of boundary conditions. A three dimensional model of the composite beam has been implemented in this study using SolidWorks. A finite element commercial software ANSYS is used to investigate the stress response and deformation behavior of the model geometry for these three polyurethane based composite shafts for these three boundary conditions. A twenty node three dimensional element has been implemented for the finite element formulation of the modeled geometry such that it is applicable for the analysis of a layered composite structure, while providing support for linear, large rotation, and large strain nonlinear loading conditions. Convergence has also been ensured for various mash configurations in this work.

In this study, accounting for large displacements a geometrically nonlinear theory, which is valid for laminated thin-walled composite beams of open and closed cross sections, is developed. The beam model incorporates a number of non-classical effects such as material anisotropy, transverse shear deformation and warping restraint. Moreover, the directionality property of thin-walled composite beams produces a wide range of elastic couplings. In this respect, symmetric lay-up configuration i.e. Circumferentially Asymmetric Stiffness (CAS) is adapted to this model to generate coupled motion of flapwise bending-torsion-flapwise transverse shear. Initially, free vibration analyses are carried out for the linear model of the shearable and the non-shearable thin-walled composite beams. Similar to the linear model, the displacement-based nonlinear equations are derived by the variational formulation, considering the geometric non-linearity in the von Karman sense. Finally, the static and the dynamic analyses for the nonlinear beam model are carried out addressing the effects of transverse shear, fiber-orientation and sweep angle on the nonlinear frequencies and the static response of the beam.

This study reports static and dynamic aeroelastic analyses of an aircraft wing in an incompressible flow. A swept thin-walled composite beam with a biconvex cross-section is used as the structural model that incorporates a number of non-classical effects such as material anisotropy, transverse shear deformation and warping restraint. A symmetric lay-up configuration i.e. circumferentially asymmetric stiffness (CAS) is further adapted to this model to generate the coupled motion of flap-wise bending-torsion-transverse shear. For this beam model, the unsteady aerodynamic loads are expressed using Wagners function in the time-domain as well as using Theodorsen function in the frequency-domain. The divergence and the flutter speeds are evaluated for several ply angles and the aeroelastic response of an aircraft wing exposed to gust load is examined. The effects of transverse shear, fiber-orientation and sweep angle on the aeroelastic instabilities and the aeroelastic response of the beam are further discussed.

This paper deals with the dynamic analysis of a delaminated composite beam under the action of moving oscillatory mass. The beam is analyzed as four interconnected sub-beams using the delamination limits as their boundaries. The constrained model is used to model the delamination region. The continuity and equilibrium conditions are satisfied between the adjoining beams. The beam response variation due to the delamination with respect to the intact beam has been investigated. Furthermore, the possible separation of the moving oscillator from the beam during the course of the motion is investigated by monitoring the contact force between the oscillator and the beam. The effect of the parameters such as the oscillator axial velocity and the size, depth and spanwise location of the delamination on the dynamic response of the beam and on the oscillator separation from the delaminated beam has been studied. It is shown that the delamination has significant influence on the dynamic response of the beam and on the oscillator separation from the beam.

The purpose of the present paper is to develop a finite element code to model a thin-walled composite beam. The beam is modeled as a thin-walled composite beam with a single-cell, rectangular cross-section featuring both CAS and CUS lay-up configurations. Analytical and finite element formulations of the flapwise bending, chordwise bending and torsional displacements of the beam are derived. Effect of the ply orientation on the natural frequencies is investigated and it is noticed that the obtained results are in good agreement with the ones in open literature.

Electrospinning is regarded as one of the most efficient processes to generate one-dimensional nano structures. The electrospinning process is simple and provides consistent mass production of nanofibers. The scalability of the electrospinning process has an excellent potential to fulfill the high volume requirements of nanofibers in the infrastructure applications. The present work emphasizes the use of interleaved electrospun nanofibers in fiber glass composite beams. The Flexural behavior of a simply supported beam under a centrally concentrated loading is studied. Flexural properties of a fiber glass composite beam with interleaved electrospun nanofibers are compared with a fiber glass composite beam without electrospun nanofibers. The material configuration of the composite beams is: woven E-glass fabric prepregs with a low temperature molding resin. In addition, interleaved between the plies are TEOS (Tetra Ethyl Orthosilicate) electrospun nanofibers. The nanofibers were produced by developing optimized operating process parameters and a stabilized sintering temperature cycle to ensure consistency in the fiber morphology and pore structure. The successful integration of the electrospun nanofibers within the prepreg layers was obtained by pre-impregnation with a B-staged resin film and de-bulking to remove excessive resin prior to vacuum bagging. A series of mechanical Flexure tests were performed per the ASTM D7264 standard specification. Micrographs were obtained to study the progressive deformation and damage mechanics due to flexural loading in the specimens and clearly illustrate the differences in the failure mechanism with and without the electrospun interface layers.

This paper presents an experimental and numerical study to estimate ballistic limit velocity, V 50 , of plain-weave hybrid S2 glass-IM7 graphite fibers/toughened SC-79 resin (cured at 177°C) composite beams. The tests were conducted on hybrid S2 glass-IM7 graphite fibers/toughened SC-79 resin and nonhybrid S2 glass-fiber/toughened SC-79 resin composites beams using high-speed gas-gun. The ballistic impact tests were then modeled using 3-D dynamic nonlinear finite element (FE) code, LS-DYNA, modified with a proposed user-defined nonlinear-orthotropic damage model. The ballistic limit velocities, V 50 , for both composite beams were then estimated using (a) only experimental tests, (b) combined experimental and numerical tests, (c) FE calculated residual velocities, and (d) FE calculated residual and transferred energies. For each type of composite beams, the parameters for the well-known Lambert-Jones equation were also computed. Good agreement between experimental and numerical results was observed.

The results of 3-point bending tests applied on 4 different types of composite beam structure and their comparison with Finite Element Modeling (FEM) are presented. Three different layups have been applied on rectangular and hexagonal foam cross sections. Experiments are realized and compared with FEM results in order to create a more confident design of an adaptive wind turbine blade that will be built using a foam core and a fiber glass/epoxy skin. Even if torsion loads and centrifugal loads are present on wind turbine blade during operation, the major loads are due to bending moments, so emphasis is put on 3-point bending tests of sandwich like composite beams. Tests and FEM show that the sandwich beam behavior is closely related to the skin and foam thicknesses.

Variations in the natural frequency and damping coefficients with cyclic fatigue testing in steel and composite beams carrying a lumped mass are assessed. The identification of these parameters is performed by exploiting the nonlinear behavior of the beam-mass system and matching an approximate solution of the representative model with quantities obtained from spectral analysis of measured vibrations. Percentage variations of the identified parameters during the tests and up to the point where cracks were observed are determined. The results show that the damping is more sensitive to damage progression than the natural frequency.

We report the fabrication and characterization of single-walled carbon nanotube (SWCNT) multilayer micropatterns and suspended micro-beams prepared by layer-by-layer (LbL) assembly. The SWCNT multilayer is etched using oxygen plasma with the masking layer of the photoresist, resulting in the feature size of 2 μm. Furthermore, it is released by etching a sacrificial layer of oxide in the hydrofluoric acid vapor. I-V measurements reveal that the resistance of suspended beams decreases upon release due to the exposed surface, excluding the effects of substrate. A high Young’s modulus has been found on the range of 500–800 GPa due to the deviation of spring constants measured and the variation in thickness of beams. It is much higher than those of the other CNT-polymer composites due to the organized structure. Stiff CNT-polymer composite micropatterns and the suspended micro-beams may have potential applications for novel physical sensors, nano-switches, other M/NEMS devices, etc.

Shape Memory Alloys (SMAs) have several attractive features that make them potentially useful concepts as bending micro actuators. SMA linear actuators are among those producing the highest strains and highest forces available, and when employed in a bending mode, their deflection capability is enhanced even more leading to potential new applications. This paper addresses the basic design concept for a bi-material actuator modeled as an initially curved composite beam with one active layer, the SMA material, and one conventional elastic layer. This device must be accurately controlled to achieve an optimal range of motion and to serve in many new applications so we have designed a nonlinear and adaptive control scheme based on Lypaunove stability theory to prevent erratic motion and even component separation and partial buckling. In addition, this control scheme is able to achieve high precision tracking without the need for detailed system parameters. Simulation is conducted which confirm the effectiveness of the proposed method.

A combined experimental and 3-D dynamic nonlinear finite element approach was adopted to study composite beams subject to drop-weight or ballistic impact. The composite specimens, made of S2 glass-reinforced toughened epoxy (44% fiber volume fraction, cured at 350°F), had 24 layers (approximately 6.35 mm) with various stacking sequences. They were damaged by impacts using either an Instron-Dynatup 8520 instrumented drop-weight impact tester (low-velocity impact) or an in-house high-speed gas gun (ballistic impact). For both types of tests, the time-histories of dynamic strains induced during impact were recorded using strain gages mounted on the front and back of the composite beam specimen. For drop-weight impact tests, the time history of impact force was also recorded; whereas for ballistic impact tests, only the impact velocity was calculated from the recorded change in voltage outputs, which resulted from the traversing of the impactor through two optical paths formed by two sets of diode laser-amplified photo diode pairs. The commercially available 3-D dynamic nonlinear finite element software, LS-DYNA, incorporated with a proposed nonlinear anisotropic damage model, was then used to simulate the experimental results. Good agreement between experimental and FEM results can be seen from comparisons of dynamic strain and impact force histories and damage patterns. Once the proposed nonlinear anisotropic damage model was verified by experimental results, further finite element simulations were conducted to predict the ballistic limit velocity (V 50 ) for penetration prevention.