Clamping effects on the dynamic characteristics of composite machine tool structures

Stationary random response of non-viscously damped polymer matrix composite structure systems

Modal strain energy (MSE) method is a widely used approximation approach for parameter calculation of damped composite structures. In this paper, iterative MSE method is proposed to calculate the loss factor of composite damping structure by considering the frequency dependence of modulus and loss factor of viscoelastic damping materials. The proposed method is applied to free damping spline, free damping plate and constrain damping plate. The results show that: the proposed method obtains minimum relative errors of less than 5% and less than 20% for nature frequency and composite loss factor. The influence of different material parameters on the calculation results is also discussed. The error is smaller when using the storage modulus and loss factor measured by tensile mode as input parameter. The thickness of the sample to measure the dynamic material parameters has a great influence on accuracy. This work provides a way for the calculation of composite loss fator of damped composite structures with embedded viscoelastic layer.

In this study, a combined finite element (FE)–boundary element (BE) method is presented to investigate the dynamic characteristics of shell and plate structures in contact with fluid. The numerical procedure consists of two parts. In the first part, the dynamic characteristics of structures are obtained under in-vacuo condition by using the finite element method. Then, in the second part, fluid-structure interaction effects are computed in terms of generalized added mass coefficients by using the boundary element method. In analyses, surrounding fluid is assumed ideal, i.e. inviscid, incompressible and irrotational, in the context of linear hydroelasticity theory. In order to show the applicability of the proposed method, the dynamic characteristics of two different structures—a vertical rectangular plate in contact with fluid on one side and a horizontal cylindrical shell partially filled with fluid—are investigated and compared with the results obtained with a commercial software, ANSYS.

Nonlinear three-dimensional problems of dynamic deformation, buckling, and posteritical behavior of composite shell structures under pulsed loads are analyzed. The structure is assumed to be made of rigidly joined plates and shells of revolution along the lines coinciding with the coordinate directions of the joined elements. Individual structural elements can be made of both composite and conventional isotropic materials. The kinematic model of deformation of the structural elements is based on Timoshenko-type hypotheses. This approach is oriented to the calculation of nonstationary deformation processes in composite structures under small deformations but large displacements and rotation angles, and is implemented in the context of a simplified version of the geometrically nonlinear theory of shells. The physical relations in the composite structural elements are based on the theory of effective moduli for individual layers or for the package as a whole, whereas in the metallic elements this is done in the framework of the theory of plastic flow. The equations of motion of a composite shell structure are derived based on the principle of virtual displacements with some additional conditions allowing for the joint operation of structural elements. To solve the initial boundary-value problem formulated, an efficient numerical method is developed based on the finite-difference discretization of variational equations of motion in space variables and an explicit second-order time-integration scheme. The permissible time-integration step is determined using Neumann's spectral criterion. The above method is especially efficient in calculating thin-walled shells, as well as in the case of local loads acting on the structural element, when the discretization grid has to be condensed in the zones of rapidly changing solutions in space variables. The results of analyzing the nonstationary deformation processes and critical loads are presented for composite and isotropic cylindrical shells reinforced with a set of discrete ribs in the case of pulsed axial compression and external pressure.

Air interlayers are often used as a part of thermal insulation structure and form a system with solid materials to reduce heat transfer. However, the heat transfer process in the composite structure is affected by many factors at high temperatures. In this paper, a series of heat preservation systems with air gap and solid structure were proposed. Based on the research background of heat preservation in the riser of ingot casting, the heat transfer process in the composite structure was systematically studied by means of numerical simulation and experiment. The heat transfer laws under different geometric structures, thermophysical properties of materials, and surface emissivity were obtained, which could provide theoretical basis for the design of heat preservation structures at high temperatures.

Nonlinear dynamic characteristics of a composite aircraft wing structure modeled by a geometrically nonlinear anisotropic thin-walled beam in the presence of simultaneous 1:2 internal and 1:1 external resonances are investigated. Some prominent non-classical effects such as of transverse shear strain, warping inhibition, and three-dimensional strain are considered in the beam model. Moreover, circumferentially asymmetric stiffness lay-up configuration is adapted to generate the transverse bending-twisting elastic coupling. The solution methodology is based on the Extended Galerkin’s Method, and the method of multiple scales is applied to the system in order to obtain the equations of amplitude and modulation. Steady-state solutions and their stability are investigated. The peculiarity of the internal resonances and the conditions for saturation and jump phenomenon during the modal interactions are discussed and the commercial code ABAQUS is used to validate the theoretical results we have obtained. Finally, the prominent features of modal interactions in composite thin-walled beam structures are summarized and pertinent suggestions concerning safe design of the wing structures are given.

The paper investigates the influence of dynamic characteristics of building structures on the mechanisms of progressive collapse development. It is shown that natural frequencies, mode shapes, and damping levels significantly affect the propagation pattern of collapse following the initial failure of one or more load-bearing elements. Based on the obtained results, vulnerability assessment criteria are formulated that take into account the dynamic properties of structures. Purpose of the article. The purpose of this study is to establish the relationship between the dynamic characteristics of a structural system and the mechanisms of progressive collapse development. Special attention is given to the effect of natural frequencies, vibration modes, and damping level on the likelihood of structural excitation leading to instability or further collapse. Based on a numerical analysis of a steel-framed building, a direct relationship is demonstrated between local damage and the redistribution of stiffness in the structural system. The analysis of changes in dynamic characteristics makes it possible to identify potentially vulnerable zones with reduced resistance to progressive collapse. To assess collapse vulnerability, it is advisable to determine the first 3–5 natural frequencies and corresponding mode shapes, as well as damping properties. A significant reduction in stiffness leads to the localization of vibrations, increased amplitudes, and potential energy accumulation. If the system is unable to dissipate vibrations due to insufficient damping, cascading failure may occur. Critical warning signs include a frequency decrease of more than 30 %, an increase in deformation amplitude by over 50 %, the emergence of localized vibration modes, and a reduction in damping. Clarifications are proposed to the conditions of the energy-based approach for evaluating the propagation of progressive collapse, taking into account dynamic characteristics and the localization of deformations within vibration modes (i. e., structural vulnerability). The criteria for determining the dynamic coefficient are refined to consider the frequency spectrum and damping. Design tasks are formulated based on dynamic analysis to enhance resistance to progressive collapse. Conclusions. The use of dynamic coefficients (impact factors) recommended by building codes is justified but insufficient without considering the individual properties of the specific structure. The analysis of structural vibration modes can reveal potential weak spots where deformations and stresses are expected to be the highest. This is crucial for predicting the mechanisms of progressive collapse propagation. The results of this research can be applied in assessing the vulnerability of existing buildings and in designing new structures resistant to progressive collapse in accordance with modern safety requirements.

Hybrid isogeometric-based analysis and experimental investigation on the dynamic response characteristics of a clamped circular plate partially in contact with fluid

Damping mechanics for predicting the damped dynamic characteristics in specialty composite structures with compliant interlaminar damping layers are presented. Finite-element based mechanics incorporating a discrete layer (or layer-wise) laminate damping theory are utilized to represent general laminate configurations in terms of lay-up and fiber orientation angles, cross-sectional thickness, shape and boundary conditions. Evaluations of the method with exact solutions and experimental data illustrate its accuracy. Additional parametric studies demonstrate the unique capability of angle-ply composite laminates with cocured interlaminar damping layers to significantly enhance structural damping.

Vibration control of flexible deployable mechanism is seriously significant with the increasing application of it in aerospace field. Satellite antenna must be carried out in folded state due to small space of launch vehicle. In the process of deployment and attitude adjustment, vibration has a great influence on the contour accuracy. Based on transfer matrix method, the deployment structure of large flexible deployable satellite antenna is analysed to obtain its natural frequencies and modes. By solving the first three natural frequencies and modes in different deployment angles, the structure completely deployed is prone to be coupled and has the worst stability. Thus, damping structure to suppress vibration at all modal resonance points of fully deployed satellite antenna is necessarily to be installed. A new-type damping structure, multi-petal friction damping structure with the characteristics of simple structure and wide frequency-band, is proposed in previous paper. The dynamic analysis of deployment process at different angles for deployment component with damping structure is carried out to verify the damping effect and the feasibility of damping structure as well as the rationality of theoretical analysis.

Some recent developments on integrated damping mechanics for unidirectional composites, laminates, and composite structures are reviewed. Simplified damping micromechanics relate the damping of on-axis and off-axis composites to constituent properties, fiber volume ratio, fiber orientation, temperature, and moisture. Laminate and structural damping mechanics for thin composites are summarized. Discrete layer damping mechanics for thick laminates, including the effects of interlaminar shear damping, are developed and semianalytical predictions of modal damping in thick simply supported specialty composite plates are presented. Applications show the advantages of the unified mechanics, and illustrate the effect of fiber volume ratio, fiber orientation, structural geometry, and temperature on the damping. Additional damping properties for composite plates of various laminations, aspect ratios, fiber content, and temperature illustrate the merits and ranges of applicability of each theory (thin or thick laminates).

The fault-crossing tunnel in high geothermal areas can be severely damaged under strong earthquake. In this paper, numerical models were established in Flac3d to investigate the thermal insulation and seismic effects under the strong earthquake when using highly damped composite structure. The results showed that the thermal insulation effect of the PC, the PC highly damped composite structure and the SFRC highly damped composite structure were almost the same, which the PC highly damped composite structure was slightly better. After applying the highly damped composite structure, the maximum and minimum principal stresses on the lining decreased, it showed that highly damped composite structure could enhance the seismic effect of tunnel. The safety factor of SFRC highly damped composite structure was 2.420, which was a 28.14% increase compared to PC. Based on numerical simulations, the thermal insulation and seismic effect of SFRC highly damped composite structure was better than other seismic measures. The research can provide a reference for the design of thermal insulation and anti-earthquake for fault-crossing tunnel under strong earthquake in high geothermal area.

Investigation of the mechanical properties of double lining structure of shield tunnel with different joint surface

The dynamic thermal characteristics of external wall structures are directly related to indoor thermal comfort and energy savings in buildings; they are also complicated and worth investigating. Thermal insulation in external wall structures has become a popular topic of investigation in the domain of building energy efficiency. This study aims to find the impact of insulation type and thickness on the dynamic thermal characteristics of external wall structures using a homogeneous multi-layer building external wall structure and three types of insulation materials that are widely used in Japan. The impact of insulation type and thickness on seven thermal characteristics of external walls, including thermal transmittance, decrement factor or amplitude attenuation, time lag, thermal admittance, time lead for thermal admittance, surface factor, and thermal capacity, was evaluated by numerical methods in this study. It was shown that insulation type and thickness would have a significant effect on thermal transmittance, decrement factor and time lag, but yield no significant change in thermal admittance, time lead for thermal admittance, surface factor, and the thermal capacity of external wall structures.

The characteristics of composite materials are of high importance to engineering applications; therefore the increasing use as a substitute for conventional materials, especially in the field of aircraft and space industries. It is a known fact that researchers use finite element programs for the design and analysis of composite structures, use of symmetrical conditions especially in complicated structures, in the modeling and analysis phase of the design, to reduce processing time, memory size required, and simplifying complicated calculations, as well as considering the response of composite structures to different loading conditions to be identical to that of metallic structures. Finite element methods are a popular method used to analyze composite laminate structures. The design of laminated composite structures includes phases that do not exist in the design of traditional metallic structures, for instance, the choice of possible material combinations is huge and the mechanical properties of a composite structure, which are anisotropic by nature, are created in the design phase with the choice of the appropriate fiber orientations and stacking sequence. The use of finite element programs (conventional analysis usually applied in the case of orthotropic materials) to analysis composite structures especially those manufactured using angle ply laminate techniques or a combination of cross and angle ply techniques, as well considering the loading response of the composite structure to be identical to that of structures made of traditional materials, has made the use of, and the results obtained by using such analysis techniques and conditions questionable. Hence, the main objective of this paper is to highlight and present the results obtained when analyzing and modeling symmetrical conditions as applied to commercial materials and that applied to composite laminates. A comparison case study is carried out using cross-ply and angle-ply laminates which concluded that, if the composition of laminate structure is pure cross-ply, the FEA is well suited for predicting the mechanical response of composite structure using principle of symmetry condition. On the other hand that is not the case for angle-ply or mixed-ply laminate structure.