Elastic Responses of a Composite Shell Structure Subjected to Impact Loading

Received 17 December 2019; accepted 17 June 2020 This work investigated the elastic responses of a composite laminate shell subjected to a transverse low-velocity impact. The governing equation based on the equations of motion of both the impactor and target was developed to detetrmine the impact force. The displacement of the shell subjected to unit impulse loading was solved using the finite element method. A non-linear differential equation in terms of the indentation depth was derived by incorporating the Hertzian contact law and theory of convolution. Runge-Kutta method was employed to solve the non-linear integro-differential equation, leading to the determination of the impact force at the point of contact between the impactor and the composite shell. The elastic responses including the displacement and stress of the composite laminate shell were evaluated using the finite element method by exerting the impact force on the apex of the composite shell. Present approach was verified with the analytical, experimental and numerical results reported in the existing literatures. The influences of stacking sequence of the composite laminate shell on the impact responses were examined through a series of parametric studies. In addition, impact responses of the spherical shells with different materials such as steel, aluminum and glass were studied.

Design of the composite casing of microstrip antenna for the aerospace satellite

Purpose The paper aims to present a design and numerical verification procedure of a composite casing of a microstrip antenna for an aerospace satellite. Design/methodology/approach The casing for the microstrip antenna was designed in a form of a laminate shell with variable number of layers of reinforcing fabric. The material properties, both static and dynamic, were determined experimentally and then exported to an environment of numerical analyses. The numerical modal analysis allows optimizing the geometry and lay-up of the casing in such a way that a number of modal shapes occurring in the operational frequency band was significantly reduced, several modal shapes with high displacement in flanges of the casing were eliminated and the values of natural frequencies were increased. A final model of the composite casing was subjected to two types of analyses which simulate typical operation conditions during spacecraft mission. These analyses contained thermomechanical quasi-static analyses with 12 loadcases and thermomechanical shock analyses with 9 loadcases, which simulate various mechanical and temperature conditions. Findings Results of the performed analyses were compared with safety margins determined by following requirements to spacecraft vehicles. The obtained results confirm the design feasibility, which allow considering the proposed design during manufacturing of a prototype in further studies. Practical implications Moreover, the presented results can be considered as a design methodology guideline, which can be helpful for engineers working in the aerospace industry. Originality/value The originality of the paper lies in the proposed design and verification procedure of composite elements subjected to operational loading during a spacecraft mission.

Free vibration analysis of rotating fiber–metal laminate circular cylindrical shells

In this article, free vibration of rotating fiber–metal laminate thin circular cylindrical shells has been analyzed. Strain–displacement relations have been obtained based on Love’s first approximation shell theory. The variations of frequencies of the fiber–metal laminate cylindrical shell with rotational speeds for different axial and circumferential wave numbers, L/R ratios, metal thicknesses and volume fractions of metal have been presented. Also, free vibrations of the rotating fiber–metal laminate shell have been studied for carbon/epoxy, glass/epoxy and aramid/epoxy composite materials combining thin aluminum layers. The results showed that with increasing rotating speed, the gap between backward and forward waves frequencies increased.

Laser Doppler Vibrometer Based Examination of the Efficiency of Introducing Artificial Delaminations into Composite Shells

During its operation, the laminate shell of the watercraft hull can be exposed to local stability losses caused by the appearance and development of delaminations. The sources of these delaminations are discontinuities, created both in the production process and as a result of bumps of foreign bodies into the hull in operation. In the environment of fatigue loads acting on the hull, the delaminations propagate and lead to the loss of load capacity of the hull structure. There is a need to improve diagnostic systems used in Structural Health Monitoring (SHM) of laminate hull elements to detect and monitor the development of the delaminations. Effective diagnostic systems used for delamination assessment base on expert systems. Along with other tools, the expert diagnostic advisory systems make use of the non-destructive examination method which consists in generating elastic waves in the hull shell structure and observing their changes by comparing the recorded signal with damage patterns collected in the expert system database. This system requires introducing certain patterns to its knowledge base, based on the results of experimental examinations performed on specimens with implemented artificial delaminations. The article presents the results of the examination oriented on assessing the delaminations artificially generated in the structure of glass- and carbon-epoxy laminates by introducing local non-adhesive layers with the aid of thin polyethylene film, teflon insert, or thin layer of polyvinyl alcohol. The efficiency of each method was assessed using laser vibrometry. The effect of the depth of delamination position in the laminate on the efficiency of the applied method is documented as well.

Impact Analysis of Composite Laminate Shell Structures

In this investigation, the methodology for predicting the dynamic response of a composite laminate shell subjected to low velocity impact is presented. A non-linear integro-differential equation is derived and solved by the numerical scheme of Runge-Kutta method to obtain the time history of the contact force at the impact point of the shell. The contact force is then taken as external force acting on the apex of the shell and solved by the finite element method. The results are validated with the numerical calculation published in the literature.

Structural Stability Analyses of Composite Laminate Wind Turbine

The paper describes a structural stability analysis of fiber reinforced 10kW composite laminate wind turbine blades by using finite element method. The E-glass/epoxy orthotropic materials DB300、DBL850、L900 were employed for construction of a composite laminate shell structure. The composite laminate sheel structures were constructed by two types of lamination method. The rotating effect of wind blade was considered using the linear and the nonlinear static analysis. The results of the nonlinear analysis of displacement and stress show much lower than the linear analysis, because of the geometry nonlinear effect. From the contours of stress and displacement, the maximum stress appeared at the root of the blade, and maximum deformation occurred at the tip of the blade. Finally, the modal properties of the wind blade was investigated, including the natural frequency, modeshaps, and the centrifugal effect.

Measurement and Prediction of Tape Cupping Under Mechanical and Hygrothermal Loads and Its Influence on Debris Generation in Linear Tape Drives

Magnetic tapes, which may be modeled as three-ply laminates, exhibit transverse curvature, or cupping, as manufactured and when mechanical and hygrothermal loads are applied. Among other things, this cupping affects debris generation since it influences the contact between the flawed tape edge and head, the point where much of the debris generation occurs. This influence on debris generation is demonstrated experimentally in this study. Much more debris accumulates near the tape edge-head contact than at other contact locations. No difference in debris generation was found for two tapes with slightly different residual cupping (which is controlled during manufacturing). The target residual cupping is usually negative, which means that the tape bows out towards the tape so that the edges are farther away from the head than the center of contact is, so as to reduce contact pressure with the tape edges. However, cupping generally changes upon application of a tension and generally reduces the importance of residual cupping, which accounts for the failure to find a difference in debris generation for tapes with slightly different residual cupping. A finite element method model that uses laminate shell elements and accounts for in-plane stress stiffening, thus making it suitable for thin laminate modeling, was created. This modeling demonstrates that application of tensile and normal (used to simulate head contact) loads leads to cupping movement in the positive direction, which indicates a more severe edge contact, for an increase in front coat Young’s modulus and/or an increase in front coat thickness. The same trends hold for an increase in back coat Young’s modulus and/or an increase in back coat thickness. Modeling also demonstrates that cupping moves in the positive direction for an increase in the substrate’s Young’s modulus in the transverse direction for MP and ME tapes. An analytical model demonstrates that increases in temperature and front coat thermal expansion coefficient leads to cupping movement in the negative direction. The same trends hold for changes in relative humidity.