Effect of fiber orientation and cross section of composite tubes on their energy absorption ability in axial dynamic loading

The crushing behavior of composite tubes in axial impact loading is investigated. Tubes of circular and rectangular cross section are simulated using an LS-DYNA software. The effect of fiber orientation on the energy absorbed in laminated composite tubes is also studied. The results obtained show that rectangular tubes absorb less energy than circular ones, and their maximum crushing load is also lower. The composite tubes with a [+θ/ -θ] lay-up configuration absorb a minimum amount of energy at θ = 15°. The simulation results for a rectangular composite tube with a [+30/–30] lay-up configuration are compared with available experimental data. Cylindrical composite tubes fabricated from woven glass/polyester composites with different lay-ups were also tested using a drop-weight impact tester, and very good agreement between experimental and numerical results is achieved.     

Elastic wave propagation energy dissipation characteristics analysis on the viscoelastic damping material structures embedded with acoustic black hole based on semi-analytical homogeneous asymptotic method

Elastic wave energy dissipation and absorption properties of viscoelastic damping material (VDM) composite plates embedded with acoustic black hole (ABH) are analyzed in this paper. Considering the periodic distribution of the ABH-embedded VDM structure in the composite plate, semi-analytical homogeneous asymptotic theory is applied, which transforms the macroscopic to a microscopic problem. In-plane variables of the composite structure are defined and generated by the third-order shear deformation theory of Reddy, and the equilibrium equations are derived by extended Hamilton's principle and the internal balance is consequently determined by representative volume element theory. Determining the constitutive equations of the composite laminate structure allow the equivalent shear and strain equilibrium equations to be achieved. Subsequently, the complex equivalent stiffness is defined according to the general Hooke's law, and the dimensionless equivalent loss tangent tanδ of the composite sandwich plate is finally evaluated from the equivalent loss and storage modulus. The ABH and VDM layer factors which affect tanδ are thoroughly analyzed and discussed. The investigation can supply a new efficient method to dissipate and absorb propagation wave energy with a wide bandwidth at low frequency. Additionally, the analysis is validated by numerical simulation and Galerkin methods.     

Modeling of amplitude-dependent damping characteristics of fiber reinforced composite thin plate

A damping model of fiber reinforced composite thin plate with consideration of amplitude-dependent property is established using the Jones–Nelson nonlinear theory in conjunction with the classical laminated plate theory, polynomial fitting method and strain energy method. In this model, the elastic moduli are expressed as the function of strain energy density and the loss factors in the longitudinal, transverse and shear directions are expressed as the functions of excitation amplitude. Moreover, three TC300 carbon/epoxy composite plates are taken as research objects to carry out a case study. One of them is used to determine the amplitude-dependent coefficients of loss factors in fiber reinforced composites by combining the least square method with polynomial fitting method, and the other two plates are used to verify the correctness of the theoretical model. The results of the developed model considering amplitude dependence and experimental test show a good consistency. It is discovered that the viscoelastic effect of epoxy resin materials will contribute to the increased degree of damping. So, if such plate structures exhibit more pronounced viscoelastic characteristics, there will be more significant in the nonlinear degree of amplitude-dependent damping phenomenon.     

不同铺层厚度复合材料的低速冲击特性与损伤模式研究

复合材料凭借其轻质、高强的特性逐渐在工程材料界占据重要地位,对于复合材料的冲击损伤的研究也一直吸引着诸多研究学者的关注．为表征不同铺层厚度复合材料层合板的抗冲击性能,利用自由落体冲击设备,进行了复合材料层合板的冲击实验研究．给出了不同冲击能量下的损伤模式,并利用位移、速度、接触力以及能量的时间变化曲线,深入分析了侵入和穿透两种损伤模式的特点．研究发现,随着铺层厚度的增加,复合材料在冲击过程中吸收的能量也随之增加．引入能量平衡法,基于体系的能量守恒定律,利用Newton-Raphson数值方法求解了侵入损伤模式下的接触力大小,通过实验结果给定挠度求解了对应的速率变化情况,并将理论结果与实验结果进行比较．     

A computational-experimental method for identifying the viscoelastic properties of composites in dynamically loaded shells of revolution

A method for determining the stiffness and rheological characteristics of composite materials, based on minimizing the mismatch of experimental data and the results of numerically modeling nonstationary deformation processes in shells ofrevolution made of composites materials, is presented. This approach is used for analyzing the damping characteristics of chaotically reinforced and cloth-reinforced composites. __________ Translated from Mekhanika Kompozitnykh Materialov, Vol. 43, No. 4, pp. 449–464, July–August, 2007.     

Incremental Scheme to Homogenize Anisotropic Elastic Properties of Multi-Phase Composites

An incremental homogenization scheme for the prediction of elastic properties of composites is reviewed. Similar to the differential scheme, the inclusions are included step-by-step. This approach accounts for high volume fractions of inclusion of different shape and elastic properties. A numerical example for a composite consisting of a polymeric matrix, glass fibers and voids is shown. The fiber distribution is chosen equivalently to a distribution in an injection molded short-fiber reinforced composite. The volume fraction of the voids is varied. (© 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)     

A distributed friction model for energy dissipation in carbon nanotube-based composites

Being lighter and stiffer than traditional metallic materials, nanocomposites have great potential to be used as structural damping materials for a variety of applications. Studies of friction damping in the nanocomposites are largely experimental, and there has been a lack of understanding of the damping mechanism in nanocomposites. A new friction contact model is developed to study the energy dissipation of carbon nanotube (CNT)-based composites under dynamic loading. The model incorporates the spatially-distributed nature of the CNT in order to capture the stick/slip phenomenon at the interface and treats the total slip force in a statistical sense. The effects of several parameters on energy dissipation are investigated, including the excitation’s amplitude, the interaction between CNT’s ends and matrix, the orientation, concentration, and diameter distribution of the CNTs inside the matrix. The results are in good agreement with experimental observations in the literature.     

Fracture in Ceramic-Matrix Composites Reinforced with Strongly Bonded Metal Particles

The resistance of a ceramic matrix composite to the cleavage cracking across a field of strongly bonded, uniformly distributed metal particles is studied. The crack trapping and bridging effects of the metal particles are analyzed by means of calculating the strain energy and the traction work. An explicit expression for the critical energy release rate as a function of particle volume fraction has been obtained. The fracture resistance is independent of elastic properties of the matrix and the sample geometry and is predominantly determined by the size/spacing ratio of the particles. It is shown that the theoretical curves agree with experimental data quite well. The methodology developed in this article can be used in studying the fracture resistances of composites with high filler contents and irregular filler geometries.__________Russian translation published in Mekhanika Kompozitnykh Materialov, Vol. 41, No. 3, pp. 303–318, May–June, 2005.     

Analysis of plain-weave composites

The paper analyzes the mechanical properties of plain-weave composites by employing different micromechanical models. Their in-plane and flexural properties are estimated using analytical approaches, including the rule of mixtures and one-dimensional composite beam and two-dimensional mosaic models. The expressions of effective material properties are obtained for one-, two-, and three-ply woven composites. The results obtained are in agreement with published data.     

Singular approximation of the method of periodic components in statistical mechanics of composite materials

A quasi-periodic model is developed for random structures of composites, when the locations of inclusions are given in terms of random deviations from nodes of an ideal periodic lattice. Solution of the stochastic boundary problem of the theory of elasticity is examined for a quasi-periodic component by the method of periodic components, which is reduced to determination of the field of deviations from the known solution for a corresponding periodic composite. The solution is presented for the tensor of effective elastic properties of a quasi-periodic composite in singular approximation of the method of periodic components in terms of familiar solutions for tensors of the effective elastic properties of composites with periodic and chaotic structures and the parameters of the quasi-periodic structure: the coefficient of periodicity and the tensor of the anisotropy of inclusion disorder. A numerical calculation is performed for the effective transversally isotropic elastic properties of unidirectional fibrous composites with different degrees of fiber disorder.Perm' State Technical University, Russia. Translated from Mekhanika Kompozitnykh Materialov, Vol. 33, No. 4, pp. 460–473, July–August, 1997.     

Initial states iterative learning for three-dimensional ballistic endpoint control

In this paper, an initial states iterative learning control algorithm is proposed for control of the ballistic endpoint displacement in three-dimensional space, where the target is moving and the projectile experiences system uncertainties. The characteristics of the three-dimensional ballistic process are formulated and explored, and the learning algorithm is proposed in the spatial domain. The algorithm consists of two parts. First, the initial speed and angles are iteratively learned to make the projectile attain a fixed position. Second, the shooting time is learned to tune the arrival time of the projectile. Since the dimensions of the solution space are larger than that of the task space, three control manners, including shooting speed, shooting angle and their combination, are researched respectively. Through rigorously analyzed, it is proved that the algorithm is convergent and the multiple initial states can be adjusted simultaneously. Finally, an example of practical cannonball projection is presented to verify the effectiveness of the proposed algorithms.     

Limiting stresses in spatially reinforced composites with components-having different structural geometries nd elastic properties

A model which is proposed for calculating structural stresses in spatially reinforced composites and an invariant-polynomial criterion for evaluating their limiting values are used to predict the effect of the elastic and strength properties of the components and their relative content on the limiting stress-strain state of composites of different structures. Emphasis is given to tri-orthogonal and 4D cubic structures, in addition to structures with hexagonal and angle-ply fiber reinforcement schemes in the plane and perpendicular to it. The types of composite loading typical of standard tests are examined in separate numerical experiments for shear, tension, compression, and their proportional combination. A computational variant of a criterional estimate of the limiting stresses is substantiated for an anisotropic composite of variable strength. The limiting-stress surface is obtained along with contour maps showing stress isolines as a function of the properties of the components and the geometry of the structure. The maps are suitable for practical use. The cases of maximum resistance to shear, tension, compression, and combination loading of 3D and 4D composites are compared to the analogous cases for two-dimensional structures.Presented at the Ninth International Conference on the Mechanics of Composite Materials (Riga, October, 1995).Translated from Mekhanika Kompozitnykh Materialov, No. 5, pp. 616–639, September–October, 1995.     

Design of Dynamically Loaded Fiber-Reinforced Structures with Account of Their Vibro-Acoustic Behavior

Dynamically loaded structures for high-technology applications generally require high material damping combined with low construction weight and adequate stiffness. Advanced lightweight structures will have to meet not only these dynamic demands but also improved acoustic (low noise) standards. High-performance materials like magnesium, aluminum, or titanium, which are mainly used in today's lightweight applications, reach their limits with respect to these dynamic and especially vibro-acoustic requirements. They offer a high specific stiffness and strength, but a relatively low damping, which leads to intense acoustic radiation. Therefore, composites or compound materials with a dynamically and vibro-acoustically optimized property profile are needed. The structural dynamic and vibro-acoustic behavior of these types of lightweight structures cannot be described by the use of classical models. Here, the advanced methods developed at ILK are considered, which take into account the special mechanical properties of the fiber-matrix compound. Also, sophisticated numerical simulation techniques such as the finite and the boundary element method are successfully applied.     

Identifying the elastic moduli of composite plates by using high-order theories

The study aims to predict the elastic and damping properties of composite laminated plates from measured dynamical characteristics. The elastic constants and damping properties of a laminated element are determined by using experimental data and the results of a multilevel theoretical approach. Solution examples for particular problems are given. __________ Translated from Mekhanika Kompozitnykh Materialov, Vol. 44, No. 1, pp. 35–50, January–February, 2008.     

Prediction of hypervelocity orbital debris impact damage to the space station by neural networks

Prediction of damage to orbiting space craft due to collisions with hypervelocity space debris is an important issue in the design of Space Station Freedom. Space station wall structures are designed to absorb impact energy during a collision. A proposed wall structure consists of a multilayer insulation (MLI) directly covering the pressure wall, and a bumper layer placed 100mm from the pressure wall. In experiments at The Marshall Space Flight Center, 2.5–12.7 mm projectiles have been fired at this wall structure at speeds of 2–8 km/s. In this paper, three-layer backpropagation networks are trained with two sets of impact damage data. The input parameters for training are pressure wall thickness, bumper plate thickness, projectile diameter, impact angle, and the projectile velocity. Output from the network consists of hole dimensions for the bumper and the pressure wall in the minor and major axis directions, and damage to the MLI. To evaluate network generalization, networks are tested with experimental data points that are not used for training. Network performance is compared with that of other damage prediction methods. Network determination of qualitative damage estimation is suggested as a new direction for research. Preliminary testing of qualitative prediction of pressure wall damage is presented. The results are promising, and suggest several areas for further study.     

Analysis of elastomeric composites based on fiber-reinforced systems. 1. Development of design methods for composite materials

A method for calculating the elastic properties of fiber-reinforced composites is discussed. The method is based on the structural macroscopic theory for reinforced media [1, 2], which can be used for analysis of stiff and soft composites. As a measure of the elastic properties of composites, the parameters of macroscopic deformations of the base system of Cartesian coordinates are used, with the axes oriented in a certain direction relative to the general reinforcement and loading field. The corresponding macrostresses in the loaded composites are found by a solution of the microboundary problem for a composite macroelement with sides parallel to reinforcement planes of the system. The microboundary-value problem is multiply connected and is formulated based on the information about the homogeneous field of macroscopic displacements specified by the parameters of macroscopic deformation. The problem is solved using the local system of coordinates whose axes are directed along some of the reinforcement trajectories.State Metallurgical Academy of Ukraine, Dniepropetrovsk, Ukraine. Translated from Mekhanika Kompozitnykh Materialov, Vol. 34, No. 6, pp. 733–745, November–December, 1998.     

Residual saturated porous media – from oscillating water blobs to waves in ground earth

A model for wave propagation in residual saturated porous media is presented distinguishing enclosed fluid clusters with respect to their eigenfrequency and damping properties. The additional micro-structure information of cluster specific damping is preserved during the formal upscaling process and allows a stronger coupling between micro- and macro-scale than characterisation via eigenfrequencies alone. A numerical example of sandstone filled with air and liquid clusters of different eigenfrequency and damping distributions is given. If energy dissipation due to viscous damping dominates energy storage due to cluster oscillations, the damping distribution is more influential than the eigenfrequency distribution and vice versa. Spreading the damping distribution around a constant mean value supported the effect of capillary forces and spreading the eigenfrequency distribution around a constant mean value supported the effect of viscous damping in the investigated samples. For a wide distribution of the liquid clusters' damping properties, two damping mechanisms of propagating waves occur at the same time: damping due to viscous effects (for highly damped clusters) and energy storage by cluster oscillations (for underdamped clusters). (© 2013 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)     

Analysis of elastomeric composites based on fiber-reinforced systems. 2. Unidirectional composites

The elastic properties of unidirectionally reinforced composite materials under large deformations are studied. The applied model for deformation of materials is based on the structural macroscopic theory of stiff and soft composites, including micro- and macromechanical levels of analysis of composite media. The properties of unidirectional elastomeric composites are studied in tension and shear in the plane of reinforcement. The microscopic fields in the structural components of composites having poorly compressible and compressible matrices are also analyzed. Changes in the parameters of macroscopic deformation of the composites are examined as functions of the loading parameters and initial conditions of the structure. The evolution of the structural changes in deformed composite materials is described.State Metallurgical Academy of Ukraine, Dnepropetrovsk, Ukraine. Translated from Mekhanika Kompozitnykh Materialov, Vol. 35, No. 1, pp. 29–50, January–February, 1999.     

Aging of polymer composite materials exposed to the conditions in outer space

A comprehensive investigation is made of glass, carbon, organic fiber-reinforced plastics, and epoxy-based hybrid composite materials employed in Salyut-type spacecraft which remained in space for up to 1501 1501 days. In particular, the properties, aging mechanism, and strain-strength variations in these materials due to exposure to the conditions in outer space were studied. After a series of tests were performed in space the standard strain and strength parameters as well as the mass, density, and thickness changes in the composite materials were estimated. Electron-microscopic and dynamic-mechanical analyses were performed, and the thermal expansion was estimated for a wide range of temperatures. The principal, dominant process occurring due to the continuous presence in outer space was found to be post-curing of the resin materials, which in turn affected the mechanical characteristics of the composite materials. After 456–1501 days in space the room-temperature strength of the composite materials (except for organic plastics) did not decrease, while at high temperatures it even increased. The post-curing and restructuring of some composite materials lowered their dynamic shear moduli in the glassy state of the resin. Due to consolidation of the surface layer of hybrid composite materials irradiated and subjected to thermal cycles, failure during bending varied from transverse fracture to delamination. The negative effect of the post-curing process was expressed as higher internal tension in the hybrid composite materials with different linear thermal expansion coefficients. The magnitude of this effect depended on the amplitude of the thermal cycles. The unprotected surface of the composites bombarded by atomic oxygen, microparticles, and space garbage were subjected to pickling and microerosion, the maximum effect occurring at the initial stage of exposure. Desorption of moisture and low-molecular products during the first 100–200 days of thermal cycling in the vacuum of near-earth orbit must be considered when estimating the total mass loss of composite materials. Data from microscopic, dynamic-mechanical, and other types of analyses revealed that the outer-space factors improved the supermolecular order of the resin volume, while the subsurface layer structure of the composite materials had loosened. Microcracks formed in the plastic's surface during 1501 days in outer space did not, in general, affect the mechanical parameters of the composite materials. Most of the observed effects of exposure to conditions in outer space were less pronounced for plastics protected by aluminum foil or other plastic coatings. The data obtained can be used for designing external elements of spacecraft by selecting materials with specified and predictable properties for long-term service.Translated from Mekhanika Kompozitnykh Materialov, Vol. 29, No. 4, pp. 457–467, July–August, 1993.In conclusion we thank I. G. Zhigun and R. P. Shlits for assisting in determining the mechanical properties of PCM as well as the crew of the Salyut-6 and Salyut-7 space stations for setting up, monitoring, and delivering samples to earth.     

Calculation of the moisture concentration field in a multilayered plate

Conclusion Thus, we have developed an algorithm and program to calculate fields of moisture concentration in a laminated plate for steady external temperatures and moisture contents. A test calculation and comparison of some of the findings with previous results demonstrated the accuracy of the program for solving a number of diffusion problems. For example, the program can be used to evaluate the life of the moisture-protective properties of polymer products, as well as to model moisture absorption in fiber composites.Curves of moisture concentration were calculated for a unidirectionally reinforced (with organic fibers) plastic at different relative humidities. We also calculated sorption curves and isotherms, which were shown to agree satisfactorily with previous empirical curves. It was shown that it is possible to approximately evaluate the sorption behavior of a unidirectionally reinforced fiber composite by means of a three-layer model and to analyze the stability of the result against an increase in the number of layers. For the two-component composite examined here, sorption behavior deviates from the classical behavior described by Fick's law — although the components of the composite obey this law.The algorithm and program that were developed make it possible to evaluate the kinetics of moisture absorption in complex composite systems and determine the distribution of moisture among and within the components.The study described here was conducted under grant 93.176 from the Latvian Science Council.Translated from Mekhanika Kompozitnykh Materialov, Vol. 30, No. 4, pp. 502–511, July–August, 1994.