A composite ply failure model based on continuum damage mechanics

A material model including the failure behaviour is derived for a thin unidirectional (UD) composite ply. The model is derived within a thermodynamic framework and the failure behaviour is modelled using continuum damage mechanics. The following features describe the model: (i) The ply is assumed to be in a plane state of stress. (ii) Three damage variables associated with the stress in the fibre-, transverse and shear directions, respectively, are used. (iii) The plastic behaviour of the matrix material is modelled. (iv) The difference in the material response in tensile and compressive loading is modelled. (v) Rate dependent behavior of plasticity and damage (i.e. strength) is modelled.     

A review of research and recent trends in analysis of composite plates

The use of advance composite materials is increasing in various industrial applications such as renewable energy, transportation, medical devices, etc. As the demand for stability under high mechanical, thermal, electrical and combined loads is increasing, research is being focused on developing newer types of composites and developing analytical and numerical methods to study composite plates as well. The present work is aimed to provide a comprehensive review of research in the structural analysis of composite plates along-with research trends in the last 15 years. The article first presents the evolution of plate theories comparing their formulations, applicability and discusses some key papers, results and conclusions. Evolution of research from the equivalent shear deformation theories (ESL) such as first order theory and higher order theories based on various shape strain functions e.g., polynomial, trigonometric to layer-wise, zigzag and displacement potential theories is presented. The comparative analysis of various solution approaches is done based on a review of research work in the structural analysis of plates. This is followed by review of meshless analysis methods for composite materials highlighting problem domains where conventional finite element analysis (FEA) approach has limitations. This article also presents a discussion on the new methods of plate analysis such as region-by-region modeling, hierarchic modeling and mixed FE and neural network based modeling. An attempt has been done in this article to focus on research trends in the last 15 years.     

Recent progress in the design and fabrication of multifunctional structures based on metamaterials

Metamaterials, with unconventional properties realized through various ingenious designs of micro-architectures, have become a recent research hotspot in the fields of electromagnetics, acoustics, mechanics, and physics. Since the integration of mechanical features and specific functions is still a challenge, the application of metamaterials has so far been limited. The research in relevant areas has shown a clear trend of incorporating the multifunctional design into a single integrated structure. Here, we review the latest advances in the design and fabrication of multifunctional structures based on metamaterials, covering three main aspects, i.e., the direct design of mechanical metamaterials and their multifunctional structures, the intelligent multifunctional structures with shape-shifting capabilities, the metamaterials-based design to achieve both the load bearing capability and other specific functions. We emphasize the important roles that the mechanics-driven designs play, as well as the mechanisms and other key aspects behind the multifunctional structures. The structure-level innovations could not only improve multifunctional features, but also pave the way to function fusion structures that allow the incorporation of ‘conflicting’ functions into a single structure.     

Spirobifluorene and biphenylaminophenyl fluorene with dimesitylboron as multifunctional electroluminescent materials

By introducing triarylamino and dimesitylboron groups into fluorene derivatives, two symmetric compounds 2,7-bis(dimesitylboryl)-9,9-spirobifluorene (SFMB) and 2,7-bis(dimesitylboryl)-9,9-bis(4-diphenylaminophenyl)fluorene (PAFMB) were prepared. SFMB and PAFMB exhibited solvatochromism in the different polarities of solvents. Devices A1, A2, A3 and A4 based on SFMB displayed emissions at 444, 448, 528, and 444 nm with current efficiencies of 1.06, 1.41, 0.84, and 1.52 cd/A, respectively. The blue light was close to the National Television Standards Committee standard blue color (x = 0.14, y = 0.08). Devices B1, B2, B3 and B4 based on PAFMB emitted lights centered at 484, 472, 513 and 472 nm, their current efficiencies were 1.80, 0.1, 1.23 and 1.93 cd/A, respectively. The results demonstrated that SFMB and PAFMB were multifunctional materials acted as emitters, and hole- and electron-transporting materials.     

A combined elastoplastic damage model for progressive failure analysis of composite materials and structures

The paper is concerned with the development and verification of a combined elastoplastic damage model for the progressive failure analysis of composite materials and structures. The model accounts for the irreversible strains caused by plasticity effects and material properties degradation due to the damage initiation and development. The strain-driven implicit integration procedure is developed using equations of continuum damage mechanics, plasticity theory and includes the return mapping algorithm. A tangent operator consistent with the integration procedure is derived to ensure a computational efficiency of the Newton–Raphson method in the finite element analysis. The algorithm is implemented in Abaqus as a user-defined subroutine. The efficiency of the constitutive model and computational procedure is demonstrated using the analysis of the progressive failure of composite laminates containing through holes and subjected to in-plane uniaxial tensile loading. It has been shown that the predicted results agree well with the experimental data reported in the literature.     

多层复合包装材料的气体渗透性

系统地讨论了高分子材料的气体渗透性，并从单层包装材料的渗稼性理论导出层合包装材料的渗稼系工，讨论相对湿度对气体渗透的影响及如何计算多层结构中的阻隔层的相对湿度。给出的结果对设计多层复合包装材料有重要的参考价值。     

A model of polymer composite structure with intermediate layer

In real structures isothermal planes may be distorted, and it is necessary to take this into account while carrying out the calculations of thermal conductivity λ_k of a material. The distortion depends on thermal conductivities of constituent particles and the matrix. With computer speeds already available, we can calculate temperature fields of the structural elements and to evaluate the thermal conductivity of the material. A structural model of polymeric compositions with solid particles with a shell and with microspheres is proposed. It is possible to evaluate the influence of a particle distribution order and particle spacing on the properties of compositions using structural elements. The model is suitable for the estimation with the use of corresponding coefficients of general regularities in compositions which are different by physical nature and yet are represented by analogous mathematical expressions (Fourier, Fick and Ohm laws). Solutions of integral equations for the structural element provide relative magnitudes and are, therefore, simple to use when evaluating other physical parameters of a composition. The application of the model is illustrated by examples.     

Drilling of composite structures

Structural parts made of composites have frequently to be drilled in the aircraft industry. However, little is know about the interacting conditions between the drilling tool and the material, which may be multi-type and multi-size. This study proposes a model which links the axial penetration of the drill bit to the conditions of delamination (crack opening mode I) of the last few plies. Several types of tool/material contact conditions were analyzed and were compared with experimental measurements, and with a model taken from the literature. Our study shows a close correlation between experiment and calculation when the thrust force of the drill is modeled by taking into account the geometrical nature of the contact between the tool and a laminate composite material.     

A fatigue damage model of composite materials

The mechanical properties of composite materials degrade progressively with the increasing of the number of cyclic loadings. Based on the stiffness degradation rule of composites, a phenomenological fatigue damage model is presented in this paper, which contains two material parameters. They are proportional to the fatigue life of materials and inversely proportional to the fatigue loading level. Thirteen sets of experimental data of composite stiffness degradation were employed to verify the presented model, and the statistical results showed that this model is capable of describing the damage evolution of composite materials. The characteristics of damage development and accumulation of composite materials subjected to variable loading were studied in this paper. Four sets of two-level loading experimental data were cited to verify the damage model, and the results showed that the predicted life is in good agreement with the experimental ones.     

Current research in composite structures at NASA’s langley research center

Research on the mechanics of composite structures atnasa’s Langley Research Center is discussed. The advantages and limitations of special purpose and general purpose analysis tools used in research are reviewed. Future directions in computational structural mechanics are described to address analysis short-comings. Research results on the buckling and postbuckling of unstiffened and stiffened composite structures are presented. Recent investigations of the mechanics of failure in compression and shear are reviewed. Preliminary studies of the dynamic response of composite structures due to impacts encountered during crash-landings are presented. Needs for future research are discussed.     

A structural reliability model for composite materials

This work is a part of a project aimed at developing a model and procedure to evaluate the structural reliability of a laminate whose laminae properties are statistically known. The inputs consist of the laminae's elastic properties (deterministic in that they are not as closely related to manufacturing technology) and the derived allowable strengths (aleatoric variables), as well as the sequence (number, orientation, position) of the laminae in the laminate. The output, the laminate's structural reliability, allows determination of the laminate's collapse process, with the most probable lamina failure sequence.     

A new damage model for composite laminates

Aircraft composite structures must have high stiffness and strength with low weight, which can guarantee the increase of the pay-load for airplanes without losing airworthiness. However, the mechanical behavior of composite laminates is very complex due the inherent anisotropy and heterogeneity. Many researchers have developed different failure progressive analyses and damage models in order to predict the complex failure mechanisms. This work presents a damage model and progressive failure analysis that requires simple experimental tests and that achieves good accuracy. Firstly, the paper explains damage initiation and propagation criteria and a procedure to identify the material parameters. In the second stage, the model was implemented as a UMAT (User Material Subroutine), which is linked to finite element software, ABAQUS™, in order to predict the composite structures behavior. Afterwards, some case studies, mainly off-axis coupons under tensile or compression loads, with different types of stacking sequence were analyzed using the proposed material model. Finally, the computational results were compared to the experimental results, verifying the capability of the damage model in order to predict the composite structure behavior.     

Process-induced deformation of composite T-stiffener structures

Composite T-stiffener structures are widely used structural elements in weight sensitive structural, aerospace and marine applications for the purpose of weight reduction. A study on the process-induced deformation of composite T-stiffener structures is presented in this paper. The deformation was calculated numerically by Finite Element Analysis (FEA), and the resulting displacements show that the deformation can be represented by a single angular displacement: the spring-in of the skin. A parametric study was conducted by Design of Experiments (DOE) and FEA to investigate the influence of design parameters on the spring-in of the skin. It is shown that the spring-in of the skin increases with the radius and the bonding length, and decreases with the fiber volume fraction.     

Optimal design of composite ChamberCore structures

An optimization procedure has been developed to uniquely and efficiently determine the “best” local geometry design of a new composite ChamberCore structure. This procedure is based on minimization of the total mass of a single composite ChamberCore subject to a set of design and stress constraints. The stress constraints are obtained in closed form based on the composite box-beam model for various composite lamination designs and loading conditions. The optimization problem statement is constructed and then solved using the VMCON optimization program, which is an iterative sequential quadratic programming (SQP) technique based on Powell's algorithm. The sensitivity of the solution of the optimal geometry to the values of parameters that characterize the structural durability and the failure mechanism is discussed.     

Discoloration mechanism,structures and recent applications of thermochromic materials via different methods: A review

Thermochromic material is a kind of smart material whose color will vary as the result of the phase transition caused by the temperature change. The characteristics of thermochromic materials are the memory functions to the temperature, having great potential applications in aerospace, military, anti-counterfeiting technology, construction and other fields. In recent years, many kinds of thermochromic materials have been prepared by different methods and their discoloration mechanisms are various according to published literatures. In this paper, the classification, discoloration mechanism, preparation methods, application fields and development trend of thermochromic materials are reviewed.     

Aramid fibers; a multifunctional sensor for monitoring stress/strain fields and damage development in composite materials

A multifunctional non-destructive technique, based on the Raman response of aramid fibers, is employed for (a) assessing the interface integrity and the overall stress distribution in a unidirectional Kevlar 29^®/epoxy composite (b) measuring the stress concentration and its development with applied load in Kevlar 49^®/epoxy composites incorporating a circular notch and finally, (c) determining the strain arising in 0° plies due to partial and full crack growth within the θ° plies in multidirectional 0°/θ°/0° composites. It is shown that this technique can be used effectively to study the damage development in composite materials that arise from the presence of different length scale discontinuities.     

Integrated structures and materials design

This paper introduces the concept of␣Integrated Structures and Materials Design (ISMD). ISMD combines materials engineering and structural engineering for the purpose of more effectively achieving targeted structural performance, by adopting material composite properties as the shared link. An application example, design of a bridge deck link-slab, is used to illustrate the essential elements of ISMD. It is shown that the composite hardened properties—tensile strain capacity, microcrack width, and Young’s Modulus, as well as composite self-consolidating fresh properties, are amongst the most important composite parameters that govern the targeted structural performance of safety, durability and ease of design and implementation. These are also properties that can be controlled in an Engineered Cementitious Composite—an ultra ductile concrete, by tailoring the ingredients for desired fiber, matrix and interface micromechanical parameters. Broad implications of ISMD on educational approach, research collaboration, and next generation infrastructure development, are briefly discussed.     

Recent research and development,future problems and trends in advanced composite materials in Japan

The progress and contributions of the national research and development project on advanced composites so far are described, some structural applications of composites in Japan are outlined to examine the structural utility. Future problems and trends are also considered.