Behavior of Composite Materials Under Impact: Strain Rate Effects, Damage, and Plasticity

2001 ◽  
Author(s):  
Serge Abrate
Keyword(s):  
Composite Materials ◽  
Strain Rate ◽  
Composite Structures ◽  
Current Knowledge ◽  
Matrix Material ◽  
Material Behavior ◽  
Elastic Behavior ◽  
Linear Elastic ◽  
Matrix Cracks ◽  
Different Types

Abstract Composite materials are often subjected to low velocity impacts, ballistic impacts, or crash impacts. In order to analyze such events, realistic model of the material behavior must be used to capture phenomena no included in linear elastic models. Nonlinear behavior occurs when a unidirectional lamina is loaded in the transverse direction or in shear when the matrix material deforms plastically. The stiffness and strength of composite materials at high strain rates is often very different from what is measured in quasi-static tests. In addition, different types of damage are introduced during impart: matrix cracks, delaminations, fiber failures, fiber-matrix debonding. The introduction of this damage will affect the subsequent behavior of the material. Many different approaches have been taken to account for the effects of strain rate, plasticity and damage on the mechanical behavior of composite materials. The objective of this paper is to assess current knowledge in this area, review and compare models used to describe the stress-strain behavior and predict failure of such materials. Continuum mechanics approaches are used to describe the behavior of laminas with different types of damage, and to model the behavior of interfaces between plies. Phenomenological plasticity models account for the nonlinear effects under transverse and shear loads. Some of these models are shown to be similar even though they were derived by very different approaches. Many accurate analyses of composite structures under impact assume linear elastic behavior and do not considered the complicating effects discussed here. The applicability of the different models for material behavior is also discussed in terms of selecting an appropriate model for analyzing a particular impact.

scholarly journals Modeling and simulation of anisotropic linear viscoelasticity

2020 ◽  
Author(s):  
Heinz E. Pettermann ◽  
Camille Cheyrou ◽  
Antonio DeSimone
Keyword(s):  
Linear Viscoelasticity ◽  
Matrix Material ◽  
Temperature Shift ◽  
Unit Cell ◽  
Material Behavior ◽  
Elastic Behavior ◽  
Simple Material ◽  
Linear Viscoelastic ◽  
Anisotropic Elastic ◽  
The Time Domain

Abstract A constitutive material law for linear viscoelasticity in the time domain is presented. It does not only allow for anisotropic elastic behavior but also for anisotropic (i.e. direction dependent) relaxation response. Under the assumption of thermo–rheological simple material behavior, the model is capable to account for direction dependent time–temperature-shift functions. The application is demonstrated for a linear viscoelastic matrix material reinforced by linear viscoelastic continuous fibers. The effective orthotropic linear viscoelastic response of the composite is computed by means of a periodic unit cell approach. These data, evaluated at different temperatures, are used to calibrate the input for the developed material law. Predictions from the latter are compared to the results from the unit cell simulations.

scholarly journals Modeling of Mechanical Properties of the Polymeric Composite Reinforced with Braided Preform

2021 ◽  
Vol 1199 (1) ◽  
pp. 012007
Author(s):  
A Kondratiev ◽  
O Andrieiev ◽  
A Tsaritsynskyi ◽  
T Nabokina
Keyword(s):  
Composite Materials ◽  
Composite Structures ◽  
High Speed ◽  
Experimental Studies ◽  
Polymeric Composite ◽  
Structural Behavior ◽  
Elastic Behavior ◽  
Design Parameters ◽  
Polymeric Composite Materials ◽  
Reinforcement Angle

Abstract Braided composite structures based on preforms are widely used in various industries. Owing to use of such preforms high speed and efficiency of the process of manufacturing of polymeric composite materials and structures on their basis can be provided. Knowledge of their properties in the design allows optimizing the production of structures with the specified parameters. The paper gives the review of three approaches to the description of physical and mechanical characteristics of the composite with braided fixtures – based on the classical theory of layered media, rod-based model, and the method of polynomial approximation. The necessary estimated dependencies were derived in order to predict the elastic and structural behavior of the composites under study at any reinforcement angle according to the known characteristics of predetermined angles. Synthesized design parameters, as distinct from the existing ones, allow predicting strength characteristics of the composite based on the braided hoses depending on the positioning and location of the material on the shape-generating surface. For the verification of theoretical results, a number of experimental studies have been carried out with the formation of samples of the material with the different reinforcing angles. Comparison of the analytical and experimental results allows drawing the conclusions that rod-based model gives the best results for the description of elastic behavior of the polymeric composite materials, whereas the obtained polynomial dependences are recommended for the structural behavior. The results of the work represent the basis for solving the problems of calculation of strength of the structures made of composite materials based on the braided preforms

Load Transfer Index for Composite Materials

2015 ◽  
Author(s):  
Qingguo Wang ◽  
Khashayar Pejhan ◽  
Christine Q. Wu ◽  
Igor Telichev
Keyword(s):  
Composite Materials ◽  
Composite Structures ◽  
Load Transfer ◽  
External Loading ◽  
Load Path ◽  
New Paradigm ◽  
Linear Elastic ◽  
Transfer Index ◽  
Fundamental Equations ◽  
Load Transfer Analysis

Load transfer analysis is a new paradigm for lightweight vehicle design. U* index has been proved to be an effective indicator for the load path. The U* theory indicates that the external loading mainly transfers through the parts with higher U* values in the structure. However, the fundamental equations of the theory are based on isotropic, homogenous, and linear elastic assumptions for the materials. Consequently, U* index is inadequate for composite materials which are increasingly used in automotive structures. In this study, a new load transfer index for composite structures, U*O, is proposed for the first time inspired by the basic U* theory. The U*O index considers the composite material as orthotropic instead of isotropic and eliminates the limitation of the basic U*. The effectiveness of the new U*O index on load path prediction is demonstrated by a case study for a general Graphite-epoxy lamina. The U*O index is capable to evaluate the accurate load path for the composite specimen. By contrast, the basic U* analysis shows the incorrect results.

scholarly journals Variability in Composite Materials Properties

2015 ◽  
Vol 807 ◽  
pp. 23-33
Author(s):  
Andy Vanaerschot ◽  
Stephan Lomov ◽  
David Moens ◽  
Dirk Vandepitte
Keyword(s):  
Composite Materials ◽  
Composite Structures ◽  
Structural Characteristics ◽  
Matrix Material ◽  
Geometrical Parameters ◽  
Fibre Reinforcement ◽  
Reinforcement Structure ◽  
Material Parameters ◽  
Composites Processing ◽  
Complex Architecture

Composite materials are created as a quite complex architecture which includes a fibre reinforcement structure and matrix material. Many material parameters play a role when composite structures are modelled, e.g. in finite element models. In addition to the properties of the raw fibre and matrix materials which are used, also geometrical parameters have a significant effect on structural characteristics. Fibre reinforcement geometry together with material properties of fibre and matrix determine homogenised material properties.The first part of the paper gives an overview of the most important processes which are used in composites processing industry. The factors which affect variability are also listed, and the effect of variability on material parameters is mentioned as well. The second part of the paper elaborates the identification of geometrical variability of the fibre reinforcement structure which is encountered with one particular type of composite material, namely a twill 2/2 carbon fibre weave with an epoxy matrix.

scholarly journals Constitutive Modeling of the Densification Behavior in Open-Porous Cellular Solids

Materials ◽  
2021 ◽  
Vol 14 (11) ◽  
pp. 2731
Author(s):  
Ameya Rege
Keyword(s):  
Constitutive Model ◽  
Cell Walls ◽  
Compressive Strain ◽  
Pore Collapse ◽  
Compressive Response ◽  
Linear Elastic ◽  
Nonlinear Springs ◽  
Different Types ◽  
Point Of Intersection ◽  
Good Agreement

The macroscopic mechanical behavior of open-porous cellular materials is dictated by the geometric and material properties of their microscopic cell walls. The overall compressive response of such materials is divided into three regimes, namely, the linear elastic, plateau and densification. In this paper, a constitutive model is presented, which captures not only the linear elastic regime and the subsequent pore-collapse, but is also shown to be capable of capturing the hardening upon the densification of the network. Here, the network is considered to be made up of idealized square-shaped cells, whose cell walls undergo bending and buckling under compression. Depending on the choice of damage criterion, viz. elastic buckling or irreversible bending, the cell walls collapse. These collapsed cells are then assumed to behave as nonlinear springs, acting as a foundation to the elastic network of active open cells. To this end, the network is decomposed into an active network and a collapsed one. The compressive strain at the onset of densification is then shown to be quantified by the point of intersection of the two network stress-strain curves. A parameter sensitivity analysis is presented to demonstrate the range of different material characteristics that the model is capable of capturing. The proposed constitutive model is further validated against two different types of nanoporous materials and shows good agreement.

scholarly journals Defects and uncertainties of adhesively bonded composite joints

2021 ◽  
Vol 3 (9) ◽  
Author(s):  
Sadik Omairey ◽  
Nithin Jayasree ◽  
Mihalis Kazilas
Keyword(s):  
Composite Materials ◽  
Composite Structures ◽  
Production Efficiency ◽  
Adhesive Bonding ◽  
Detection Methods ◽  
Bonded Joints ◽  
Adhesively Bonded ◽  
Adhesively Bonded Joints ◽  
Wide Range ◽  
Bonded Composite

AbstractThe increasing use of fibre reinforced polymer composite materials in a wide range of applications increases the use of similar and dissimilar joints. Traditional joining methods such as welding, mechanical fastening and riveting are challenging in composites due to their material properties, heterogeneous nature, and layup configuration. Adhesive bonding allows flexibility in materials selection and offers improved production efficiency from product design and manufacture to final assembly, enabling cost reduction. However, the performance of adhesively bonded composite structures cannot be fully verified by inspection and testing due to the unforeseen nature of defects and manufacturing uncertainties presented in this joining method. These uncertainties can manifest as kissing bonds, porosity and voids in the adhesive. As a result, the use of adhesively bonded joints is often constrained by conservative certification requirements, limiting the potential of composite materials in weight reduction, cost-saving, and performance. There is a need to identify these uncertainties and understand their effect when designing these adhesively bonded joints. This article aims to report and categorise these uncertainties, offering the reader a reliable and inclusive source to conduct further research, such as the development of probabilistic reliability-based design optimisation, sensitivity analysis, defect detection methods and process development.

scholarly journals Introduction to Macroscopic Optimal Design in the Mechanics of Composite Materials and Structures

2021 ◽  
Vol 5 (2) ◽  
pp. 36
Author(s):  
Aleksander Muc
Keyword(s):  
Composite Materials ◽  
Composite Structures ◽  
Constitutive Relations ◽  
A Priori ◽  
Chemical Properties ◽  
Composite Plates ◽  
Failure Criteria ◽  
Lagrange Equations ◽  
Homogenization Methods ◽  
Mechanics Of Composite Materials

The main goal of building composite materials and structures is to provide appropriate a priori controlled physico-chemical properties. For this purpose, a strengthening is introduced that can bear loads higher than those borne by isotropic materials, improve creep resistance, etc. Composite materials can be designed in a different fashion to meet specific properties requirements.Nevertheless, it is necessary to be careful about the orientation, placement and sizes of different types of reinforcement. These issues should be solved by optimization, which, however, requires the construction of appropriate models. In the present paper we intend to discuss formulations of kinematic and constitutive relations and the possible application of homogenization methods. Then, 2D relations for multilayered composite plates and cylindrical shells are derived with the use of the Euler–Lagrange equations, through the application of the symbolic package Mathematica. The introduced form of the First-Ply-Failure criteria demonstrates the non-uniqueness in solutions and complications in searching for the global macroscopic optimal solutions. The information presented to readers is enriched by adding selected review papers, surveys and monographs in the area of composite structures.

scholarly journals Melatonin in Cancer Treatment: Current Knowledge and Future Opportunities

Molecules ◽  
2021 ◽  
Vol 26 (9) ◽  
pp. 2506
Author(s):  
Wamidh H. Talib ◽  
Ahmad Riyad Alsayed ◽  
Alaa Abuawad ◽  
Safa Daoud ◽  
Asma Ismail Mahmod
Keyword(s):  
Clinical Trials ◽  
Current Knowledge ◽  
Biological Activities ◽  
Experimental Studies ◽  
Therapeutic Effects ◽  
Cell Proliferation Inhibition ◽  
Different Types ◽  
Solid Foundation

Melatonin is a pleotropic molecule with numerous biological activities. Epidemiological and experimental studies have documented that melatonin could inhibit different types of cancer in vitro and in vivo. Results showed the involvement of melatonin in different anticancer mechanisms including apoptosis induction, cell proliferation inhibition, reduction in tumor growth and metastases, reduction in the side effects associated with chemotherapy and radiotherapy, decreasing drug resistance in cancer therapy, and augmentation of the therapeutic effects of conventional anticancer therapies. Clinical trials revealed that melatonin is an effective adjuvant drug to all conventional therapies. This review summarized melatonin biosynthesis, availability from natural sources, metabolism, bioavailability, anticancer mechanisms of melatonin, its use in clinical trials, and pharmaceutical formulation. Studies discussed in this review will provide a solid foundation for researchers and physicians to design and develop new therapies to treat and prevent cancer using melatonin.

scholarly journals Structural Damage Identification of Composite Rotors Based on Fully Connected Neural Networks and Convolutional Neural Networks

Sensors ◽  
2021 ◽  
Vol 21 (6) ◽  
pp. 2005
Author(s):  
Veronika Scholz ◽  
Peter Winkler ◽  
Andreas Hornig ◽  
Maik Gude ◽  
Angelos Filippatos
Keyword(s):  
Neural Networks ◽  
Convolutional Neural Networks ◽  
Composite Structures ◽  
Damage Identification ◽  
Vibration Response ◽  
Damage Initiation ◽  
Matrix Cracks ◽  
Operational Life ◽  
Multiple Data Sets ◽  
Fully Connected

Damage identification of composite structures is a major ongoing challenge for a secure operational life-cycle due to the complex, gradual damage behaviour of composite materials. Especially for composite rotors in aero-engines and wind-turbines, a cost-intensive maintenance service has to be performed in order to avoid critical failure. A major advantage of composite structures is that they are able to safely operate after damage initiation and under ongoing damage propagation. Therefore, a robust, efficient diagnostic damage identification method would allow monitoring the damage process with intervention occurring only when necessary. This study investigates the structural vibration response of composite rotors by applying machine learning methods and the ability to identify, localise and quantify the present damage. To this end, multiple fully connected neural networks and convolutional neural networks were trained on vibration response spectra from damaged composite rotors with barely visible damage, mostly matrix cracks and local delaminations using dimensionality reduction and data augmentation. A databank containing 720 simulated test cases with different damage states is used as a basis for the generation of multiple data sets. The trained models are tested using k-fold cross validation and they are evaluated based on the sensitivity, specificity and accuracy. Convolutional neural networks perform slightly better providing a performance accuracy of up to 99.3% for the damage localisation and quantification.

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