Effects of local stress fields around broken fibres on the longitudinal failure of composite materials (original) (raw)
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Engineering Fracture Mechanics, 2020
This paper investigates the role of dynamic stress concentrations, and of fracture mechanics-driven growth of critical clusters of fibres, on the longitudinal tensile failure of fibre-reinforced composites. For this purpose, we developed a semi-analytical fibre bundle model to simulate the longitudinal tensile failure of large composite bundles of continuous fibres. The model uses shear-lag to calculate the stress recovery along broken fibres, and an efficient field superposition method to calculate the stress concentration on the intact fibres, which has been validated against analytical and Finite Element (FE) results from the literature.
2018
A semi-analytical Monte Carlo fibre bundle model was developed to investigate the role of dynamic effects and fracture mechanics in the longitudinal tensile failure of fibre-reinforced composites. To the knowledge of the authors, it is the first time that both effects are implemented in a fibre bundle model through direct simulation. The formulation includes a field superposition method to calculate the stress concentration around broken fibres which captures the effect of clusters of broken fibres. The Monte Carlo process was optimized to allow the simulation of bundles with thousands of fibres. The comparison between the predicted bundle strengths and experimental data suggests that, although the dynamic stress concentration significantly decreases the bundle strength, the trend and magnitude of the size effects in large composite bundles can only be explained considering fracture mechanics as the failure mechanism.
Computer Research and Modeling, 2020
The article proposes a model for assessing the potential strength of a composite material based on modern fibers with brittle fracture. Materials consisting of parallel cylindrical fibers that are quasi-statically stretched in one direction are simulated. It is assumed that the sample is not less than 100 pieces, which corresponds to almost significant cases. It is known that the fibers have a distribution of ultimate deformation in the sample and are not destroyed at the same moment. Usually the distribution of their properties is described by the Weibull–Gnedenko statistical distribution. To simulate the strength of the composite, a model of fiber breaks accumulation is used. It is assumed that the fibers united by the polymer ma- trix are crushed to twice the inefficient length — the distance at which the stresses increase from the end of the broken fiber to the middle one. However, this model greatly overestimates the strength of composites with brittle fibers. For example, carbon and glass fibers are destroyed in this way. In some cases, earlier attempts were made to take into account the stress concentration near the broken fiber (Hedgepest model, Ermolenko model, shear analysis), but such models either required a lot of initial data or did not coincide with the experiment. In addition, such models idealize the packing of fibers in the composite to the regular hexagonal packing. The model combines the shear analysis approach to stress distribution near the destroyed fiber and the statistical approach of fiber strength based on the Weibull–Gnedenko distribution, while introducing a number of assumptions that simplify the calculation without loss of accuracy. It is assumed that the stress concentration on the adjacent fiber increases the probability of its destruction in ac- cordance with the Weibull distribution, and the number of such fibers with an increased probability of destruction is directly related to the number already destroyed before. All initial data can be obtained from simple experiments. It is shown that accounting for redistribution only for the nearest fibers gives an accurate forecast. This allowed a complete calculation of the strength of the composite. The experimental data we obtained on carbon fibers, glass fibers and model composites based on them (CFRP, GFRP), confirm some of the conclusions of the model. Keywords: carbon fibers, modulus of elasticity, tensile deformation, speed of sound
Applied Composite Materials, 2014
The purpose of these three papers is not to just revisit the modelling of unidirectional composites. It is to provide a robust framework based on physical processes that can be used to optimise the design and long term reliability of internally pressurised filament wound structures. The results given in paper Parts 1 and 2 concerning the behaviour of unidirectional composites, such as carbon fibre reinforced epoxy resin, are, here, extended to the behaviour of cross-plied composites consisting of unidirectional plies orientated at different angles with respect to the loading direction. In these laminates the plies orientated parallel to the loading direction (at 0 •) control the ultimate failure of the composite. This paper shows that the development of fibre breaks in analogous to that seen in the studies described in Part 1 and 2. Clustering of fibre breaks, shown by the development of 32plets, preceedes failure just before specimen loaded monotonically break but develop in a more stable manner when subjected to steady high level loads. The effect of separating the 0 • plies into thinner layers impedes the development of fibre breaks clusters and increases ultimate lifetimes.
Characterization of the failure process in composite materials by the Fiber Bundle Model
Superlattices and Microstructures, 2014
Our aim in this paper is to investigate the time distribution of the monomer intact fiber of a bundle model of fibers subject to a constant external load. Breaking process is created by thermally induced stress fluctuations followed by load redistribution with the local load-sharing rule (LLS) which subsequently leads to an avalanche of breakings. The results showed that the maximum number of the intact fiber monomer (MNIFM) was observed at time t 1 proportional to the materials failure time t f independently of the temperature value ( f t t 3 1 1 ≈
Methods and Models for Failure Analysis of Fiber Reinforced Composites: A Critical Literature Review
IAEME PUBLICATION, 2013
The present paper deals with a critical literature review of the research work regarding methods and models for Failure Analysis of Fiber Reinforced Composites. Nowadays, composites have attracted substantial importance as a potential structural material. The most basic & common attractive features composites that make them useful for industrial applications are low cost, light weights, high specific modulus, renewability and biodegradability. An overview of methods of the mathematical modeling of deformation, damage and fracture in fiber reinforced composites are presented in this paper. The models are classified into 4 main groups: shear lag-based, analytical models, fiber bundle model and its generalizations, fracture mechanics based models and numerical micromechanical models. The advantages and preferable areas of application of each approach are discussed.
In this research, the effect of break in a composite material containing one fibre with non-uniform cross section area was investigated depending on Nearest Neighboring Load Theory. Using Shear Lag Theory, a new equation described the redistribution phenomena was derived starting from the Beyerlein and Landis s equation that deals with the redistribution phenomena in a uniform fiber composite material. A mathematical model described the redistribution stresses phenomena in normal stress due to break in non-uniform fiber of composite material was made. Also, the finite elements model was built using ANSYS 11.0 software.A set of numerical calculating was done in order to study the parameters (Width of the matrix and diameter of the fibre )affecting on the normal stress values and to verify the new equation. The comparison between the ANSYS results and new equation results was done and a good agreement was found.
Model of fracture of composite material with brittle fiber
Mechanics of Composite Materials, 1982
An analysis of the fracture process in high-strength composite materials is made difficult by the randomness of both occurrence and location of breaks in the reinforcement elements as well as by the intricate distribution of internal stresses. For such an analysis, therefore, it is necessary to use methods of mathematical simulation [1, 2]. It is simpler to directly simulate fracture of a composite material than of a homogeneous one, on the other hand, inasmuch as disruption of continuity can beforehand be assumed to occur in defective sites in fibers and the criteria of fracture of a composite material can be formulated on the basis of an analysis of the spatial distribution of fiber breaks alone.
Composites Science and Technology, 2005
Constitutive damage models for fibre-reinforced composite materials should take into account the occurrence of the different damage mechanisms, their interaction and their influence on the resulting mechanical properties. Fibre breakage has usually been considered in damage models by means of deterministic failure criteria which thus leads to non-progressive behaviour or to a complete material collapse which is not realistic. This work presents a progressive damage model for fibre-reinforced composites based on the fragmentation analysis of the fibres. The stiffness loss of a unidirectional composite comes from the parameters of the Weibull distribution of the fibre strength and the mechanical properties of the fibre, matrix and the interface. The model has been developed for the initial stages of damage. The model is formulated in the framework of the mechanics of the continuous media. The constitutive model can be employed to simulate the contribution of fibres in damage models based on the rule of mixtures.