Failure Criteria For Composite Materials Research Articles

FE analysis and experimental validation of mechanical wedge–barrel anchors for CFRP rods

This paper presents a comparative study of the geometrical optimization of mechanical wedge–barrel anchors for prestressed carbon fiber-reinforced polymer (CFRP) rods. Various anchor configurations were simulated using three-dimensional finite-element (FE) models. The FE models were validated using the draw-ins of the wedges, which were measured in static tensile tests. The configurations consisted of a steel barrel and aluminum wedges, taking advantage of the previous anchors. The conical profile of the wedge and barrel in different configurations had either a curve or a constant differential angle. In addition, a series of geometric modifications were introduced to the wedge at the loading using a fillet or cut. The stress concentration on the CFRP rod was evaluated using failure index Fs in the Tsai–Wu failure criterion for composite materials. The results of the FE simulations showed that a greater differential angle resulted in a smaller stress concentration at the loading end of the anchor and the modifications led to a reduction in the stress concentration. In addition, the anchor with a curved profile was selected as the optimal design because it had the smallest stress concentration owing to the smooth transition of the differential angle distribution along the wedge profile.

Theoretical prediction model of mean crushing force of CFRP‐Al hybrid circular tubes under axial compression

AbstractThe CFRP‐Al hybrid thin‐walled structure combines the dual advantages of carbon fiber reinforced plastics (CFRP) and metal, which is one of the crucial methods for both lightweight and high strength. This study aimed to explore the theoretical prediction of the mean crushing force of the hybrid tubes with different winding angles subjected to axial compression. In order to construct the theoretical model of the hybrid structural energy absorption response, the failure modes, and deformative behavior of the hybrid tubes are analyzed and summarized based on the axial compression experiments. Considering the effects of winding angles on the energy dissipation and deformation characteristic of hybrid circular tubes, the expressions of membrane force and bending energy per unit length are obtained. Then, the analytical model is established to predict the mean crushing force of the CFRP‐Al hybrid circular tube. Furthermore, the results of the prediction model are compared according to different failure criteria of composite materials. The findings show that the predicted values of the maximum stress failure are more consistent with the experimental values, in which the discrepancy between analytically predicted and experimentally tested mean crushing forces of these hybrid tubes is no more than 10%. The results can provide a basis for the design of the composite‐metal hybrid thin‐walled tube.

Rationalized improvement of Tsai–Wu failure criterion considering different failure modes of composite materials

Different failure modes are not explicitly accounted for in the Tsai–Wu failure criterion for composite materials, and the factor F12 in the expression cannot be determined by the basic strength values of the materials. In view of these two shortcomings of the Tsai–Wu criterion, an improved criterion was proposed based on the reasonable assumption that composites exhibit infinite strength under pure hydrostatic pressure. Some coefficients in the quadratic tensor expression of the Tsai–Wu failure criterion are redetermined using the basic strength value of the material, including the coefficient F12, under four different stress states (fiber tension and compression, matrix tension and compression). The reconstructed Tsai–Wu failure criterion can distinguish the failure modes based on different coefficient values under different stress states. In the progressive damage analysis of composite materials, the stiffness can be reduced in different manners based on each failure mode. Experimental verification for different kinds of unidirectional composites under various stress states was conducted, demonstrating that the improved Tsai–Wu failure criterion has a better prediction ability and accuracy than the original criterion.

Experimental and Numerical Study of the Static Performance of a Hoop-Wrapped CNG Composite Cylinder Considering Its Variable Wall Thickness and Polymer Liner

The static performance of a composite type 4 CNG cylinder was investigated using a finite-element simulation and experimental validation. This cylinder involved a liner hoop wrapped with a fiber impregnated by a suitable resin. Tensile tests were performed on standard specimens to examine the mechanical properties of the composite material. Next, a finite-element simulation was performed to determine the static strength of a natural gas tank based on an appropriate criterion. To this end, using a stress analysis, the von Mises stresses were obtained in different parts of the tank to detect the critical area apt to fail. Then, a safety factor was calculated along composite layers, and components of the 3D stress tensor were determined for the critical layer failing before other layers. Eventually, the static performance of the full-scale tank was investigated using various well-known failure criteria of composite materials. Results indicated that the most accurate criteria should include the effects of compressive strength and 3D components of the shear stress.

Mechanical Properties Research of Carbon Fiber Composite Laminates

This paper expounds the basic theory of composite mechanics, and discusses the damage forms, damage analysis and failure criteria of composite materials. Then, the basic mechanical properties of unidirectional CFRP laminates with different layers, including modulus of elasticity, strength and so on, were obtained through a large number of experiments. Based on the experimental data, the relationship between the number of layers and the properties of materials was studied. The brittle fracture process of CFRP laminates was simulated by finite element analysis based on progressive damage model and compared with the force-displacement curves obtained by experiments. The validity of progressive damage model was proved.

General mixed mode I/II failure criterion for composite materials based on matrix fracture properties

The available mixed mode I/II fracture failure criteria for orthotropic materials have been proposed mostly for cracks along fibers. The important fracture parameter in these criteria is the mode I fracture toughness that can be derived by utilizing standard tests. Whenever the crack is not along the fibers, the prediction of mode I fracture toughness is impossible due to mode mixity. Therefore, a comprehensive criterion that can predict the crack initiation instance has not been proposed so far. In this study, in line with the definition of equivalent fracture toughness for off-axis orthotropic materials, a general mixed mode I/II fracture failure criterion is proposed, which is independent of the orthotropic fracture properties. As per this criterion, it is assumed that the fracture occurs in the isotropic matrix and it is the effect of the fibers modeled as tensile or shear reinforcements. On the other hand, only elastic and fracture properties of the isotropic matrix are included in the proposed criterion, which can be derived easily by simple standard experimental tests. In providing this general criterion, the strain energy release rate approach was considered. The concept of crack initiation and propagation energy is employed for investigating the wasted energy in the fracture process zone due to toughening micro-mechanisms. Moreover, comprehensive experimental tests and the required finite element simulations are performed for validation of the proposed criterion.

Optimisation and failure criteria for composite materials by the bound-ary element method

The present paper deals with the analysis of the main failure, considering two quadratic criteria: the Tsai-Hill criterion and the Tsai-Wu criterion, for composite materials using the method of boundary elements. The developed formulation is applied to compute the stress and displacements of laminated composite structures plain submitted to loads in the structure plane, to show the influence of the direction of fibre in failure of the first lamina in a laminated composite materials, and the value of maximum tension that causes the failure, to find the optimum orientation of the directions of fibers into a symmetrical laminate, to minimize the failure criteria of Tsai-Hill and Tsai-Wu, and to optimum values for the fibers orientation angles that maximize the strength of the structure. The results are compared with other results from literature and show a good agreement.DOI: http://dx.doi.org/10.5755/j01.mech.23.4.14881

A review on analytical failure criteria for composite materials

Fiber-reinforced composite materials have found increasing industrial applications in the last decades, especially in the aerospace and ground transport fields, due to their high specific strength. However, even though this property allows having a lightweight and strong structure, some critical aspects still limit their use. Most of these depend on several types of undetectable defects and damages, which could affect the residual strength of the composite structures. The paper deals with failure mechanisms involving composite materials under several critic loading conditions, with the aim to assess the limits of currently used failure criteria for composite materials and to show the actual request of developing new failure criteria in order to increase the effectiveness of current design practices. Nowadays, such design practice is based on a damage tolerance philosophy, which allows a structure to tolerate the presence of damages during its in service life, only if the residual strength is kept higher than specific threshold values depending on the damage severity. Hence, the main goal of such paper is to assess the failure criteria’s capability to predict the life of composite components under several quasi-static and dynamic loading conditions. Intra-laminar and inter-laminar failure criteria have been investigated and considerations have been provided about the possibility to model the post-failure phase and to implement them within numerical predictive tools, based on finite element method.

Structural behaviour of hybrid FRP pultruded columns. Part 2: Numerical study

The structural behaviour of hybrid fibre reinforced polymer (FRP) pultruded members under concentric compression is studied in this paper (Part 2) through the use of numerical models – the experimental characterisation was presented in preceding paper (Part 1, Nunes et al., 2015). The hybridization of glass-FRP (GFRP) profiles is made through the partial replacement of the glass reinforcement with (stiffer) carbon fibres. First, a brief literature review shows the absence of available finite element (FE) models that take into account all the nonlinearities (material and geometrical) that influence the FRP column behaviour, and indicates the need to develop reliable and consistent models. Then, the FE model developed in this paper is described in detail. The elastic buckling behaviour of the columns tested in Part 1, with similar I-section shape but different configurations of carbon fibre reinforcement and different lengths, is evaluated. Three failure criteria for composite materials (Maximum Stress, Tsai–Hill and Hashin) are presented, implemented and their differences discussed. Using the Hashin criterion associated with a material damage model, progressive failure analyses were performed to simulate the nonlinear behaviour and failure of the hybrid columns. The numerical results comprise load–displacement curves, ultimate loads, stress–strain curves and failure modes, which are validated by comparison with the experimental results. Finally, the available design procedures for FRP columns are critically reviewed and applied to evaluate the columns’ ultimate loads. In this regard, it is shown that buckling prevails over material strength and that existing standards do not predict accurately the ultimate load of short columns or laterally braced columns.

Stress wave propagation in composite materials

The linear constitutive relations and the failure criteria of composite materials made of thermoviscoelastic solids are presented. The post-failure material behavior is proposed and the dynamic finite element equations are formulated. However, a nonlinear term is kept in the energy equation because it represents the effect of the second law of thermodynamics. A general purpose nonlinear three-dimensional dynamic finite element program COMPASS is upgraded and employed in this work to investigate the interdependence among stress wave propagation, stress concentration, failure progression and temperature elevation in composite materials. The consequence of truthfully incorporating the second law of thermodynamics is clearly observed: it will always cause temperature rise if there exists a dynamic mechanical process.

Fatigue Strength Prediction under Multiaxial Stress

A multiaxial fatigue failure criterion for composite materials is presented in this paper along with an assessment of the capability it offers for design under multiaxial constant or variable amplitude stresses. The applicability of this criterion, based on the well known quadratic failure tensor polynomial criterion for static loading, is validated through comparisons with uniaxial and multiaxial fatigue experimental data. Static and fatigue tests were carried out during this study on glass/polyester specimens cut off-axis from a multidirectional laminate at different angles. The agreement between experimental values and theoretical predictions is good. The proposed criterion is also compared to existing fatigue criteria and an overall assessment of their performance is given. Some theoretical design considerations for the case of irregular stress spectra, introducing the concept of multiaxial Miner coefficient, are finally presented.

A comparative study of failure criteria in probabilistic fields and stochastic failure envelopes of composite materials

One of the major objectives of this paper is to offer a practical tool for materials design of unidirectional composite laminates under in-plane multiaxial load. Design-oriented failure criteria of composite materials are applied to construct the evaluation model of probabilistic safety based on the extended structural reliability theory. Typical failure criteria such as maximum stress, maximum strain and quadratic polynomial failure criteria are compared from the viewpoint of reliability-oriented materials design of composite materials. The new design diagram which shows the feasible region on in-plane strain space and corresponds to safety index or failure probability is also proposed. These stochastic failure envelope diagrams which are drawn in in-plane strain space enable one to evaluate the stochastic behavior of a composite laminate with any lamination angle under multi-axial stress or strain condition. Numerical analysis for a graphite/epoxy laminate of T300/5208 is shown for the comparative verification of failure criteria under the various combinations of multi-axial load conditions and lamination angles. The stochastic failure envelopes of T300/5208 were also described in in-plane strain space.

Scaling effects in the flexural response and failure of composite beams

An experimental program was conducted in which scale model graphite-epoxy composite beams were loaded in bending until failure to investigate the effects of specimen size on flexural response and strength. Tests were performed on unidirectiona l, angle-ply, cross-ply, and quasi-isotropic beams of eight different scaled sizes ranging from 1/6 scale to full scale. The beams were subjected to an eccentric axial compressive load designed to promote large bending deformations and rotations. Results indicated that, although normalized flexural response was independent of specimen size, a significant scale effect in strength was observed for all laminate types. Typically, failure stresses and strains decreased as the size of the beam specimen increased from subscale to the full-scale prototype. Standard failure criteria for composite materials, such as the maximum stress, maximum strain, and tensor polynomial criteria, cannot predict the strength degradation with increasing specimen size. Consequently, a Weibull statistical model and a fracture mechanics model were used to analyze the strength scale effect.

A Failure Criterion for Composite Materials

A failure criterion for composite materials based upon the strain invariants of finite elasticity is introduced. The failure criterion assumes that the material is transversely isotropic and that failure occurs when the strain energy density reaches its maximum value. The failure criterion is further simplified by assuming that the fiber and matrix failure modes can be decoupled. An experimental test is proposed for determining the failure surface. A special case, the failure criterion for infinitesimal-strain elasticity theory, is introduced. The failure surfaces in the strain invariants' space are determined for two composite materials.

Failure of composite laminae under biaxial loading

AbstractThe failure of thin, fiber‐reinforced composite laminae is considered. A parametric failure criterion applicable to plane stress loading conditions is presented. Both static and fatigue‐type loadings are treated. In general, the formulation of failure criteria for composite materials has closely followed the development of yield criteria in metal plasticity. The parametric failure criterion presented here was inspired by a general formulation recently proposed for the plastic yielding of sheet metals. The criterion satisfies the essential conditions that must be met in developing phenomenological strength criteria for composite materials. This entirely general formulation encompasses all previously proposed failure theories for fiber‐reinforced orthotropic laminae. The inherent advantages and drawbacks of the proposed parametric approach are discussed. An example of application for static loading is presented in detail. Possible extensions of the approach to fatigue‐type loading are also suggested.

Phenomenological theory of failure criterion for composite materials

In this paper, some current anisotropic failure criteria in the forms of tensor polynomials are investigated. In order to determine the interaction coefficients of the failure criterion, a non-linear optimization method is proposed. The results obtained by different theories as well as the optimization method are compared with the test data of some composite materials. The comparison shows that the optimization method is effective.

Optimum design of helically wound composite pressure vessels

The optimum design of dome shapes in helically wound composite pressure vessels which have been used as rocket motor cases, etc. is discussed, as a first step, based on the membrane stress theory. Some methods for determining the optimum dome shapes are proposed based on the two different kinds of criteria. One is based on the failure criteria of composite materials, and the simple formulae for determining the dome shapes are derived. The other is based on the performance factor for a rocket motor case, and the dome shape is analyzed by using mathematical optimization techniques. The dome shapes obtained are compared with the isotensoid dome shape derived from the netting analysis.

Evaluation of the tensor polynomial failure criterion for composite materials: Tennyson, R.C., MacDonald, D. and Nanyaro, A.P. Journal of Composite Materials Vol 12 (January 1978) p 63

Evaluation of the tensor polynomial failure criterion for composite materials: Tennyson, R.C., MacDonald, D. and Nanyaro, A.P. Journal of Composite Materials Vol 12 (January 1978) p 63