Prediction Of Tensile Failure Research Articles

Micromechanical modeling for longitudinal tensile property of unidirectional CFRP considering dispersion of fiber properties

Longitudinal tensile failure prediction has always been the focus of research on unidirectional (UD) Carbon Fiber Reinforced Polymer (CFRP). In this paper, the longitudinal tensile tests of unidirectional T800 grade carbon fiber reinforced epoxy resin composite were carried out first. The experimental stress–strain curves show that there are obvious progressive damages before the final failures of the specimens. However, this phenomenon is usually neglected in most of the existing investigations and tests to only obtain elastic modulus and ultimate strength. Thus, a Representative Volume Element (RVE) model based on micromechanics was established using finite element method, considering the randomness of fiber spatial distribution and fiber strength. The tensile strength of fiber monofilaments was assumed to follow a statistical two-parameter Weibull distribution. The failure process of UD composite under longitudinal tensile load was simulated by explicit finite element method. The stress–strain curves obtained by simulation are in good agreement with the experimental results. Finally, the influence of different boundary conditions on the calculation of the RVE was studied. It is found that the final failure strengths of the RVE with uniform displacement boundary conditions are similar to the case of periodic boundary conditions, while the former has higher computational efficiency.

Multi-scale modeling and tensile failure prediction of 3D needled C/C–SiC composites considering real microstructure

Three-dimensional (3D) needled carbon fiber reinforced carbon and silicon carbide (C/C–SiC) composites have the significant advantages of low density, high strength, and long lifespan, which are widely used in aerospace and other industrial fields. In this paper, based on the microstructure of the composites, a multi-scale finite element model is established to predict their mechanical properties and failure behaviors under the tensile load. The multi-scale model has been validated by the static tensile test and the microstructure of fracture. With this model, the effects of the fiber volume fraction, the interfacial bonding strength, the content of residual silicon (Si) elements, and the porosity on the mechanical properties of needled C/C–SiC composites are systematically analyzed. The results show that the stress-strain curve of the composites under the longitudinal tensile load has two nearly linear segments. The final failure strength of the composites increases with the increase of the interfacial bonding strength, the fiber volume fraction and residual Si elements, while decreases with the increase of the porosity. In addition, based on the established multi-scale finite element model, the damage evolution process and failure mechanism of the needled composites are investigated in detail. The proposed scheme could effectively predict the mechanical properties of the needled C/C–SiC composites and capture the microscopic damage evolution, which would help to optimize the design of composites.

Real meso-scale model reconstruction and tensile failure prediction of 3D braided PIP-SiCf/SiC composites considering pore defects

• A combination of parametric and statistical methods is proposed for the real meso-scale model reconstruction. • The finite element model of 3D6d braided SiCf/SiC composite considering yarn shape and pore defects is established. • To predict well the material tensile properties and failure mechanisms, the effect of the fiber damage and pore defects is considered. • The simulation values and damage modes are consistent with the experimental ones when the damage factor of the fiber bundle is 0.8. This paper presents the real meso-scale model reconstruction and tensile failure prediction of three-dimensional six-directional (3D6d) braided precursor impregnation and pyrolysis (PIP) SiC f /SiC composites. A combination of parametric and statistical methods is proposed, and the real meso-scale finite element model considering yarn shape and pore defects is built. The damage factor is introduced into the mixing law and the progressive damage model is developed. The results reveal that the simulation values and damage modes are consistent with the experimental ones when the damage factor is 0.8. In detail, the predicted errors of modulus, stress and strain are 3%, 9% and 5%, respectively. The main damage modes of 3D6d braided SiC f /SiC composites are braiding yarn shear fracture, fifth yarn tensile fracture, and matrix cracking. Furthermore, the initial damage firstly appears in the braiding yarn, and when the load is near the maximum value, the fifth yarn and matrix also occur the damage.

A nonlinear analytical model for tensile failure prediction of pseudo-ductile composite laminates

In this study, the tensile nonlinear responses of composite laminates with ±θns and ±θn/0s layups are investigated. An analytical model that integrates the progressive failure, shear nonlinearity, fiber rotation, and fragmentation is established to characterize the nonlinear tensile behavior. A nonlinear factor is used to describe the shear nonlinearity of the resin matrix, which is governed by shear stress, while progressive damage indexes are determined by normal stresses. The degree of fiber rotation and the fragmentation between layers are analytically formulated. Tensile results from experiments conducted in this study and from others in the literature are used to verify the model’s prediction accuracy. The proposed model provides acceptably good predictions of nonlinear behavior for pseudo-ductile carbon fiber reinforced composite laminates. A sensitivity analysis shows that the dominant model parameter changes from axial modulus to shear modulus, and eventually to transverse modulus as the off-axial angle increases from 0° to 90°.

Prediction of tensile failure of stochastic tow-based discontinuous composites via mesoscale finite element analysis

Stochastic tow-based discontinuous composite (STBDC) laminates are made from compression-molded tows of carbon fiber reinforced polymer (CFRP). STBDCs are a material system that can be manufactured in complex three-dimensional geometries which provides an alternative to metallic components for primary and secondary structures. The effective elastic properties of STBDCs are often approximated as quasi-isotropic; however, this approximation does not adequately represent the material properties. A random sequential addition representative volume element (RVE) generation algorithm has been developed that considers the mesostructural morphology of STBDCs using a non-conforming voxel-based mesh framework. Using the framework, a full factorial design of experiments is performed on unnotched tension coupons. Simulations are performed using the Abaqus/Explicit solver. Results are compared to reported values found in the available literature, demonstrating good correlation compared effective stiffnesses and unnotched tensile failure strengths.

A bundle-based shear-lag model for tensile failure prediction of unidirectional fiber-reinforced polymer composites

In this study, a novel shear-lag model based on impregnated fiber bundle (IFB) element is developed to predict the tensile behavior of unidirectional fiber-reinforced polymer (FRP) composites. Rather than using a fiber element, the new model enables a full-field failure simulation due to its finite number of elements. Based on the micromechanical difference equation, we validated the effectiveness of the model and identified the damage evolution pattern by applying it to a basic model of 6 mm FRP tendon. Then, the effect of varied constituent properties, hybrid fibers and initial defects were investigated using the Monte Carlo (MC) method. Several interesting results were found and compared with the findings of earlier studies. For instance, it was found that a more stable IFB strength and higher matrix shear strength reduced variations in composite strength. A moderate hybrid ratio and careful packing of high- and low-elongation fibers helped to achieve optimum composite properties. In the thin-ply composite, transverse initial defects were more detrimental to composite strength than longitudinal defects. These findings prove the value of the bundle-based model, which can be used in future studies as an effective tool for evaluating the strength of various composites.

Examination of a small radius of curvature composite notch with a novel chevron feature to improve damage tolerance

Discrete damage modelling (DDM) has been used successfully for open-hole composite tensile failure prediction with the aid of Critical Failure Volume (CFV) statistical criteria. The current study considered the chevron feature, a more complex notched geometry that due to its taper has the potential to be used in aerospace design to accommodate small radius notches without a significant strength knockdown. The current study used DDM in combination with detailed experimental characterization of failure to (a) examine sub-critical damage conditions of the chevron specimen (using the open-hole specimen for comparison). Then (b), provide new understanding of the Critical Failure Volume (CFV) failure prediction method in so far as what additional verification steps are needed when predicting the strength of chevron notch composites using finite elements. The predicted development of sub-critical damage and failure predictions of the chevron notch (and open-hole) coupons matched reasonably closely with experimental observations. This study presents a new notch feature that can accommodate small radius discontinuities in aerospace composite laminates without a significant strength knockdown and proposes DDM with CFV as a reasonable method for accurately predicting its failure.

Tensile failure prediction of U-notched plates under moderate-scale and large-scale yielding regimes

The main goal of the present research is to check if the recently published experimental results on tensile load-carrying capacity (LCC) of ductile U-notched Al 7075-T6 and Al 6061-T6 plates could successfully be predicted by means of combining the Equivalent Material Concept (EMC) with the Averaged Strain Energy Density (ASED) criterion, which is fundamentally a brittle fracture criterion. By using the two main material properties, namely the fracture toughness and the tensile strength of the equivalent material, which is extracted from the EMC, the maximum load that each notched plate could sustain is predicted by means of the combined EMC-ASED criterion. It is revealed that the EMC-ASED criterion is capable of predicting well the LCC of both aluminum plates, independent of the level of ductility of materials and the size of plastic region around the notch at crack initiation instance.

Influence of Calcium Sulfoaluminate (CSA) Cement Content on Expansion and Hydration Behavior of Various Ordinary Portland Cement‐CSA Blends

Calcium sulfoaluminate (CSA) cements have lower carbon footprint than that of portland cement, which makes them a suitable alternative as a sustainable cementitious binder. Early‐age expansion of CSA cements can be exploited to induce compressive stress in restrained concrete which can later counteract tensile stress developed during drying shrinkage, thus enhancing the resistance against shrinkage cracking. However, a proper understanding of the expansion behavior is critical to eliminate any risk related to expansion‐induced cracking. This study examines the expansion and hydration characteristics of various ordinary portland cement (OPC)‐CSA blends. Early‐age expansion of paste samples was monitored. The increase in CSA cement content increased the extent of expansion. Samples having the highest CSA content (30% by mass) exhibited excessive expansion which led to their cracking. Quantitative X‐ray diffraction, pore solution extraction, porosity, tensile strength, and dynamic modulus tests were performed to monitor the physico‐chemical changes in OPC‐CSA blends. It was shown that the ettringite supersaturation in the investigated systems gave rise to the crystallization stress, responsible for the expansion. Thermodynamic models enabled a reasonable prediction of tensile failure, particularly in the blends with the higher CSA content.

Hybrid cork–polymer composites containing sisal fibre: Morphology, effect of the fibre treatment on the mechanical properties and tensile failure prediction

In this study, we investigated the use of short sisal fibre with and without polyethylene-graft-maleic anhydride (PE-g-MA) as a strategy to reinforce cork–polymer composite (CPC) materials. The use of alkali treatment of sisal to improve fibre–matrix adhesion was evaluated. High density polyethylene (HDPE) was used as matrix and the composites were produced in a two-step process using twin-screw extruder followed by compression moulding. FTIR, TGA and XRD were used to confirm the sisal fibre modification. Additionally, morphology, density, diameter and tensile properties of the fibres were evaluated before processing. The hybrid composites containing cork powder (40wt.%) and randomly distributed sisal fibres were evaluated in terms of morphology and mechanical properties. The use of a 10wt.% sisal fibre in the presence of a 2wt.% coupling agent based on maleic anhydride, has shown to improve the tensile and flexural properties of the composites. The higher mechanical properties were achieved by using alkali treated sisal fibres and PE-g-MA. In the presence of the coupling agent the composite morphology revealed good interfacial adhesion between the natural components and the polypropylene matrix, being in accordance with the mechanical results. Weibull cumulative distribution was successfully used to accurately predict the tensile strength failure of the hybrid CPC materials.

Improving the prediction of tensile failure in unidirectional fibre composites by introducing matrix shear yielding

A Monte Carlo simulation is established to predict the failure strain of unidirectional fibre composites. The effect of matrix shear yielding of a high performance epoxy resin is introduced into the model through load sharing factors between the fibres adjacent to fibre-break(s). Strain concentration factors (SCF) of fibres are obtained using Finite Element Methods (FEM) in a three dimensional multi-fibre unit cell containing one, two and three adjoining fibre-break(s). The tensile strains of the surviving adjacent fibres are intensified as a function of their distances from the fracture. A statistical simulation is carried out to predict the failure strain of a single layer of unidirectional (UD) fibre composites with the thickness of the fibre ineffective length. Using the weakest link theory, the ultimate failure strain of a real size UD composite is predicted.

Tensile failure prediction of single wall carbon nanotube

Carbon nanotubes (CNT) possess remarkable mechanical, thermal and electrical properties, which combined with their low density and high aspect ratio, make them a very attractive candidate as reinforcing materials for the development of an entirely new class of composites. However, to determine CNTs mechanical properties in a direct experimental way is a challenging and not economical task, because of the technical difficulties and the costs involved in the manipulation of nanoscale objects. Moreover, there is still a lack of the fundamental knowledge regarding the strength and failure behaviour of carbon nanotubes. Due to nanoscale, most of the continuum based classical fracture mechanics are not really suitable to describe the failure evolution. Failure of nanotubes has been mainly investigated using molecular dynamics theory. In this paper, we present an innovative method for modelling the failure of carbon nanotubes under uniaxial tensile loading. CNT can be thought as structural systems, where the primary bond between two nearest-neighbouring atoms forms the axially loaded-bearing components member and the individual atom acts as joints of the related load-bearing members. A Finite Element Model, based on the molecular mechanics theory, is proposed in this paper in order to investigate the fracture progress in Zig-Zag and Armchair carbon nanotube with defects under uniaxial tensile stress. The novelty of the proposed approach lies in the use of nonlinear axial and torsional springs to model the local interaction and breakage of bonds of CNT atoms under axial loads. The complete load–displacement relationship of Force/Displacement curve for a (5, 5) and a (9, 0) nanotube up to the complete fracture was obtained. Further, with a continuum assumption, it was possible to define a Stress/Strain curve with ultimate strength and strain. The results show that the effect of chirality on the mechanical properties and failure mode of CNTs was quite significant and cannot be neglected. Moreover, the results are in good agreement with experimental data and classical molecular dynamics simulation validating, therefore, the proposed modelling approach.

The prediction of tensile failure in titanium-based thermoplastic fibre–metal laminates

The tensile properties of a titanium-based fibre–metal laminate have been investigated at quasi-static rates of strain. Initial attention focused on investigating the effect of varying the fibre orientation, θ, on the tensile modulus and strength of a range of [Ti, ± θ] s carbon-fibre/PEEK FMLs. Here, as expected, increasing the offset angle, θ, resulted in a decrease in the tensile properties of the FMLs. The failure mechanisms in the hybrid laminates were investigated through a series of cyclic tensile tests on a number of edge-polished samples. An examination of the specimen edges indicated that failure in laminates whose fibres were oriented at angles between 0° and 15° occurred as a result of fracture of individual carbon fibres. At offset angles greater than 15°, initial failure took the form of localised debonding at the fibre–matrix interface. In addition to this debonding, laminates with values of θ between 15° and 45° exhibited delamination between the composite plies. First ply failure (FPF) as well as the tensile strength of the FMLs was predicted using a number of simple failure criteria. Here, it was shown that the onset of damage under tensile loading conditions can be successfully predicted over a wide range of offset angles.

Local stress concentration and the prediction of tensile failure in unidirectional composites

The aim of this paper is to present a new representation of the tensile failure of a composite material which accounts for the normal stress supported by the matrix and allows a study of the influence of constituent material properties and fibre volume fraction on the stress-concentration factors. This is done by micromechanical analysis which allows the stress and strain in the fibres and the matrix to be related to the applied stress or strain on the composite. Stress-concentration factors are calculated in the composite transverse section and are found to be smaller than previously published analytical solutions. The difference is essentially due to the normal stress supported by the matrix which is neglected by the shear-lag analysis but is taken into account in our model. The tensile strength is calculated firstly by numerical simulations and secondly by Batdorf's methodology which addresses the formation and propagation of fibre fractures. Comparisons with experimental measures are satisfactory.