Simulation methodology for fracture processes of composite laminates using damage-based models

Fiber-reinforced polymer composite (FRP) laminates have found increasing use in advanced industrial applications. However, the limited knowledge and validated material models of the failure processes of the laminated composites continue to pose challenges in ensuring reliability and integrity of the structures. This research aims at establishing a validated simulation methodology for fracture assessment of FRP composite laminates. The approach accounts for the failure processes and the associated damage mechanisms through finite element (FE) simulations. The FE model development considers the existence of the physical interfaces between the laminas due to the manufacturing processes. A hybrid experimental-computational approach is developed for systematic implementation of the simulation methodology. Different combinations of the failure modes were observed, including matrix cracking-crushing, fiber/matrix interface debonding, interface multi-delamination, and fiber fracture-buckling. Local material failure is modeled by a damage initiation event followed by the evolution of the damage to fracture. Two types of damage-based models are investigated; the continuum damage model encompassing the multi-damage criteria for the FRP composite lamina and the cohesive zone model for interface delamination. A full derivation of the continuum damage model for the anisotropic material is given and employed for prediction of the damage evolution in the lamina. A series of experiments on CFRP and GFRP composite laminate specimens are conducted to establish the flexural and fracture behaviors of the materials. Complementary 3D FE models of the specimens and test setups are developed. Two different FE-based models, namely the conventional and Prepreg model, are developed and examined for GFRP and CFRP composites. Results show that accurate prediction of elastic-damage behavior and the progressive damage process in FRP composites depend on the chosen FE-based model of the FRP composite laminates and the damage-based material model used. The flexural test of a 12-ply antisymmetric CFRP composite beam specimen under four-point bending displayed the occurrence of multiple failure events. These include matrix cracking at lamina No. 9 (90o), and delamination at interfaces No. 8 (-45o/90o) and No. 9 (90o/45o). In addition, intralaminar multi-failure events are predicted in lamina No. 1 (-45o) due to matrix shear and fiber buckling failures. FE simulation of the test predicted an accurate flexural response with less than 4% average error when compared with measured data, along with similar multiple failure zones in the specimen. Damage dissipation energy is used to illustrate the quantity of the overall progressive damage in FRP laminas, interfaces and the laminated composite. The simultaneous use of lamina and interface damage models in the FE simulation of the FRP composite laminate is recommended in view of the occurrence of multiple intralaminar-interlaminar failure modes and fractures under general loading conditions

Dynamic response of aluminium sheet 2024-T3 subjected to close-range shock wave: experimental and numerical studies

Abstract This present study investigates experimentally and numerically the behaviour of 1 mm thick aluminium 2024-T3 alloy sheets from near field shock waves. A comparison and examination are undertaken with respect to global deformation and plastic damage formation from two different stand-off distances of 4 mm and 50 mm that were exposed to a constant charged mass. A 4-cable instrumented pendulum blast set-up was used to carry out and monitor the blast test. The results of the blast test were subsequently used to simulate the pressure history for different stand-off distances. The simulation involved implementing a user subroutine in ABAQUS/Explicit solver to model non-uniform pressure fields for use in finite element simulation. The results provided a strong alignment of the numerical method when compared with the experimental data. The main outcome of this study is to show the significant effect of the changing damage from highly localised perforation to global deformation when the stand-off distance is changed from 4 mm to 50 mm

Finite element analysis of TMJ implant under clenching loads

The temporomandibular joint is one of the most complex anatomical structures and is exposed to high stress conditions during daily movements. Replacing the joint is normally done only in severe cases as success rate of the replaced joint is not as encouraging as other joint replacements. The design of TMJ implant which includes material selection plays a significant role in its success. Two different biomaterials—Ti–6Al–4V and CoCrMo— under static loads simulating five clenching tasks were analysed in this study. A three dimensional model of an adult mandible was developed from Computed Tomography image dataset, as well as a generic TMJ implant with fixation. All the applied clenching tasks consisted of nine principle muscles. The results showed that both materials were totally safe under these loading conditions. However Ti–6Al–4V showed a comparatively lower stress level

The Effect of Lateral Load Type on Shear Lag of Concrete Tubular Structures with Different Plan Geometries

Tubular structures are extensively recognized as a high efficiency and economically reasonable structural system for the design and construction of skyscrapers. The periphery of the building plan in a tubular system consists of closely spaced columns connected by circumferential deep spandrels. When a cantilever tube is subjected to a lateral load, it is expected that the axial stress in each column located in the flange frame of the tube is the same, but because of the flexibility of peripheral beams, the axial stress in the corner columns and middle columns is distributed unequally. This anomaly is called “shear lag”, and it is a leading cause of the reduction in efficiency of the structure. In this paper, the possible relation between shear lag and the type of lateral load subjected to these systems is investigated. The above relation is not yet considered in previous literatures. Three various plan shapes including rectangular, triangular and hexagon were modeled, analyzed, designed and subjected to the earthquake and wind load, separately. Further work is carried out to compare the shear lag factor of these structures with distinct plan shapes against different types of lateral load. It is observed that all types of structures with various plan geometry subjected to the wind load had a greater amount of shear lag factor in comparison with structures subjected to the static and dynamic earthquake loads. In addition, shear lag in structures with the hexagon shaped plan was at the minimum

Effects of cell aspect ratio and relative density on deformation response and failure of honeycomb core structure

The extensive applications of honeycomb (HC) core in sandwich structures necessitates the influence of the cellular geometry and cell wall base material on the mechanical response to be quantified. In this respect, this paper establishes the mechanics of the deformation and the failure processes of the HC core under the out-of-plane compressive, tensile, and shear loading. The corresponding mechanical properties are determined and the mechanisms of failure of the HC core structure are identified. The influence of the relative density (ρ∗/ρ s) and the cell aspect ratio (H/c) of the hexagonal HC core on the compressive deformation response, the out-of-plane properties and the characteristic dissipation energy density (DED) of the structure is established. Results show that the compressive strength increases exponentially from 1.5 to 10.6 MPa over the relative density range of 0.028 ≤ (ρ∗/ρ s) ≤ 0.125. The out-of-plane shear modulus, G 13 and G 23 are 33.9 and 58.2 MPa, while the shear strength, τ 13 and τ 23 are 1.07 and 2.03 MPa, respectively. The HC core with a low aspect ratio (H/c < 2.64) failed due to the early debonding of the double-wall hexagonal cells, while at H/c ≥ 2.64, by elastic buckling of the cells. A phenomenological model is formulated to highlight the combined effects of both parameters on the compressive strength (σ c) of the HC cores, covering the range of 0.028 ≤ (ρ∗/ρ s) ≤ 0.056 and 2.5 ≤ (H/c) ≤ 5.62. Furthermore, the characteristic dissipation energy density (DED) under the out-of-plane compression varies linearly within the range of 2.5 < (H/c) < 5.62 for the HC core with ρ∗/ρ s = 0.056. The HC core with H/c = 3.96, but with twice higher ρ∗/ρ s exhibits about twice larger DED. These resulting properties and failure mechanisms of the anisotropic paper-based HC core are useful for the validation of the predictive computational models

On the Performance of Small-Scale Horizontal Axis Tidal Current Turbines. Part 1: One Single Turbine

The blade number of a current tidal turbine is one of the essential parameters to increase the stability, performance and efficiency for converting tidal current energy into rotational energy to generate electricity. This research attempts to investigate the effect of blade number on the performance of a small-scale horizontal tidal current turbine in the case of torque, thrust coefficient and power coefficient. Towards this end and according to the blade element momentum theory, three different turbines, i.e., two, three and four-bladed, were modeled using Solidworks software based on S-814 airfoil and then exported to the ANSYS-FLUENT for computational flow dynamics (CFD) analysis. SST-K-ω turbulence model was used to predict the turbulence behavior and several simulations were conducted at 2 ≤ tip speed ratio ≤ 7. Pressure contours, turbulence kinetic energy contours, cut-in-speed-curves, and streamlines around the blades and rotors were extracted and compared to provide an ability for a deep discussion on the turbine performance. The results show that in the case of obtainable power, the optimal value of tip speed ratio is around 5, so that the maximum power was achieved for the four-bladed turbine. Out of optimal condition, higher blade number and lower blade number turbines should be used at less than and greater than the optimal values of tip speed ratio, respectively. The results of simulations for the three-bladed turbine were validated against the experimental data with good agreement

Analytical prediction of highly sensitive CNT-FET-based sensor performance for detection of gas molecule

In this study, a set of new analytical models to predict and investigate the impacts of gas adsorption on the electronic band structure and electrical transport properties of the single-wall carbon nanotube field-effect transistor (SWCNT-FET) based gas sensor are proposed. The sensing mechanism is based on introducing new hopping energy and on-site energy parameters for gas-carbon interactions representing the charge transfer between gas molecules (CO2, NH3, and H2O) and the hopping energies between carbon atoms of the CNT and gas molecule. The modeling starts from the atomic level to the device level using the tight-binding technique to formulate molecular adsorption effects on the energy band structure, density of states, carrier velocity, and I-V characteristics. Therefore, the variation of the energy bandgap, density of states and current-voltage properties of the CNT sensor in the presence of the gas molecules is discovered and discussed. The simulated results show that the proposed analytical models can be used with an electrical CNT gas sensor to predict the behavior of sensing mechanisms in gas sensors

Moisture absorption effects on mode II delamination of carbon/epoxy composites

It is necessary to consider the influence of moisture damage on the interlaminar fracture toughness for composite structures that are used for outdoor applications. However, the studies on the progressive variation of the fracture toughness as a function of moisture content M (%) is rather limited. In this regard, this study focuses on the characterization of mode II delamination of carbon/epoxy composites conditioned at 70 °C/85% relative humidity (RH). End-notched flexure test is conducted for specimens aged at various moisture absorption levels. Experimental results reveal that mode II fracture toughness degrades with the moisture content, with a maximum of 23% decrement. A residual property model is used to predict the variation of the fracture toughness with the moisture content. Through numerical simulations, it is found that the approaches used to estimate the lamina and cohesive properties are suitable to obtain reliable simulation results. In addition, the damage initiation is noticed during the early loading stage; however, the complete damage is only observed when the numerical peak load is achieved. Results from the present research could serve as guidelines to predict the residual properties and simulate the mode II delamination behavior under moisture attack

A Review on Vehicle Classification and Potential Use of Smart Vehicle-Assisted Techniques

Vehicle classification (VC) is an underlying approach in an intelligent transportation system and is widely used in various applications like the monitoring of traffic flow, automated parking systems, and security enforcement. The existing VC methods generally have a local nature and can classify the vehicles if the target vehicle passes through fixed sensors, passes through the short-range coverage monitoring area, or a hybrid of these methods. Using global positioning system (GPS) can provide reliable global information regarding kinematic characteristics; however, the methods lack information about the physical parameter of vehicles. Furthermore, in the available studies, smartphone or portable GPS apparatuses are used as the source of the extraction vehicle’s kinematic characteristics, which are not dependable for the tracking and classification of vehicles in real time. To deal with the limitation of the available VC methods, potential global methods to identify physical and kinematic characteristics in real time states are investigated. Vehicular Ad Hoc Networks (VANETs) are networks of intelligent interconnected vehicles that can provide traffic parameters such as type, velocity, direction, and position of each vehicle in a real time manner. In this study, VANETs are introduced for VC and their capabilities, which can be used for the above purpose, are presented from the available literature. To the best of the authors’ knowledge, this is the first study that introduces VANETs for VC purposes. Finally, a comparison is conducted that shows that VANETs outperform the conventional techniques