467 research outputs found
An efficient multiscale virtual testing platform for composites via component-wise models
No full textThe aim of the current work is to develop a multiscale framework based on higher-order 1D finite elements developed using the Carrera Unified Formulation (CUF). The multiscale framework consists of a macroscale model to describe the global structure, and a CUF micromechanical model described using the Component-Wise approach. Such an approach allows for the explicit modelling of the fiber and matrix at the microscale, resulting in a high-fidelity finite element model at both scales. The use of refined CUF elements result in a computationally efficient analysis, due to a reduction in the degrees of freedom at both scales, as well as the reduction in total computational time when compared to standard 3D finite element analysis. The parallel implementation of the multiscale framework results in additional savings in computational time
Finite element modelling of mixed-mode delamination propagation in Abaqus/Explicit with linear and nonlinear cohesive softening laws
No full textAccurate modelling of delamination propagation in laminates is key to predicting the failure of composite structures. In this study, an implementation of the Cohesive Zone Model (CZM) using a novel mixed-mode formulation based on defining an effective separation and allowing for generalizable non-linear cohesive traction-separation softening laws, is presented and evaluated. To this end, several finite element models representing a laminate specimen under pure mode I, pure mode II, or mixed-mode conditions, respectively, are constructed and benchmarked against other studies from literature. Then, the influence of the cohesive softening law shapes on the load-displacement response of the specimen is evaluated. Results show that, with the appropriate softening law shape, the novel implementation successfully captures delamination growth and most load-displacement characteristics without the need for an empirical energy criterion.NAhttp://deepblue.lib.umich.edu/bitstream/2027.42/176691/1/Finite_element_modelling_of_mixed_mode_delamination_propagation_in_Abaqus_Explicit_with_linear_and_nonlinear_cohesive_softening_laws_-_Theo_Rulko.pdfhttp://deepblue.lib.umich.edu/bitstream/2027.42/176691/2/Honors_Capstone_Poster_Theo_Rulko_-_Theo_Rulko.pd
Computationally-efficient multiscale models for progressive failure and damage analysis of composites
No full textA class of computationally-efficient tools to undertake progressive failure and damage analysis of composites across scales is presented. The framework is based on a class of refined one-dimensional (1D) theories referred to as the Carrera Unified Formulation (CUF), a generalized hierarchical formulation that generates a class of refined structural theories through variable kinematic description. 1D CUF models can provide accurate 3D-like stress fields at a reduced computational cost, e.g., approximately one to two orders of magnitude of degrees of freedom less as compared to standard 3D brick elements. The effectiveness of 1D CUF models to undertake physically nonlinear simulation is demonstrated through a class of problems with varying constitutive models. The virtual testing platform consists of a variety of computational tools such as failure index evaluations using component-wise modeling approaches (CUF-CW), CUF-CW micromechanics, concurrent multiscale framework, interface, and impact modeling. Failure index evaluation of a class of composite structures underlines the paramount importance of the accurate stress resolutions.
Within the micromechanical framework, the Component-Wise approach (CW) is utilized to represent various components of the RVE. The crack band theory is implemented to capture the damage propagation within the constituents of composite materials and the pre-peak nonlinearity within the matrix constituents is modeled using the von-Mises theory. A novel concurrent multiscale framework is developed for nonlinear analysis of fiber-reinforced composites. The two-scale framework consists of a macro-scale model to describe the structural level components, e.g, open-hole specimens, coupons, using CUF-LW models and a sub-scale micro-structural model encompassed with a representative volume element (RVE). The two scales are interfaced through the exchange of strain, stress and stiffness tensors at every integration point in the macro-scale model. Explicit finite element computations at the lower scale are efficiently handled by the CUF-CW micromechanics tool. The macro tangent computation based on perturbation method which leads to meliorated performances. A novel numerical framework to simulate progressive delamination in laminated structures based on component-wise models is presented. A class of higher-order cohesive elements along with a mixed-mode cohesive constitutive law are integrated within the CUF-CW framework to simulate interfacial cohesive mechanics between various components of the structure. A global dissipation energy-based arc -length method to trace the complex equilibrium path exhibited by delamination problem. The capabilities of the framework are further extended through the introduction of contact kinematics to handle impact problems.
A combination of the above tools is used to obtain an accurate material response of the structure in the non-linear regime, from the structural level i.e. macro-scale to the material constituent level i.e. the micro-scale, in a computationally efficient manner, providing a suitable virtual testing environment for the progressive damage analysis of composite structures. The accuracy and efficiency of the proposed computational platform are assessed via comparison against the traditional approaches as well as experimental results found in the literature
Non-local damage modeling for composite laminates: application to isogeometric analysis for impact simulations
No full textHigh-fidelity progressive damage simulations of composite materials are important for advancements in damage tolerant design. We recently proposed a novel modeling approach for damage analysis of composite laminates, in which multi-layer structures are represented as individual plies connected through zero-Thickness cohesive interfaces. The model is developed in the framework of Isogeometric Analysis (IGA). By using Non-Uniform Rational B-Spline (NURBS) basis functions for representing geometries and discretizing the displacement field, IGA allows for a more direct connection between numerical simulation and CAD software. In addition, compared to traditional polynomial basis functions, NURBS functions allow for better representation of geometries and higher order inter-element continuity properties. The computational efficiency of the proposed modeling approach stems from the adoption of Kirchhoff-Love shell elements for the modeling of individual lamina. Intralaminar damage is introduced in the framework of continuum damage mechanics, in which a strain-softening damage model drives the degradation of material elastic properties. However, the use of local strain measures, in combination with strainsoftening degradation models, may lead to damage localization problems. These cause the governing equations to become ill-posed and their approximate solution to be highly mesh-sensitive. Our work aims to re-establish the objectivity with respect to the adopted discretization. We extend our analysis framework by introducing a smoothed strain field to re-place the local strain measures used in the damage model. Our approach builds on the Gradient-Enhanced Damage (GED) model and is specialized for the Kirchhoff-Love shell structural model. The smoothed strain field is obtained by solving an additional set of partial differential equations on each ply of the composite laminate. The GED model can be applied to smooth tensor-valued quantities, such as strains, on generic-shaped geometries in the three-dimensional space, including complex and curved aerospace structures modeled by means of shell elements. In this work, we propose numerical examples in order to illustrate the validity of the GED model
Fast two-scale computational model for progressive damage analysis of fiber reinforced composites
No full textA fast two-scale finite element framework based on refined finite beam models for progressive damage analysis (PDA) of fiber reinforced composite is presented. The framework consists of a macroscale model to define the structural-level components, interfaced with a second sub-scale model at the fiber-matrix level. Refined finite beam elements are based on Carrera Unified Formulation (CUF), a hierarchical formulation which offers a procedure to obtain refined structural theories that account for variable kinematic description. The representative volume element (RVE) at the subscale is modeled with real material, e.g., fiber and matrix with details about packing and heterogeneity. Component-Wise approach (CW), an extension of refined beam kinematics based on Lagrange-type polynomials is used to model the constituents in the subscale. Each constituent in the subscale is modeled by the same finite element in the framework of the CW. The energy based crack band theory (CBT) is implemented within the subscale constitutive laws to predict the damage propagation in individual constituents. The communication between the two scales is achieved through the exchange of strain, stress and stiffness tensor at every integration point in the macroscale model. The efficiency of the framework is derived from the ability of CUF models to provide accurate three-dimensional displacement and stress fields at a reduced computational cost (approximately one order of magnitude of degrees of freedom less as compared to standard 3D brick elements). Numerical predictions are validated against the experimental results
The Ionospheric Impact of the October 2003 Storm Event on WAAS
No full textThe United States Federal Aviation Administration's (FAA) Wide Area Augmentation System (WAAS) for civil aircraft navigation is focused primarily on the Conterminous United States (CONUS). Other Satellite- Based Augmentation Systems (SBAS) include the European Geostationary Navigation Overlay Service (EGNOS) and the Japanese Global Navigation Satellite System (MSAS). Navigation using WAAS requires accurate calibration of ionospheric delays. to provide delay corrections for single frequency GPS users, the wide area differential GPS systems depend upon accurate determination of ionospheric total electron content (TEC) along radio links. Dual frequency transmissions from GPS satellites have been used for many years to measure and map ionospheric TEX on regional and global scales
Damage location and model refinement for large flexible space structures using a sensitivity-based eigenstructure assignment method.
No full textThe complexity and size of the next generation of spacecraft, along with the exceedingly high performance and pointing accuracy requirements, mandate that the load carrying capability of the structures by maintained at all times. This work describes a systematic method by which large structures, such as the Space Station Freedom, can be examined periodically to evaluate the integrity of the load carrying structures and determine the location and magnitude of damage to the structure if such damage exists. The Eigenstructure Assignment Damage Location method is developed and successfully demonstrated using modal data from a comprehensive set of tests on a hybrid scaled Space Station truss. The algorithm computes the distance between the measured eigenvectors and a subspace that is spanned by the columns of the damaged structure's system matrix. Damage is located when this distance is zero (for exact data). Once the damage has been located, a simple calculation provides the magnitude of the damage. The method has several unique features, including the ability to easily include loss of mass as well as the ability to filter noise from the measured data. The Model Sensitivity parameter, a scalar measure of each eigenpair's sensitivity to damage in a particular truss member, was developed to assist in pre-test determination of the ability to detect damage in different critical members. The modal strain energy distribution and the Modal Assurance Criterion are also shown to be useful indicators of the ability to detect damage.PhDAerospace EngineeringUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/105925/1/9226935.pdfDescription of 9226935.pdf : Restricted to UM users only
Micromechanical progressive failure analysis of fiber-reinforced composite using refined beam models
No full textAn efficient and novel micromechanical computational platform for progressive failure analysis of fiber reinforced composites is presented. The numerical framework is based on a class of refined beam models called Carrera Unified Formulation (CUF), a generalized hierarchical formulation which yields a refined structural theory via variable kinematic description. The crack band theory is implemented in the framework to capture the damage propagation within the constituents of composite materials. A representative volume element (RVE) containing randomly distributed fibers is modeled using the Component-Wise approach (CW), an extension of CUF beam model based on Lagrange type polynomials. The efficiency of the proposed numerical framework is achieved through the ability of the CUF models to provide accurate three-dimensional displacement and stress fields at a reduced computational cost
Computational modeling of progressive failure and damage in composite laminates.
No full textCurrent and future aerospace systems utilize an ever-increasing amount of fiber reinforced composite laminates in various mission critical structural components making it imperative to understand their damage tolerance capacity under a multitude of loading envelopes. Their comparatively low strength under predominantly axial compressive loading severely limits the design loads of such structures. In the current work, a mechanism based lamina level computational methodology is developed for progressive failure analysis (PFA) of composite laminates beyond initial failure. A combination of analytical and micromechanical studies are used to identify the underlying mechanism of failure under predominantly compressive loading. Under such loading, the class of carbon fiber reinforced laminates considered in this thesis fails by fiber kinking. Results from an analytical study dispel the notion of a fixed compressive strength and show that it is a function of the in-situ geometric and material properties and stress state. These observations and finite element based micromechanical studies have identified the in-situ fiber rotation in the presence of initial fiber misalignment and the degradation of the in-situ shear modulus due to microcracking as the two main drivers of the kinking failure mechanism. A previously developed thermodynamics based lamina constitutive model is utilized to develop a PFA methodology for laminated composites. Laminae are assumed to be damaged by microcraking that is manifested in the degradation of the shear modulus and the transverse modulus. The amount of irrecoverable energy, expressed as a thermodynamic state variable S, provides a measure of the damage state inside a lamina. Lamina level coupon tests are used to obtain relations between S and the degrading moduli. These relations in conjunction with the lamina elastic constants and the geometric information such as the lamina thickness and the lamina lay-up are used as the PFA inputs. Damage accumulates in a lamina when an energy balance condition is satisfied and the in-situ secant stiffnesses in shear and in the transverse direction are degraded. The complete laminate response under loading is modeled by the classical lamination theory. Beyond reaching a critical value of S, denoted as S* (obtained experimentally), all lamina moduli are degraded steeply. For numerical implementation, in essence, this models an abrupt catastrophic event in a finite number of gradual steps. This method is demonstrated via numerical examples of single and multi element meshes under uniaxial compression that generate the characteristic load-deflection curves observed for detailed micromechanical studies. The maximum load predictions are seen to match the results obtained with rigorous micromechanical analyses, and corresponding laboratory experiments. The PFA developed in this thesis is demonstrated, verified and validated by modeling the responses of composite panels tested by the author and elsewhere. The PFA predictions are very close to the experimental observations.PhDAerospace engineeringApplied SciencesMechanical engineeringUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/125294/2/3192575.pd
Rate Dependent Strength Characterization of Carbon Fiber Composite Laminates
No full textThesis (Master's)--University of Washington, 2017-06The implementation of carbon fiber laminates in commercial vehicles is becoming increasingly common. Characterization of these materials for modeling is often completed at quasi-static loading rates regardless of the loading rates the final part will experience. This thesis will discuss the rate dependency of strength characteristics and Schapery parameters of a composite laminate under quasi-static, intermediate, and high rate loading conditions
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