320 Beal Avenue

Ann Arbor, MI, United States

320 Beal Avenue

Ann Arbor, MI, United States
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Rastgoftar H.,320 Beal Avenue | Ni X.,320 Beal Avenue | Atkins E.M.,320 Beal Avenue
AIAA Guidance, Navigation, and Control Conference, 2017 | Year: 2017

This paper demonstrates stable level flight control given nonlinear dynamics in the presence of uncertainty in pitot tube airspeed measurements. It is first shown that a commanded cruise altitude can be reached in finite time by applying a recently-proposed finite-time reachability model. Then, the paper proposes a new dynamic decision making unit (DMU) to govern level flight in the presence of uncertain pitot tube readings. The DMU uses a Markov Decision Process to update the controls over a finite time-horizon, where MDP states are obtained from discretization of the output and MDP cost is proportional to the deviation from the desired output. A transition probability calculator learns MDP transition probabilities over time. © 2017, American Institute of Aeronautics and Astronautics Inc, AIAA. All rights reserved.


Heinrich C.,320 Beal Avenue | Aldridge M.,300 Hayward Street | Kieffer J.,300 Hayward Street | Waas A.M.,320 Beal Avenue | And 2 more authors.
Journal of the Mechanics and Physics of Solids | Year: 2013

An integrated computational framework for textile polymer composites is introduced. A novel polymer curing model is used in connection with modeling the polymer curing process during manufacturing of textile composites. The model is based on the notion of polymer networks that are continuously formed in a body of changing shape due to changes in temperature, chemistry and external loads. Nonlinear material behavior is incorporated through nonlocal continuum damage mechanics that preserves mesh objectivity in calculations that go beyond maximum loads. The integrated model is applied to the curing of plain weave textile composites made from carbon fiber tows and Epon™862 resin. The mechanical and chemical properties are measured during curing using concurrent Brillouin and Raman light scattering. It is shown that significant stresses can develop during cure. The effect of these stresses on the manufactured part performance, when subsequent service loads are applied, is evaluated and a reduction in ultimate load, in agreement with experimental observations, is observed. © 2012 Elsevier Ltd.


Prabhakar P.,320 Beal Avenue | Waas A.M.,320 Beal Avenue
54th AIAA/ASME/ASCE/AHS/ASC Structures, Structural Dynamics, and Materials Conference | Year: 2013

Of interest in this paper are failure mode interactions when laminated fiber reinforced composites are subjected to compressive loading. Delamination, fiber kink-banding and their interactions are seen to dominate the failure response. This interaction is captured through a computational model that includes interface elements to capture delamination, and, geometric and material nonlinearity to capture kink banding. A 2D cross-section analysis is used to guide the choice of interfaces that require cohesive elements, thus reducing computational complexity. Two different stacking sequences are investigated, and their compressive strength and failure modes are compared, between prediction and experiments. © 2013 by Pavana Prabhakar.


Prabhakar P.,320 Beal Avenue | Waas A.M.,320 Beal Avenue
54th AIAA/ASME/ASCE/AHS/ASC Structures, Structural Dynamics, and Materials Conference | Year: 2013

A new finite element formulation that can seamlessly model the transition from a continuum to a non-continuum (through fracture) is introduced in this paper. In-plane fiber-matrix fracture (also referred to as splitting) is frequently observed in tensile failure of fiber reinforced polymer matrix composites (FRPC). This mechanism is modeled through the development of a continuum-decohesive finite element (CDFE) by considering a single lamina. The transition from a continuum to a non-continuum in the CDFE method is modeled directly (physically) without resorting to enrichment of the shape functions of the element, as is done in other methods, such as the variational multiscale cohesive method (VMCM) or through nodal enrichment as in extended finite element method (XFEM). The CDFE is a natural merger between cohesive elements and continuum elements. Predictions using the CDFE method were found to be in very good agreement with corresponding experimental data for open hole tension tests of fiber reinforced lamina. © 2013 by Pavana Prabhakar.


Prabhakar P.,320 Beal Avenue | Waas A.M.,320 Beal Avenue
Computational Materials Science | Year: 2013

Analyzing failure mechanics of fiber-reinforced media that correspond to different length scales with the goal of up-scaling is addressed in this paper with respect to compressive kinking instability in fiber reinforced laminae. Using the concentric cylinder model (CCM) as a representative element of a lamina, J2 deformation theory along with Hill's anisotropic plasticity theory is used to extend the constitutive model for the fiber-matrix cylinder, and hence the lamina, into the nonlinear regime. The model requires the elastic properties of fiber and matrix, the fiber volume fraction and the nonlinear shear response of the polymer matrix. An 8-layer laminate is up-scaled using this method by homogenizing the off-axis laminae and retaining micro-mechanics in the 0° laminae, and results are compared against a discrete fiber-matrix micro-mechanical model of the laminate. The effect of homogenizing the laminae on the compressive response of the laminate is investigated. © 2011 Elsevier B.V. All rights reserved.


Heinrich C.,320 Beal Avenue | Heinrich C.,HIGH-TECH | Waas A.M.,320 Beal Avenue | Waas A.M.,Imperial College London
Computers, Materials and Continua | Year: 2013

The smeared crack approach (SCA) is revisited to describe post-peak softening in laminated composite materials. First, predictions of the SCA are compared against linear elastic fracture mechanics (LEFM) based predictions for the debonding of an adhesively bonded double cantilever beam. A sensitivity analysis is performed to establish the influence of element size and cohesive strength on the load-deflection response. The SCA is further validated by studying the in-plane fracture of a laminated composite in a single edge bend test configuration. In doing so, issues related to mesh size and their effects (or non-effects) are discussed and compared against other predictive computational techniques. Finally, the SCA is specialized to orthotropic materials. The application of the SCA is demonstrated for failure mechanics of the open hole tension test, where fiber/matrix fracture is predominant and predicted well by the present approach. Copyright © 2013 Tech Science Press.


Prabhakar P.,320 Beal Avenue | Waas A.M.,320 Beal Avenue
Composites Science and Technology | Year: 2013

A new finite element to seamlessly model the transition from a continuum to a non-continuum (through fracture) is introduced in this paper, motivated by the variational multi-scale cohesive (VMCM) method. In-plane fiber-matrix fracture (also referred to as splitting) is frequently observed in tensile failure of fiber reinforced polymer matrix composites (FRPCs). By considering a single lamina, this mechanism is modeled through the development of a continuum-decohesive finite element (CDFE). In the CDFE method, the transition from a continuum to a non-continuum is modeled directly (physically) without resorting to enrichment of the shape functions of the element, as is done in other methods, such as the VMCM or through nodal enrichment, as is done with the extended finite element method (XFEM). The CDFE is a natural merger between cohesive elements and continuum elements. The predictions of the CDFE method were found to be in very good agreement with corresponding experimental data. © 2013 Elsevier Ltd.


Prabhakar P.,320 Beal Avenue | Waas A.M.,320 Beal Avenue
Composites Part A: Applied Science and Manufacturing | Year: 2013

Computational models to predict the compressive strength of carbon fiber reinforced polymer matrix composites are proposed here, motivated by the failure mechanisms observed in compression tests. Delamination, fiber kink-banding and their interaction are seen to dominate the failure response. An upscaled semi-homogenized laminate model is developed to predict the observed compressive response of multidirectional laminates. A generalized 2-D formulation is presented to determine the interfaces most susceptible to delamination. Subsequently, cohesive elements are added along these interfaces to introduce delamination capability in the model. Predictions of the model are compared against experimental data, and are found to be in agreement with respect to compressive strength and failure modes. Further, the effect of stacking sequence on the compressive strength and failure mode is investigated. © 2013 Elsevier Ltd.


Prabhakar P.,320 Beal Avenue | Waas A.M.,320 Beal Avenue
Composite Structures | Year: 2013

The interaction between fiber kink banding and splitting in the compressive response of fiber composites is investigated by adopting a micromechanics based 2D finite element representation of the composite. The effect of scaling of the computational model (size of model) on the compressive strength and post critical response is also studied. The size of the computational model is scaled in a systematic manner by increasing the number of fibers in the model, but maintaining a fixed aspect ratio and fiber volume fraction. The response of the model changes with change in model size, and therefore, a converged model size (baseline) for predicting compressive strength is first established. Since the strains experienced within the kink band are very large, the baseline model is extended to account for splitting as a potential mode of failure by adopting a discrete cohesive zone model. A parametric study is carried out to investigate the interaction between kinking and splitting in limiting the compressive strength of the composite. © 2012 Elsevier Ltd.


Prabhakar P.,320 Beal Avenue | Waas A.M.,320 Beal Avenue
Collection of Technical Papers - AIAA/ASME/ASCE/AHS/ASC Structures, Structural Dynamics and Materials Conference | Year: 2013

A new finite element formulation that can seamlessly model the transition from a continuum to a non-continuum (through fracture) is introduced in this paper. In-plane fibermatrix fracture (also referred to as splitting) is frequently observed in tensile failure of fiber reinforced polymer matrix composites (FRPC). This mechanism is modeled through the development of a continuum-decohesive finite element (CDFE) by considering a single lamina. The transition from a continuum to a non-continuum in the CDFE method is modeled directly (physically) without resorting to enrichment of the shape functions of the element, as is done in other methods, such as the variational multiscale cohesive method (VMCM) or through nodal enrichment as in extended finite element method (XFEM). The CDFE is a natural merger between cohesive elements and continuum elements. Predictions using the CDFE method were found to be in very good agreement with corresponding experimental data for open hole tension tests of fiber reinforced lamina. © 2012 AIAA.

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