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Hua Y.,University of Nebraska - Lincoln | Akula P.K.,University of Nebraska - Lincoln | Gu L.,University of Nebraska - Lincoln | Gu L.,Nebraska Center for Materials and Nanoscience
Composites Part B: Engineering | Year: 2014

The objective of this paper is to investigate the structural response of carbon fiber sandwich panels subjected to blast loading through an integrated experimental and numerical approach. A total of nine experiments, corresponding to three different blast intensity levels were conducted in the 28-inch square shock tube apparatus. Computational models were developed to capture the experimental details and further study the mechanism of blast wave-sandwich panel interactions. The peak reflected overpressure was monitored, which amplified to approximately 2.5 times of the incident overpressure due to fluid-structure interactions. The measured strain histories demonstrated opposite phases at the center of the front and back facesheets. Both strains showed damped oscillation with a reduced oscillation frequency as well as amplified facesheet deformations at the higher blast intensity. As the blast wave traversed across the panel, the observed flow separation and reattachment led to pressure increase at the back side of the panel. Further parametric studies suggested that the maximum deflection of the back facesheet increased dramatically with higher blast intensity and decreased with larger facesheet and core thickness. Our computational models, calibrated by experimental measurements, could be used as a virtual tool for assessing the mechanism of blast-panel interactions, and predicting the structural response of composite panels subjected to blast loading. © 2013 Elsevier Ltd. All rights reserved.


Hua Y.,University of Nebraska - Lincoln | Gu L.,University of Nebraska - Lincoln | Gu L.,Nebraska Center for Materials and Nanoscience | Trogdon M.,University of Nebraska - Lincoln
International Journal of Adhesion and Adhesives | Year: 2012

The objective of this paper was to investigate the performance of recessed single-lap joints with dissimilar adherends through the finite element method. The influence of material and geometric nonlinearity of the adhesive as well as the impact of the recess length was examined in terms of maximum principal stresses. The strength of the joint was obtained as the load to initiate the crack propagation. Results suggested that either adding a spew fillet or considering the adhesive plasticity led to reduced peak stresses at the edge of the adhesive layer. The presence of a spew fillet in the single-lap joint with a recess length of 50% of the overlap length reduced the peak stress concentrations in the adhesive layer by 45.2% and subsequently improved the strength of the joint by 36.3%. Mitigation of stress concentration was observed in cases of an adhesive layer with a smaller recess length. The strength of recessed joints with a gap less than 50% of the overlap length decreased slightly. For the recess length as 70% and 90% of the total overlap length, the strength of the joints reduced 36.4% and 66.3%, respectively. This study suggested a recess of less than 50% of the overlap length may be beneficial for the performance of the joints. © 2012 Elsevier Ltd.


Gu L.,University of Nebraska - Lincoln | Gu L.,Nebraska Center for Materials and Nanoscience | Chafi M.S.,University of Nebraska - Lincoln | Ganpule S.,University of Nebraska - Lincoln | Chandra N.,University of Nebraska - Lincoln
Composites Part B: Engineering | Year: 2012

In the modeling of brain mechanics subjected to primary blast waves, there is currently no consensus on how many biological components to be used in the brain-meninges-skull complex, and what type of constitutive models to be adopted. The objective of this study is to determine the role of layered meninges in damping the dynamic response of the brain under primary blast loadings. A composite structures composed of eight solid relevant layers (including the pia, cerebrospinal fluid (CSF), dura maters) with different mechanical properties are constructed to mimic the heterogeneous human head. A hyper-viscoelastic material model is developed to better represent the mechanical response of the brain tissue over a large strain/high frequency range applicable for blast scenarios. The effect of meninges on the brain response is examined. Results show that heterogeneous composite structures of the head have a major influence on the intracranial pressure, maximum shear stress, and maximum principal strain in the brain, which is associated with traumatic brain injuries. The meninges serving as protective layers are revealed by mitigating the dynamic response of the brain. In addition, appreciable changes of the pressure and maximum shear stress are observed on the material interfaces between layers of tissues. This may be attributed to the alternation of shock wave speed caused by the impedance mismatch. © 2011 Elsevier Ltd. All rights reserved.


Lin S.,University of Nebraska - Lincoln | Gu L.,University of Nebraska - Lincoln | Gu L.,Nebraska Center for Materials and Nanoscience
Materials | Year: 2015

The mechanical properties of type I collagen gel vary due to different polymerization parameters. In this work, the role of crosslinks in terms of density and stiffness on the macroscopic behavior of collagen gel were investigated through computational modeling. The collagen fiber network was developed in a representative volume element, which used the inter-fiber spacing to regulate the crosslink density. The obtained tensile behavior of collagen gel was validated against published experimental data. Results suggest that the cross-linked fiber alignment dominated the strain stiffening effect of the collagen gel. In addition, the gel stiffness was enhanced approximately 40 times as the crosslink density doubled. The non-affine deformation was reduced with the increased crosslink density. A positive bilinear correlation between the crosslink density and gel stiffness was obtained. On the other hand, the crosslink stiffness had much less impact on the gel stiffness. This work could enhance our understanding of collagen gel mechanics and shed lights on designing future clinical relevant biomaterials with better control of polymerization parameters. © 2015 by the authors.


Hua Y.,University of Nebraska - Lincoln | Gu L.,University of Nebraska - Lincoln | Gu L.,Nebraska Center for Materials and Nanoscience
Composites Part B: Engineering | Year: 2013

The objective of this paper was to predict the thermomechanical behavior of 2080 aluminum alloy reinforced with SiC particles using the Mori-Tanaka theory combined with the finite element method. The influences of particle volume fraction, stiffness, aspect ratio and orientation were examined in terms of effective Young's modulus, Poisson's ratio and coefficient of thermal expansion (CTE) of the composite. The microstructure induced local stress and strain field was obtained through the numerical models of the representative volume element. Results suggested that particle volume fraction had significant impact on the effective Young's modulus, Poisson's ratio and CTE of the composite. Stiffer particles could improve the effective Young's modulus of the composite, while the overall sensitivity of the effective Poisson's ratio and CTE with respect to the particle stiffness was minimal. Particles with larger aspect ratio generally led to a composite with increased effective Young's modulus, as well as reduced Poisson's ratio and CTE. The overall material properties of the composite were insensitive to the particle aspect ratio beyond 10. The particle orientations significantly impacted the effective material properties of the composite, especially along the longitudinal direction. Random 3D dispersed particles exhibited the effective isotropic behavior, whereas anisotropy has been observed for random 2D and unidirectional aligned particles. Our results could help create tailorable bulk composite. © 2012 Elsevier Ltd. All rights reserved.

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