Skip to Main Content
 

Global Search Box

 
 
 
 

Files

File List


29136.pdf (11.29 MB)

ETD Abstract Container

Abstract Header

Micro-Mechanical Models for Impact and Non-Local Averaging in Composites

Medikonda, Sandeep
http://rave.ohiolink.edu/etdc/view?acc_num=ucin1522419945945237

Abstract Details

2018, PhD, University of Cincinnati, Engineering and Applied Science: Mechanical Engineering.
In the past few decades, Laminated composites have become the most favored material system for a wide range of industrial applications. Factors such as the potential for structural tailoring, superior strength, and stiffness for a given weight along with higher toughness and mechanical damping etc., have justified their increased use. Due to this high usage, the accurate behavior of laminated composites under various loading conditions remains a concern and hence this dissertation focuses on building simple and accurate uni-directional micro-mechanical material models. Firstly, an elastic micromechanical model based on the physically viable sub-cell boundary conditions is developed and implemented for use with uni-directional composite laminates in the explicit finite element software LS-DYNA®. Stress-strain relations have been presented in a three-dimensional context and hence can be used with solid elements. The effect of these boundary conditions in accurately estimating the elastic properties has been studied. Transverse and shear modulus have been analyzed in detail alongside popular analytical methods and verified against available experimental results for various volume fractions. Good agreements have been observed for the presented model in comparison with the experimental results. Secondly, a non-linear micro-mechanical composite material model is developed to simulate the behavior of uni-directional composites under impact loading conditions. The strain-rate and pressure dependency in the composite material model is accounted by the resin, which uses previously developed state-variable viscoplastic equations. These equations were modified to account for the significant contributions of hydrostatic stresses typically observed in polymers. The material model also uses a continuum damage mechanics (CDM) based failure model to incorporate the progressive post-failure behavior. A set of Weibull distribution functions are used to quantify this behavior and an iterative methodology of characterizing the softening parameters used in these functions is presented. The impact response of composite laminate plates has been simulated and compared to the experiments. It has been observed that the predicted results compare favorably to the experiments. In addition, the effectiveness of studying inter-laminar delamination in laminated composites with the help of thickness-stretch shell elements which utilize a 3-D material model sub-routine as compared to the traditional plane-stress shell elements has also been investigated. Ply-level progressive failure criteria have been used to simulate the initiation and propagation of delamination. The numerical delamination growth has been qualitatively analyzed against the experimental C-scan images for multiple impact events on different composite plates. Lastly, since it is well known that strain-softening behavior in composite material models leads to a pathological mesh sensitivity in finite element simulations. Non-local continuum theory has been used and three non-local damage models with isotropic weight function have been implemented to work in conjunction with the non-linear composite micro-mechanical material to address this problem. The effect of weighing function on each of these formulations has also been studied in detail. All three non-local formulations have been observed to produce a nice smeared effect of damage, unlike the local damage models.
Ala Tabiei, Ph.D. (Committee Chair)
Richard Hamm, M.S (Committee Member)
Yijun Liu, Ph.D. (Committee Member)
David Thompson, Ph.D. (Committee Member)
Kumar Vemaganti, Ph.D. (Committee Member)
158 p.
Mechanical Engineering
Unidirectional composites; Micro-mechanical model; Representative Volume Cell; Non-local damage; Delamination; Impact

Recommended Citations

Citations

  • Medikonda, S. (2018). Micro-Mechanical Models for Impact and Non-Local Averaging in Composites [Doctoral dissertation, University of Cincinnati]. OhioLINK Electronic Theses and Dissertations Center. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1522419945945237

    APA Style (7th edition)

  • Medikonda, Sandeep. Micro-Mechanical Models for Impact and Non-Local Averaging in Composites. 2018. University of Cincinnati, Doctoral dissertation. OhioLINK Electronic Theses and Dissertations Center, http://rave.ohiolink.edu/etdc/view?acc_num=ucin1522419945945237.

    MLA Style (8th edition)

  • Medikonda, Sandeep. "Micro-Mechanical Models for Impact and Non-Local Averaging in Composites." Doctoral dissertation, University of Cincinnati, 2018. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1522419945945237

    Chicago Manual of Style (17th edition)

ucin1522419945945237
208
© 2018, all rights reserved.
This open access ETD is published by University of Cincinnati and OhioLINK.