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Ruize Hu presented his research at ASME IMECE 2016 Conference

Posted by on Wednesday, November 16, 2016 in News.


Ruize presented his research in two different areas through one poster and two oral presentations. One of the oral presentation and poster is entitled: “Nonlocal Homogenization Model for Wave Dispersion and Attenuation in Elastic and Viscoelastic Heterogeneous Media”.

Presentation Abstract:
Heterogeneous materials exhibit complex response patterns when subjected to dynamic loading due to the intrinsic wave interactions induced by reflections and refractions at material constituent interfaces. Controlling these interactions offer tremendous opportunities in many engineering applications. By tailoring the constituent material properties and microstructure, the heterogeneous materials exhibit favorable properties within targeted frequency ranges, including cloaking, energy harvesting and sensing, vibration control and impact survivability. Acoustic metamaterials have received significant recent attention due to the unique and tailorable properties including negative effective density and bulk modulus, and wave attenuation within band gaps. We present a nonlocal homogenization model for capturing dispersion, acoustic band gap and wave propagation in elastic and viscoelastic heterogeneous media in one-dimension. Mathematical homogenization based on asymptotic expansions with multiple spatial scales is employed to formulate the nonlocal homogenization model. The proposed model is derived by performing asymptotic expansions up to eighth order. A momentum balance equation of gradient elasticity type that is nonlocal in both space and time is consistently derived. We demonstrate that by employing the high order corrections, the homogenization model captures the characteristics of wave propagation at high frequency, where the microstructural size is smaller than, but comparable to, the wave length, i.e., separation of scale is weakly satisfied. Contributions from the high order terms in the momentum balance equation account for the heterogeneity induced wave dispersion and stop band formation. The coefficients of the higher order momentum balance equation is derived directly from microstructural material parameters, as well as the high order boundary conditions. The derivation procedure for the model coefficients and high order boundary conditions can serve as an alternative for gradient elasticity models. The capability of the proposed model is assessed against analytical solution and direct numerical simulation. The performance of the proposed model is also discussed by comparing with other homogenization models. The proposed model shows high accuracy in predicting the dispersion and band gap formation of elastic and viscoelastic composites. The key contributions of our work are: (1) the proposed model precisely captures the dispersion and attenuation within band gap for elastic and viscoelastic composites; (2) all the model parameters are computed directly from the microscale initial-boundary value problems and depend on the constituent material properties only, which permits the application in multiple dimensional problems with more complex microstructures; and (3) this model is derived in the context of multi-layered microstructure and the computation of model parameters is independent of the solution of the macroscopic momentum balance equation, which opens the gate towards modeling acoustic metamaterial with high computational efficiency.


Ruize’s second oral presentation is entitled: “Mesoscale modeling of the coupled mechanical-thermal response of HTPB-AP energetic material under transient load”.

Presentation Abstract:
Hydroxyl-terminated polybutadiene (HTPB) bonded ammonium perchlorate (AP) composite material is one type of plastic-bonded explosives (PBXs). It is composed of high volume fraction of AP particles with HTPB as the binder material. Significant material heterogeneity exists in the HTPB-AP material system due to the phase material properties and mesostructural morphology. Microscale simulation approaches (e.g., molecular dynamics) that resolve the details (e.g., hot spot, chemical reaction, etc.) about the material system are usually limited to a small mesoscale volume of material due to the extremely computational cost. Macroscale phenomenological models allow for large scale simulation, but usually miss the effects of heterogeneity at meso- or microscale level. A multiscale framework with experimentally validated mesoscale model may be an alternative to characterize the heterogeneous material system. We present the formulation and implementation of an experimentally validated coupled mesoscale mechanical-thermal model for analysis of the mechanical response considering interface damage and temperature rise due to viscoelastic dissipation and interface friction. We propose a coupled mechanical-thermal cohesive finite element approach to properly account for the interface debonding, contact and temperature rise due to friction. A bilinear cohesive law is employed to describe the traction separation relation. Penalty method is used to suppress the interpenetration and a damage dependent regularized Coulomb’s law is applied to account for interface post damage friction. The HTPB binder material is modeled as viscoelastic with Prony series. The rate and temperature dependent material property and energy dissipation are embedded in the constitutive model. The AP particle is modeled as elastic since HTPB is much softer than AP and deformation is largely occurs in HTPB and interface. No plastic deformation and damage is observed in AP particle in the experiment. Temperature rise due to viscoelastic dissipation and interface friction is modeled as adiabatic. The material property of HTPB is calibrated by the stress-strain data available in literature as well as data collected in the experiments. The cohesive zone model parameters are calibrated by the experiment observations. The finite element model of HTPB-AP material system is solved with commercial software Abaqus using explicit solver with VUMAT and VUEL user subroutines for HTPB constitutive model and cohesive element, respectively. The calibrated mesoscale model shows good match with experiments in terms of the measured force and observed interface debonding. It also predicts temperature rise within HTPB and at interface. The key contributions of our work are: (1) the proposed experimentally validated model well characterizes the failure mechanism and heat generation; (2) the model is built in mesoscale level, it potentially allows for a macroscale description by reduced order modeling.