Rudraprasad Bhattacharrya, Ruize Hu, Shuhai Zhang and Xiang Zhang present their research at EMI 2016 conference
The title of the Rudra’s presentation is: “Micromechanical Damage Model for Mode I Fracture of Fiber Composite Under Static Loading”.
Presentation Abstract:
Composite structural components of aircraft and aerospace structures degrade during operating conditions, the progression of which may be complicated due to the complex microstructural mechanisms. In this study, we present a micromechanics-based delamination model for fibrous composites to predict delamination without resorting to traditional cohesive zone modeling approaches. The primary purpose of the proposed approach is to alleviate the increase in computational cost and numerical convergence difficulties associated with explicitly accounting for ply delamination using di
screte modeling techniques, and idealizing delamination as coalescence of microstructural damage. The ply delamination due of mode I fracture under static tensile loading is modeled through simulating the double cantilever beam experiments performed on IM7/977-3, a graphite fiber reinforced epoxy composite. The modeling approach employed in this study is the eigendeformation-based reduced order
homogenization, due to its computational efficiency and its ability to incorporate distinct damage modes. The reduced model is designed such that the delamination could be interpreted directly from the damage state in the material microstructure (modeled in an approximate fashion due to model order reduction). The spurious residual stresses that occur in the reduced model are alleviated by using the concept of compatible eigenstrains, derived based on the Mura’s impotent eigenstrain concept. The capabilities of the proposed approach in approximating the mode I crack propagation is compared to elaminati
on based on cohesive zone modeling. The sensitivity of the proposed approach to element shape and size are investigated.
The title of the Ruize’s presentation is: “Mesoscale Thermomechanical Modeling of Energetic Material Interfaces Under Transient Loading”.
Presentation Abstract:
We present the formulation and implementation of a mesoscale thermomechanical model for analysis of interface damage and associated temperature rise of energetic material under transient loading. We propose a fully coupled thermomechanical cohesive finite element approach to properly account for the interface debonding, traction separation relation, heat flux generation and interface temperature increasing. The coupling roots from the fact that the energy released by decohesion and the heat flux generated due to the friction in post interface debonding directly contribute to the temperature rise at interface, on the other hand the binder material typically shows temperature dependent constitutive behavior and the thermal strain becomes an important factor in the displacement field around the interface neighborhood. A linear cohesive law is employed to describe the traction separation relation. The 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 phase materials used in this study are HTPB for binder and HMX for particles, respectively. A viscoelastic constitutive law is employed for HTPB, and HMX particles are modeled as brittle material with damage evolution law. The finite element model of the energetic material system is solved with fully coupled explicit thermomechanical dynamic solver.
The title of the Shuhai’s presentation is: “Reduced Order Variational Multiscale Enrichment Method for Thermo-mechanical Problems”.
Presentation Abstract:
We present the formulation and implementation of the reduced order variational multiscale enrichment (ROVME)
method for the analysis of coupled thermo-mechanical problems. Based on the variational multiscale enrichment (VME) method [1], ROVME provides a model order reduction technique for elsto-viscoplastic problems [2]. It eliminates the requirement of fine scale discretization at subdomains of interests and significantly enhances the computational efficiency of the direct VME method. We extend the ROVME method for coupled thermo-mechanical problems, since the properties of temperature sensitive materials vary at different temperatures. In such case, the coefficient tenors of the ROVME method vary along with temperature changing. A numerical approach is incorporated to evaluate the temperature sensitive coefficient tensors in an efficient manner. The novel contribution of this presentation are: 1) extending the eigen-deformation based model order reduction technique to strongly coupled thermo-mechanical problems, under the context of scale-inseparable multiscale computational framework; 2) the temperature dependent coefficient tensors are accurately approximated through temperature finite element method, rather than evaluating at every temperature. Numerical verifications are performed to assess the capabilities of the computational framework, against the direct finite element analysis method and direct VME method. To ensure the accuracy of the proposed method, the coupled thermo-mechanical effect is tested from different perspectives, such as structures with uniform temperature field, structures with temperature gradient and temperature induced plastic deformation. The results of the numerical verifications reveal high accuracy of the ROVME computational methodology, comparing with the direct finite element analysis and direct VME results
The title of the Xiang’s presentation is: “Eigenstrain based Reduced Order Homogenization for Polycrystalline Materials”.
Presentation Abstract:
Microstructural morphology significantly affects the mechanical performance of structures made of polycrystalline metals and alloys. Crystal Plasticity Finite Element Method (CPFE) has the flexibility to leverage available constitutive formulations and relies on discretization of the realistic polycrystalline microstructure, providing satisfactory performance on the microstructure scale. Multiscale computational methods (such as computational homogenization, variational multiscale enrichment, heterogeneous multiscale method, multiscale finite element method) on the other hand, provide the computational framework to upscale the microstructure scale response to the macroscopic scale. However, the high computational complexity of a CPFE simulation performed over a representative volume element (RVE) typically prohibits straightforward application of these methods to homogenize polycrystal response. In this talk, we will present an eigenstrain based reduced order homogenization method for polycrystalline materials, where model reduction is achieved through reduced order modeling of the RVE simulations and provides an approximation to the microscale problem with orders of magnitude computational efficiency. A two-scale asymptotic analysis is used to decompose the original equations of polycrystal plasticity into micro- and macroscale problems. Eigenstrain based representation of the inelastic response field is employed to approximate the microscale boundary value problem using an approximation basis of much smaller order. The reduced order model takes into account the grain-to-grain interactions through influence functions that are numerically computed over the polycrystalline microstructure. The proposed approach is also endowed with a hierarchical model improvement capability that allows accurate representation of stress and deformation state within subgrains. The proposed approach was implemented and its performance was assessed against crystal plasticity finite element simulations. Numerical studies point to the capability to efficiently compute the mechanical response of the polycrystal RVEs with good accuracy and the ability to capture stress risers near grain boundaries. The capability of efficient macroscale modeling of the proposed model is also demonstrated.