Advanced Material Models and Geomechanics

Transcription

1 Advanced Material Models and Geomechanics Giovanni Federico, Mark Robinson ANSYS UK Ltd ANSYS, Inc. April 28, 2017

2 ANSYS, Inc. April 28, 2017 Advanced Material Models

3 NEW Unified Viscoplasticity with Kinematic Static Recovery Term For thermo-mechanical cyclic loading of metals, the plastic behavior is a complex phenomenon At high temperatures in strain rate-dependent engineering materials, a annealing-like behavior is observed which results in a relaxation in the kinematic back stress of the component. We refer to this as kinematic Static recovery i.e. the partial restoration of the back-stress (kinematic hardening) This often results in a low cycle fatigue behavior This knowledge of Kinematic Static Recovery can therefore be used to estimate operating life of the component Ratcheting with static recovery simulation and life time evaluation (cf.[3]) Predicted life-time based on Lemaitre s isotropic damage model [2] ANSYS, Inc. April 28, 2017

4 Unified Viscoplasticity (TB,RATE + TB,CHAB) For thermo-mechanical cyclic loading of metals, plastic behavior is complex Rate dependent viscoplasticity and/or creep Nonlinear Chaboche kinematic hardening Temperature dependent Time dependent kinematic and isotropic static recovery Backstress and isotropic yield stress anneal back to the virgin state We had many of these pieces, but not available in a combined material CREEP+CHAB or RATE+CHAB, but not CREEP+RATE+CHAB Static recovery only available with our CREEP+CHAB model Added kinematic static recovery to Unified Viscoplasticity Time dependent recovery of the backstress Often significant at elevated temperatures Chaboche Kinematic Hardening el n m 1 Ci n i i Di i i 3 i 1/ m Rate Dependent Plasticity Kinematic Static Recovery ANSYS, Inc. April 28, 2017

5 Enhanced: Field Dependent Material Properties Material property support for predefined field variables has been expanded to include Time Pore Pressure Spatial Location Displacement Thermal expansion Density 6.00E E E+11 YOUNG'S MODULUS(GPa) Vs LOCATION (mm) ALPHA=0.1 ALPHA=0.3 ALPHA=0.5 ALPHA=1.0 ALPHA=3 ALPHA=5 ALPHA=10 Material Property as a function of Location Powder compaction of a Metal/Ceramic FGM material The MAPDL solver uses linear interpolation between the data points you provide to determine specific material property values ANSYS, Inc. April 28, 2017

6 Predefined Field Variables Material property support for solver predefined field variables has been expanded to include time (TIME), pressure (PPRE), location (XCOR, YCOR, ZCOR), and displacement (UX, UY, UZ). The MAPDL solver uses linear interpolation between the data points you provide to determine specific material property values. To do so, the program: Creates a grid using your defined field data values. Assumes that you have defined curve-based data and automatically provides the missing grid data points. Performs linear interpolation on this populated grid to find material property values. Enables editing of the initialized field variables during solution, if necessary ANSYS, Inc. April 28, 2017

7 Application example Calculation of structural response of short fiber reinforced tensile specimen Material properties table Interpolation grid (XCOR, YCOR, ZCOR - table) Stress distribution ANSYS, Inc. April 28, 2017

8 ANSYS, Inc. April 28, 2017 Geo-Mechanics

9 Concrete: NEW Menetrey Willam Model Concrete is a pressure sensitive material with very low strength in tension than in compression. Menetrey Willam failure envelope nicely matches typical concrete behavior Yield surface is specified by yield strength in compression, tension and biaxial compression No parameter fitting required Includes models for compression hardening/softening and tension softening evistudio.com Menetrey Willam yield surface in principal stress space ANSYS, Inc. April 28, 2017

10 Ability of Failure Models to Represent the Biaxial Failure of Concrete a) Von Mises b) Drucker-Prager Failure envelopes corresponding to different failure criteria plotted against the experimental data of Kupfer and Getrstle (marked by isolated points) are plotted on the left. Notice that Menetrey Willam failure envelope nicely matches the experimental results (cf. [4]). c) Mohr -Coulomb d) Menetrey-Willam ANSYS, Inc. April 28, 2017

11 Symmetry BC Footing on Concrete Foundation Footing 6 in. Concrete Slab 24 in. 6 inch concrete slab foundation 3000 psi concrete Unreinforced Supported by soil substrate 12 inch footing General contact between materials 6 in. Yield Strength: Compression= 3000 psi Tension = 500 psi Biaxial = 4000 psi Linear hardening Dilatancy = 10 o Effective plastic strain contours show a band of compression failure through the thickness of the foundation. Soil (elastic) ANSYS, Inc. April 28, 2017

12 Application example: Simulation of slab with ring reinforcement Benchmark problem from [1] ANSYS, Inc. April 28, 2017

13 Enhancements: Coupled Structural-Pore-Fluid-Diffusion-Thermal Partially saturated porous media i.e. Pores partly filled with fluid can now be analyzed e.g. soil embankments, dams, polymeric materials such as sponges Fully coupled poro-thermo-mechanical coupling is now supported which enables study of Heat transfer due to conduction in such structures Field variable dependent Rayleigh damping is now supported for CPT elements ANSYS, Inc. April 28, 2017

14 ANSYS, Inc. April 28, 2017 Mesh Reinforcement

15 Introduction Reinforcing (REINF) Elements Elements embedded in other structural elements (the base elements) to simulate reinforcing members, such as the steel rebars in reinforced concrete, carbon fibers in layered composites. Two Basic Forms: Discrete (REINF264) for individual fibers. Typical applications: civil engineering, biomedical devices Smeared (REINF263 for 2D and REINF265 for 3D) for cluster of fibers with uniform orientation, spacing, cross section area, and material. Typical applications: tires, fiber reinforced composites Special Modeling Considerations The reinforcing and the base elements are assumed to be securely bonded the motion of these two sets of elements are conformable. The ensure this compatibility, the geometrical relationship between the reinforcing and base elements must be properly defined ANSYS, Inc. April 28, 2017

16 Examples: Mesh Independent ReBars (Tire Modeling) Tire cross section has complicated geometry shape and the belts/plys that are embedded in as reinforcement have different shapes, material properties and its orientation ANSYS, Inc. April 28, D Discrete REINFs in Distorted Base Mesh Base mesh can be easily changed without affecting the Reinforcements

17 Realistic Example: Fixation of a Femur Fracture Variable Material Data Example In collaboration with CADFEM Germany GmbH by courtesy of BGU Tuebingen: MD B Koenig, MD S Doebele, MD C Ihle ANSYS, Inc. April 28, 2017

18 Motivation Optimal design of implant and surgery planning by means of FEanalysis AnyBody: Physical load cases DocQ: Automatic generation of WB-project including load cases Variable material data: Account for local variation in bone density and hence mechanical properties AnyBody Stepping downstairs AnyBody, AnyBody Technology A/S DocQ, CADFEM Medical GmbH Implant and load case import through DocQ ANSYS, Inc. April 28, 2017

19 Workflow: Model Generation in 40 Minutes Motion capture data Musculo-skeletal simulation Calculation of muscle forces AnyBody DocQ Preparation of the model for meshing and boundary condition application Wizard for easy model set up Define propertydependencies Import user-fields ANSYS Mechanical ANSYS, Inc. April 28, 2017

20 Definition of Variable Material Data in EDA New variable material data functionality for straightforward set up of locally effective Young s modulus as function of HU-field Mathematical relation between HUfield bone density Young s modulus J Eng in Medicine, 2014, Vivanco et al J Biomech, 1994, Keller et al J Biomech, 2007, Schielo et al J Biomech, 2003, Morgan et al Example data only ANSYS, Inc. April 28, 2017

21 User-Field Import in Mechanical DocQ: automatic generation of WB-project including load cases with fiber attachments, screws and contacts, and implant CSV-file import to define HU-field over bone: the corresponding E varies from a few MPa to 14 GPa!! (x, y, z, HU) ANSYS, Inc. April 28, 2017