Information about PhD Dissertation Defense

Presentation used for Ian Nieves dissertation. It summarizes using FEA simulation to model impact mechanics and damping in a novel materials characterization device, and in biomedical materials designed to promote bone regeneration.

Objectives Damping and Percussion Periometer Modeling with Finite Element Analysis (FEA) Modeling Periometer Testing Laminated Materials - Damping Glass Columns - Defects

Damping and Percussion

Periometer

Modeling with Finite Element Analysis (FEA)

Modeling Periometer Testing

Laminated Materials - Damping

Glass Columns - Defects

Damping Energy dissipation during mechanical action Intrinsic damping : energy thermally dissipated through microstructural changes Damping a function of material structure

Energy dissipation during mechanical action

Intrinsic damping : energy thermally dissipated through microstructural changes

Damping a function of material structure

Intrinsic Damping and Tissue Regeneration Dominant paradigm of bone maintenance (Mechanostat) = skeletal remodeling and repair mediated by damping + dynamic stresses Clinical studies implement damping in prosthetics integration 2 2 James C. Earthman, Cherilyn Sheets, J. Paquete, et al, Tissue Engineering in Dentistry, Clin. Plastic Surg. , Vol. 30, pp. 621 – 639, 2003 2 James C. Earthman, Cherilyn Sheets, J. Paquete, et al, Tissue Engineering in Dentistry, Clin. Plastic Surg. , Vol. 30, pp. 621 – 639, 2003

Dominant paradigm of bone maintenance (Mechanostat) = skeletal remodeling and repair mediated by damping + dynamic stresses

Clinical studies implement damping in prosthetics integration 2

Percussion Generate mechanical pulses through impact Pulse parameters (intensity, duration, etc.) modified in situ through damping Pulsate mechanics similar to biological activities (Running, etc.) *Bakos et al., Acta Veterinaria Hungarica (2003).

Generate mechanical pulses through impact

Pulse parameters (intensity, duration, etc.) modified in situ through damping

Pulsate mechanics similar to biological activities (Running, etc.)

Periometer Workstation with Virtual Instrumentation Percussion Probe Control Instrumentation and Sensors

Periometer

Calculation of Force and Acceleration Energy Return (ergs) Time (ms) Energy Return = ER = C 1 x F 2

Periometer Wave Dynamics

DEFECT DETECTION

Modeling Percussion Validate percussion response Elucidate mechanisms underlying response Predict facets of percussion profile Taylor and refine detection capabilities Facilitate construction of “Percussion Spectrum”

Validate percussion response

Elucidate mechanisms underlying response

Predict facets of percussion profile

Taylor and refine detection capabilities

Facilitate construction of “Percussion Spectrum”

Finite Element Analysis (FEA) Creates representations of geometry Uses geometry as template for network (mesh) of discrete lattice points (nodes) Nodes are vertices for line, planar or polyhedral elements Uses Shape Functions to solve to produce predictions of nodal (acceleration, displacement) and elemental (stress) results in response to inputs (initial and boundary conditions)

Creates representations of geometry

Uses geometry as template for network (mesh) of discrete lattice points (nodes)

Nodes are vertices for line, planar or polyhedral elements

Uses Shape Functions to solve to produce predictions of nodal (acceleration, displacement) and elemental (stress) results in response to inputs (initial and boundary conditions)

Elements Idealized Hexagonal element used for virgin testing materials and full-scale Hexagonal elements in cylindrical probe with nodes adjacent to accelerometer

Dytran vs. MARC Dytran specialized for ballistic modeling – more detailed results Explicit solver – ∆t Crit automatically calculated DYMAT 24 Piecewise Linear Plasticity (elastoplastic) material model Matrig rigid material model – only requires mass input MARC capable of ballistic modeling, specialized for elastomeric analysis Implicit Solver - ∆t Crit calculated through inspection Elastic Material model Rayleigh damping model – intrinsic damping input Dytran MARC

Dytran specialized for ballistic modeling – more detailed results

Explicit solver – ∆t Crit automatically calculated

DYMAT 24 Piecewise Linear Plasticity (elastoplastic) material model

Matrig rigid material model – only requires mass input

MARC capable of ballistic modeling, specialized for elastomeric analysis

Implicit Solver - ∆t Crit calculated through inspection

Elastic Material model

Rayleigh damping model – intrinsic damping input

Stepped Probe Construction

Rigid Probe and Glass Column Construction

Meshes

Boundary Conditions for Laminated Materials

Initial and Boundary Conditions for Rigid Probe and Glass Columns

Material Parameters Material Model Material E (KPa) ρ (kg/mm 3 ) ν σ ys (KPa) Code DYMAT 24 Steel 1.9310 8 8.00x10 -6 0.30 4.40x10 4 Dytran Al 6061 7.00x10 7 2.70x10 -6 0.35 3.95x10 5 PTFE 5.00x10 5 2.10x10 -6 0.40 9.00x10 4 Glass 7.03x10 7 2.47x10 -6 0.22 6.90x10 4 PMMA 3.30x10 6 1.19x10 -6 0.37 1.07x10 5 PLGA 3.50x10 6 1.19x10 -6 0.40 4.4x10 4 Elastic Steel 1.9310 8 8.00x10 -6 0.30 MARC Al 6061 7.00x10 7 2.70x10 -6 0.35 PTFE 5.00x10 5 2.10x10 -6 0.40 Glass 7.03x10 7 2.47x10 -6 0.22 PMMA 3.30x10 6 1.19x10 -6 0.37 PLGA 3.50x10 6 1.19x10 -6 0.40

Intrinsic Damping in MARC Rayleigh Damping Function: C = αM + (β+gt)K, M = Mass Matrix, K = Stiffness Matrix, C = Damping Matrix Damping is proportional to stiffness and mass Stiffness Matrix Factor( β) = 2(η)/π(lowest modal frequency(Hz)) η = Loss Coefficient Modal frequency material specific, derived through MARC modal analysis Material Al PTFE PMMA η 0.0003 0.1038 0.0400

Rayleigh Damping Function: C = αM + (β+gt)K, M = Mass Matrix, K = Stiffness Matrix, C = Damping Matrix

Damping is proportional to stiffness and mass

Stiffness Matrix Factor( β) = 2(η)/π(lowest modal frequency(Hz))

η = Loss Coefficient

Modal frequency material specific, derived through MARC modal analysis

Al Monoliths

3.175 mm thick Al Monolith: Results Stepped Probe Stepped Probe: MARC Cylindrical Probe: Dytran Cylindrical Probe: Dytran Cylindrical Probe: MARC

Size Effects: 500 x 500 x 3.175 mm Al Monolith and 27 gram Probe 27 gram Probe 500 mm x 500 mm x 3.175 mm Monolith

Al – PTFE Scaffolds with Rigid Probe

Al – PTFE Scaffolds with Stepped Probe and Intrinsic Damping

3.175 PTFE: 3.175 Al 1.58 PTFE: 3.175 Al

PMMA Scaffold with Intrinsic Damping Scaffold and Probe Layer with Defect

PMMA Scaffold with Intrinsic Damping: Origin of Shoulder Intrinsic Damping No Intrinsic Damping

PLGA Scaffold: Mesh re-Enforcement and Stress Attenuation 1 J . Calvert, L. Weiss, New Frontiers in Bone Tissue Engineering , Clin. Plast. Surg. , Vol. 30, pp. 641 – 648, 2003 PLGA demonstrated to stimulate bone and vascular regeneration 1 Re-enforced Virgin

PLGA demonstrated to

stimulate bone

and vascular regeneration 1

Glass Defect 0.2 mm Glass used to model rigid biological materials: bone, enamel, etc.

Cylindrical Probe and Glass Control MARC Dytran

Stepped Probe and Glass Control: Acceleration Results T ≈ 0.18 msec T ≈ 0.25 msec T ≈ 0.25 msec MARC Dytran

Rigid Probe and Glass Control

Stepped Probe and Trench Defect “ T ” ≈0.58 msec “ T ” ≈0.58 msec

Trench Crack: Averaged Probe Acceleration (Dytran) Averaged Probe nodal accelerations for indicated planes

Wedge Crack Geometry Shoulder Peak

Semi-Circular Aligned Crack: Acceleration Shoulder Peak 1 mm Cross Section Perpendicular to Impact Plane

Crack Boundary Effects

Rigid Probe with 1 mm transverse Crack

Glass Controls: FEA vs. Percussion Y – Axis Acceleration (mm/sec 2 ) Time (sec) Glass control acceleration accurately modeled with stepped probe

Cracked Glass : FEA vs. Percussion Y – Axis Acceleration (mm/sec 2 ) Y – Axis Acceleration (mm/sec 2 ) Y – Axis Acceleration (mm/sec 2 ) Time (sec) Time (sec) Time (sec)

Crack Stresses (KPa) Semi-circular crack with square edge Semi-circular crack with round edg e Wedge-form crack with round edge

Interference Effects

Summary FEA can elucidate mechanical origin of probe signals FEA – based modeling can accurately model defect detection in rigid materials FEA can qualitatively evaluate energy dissipation in biomedical scaffolds Modeling indicates dependence of Periometer function on interference effects Further modeling – experimental is required to refine intrinsic damping modeling

FEA can elucidate mechanical origin of probe signals

FEA – based modeling can accurately model defect detection in rigid materials

FEA can qualitatively evaluate energy dissipation in biomedical scaffolds

Modeling indicates dependence of Periometer function on interference effects

Further modeling – experimental is required to refine intrinsic damping modeling

Acknowledgements Dr. James Earthman MSC Software Corporation, Santa Ana, CA

Dr. James Earthman

MSC Software Corporation, Santa Ana, CA

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