(c) B. Ravi, IIT Bombay 1

Transcription

1 Collaborative Engineering Evaluation, Testing TKP Safety, TKP System Mechanism FEA Physical testing Fatigue Wear What How Evaluate Testing Judgement Criteria's Testing Conditions Parameters Measured OrthoCAD Lab, I.I.T. Bombay Performance Performance HOW! Performance Based on TESTING Virtual Physical Biological Metrology (c) B. Ravi, IIT Bombay 1

2 LEVEL - 3 LEVEL - 2 LEVEL - 1 LEVEL - 0 Safety,...Conditions Overall Evaluation Plan More General Activities Standing Walking Sitting Human body environment Surgical New Prosthesis Functional Biocompatibility GOAL CRITERIA Factor of safety Jump Impact Replacement/ Revision Morphological Implantability & Revisability Patient Comfort Kinematic Freedom of Motion Limits of Motion Static Safety Structural Integrity Longevity Wear Sub- CRITERIA Loosening More Specific Evaluation Criteria s Evaluation Criteria s Morphological Kinematic Degrees of Freedom Range of Motion Upper Limit Range of Motion Lower Limit Limit of Motion Linear Dimensional Congruence Angular Dimensional Congruence Shape Weight Implantability & Revisability Structural Integrity Time (assemble & dissemble) Direction Component Handling Effort Modularity Static Safety Loosening Longevity Wear Testing FEA Methodology Pre-Processing Solid Modelling Meshing Connectivity / Interfaces Material Modelling Boundary Conditions Processing Stiffness generation & modification Solutions to equations (nodal variables) Post Processing Result visualisation Plots and graphs Animation CAD Model & Meshing Force Boundary conditions SOLVER Restrains FMEA - Components Failure history, Low FOS MESHING Virtual Static Loading of Individual Components Identification of Critical Components Physical Validation Calibration of Meshing Parameters Virtual Assembly Calibrated FEA Pre-processed Model CONTACTS Virtual Static Loading of Paired Components Identification of Contacts Physical Validation Calibration of Contact Parameters Reliable FEA Solution (c) B. Ravi, IIT Bombay 2

3 Paired Component Individual Component FEA Imported Prosthesis Prosthesis Critical components Individual Geometries Paired Geometries FEA Indian Prosthesis Prosthesis Critical components Individual Geometries Paired Geometries FILLET STEM FILLET STEM STEM STEM TWO PIECE TAPERED JOINT TWO PIECE TAPERED JOINT FEA New Prosthesis Prosthesis Critical components Individual Geometries Paired Geometries Stem Testing Virtual Meshing/ Boundary Conditions Element Density and Type CHAMFER STEM Density = Element Quarter of Edge STEM TWO PIECE TAPERED JOINT CONSTRAINT 20 node - Hexahedron Element FORCE FEA Results - HyperWorks Stem Testing Physical Individual Component Testing Paired Component Testing 200 MPa 181 MPa 178 MPa 48 MPa 38 MPa 35 MPa Bending Compression (c) B. Ravi, IIT Bombay 3

4 FEA Validation UTM Standardization of FEA Parameters Physical strain (µε) Loading ( 2600 N) Strain gauge 1 Strain gauge 2 Strain gauge 3 SPECIMEN 1 FEA EXPERIMENTAL ERROR % SPECIMEN 2 FEA EXPERIMENTAL ERROR % SPECIMEN 3 FEA EXPERIMENTAL ERROR % Single Components Standardization of parameters Hexahedron element Boundary conditions Bending Load Paired Components Element size range mm Warpage < 4 Skew < 60 Jacobian < N, 360 N, Highest values during walking Material Law Elastic Law Density 8290 Young s modulus 225 Gpa Poisson s ratio 0.31 Analysis Type Linear Static analysis Contact Slide Type (Relative motion between nodes) Friction Point Bending Photostress FEA Validation Photostress No load 5 N 10 N Strains at 3 points 15 N 20 N Relative FEA % Photoelasticity % Error in Relative Difference =(Pt1-Pt3)(100)/(Pt3) =(Pt1-Pt3)(100)/(Pt3) Difference % (No Load) (5 N) (10 N) (15 N) Imported Prosthesis Indigenous Prosthesis FOS = 5.4 FOS = 7.0 FOS = 10.2 FOS = 6.9 FOS = 8.3 FOS = 1.8 FOS = 1.3 (c) B. Ravi, IIT Bombay 4

5 News Prosthesis Comparison of Static Testing Results FOS = 5.01 FOS = 14.5 FOS of HIGHEST STRESS Component Lowest FOS Prosthesis Imported Indigenous New 5.4 (Femoral Stem) 1.8 (Bumper) 6.9 (Axle) 1.3 (Bumper) 5.0 (Femoral Stem) 2.4 (Poly) FOS = 2.4 Materials used: Ti-6Al-4V UHMWPE Cross sectional view Stress mapping Localised Stress mapping Material Information Stress Comparison Ball & Pin Material UHMWPE Ti-6Al-4V Parts All bushing parts (Bearing Bush, Tibial Poly) Remaining metallic parts Component Material Yield Factor of Permissible Experienced Strength Safety Stress (MPa) Stress (MPa) (MPa) Ball Pin Ti-6Al-4V Bearing Bush UHMWPE (c) B. Ravi, IIT Bombay 5

6 Axial Force (N) Axial Force (N) Tibial Poly Contact Stress Video Testing Dynamic Loading Knee Simulator Testing Machine Wear Results Initial KST-2 (NFTDC) Hydraulic pack, gear box Fixed tibia, hinge design Centering easier than KST-1 Flexion angle & axial load ISO ΔW TP = gm Depth = 0.1mm ΔW CB =0.034gm Wear Results 10K cycles Wear Results 20K cycles Load Pattern cycles run Load Pattern cycles run ΔW TP = gm ΔW TP = gm Time (1 Cycle) 0 Time (1 Cycle) ΔW CB =0.053gm ΔW CB =0.115gm (c) B. Ravi, IIT Bombay 6

7 KST 2.0: TKP Test Results 2 Million As Machined SEM image 1 million cycles SEM image 2 million cycles SEM image SUMMARY FEA Tool for Structural Strength Analysis Standardization of FEA Rapid & Reliable Results Comparison Evaluation of Various Concepts Safety Failure analysis Life, Longevity POLISHING LIKE EFFECT INCREASED WEAR (c) B. Ravi, IIT Bombay 7