Laboratory of Applied Mechanics and Reliability: Research Activities

Transcription

1 Laboratory of Applied Mechanics and Reliability: Research Activities Experimental mechanics Static, cyclic & fatigue testing, uniaxial / biaxial test, climatic chamber (- 10 C to 250 C). Vibration testing for reliability analysis and characterization Bio-material testing: bone & ligament tensile testing (hydrostatic pressure, controlled environment). J.Cugnoni, joel.cugnoni@epfl.ch 1

2 Finite element simulation & design optimization Stresses in a composite insulator subjected to bending (plasticity, contacts, composites, SEFAG AG) Non-linear static, temperature dependent elasto-visco-plasticity & contact mechanics (Abaqus Standard / TACT) Non-linear transient analysis (Abaqus Explicit): impacts, drop tests Vibration and modal dynamics: identification & optimization (MAFE) Simulation of composite structures (static / dynamic) and design optimization (failure stress, residual stresses) Bio materials: characterization of constitutive relations (bone, ligament, muscle), non-linear simulation & optimization (prosthetics) Deformation of a race catamaran (carbon-nomex sandwich, Decision D35) J.Cugnoni, joel.cugnoni@epfl.ch 2

3 Innovative measurement / computing technologies Deformation in a lead-free solder joint (DIC) Experimental data Mixed num. / exp. identification Initial parameters FE Solution Error norm δ < δ min Identified parameters δ > δ min Deformation of a cracked epoxy plate (ESPI) Optimization 0.5 mm Mixed num/exp identification for in-situ characterization of material properties embedded Bragg fiber sensors (OLCR) for measuring strain/stress distributions inside polymeric materials in-plane and out-of-plane electronic speckle pattern interferometry (ESPI, resolution < 0.3μm) versatile 2D digital image correlation (DIC, resolution up to 0.1μm) mixed numerical experimental identification for in-situ characterization of materials multi-parametric finite element analysis & automated design optimization Custom finite element softwares and tools for advanced simulations topics (adhesioncontact models, damping of thick composite shells, ) J.Cugnoni, joel.cugnoni@epfl.ch 3

4 On-going projects Composite brazing material for ceramic-metal joints Sandwich panel FEA Lead-free solder joints: simulation & testing Deformation and damage of lead-free solder joints (in collaboration with EMPA, part of COST Action 531 Lead-free solders) Ceramic-metal joints produced by novell brazing fillers (in collaboration with EMPA) Collaboration with EMPA on the development of particle reinforced lead-free solder materials Characterization of the elastic and damping properties in composite shells Coupling adhesion and friction for modeling the interfaces in composite materials Crack bridging and crack fiber interaction in composites Experimental stress analysis using optical fiber sensors Experimental and numerical studies in dental biomechanics Durability of composite-metal joints: optimization of composite insulators (KTI / SEFAG AG) Design and optimization of ultralight sandwich-core snowboards (KTI / Nidecker SA) J.Cugnoni, joel.cugnoni@epfl.ch 4

5 Project: deformation and damage of lead-free solder joints Objectives Nature of Irreversible Deformations Methodology Interface Micro Structure Micro Structure Analysis Design of Experiments Experimental Optical Strain Measurement Thermomechanical History Constitutive Equations Manufacturing Size / Constraining Effects Constitutive Law Type Finite Element Model Modelling Mixed Num. / Exp. Identification J.Cugnoni, joel.cugnoni@epfl.ch 5

6 Problem description Mechanical properties of lead-free solder joints are highly process dependant In-situ characterization of the mechanical properties in real solder joints can provide accurate data for modelling and optimizing the reliability of solder joints Stress / strain fields inside the solder joints are very heterogeneous and classical characterization techniques are not suitable (no analytical solution) By combining the advantages of finite element modelling and digital image correlation, a novell mixed numerical experimental identification procedure can be used to extract accurate constitutive properties of the solder material from a real solder joint J.Cugnoni, joel.cugnoni@epfl.ch 6

7 In-situ characterization of solder properties Numerical experiment Finite element model with initial constitutive parameters (elasto plasticity) Real experiment Tensile test on a real joint, DIC strain measurement (optical microscopy) 200μm Optimization method Fit the constitutive parameters of FEM on experimental data (iterative non-linear leastsquare minimization) Measured & simulated load displacement curves J.Cugnoni, joel.cugnoni@epfl.ch 7

8 Identification results Load - displacement curves Red: identified load-displ. curve Black: measured load-displ. curve Relative errors Identified parameters: Young s modulus, yield stress, ultimate stress, exponential hardening rate Solution time: ~1h / 40 FE solutions required to identify the material properties Accuracy: max error +/-4% on load displacement curve J.Cugnoni, joel.cugnoni@epfl.ch 8

9 Evolution of plastic deformations FEA 5.00E+07 Stress-strain curve 1B 4.50E E E E+07 stress 2.50E E E+07 Exp 1.00E E E strain J.Cugnoni, joel.cugnoni@epfl.ch 9

10 Effects of constraints & processing 6.00E+07 Comparison of stress-strain curves 5.00E+07 1 Stress (Pa) 4.00E E E+07 1) Effects of the constraints imposed by the substrates (geometry dependant): comparison of the joint avg.stress / avg.strain curve and the actual solder stressstrain curve 2) Effects of the processing parameters: comparison of bulk & actual solder properties 1.00E E Strain (-) Bulk specimen Joint properties Identified constitutive law J.Cugnoni, joel.cugnoni@epfl.ch 10

11 FEA of plastic deformations in a solder joint Average Strain: 2% Max Strain: 10% 1 Outside Inside 2 Two plastic deformation regions: 1) At the interface on the outside surface 2) In the center of the joint J.Cugnoni, joel.cugnoni@epfl.ch 11

12 Plasticity - Damage evolution: remarks Need to distinguish two phenomena: Elasto-plastic deformation: global behavior of the solder joint Failure : local behavior, depends on the interfacial properties Evolution during testing: Plasticity is homogeneous up to 90% of max load => most of the stress-strain curve can be used for characterization Failure in the last 15 seconds of the test: concentration of deformations in the corner & on the interface crack propagation: 1 crack on each interface (A), 1 single crack (B) A B J.Cugnoni, joel.cugnoni@epfl.ch 12

13 Next steps in the present project Sn-4.0Ag-0.5Cu: Evaluate the possible size effects Identify the dependency of the mechanical properties wrt strain rate (viscous effects) & temperature Particle-reinforced lead-free solder (with EMPA): Sn-4.0Ag-0.5Cu + 5% Cu or Ni particles Improvement of the processing parameters / material composition, study of the microstructure (EMPA) Testing, in-situ characterization of the mechanical properties, modelling of the composite solder material, FE studies (EPFL) J.Cugnoni, joel.cugnoni@epfl.ch 13

14 Future developments Design / process validation Realistic Experiment (DIC) FE Analysis & optimization Mixed num-exp identification: realistic properties Industrial aspects: Apply the in-situ characterization method (DIC / mixed num./exp. Identification) to a real industrial package Determination of the mechanical properties of a solder joint unter realistic loading conditions (power-cycles) FE simulation, parametric study & optimization of a real package (geometry / material / processing) under realistic loading conditions (thermocycling, vibrations, ) J.Cugnoni, joel.cugnoni@epfl.ch 14