Structural Adhesive Distribution

Transcript

1 Structural Adhesive Distribution Using NASTRAN SOL200 Topology Optimization A case study in automotive development MSC University Roadshow Politecnicodi Torino -June Maurizio Chiarbonello Mirjana Milic Paolo Pagella Italdesign Giugiaro

2 Introduction Why use structural adhesives in Automotive? Benefits: Faster, easier production process. Possibility of joining different materials with different thicknesses. Sealing capability, and reduction of the galvanic corrosion. High fatigue resistance. Disadvantages: The flanges surfaces must be prepared. Problems in disassembling. Long polymerization cycles at high temperature Problems in reliability for the performance in aging.

3 Introduction Topology optimization analysis to support design department in adhesive positioning Constraints on adhesive positioning: o Feasibility o Costs o Experience on previous development phases Request to reduce the amount of adhesive, concentrating it in the zones with higher sensitivity on the performance. INPUT from design department Topology Optimization Procedure OUTPUT to design department Clear and easy-to-read map of the zones where to add adhesive lines. Prompt answer to satisfy the development planning.

4 Metodology and procedure: Case study definition Topology optimization analysis target Reducing the amount of adhesives, containing the loss in static and modal performance. For this case study only the torsional behavior has been taken into account Optimization phase: Setup of the optimization objective, constraints and parameters, run of the analysis and post-processing Model setup: o Body in gray Loadcases: o Static torsion Static torsion stiffness o Modal analysis 1 st torsion mode frequency Verification phase: Run of a model with the optimized glue distribution and setup of a report for the design department Model setup: o TB (Trimmed body model) Loadcases: o Modal analysis 1 st torsion mode frequency

5 Metodology and procedure: Pre-processing Adhesive modeling: HEXA Element + RBE3 Connection Hexa: o Length: 10 mm o Width: 10 mm o Thickness: 0.2 mm o Collapsed nodes for adjacent hexa RBE3: o 1 dependent node on hexa element o 4 independent nodes on shell elements o Nodes weight calculated with area ratio Initial length of adhesives on the body: Up to 100 m

6 Metodology and procedure: Pre-processing Optimization analysis setup Modal analysis (MODES): o Design Objective (DESOBJ): Maximize the 1 st Torsion mode frequency (FREQ) o Design Constraints (DESSUB o DESGLB): Fractional mass (FRMASS) 1 st Bending mode freqency (FREQ) Static analysis (STATICS): o Design Objective (DESOBJ): Minimize compliance (COMP) o Design Constraints (DESSUB o DESGLB): Fractional mass (FRMASS) Torsional stiffness value (DEQATN)

7 Metodology and procedure: Pre-processing Topology optimization analyzed parameters: Fractional mass starting value (TOPVAR XINIT): Value of the fractional mass of the optimized components at the first optimization cycle. It is suggested to use the value of the constraint to avoid violated constraint at the start of the optimization. Penalty factor (TOPVAR POWER): Factor used in relation between topology design variable and element Young modulus ρ = ρ x E = E 0 0 x P $-----1><-----2><-----3><-----4><-----5><-----6><-----7><-----8><-----9> TOPVAR 1 OPT PSOLID SYM ZX $-----1><-----2><-----3><-----4><-----5><-----6><-----7><-----8><-----9> Symmetry constraint (TOPVAR SYM): To enforce the XZ plane symmetry in the adhesive distribution. Convergence parameters (DOPTPRM GMAX, DESMAX, CONV1, ): Parameters to control the convergence of the optimization process or the maximum number of cycles. They must be analyzed to have good results in short run times.

8 Metodology and procedure: Pre-processing Studying the topology optimization parameters Optimization parameter set: o Starting fractional mass: 1.0 o Target fractional mass: 0.2 o Penalty factor: 4 o Simmetry constraints: XZ This parameter set gives the highest performance with a good distribution of the element mass fraction and an high reduction of the total adhesive length NOTE: Results from the static loadcase

9 Metodology and procedure: Post-processing NOTE: Results from the modal loadcase Masking Single Threshold: element filter Average post processing: the mass fraction value of each element is averaged with the mass fraction of the adjacent elements. The value of the mass fraction of the element itself has a weight value of 2 in the average calculation. Averaging the results and masking with a contour threshold a clearer map can be obtained, and the high sensitive zones become more evident Averaged Mass fraction contour result Mass fraction contour result Single element filter: the filter masks All the elements with mass fraction lower than All the elements with mass fraction higher than 0.995, and with adjacent elements with mass fraction lower than The aim of the filter is to point out and isolate the high sensitive adhesive lines with a length of more than 1 element. Masking Single Threshold: element filter 0.995

10 Metodology and procedure: Post-processing Verification model Optimized adhesive distribution proposal Modal Topology Optimization Result Analyst engineering judgment Static Topology Optimization Result

11 Metodology and procedure: Verification step 5% of the initial adhesive 25% of the initial adhesive

12 Metodology and procedure CAE Report to Construction Dept.

13 Structural Adhesive Distribution Using NASTRAN SOL200 Topology Optimization A case study in automotive development Questions and (..hopefully..) answers. Thank you. Mirjana Milic mirjana.milic@italdesign.it Maurizio Chiarbonello maurizio.chiarbonello@italdesign.it Italdesign Giugiaro