SR 1460 Effect of welded properties on Aluminum Structures Progress Report 11/25/09

1. SR 1460Effect of welded properties on Aluminum StructuresProgress Report11/25/09 Dr. Pradeep Sensharma & Joey Harrington BMT Designers & Planners psensharma@dandp.com 703 920 7070 x 275 Dr. Matt Collette University of Michigan mdcoll@umich.edu (734) 764-8422

2. Agenda • Objective • Tasks • Schedule • Literature Survey • Failure Criteria • Stress-Strain Curves • Finite Element Models • Results • Future Work

3. Objective The goal of this project is to provide a basis for design of aluminum structures that will minimize the penalty on scantling selection Study all possible methods of modeling aluminum stiffened plate structure Provide basis for modification to existing design standard

4. Tasks Task 1 - Develop Project Plan Based on the SOW Task2 - Perform literature survey Task 3 - Develop Matrix of Plate-Stiffener Combinations to be analyzed Task 4 - Develop Stress-Strain relationship Task 5 – Develop & Analyze FE Models Task 6 – Volumetric Yield strength using Dr. Paik’s formula Task 7 – Analyze results & Recommend changes to existing design standard Task 8 – Prepare Final report

5. Schedule (cont.)

6. Schedule

7. Finite Element Models Matrix of Plate-Stiffener Combinations to be analyzed

8. Compressive Load • Tabulated results shown in next four slides • Observation • Modeling entire structure as HAZ is extremely conservative. • In most cases modeling entire structure with Base Metal properties gives about 10% higher strength than Combined models (Base + HAZ) for conventional model. • Extruded models have higher strength than conventional models • Variation in strength prediction is large between models for extruded case

9. Results (compressive load)

10. Results (cont.)

11. Results (cont.)

12. Results (cont.)

13. Preliminary ObservationCompressive Load • Is it possible to model aluminum structure as base metal with reduced proof stress (about 10%)?

14. Preliminary ObservationCompressive Load • Developed new Stress-Strain curve for AL5083 and AL6082 by reducing proof stress by 10% • Analyzed models 1 through 8 using this stress-strain curve with no HAZ • Results with Modified stress-strain curve compared against the combined model (base + HAZ) in next two slides

15. Results with Modified Stress-Strain Curve

16. Results with Modified Stress-Strain Curve

17. Results with Modified Stress-Strain Curve

18. Compressive Load (cont) • In early stages of design, aluminum structure can be modeled as base metal with reduced proof stress (about 10%). This will avoid time consuming analysis of fine mesh models with small HAZ elements. • Dr. Paik’s empirical formula compares well with FEA and may also be used in the early stages design. • In critical areas, structure should be modeled as combination of base metal and HAZ.

19. Failure Criteria for Tensile & bending Loads • Tensile and bending loads – what failure criteria? • Compressive loads reach distinct peak – well defined ultimate strength • Tensile and bending loads – distinct peak may not be present • When to stop analysis? • Fracture of weld – difficult without solid element or enriched shell-element model – not practical • Limiting stress • Limiting strain or overall deflection • Stress is current acceptance criteria by Classification societies and used in this study

20. Tensile Load Case • Run analysis with base, base + HAZ, all HAZ models • 36 models • Applied displacement range from 10-20mm • Compared the overall tensile force that causes a fixed portion of the local material’s proof stress to be reached anywhere in the model • Average stress versus strains are graphed for all 12 models (next 12 slides) along with Yield Point

21. Results – Tensile Load

22. Results (cont.)

23. Results (cont.)

24. Results (cont.)

25. Results (cont.)

26. Results (cont.)

27. Results (cont.)

28. Results (cont.)

29. Results (cont.)

30. Results (cont.)

31. Results (cont.)

32. Results (cont.)

33. Results – Tensile Load

34. Results – Tensile Load

35. Tensile Load (cont) • Results for Models 1- 8 show small difference between combined and base model (max 6%). • Modeling with properties of HAZ is very conservative (17%-30%). • Results for Models 9 – 12 (AL 6082) indicate large differences depending on the model properties. • In early stages of design, aluminum structure can be modeled as base metal with reduced proof stress (about 10%). This will give slightly conservative results.

36. Pressure Load Case • Run analysis with base, base + HAZ, all HAZ models • 36 models • Applied Pressure range from 0.1 – 0.2 N/mm^2 • Compared overall pressure that causes a fixed portion of the local material’s proof stress to be reached anywhere in the model

37. Results – Lateral pressure

38. Results – Lateral pressure

39. Pressure Load (cont) • Results for Models 1- 8 indicate about 10% difference between combined and base model. • Modeling with properties of HAZ is again very conservative (10%-30%). • Results for Models 9 – 12 (AL 6082) indicate large differences depending on the model properties. • In early stages of design, aluminum structure can be modeled as base metal with reduced proof stress (about 10%).

40. Future Work • Further study to separate impact of material and weld location for 6082. • Study effect of combined axial and lateral loads. • Perform experiment under tensile, lateral and combined loads.

41. Thank You