lightweight structures

Transcription

1 Calculation methodology for lightweight structures Chalmers University of Technology Göteborg, Sweden Page 1

2 Acknowledgements Chalmers University of Technology,, PhD student Luis Sanchez SP Technical Research Institute of Sweden, Technical Department Building Technology and Mechanics Adjunct Professor Erland Johnson PhD Torsten Sjögren MSc Henrik Snygg Kockums AB/ThyssenKrupp Marine Systems Lic Eng Sven Erik Hellbratt MSc Johan Edvardsson MSc (and PhD student) Måns Håkansson Page 2

3 The LASS project Aluminium hull and composite super structure Page 3

4 Outline Ongoing research projects on lightweight structures Design criteria i Examples of sources of uncertainties Computational methodology Example: tensile test of composite material ii li l i ( IC) h i Digital image correlation (DIC) technique Acoustic emission (AE) measurements Page 4

5 Ongoing research projects on lightweight g structures Chalmers SMT, SP and Kockums Partners in three ongoingresearch projects onlightweight structures res FP7EU project BESST (Breakthrough in European Ship and Shipbuilding Technologies) A holistic life cycle performance assessment onship level will guide the technical developments on system level, clustered in System Groups. The results will be integrated in virtual show cases (ship concepts) demonstrating ti the technical solutions as well as the life cycle impact compared to current designs. Page 5

6 Ongoing research projects on lightweight g structures Lightweight design using composite structures PhD student Måns Håkansson PhD student: Måns Håkansson Objective: To explore the benefits and potential of using composite materials in structures of commercial vessels. Fatigue and ageing of lightweight structures PhD student: Luis Sanchez Objective: To develop numerical models that can mimic the characteristics of virgin, i aged and fti fatigued structures/materials. t t Page 6

7 Design criteria Ultimate tensile/fracture strength Buckling strength Fatigue strength Page 7

8 Examples of sources of uncertainties Physical uncertainties External loads Boundary conditions Geometrical dimensions Fabrication imperfections and residual stresses Material properties Model uncertainties Representation of test/structure by a numerical model Constitutive material model, failure and fracture models Statistical uncertainties Number of tests that have been carried out Representative population of specimens used in the study Hogström et al. (2009) Page 8

9 Examples of sources of uncertainties What motivates uncertainty analysis? Failure mode in real life may not be according to the assumed one during design Load level lat failure is underestimated/overestimated d/ d Unnecessary maintenance and repair costs Component/structure has not been fully optimised with regard to its intended functionality Wiht/ Weight/cost toptimisation i versus strength/buckling/durability th/b /d bilit Page 9

10 Computational methodology For the analysis (design criterion) under consideration: Identify uncertainty sources For each source of uncertainty: Identify all random variables Define the random variables distributions with corresponding expectancy, standard deviation, etc. Select type of assessment method depending on objective of the analysis, such as: Analytical method e.g. eg Gauss approximation formula Finite element analysis Monte Carlo analysis Neural network analysis or genetic algorithm Page 10

11 Example: tensile test of composite material Presentation of recent experimental results and initial numerical analyses Page 11

12 Design criterion and sources of uncertainties Material: carbon fiber reinforced plastic (CFRP) Design criterion: Ultimate t tensile/fracture t strength th Sources of uncertainties: titi Geometrical dimensions Material properties Model uncertainty Page 12

13 Experimental method Digital image correlation (DIC) technique using the ARAMIS system Non contact optical 3D deformation measuring system A surface pattern is applied by spray painting of the specimen s surface The deformation of the pattern is analysed by DIC It analyses, calculates and documents material deformations The analysis results in a 3D strain field image of the analysed volume Page 13

14 DIC compared to standard tensile tests Tensile test with classical measurement techniques: Measures strain (longitudinal not transversal) with an extensometer mean strain over the measuring length Often the extensometer is taken away prior to fracture no good monitoring of the strain at later deformation stages and fracture Tensile test with DIC measurement techniques : Calculates the strain at every point of the test specimen in all directions Localization of strain can be studied Gives the strain up to fracture Virtual extensometers can be put at any place, length and direction after the test has been performed Page 14

15 DIC compared to standard tensile tests x Hogström et al. (2009) Page 15

16 Strain field for 0 CFRP laminate Load ~ 10 kn Global strain ~ 0.38 % Load ~ 30 kn Global strain ~ 1.19 % Load ~ 40 kn Global strain ~ 1.63 % Page 16

17 Results from tensile tests 0 CFRP laminates: Fracture strength: 627±30MPa Strain at fracture: 1.74±0.11 % 45 CFRP laminates: Fracture strength: 606±44 MPa Strain at fracture: 1.80±0.09 % 90 CFRP laminates: Fracture strength: 621±20 MPa Strain at fracture: 174±0 1.74±0.10% Page 17

18 Acoustic emission (AE) measurement Multidirectional 0 DIC strain field for 0 CFRP laminate AE data In composites the AE signals originate from: Fiber break up Debonding Matrix cracking Page 18

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20 E 2 Transition point E 1 Fracture strain Page 20

21 Ongoing work... Model making: Sources of uncertainties: Laminate theory Geometrical dimensions FE model Material properties Constitutive material model Model uncertainty Failure/fracture models Page 21

22 Ongoing work... Fracture strength Buckling strength Fatigue strength Influence from ageing Influence from imperfections Influence from residual stresses Upper, expected and lower limits Models based on physics and statistics Safe designs Page 22