A Novel Full-scale Validation of Thermal Degradation of Polymer Foam Cored Sandwich Structures R.K. Fruehmann, J.M. Dulieu-Barton, O.T. Thomsen

2 Outline Background Review of design brief Design for mechanical boundary conditions Thermal gradient measurement Validation tests Conclusions

3 Background EC1EC1 EC2EC2 E C1 < E C2 PVC foam core Metal or composite face sheet T out T in

4 Background Thermal degradation of PVC foam stiffness

5 Background Face sheet displacement at different loads Force / mid-span displacement results from 3 different models (Frostig et al. 2004) High-order sandwich panel theory (HSAPT) predicts strongly non-linear interactions between mechanical and thermal loads. Strongly non-linear and unstable load response and limit point behaviour in some cases. Load response strongly sensitive to boundary conditions. Experimental validation is required.

6 Design Brief Mechanical 1.Simply supported 2.Lower corner fixed – free to rotate 3.Fully clamped Thermal 1.Uniform across width 2.Linear through thickness Measurement 1.Non-contact (DIC & IR) Condition 1 Condition 2 Condition 3

7 Design space Loading frame Actuator 3 point bend rig Load cell

8 Design – End constraint fixture Platform Fork Specimen clamp Axis CG Counter balance

9 Face sheet thickness Design – End constraint fixture Axis Height adjustment Platform height

10 Design – Boundary condition 3

11 Design – Boundary condition 3 Main platform shaft Platform Axis Fixation bolt Vertical supports

12 Design – General arrangement Radiator Insulation Mirror to monitor top face sheet Mirror to monitor bottom face sheet

13 Thermal gradient

14 Thermal gradient

15 Thermal gradient

16 Thermal gradient

17 Thermal gradient Thermal degradation of PVC foam stiffness

18 Thermal gradient Thermal degradation of PVC foam stiffness

19 Thermal gradient Thermal degradation of PVC foam stiffness

20 Validation tests Specimen dimensions: –450 x 50 x 27 mm –1 mm thick aluminium face sheets –25 mm thick H100 PVC foam Temperature profile across the width and through the thickness Recorded the deformations at the mid-span using DIC

21 Thermal gradient 1 second 5 seconds 10 seconds 15 seconds

22 Thermal gradient

23 Mid-span deformation 1 2

24 Mid-span deformation

25 Mid-span deformation

26 Mid-span deformation Careful consideration of face sheet failure loads to avoid indentation failure preceding geometric non-linearity.

27 Conclusions Thermal and mechanical boundary conditions have been achieved. Mid-span deflections correspond qualitatively with model predictions for the simply supported case.

28 Future challenges Optimise specimen configuration (material and geometry) to remain in the elastic region. Obtain DIC data from the thin face sheets. Obtain DIC data below the roller during indentation.

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