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CompTest 20031 Residual Curing Stresses in Thin [0/90] Unsymmetric Composite Plates Marco Gigliotti°, Michael R. Wisnom, Kevin Potter Department of Aerospace.

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Presentation on theme: "CompTest 20031 Residual Curing Stresses in Thin [0/90] Unsymmetric Composite Plates Marco Gigliotti°, Michael R. Wisnom, Kevin Potter Department of Aerospace."— Presentation transcript:

1 CompTest Residual Curing Stresses in Thin [0/90] Unsymmetric Composite Plates Marco Gigliotti°, Michael R. Wisnom, Kevin Potter Department of Aerospace Engineering, University of Bristol, UK °current address: Département MEM, Ecole des Mines de Saint-Etienne, France contact:

2 CompTest COMPAVS Research Program Uni of Bristol, Airbus UK, QuinetiQ, AugustaWestland, Bombardier Shorts Aim : Understanding, predicting and controlling residual stresses, distortions and variability coming from the cure of high temperature composite parts Understanding of basic phenomena is needed

3 CompTest Introduction 1. Introduction Experimental activity Simulations Conclusions

4 CompTest Main sources of residual curing stresses are: - Cooling (T cure -T room ) - Resin Chemical Shrinkage - Tool interaction - Thermal, degree of cure and V f gradients - …. AUTOCLAVE Tool Laminate Curing cycle t T P Generalities on Residual Curing Stresses AUTOCLAVE MOULDING TECHNIQUE Introduction (1/2) Tg

5 CompTest Introduction (2/2) Use of flat thin [0/90] unsymmetric samples Aim : Elimination or minimisation of many parameters, such as: - thermal, degree of cure and V f gradients through the thickness - cure shrinkage - tool interaction Investigation on the residual deformation of partially or totally cured samples Method :

6 CompTest Introduction 2.Experimental activity 2. Experimental activity Simulations Conclusions

7 CompTest Experimental activity (1/13) Physical principles : What we measure : - the curvature k after partial or total cure - the stress free temperature T sf, at which samples are flat - intermediate curvatures between T room and T sf 0°0°/90° TT 90°

8 CompTest Experimental activity (2/13) Physical principles : T sf  T g T Strain/Curvature T initial > T g Cooldown + Reheating T initial tT Tg

9 CompTest Experimental activity (3/13) Physical principles : A: only thermoelastic strains are in the structure B: non-thermoelastic strains are in the structure T initial T T initial  T g Strain/Curvature A B Cooldown tT Tg

10 CompTest Experimental activity (4/13) Physical principles : A: only thermoelastic strains are in the structure B: non-thermoelastic strains are in the structure T initial  T sf T initial  T g T Strain/Curvature T sf > T initial A B Reheating tT Tg

11 CompTest Experimental activity (5/13) Measurement apparatus : oven CCD video-camera PC L’ h t then k 

12 CompTest Experimental activity (6/13) Interrupted Cure Cycles (ICC) : material: AS4/8552, oven curingsamples: 300mm x 30mm x 1mm

13 CompTest Experimental activity (7/13) Results : Residual curvatures

14 CompTest Experimental activity (8/13) Results : Stress free temperatures The reaction rate slows down at the vitrification point T sf > T cure for samples cured beyond vitrification

15 CompTest Experimental activity (9/13) Results : Reheating sample B T sf The increase of T sf indicates post-cure

16 CompTest Experimental activity (10/13) Results : Post curing effects

17 CompTest Experimental activity (11/13) Results : Reheating curves Linear behaviour, curves have the same slope

18 CompTest Experimental activity (12/13) Results : Tool effect No significant differences (level of confidence 5%) Autoclave cured samples

19 CompTest Experimental activity (13/13) Results : Tool effect No significant differences (level of confidence 5%) Oven cured samples

20 CompTest Introduction Experimental activity 3.Simulations 3. Simulations Conclusions

21 CompTest Simulations (1/6) Model generalities A FE Abaqus code is used for modelling the thermoelastic behaviour of 0/90 thin plates during the cooldown from the stress free temperature - shell 4 node elements with reduced integration (S4R) - temperature differentials applied uniformly in one static step - option nlgeom (small strain, moderate rotations) Material properties AS4/8552

22 CompTest Simulations (2/6) Remarks on the thermoelastic behaviour of 0/90 thin plates: - according to the Classical Lamination Theory (small strain, small displacement) deformed shapes are saddles - due to large displacements, plates in some range of in-plane dimensions (or thickness) exhibit cylindrical deformed shapes and/or strong non-linear behaviour with temperature

23 CompTest Simulations (3/6) Remarks on the thermoelastic behaviour of 0/90 thin plates: For narrow plates (AR>10) the deformed shape is almost a saddle with curvatures which vary almost linearly with temperature. AR>10 principal curvature lateral bow For such samples, predictions from CLT are good

24 CompTest Simulations (4/6) Results :

25 CompTest Simulations (5/6) Results :  3* /°C The offset indicates the non-thermoelastic portion of residual curvature (< 5%)

26 CompTest Simulations (6/6) Results : HTA/913C Composite system (cured at 120°C)

27 CompTest Introduction Experimental activity Simulations 4.Conclusions 4. Conclusions

28 CompTest Conclusions (1/1) residual curvature and stress free temperature monitoring gives exhaustive information about the cure process of composites the stress free temperature of AS4/8552 samples cured beyond the vitrification point is found to be higher than T cure the stress free temperature of HTA/913C samples is found to be equal to T cure simulations allow us to find values of  T (below T g ) and to estimate non-thermoelastic sources of residual stress for the AS4/8552 non-thermoelastic sources of stress may be ascribed to resin chemical shrinkage


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