Fiber Patch Placement

Transcription

1 Fiber Patch Placement Interaction of lay-up pattern and mechanical performance of the composite Bernhard Horn A Comprehensive Approach to Carbon Composites Technology Symposium on the occasion of the 5 th anniversary of the Institute for Carbon Composites Research Campus Garching, September 11 th - 12 th 2014 Institute for Carbon Composites donated by

2 Agenda Motivation Introduction to FPP laminate design Influence of the patch pattern on tensile strength Approach to predict the tensile strength of a FPP laminate Summery and Outlook 2

3 Agenda Motivation Introduction to FPP laminate design Influence of the patch pattern on tensile strength Approach to predict the tensile strength of a FPP laminate Summery and Outlook 3

4 Motivation Idea of lightweight design Maximum lightweight design requires load path optimized design Fig. 1: Load paths in a component [1] Fig. 2: Snowboard reinforcement Variable angle tow composites [1] Mattheck, C. Design in der Natur: Der Baum als Lehrmeister, 3rd edn. Freiburg im Breisgau;

5 Motivation Limitations of typical automated manufacturing processes using UD fibers Uneven thickness distribution Buckling on inner radius Tow gap Fig. 1: TFP: Uneven thickness distribution and fiber misalignment for steered roving cf. [1] Fig. 2: AFP: Buckling of steered tapes cf. [2] Fig. 3: Curved endless fibers In-plane bending deformation reduces the design flexibility and weakens the mechanical properties [1] Kim BC. Limitations of Fibre Placement Techniques for Variable Angle Tow Composites and their process-induced Defects; 2011 [2] Blom AW. Structural Performance of Fiber-Placed, Variable-Stiffness Composite Conical and Cylindrical Shells. Dissertation. Delft;

6 Motivation Different approach to reduce the process induced defects Use of long fiber patches instead of endless fibers Fig. 1: Curved endless fibers Fig. 2: Cut fiber patches Fig. 3: Small radi possible due to cut fiber patches High flexibility for load path optimized layup design Butt splices reduce the maximum strength of the composite Optimization of butt splices distribution necessary 6

7 Motivation Video demonstration 6 steps of the FPP-process: 1. Feeding dry, bindered tape 2. Cutting tape into patches 3. Quality inspection of patches 4. Picking up patches 5. Checking patch position at gripper 6. Positioning patch (1) (2) (3) (4&5) (6) Technical Specifications: Patching rate: Performance: up to 1 Patch/s up to 500 g/h 7

8 Agenda Motivation Introduction to FPP laminate design Influence of the patch pattern on tensile strength Approach to predict the tensile strength of a FPP laminate Summery and Outlook 8

9 Introduction to FPP laminate design Structure of a FPP laminate Each laminate consists of a specific amount of patch pattern FPP-Laminate Patch pattern Butt splice Fiber patch Sublayer Patch pattern Fiber orientation 9

10 patch pattern Introduction to FPP laminate design Structure of a patch pattern Assumption Crack propagation F [N] F [N] Fiber orientation Design characteristics Each sublayer can be shifted in-plane Position of butt splice in thickness direction can vary σ σ endless fiber σ resin Overall aim: Crack length should be maximized ε c.f. Oliver Meyer. Kurzfaser-Preform-Technologie zur kraftflussgerechten Herstellung von Faserverbundbauteilen. Dissertation. Stuttgart;

11 Agenda Motivation Introduction to FPP laminate design Influence of the patch pattern on tensile strength Approach to predict the tensile strength of a FPP laminate Summery and Outlook 11

12 Influence of the patch pattern on tensile strength Influence of the critical fiber overlap length The layup problem can be visualized as a double lap joint Redirection of force flow from one layer to another y z x l overlap Patch Postulation [1]: Critical overlap length depends on fiber architecture F σ F Expected laminate failure [1] τ l overlap < l crit l overlap > l crit Fiber pull out Fiberfracture Fig. 1: Schematic stress and shear distribution in a double lap joint For maximum strength of the laminate: overlap length > critical fiber length [1] Och G. Berechnung der Elastizitätskonstanten und der Zugfestigkeit: MBB Technische Niederschrift;

13 patch pattern Influence of the patch pattern on tensile strength Strength model for FPP-laminates by O. Meyer [1] (1/2) Restrictions l overlap > l crit l crack = max Prediction: Every section with a butt splice has the same probability to fail section with butt splice patch butt splice sublayer There are always n-1 sublayers which can transfer the load in a pattern σ t,composite = n 1 n σ t,fiber for n = number of sublayer and σ t,fiber σ t,resin [1] Oliver Meyer. Kurzfaser-Preform-Technologie zur kraftflussgerechten Herstellung von Faserverbundbauteilen. Dissertation. Stuttgart;

14 Maximum Maximum Strength Strength Influence of the patch pattern on tensile strength Strength model for FPP-lamintes by O. Meyer [1] (2/2) σ t,composite = n 1 n σ t,fiber 100% 90% 80% 70% 60% 50% 40% 30% 20% 10% 0% Amount of sublayer per patch pattern Experimental Results continuous fiber Model by Mayer Fig. 1: Influence of sublayer on maximum strength [2] Fig. 2: Failure for different patch pattern [1] Model by Mayer overpredicts the maximum tensile strength [1] Oliver Meyer. Kurzfaser-Preform-Technologie zur kraftflussgerechten Herstellung von Faserverbundbauteilen. Dissertation. Stuttgart; 2008 [2] unpublished LCC bachelor thesis: 2012 Philipp Stahl, Untersuchungen der mechanischen kennwerte von unidirektionalm Faserverbundmaterial erstellt im FPP-Prozess 14

15 Agenda Motivation Introduction to FPP laminate design Influence of the patch pattern on tensile strength Approach to predict the tensile strength of a FPP laminate Summery and Outlook 15

16 Approach to predict the tensile strength of a FPP laminate New approach to predict maximum tensile strength for straight patch path Assumption by Mayer Every layer has the same contribution to the strength of the composite New approach considers two main influencing factor Overlap length for each sublayer l 4,5 l 3,4 Influence of butt splice with each other z y x l 1,2 l 2,3 Quality-Value QL z Weighting -Value G z [unpublished LCC diploma thesis: 2014, Yannik Blößl, Untersuchungen zur Qualitätsbewertung der Patchanordnung von unidirektionalem FPP-Material ] 16

17 Quality function Weighting function Scaling factor Approach to predict the tensile strength of a FPP laminate Transformation of approach into a formula Consideration of overlap length Consideration of butt splices in z-direction Material properties Quality-Value QL z Weighting -Value G z Scaling-Factor S Material Overlap length l z Empirical finding: Asymptotic behavior for higher overlap length Distance between butt splices Assumption: Decreasing influence for higher distance between butt splices Material Empirical value Estimated maximum tensile strength: X tensile = S Material z max (G z QL Z ) z=1 17

18 Maximum Strength Approach to predict the tensile strength of a FPP laminate Comparison of both models with experimental results 100% 90% 80% 70% 60% 50% 40% 30% 20% 10% 0% Influence of the amount of sublayer on maximum strength Amount of sublayer per patch pattern Experimental Results Model by Mayer New Approach New prediction of maximum strength leads to better results Further investigation for different materials necessary 18

19 Agenda Motivation Introduction to FPP laminate design Influence of the patch pattern on tensile strength Approach to predict the tensile strength of a FPP laminate Summery and Outlook 19

20 Quality function Weighting function Scaling factor Maximum Strength Summary & Outlook Summary Patch pattern influences the tensile strength of the composite New approach includes overlap length and butt splice distribution in z-direction for each sublayer New model and experimental results show a high similarity Consideration of overlap length Consideration of butt splices in z-directionmaterial properties 100% Influence of the amount of sublayer on maximum strength Quality-Value QL z Weighting -Value G z Scaling-Factor S Material 50% Overlap length l z Distance between of butt splices Material 0% Amount of sublayer per patch pattern Experimental Results Model by Mayer 20

21 Summery and Outlook Outlook Understanding of the failure mechanism and their contribution to maximum tensile strength Validation for different material combinations Expansion of the model for curvilinear patch path 21

22 Summery and Outlook Project Patchwork Key facts Government-funded project to transfer the FPP technology into commercial applications (EXIST Forschungstransfer) Focus on individual components and tailored reinforcement layers Automated production of geometrically-complex and high-performance components Tailored reinforcement layers in combination with other preforming technologies Engineering objectives CAE Preforming Production Injection CFR component Contact / Info Dipl.-Ing. Felix Michl michl@lcc.mw.tum.de Tel: Method for efficient simulation and optimization of FPP structures Automated handling of FPP-preform and automated resin injection process The team is currently looking for prototypes to demonstrate the unique benefits of FPP in commercial applications! Objective: develop a continuous process chain to leverage the FPP technology in automated serial productions 22

23 Contact Bernhard Horn Room Tel Fax / / horn@lcc.mw.tum.de Address Technische Universität München Institute for Carbon Composites Boltzmannstraße Garching Institute for Carbon Composites donated by 23