fibermatrix 1-8-08 - Microscale Testing of FiberMatrix...

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1 Microscale Testing of Fiber- Matrix Interactions Douglas J. Gardner Professor Wood-Polymer Hybrid Composites William T. Y. Tze Assistant Professor University of Minnesota Analytical Techniques • Fiber Fragmentation (Critical Fiber Length) • Fiber Pull-out • Micro-debond • Dynamic Mechanical Analysis • Inverse gas chromatography • Raman Spectroscopy
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2 Fiber Fragmentation • Advantages – Direct measure of Fiber/Polymer interface strength – Stress optical analysis • Disadvantages – Requires ductile matrix polymer – Requires information on in situ fiber strength Fiber Fragmentation c f c l d 2 σ τ= Under load, the fiber will fracture decreasing the segment size until a critical length, lc, is reached which is too short to transfer the stress to break the fiber. The critical fiber length is related to the interfacial shear strength τ c by σ f = the fiber tensile strength and d the fiber diameter
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3 Fiber Pull-out • Advantages – Indirect measure of fiber/polymer interface strength – Information on interfacial failure mechanism • Disadvantages – Sample preparation with fibers is difficult – Tapered fiber end complicates data analysis Fiber Pull-out r G E n f f d = τ The interfacial debonding shear strength τ d for the fracture process can be obtained as follows: Where E f = the fiber modulus G i = the work of the interphase, r = the fiber radius, n = constant related to the properties of the two components
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4 Micro-debond • Advantages – Eliminates tapered end problems – Fiber strength information not required – Relatively fast and simple • Disadvantages – Fiber failure may be dominant for strong interface Micro-debond l D P π τ max max = The fiber/matrix interfacial strength ( τ max ) is estimated from the relation: Where P max is the maximum load D is the fiber diameter l is the embedded fiber length
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5 Typical Micro-debond Test Results Methods To Study Adhesion • Dynamic Mechanical Analysis • Surface energy characterization – contact angle analysis – inverse gas chromatography • Micro-bond testing • Raman Spectroscopy
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6 Dynamic Mechanical Analysis • Mechanical properties over a wide range of temperatures • Sub ambient to 500 C • Measure Tg and crystalline transitions in polymers • Interfacial information in composites •T a n δ peak at -40 C is Tg of polyurethane phase • Unmodified TMP fiber is more reactive in this system and exhibits a high temp. shoulder at -25 to 10 C. • The influence of this fiber/polymer interphase exhibits a higher storage modulus.
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7 Synopsis of dissertation project Surface treatments 3 1. Inverse gas chromatography • Monitor surface treatments • Deduce fiber/matrix interactions 2. Raman spectroscopy • Identify strain and stress distributions • Infer levels of practical adhesion 1. Inverse gas chromatography (IGC) studies: Inference of fiber/matrix acid- base interactions
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8 Modification of cellulose fibers
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This note was uploaded on 12/21/2010 for the course AEWC 430 taught by Professor Dg during the Fall '08 term at University of Maine Orono .

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fibermatrix 1-8-08 - Microscale Testing of FiberMatrix...

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