LECTURE #1 :3.11 MECHANICS OF MATERIALS F02INSTRUCTOR : Professor Christine OrtizOFFICE : 13-4022 PHONE : 452-3084WWW : http://web.mit.edu/cortiz/www• COURSE OVERVIEW• INTRODUCTION TO MECHANICS OF MATERIALSMechanical Properties of MaterialsCOMPRESSIONTENSION(*squeezing)(*stretching)(*tearing)BENDING(*flexure)TORSION(*twisting)Why Study Mechanics of Materials?Uniaxial Mechanical Testing(*http://www.me.udel.edu/~tierney/mechanics.html#+/- 45o Tension)TENSIONCOMPRESSIONUniaxial Tensile Testing(*http://www.me.udel.edu/~tierney/mechanics.html#+/- 45o Tension)samples are made from thesame exact material???Composite Fracture Surfacehttp://www.fpchem.com/fap_5a-en_fig.html#fig2aShort-glass-fiber-reinforced homo-polypropylene. Conventional fiber sizing composition. SEM micrograph of the (tensile) fracture surface (average fiber diameter = 13 microns).Microstructure of Trochus Niloticus(Gastropod Mollusk)5 different types of microscopic layers observable:● Outermost: periostracum, a thin organic layer composed mainly of sclerotized protein● Prismatic (aragonite+calcite)● Laminar columnar, nacreous (aragonite)● Laminar foliated (argonite+calcite)● Innermost : irregular crossed-lamellar (calcite)prismaticlayercolumnarnacreouslayerTrochus NiloticusAFM Image (4 µm)SEM imagesNacreous (mother of pearl)columnar microstructure● ~95 wt% polygonal to rounded aragonite (a form of CaCO3) single crystal tablets in parallel sheets (Carter and Clark, 1985. Stucky, 1998)● Coinciding centers determine the nucleation site of the overlying tablet (Mutzei, 1980)● Mineral is continuous through bulk via c-axis bridges (Stucky, 1998) ● Up to 5 wt% biomacromolecules, nm-thick layer between ceramic plates (Wang, 2001) also within plates (Morse, 1996)SEM : top viewrounded polygonal ceramic platesSEM : side view ceramic microlaminate columnar structured = = = = 5.8 ± 0.4 µµµµmt = = = = 0.87 ± 0.07 µµµµmMicrostructure of Trochus Niloticus(Gastropod Mollusk)Microscopic Fracture Mechanisms of T. Niloticus Nacre in Uniaxial CompressionStructural Hierarchy and Function of the Components of Articular CartilageStructural Hierarchy and Function of the Components of Articular Cartilagechondrocyte cell :produces and maintainscartilage ECM <5% vol.collagen fibrils :fiber-reinforcement responsible for shear andtensile strength, shape-retaining properties ~55-60% dry weighthyaluronic acid :central GAG filament which serves asthe backbone for assembly of supramolecular aggregates of proteoglycansextracellular matrix :dense, sponge-like composite network wherewater ~65-80% vol.aggrecan :large, soluble,molecule responsible for compressive strength~35% dry weight• highly specialized, organized, and dense connective tissue in higher vertebrates• found in the weight-bearing surfaces of movable articular joints• high strength, resiliency, toughness, shock absorption, lubrication, wearlink protein : glycoprotein thatstabilizes the noncovalentattachment of aggrecanto
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