LECTURE 1 3 11 MECHANICS OF MATERIALS F02 INSTRUCTOR Professor Christine Ortiz OFFICE 13 4022 PHONE 452 3084 WWW http web mit edu cortiz www COURSE OVERVIEW INTRODUCTION TO MECHANICS OF MATERIALS Mechanical Properties of Materials COMPRESSION squeezing TENSION stretching tearing BENDING flexure TORSION twisting Why Study Mechanics of Materials Uniaxial Mechanical Testing http www me udel edu tierney mechanics html 45o Tension TENSION COMPRESSION Uniaxial Tensile Testing http www me udel edu tierney mechanics html 45o Tension samples are made from the same exact material Composite Fracture Surface http www fpchem com fap 5a en fig html fig2a Short 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 layer Prismatic aragonite calcite Laminar columnar nacreous aragonite Laminar foliated argonite calcite Innermost irregular crossed lamellar calcite columnar nacreous layer Trochus Niloticus AFM Image 4 m SEM images Microstructure of Trochus Niloticus Gastropod Mollusk t 0 87 0 07 m SEM side view ceramic microlaminate columnar structure d 5 8 0 4 m Nacreous 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 SEM top view rounded polygonal ceramic plates Up to 5 wt biomacromolecules nm thick layer between ceramic plates Wang 2001 also within plates Morse 1996 Microscopic Fracture Mechanisms of T Niloticus Nacre in Uniaxial Compression Structural Hierarchy and Function of the Components of Articular Cartilage Structural Hierarchy and Function of the Components of Articular Cartilage 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 wear collagen fibrils fiber reinforcement responsible for shear and tensile strength shape retaining properties 55 60 dry weight link protein glycoprotein that stabilizes the noncovalent attachment of aggrecan to HA chondrocyte cell produces and maintains cartilage ECM 5 vol extracellular matrix dense sponge like composite network where water 65 80 vol aggrecan large soluble molecule responsible for compressive strength 35 dry weight hyaluronic acid central GAG filament which serves as the backbone for assembly of supramolecular aggregates of proteoglycans
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