Engineering Notes PDF

Structuring: Topic Subtopic Short description Y11 Content: Mechanics Nature and types of forces Push, pull, or twist Measured in Newtons Types: Concurrent forces (lines of action share a common point) Collinear forces (act along common line of action) Coplanar forces (contained in same 2D plane...

Structuring: Topic Subtopic Short description Y11 Content: Mechanics Nature and types of forces Push, pull, or twist Measured in Newtons Types: Concurrent forces (lines of action share a common point) Collinear forces (act along common line of action) Coplanar forces (contained in same 2D plane) Adding vectors Magnitude and direction Joining head to tail Can use trigonometry or graphical (draw to scale) method of solving Moments of a force Torque Moment (Nm) = Force (N) x Distance (m) Forces at angles must be analysed by vertical and horizontal components ∑MA⤾ = 0 = Fd + Fd + … Force couple systems Pair of parallel forces, equal in magnitude and opposite in direction ​ ​ MC = F1M x d Magnitude of Couple = Magnitude of one force x perpendicular distance between forces Y11 Content: Materials Structure of materials BCC (Brittle, limited slip planes), FCC (Ductile, more slip planes), CPH (less slip planes due to orientation of atoms) Primary bonds: ionic, covalent, metallic Secondary bonds: Intermolecular forces Ferrous metals Ferrous: iron alloyed with carbon Main allotropes (microstructures) of iron: Ferrite - soft, ductile, low carbon (white) Cementite - hard, brittle (thin black strip) Pearlite - Alternating plates of Ferrite and Cementite Austenite - 911C, high temp phase, same % Carbon as Cementite Martensite - Quenched austenitic structure, brittle and highly packed Dead mild steel / low carbon steel Up to 0.15% carbon Soft, ductile, Sustains large amounts of cold working Large equiaxed grains of F, small grains of P Mild steel 0.15-0.30% carbon Same properties Medium equiaxed grains of F, mid sized grains P Structural steel Medium carbon steel 0.3-0.6% carbon Tough, hard, machinable Small equiaxed grains of F, large grains of P High carbon steel 0.6-0.9% carbon Poor machinability, high tensile estrength Grains of P surrounded by precipiates of C Ultra-high carbon steel 1-2% carbon High strength and hardness General rule: AS carbon content increases, pearlite increases, ferrite decreases until replaced by cementite. Cast irons: allotropes by silicon % because silicon catalyses formation of graphite White Cast iron Less than 1% Silicon Dendrites of pearlite in cementite matrix Hard, Brittle, good castability Grey Cast iron Enough silicon to form graphite Graphite flakes in pearlite or ferrite matrix Soft, machinable, good castability, self-lubricating, corrosion resistant Sharp ends of graphite → stress concentration → fracture Malleable cast iron High carbon and silicon Graphite rosettes in pearlite or ferrite matrix Formed by heat-treating white cast iron Soft, malleable, ductile, tough, machinable Ductile / Nodular / Spheroidal cast iron High carbon and silicon, Magnesium or cerium involved Graphite spheroids in pearlite or ferrite matrix Spherical shape no stress conc., higher tensile strength and ductility Soft, malleable, ductile, tough General rule: As silicon increases, cast iron becomes more ductile / malleable, less brittle For below 0.8% Carbon: Hypoeutectoid: At 0.2%: Ferrite 80%, Pearlite 20% At 0.4%: Ferrite 50%, Pearlite 50% At 0.6%: Ferrite 20%, Pearlite 80% At 0.8% Eutectoid point: Ferrite 0%, Pearlite 100% Hypereutectoid: 0.8% onwards: Cementite begins to precipitate out slowly.