HSC Engineering Studies flashcards
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32 cards. Read the term and the definition here. The deck at the top of this page is optional.
- Stress formula
- Normal stress equals applied force divided by cross-sectional area, measured in pascals. It describes internal load intensity and must be compared with the material's yield stress in design.
- Strain definition
- Strain is the change in length divided by original length, a dimensionless ratio. Multiplying by 100 gives percentage elongation, which indicates ductility in a tensile test.
- Young's modulus
- The slope of the linear-elastic part of a stress–strain graph, equal to stress divided by strain. A higher modulus means a stiffer material that deflects less under the same load.
- Factor of safety
- The ratio of the material's yield or ultimate stress to the allowable working stress. It accounts for uncertainty in loads, material properties and consequences of failure.
- Yield strength
- The stress at which a material begins to deform permanently. For metals lacking a distinct yield point, the 0.2 percent proof stress is used as the equivalent value.
- Ultimate tensile strength
- The maximum stress a material withstands before necking and fracture in a tensile test. It is higher than yield strength for ductile metals and marks the onset of localised deformation.
- Ductility vs brittleness
- Ductile materials deform greatly before fracture and absorb energy; brittle materials fracture with little plastic deformation. Ductility is measured by elongation or reduction in area.
- Toughness definition
- The energy a material absorbs before fracture, represented by the area under the stress–strain curve. It differs from hardness, which only resists surface indentation.
- Second moment of area
- A geometric property of a cross-section describing resistance to bending, equal to bd cubed over twelve for a rectangle. Larger values reduce bending stress and deflection.
- Bending stress formula
- Bending stress equals bending moment times distance from the neutral axis divided by second moment of area. Maximum stress occurs at the outermost fibres of the section.
- Shear stress in joints
- Shear stress equals shear force divided by the area resisting sliding. In a bolted lap joint, the fastener cross-section carries the shear, and multiple shear planes share the load.
- Thermal expansion stress
- Free thermal strain equals coefficient of expansion times temperature change. If expansion is fully restrained, the induced stress equals modulus times coefficient times temperature change.
- Carbon steel properties
- Raising carbon content in steel increases hardness and tensile strength but reduces ductility and weldability. Low-carbon steel is therefore chosen for forming and welded structures.
- Quenching and tempering
- Rapid cooling of austenitised steel forms hard, brittle martensite. Reheating to a lower temperature, called tempering, restores toughness while retaining much of the hardness.
- Annealing purpose
- Annealing heats metal and cools it slowly to soften it, relieve internal stresses and refine grain structure. It improves machinability and removes work-hardening from prior forming.
- Galvanic corrosion control
- When two dissimilar metals contact in an electrolyte, the more active one corrodes. Sacrificial anodes such as zinc protect steel because zinc corrodes preferentially.
- Thermoplastic vs thermoset
- Thermoplastics soften repeatedly on heating because their polymer chains are not cross-linked. Thermosets have permanent cross-links, so they char and cannot be remelted or reshaped.
- Composite anisotropy
- Fibre-reinforced composites are strongest along the fibre direction and weak across it. Designers orient plies to align stiffness with the expected load paths in a component.
- Velocity ratio of gears
- For a gear pair the velocity ratio equals driven teeth divided by driver teeth. It also equals the ratio of their rotational speeds and of their pitch-circle diameters.
- Mechanical efficiency
- Efficiency equals useful work output divided by work input, expressed as a percentage. Losses arise from friction in bearings, sliding contact and deformation of components.
- Hydrostatic pressure
- Pressure in a static fluid equals density times gravitational acceleration times depth below the free surface. It acts equally in all directions at a given depth.
- Flow continuity equation
- For incompressible flow, volume flow rate equals cross-sectional area times velocity and is constant along a pipe. A narrower section therefore produces a higher velocity.
- Electrical power formula
- Electrical power equals voltage multiplied by current, and also current squared times resistance. Energy consumed is power multiplied by the time of operation.
- Stress concentration
- Sharp changes in section, holes and notches raise local stress above the nominal value. Rounded fillets reduce the concentration factor and lower the risk of fatigue cracking.
- Fatigue failure
- Repeated or fluctuating loads can crack a component at stresses below its yield strength. Fatigue life is improved by smooth surfaces, fillets and compressive surface treatments.
- Hooke's law
- Within the elastic limit, stress is proportional to strain, giving a straight-line stress–strain graph. Beyond the proportional limit, deformation becomes non-linear and then permanent.
- Poisson's ratio
- The negative ratio of lateral strain to axial strain in a loaded member. Typical metals have values near 0.3, meaning the member narrows as it is stretched.
- Stress–strain curve regions
- The curve progresses through elastic, yielding, strain-hardening and necking regions. The elastic region is recoverable; plastic deformation after yield is permanent.
- Hardness testing purpose
- Hardness measures resistance to local indentation and correlates with wear resistance and strength. It is a quick, low-cost quality check that leaves a small surface mark.
- Cantilever deflection
- A cantilever with an end point load deflects by load times length cubed divided by three times modulus times second moment of area. Deflection grows rapidly with span.
- Alloying element effects
- Adding elements such as chromium, nickel or manganese changes steel properties. Chromium improves corrosion resistance; nickel improves toughness; manganese aids hardenability.
- Design process stages
- Engineering design proceeds from identifying need and constraints, through concept generation and evaluation, to detailed design, prototype testing and iterative refinement against specifications.