HSC Engineering Studies key terms

The internal force per unit area carried by a material at a given cross-section, usually expressed in megapascals. It shows how heavily loaded the material is and is compared with the material's strength to judge safety.

The change in length of a member divided by its original length, a dimensionless measure of deformation. It describes how much a component stretches or compresses under load and pairs with stress to give the material's stiffness.

The ratio of tensile stress to tensile strain while a material behaves elastically, measured in gigapascals. A high value means the material is stiff and deflects little under load, which matters for beams and shafts.

The stress at which a material begins to deform permanently, leaving residual strain when the load is removed. Designers keep working stress below this value so components return to shape after loading.

The maximum stress a material can withstand while being pulled before necking and fracture occur. It marks the peak of the stress-strain curve and is used to compare materials' load capacity.

The greatest stress a material can carry and still return exactly to its original dimensions when unloaded. Loading past it leaves permanent deformation, so it defines the boundary of safe reversible behaviour.

The ability of a material to be stretched into wire or undergo large plastic deformation before breaking. Ductile metals give warning before failure and suit forming processes such as drawing and bending.

The ability of a material to be hammered or rolled into thin sheets without cracking. It depends on how easily planes of atoms slide, and it governs whether a metal suits pressing or rolling operations.

The amount of energy a material absorbs before it fractures, found from the area under the stress-strain curve. Tough materials resist impact and crack growth, which suits structures subject to shock loading.

A material's resistance to local surface indentation, scratching or wear. Hardness often rises as strength rises but usually comes with reduced ductility, so it is traded off against toughness in design.

The ratio of a material's failure or yield strength to the maximum working stress expected in service. A value above one allows for uncertainty in loads, material variation and unexpected overloads.

Progressive cracking and weakening of a material caused by repeated or fluctuating stress cycles well below its static strength. It explains many sudden shaft and aircraft failures and drives the need for smooth surfaces.

Localised increase in stress where a component changes section abruptly, such as at holes, notches or sharp corners. It can raise local stress far above the average and promote cracking, so radii are rounded.

Slow, permanent deformation of a material under sustained load, significant at elevated temperatures. It limits the service life of turbine blades, boiler tubes and other hot components held under stress for long periods.

Controlled heating and cooling of a metal to change its internal structure and therefore its properties. Processes such as annealing, quenching and tempering adjust hardness, strength and ductility for particular applications.

A metallic material made by combining a base metal with other elements to improve properties. Alloying can raise strength, hardness or corrosion resistance beyond what the pure metal offers.

Gradual chemical attack that degrades a metal, commonly by oxidation or electrochemical action in the presence of moisture and electrolytes. It reduces section thickness and strength, so protective coatings and suitable alloys are used.

Coating steel with zinc to protect it from corrosion, either by hot dipping or electroplating. The zinc corrodes in preference to the steel, giving sacrificial protection even where the coating is scratched.

An electrochemical process that thickens the natural oxide layer on aluminium to improve corrosion resistance and wear resistance. The porous coating can also be dyed, making it common on architectural and consumer parts.

A material made from two or more distinct constituents that remain separate and combine their best properties. Fibre-reinforced plastics, for example, give high strength with low mass, suiting aircraft and sporting equipment.

A composite of strong fibres such as glass or carbon embedded in a polymer matrix. Fibres carry tensile load while the matrix binds them and spreads load, giving high strength-to-weight ratios.

The condition where a material's properties differ depending on the direction in which they are measured. Rolled metals, timber and fibre composites are anisotropic, so designers must align loading with the strong direction.

The condition where a material has the same properties in every direction. Most fine-grained metals and cast materials are treated as isotropic, which simplifies stress analysis and design calculations.

The strength of a material divided by its density, sometimes called strength-to-weight ratio. High values are prized in transport and aerospace design because they allow lighter structures carrying the same load.

A sketch showing one body isolated from its surroundings with all external forces and moments drawn as vectors acting on it. It is the starting point for applying equilibrium equations to solve for unknown reactions.

The state in which the sum of all forces and the sum of all moments acting on a body are both zero. Static equilibrium equations let engineers find unknown support reactions and check that structures do not move.

The turning effect of a force about a point, calculated as force multiplied by the perpendicular distance from the point to the force's line of action. It is measured in newton metres and governs levers and beams.

The turning effect of a force applied about the axis of a rotating shaft, equal to force times radius in simple cases. It relates to power and rotational speed and is central to gear, motor and driveshaft calculations.

Two equal, opposite and parallel forces whose lines of action are separated by a distance, producing rotation without any net translation. The turning effect equals one force times the perpendicular separation.

The single force that has the same effect as all the individual forces acting together on a body. It is found by vector addition and indicates the direction and size of any unbalanced force.

A quantity that has both magnitude and direction, such as force, velocity or acceleration. Vectors are added using triangle or parallelogram methods, unlike scalars which combine by simple arithmetic.

A quantity described fully by magnitude alone, such as mass, time, temperature or energy. Scalars are added arithmetically, which distinguishes them from vectors that also require direction.

The rate at which work is done or energy is transferred, measured in watts. For rotating machinery it equals torque multiplied by angular velocity, so it links motor specifications to load requirements.

The ratio of useful output energy or power to total input energy or power, often expressed as a percentage. Losses from friction, heat and electrical resistance mean efficiency is always below one hundred percent.

The ratio of load force overcome to effort force applied in a machine. It shows how much a mechanism multiplies force, and for an ideal machine it relates to the ratio of distances moved.

The ratio of the distance moved by the effort to the distance moved by the load in a machine. It depends on geometry alone, and comparing it with mechanical advantage reveals the machine's efficiency.

The ratio of the number of teeth on a driven gear to that on the driving gear, which sets the change in speed and torque. A larger ratio reduces output speed while increasing output torque.

A precise graphical representation of a component or assembly using standard conventions, views, dimensions and tolerances. It communicates design intent unambiguously so the part can be manufactured and inspected.

A drawing method showing a three-dimensional object as separate two-dimensional views, typically front, top and side, arranged in fixed positions. It conveys true shape and size without perspective distortion.

A pictorial drawing in which the three principal axes are spaced 120 degrees apart, giving a three-dimensional view without perspective. It is used to show overall form before detailed orthographic views are prepared.

A drawing that shows the interior of an object as if it were cut by a plane, with the cut surface hatched. It reveals internal features such as holes and bores that hidden lines would show poorly.

The permissible variation in a dimension, given as the difference between upper and lower limits. It balances manufacturing cost against the fit and function required of mating parts.

The small-scale roughness and texture of a manufactured surface, specified by symbols and roughness values. It affects friction, wear, fatigue life and sealing, and influences the machining process chosen.

Computer-aided design: software used to create, modify and analyse digital models of parts and assemblies. Models can be shared for simulation, drafting and computer-aided manufacturing, speeding up design iteration.

Computer-aided manufacturing: the use of computer software to plan and control machine tools from digital design data. It converts CAD geometry into tool paths and instructions for numerically controlled equipment.

Computer numerical control machining, where a program directs machine tools such as lathes and mills to cut parts automatically. It gives repeatable accuracy and suits small batches of complex components.

The capacity of a system to do work, measured in joules and existing in forms such as kinetic, potential, thermal and electrical. The principle of conservation of energy underpins analysis of machines and power systems.

The energy transferred when a force moves an object along its line of action, calculated as force times displacement. It is measured in joules and underlies calculations of power and machine performance.