Editing Mechanical engineering (section)

==Subdisciplines==
The field of mechanical engineering can be thought of as a collection of many mechanical engineering science disciplines. Several of these subdisciplines which are typically taught at the undergraduate level are listed below, with a brief explanation and the most common application of each. Some of these subdisciplines are unique to mechanical engineering, while others are a combination of mechanical engineering and one or more other disciplines. Most work that a mechanical engineer does uses skills and techniques from several of these subdisciplines, as well as specialized subdisciplines. Specialized subdisciplines, as used in this article, are more likely to be the subject of graduate studies or on-the-job training than undergraduate research. Several specialized subdisciplines are discussed in this section.

===Mechanics===
[[File:Mohrs circle.svg|thumb|[[Mohr's circle]], a common tool to study [[Stress (physics)|stresses]] in a mechanical element]]
{{main|Mechanics}}

Mechanics is, in the most general sense, the study of [[force]]s and their effect upon [[matter]]. Typically, engineering mechanics is used to analyze and predict the acceleration and deformation (both [[Elastic Deformation|elastic]] and [[Plastic Deformation|plastic]]) of objects under known forces (also called loads) or [[Stress (physics)|stresses]]. Subdisciplines of mechanics include
* [[Statics]], the study of non-moving bodies under known loads, how forces affect static bodies
* [[dynamics (mechanics)|Dynamics]], the study of how forces affect moving bodies. Dynamics includes kinematics (about movement, velocity, and acceleration) and kinetics (about forces and resulting accelerations).
* [[Mechanics of materials]], the study of how different materials deform under various types of stress
* [[Fluid mechanics]], the study of how fluids react to forces<ref>Note: fluid mechanics can be further split into fluid statics and fluid dynamics, and is itself a subdiscipline of continuum mechanics. The application of fluid mechanics in engineering is called [[hydraulics]] and [[pneumatics]].</ref>
* [[Kinematics]], the study of the motion of bodies (objects) and systems (groups of objects), while ignoring the forces that cause the motion. Kinematics is often used in the design and analysis of [[Mechanism (engineering)|mechanisms]].
* [[Continuum mechanics]], a method of applying mechanics that assumes that objects are continuous (rather than [[wikt:discrete|discrete]])

Mechanical engineers typically use mechanics in the design or analysis phases of engineering. If the engineering project were the design of a vehicle, statics might be employed to design the frame of the vehicle, in order to evaluate where the stresses will be most intense. Dynamics might be used when designing the car's engine, to evaluate the forces in the [[piston]]s and [[Cam (mechanism)|cam]]s as the engine cycles. Mechanics of materials might be used to choose appropriate materials for the frame and engine. Fluid mechanics might be used to design a ventilation system for the vehicle (see [[HVAC]]), or to design the [[intake]] system for the engine.

===Mechatronics and robotics===
[[File:FMS1 small.JPG|thumb|Training FMS with learning robot SCORBOT-ER 4u, workbench CNC Mill and CNC Lathe]]
{{main|Mechatronics|Robotics}}

Mechatronics is a combination of mechanics and electronics. It is an interdisciplinary branch of mechanical engineering, [[electrical engineering]] and [[software engineering]] that is concerned with integrating electrical and mechanical engineering to create hybrid automation systems. In this way, machines can be automated through the use of [[electric motor]]s, [[servomechanism|servo-mechanisms]], and other electrical systems in conjunction with special software. A common example of a mechatronics system is a CD-ROM drive. Mechanical systems open and close the drive, spin the CD and move the laser, while an optical system reads the data on the CD and converts it to [[bit]]s. Integrated software controls the process and communicates the contents of the CD to the computer.

Robotics is the application of mechatronics to create robots, which are often used in industry to perform tasks that are dangerous, unpleasant, or repetitive. These robots may be of any shape and size, but all are preprogrammed and interact physically with the world. To create a robot, an engineer typically employs kinematics (to determine the robot's range of motion) and mechanics (to determine the stresses within the robot).

Robots are used extensively in industrial automation engineering. They allow businesses to save money on labor, perform tasks that are either too dangerous or too precise for humans to perform them economically, and to ensure better quality. Many companies employ [[assembly lines]] of robots, especially in Automotive Industries and some factories are so robotized that they can run [[Lights out (manufacturing)|by themselves]]. Outside the factory, robots have been employed in bomb disposal, [[space exploration]], and many other fields. Robots are also sold for various residential applications, from recreation to domestic applications.<ref>Bolton, W. Mechatronics. Pearson; 6th ed. edition, 2015. ISBN 9781292076683</ref>

===Structural analysis===
{{main|Structural analysis|Failure analysis}}

Structural analysis is the branch of mechanical engineering (and also civil engineering) devoted to examining why and how objects fail and to fix the objects and their performance. Structural failures occur in two general modes: static failure, and fatigue failure. ''Static structural failure'' occurs when, upon being loaded (having a force applied) the object being analyzed either breaks or is deformed [[plastic deformation|plastically]], depending on the criterion for failure. ''Fatigue failure'' occurs when an object fails after a number of repeated loading and unloading cycles. Fatigue failure occurs because of imperfections in the object: a microscopic crack on the surface of the object, for instance, will grow slightly with each cycle (propagation) until the crack is large enough to cause [[ultimate failure]].<ref>{{Cite web|url=http://www.virginia.edu/bohr/mse209/chapter8.htm|title=Chapter 8. Failure|website=virginia.edu|access-date=9 September 2018}}</ref>

Failure is not simply defined as when a part breaks, however; it is defined as when a part does not operate as intended. Some systems, such as the perforated top sections of some plastic bags, are designed to break. If these systems do not break, failure analysis might be employed to determine the cause.

Structural analysis is often used by mechanical engineers after a failure has occurred, or when designing to prevent failure. Engineers often use online documents and books such as those published by ASM<ref>[http://asmcommunity.asminternational.org/portal/site/asm/ ASM International's site many documents, such as the ''ASM Handbook'' series] {{webarchive|url=https://web.archive.org/web/20070901014247/http://asmcommunity.asminternational.org/portal/site/asm/ |date=1 September 2007}}. [[ASM International (society)|ASM International]].</ref> to aid them in determining the type of failure and possible causes.

Once theory is applied to a mechanical design, physical testing is often performed to verify calculated results. Structural analysis may be used in an office when designing parts, in the field to analyze failed parts, or in laboratories where parts might undergo controlled failure tests.

===Thermodynamics and thermo-science===
{{main|Thermodynamics}}

[[Thermodynamics]] is an applied science used in several branches of engineering, including mechanical and chemical engineering. At its simplest, thermodynamics is the study of energy, its use and transformation through a [[physical system|system]].<ref>{{Cite web|url=https://www.grc.nasa.gov/www/k-12/airplane/thermo.html|title=Thermodynamics|website=grc.nasa.gov|access-date=9 September 2018}}</ref> Typically, engineering thermodynamics is concerned with changing energy from one form to another. As an example, automotive engines convert chemical energy ([[enthalpy]]) from the fuel into heat, and then into mechanical work that eventually turns the wheels.

Thermodynamics principles are used by mechanical engineers in the fields of [[heat transfer]], [[thermofluids]], and [[energy conversion]]. Mechanical engineers use thermo-science to design [[engine]]s and [[power plant]]s, heating, ventilation, and air-conditioning (HVAC) systems, [[heat exchanger]]s, [[heat sink]]s, [[radiator]]s, [[refrigeration]], [[Thermal insulation|insulation]], and others.<ref>{{Cite web|url=https://www.brighthubengineering.com/thermodynamics/38344-thermodynamics-integral-part-of-our-life/|title=Applications of Thermodynamics Laws. Carnot, Stirling, Ericsson, Diesel cycles|website=Brighthub Engineering|access-date=9 September 2018|date=10 June 2009}}</ref>

===Design and drafting===
[[File:Mech 2 3D.png|thumb|right|A CAD model of a [[mechanical seal|mechanical double seal]] ]]
{{main|Technical drawing|CNC}}

[[Technical drawing|Drafting]] or technical drawing is the means by which mechanical engineers design products and create instructions for [[manufacture|manufacturing]] parts. A technical drawing can be a computer model or hand-drawn schematic showing all the dimensions necessary to manufacture a part, as well as assembly notes, a list of required materials, and other pertinent information.<ref>{{Cite web|url=https://www.solidworks.com/product/solidworks-3d-cad|title=SOLIDWORKS 3D CAD|website=SOLIDWORKS|language=en|access-date=9 September 2018|date=27 November 2017}}</ref> A U.S. mechanical engineer or skilled worker who creates technical drawings may be referred to as a drafter or draftsman. Drafting has historically been a two-dimensional process, but [[computer-aided design]] (CAD) programs now allow the designer to create in three dimensions.

Instructions for manufacturing a part must be fed to the necessary machinery, either manually, through programmed instructions, or through the use of a [[computer-aided manufacturing]] (CAM) or combined CAD/CAM program. Optionally, an engineer may also manually manufacture a part using the technical drawings. However, with the advent of [[Numerical control#CNC arrives|computer numerically controlled]] (CNC) manufacturing, parts can now be fabricated without the need for constant technician input. Manually manufactured parts generally consist of [[thermal spray|spray coatings]], surface finishes, and other processes that cannot economically or practically be done by a machine.

Drafting is used in nearly every subdiscipline of mechanical engineering, and by many other branches of engineering and architecture. Three-dimensional models created using CAD software are also commonly used in [[finite element analysis]] (FEA) and [[computational fluid dynamics]] (CFD).