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 , a common tool to study
stresses in a mechanical element Mechanics is, in the most general sense, the study of
forces and their effect upon
matter. Typically, engineering mechanics is used to analyze and predict the acceleration and deformation (both
elastic and
plastic) of objects under known forces (also called loads) or
stresses. Subdisciplines of mechanics include •
Statics, the study of non-moving bodies under known loads, how forces affect static bodies •
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 •
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
mechanisms. •
Continuum mechanics, a method of applying mechanics that assumes that objects are continuous (rather than
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
pistons and
cams 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 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 motors,
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
bits. 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
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.
Structural 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
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. 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 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 thermal engineering Thermodynamics is a physical science concerned with heat, work, energy, and the physical properties of matter. It is used in several branches of engineering, including mechanical and chemical engineering. Engineering thermodynamics focuses on systems that change energy from one form to another. More broadly, thermal engineering combines thermodynamics and the science of
transport phenomena to study
heat transfer,
combustion, and
compressible fluid flow in engineered systems. Mechanical engineers use thermal engineering to design equipment such as
engines,
power plants,
heat exchangers,
heat sinks,
radiators,
refrigerators,
insulation, and heating, ventilation, and air-conditioning (
HVAC) systems. As an example, automotive engines convert the chemical energy of fuel (
enthalpy) into heat and then into the mechanical work that turns a car's wheels. A mechanical engineer will aim for an engine design that maximizes the fraction of the initial chemical energy that is converted to mechanical work, rather than being lost as heat or friction. An ideal design would approach
Carnot efficiency. (In fact,
Sadi Carnot was a French military engineer.)
Design and drafting Drafting or technical drawing is the means by which mechanical engineers design products and create instructions for
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. 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
computer numerically controlled (CNC) manufacturing, parts can now be fabricated without the need for constant technician input. Manually manufactured parts generally consist of
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). ==Modern tools==