Mechanical engineering
Mechanical engineering is one of the oldest and broadest of the engineering branches, and its tools once moved blocks of stone before they ever rendered a 3D model. The lever first appeared around 5,000 years ago in the Near East, used in a simple balance scale and to shift large objects in ancient Egypt. From that simple device to silicon components measured in microns, this is a discipline that studies physical machines and mechanisms involving force and movement. It combines engineering physics and mathematics with materials science to design, analyze, manufacture, and maintain mechanical systems. So how did the six classic simple machines of the ancient Near East become a field employing hundreds of thousands of people? What does a mechanical engineer actually study, and what do they do once they leave school? And where is the field heading at scales too small to see?
The wedge and the inclined plane were known since prehistoric times, long before anyone wrote the word engineering. Mesopotamian civilization is credited by several mainly older sources with inventing the wheel, though some recent sources suggest it arose independently in both Mesopotamia and Eastern Europe. The earliest evidence of pulleys dates back to Mesopotamia in the early 2nd millennium BC. The shadoof, a lever-based water-lifting device and the first crane machine, appeared in Mesopotamia circa 3000 BC.
The Saqiyah was developed in the Kingdom of Kush during the 4th century BC, relying on animal power to reduce the demand on human energy. Reservoirs called Hafirs stored water and boosted irrigation in Kush, and bloomeries and blast furnaces appeared during the seventh century BC in Meroe. Kushite sundials applied advanced trigonometry to track the sun.
The earliest practical water-powered machines, the water wheel and watermill, appeared in the Persian Empire by the early 4th century BC, in what are now Iraq and Iran. In ancient Greece, the works of Archimedes, who lived from 287 to 212 BC, shaped mechanics in the Western tradition. The geared Antikythera mechanism, an analog computer, was invented around the 2nd century BC. Centuries of such invention set the stage for the engineers who would put steam and gears to work.
Heron of Alexandria, working in Roman Egypt around 10 to 70 AD, created the first steam-powered device, the Aeolipile. In China, Zhang Heng, who lived from 78 to 139 AD, improved a water clock and invented a seismometer. Ma Jun, active between 200 and 265 AD, built a chariot with differential gears. The medieval Chinese horologist Su Song, who lived from 1020 to 1101 AD, put an escapement mechanism into his astronomical clock tower two centuries before such devices appeared in European clocks. Su Song also invented the world's first known endless power-transmitting chain drive.
The cotton gin was invented in India by the 6th century AD, and the spinning wheel emerged in the Islamic world by the early 11th century. Dual-roller gins appeared in India and China between the 12th and 14th centuries, and the worm gear roller gin arose in the Indian subcontinent during the early Delhi Sultanate era of the 13th to 14th centuries.
During the Islamic Golden Age, spanning the 7th to 15th century, Muslim inventors made notable contributions to mechanical technology. Al-Jazari wrote his Book of Knowledge of Ingenious Mechanical Devices in 1206, presenting many mechanical designs. The intellectual foundations of the modern field, however, would be laid in 17th-century Europe.
Christiaan Huygens, the Dutch mathematician and physicist, invented the pendulum clock in 1657, the first reliable timekeeper for almost 300 years. In England, Isaac Newton formulated his laws of motion and developed calculus, the mathematical basis of physics. Newton was reluctant to publish for years, but colleagues such as Edmond Halley finally persuaded him. Gottfried Wilhelm Leibniz, who earlier designed a mechanical calculator, is also credited with developing calculus in the same period.
During the early 19th century Industrial Revolution, machine tools were developed in England, Germany, and Scotland, allowing mechanical engineering to grow as a separate field. The first British professional society of mechanical engineers, the Institution of Mechanical Engineers, formed in 1847, thirty years after the civil engineers formed the Institution of Civil Engineers. Johann von Zimmermann, who lived from 1820 to 1901, founded the first factory for grinding machines in Chemnitz, Germany, in 1848.
In the United States, the American Society of Mechanical Engineers formed in 1880, the third such professional engineering society after the civil engineers in 1852 and the mining engineers in 1871. The first US schools to offer engineering education were the United States Military Academy in 1817, the institution now known as Norwich University in 1819, and Rensselaer Polytechnic Institute in 1825. Those classrooms set a pattern still built on a strong foundation in mathematics and science.
Mechanical engineering programs typically take four to five years and lead to degrees such as a Bachelor of Engineering, a Bachelor of Science, or a Bachelor of Technology. In Spain, Portugal, and most of South America, where neither B.S. nor B.Tech. programs were adopted, the degree is formally called Mechanical Engineer and runs five or six years. In Italy the coursework spans five years, but qualifying as an engineer requires passing a state exam at the end. Greece uses a five-year curriculum.
The fundamental subjects usually include calculus, differential equations, and linear algebra, plus statics and dynamics, strength of materials, thermodynamics, fluid mechanics, and computer-aided design. Many programs add specialized classes such as robotics, cryogenics, automotive engineering, and biomechanics. Most programs also require research or community projects to give students practical problem-solving experience, and in the US it is common, though not usually mandated, for students to complete internships.
Accreditation keeps these programs consistent. In the United States the Accreditation Board for Engineering and Technology listed 302 accredited mechanical engineering programs as of the 11th of March 2014. Canada uses the Canadian Engineering Accreditation Board, and Australia's degrees are accredited by Engineers Australia under the global Washington Accord. Before an Australian degree can be awarded, the student must complete at least three months of on-the-job experience in an engineering firm.
Professional Engineer is the title earned by certified engineers in the US, Canada, Japan, South Korea, Bangladesh, and South Africa, while Chartered Engineer is used in the United Kingdom, Ireland, India, and Zimbabwe. In the US, becoming a licensed Professional Engineer means passing the Fundamentals of Engineering exam, working a minimum of four years as an Engineer-in-Training, and passing the Principles and Practice exam. These steps are set by the National Council of Examiners for Engineering and Surveying, made up of licensing boards from all US states and territories.
The license carries legal weight. In most developed countries, certain tasks such as the design of bridges, electric power plants, and chemical plants must be approved by a professional or chartered engineer. As the source puts it, "Only a licensed engineer, for instance, may prepare, sign, seal and submit engineering plans and drawings to a public authority for approval, or to seal engineering work for public and private clients." In the UK no such legislation exists, yet certifying bodies maintain codes of ethics that members must follow or risk expulsion.
The numbers show how large the field has grown. The total number of engineers employed in the US in 2015 was roughly 1.6 million, and 278,340 of them were mechanical engineers, about 17.28 percent and the largest discipline by size. In 2012 the median annual income of mechanical engineers in the US was $80,580, highest in government work at $92,030 and lowest in education at $57,090.
Mechanics, in its most general sense, is the study of forces and their effect upon matter, and engineers use it to predict the acceleration and deformation of objects under known loads. Its subdisciplines include statics, the study of non-moving bodies under known loads, and dynamics, the study of how forces affect moving bodies. In designing a vehicle, statics might shape the frame while dynamics evaluates the forces in the pistons and cams as the engine cycles, and fluid mechanics might design the ventilation system.
Structural analysis examines why and how objects fail, then fixes them. Static failure occurs when a loaded object breaks or deforms plastically, while fatigue failure occurs after repeated loading and unloading cycles. A microscopic crack on a surface grows slightly with each cycle until it is large enough to cause ultimate failure. Yet failure is not simply when a part breaks; the perforated top of some plastic bags is designed to break, and analysis may be used when it does not.
Thermodynamics is the physical science concerned with heat, work, energy, and the properties of matter. Automotive engines convert the chemical energy of fuel into heat and then into mechanical work that turns a car's wheels, and an ideal design would approach Carnot efficiency. As the source notes, Sadi Carnot, whose name marks that limit, was a French military engineer.
Friction stir welding was discovered in 1991 by The Welding Institute, a steady-state non-fusion technique that joins materials previously un-weldable, including several aluminum alloys. It has welded the seams of the aluminum Space Shuttle external tank, the Orion Crew Vehicle, the Boeing Delta II and Delta IV launch vehicles, and the SpaceX Falcon 1 rocket. It also armors amphibious assault ships and joins the wings and fuselage panels of the Eclipse 500 aircraft.
Micro electro-mechanical systems shrink springs, gears, and heat transfer devices to the micron scale, fabricated from silicon, glass, and polymers like SU8. Their accelerometers serve as car airbag sensors and live inside modern cell phones, while gyroscopes handle precise positioning. At the smallest scales, mechanical engineering becomes nanotechnology, where one speculative goal is a molecular assembler that builds materials through mechanosynthesis.
Finite Element Analysis estimates stress, strain, and deflection using a mesh of nodes, and the more nodes there are, the higher the precision. Its basis dates back to 1941, but the evolution of computers made it viable, with commercial applications such as NASTRAN, ANSYS, and ABAQUS used widely in industry. Reverse engineering of natural materials such as bone, optimized to bear large compressive stress per unit weight, now draws academic funding, with the goal of replacing crude steel with bio-material for structural design.
Common questions
What is mechanical engineering?
Mechanical engineering is the study of physical machines and mechanisms that may involve force and movement. It combines engineering physics and mathematics with materials science to design, analyze, manufacture, and maintain mechanical systems, and it is one of the oldest and broadest of the engineering branches.
When did mechanical engineering emerge as a field?
Mechanical engineering emerged as a field during the Industrial Revolution in Europe in the 18th century, though its development can be traced back several thousand years around the world. In the 19th century, developments in physics led to the development of mechanical engineering science.
How long does a mechanical engineering degree take?
Mechanical engineering programs typically take four to five years of study depending on the place and university. In Spain, Portugal, and most of South America the coursework is based on five or six years, while Italy and Greece use five-year curricula.
How do you become a licensed Professional Engineer in mechanical engineering in the US?
In the US, an engineer must pass the Fundamentals of Engineering exam, work a minimum of four years as an Engineer-in-Training, and pass the Principles and Practice exam. These requirements are set by the National Council of Examiners for Engineering and Surveying.
How much do mechanical engineers earn in the US?
In 2012, the median annual income of mechanical engineers in the US workforce was $80,580. The median income was highest in government work at $92,030 and lowest in education at $57,090.
What are the subdisciplines of mechanical engineering?
Mechanical engineering subdisciplines include mechanics, mechatronics and robotics, structural analysis, thermodynamics and thermal engineering, design and drafting, biomechanics, computational fluid dynamics, and acoustical engineering. Mechanics itself includes statics, dynamics, mechanics of materials, fluid mechanics, kinematics, and continuum mechanics.
What new technologies are at the cutting edge of mechanical engineering?
Cutting-edge areas include micro electro-mechanical systems, friction stir welding discovered in 1991 by The Welding Institute, composites, mechatronics, nanotechnology, finite element analysis, and computational fluid dynamics. Mechanical engineers are also pursuing developments in composites, mechatronics, and nanotechnology.