Materials for Engineers and Technicians

 Materials for Engineers  and Technicians

Materials for Engineers  and Technicians

In modern times, we have a multiplicity of materials in widespread use. In olden times there was no such great multiplicity, and the history of the human race can be divided into periods named according to the materials that were predominantly in use:

• The Stone Age (about 10 000 BCE–3000 BCE). People could only use the materials they found around them, such as stone, wood, clay, animal hides, and bone. The products they made were limited to what they could fashion out of these materials; therefore, they had tools made from stone, fint, bone and horn, with weapons – always at the forefront of technology at any time – of wood and fint.
• The Bronze Age (3000 BCE–1000 BCE). By about 3000 BCE, people were able to extract copper from its ore. Copper is a ductile material which can be hammered into shapes, thus enabling a greater variety of items to be fashioned than was possible with stone. The copper ores contained impurities that were not completely removed by the smelting and so copper alloys were produced. It was found that when tin was added to copper, an alloy, bronze, was produced. This had an attractive colour, was easy to form and harder than copper alone.
• The Iron Age (1000 BCE–1620 CE). About 1000 BCE, the extraction of iron from its ores signalled another major development. Iron in its pure form was inferior to bronze but by heating items fashioned from iron in charcoal and hammering them, a tougher material, called steel, was produced. Plunging the hot metal into cold water, i.e. quenching, was found to improve the hardness. Slowly reheating and cooling the metal produced a softer, but tougher and less brittle, material; this process now being termed tempering. Thus, heat-treatment processes were developed.
• The Cast Iron Age (1620–1850). Large-scale iron production with the frst cokefuelled blast-furnace started in 1709. The use of cast iron for structures and machine You sent parts grew rapidly after 1750, including its use for casting cannon. In 1777, the first cast-iron bridge was built over the River Severn near oalbrookdale. Cast iron established the dominance of metals in engineering. The term Industrial Revolution is used for the period that followed as the pace of developments of materials and machines increased rapidly and resulted in major changes in the industrial environment and the products generally available. During this period, England led the world in the production of iron.
• The Steel Age (1860 onwards). Steel was a special-purpose material during the frst half of the nineteenth century. However, the year 1860 saw the development of the Bessemer and open hearth processes for the production of steel, and this date may be considered to mark the general use of steel as a constructional material. This development reinforced the dominance of metals in engineering.
• The Light Alloys Age (such alloys produced in early 1900s but only widely used from 1940 onwards). Although aluminium was frst produced, in minute quantities, by H. C. Oersted in 1825, it was not until 1886 that it was produced commercially.
The high-strength aluminium alloy duralumin was developed in 1909, high-strength nickel-chromium alloys for high temperature use were developed in 1931 and titanium was frst produced commercially in 1948.
• The Plastics Age (1930 onwards). The frst manufactured plastic, celluloid, was developed in 1862; in 1906, Bakelite was developed. The period after about 1930 saw a major development of plastics and their use in a wide range of products. In 1933, a Dutch scientist, A. Michels, was carrying out research into the effects of high pressure on chemical reactions when he obtained a surprise result – the chemical reaction between ethylene and benzaldehyde was being studied at 2000 times the atmospheric pressure and a temperature of 170°C when a waxy solid was found to form. This is the material we call polyethylene. The commercial production of polyethylene started in England in 1941. The development of polyvinyl chloride (PVC) was, unlike the accidental discovery of polythene, a deliberate attempt to source a new material. In 1936, just prior to the Second World War, there was no readily available material that could replace natural rubber. In the event of a war, Britain’s natural rubber supply from the Far East would be at risk, so a substitute was required. In July 1940, a small amount of PVC was produced, and commercial production of PVC started in 1945.

• The Composites Age (from about 1950 onwards). Though composites are not new, bricks and concrete being very old examples, it is only in the second half of the twentieth century that synthetic composites became widely used. Reinforced plastics are now widely used, and carbon-fbre reinforced composites are, from their initial development in the 1960s, now becoming widely enough used to become known to the general public.
When tools and weapons were limited to those that could be fashioned out of stone, there were severe limitations on what could be achieved with them. The development of metals enabled fner products to be fashioned, e.g. bronze swords, which were far superior weapons to stone eapons. The development of cast iron can be considered one of the signifcant developments which ushered in the Industrial Age. The development of plastics enabled a great range of products to be produced cheaply and in large numbers – what would the world be like today if plastics had not been developed? As a consequence of the evolution of
materials over the years, our lifestyles have changed.

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