Ductility

Ductility is a measure of a material's ability to undergo significant plastic deformation before rupture, which may be expressed as percent elongation or percent area reduction from a tensile test. According to Shigley's Mechanical Engineering Design (10th Ed.) [1] significant denotes about 5.0 percent elongation (Section 5.3, p. 233). See also Eq. 2–12, p. 50 for definitions of percent elongation and percent area reduction. Ductility is often characterized by a material's ability to be stretched into a wire.

From examination of data in Tables A20, A21, A22, A23, and A24 in Shigley's Mechanical Engineering Design, 10th Edition,[1] for both ductile and brittle materials, it is possible to postulate a broader quantifiable definition of ductility that does not rely on percent elongation alone. In general, a ductile material must have a measurable yield strength, at which unrecoverable plastic deformation begins (see Yield (engineering)), and also must satisfy one of the following conditions: either have an elongation to failure of at least 5%, or area reduction to rupture at least 20%, or true strain to rupture at least 10%.

Malleability, a similar property, is a material's ability to deform under compressive stress; this is often characterized by the material's ability to form a thin sheet by hammering or rolling. Both of these mechanical properties are aspects of plasticity, the extent to which a solid material can be plastically deformed without fracture. Also, these material properties are dependent on temperature and pressure (investigated by Percy Williams Bridgman as part of his Nobel Prize-winning work on high pressures).

Ductility and malleability are not always coextensive – for instance, while gold has high ductility and malleability, lead has low ductility but high malleability.[2] The word ductility is sometimes used to encompass both types of plasticity.[3]

Al tensile test
Tensile test of an AlMgSi alloy. The local necking and the cup and cone fracture surfaces are typical for ductile metals.
Cast iron tensile test
This tensile test of a nodular cast iron demonstrates low ductility.

Materials science

Au atomic wire
Gold is extremely ductile. It can be drawn into a monatomic wire, and then stretched more before it breaks.[4]

Ductility is especially important in metalworking, as materials that crack, break or shatter under stress cannot be manipulated using metal-forming processes such as hammering, rolling, drawing or extruding. Malleable materials can be formed cold using stamping or pressing, whereas brittle materials may be cast or thermoformed.

High degrees of ductility occur due to metallic bonds, which are found predominantly in metals, leading to the common perception that metals are ductile in general. In metallic bonds valence shell electrons are delocalized and shared between many atoms. The delocalized electrons allow metal atoms to slide past one another without being subjected to strong repulsive forces that would cause other materials to shatter.

Ductility can be quantified by the fracture strain , which is the engineering strain at which a test specimen fractures during a uniaxial tensile test. Another commonly used measure is the reduction of area at fracture .[5] The ductility of steel varies depending on the alloying constituents. Increasing the levels of carbon decreases ductility. Many plastics and amorphous solids, such as Play-Doh, are also malleable. The most ductile metal is platinum and the most malleable metal is gold.[6][7] When highly stretched, such metals distort via formation, reorientation and migration of dislocations and crystal twins without noticeable hardening.[8]

Ductile–brittle transition temperature

Ductility
Schematic appearance of round metal bars after tensile testing.
(a) Brittle fracture
(b) Ductile fracture
(c) Completely ductile fracture

The ductile–brittle transition temperature (DBTT), nil ductility temperature (NDT), or nil ductility transition temperature of a metal is the temperature at which the fracture energy passes below a predetermined value (for steels typically 40 J[9] for a standard Charpy impact test). DBTT is important since, once a material is cooled below the DBTT, it has a much greater tendency to shatter on impact instead of bending or deforming. For example, zamak 3 exhibits good ductility at room temperature but shatters when impacted at sub-zero temperatures. DBTT is a very important consideration in selecting materials that are subjected to mechanical stresses. A similar phenomenon, the glass transition temperature, occurs with glasses and polymers, although the mechanism is different in these amorphous materials.

In some materials, the transition is sharper than others and typically requires a temperature-sensitive deformation mechanism. For example, in materials with a body-centered cubic (bcc) lattice the DBTT is readily apparent, as the motion of screw dislocations is very temperature sensitive because the rearrangement of the dislocation core prior to slip requires thermal activation. This can be problematic for steels with a high ferrite content. This famously resulted in serious hull cracking in Liberty ships in colder waters during World War II, causing many sinkings. DBTT can also be influenced by external factors such as neutron radiation, which leads to an increase in internal lattice defects and a corresponding decrease in ductility and increase in DBTT.

The most accurate method of measuring the DBTT of a material is by fracture testing. Typically four point bend testing at a range of temperatures is performed on pre-cracked bars of polished material.

For experiments conducted at higher temperatures, dislocation activity increases. At a certain temperature, dislocations shield the crack tip to such an extent that the applied deformation rate is not sufficient for the stress intensity at the crack-tip to reach the critical value for fracture (KiC). The temperature at which this occurs is the ductile–brittle transition temperature. If experiments are performed at a higher strain rate, more dislocation shielding is required to prevent brittle fracture, and the transition temperature is raised.

See also

References

  1. ^ a b Budynas, Richard G. (2015). Shigley's Mechanical Engineering Design—10th ed. McGraw Hill. p. 233. ISBN 978-0-07-339820-4..
  2. ^ Rich, Jack C. (1988). The Materials and Methods of Sculpture. Courier Dover Publications. p. 129. ISBN 978-0-486-25742-6..
  3. ^ "Ductile". TheFreeDictionary.com. Farlex. Retrieved January 30, 2011. Includes definitions from American Heritage Dictionary of the English Language, Collins English Dictionary: Complete and Unabridged, American Heritage Science Dictionary, and WordNet 3.0.
  4. ^ Masuda, Hideki (2016). "Combined Transmission Electron Microscopy – In situ Observation of the Formation Process and Measurement of Physical Properties for Single Atomic-Sized Metallic Wires". In Janecek, Milos; Kral, Robert (eds.). Modern Electron Microscopy in Physical and Life Sciences. InTech. doi:10.5772/62288. ISBN 978-953-51-2252-4.
  5. ^ Dieter, G. (1986) Mechanical Metallurgy, McGraw-Hill, ISBN 978-0-07-016893-0
  6. ^ Vaccaro, John (2002) Materials handbook, Mc Graw-Hill handbooks, 15th ed.
  7. ^ Schwartz, M. (2002) CRC encyclopedia of materials parts and finishes, 2nd ed.
  8. ^ Che Lah, Nurul Akmal and Trigueros, Sonia (2019). "Synthesis and modelling of the mechanical properties of Ag, Au and Cu nanowires". Sci. Technol. Adv. Mater. 20 (1): 225–261. doi:10.1080/14686996.2019.1585145. PMC 6442207. PMID 30956731.CS1 maint: Multiple names: authors list (link)
  9. ^ John, Vernon (1992). Introduction to Engineering Materials, 3rd ed. New York: Industrial Press. ISBN 0-8311-3043-1.

External links

3003 aluminium alloy

3003 aluminium alloy is an alloy in the wrought aluminium-manganese family (3000 or 3xxx series). It can be cold worked (but not, unlike some other types of aluminium alloys, heat-treated) to produce tempers with a higher strength but a lower ductility. Like most other aluminium-manganese alloys, 3003 is a general-purpose alloy with moderate strength, good workability, and good corrosion resistance. It is commonly rolled and extruded, but typically not forged. As a wrought alloy, it is not used in casting. It is also commonly used in sheet metal applications such as gutters, downspouts, roofing, and siding.Alternate designations include 3.0517 and A93003. 3003 aluminium and its various tempers are covered by the ISO standard 6361 and the ASTM standards B209, B210, B211, B221, B483, B491, and B547.

3102 aluminium alloy

3102 aluminium alloy is an alloy in the wrought aluminium-manganese family (3000 or 3xxx series). It is one of the most lightly alloyed grades in the 3000 series, with at least 97.85% aluminium by weight. Like most other aluminium-manganese alloys, 3102 is a general-purpose alloy with moderate strength, good workability, and good corrosion resistance. Being lightly alloyed, it tends on the lower strength and higher corrosion resistance side. It can be cold worked to produce tempers with a higher strength but a lower ductility. It can be formed by rolling, extrusion, and forging. As a wrought alloy, it is not used in casting.3102 aluminium can be alternately referred to by the UNS designation A93102. The alloy and its various tempers are covered by the following ASTM standards:

ASTM B 210: Standard Specification for Aluminum and Aluminum-Alloy Drawn Seamless Tubes

ASTM B 221: Standard Specification for Aluminum and Aluminum-Alloy Extruded Bars, Rods, Wire, Profiles, and Tubes

ASTM B 483: Standard Specification for Aluminum and Aluminum-Alloy Drawn Tube and Pipe for General Purpose Applications

ASTM B 491: Standard Specification for Aluminum and Aluminum-Alloy Extruded Round Tubes for General-Purpose Applications

5454 aluminium alloy

5454 aluminium alloy is an alloy in the wrought aluminium-magnesium family (5000 or 5xxx series). It is closely related to 5154 aluminium alloy. As an aluminium-magnesium alloy, it combines moderate-to-high strength with excellent weldability. Like 5154, 5454 aluminium is commonly used in welded structures such as pressure vessels and ships. As a wrought alloy, it can be formed by rolling, extrusion, and forging (although forging is not common), but not casting. It can be cold worked to produce tempers with a higher strength but a lower ductility. It is generally not clad.Alternate names and designations include 3.3537, N51, and A95454. The alloy and its various tempers are covered by the following standards:

ASTM B 209: Standard Specification for Aluminum and Aluminum-Alloy Sheet and Plate

ASTM B 221: Standard Specification for Aluminum and Aluminum-Alloy Extruded Bars, Rods, Wire, Profiles, and Tubes

ASTM B 547: Standard Specification for Aluminum and Aluminum-Alloy Formed and Arc-Welded Round Tube

ISO 6361: Wrought Aluminium and Aluminium Alloy Sheets, Strips and Plates

6060 aluminium alloy

6060 aluminium alloy is an alloy in the wrought aluminium-magnesium-silicon family (6000 or 6xxx series). It is much more closely related to the alloy 6063 than to 6061. The main difference between 6060 and 6063 is that 6063 has a slightly higher magnesium content. It can be formed by extrusion, forging or rolling, but as a wrought alloy it is not used in casting. It cannot be work hardened, but is commonly heat treated to produce tempers with a higher strength but lower ductility.Alternate names and designations include AlMgSi, 3.3206, and A96060. The alloy and its various tempers are covered by the following standards:

ASTM B 221: Standard Specification for Aluminum and Aluminum-Alloy Extruded Bars, Rods, Wire, Profiles, and Tubes

EN 573-3: Aluminium and aluminium alloys. Chemical composition and form of wrought products. Chemical composition and form of products

EN 754-2: Aluminium and aluminium alloys. Cold drawn rod/bar and tube. Mechanical properties

EN 755-2: Aluminium and aluminium alloys. Extruded rod/bar, tube and profiles. Mechanical properties

ISO 6361: Wrought Aluminium and Aluminium Alloy Sheets, Strips and Plates

Alloy wheel

In the automotive industry, alloy wheels are wheels that are made from an alloy of aluminium or magnesium. Alloys are mixtures of a metal and other elements. They generally provide greater strength over pure metals, which are usually much softer and more ductile. Alloys of aluminium or magnesium are typically lighter for the same strength, provide better heat conduction, and often produce improved cosmetic appearance over steel wheels. Although steel, the most common material used in wheel production, is an alloy of iron and carbon, the term "alloy wheel" is usually reserved for wheels made from nonferrous alloys.

The earliest light-alloy wheels were made of magnesium alloys. Although they lost favor on common vehicles, they remained popular through the 1960s, albeit in very limited numbers. In the mid-to-late 1960s, aluminium-casting refinements allowed the manufacture of safer wheels that were not as brittle. Until this time, most aluminium wheels suffered from low ductility, usually ranging from 2-3% elongation. Because light-alloy wheels at the time were often made of magnesium (often referred to as "mags"), these early wheel failures were later attributed to magnesium's low ductility, when in many instances these wheels were poorly cast aluminium alloy wheels. Once these aluminium casting improvements were more widely adopted, the aluminium wheel took the place of magnesium as low cost, high-performance wheels for motorsports.

Annealing (metallurgy)

Annealing, in metallurgy and materials science, is a heat treatment that alters the physical and sometimes chemical properties of a material to increase its ductility and reduce its hardness, making it more workable. It involves heating a material above its recrystallization temperature, maintaining a suitable temperature for a suitable amount of time, and then cooling.

In annealing, atoms migrate in the crystal lattice and the number of dislocations decreases, leading to a change in ductility and hardness. As the material cools it recrystallizes. For many alloys, including carbon steel, the crystal grain size and phase composition, which ultimately determine the material properties, are dependent on the heating, and cooling rate. Hot working or cold working after the annealing process alter the metal structure, so further heat treatments may be used to achieve the properties required. With knowledge of the composition and phase diagram, heat treatment can be used to adjust between harder and more brittle, to softer and more ductile.

In the cases of copper, steel, silver, and brass, this process is performed by heating the material (generally until glowing) for a while and then slowly letting it cool to room temperature in still air. Copper, silver and brass can be cooled slowly in air, or quickly by quenching in water, unlike ferrous metals, such as steel, which must be cooled slowly to anneal. In this fashion, the metal is softened and prepared for further work—such as shaping, stamping, or forming.

Carbon steel

Carbon steel is a steel with carbon content up to 2.1% by weight. The definition of carbon steel from the American Iron and Steel Institute (AISI) states:

Steel is considered to be carbon steel when:

no minimum content is specified or required for chromium, cobalt, molybdenum, nickel, niobium, titanium, tungsten, vanadium or zirconium, or any other element to be added to obtain a desired alloying effect;

the specified minimum for copper does not exceed 0.40 percent;

or the maximum content specified for any of the following elements does not exceed the percentages noted: manganese 1.65, silicon 0.60, copper 0.60.The term "carbon steel" may also be used in reference to steel which is not stainless steel; in this use carbon steel may include alloy steels.

As the carbon percentage content rises, steel has the ability to become harder and stronger through heat treating; however, it becomes less ductile. Regardless of the heat treatment, a higher carbon content reduces weldability. In carbon steels, the higher carbon content lowers the melting point.

Coining (metalworking)

Coining is a form of precision stamping in which a workpiece is subjected to a sufficiently high stress to induce plastic flow on the surface of the material. A beneficial feature is that in some metals, the plastic flow reduces surface grain size, and work hardens the surface, while the material deeper in the part retains its toughness and ductility. The term comes from the initial use of the process: manufacturing of coins.

Coining is used to manufacture parts for all industries and is commonly used when high relief or very fine features are required.

For example, it is used to produce coins, badges, buttons, precision-energy springs and precision parts with small or polished surface features.

Coining is a cold working process similar in other respects to forging, which takes place at elevated temperature; it uses a great deal of force to plastically deform a workpiece, so that it conforms to a die. Coining can be done using a gear driven press, a mechanical press, or more commonly, a hydraulically actuated press. Coining typically requires higher tonnage presses than stamping, because the workpiece is plastically deformed and not actually cut, as in some other forms of stamping. The coining process is preferred when there is a high tonnage.

Copper conductor

Copper has been used in electrical wiring since the invention of the electromagnet and the telegraph in the 1820s. The invention of the telephone in 1876 created further demand for copper wire as an electrical conductor.Copper is the electrical conductor in many categories of electrical wiring. Copper wire is used in power generation, power transmission, power distribution, telecommunications, electronics circuitry, and countless types of electrical equipment. Copper and its alloys are also used to make electrical contacts. Electrical wiring in buildings is the most important market for the copper industry. Roughly half of all copper mined is used to manufacture electrical wire and cable conductors.

Ductility (Earth science)

In Earth science, as opposed to Materials Science, Ductility refers to the capacity of a rock to deform to large strains without macroscopic fracturing. Such behavior may occur in unlithified or poorly lithified sediments, in weak materials such as halite or at greater depths in all rock types where higher temperatures promote crystal plasticity and higher confining pressures suppress brittle fracture. In addition, when a material is behaving ductilely, it exhibits a linear stress vs strain relationship past the elastic limit.Ductile deformation is typically characterized by diffuse deformation (i.e. lacking a discrete fault plane) and on a stress-strain plot is accompanied by steady state sliding at failure, compared to the sharp stress drop observed in experiments during brittle failure.

Elgiloy

Elgiloy (Co-Cr-Ni Alloy) is a "super-alloy" consisting of 39-41% Cobalt, 19-21% Chromium, 14-16% Nickel, 11.3-20.5% Iron, 6-8% Molybdenum, and 1.5-2.5% Manganese.

It is used to make springs that are corrosion resistant and exhibit high strength, ductility, and good fatigue life. These same properties led to it being used for control cables in the Lockheed SR-71 Blackbird airplane.Elgiloy meets specifications AMS 5876, AMS 5833, and UNS R30003.

Due to its chemical composition, Elgiloy is highly resistant to sulfide stress corrosion cracking and pitting, and can operate at temperatures up to 454°C.

Embrittlement

Embrittlement is a loss of ductility of a material, making it brittle. Various materials have different mechanisms of embrittlement.

Hydrogen embrittlement is the effect of hydrogen absorption on some metals and alloys.

Sulfide stress cracking is the embrittlement caused by absorption of hydrogen sulfide.

Adsorption embrittlement is the embrittlement caused by wetting.

Liquid metal embrittlement (LME) is the embrittlement caused by liquid metals.

Metal-induced embrittlement (MIE) is the embrittlement caused by diffusion of atoms of metal, either solid or liquid, into the material.

Neutron embrittlement causes embrittlement of some materials, notably certain metals. neutron-induced swelling, and buildup of Wigner energy. This is a process especially important for neutron moderators and nuclear reactor vessels (see ductility).

The primary embrittlement mechanism of plastics is gradual loss of plasticizers, usually by overheating or aging.

The primary embrittlement mechanism of asphalt is by oxidation, which is most severe in warmer climates. Asphalt pavement embrittlement can lead to various forms of cracking patterns, including longitudinal, transverse, and block (hexagonal). Asphalt oxidation is related to polymer degradation, as these materials bear similarities in their chemical composition.

Formability

Formability is the ability of a given metal workpiece to undergo plastic deformation without being damaged. The plastic deformation capacity of metallic materials, however, is limited to a certain extent, at which point, the material could experience tearing or fracture (breakage).

Processes affected by the formability of a material include: rolling, extrusion, forging, rollforming, stamping, and hydroforming.

Hot working

Hot working process metals are plastically deformed above their recrystallization temperature. Being above the recrystallization temperature allows the material to recrystallize during deformation. This is important because recrystallization keeps the materials from strain hardening, which ultimately keeps the yield strength and hardness low and ductility high. This contrasts with cold working.

Many kinds of working, including rolling, forging, extrusion, and drawing, can be done with hot metal.

Post weld heat treatment

Post weld heat treatment (PWHT) is a controlled process in which a material that has been welded is reheated to a temperature below its lower critical transformation temperature, and then it is held at that temperature for a specified amount of time. It is often referred to as being any heat treatment performed after welding; however, within the oil, gas, and petrochemical industries, it has a specific meaning. Industry codes, such as the ASME Pressure Vessel and Piping Codes, often require mandatory performance of PWHT on certain materials to ensure a safe design with optimal mechanical and metallurgical properties.The need for PWHT is mostly due to the residual stresses and micro-structural changes that occur after welding has been completed. During the welding process, a high temperature gradient is experienced between the weld metal and the parent material. As the weld cools, residual stress is formed. For thicker materials, these stresses can reach an unacceptable level and exceed design stresses. Therefore, the part is heated to a specified temperature for a given amount of time to reduce these stresses to an acceptable level. In addition to residual stresses, microstructural changes occur due to the high temperatures induced by the welding process. These changes can increase hardness of the material and reduce toughness and ductility. The use of PWHT can help reduce any increased hardness levels and improve toughness and ductility to levels acceptable for design.The requirements specified within various pressure vessels and piping codes are mostly due to the chemical makeup and thickness of the material. Codes such as ASME Section VIII and ASME B31.3 will require that a specified material be post weld heat treated if it is over a given thickness. Codes also require PWHT based solely on the micro-structural make-up of the material. A final consideration in deciding the need for PWHT is based on the components' intended service, such as one with a susceptibility to stress corrosion cracking. In such cases, PWHT is mandatory regardless of thickness.

Shear zone

A shear zone is a very important structural discontinuity surface in the Earth's crust and upper mantle. It forms as a response to inhomogeneous deformation partitioning strain into planar or curviplanar high-strain zones. Intervening (crustal) blocks stay relatively unaffected by the deformation. Due to the shearing motion of the surrounding more rigid medium, a rotational, non co-axial component can be induced in the shear zone. Because the discontinuity surface usually passes through a wide depth-range, a great variety of different rock types with their characteristic structures are produced.

Titanium aluminide

Titanium aluminide, TiAl, is an intermetallic chemical compound. It is lightweight and resistant to oxidation and heat, however it suffers from low ductility. The density of gamma TiAl is about 4.0 g/cm³. It finds use in several applications including automobiles and aircraft. The development of TiAl based alloys began about 1970; however the alloys have been used in these applications only since about 2000.

Toughness

In materials science and metallurgy, toughness is the ability of a material to absorb energy and plastically deform without fracturing. One definition of material toughness is the amount of energy per unit volume that a material can absorb before rupturing. It is also defined as a material's resistance to fracture when stressed.

Toughness requires a balance of strength and ductility.

Work hardening

Work hardening, also known as strain hardening, is the strengthening of a metal or polymer by plastic deformation. Work hardening may be desirable, undesirable, or inconsequential, depending on the context.

This strengthening occurs because of dislocation movements and dislocation generation within the crystal structure of the material. Many non-brittle metals with a reasonably high melting point as well as several polymers can be strengthened in this fashion. Alloys not amenable to heat treatment, including low-carbon steel, are often work-hardened. Some materials cannot be work-hardened at low temperatures, such as indium, however others can only be strengthened via work hardening, such as pure copper and aluminum.

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