|
Split-Hopkinson Pressure Bar
The split-Hopkinson pressure bar, named after Bertram Hopkinson, sometimes also called a Kolsky bar, is an apparatus for testing the dynamic stress–strain response of materials. History The Hopkinson pressure bar was first suggested by Bertram Hopkinson in 1914 as a way to measure stress pulse propagation in a metal bar. Later, in 1949 Herbert Kolsky refined Hopkinson's technique by using two Hopkinson bars in series, now known as the split-Hopkinson bar, to measure stress and strain, incorporating advancements in the cathode ray oscilloscope in conjunction with electrical condenser units to record the pressure wave propagation in the pressure bars as pioneered by Rhisiart Morgan Davies a year earlier in 1948. Later modifications have allowed for tensile, compression, and torsion testing. Operation Although there are various setups and techniques currently in use for the split-Hopkinson pressure bar, the underlying principles for the test and measurement are the same. The sp ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Bertram Hopkinson
Bertram Hopkinson (11 January 1874 – 26 August 1918) was a British patent lawyer and Professor of Mechanism and Applied Mechanics at Cambridge University. In this position he researched flames, explosions and metallurgy and became a pioneer designer of the internal combustion engine. Hopkinson was born in Birmingham, in 1874, the son of John Hopkinson, an electrical engineer. He read law at Trinity College, Cambridge, and became a lawyer after his graduation. Following the death of his father, brother and two of his sisters in a mountaineering accident in 1898, Hopkinson switched to a career in engineering instead. In 1903, Hopkinson was elected to the Cambridge chair in mechanism and applied mechanics, and in 1910 he was elected a Fellow of the Royal Society. During World War I he was commissioned into the Royal Engineers, and opened a research establishment at Orford Ness where he and his team researched weapons, sights, and ammunition. In 1915, Hopkinson discovered a s ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Stress (physics)
In continuum mechanics, stress is a physical quantity. It is a quantity that describes the magnitude of forces that cause deformation. Stress is defined as ''force per unit area''. When an object is pulled apart by a force it will cause elongation which is also known as deformation, like the stretching of an elastic band, it is called tensile stress. But, when the forces result in the compression of an object, it is called compressive stress. It results when forces like Tension (physics), tension or Compression (physics), compression act on a body. The greater this force and the smaller the cross-sectional area of the body on which it acts, the greater the stress. Therefore, stress is measured in newton per square meter (N/m2) or pascal (Pa). Stress expresses the internal forces that neighbouring particles of a continuous material exert on each other, while deformation (mechanics)#Strain, strain is the measure of the deformation of the material. For example, when a solid vertic ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Strain (materials Science)
In physics, deformation is the continuum mechanics transformation of a body from a ''reference'' configuration to a ''current'' configuration. A configuration is a set containing the positions of all particles of the body. A deformation can occur because of external loads, intrinsic activity (e.g. muscle contraction), body forces (such as gravity or electromagnetic forces), or changes in temperature, moisture content, or chemical reactions, etc. Strain is related to deformation in terms of ''relative'' displacement of particles in the body that excludes rigid-body motions. Different equivalent choices may be made for the expression of a strain field depending on whether it is defined with respect to the initial or the final configuration of the body and on whether the metric tensor or its dual is considered. In a continuous body, a deformation field results from a stress field due to applied forces or because of some changes in the temperature field of the body. The relat ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Hopkinson Bars
Hopkinson is a surname of English and Welsh origin. Notable people with the surname include: * Abdur Rahman Slade Hopkinson (born 1934), West Indian writer * Alfred Hopkinson (18511939), British politician * Alister Hopkinson (194199), New Zealand rugby union player * Amanda Hopkinson (born 1948), British scholar and literary translator * Austin Hopkinson (18791962), British politician * Barney Hopkinson (born before 1965), British Anglican priest * Bertram Hopkinson (18741918), British engineer ** Split-Hopkinson pressure bar, an apparatus for testing the dynamic stress-strain response of materials, named after Bertram Hopkinson * Bobby Hopkinson (born 1990), English footballer * Carl Hopkinson (born 1981), English cricketer * Charles Hopkinson (18691962), American artist * Deborah Hopkinson (born before 2004), American writer of children's books * Eddie Hopkinson (19352004), English football goalkeeper * Edward Hopkinson (18591922), British politician and engineer * Emilius Hop ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Cathode Ray
Cathode rays or electron beam (e-beam) are streams of electrons observed in discharge tubes. If an evacuated glass tube is equipped with two electrodes and a voltage is applied, glass behind the positive electrode is observed to glow, due to electrons emitted from the cathode (the electrode connected to the negative terminal of the voltage supply). They were first observed in 1859 by German physicist Julius Plücker and Johann Wilhelm Hittorf, and were named in 1876 by Eugen Goldstein ''Kathodenstrahlen'', or cathode rays. In 1897, British physicist J. J. Thomson showed that cathode rays were composed of a previously unknown negatively charged particle, which was later named the ''electron''. Cathode-ray tubes (CRTs) use a focused beam of electrons deflected by electric or magnetic fields to render an image on a screen. Description Cathode rays are so named because they are emitted by the negative electrode, or cathode, in a vacuum tube. To release electrons into the tube, th ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Oscilloscope
An oscilloscope (informally a scope) is a type of electronic test instrument that graphically displays varying electrical voltages as a two-dimensional plot of one or more signals as a function of time. The main purposes are to display repetitive or single waveforms on the screen that would otherwise occur too briefly to be perceived by the human eye. The displayed waveform can then be analyzed for properties such as amplitude, frequency, rise time, time interval, distortion, and others. Originally, calculation of these values required manually measuring the waveform against the scales built into the screen of the instrument. Modern digital instruments may calculate and display these properties directly. Oscilloscopes are used in the sciences, medicine, engineering, automotive and the telecommunications industry. General-purpose instruments are used for maintenance of electronic equipment and laboratory work. Special-purpose oscilloscopes may be used to analyze an automotive ign ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Rhisiart Morgan Davies
Rhisiart Morgan Davies (4 February 1903 – 1958) was a Welsh physicist. He was born in Corris, Gwynedd, and attended schools in Machynlleth and Dolgellau before, in 1921, winning a scholarship to study physics at the University College of Wales, Aberystwyth. After graduating first-class honours in physics in 1924, he was appointed to the research staff team in H.M. Signals School in Portsmouth, but did not remain in the position for long, instead returning to Aberystwyth to work, initially, as an assistant lecturer in the physics department, before being appointed a lecturer in 1928. Whilst there he worked on a D.Sc. (Wales) degree for important work on the measurement of dielectric and elastic constants under dynamic conditions, which he completed in 1937. In 1938 he received a Leverhulme Research Fellowship award, enabling him to work in Cambridge, where he became one of the leading specialists in the study of 'stress waves'. He received a Ph.D. degree from Cambridge for his ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Stress Wave
Linear elasticity is a mathematical model of how solid objects deform and become internally stressed due to prescribed loading conditions. It is a simplification of the more general nonlinear theory of elasticity and a branch of continuum mechanics. The fundamental "linearizing" assumptions of linear elasticity are: infinitesimal strains or "small" deformations (or strains) and linear relationships between the components of stress and strain. In addition linear elasticity is valid only for stress states that do not produce yielding. These assumptions are reasonable for many engineering materials and engineering design scenarios. Linear elasticity is therefore used extensively in structural analysis and engineering design, often with the aid of finite element analysis. Mathematical formulation Equations governing a linear elastic boundary value problem are based on three tensor partial differential equations for the balance of linear momentum and six infinitesimal str ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Plasticity (physics)
In physics and materials science, plasticity, also known as plastic deformation, is the ability of a solid material to undergo permanent Deformation (engineering), deformation, a non-reversible change of shape in response to applied forces. For example, a solid piece of metal being bent or pounded into a new shape displays plasticity as permanent changes occur within the material itself. In engineering, the transition from Elasticity (physics), elastic behavior to plastic behavior is known as Yield (engineering), yielding. Plastic deformation is observed in most materials, particularly metals, soils, Rock (geology), rocks, concrete, and foams. However, the physical mechanisms that cause plastic deformation can vary widely. At a crystalline scale, plasticity in metals is usually a consequence of dislocations. Such defects are relatively rare in most crystalline materials, but are numerous in some and part of their crystal structure; in such cases, plastic crystallinity can res ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Strain Gauge
A strain gauge (also spelled strain gage) is a device used to measure strain on an object. Invented by Edward E. Simmons and Arthur C. Ruge in 1938, the most common type of strain gauge consists of an insulating flexible backing which supports a metallic foil pattern. The gauge is attached to the object by a suitable adhesive, such as cyanoacrylate. As the object is deformed, the foil is deformed, causing its electrical resistance to change. This resistance change, usually measured using a Wheatstone bridge, is related to the strain by the quantity known as the gauge factor. History Edward E. Simmons and Professor Arthur C. Ruge independently invented the strain gauge. Simmons was involved in a research project by Dätwyler and Clark at Caltech between 1936 and 1938. They researched the stress-strain behavior of metals under shock loads. Simmon came up with an original way to measure the force introduced into the sample by equipping a dynamometer with fine resistance wires ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Strain Rate
In materials science, strain rate is the change in strain (deformation) of a material with respect to time. The strain rate at some point within the material measures the rate at which the distances of adjacent parcels of the material change with time in the neighborhood of that point. It comprises both the rate at which the material is expanding or shrinking (expansion rate), and also the rate at which it is being deformed by progressive shearing without changing its volume (shear rate). It is zero if these distances do not change, as happens when all particles in some region are moving with the same velocity (same speed and direction) and/or rotating with the same angular velocity, as if that part of the medium were a rigid body. The strain rate is a concept of materials science and continuum mechanics that plays an essential role in the physics of fluids and deformable solids. In an isotropic Newtonian fluid, in particular, the viscous stress is a linear function of the ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
