DAMPING – Damping is an influence within or upon an oscillatory system that has the effect of reducing or preventing its oscillation. In physical systems, damping is produced by processes that dissipate the energy stored in the oscillation.
Damping, in physics, restraining of vibratory motion, such as mechanical oscillations, noise, and alternating electric currents, by dissipation of energy. Unless a child keeps pumping a swing, its motion dies down because of damping.
In most cases, damping converts electrical or mechanical energy into thermal energy. In layman’s terms, damping reduces or eliminates vibrations, movement, or noise by converting the vibration, movement, or noise energy into heat.
DEFLASHING – cryogenic de-flashing uses a cryogenic-grade polycarbonate media that’s extruded into cylinders or beads and supplied in various sizes. Cryogenic tumble de-flashing and dry ice de-flashing use dry ice particles instead.
Cryogenic de-flashing is used to remove unwanted residual mould flash from newly moulded or cast rubber and plastic parts. This die cast de-flashing method utilizes cryogenic temperatures that cause the flash to become stiff or brittle and to break away cleanly, even from oddly shaped parts.
Cryogenics is the production of and behaviour of materials at very low temperatures. Ultra-cold temperatures change the chemical properties of materials, which provide an interesting area of study for researchers who wish to examine the materials as they transition from gas to liquid to a solid state.
DELAMINATION – Delamination is a mode of failure where a material fractures into layers. A variety of materials including laminate composites and concrete can fail by delamination. Processing can create layers in materials such as steel formed by rolling and plastics and metals from 3D printing which can fail from layer separation.
Delamination is a critical failure mechanism in laminated fibre-reinforced polymer matrix composites, and is one of the key factors differentiating their behaviour from that of metallic structures. It is caused by high interlaminar stresses in conjunction with the typically very low through-thickness strength.
Delamination can be described as the separating of layers from each other or the formation of unconnected layers. Delamination irregularity can be formed during the manufacturing stage of a structural element, service loads and other effects such as corrosion.
DeMATTIA FLEX TEST – Once a crack has formed, it will keep growing, and this can eventually cause the product to break completely. This test distinguishes between two methods: flex cracking: how long does it take before a crack forms. crack growth: measuring the crack growth after intentionally making a cut.
Specimens are subject to repeated flexing through a given distance for a specified period of time so that the flex cracking and crack growth can be known. The instrument has a solid aluminum and stainless steel structure that ensures long life time and ensures repeatable results. The special movement system with both sample holders moving in opposite direction ensures considerable reduction of vibration and noise in comparison with other testers. The oscillation speed can be adjusted from 60 to 300 cycles / min. The number of cycles can be defined by the user and the test automatically stops when the set number of cycles has been reached. The flexure stroke can be adjusted from 0 to 56 mm and the distance of the clamps can be adjusted.
Up to 16 test pieces can be mounted simultaneously. The system is with a temperature chamber, the sample holding system is located in a thermal chamber for the execution of flexure tests with temperature control.
Thermal chambers are for tests above room temperature and up to 250 °C. The door of the heat chamber is fitted with a safety switch.
DENSITY– A material’s density is defined as its mass per unit volume. Put another way, density is the ratio between mass and volume or mass per unit volume. … Density is essentially a measurement of how tightly matter is crammed together.
Density is a measure of mass per volume. The average density of an object equals its total mass divided by its total volume. An object made from a comparatively dense material (such as iron) will have less volume than an object of equal mass made from some less dense substance (such as water).
the quantity per unit volume, unit area, or unit length: as. a : the mass of a substance per unit volume. b : the distribution of a quantity (as mass, electricity, or energy) per unit usually of space. c : the average number of individuals or units per space unit a population density of 500 per square mile.
DISPERSION – Dispersion, in wave motion, any phenomenon associated with the propagation of individual waves at speeds that depend on their wavelengths. … Dispersion is sometimes called the separation of light into colours, an effect more properly called angular dispersion.
In statistics, dispersion (also called variability, scatter, or spread) is the extent to which a distribution is stretched or squeezed. Common examples of measures of statistical dispersion are the variance, standard deviation, and interquartile range.
DRUM CURE– At home, you can ease the pain of a ruptured eardrum with heat and pain relievers. Placing a warm, dry compress on your ear several times daily can help. Promote healing by not blowing your nose any more than absolutely necessary.
All types of eardrum repairs are performed by an ENT surgeon in the operating room under general anesthesia. In this day and age, general anesthesia is very safe and your child will be carefully monitored during the procedure. This simplest kind of repair is called a patch myringoplasty [mer-RING-go-plass-tee].
While there is no cure currently for this type of hearing loss to regenerate the damaged parts of the inner ear your hearing loss can be treated rather effectively with hearing aids.
DUMBBELL – Stand with a weight in each hand, near hips, palms forward. Shoulders and elbows should be pinned against the wall. Without moving upper arms, curl weights up until dumbbells are shoulder level, then lower to starting position.
DUROMETER – Durometer or Shore durometer is a standardized way to measure the hardness of materials like rubber (elastomers) and plastics. Durometer measurement scales range from 0 to 100 but there is no such thing as a durometer unit of measurement. Another way of saying this is that durometer is a dimensionless measurement.
Each durometer or hardness tester measures the depth of an indentation in the material caused by a defined force of a given geometric presser foot. … The depth of the indentation reflects the hardness of the material. A general distinction is made between static and dynamic methods.
Durometer utilizes an indenter loaded by a calibrated spring. The measured hardness is determined by the penetration depth of the indenter under the load. Two different indenter shapes (see the picture below) and two different spring loads are used for two Shore scales (A and D).
DUROMETER HARDNESS– Durometer or Shore durometer is a standardized way to measure the hardness of materials like rubber (elastomers) and plastics. Durometer measurement scales range from 0 to 100 but there is no such thing as a durometer unit of measurement. Another way of saying this is that durometer is a dimensionless measurement.
Durometer numbers simply represent a relative comparison of hardness between different but similar materials that have had their hardness measured using the same durometer scale, device and measurement standard.
In general, a higher durometer elastomer is harder than a lower durometer elastomer. For example, a 90A durometer polyurethane tubing is harder than a 70A polyurethane tubing.
Shore hardness or durometer is actually a collection of internationally recognized measurement standards based on Shore durometers. Shore durometers themselves are measuring devices that use specific, standardized techniques for measuring hardness. Shore hardness standards provide a consistent, universal, easily reproducible reference that anyone can use to compare material hardness.
DYNAMIC PROPERTIES – Dynamic properties of viscoelastic materials are generally recognized on the basis of dynamic modulus, which is also known as the complex modulus. Theoretically, it can be defined as the ratio of stress to strain resulting from an oscillatory load applied under tensile, shear, or compression mode.
Datal – Day wage work, minimum wage.
Dead work – Work for which the miner is not paid.
Deep – Workings below the level of the pit bottom or main levels extending there from.
Demonstrated reserves – A collective term for the sum of coal in both measured and indicated resources and reserves.
Deposit – Mineral deposit or ore deposit is used to designate a natural occurrence of a useful mineral, or an ore, in sufficient extent and degree of concentration to invite exploitation.
Depth – The word alone generally denotes vertical depth below the surface. In the case of incline shafts and boreholes it may mean the distance reached from the beginning of the shaft or hole, the borehole depth, or the inclined depth.
Detectors – Specialized chemical or electronic instruments used to detect mine gases.
Detonator – A device containing a small detonating charge that is used for detonating an explosive, including, but not limited to, blasting caps, exploders, electric detonators, and delay electric blasting caps.
Development mining – Work undertaken to open up coal reserves as distinguished from the work of actual coal extraction.
Diffusion – Blending of a gas and air, resulting in a homogeneous mixture. Blending of two or more gases.
Diffuser fan – A fan mounted on a continuous miner to assist and direct air delivery from the machine to the face.
Dilute – To lower the concentration of a mixture; in this case the concentration of any hazardous gas in mine air by addition of fresh intake air.
Dilution – The contamination of ore with barren wall rock in stopping.
Dip – The inclination of a geologic structure (bed, vein, fault, etc.) from the horizontal; dip is always measured downwards at right angles to the strike.
Downcast – The passage through which air is drawn through the mine.
Draeger men – A mine worker or official, engaged in mine rescue while wearing a self-contained breathing apparatus.
Dragline – A large excavation machine used in surface mining to remove overburden (layers of rock and soil) covering a coal seam. The dragline casts a wire rope-hung bucket a considerable distance, collects the dug material by pulling the bucket toward itself on the ground with a second wire rope (or chain), elevates the bucket, and dumps the material on a spoil bank, in a hopper, or on a pile.
Drainage – The process of removing surplus ground or surface water either by artificial means or by gravity flow.
Draw slate – A soft slate, shale, or rock from approximately 1 cm to 10 cm thick and located immediately above certain coal seams, which falls quite easily when the coal support is withdrawn.
Drift – A horizontal passage underground. A drift follows the vein, as distinguished from a crosscut that intersects it, or a level or gallery, which may do either.
Drift mine – An underground coal mine in which the entry or access is above water level and generally on the slope of a hill, driven horizontally into a coal seam.
Drill – A machine utilizing rotation, percussion (hammering), or a combination of both to make holes. If the hole is much over 0.4m in diameter, the machine is called a borer.
Drive – To excavate a passage.
Driver – A workman, usually a boy, who drives an underground work horse.
Drilling – The use of such a machine to create holes for exploration or for loading with explosives.
Drum – A revolving cylinder on a stationary hoisting or hauling engine, around which the hoisting or hauling cable is wound.
Dummy – A bag filled with sand, clay, etc., used for stemming a charged hole.
Dump – To unload; specifically, a load of coal or waste; the mechanism for unloading, e.g. a car dump (sometimes called tipple); or, the pile created by such unloading, e.g. a waste dump (also called heap, pile, tip, spoil pike, etc.).