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Buff strength is a design term used in the certification of rail rolling stock. It refers to the required resistance to deformation or permanent damage due to loads applied at the car's ends, such as in a collision. Particular emphasis on buff strength is placed in the United States, with buff strength requirements there being higher than in Europe.
Buff strength requirements grew out of best-practice design standards during the latter part of the nineteenth century. By the twentieth century, a design limit of 400,000 pounds-force (1.8 MN) was required by federal approval agencies. This was upped to 800,000 pounds-force (3.6 MN) for certain categories in 1945. [1]
Federal requirements for buff strength were set in 1999 at 800,000 pounds-force (3.6 MN) for all passenger-carrying units, unless reduced by waivers or special order. The Federal Static and Strength Regulation (49 Code of Federal Regulations § 238.203) requires that a passenger rail car be able to support a longitudinal static compressive load of 400,000 pounds-force (1.8 MN) without permanent deformation.
There are other strength requirements associated with end-structure design. 49 CFR § 238.211 specifies that the cab ends of locomotives, cab cars, and self-powered multiple-unit cars have lead ends capable of supporting 500,000 pounds-force (2.2 MN) longitudinal force at the top of the underframe, and 200,000 pounds-force (0.89 MN) of force above the top of the underframe. [2]
There are multiple certifying and approving agencies in Europe, so universal agreement on strength standards is not guaranteed. A 1977 German standard (VÖV 6.030.1/1977) presented values which have been followed by some other countries. The document was revised in 1992 and is presently known as VDV Recommendation 152 - Structural Requirements to Rail Vehicles for Public Mass Transit in Accordance with BOStrab.
In 1995 the European Common Market Committee for Standardization issued a draft document, Structural Requirements of Railway Vehicle Bodies. It mandated differing design loads for vehicles in differing categories, ranging from 45,000 pounds-force (0.20 MN) for tramways to 450,000 pounds-force (2.0 MN) for passenger coaches and locomotives. [3]
In general the European approach to crashworthiness of passenger coaches puts more emphasis on crumple zones rather than buff strength, meaning that the required design loads are less than those in the United States. This is generally agreed to reduce construction costs. [4]
Crumple zones, crush zones, or crash zones are a structural safety feature used in vehicles, mainly in automobiles, to increase the time over which a change in velocity occurs from the impact during a collision by a controlled deformation; in recent years, it is also incorporated into trains and railcars.
The field of strength of materials typically refers to various methods of calculating the stresses and strains in structural members, such as beams, columns, and shafts. The methods employed to predict the response of a structure under loading and its susceptibility to various failure modes takes into account the properties of the materials such as its yield strength, ultimate strength, Young's modulus, and Poisson's ratio. In addition, the mechanical element's macroscopic properties such as its length, width, thickness, boundary constraints and abrupt changes in geometry such as holes are considered.
In mechanics, compressive strength is the capacity of a material or structure to withstand loads tending to reduce size. In other words, compressive strength resists compression, whereas tensile strength resists tension. In the study of strength of materials, tensile strength, compressive strength, and shear strength can be analyzed independently.
The most common type of spring is the coil spring, which is made out of a long piece of metal that is wound around itself. Coil springs were in use in Roman times, evidence of this can be found in bronze Fibulae — the clasps worn by Roman soldiers among others. These are quite commonly found in Roman archeological digs.
In mechanics, compression is the application of balanced inward ("pushing") forces to different points on a material or structure, that is, forces with no net sum or torque directed so as to reduce its size in one or more directions. It is contrasted with tension or traction, the application of balanced outward ("pulling") forces; and with shearing forces, directed so as to displace layers of the material parallel to each other. The compressive strength of materials and structures is an important engineering consideration.
A bumper is a structure attached to or integrated with the front and rear ends of a motor vehicle, to absorb impact in a minor collision, ideally minimizing repair costs. Stiff metal bumpers appeared on automobiles as early as 1904 that had a mainly ornamental function. Numerous developments, improvements in materials and technologies, as well as greater focus on functionality for protecting vehicle components and improving safety have changed bumpers over the years. Bumpers ideally minimize height mismatches between vehicles and protect pedestrians from injury. Regulatory measures have been enacted to reduce vehicle repair costs and, more recently, impact on pedestrians.
In structural engineering, buckling is the sudden change in shape (deformation) of a structural component under load, such as the bowing of a column under compression or the wrinkling of a plate under shear. If a structure is subjected to a gradually increasing load, when the load reaches a critical level, a member may suddenly change shape and the structure and component is said to have buckled. Euler's critical load and Johnson's parabolic formula are used to determine the buckling stress of a column.
A coupling is a mechanism typically placed at each end of a railway vehicle that connects them together to form a train. A variety of coupler types have been developed over the course of railway history. Key issues in their design include strength, reliability, ease of making connections and operator safety.
Rolling resistance, sometimes called rolling friction or rolling drag, is the force resisting the motion when a body rolls on a surface. It is mainly caused by non-elastic effects; that is, not all the energy needed for deformation of the wheel, roadbed, etc., is recovered when the pressure is removed. Two forms of this are hysteresis losses, and permanent (plastic) deformation of the object or the surface. Note that the slippage between the wheel and the surface also results in energy dissipation. Although some researchers have included this term in rolling resistance, some suggest that this dissipation term should be treated separately from rolling resistance because it is due to the applied torque to the wheel and the resultant slip between the wheel and ground, which is called slip loss or slip resistance. In addition, only the so-called slip resistance involves friction, therefore the name "rolling friction" is to an extent a misnomer.
In mechanics, an impact is when two bodies collide. During this collision, both bodies decelerate. The deceleration causes a high force or shock, applied over a short time period. A high force, over a short duration, usually causes more damage to both bodies than a lower force applied over a proportionally longer duration.
Crashworthiness is the ability of a structure to protect its occupants during an impact. This is commonly tested when investigating the safety of aircraft and vehicles. Different criteria are used to figure out how safe a structure is in a crash, depending on the type of impact and the vehicle involved. Crashworthiness may be assessed either prospectively, using computer models or experiments, or retrospectively, by analyzing crash outcomes. Several criteria are used to assess crashworthiness prospectively, including the deformation patterns of the vehicle structure, the acceleration experienced by the vehicle during an impact, and the probability of injury predicted by human body models. Injury probability is defined using criteria, which are mechanical parameters that correlate with injury risk. A common injury criterion is the head impact criterion (HIC). Crashworthiness is measured after the fact by looking at injury risk in real-world crashes. Often, regression or other statistical methods are used to account for the many other factors that can affect the outcome of a crash.
The British Rail Class 140 was the prototype of the Pacer diesel multiple unit.
In a railway accident, telescoping occurs when the underframe of one vehicle overrides that of another, and smashes through the second vehicle's body. The term is derived from the resulting appearance of the two vehicle bodies: the body of one vehicle may appear to be slid inside the other like the tubes of a collapsible telescope – the body sides, roof and underframe of the latter vehicle being forced apart from each other.
A vehicle frame, also historically known as its chassis, is the main supporting structure of a motor vehicle to which all other components are attached, comparable to the skeleton of an organism.
The container compression test measures the compressive strength of packages such as boxes, drums, and cans. It usually provides a plot of deformation vs compressive force.
Janney couplers are a semi-automatic form of railway coupling that allow rail cars and locomotives to be securely linked together without rail workers having to get between the vehicles. They are also known as American, AAR, APT, ARA, MCB, knuckle, Buckeye, tightlock, Henricot or Centre Buffer Couplers.
The State-of-the-Art Car (SOAC) was a heavy rail mass transit demonstrator vehicle produced for the United States Department of Transportation's Urban Mass Transportation Administration in the 1970s. It was intended to demonstrate the latest technologies to operating agencies and the riding public, and serve to promote existing and proposed transit lines. A single married pair was produced by the St. Louis Car Company in 1972. It operated in intermittent revenue service on six rapid transit systems in five United States cities between May 1974 and January 1977. Since 1989, the two cars have been on display at the Seashore Trolley Museum in Kennebunkport, Maine.
Railworthiness is the property or ability of a locomotive, passenger car, freight car, train or any kind of railway vehicle to be in proper operating condition or to meet acceptable safety standards of project, manufacturing, maintenance and railway use for transportation of persons, luggage or cargo.
A headstock of a rail vehicle is a transverse structural member located at the extreme end of the vehicle's underframe. The headstock supports the coupling at that end of the vehicle, and may also support buffers, in which case it may also be known as a buffer beam. The headstocks form part of the underframe of a locomotive or a railroad car. The headstocks of locomotives, railcars and cabcars also support headlamps and the hoses for air brakes, vacuum brakes as well as the cables for train control and head end power.
EN 15227 is a European standard about the crashworthiness requirements for railway vehicle bodies. It was first resolved in 2008 and it is binding since 2012 for all new vehicles in the European Union.
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