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What's Bend Testing?
Bend testing, sometimes called flexure testing or transverse beam testing, measures the behavior of supplies subjected to simple beam loading. It's commonly carried out on relatively versatile materials equivalent to polymers, wood, and composites. At its most basic level a bend test is performed on a universal testing machine by inserting a specimen on support anvils and bending it by utilized pressure on 1 or 2 loading anvils with a purpose to measure its properties.
Bend or flex tests apply drive with either a single higher anvil on the midpoint, which is a 3-point bend test, or two higher anvils equidistant from the center, a 4-level bend test. In a 3-level test the area of uniform stress is quite small and concentrated under the middle loading point. In a four-level test, the realm of uniform stress exists between the interior span loading points (typically half the size of the outer span). Depending on the type of fabric being tested, there are lots of different flex fixtures that may be appropriate.
Engineers often want to understand varied features of fabric’s behavior, but a easy uniaxial tension or compression test may not provide all necessary information. As the specimen bends or flexes, it is subjected to a posh mixture of forces including rigidity, compression, and shear. For this reason, bend testing is commonly used to guage the response of materials to realistic loading situations. Flexural test data may be particularly useful when a cloth is to be used as a assist structure. For example, a plastic chair needs to provide assist in many directions. While the legs are in compression when in use, the seat will need to withstand flexural forces utilized from the person seated. Not only do producers want to provide a product that can hold anticipated loads, the material also needs to return to its unique shape if any bending occurs.
Bend tests are typically performed on a common testing machine utilizing a three or four point bend fixture. Variables like test speed and specimen dimensions are determined by the ASTM or ISO standard being used. Specimens are generally rigid and could be made of varied materials corresponding to plastic, metal, wood, and ceramics. The most common shapes are rectangular bars and cylindrical-shaped specimens.
A bend test produces tensile stress in the convex side of the specimen and compression stress in the concave side. This creates an area of shear stress along the midline. To make sure that main failure comes from tensile or compression stress, the shear stress must be minimized by controlling the span to depth ratio; the size of the outer span divided by the height (depth) of the specimen. For many supplies S/d=16 is settle forable. Some supplies require S/d=32 to 64 to keep the shear stress low enough.
Maximum fiber stress and most strain are calculated for increments of load. Results are plotted on a stress-strain diagram. Flexural power is defined as the maximum stress in the outermost fiber. This is calculated on the surface of the specimen on the convex or rigidity side. Flexural modulus is calculated from the slope of the stress vs. deflection curve. If the curve has no linear region, a secant line is fitted to the curve to determine slope.
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