Bend testing, sometimes called flexure testing or transverse beam testing, measures the habits of supplies subjected to simple beam loading. It is commonly carried out on relatively flexible supplies such as polymers, wood, and composites. At its most elementary degree a bend test is carried out on a universal testing machine by inserting a specimen on help anvils and bending it through utilized drive on 1 or 2 loading anvils with a view to measure its properties.
Bend or flex tests apply force with either a single higher anvil on the midpoint, which is a three-point bend test, or two higher anvils equidistant from the middle, a four-level bend test. In a 3-level test the world of uniform stress is quite small and concentrated under the center loading point. In a 4-level test, the world of uniform stress exists between the inside span loading points (typically half the size of the outer span). Relying on the type of fabric being tested, there are various totally different flex fixtures which may be appropriate.
Engineers usually need to understand varied features of fabric’s conduct, but a simple uniaxial stress or compression test may not provide all mandatory information. As the specimen bends or flexes, it is subjected to a fancy mixture of forces including rigidity, compression, and shear. For this reason, bend testing is commonly used to judge the response of supplies to realistic loading situations. Flexural test data might be particularly useful when a material is to be used as a support structure. For instance, a plastic chair wants to provide assist in lots of 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 manufacturers want to provide a product that can hold anticipated loads, the fabric additionally needs to return to its original form if any bending occurs.
Bend tests are typically performed on a universal testing machine utilizing a three or four level bend fixture. Variables like test speed and specimen dimensions are decided by the ASTM or ISO commonplace being used. Specimens are generally inflexible and could be made of various supplies akin to plastic, metal, wood, and ceramics. The most common shapes are rectangular bars and cylindrical-formed specimens.
A bend test produces tensile stress in the convex side of the specimen and compression stress within the concave side. This creates an space of shear stress alongside the midline. To make sure that primary failure comes from tensile or compression stress, the shear stress have to be minimized by controlling the span to depth ratio; the length of the outer span divided by the height (depth) of the specimen. For many supplies S/d=sixteen is settle forable. Some materials require S/d=32 to sixty four to keep the shear stress low enough.
Maximum fiber stress and most strain are calculated for increments of load. Outcomes are plotted on a stress-strain diagram. Flexural strength is defined as the utmost stress within the outermost fiber. This is calculated at the surface of the specimen on the convex or pressure side. Flexural modulus is calculated from the slope of the stress vs. deflection curve. If the curve has no linear area, a secant line is fitted to the curve to determine slope.
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