Bend testing, sometimes called flexure testing or transverse beam testing, measures the habits of supplies subjected to simple beam loading. It is commonly performed on relatively flexible materials comparable to polymers, wood, and composites. At its most simple level a bend test is carried out on a common testing machine by placing a specimen on two help anvils and bending it by means of utilized power on 1 or 2 loading anvils to be able to measure its properties.
Bend or flex tests apply pressure with either a single upper anvil at the midpoint, which is a 3-level 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 four-level test, the area of uniform stress exists between the inner span loading points (typically half the length of the outer span). Relying on the type of material being tested, there are numerous totally different flex fixtures that could be appropriate.
Engineers often wish to understand various facets of fabric’s habits, but a simple uniaxial tension or compression test might not provide all vital information. Because the specimen bends or flexes, it is subjected to a posh combination of forces including stress, compression, and shear. For this reason, bend testing is commonly used to evaluate the response of supplies to realistic loading situations. Flexural test data can be particularly helpful when a cloth is for use as a assist structure. For example, a plastic chair wants to give assist in lots of directions. While the legs are in compression when in use, the seat will need to withstand flexural forces applied from the particular person seated. Not only do manufacturers need to provide a product that can hold expected loads, the fabric also must return to its authentic form if any bending occurs.
Bend tests are typically carried out on a universal testing machine using a 3 or four point bend fixture. Variables like test speed and specimen dimensions are decided by the ASTM or ISO customary being used. Specimens are typically inflexible and can be made of varied supplies akin 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 within the concave side. This creates an space of shear stress alongside the midline. To make sure that major failure comes from tensile or compression stress, the shear stress should be minimized by controlling the span to depth ratio; the size of the outer span divided by the height (depth) of the specimen. For most supplies S/d=16 is settle forable. Some supplies require S/d=32 to sixty four to keep the shear stress low enough.
Most fiber stress and maximum strain are calculated for increments of load. Outcomes are plotted on a stress-strain diagram. Flexural energy is defined as the utmost stress in 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 region, a secant line is fitted to the curve to determine slope.
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