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What's Bend Testing?
Bend testing, generally called flexure testing or transverse beam testing, measures the habits of supplies subjected to easy beam loading. It is commonly carried out on relatively versatile materials such as polymers, wood, and composites. At its most simple stage a bend test is carried out on a common testing machine by placing a specimen on assist anvils and bending it by way of utilized power on 1 or 2 loading anvils with the intention to measure its properties.
Bend or flex tests apply force with either a single upper anvil at the midpoint, which is a 3-level bend test, or two upper anvils equidistant from the middle, a 4-level bend test. In a 3-point test the area of uniform stress is quite small and concentrated under the middle loading point. In a 4-level test, the realm of uniform stress exists between the inner span loading factors (typically half the size of the outer span). Relying on the type of fabric being tested, there are many completely different flex fixtures that could be appropriate.
Engineers usually wish to understand numerous elements of fabric’s habits, however a simple uniaxial tension or compression test might not provide all crucial information. Because the specimen bends or flexes, it is subjected to a posh mixture of forces including stress, compression, and shear. For this reason, bend testing is commonly used to evaluate the reaction of materials to realistic loading situations. Flexural test data can be particularly helpful when a material is for use as a help structure. For instance, a plastic chair wants to offer support in many directions. While the legs are in compression when in use, the seat might want to withstand flexural forces utilized from the particular person seated. Not only do manufacturers wish to provide a product that can hold expected loads, the fabric also needs to return to its original shape if any bending occurs.
Bend tests are generally performed on a universal testing machine using 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 usually rigid and may be made of assorted supplies reminiscent of 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 area of shear stress along the midline. To make sure that major failure comes from tensile or compression stress, the shear stress have to 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=sixteen is acceptable. Some supplies require S/d=32 to 64 to keep the shear stress low enough.
Maximum fiber stress and maximum strain are calculated for increments of load. Results are plotted on a stress-strain diagram. Flexural energy is defined as the utmost stress within the outermost fiber. This is calculated at the surface of the specimen on the convex or tension 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 find out slope.
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