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What's Bend Testing?

 

Bend testing, typically called flexure testing or transverse beam testing, measures the behavior of materials subjected to simple beam loading. It's commonly carried out on relatively versatile supplies comparable to polymers, wood, and composites. At its most elementary degree a bend test is carried out on a universal testing machine by putting a specimen on assist anvils and bending it by way of applied drive on 1 or 2 loading anvils as a way to measure its properties.

 

 

Bend or flex tests apply drive with either a single higher anvil at the midpoint, which is a 3-point bend test, or higher anvils equidistant from the center, a 4-level bend test. In a 3-point test the world of uniform stress is quite small and concentrated under the middle loading point. In a four-point test, the area 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 numerous totally different flex fixtures that may be appropriate.

 

 

Engineers often need to understand various points of material’s conduct, however a easy uniaxial pressure or compression test may not provide all needed information. Because the specimen bends or flexes, it is subjected to a complex 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 will be particularly useful when a material is for use as a support structure. For instance, a plastic chair needs to offer support in many 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 want to provide a product that can hold expected loads, the material also needs to return to its original form if any bending occurs.

 

 

Bend tests are usually performed on a universal testing machine utilizing a 3 or four level bend fixture. Variables like test speed and specimen dimensions are determined by the ASTM or ISO commonplace being used. Specimens are generally inflexible and will be made of varied materials akin to plastic, metal, wood, and ceramics. The most common shapes are rectangular bars and cylindrical-formed specimens.

 

 

A bend test produces tensile stress within the convex side of the specimen and compression stress in the concave side. This creates an area of shear stress alongside the midline. To ensure that primary 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=sixteen is acceptable. 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 power is defined as the maximum 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 area, a secant line is fitted to the curve to find out slope.

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