Types of Tests
Flexural
A flexure test, also called a transverse test, simply measures the bending behavior of material subjected to simple beam loading. The most commonly recorded results from this test are maximum fiber stress and maximum strain, and are plotted on a stress vs strain graph. The flexural strength is defined as the maximum stress in the outermost fiber and is calculated at the tensile surface of the specimen. Flexural modulus is calculated from the initial slope of the stress vs. strain graph and if the curve has no linear region, a secant line through the graph origin is fitted to the curve to determine slope.
Why Perform a Flexure Test?
A flexure test introduces tensile stresses in the convex side of the bending specimen and compressive stresses in the concave side, so creating an area of shear stress throughout the specimen. To ensure the specimen failure comes from tensile or compression stresses, these shear stresses must be minimized; which is done by controlling the span to depth ratio (S/d, where S is the length of the outer span and d is the height (depth) of the specimen). For most materials a span to depth ratio of 16 is acceptable but some materials require the ratio to be between 32 and 64 to keep the shear stress low enough.
Flexure testing is often done on relatively flexible materials such as polymers, wood and composites, using either a 3-point or a 4-point flex configuration. In a 3-point test the area of uniform stress is quite small and concentrated under the center loading point; in a 4-point test, the area of uniform stress exists between the inner span loading points (typically half the outer span length).
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