Bend and Flexural Testing

An Introduction

Bend testing, also known as flexure testing or transverse beam testing, evaluates materials' behavior under simple beam loading. This test is commonly performed on relatively flexible materials such as polymers, wood, and composites. It involves placing a specimen on two support anvils and bending it through applied force on one or two loading anvils using a universal testing machine to measure its properties.

WHY PERFORM A BEND/FLEX TEST?

Engineers often require a comprehensive understanding of a material's behavior, which a uniaxial tensile or compression test may not provide. Bend testing subjects the specimen to a complex combination of forces including tension, compression, and shear, making it valuable in evaluating materials' reactions to realistic loading situations.

Flexural test data proves particularly useful when a material is utilized as a support structure. For instance, a plastic chair must offer support in multiple directions. While the legs are in compression during use, the seat needs to endure flexural forces from the person seated. Manufacturers not only aim to provide a product capable of bearing expected loads but also demand the material to revert to its original shape if any bending occurs.

TYPES OF BEND/FLEX TESTS

3 Point Bend Test

A 3-point flex test suspends a specimen between two lower anvils while applying force from a single upper anvil centered at the midpoint. Stress is concentrated under the center loading point. Depending on testing standards, the anvils may be fixed, rotated, or rocking.

4 Point Bend Test

A 4-point flex test differs by having two upper anvils equidistant from the specimen's center. The area of uniform stress exists between the inner span loading points, typically half the length of the outer span. Anvils may need to be fixed, rotated, or rocking based on testing requirements. Typically, 4-point tests measure modulus of elasticity in bending for brittle materials.