Bend Test Fixtures are used to convert the axial motion or rotary motion of the ELF and Instron fatigue testers into various forms of bending motion or motions that combine bending and other motions. MDT has developed many types of fixtures for this purpose and the various designs center on the primary purpose of the test. These fixtures are designed to accommodate a statistically significant number of specimens and are often modified to meet the specific test requirements for the customer's device design. All of these test fixtures can be used with PBS baths or fluid flow to provide physiologically relevant environmental conditions. The attached list of fixtures include descriptions of the types of bending performed.
Pure bending test fixtures apply a bend moment to the proximal and distal ends of the device so that the center of the device is in a pure bending configuration.
With cantilevered bend test fixtures, the proximal end of the specimen is fixed while an orthogonal displacement is applied to the distal end. As a result the portion of the device near the fixed end moves in a bending motion.
With the combined cantilevered/pure bend test fixture, the proximal end of the specimen is fixed while the distal end of the specimen is moved through an arc with a fixed radius. This is sometimes referred to as the "wag" test as it resembles the wagging of a tail. The specimen is allowed to either "find" it's own radius of curvature or it is wrapped around a mandrel of known radius.
Constant radius bend fixtures are designed to apply a bending moment at a fixed radius. This type of testing is sometimes referred to as "Bending on a Mandrel". With this approach the proximal end of the specimen is fixed while the distal end of the specimen is moved through an arc.T o ensure the specimen bend achieves a fixed radius, the specimen is bent over a mandrel of known radius. This test is useful for achieving predictable positive and compressive stresses.
Compression bend fixtures apply axial motions to the distal and proximal ends of a device that is preformed into an omega (or "inch-worm") shape. As the ends are brought together the radius of the specimen bend decreases. Unlike pure bending where only one bend radius is created, the compression bend fixture creates three bend radii (distal, center, proximal).
Shear induced bend fixtures apply a shear motion to one or both ends of the specimen to induce both bending and shearing into the device. The specimen is generally left to find it's own radius of curvature based on the applied motions.
If you don't see the bend fixture you are looking for chances are we have already designed it but have not listed it here. Contact us with your requirements and we will provide an estimate for creating the applied bending you are looking for.