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Biomechanics Overview   Torsion   Bending   Compression   Fracture  


3pt.jpg (43233 bytes)

Bending tests are performed to measure the bending properties of the cortical bone of long bones. Bending causes tensile forces on the lower side of the bone and compressive forces on the upper side of the bone, where the deformation is applied. The bone is loaded until failure and since bone mineral is weaker in tension than compression, the side in tension fails first leading to catastrophic failure. Two different types on bending tests can be conducted on bone: (i) three-point (image on the left) and (ii) four-point bending (diagram on the right). In three-point bending, although a simple test to conduct, the bone has a higher chance of fracture due to the large shear stresses developed at the mid-section of the bone. In four-point bending, however, these transverse shear stresses are minimized, but this test is more complicated to perform. In both tests, the bone is placed on two supports and is bent by lowering an another support(s) in the mid-shaft of the bone using a material testing system (Instron™). The applied force is measured by a load-cell located at the top of the device. The resulting deformation is measured with a LVDT attached to the crosshead that is lowered to induce bending.4ptbend diagram.gif (8887 bytes)