Testing Talk: Tensile strengths
Typical points of interest when tensile testing a material include ultimate tensile strength or peak stress; modulus of elasticity, offset yield strength, which represents a point just beyond the onset of permanent deformation; and elongation at break.
The modulus of elasticity is calculated as the slope in the linear elastic region of the stress-strain curve. The linear elastic region is prior to the proportional limit (see point A – Figure 1). Beyond the proportional limit, the material undergoes permanent plastic deformation.
Testing bone screws
ASTM F543 Annex A2 is used to measure the torque required to drive a bone screw into a test block made of rigid, unicellular polyurethane foam. The results obtained from this test bear no direct correlation to the torque required to insert a bone screw in human or animal bone. This method is used as a quality control check for maintaining product uniformity.
The basic test procedure for determining the insertion and removal torque is as follows:
Torsion testing conical fittings and connectors for medical devices
Torque, also called moment or moment of force, is the tendency of a force to rotate an object about an axis or pivot. Torque is rotational force. Twisting the female to male fitting, to remove or replace the connection, is an example of applying torque. The amount of torque developed is proportional to the force applied and to how far from the center of the rotation the force is applied.
ASTM F382-99 Metallic Bone Plate Material 4-point Bend Test
Metallic bone plates need to undergo several tests before gaining approval as internal fixation devices for the skeletal system. One standard, ASTM F382-99, defines the test methods for single cycle bend testing (annex A1) and for determining the bending fatigue properties (annex A2) of metallic bone plates. A summary of the test methods for annex A1 and A2 follows. For a complete description of ASTM F382-99, refer to the specification from the ASTM International organization.
Testing Talk: ASTM F1717 spinal implant biaxial testing
Spinal implants are tested according to several ASTM standards. ASTM F1717 is intended to provide a basis for the mechanical comparison among past, present and future spinal implant assemblies. Three static and one fatigue mechanical test of a spinal construct are governed by ASTM F1717. The three static tests are compression bending, tension bending and torsion. The fatigue test is a compression bending test. The mechanical tests are conducted in vitro using simplified loading schemes and do not attempt to mimic the complex loads of the spine.