Product Overview:

In this tutorial, we will explore the simulation of the pull-out process of a medical screw from bone in Abaqus, with a focus on damage investigation. Medical screws, which are threaded fasteners, are typically screwed into the bone without applying tension or clamping force. These screws are commonly used in surgeries related to neck and spine injuries, as well as hip and knee replacements. The strength of the screw connection is a crucial factor affecting post-surgery recovery and the long-term mobility of patients. Therefore, ensuring a high level of reliability for self-tapping screws used in medical devices is essential.

In the simulation, the bone is modeled as a three-dimensional solid part, while the screw is treated as a rigid part imported into Abaqus due to its complex geometry.

To analyze the dynamic behavior of the medical screw and its interaction with bone, the Johnson-Cook hardening law is employed. This hardening law is commonly utilized for metal alloys and is pre-implemented in finite element codes such as ABAQUS/Explicit. For modeling the bone’s behavior under dynamic loading, both elastic and Johnson-Cook plasticity are used. The Johnson-Cook damage criterion is applied to consider the damage parameter effectively.

As the simulation runs, the contact zone between the screw and the bone experiences damage and potential failure due to the dynamic pull-out forces. A dynamic explicit step is selected for this analysis. To expedite the simulation process, the mass scaling technique is implemented. Furthermore, the general contact capability is utilized to account for failure and erosion in the contact zone.

Fixed boundary conditions are assigned to the bone, while axial displacement (without rotation) is applied to the screw. A fine mesh is specified in the contact zone to achieve accurate results.

After completing the simulation, various results, including damage, failure, stress, and strain, can be analyzed.