Biomechanical modelling of the human hand-arm to study stresses caused by hand-arm vibration

Hand-arm vibration syndrome (HAVS) is a common occupational disease caused by vibrations transmitted to the hand-arm from hand-held power tools. The aim of the present work was to compute the biodynamic responses, viz., displacements and stresses induced in the bones and tissues of the human hand-arm from a hand-held power tool through (i) Finite element (FE) analysis and (ii) Multibody dynamics (MBD) simulations. For this an anatomically correct 3-D hand-arm model with bones, muscles, tendons and ligaments from Turbosquid TM , was used. Most works reported in literature however use bone-only models. The Turbosquid model was opened in AUTODESK 3DS MAX and imported into Altair-HyperMesh to obtain an FE model constrained at the shoulder joint. Accurate modelling of the anatomical details of each bone was done using 10-noded tetrahedral elements. Modal analysis was performed to get the natural frequencies and mode shapes with a number of modes in the 0 to 150 Hz range. Sinusoidal sweep excitation was imparted at the hand-tool interface to identify the predominant frequencies and locations of the resulting vibrations. The hand-arm model was converted into a flexible body using component mode synthesis (CMS) with the Craig-Bampton reduction method using Optistruct solver. The first 100 modes were used for this and two boundary conditions were imposed at the excitation location and the scapula respectively. A mechanism with two linear actuators was designed with Altair-MotionView to excite the hand-arm in the longitudinal and vertical directions simultaneously, the motion corresponding to an operating angle drill. The modal participation coefficients were computed for the flexible bodies.These coefficients were then multiplied by the modal stresses obtained from CMS to obtain the transient elemental stresses. It was observed that the stresses in the bones were 10-15 MPa and were higher than in the muscles.