Abstract

Prolong and intensive exposure to hand-transmitted vibration could cause a series of disorders in the vascular, neurosensorial, and musculoskeletal structures, which have been collectively termed as hand-arm vibration syndrome (HAVS). From the review of literature, it is apparent that biodynamic response of the hand-arm system is one of the important foundations for understanding the causations of HAVS and for developing effective methods for exposure assessment. Although considerable efforts have been made to characterize the biodynamic responses of the hand-arm system and develop biodynamic models, only little knowledge exists on distribution of biodynamic response and power absorption for assessing health risks to the localized substructures. This dissertation research is concerned with development of an effective hand-arm vibration model that can predict distributed mechanical impedance and power absorption properties various substructures within the hand-arm system. This dissertation research proposes a new model structure that mimics the basic structures of the hand-arm system grasping a handle. The proposed model comprises two driving-points as opposed to the single driving-point invariably considered in the reported models. The model thus permits analyses of biodynamic forces developed on the fingers and palm-sides. The model parameters are identified based on the selected experimental data using a curving fitting method. The model structure revealed reasonably good agreements with the reported experimental data acquired under selected hand actions. The model also revealed very good agreements in terms of biodynamic responses distributed in the fingers and the palm in both the impedance magnitudes and phase. The model was applied to predict biodynamic responses of the human hand-arm system exposed to forearm direction of vibration. These were evaluated in terms of mechanical impedance, vibration transmissibility, dynamic force and power absorption. The basic characteristics of distributed biodynamic responses are analyzed to gain insight into relative health risks of vibration posed to various substructures of the hand-arm system. The results showed that the vibration power absorption (VPA) is mainly distributed in the forearm and shoulder structures under low frequency vibration. At higher frequencies, the vibration power is mostly absorbed in the tissues close to the hand-tool contact area, which can be associated with potential disorders of the fingers caused by operation of high frequency tools. This study also suggests that the distributed power absorption may be used as an alternative vibration measure for assessing various risks of the hand-transmitted vibration exposure.