Hand-operated tool handles transmit a large magnitude of vibration to the hand-arm system during low-frequency operations. Therefore, the precise design of a hand tool is very important to overcome musculoskeletal disorders, hand-arm vibration, etc. This study was aimed at developing optimal tool handles with an increased contact area and to overcome the contact pressure, which causes discomfort and pain. Six different human hand-based optimal handles (handles B to G) and one optimal cylindrical handle (handle A) were designed and fabricated using 3D printing technology, in order to assess the effect of low-frequency vibrations. The effect of handle shapes was evaluated with objective and subjective measurements using 15 subjects. Objective measurements were performed to assess the vibration transmissibility by experimental study at the frequency range of 0–100 Hz, and subjective measurements were performed to rate the handles based on comfort descriptors and overall comfort of the handles. Root mean square vibration accelerations were recorded at the wrist, elbow, and shoulder of each subject and at the base of the handle fixture to evaluate the vibration transmissibility for each handle. The mean vibration transmissibility was found to be minimum for handle B and was rated to be more comfortable by the subjects. The results indicated that all the human hand-based handles transmit less vibration and were rated to be more comfortable than the optimal cylindrical handle.

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SummaryStudy aim: Interactions between the fingers and a handle can be analyzed using a finite element finger model. Hence, the biomechanical response of a hybrid human finger model during contact with varying diameter cylindrical handles was investigated numerically in the present study using ABAQUS/CAE.Materials and methods: The finite element index finger model consists of three segments: the proximal, middle, and distal phalanges. The finger model comprises skin, bone, subcutaneous tissue and nail. The skin and subcutaneous tissues were assumed to be non-linearly elastic and linearly visco-elastic. The FE model was applied to predict the contact interaction between the fingers and a handle with 10 N, 20 N, 40 N and 50 N grip forces for four different diameter handles (30 mm, 40 mm, 44mm and 50 mm). The model predictions projected the biomechanical response of the finger during the static gripping analysis with 200 incremental steps.Results: The simulation results showed that the increase in contact area reduced the maximal compressive stress/strain and also the contact pressure on finger skin. It was hypothesized in this study that the diameter of the handle influences the stress/strain and contact pressure within the soft tissue during the contact interactions.Conclusions: The present study may be useful to study the behavior of the finger model under the static gripping of hand-held power tools.

Sandwich laminates are particularly important in the early stages of structural design due to their excellent mechanical, energy absorption, and other structural properties. High-strength carbon and glass fibre with honeycomb core sandwich laminates were fabricated by vacuum bag moulding. Three different energy-absorbing materials are used to develop sandwich structure laminates, such as cores filled with Rohacell, naturally available wheat husk and polyurethane foam (PUF). Some tests, such as flexural strength, vibrational behaviour, flammability analysis and impact tests, are carried out to assess the mechanical and dynamical properties of the sandwich laminates. According to the results, the PUF sandwich layer designed laminate exhibits good vibration with higher mechanical properties compared to the Rohacell and wheat husk laminates. Moreover, the PUF core laminate enhances the fire resistance property. PUF foam with fibres reinforced sandwich composite exhibited a higher natural frequency (825 Hz) and a higher damping value (0.059) than the wheat husk and Rohacell core sandwich laminates. This is because the PUF core dissipates energy more efficiently than other core sandwich laminates at all modes.

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