Lotfi Harrabi

Evaluation of the Flexibility of Protective Gloves

Two mechanical methods have been developed for the characterization of the flexibility of protective gloves, a key factor affecting their degree of usefulness for workers. The principle of the first method is similar to the ASTM D 4032 standard relative to fabric stiffness and simulates the deformations encountered by gloves that are not tight fitted to the hand. The second method characterizes the flexibility of gloves that are worn tight fitted. Its validity was theoretically verified for elastomer materials. Both methods should prove themselves as valuable tools for protective glove manufacturers, allowing their existing products to be characterized in terms of flexibility and the development of new ones better fitting workers’ needs.

Do mechanical tests of glove stiffness provide relevant information relative to their effects on the musculoskeletal system? : a comparison with surface electromyography and psychophysical methods

The main purpose of the present study was to test the construct validity of two mechanical tests of glove stiffness using a surface electromyography (SEMG) methodology that would allow estimating the effect of glove stiffness on forearm muscle activation during a standardized grip contraction. The mechanical tests [free-deforming multidirectional test (FDMT) and Kawabata Evaluation System for Fabrics (KESF)] were applied on 27 gloves covering a wide range of stiffness. In 30 human subjects, a psychophysical assessment of these gloves was also carried on in addition to the SEMG test. The results showed that the sensitivity of the different tests to glove stiffness differences was slightly better for the FDMT (75% sensitivity) than for the psychophysical assessment (72%), while the SEMG test showed much lower sensitivity (13-31%, depending on the muscle). The SEMG test was highly correlated to the psychophysical assessment (0.88-0.95, depending on the muscle tested), and the FDMT (0.88-0.94) and KESF (0.77-0.86) mechanical tests, showing the construct validity of mechanical tests, particularly for the FDMT. It was concluded that mechanical tests provide relevant information relative to the effect of glove stiffness on the musculoskeletal system of the forearm.

Prediction of Stress-Strain Behaviour and Energy Dissipation of Textile Protective Materials at Large Deformations

The aim of this study is to develop a model for the mechanical behavior of knitted fabrics, which are used in protection gloves, at large deformation and different strain rates in terms of extension/ recovery cycling. The non-linear viscoelastic model is based on the standard solid model. The choice of this model is based on its simplicity due to the limited number of elements. It contains three nonlinear spring and damper elements. The idea is to consider that, by analogy with elastomers, the mechanical behavior of the fabric in terms of hysteresis loop is due to the contribution of two parts: the first one represents the equilibrium state of the fabric and the second one is due to the deviation from this equilibrium. Then, the stress-strain behavior of the fabric at different strain rates can be computed using the same parameters determined at one value of strain rate. The dissipated energy is provided by the area under the hysteresis loop. A good agreement has been obtained between the experimental and theoretical results.