Characterization of protective gloves stiffness: Development of a ...

1026 L. Harrabi et al. / Safety Science 46 (2008) 1025–1036
constraints and reduced dexterity, two side-effects related to the glove’s material stiffness (Bishu and Muralidhar,
1999; Buhmann et al., 2000; Cadoret and Smith, 1996). Furthermore, increased muscular constraints due
to protective gloves have been associated to tendinitis (Chaffin et al., 1999). As a consequence, workers may
choose not to wear protective gloves, exposing themselves to high risks of hand injuries.
Stiffness is one of the major properties that define how a glove interferes with the worker’s ability to perform
his tasks. Studies considering the biomechanical aspects of protective gloves use the effect of wearing
gloves on the deployment of the maximum grip force (Kovacs et al., 2002; Mital et al., 1994; Nelson and
Mital, 1995; Rock et al., 2001; Sudhakar et al., 1988). According to Mital et al. (1994), wearing protective
gloves reduces the maximum gripping force by 7–30%. A recent study confirms this interval (5–23%) for a
whole range of glove models (Rock et al., 2001). However, this type of evaluation requires for the subject
to exert several maximum muscular contractions, thus limiting the number of contractions in each measurement
session and asking for very fit subjects. Moreover, procedures involving the use of human subjects are
prone to high levels of inter individual variability, leading to large uncertainty in the measurements.
Several mechanical test methods have been used for characterizing film and fabric flexibility. Most of them
are based on uniaxial bending, which may not be representative of the type of deformations subjected to a
glove in usage. For example, the Kawabata Evaluation System for Fabrics (KESF) includes a test measuring
the bending moment of a strip of material as a function of its curvature, thus providing the uniaxial bending
rigidity which is proportional to the material stiffness (Kawabata, 1980). On the other side, the test method
used in the ISO 5979 standard (1982) measures the uniaxial flexibility of elastomer coated textile fabrics; its
principle consists in forming a loop with the material, the maximum height formed by this loop being proportional
to the material stiffness. Finally, in the ASTM D 1388 standard (1996), which characterizes the flexibility
properties of fabrics, the bending length is measured according to two procedures, the cantilever test and
the heart loop test, which allows the flexural rigidity to be calculated.
When protective gloves are worn, they are subjected to uniaxial deformations as well as equibiaxial ones, as
can be seen in Fig. 1. Stiffness measured with a uniaxial deformation test may not describe well the glove performance
in service. Characterization methods making use of multidirectional deformations are thus required.
The test method used in the ASTM D 4032 standard (1994) makes use of a circular bend procedure for
measuring the stiffness of fabrics, thus creating multidirectional deformations. A flat headed cylindrical probe
forces a folded piece of the fabric sample through an orifice in a platform. The maximum force required to
push the fabric through the orifice is measured and can be used as an indication of the fabric stiffness. Some
authors have calculated the work corresponding to the entire passing of the piece of fabric through the orifice,
which is proportional to the material stiffness (Killinc-Balci, 2004). However, the much larger thickness of
gloves, in particular considering the presence of fingers, prevents the use of this method as it is. In addition,
the flat headed shape of the probe does not generate deformations typical of what is sustained by gloves in use
and may create unnecessary stress concentration.
In this study, we propose a new multidirectional test method, inspired from the ASTM D 4032 standard
method, which allows for the measurement of protective gloves stiffness. This new method is described below
as the free-deforming multidirectional technique and has been used to measure the stiffness of 28 models of
Fig. 1. Folds (a) and biaxial deformations (b) of worn protective gloves.