In the field of technical textiles, such as tarpaulins, architectural membranes or industrial fabrics, the main challenge is not only resistance to breaking, but the preservation of mechanical properties both during the application of a load and in the phase following load removal. Since materials exhibiting high energy dissipation could suffer from creep (viscous flow) and stress relaxation.
An emblematic use case of our technology focused on testing 3 truck tarpaulin samples, 2 new and one worn, focusing on how different imposed deformations influence the following parameters:
- Storage Modulus: viscoelastic property that describes the ability of the material to store and release energy during a dynamic phenomenon (rebound of the VESevo indenter)
- Loss Factor: viscoelastic property that, unlike the Storage Modulus, defines the ability of the material to dissipate energy
- Adhesion Viscoelastic Index (AVI): provides information on the adhesive component and hardness of the material. In particular, the higher its value, the softer the material will be
- Hysteresis Viscoelastic Index (HVI): provides information on the dissipative response of the material. In particular, the higher its value, the more dissipative the material will be
- Coefficient of restituition: dimensionless parameter described by the following formula
For each tarpaulin, the above-mentioned properties were evaluated at different levels of deformation:
- 0% (no deformation)
- from 1 to 10% deformation
BLUE TARPAULIN
BLACK TARPAULIN
GREEN TARPAULIN
To simulate different levels of deformation, an ad-hoc setup was developed, shown below:
- The setup consists of a clamp on which two grips are mounted. One is fixed to the clamp while the other is free to move.
- The tarpaulin sample is placed between the two grips as illustrated in the figure below.
- The movable grip can be actuated by means of a screw that allows different levels of deformation of the tarpaulin to be set. The imposed deformation is calculated as the percentage difference between the final length (after the sample has been stretched) and its initial length, measured using a caliper.
For each sample and for each level of deformation, 20 measurements were acquired, all conducted at room temperature
The BLACK and GREEN tarpaulins appear to be more affected by the imposed level of deformation compared to the BLUE tarpaulin. The effect of deformation mainly concerns the dissipative content (see Loss Factor, HVI index & Coefficient of Restitution).
The BLUE TARPAULIN and the GREEN TARPAULIN appear to exhibit the same behavior. On the other hand, independently of the level of deformation, the BLACK TARPAULIN appears to be less dissipative and more elastic than the other two. Such behavior could suggest reduced susceptibility to relaxation phenomena, improved retention of the imposed deformation over time, but at the same time provide lower flexibility.
In previously conducted tests, a relaxation effect could potentially develop, experienced by the tarpaulin between one deformation and another. In other words, gradually stretching the tarpaulin could mask or inhibit the true effect of deformation. For this purpose, in a further study, each sample was initially tested at rest (0first), then subjected to maximum deformation, and finally tested again at rest (0last), without intermediate deformation levels.
Even with such methodology, an effect of deformation was observed.