Please cite this article as: Martínez-Hergueta, F., Ridruejo, A., González, C., LLorca, J., Deformation and energy dissipation mechanisms of needle-punched nonwoven fabrics: A multiscale experimental analysis, International Journal of Solids and Structures (2015), doi: http://dx. AbstractThe deformation and energy dissipation processes in a needle-punched polyethylene nonwoven fabric were characterized in detail by a combination of experimental techniques (macroscopic mechanical tests, single fiber and multi fiber pull-out tests, optical microscopy, X-ray computed tomography and wide angle X-ray diffraction) that provided information of the dominant mechanisms at different length scales. The macroscopic mechanical tests showed that the nonwoven fabric presented an outstanding strength and energy absorption capacity. The mechanical behavior was highly anisotropic although the initial fiber and knot distribution was isotropic. The load was transferred to the fabric through a set of fibers linked to the entanglement points, which formed an active skeleton. The fraction of fibers in the skeleton depended on the orientation and it was controlled by the features of * Corresponding author the entanglement points. Most of the strength and energy dissipation was provided by the progressive extraction of the fibers in the skeleton from the entanglement points and final fracture occurred by the total disentanglement of the fiber network in a given section at which the macroscopic deformation was localized. These findings provide the fundamental observations to develop microstructure-based continuum models for the mechanical behavior of needle-punched nonwoven fabrics.

No abstract

Digital image correlation (DIC) is a widely used technique in experimental mechanics for full field measurement of displacements and strains. The subset matching based DIC requires surfaces containing a random pattern. Even though there are several techniques to create random speckle patterns, their applicability is still limited. For instance, traditional methods such as airbrush painting are not suitable in the following challenging scenarios: (i) when time available to produce the speckle pattern is limited and (ii) when dynamic loading conditions trigger peeling of the pattern. The development and application of some novel techniques to address these situations is presented in this paper. The developed techniques make use of commercially available materials such as temporary tattoo paper, adhesives and stamp kits. The presented techniques are shown to be quick, repeatable, consistent and stable even under impact loads and large deformations. Additionally, they offer the possibility to optimise and customise the speckle pattern. The speckling techniques presented in the paper are also versatile and can be quickly applied in a variety of materials.

a b s t r a c tThe influence of the initial fiber orientation distribution on the ballistic performance of a needlepunched nonwoven polyethylene fabric was analyzed. To this end, ballistic tests were carried out in specimens pre-deformed along the machine or the transverse directions and the influence of pre-deformation on the fiber orientation was measured by means of wide angle X-ray diffraction. It was found that pre-deformation along the machine direction (the soft orientation of the fabric) led to more isotropic in-plane mechanical response and to a marked increase in the specific ballistic limit and in the energy dissipated by unit weight while the opposite behavior was found after stretching the fabric along the transverse direction. These differences were accompanied by changes in the penetration mechanics from extensive fiber pull-out to slippage between fibers in the network. These results highlight how the nature of the nonwoven microstructure (connectivity of the entanglement points and fiber orientation distribution) can be tailored to improve the impact performance.

No abstract