Mouldability analysis and impact performance of 3D aramid angle-interlock fabric panels for ballistic helmets

Modern ballistic helmets made from textile composites offer enhanced protection with lightweight, but the discontinuity of the reinforcing materials is a potential problem affecting the helmet performance. This work uses 3D angle-interlock fabrics to provide reinforcement continuity, and evaluates 3D through-the-thickness angle-interlock (TTAI) fabrics to study the influence of fabric structural parameters on fabric mouldabilty and ballistic performance for ballistic helmet application. The mouldability was measured through experiments and modelled numerically, and the ballistic impact test was carried out to identify the optimal fabric structures for constructing ballistic helmet shells. The results show that increase in weft density of the TTAI fabrics causes decrease in the mouldability of the TTAI fabrics, and that the addition of wadding yarns into the TTAI fabrics has little influence on fabric mouldability compared to the conventional TTAI fabrics with the same weft density. However, the involvement of wadded TTAI fabrics demonstrates a 34% increase in ballistic energy absorption and 3% higher estimated ballistic limit over the conventional counterpart. Taking both mouldability and ballistic protection into account, the wadded TTAI fabric structure is an effective continuous reinforcement for ballistic helmet shells, offering required mouldability and improved ballistic performance.

Damage Location Sensing in Carbon Fiber Composites Using Extrusion Printed Electronics

Structural Health Monitoring (SHM) uses sensors in advanced engineering structures to evaluate integrity and detect damage or deformation affecting structural performance, e.g., cracks, holes, or corrosion. Carbon fiber textile composites are commonly used to reinforce structures such as aircraft, vehicles, or bridges due to their high tensile strength to weight ratio, chemical resistance, and thermal and electrical conductivity. Printing electronics on textiles is a scalable manufacturing technology combining the physical properties of textile materials with the added functionality of electronic elements making them self-sensing. Extrusion printing is a contactless digital printing method to print electrical conductors and passive circuit elements. This paper proposes to combine conventional carbon fiber composite manufacturing processes with printed conductors to create self-sensing carbon fiber textile composites. Damage is sensed by measuring resistance changes in a carbon fiber sheet. Contacts are extrusion printed directly on woven carbon fiber sheets using silver flake ink. A multiplexed Kelvin Double Bridge circuit is the read-out interface. This allows small resistance changes due to damage to be measured in a 4-point configuration. The circuit is connected to the printed contacts on the carbon fiber sheet through multiplexers to detect damage in different locations. This 2D digital sensor can detect the location and size of damage holes for SHM. The resolution of the sensor is controlled by the location and spacing of the silver electrodes, which were studied experimentally and by simulation. The resolution is 26 mm in the current direction and 16 mm in the orthogonal direction. The threshold of detectable damage is 4 mm2. Simulation of the sensor as an isotropic 2D conductor shows good agreement with experimental results for the orthotropic fabric. The resultant sensing device could be integrated into many composite structures as one of its layers or simply printed on the surface to create smart structures.