Hossein Hasani

This paper undertakes the effect of fabric structure and matrix type on the auxeticity of the composites reinforced with weft knitted fabrics. Four topologies—Star, Foldable Rectangular, zigzag, and Ribbon (large and small unit cell)—were fabricated on an electronic flat‐knitting machine and characterized in both dry and resin‐consolidated states. The most corrugated topology, zigzag, produced the largest dry‐fabric NPR (−0.60), consistent with its greater out‐of‐plane folding (“kinematic reservoir”); flatter Ribbon geometries reverted to conventional (positive) Poisson behavior after limited strain. To assess how matrix rheology governs transfer of this geometric auxetic effect into a solid composite, foldable rectangular preforms were consolidated with three resins spanning roughly three orders of magnitude in stiffness: rigid Epoxy (2.2 GPa), Unsaturated Polyester (1.5 GPa), and a hyper‐elastic carboxylated styrene‐butadiene rubber (SBR, ~6 MPa). Rigid thermosets constrained geometric unfolding and failed by brittle matrix cracking near 10% strain, attenuating the composite NPR to −0.15 to −0.20. The SBR matrix, by contrast, offered minimal mechanical resistance and preserved a composite NPR of −0.40—close to the −0.42 value of the unconsolidated fabric—while extending strain‐to‐failure to roughly 45%. Charpy impact testing (50 J) showed that, with one exception among the weakly auxetic Ribbon samples, energy absorption broadly tracked NPR magnitude, ranging from 12.7% to 5.5% for the flat Ribbon composites to 45% for Zigzag/epoxy and 68% for rectangular/SBR, consistent with a strain‐induced densification mechanism beneath the impact zone. These findings suggest a design framework for impact‐mitigating textile composites for protective and energy‐absorbing applications.

Purpose: This study investigates the flexural performance and failure mechanisms of additively manufactured sandwich panels featuring 3D-printed corrugated cores and face sheets reinforced with E-glass fibers. The research aims to quantify the effects of core geometry, thermoplastic matrix selection and fiber reinforcement on peak load, stiffness and energy absorption, while critically evaluating the predictive accuracy of classical Gibson–Ashby models for extrusion-based composites. Design/methodology/approach: Sandwich panels were fabricated using a modified dual-feed fused deposition modeling (FDM) process. To mitigate nozzle wear and facilitate the extrusion process, 100-tex continuous E-glass yarns were pre-coated with a styrene-butadiene rubber solution. Eight distinct sample configurations were produced and evaluated, utilizing two thermoplastic matrices (polylactic acid [PLA] and acrylonitrile butadiene styrene [ABS]) across three core cross-sections: rectangular, triangular and trapezoidal. These included both unreinforced polymer panels and continuous fiber-reinforced composites containing a ∼15% fiber volume fraction. Specimens were subjected to three-point bending tests in accordance with ASTM C393. Findings: Experimental results demonstrated that structural performance is highly dictated by core geometry and matrix integrity. The trapezoidal composite panel (TRCP) achieved the highest peak flexural load (726.8 N) with stable post-peak progressive collapse. The rectangular composite panel (RCP) exhibited superior ductility and the highest specific energy absorption (SEA) at 118.9 N·mm/g due to progressive core wall buckling, dramatically outperforming the triangular core panel, which suffered a brittle, premature collapse at 558.8 N with an SEA of only 12.5 N·mm/g. Regarding matrix selection, PLA-based panels significantly outperformed their ABS counterparts (e.g. RCP peak load of 706.3 N versus RCA at 448.8 N) due to ABS’s susceptibility to severe intra-face layer delamination under compressive bending loads. Furthermore, the addition of continuous glass fibers improved the peak load by ∼19% and SEA by ∼24% compared to unreinforced PLA equivalents (RPP). Furthermore, while classical Gibson–Ashby theory predicted global core shear failure due to the high face-thickness-to-span ratio (t/L = 0.022), experimental observations revealed premature localized face indentation. Quantitative analysis confirmed that the printed cores only utilized 13% to 83% of their theoretical shear capacities, highlighting the critical limitations of applying continuous-foundation analytical models to discrete 3D-printed corrugated topologies. Originality/value: This research provides robust quantitative benchmarking for continuous glass-fiber FDM sandwich structures. It demonstrates that classical sandwich theories require adjustment before application to 3D-printed composites, as they fail to account for real-world discrete support conditions, epoxy interface compliance and localized post-buckling behaviors. The findings offer vital, application-specific design guidelines for the geometric optimization of additively manufactured lightweight structures.

This study aims at examining the effect of structural and process variables on thermal comfort properties of thecompression garments produced with single-jersey weft knitted construction. The considered variables are elastane yarncount, elastane yarn tension during yarn positive feeding, reduction factor and fabric structure. To this end, 18 samples aremanufactured according to Taguchi orthogonal array on a circular knitting machine. Heat transfer per cent, moisture transferin the liquid phase and air permeability of the knitted fabrics have been measured and reported. The compression garmentsare sewn in cylindrical shape and the pressure applied on a cylinder is also measured by Kikuhime pressure sensor.The results demonstrate that the samples containing knit and miss stitches apply the highest amount of pressure and the sample having more tuck stitches represents the lowest pressure. Also, increasing the linear density of the elastic yarn and using a higher reduction factor provide a higher pressure. The results indicate that fabrics exerting greater pressure on the body have a tighter structure when stretched. Therefore, they show less air permeability, heat and moisture transfer. Also, for a certain fabric structure, an increase in reduction factor leads to open structure and creating more pressure. Consequently, air permeability and the heat and moisture transfer are increased. Samples which apply less pressure, are more permeable and transfer greater amount of heat, and moisture through their structure due to creation of an open structure in extended state.