Fibers, Volume 10, Issue 12 (December 2022) – 8 articles

Ceramic reinforced friction stir spot-welding (FSSW) is one of the unique welding techniques used to fabricate spot joints. This study is intended to investigate the effect of reinforcement additive particle size in achieving higher weld strengths. AA5083-H116 aluminum alloy plates were welded with nano- and micro-sized silicon carbide (SiC) particles. Investigations of the weld joints prepared using a tool rotational speed of 1300 rpm, tool plunge rate of 25 mm/min, and dwell time of 10 s revealed that the lap shear tensile strength and hardness of the nano-SiC particles added to aluminum joints were higher than those of the micro-SiC particles added to joints. In particular, the nano-SiC particles provided 29.6% higher strength and 23.3% higher hardness than the unfilled FSSW. The uniformly dispersed fine SiC particles in the processed zone provided more nucleation sites for the re-precipitation of new grains and the precipitates in the aluminum matrix. The X-ray diffraction results confirmed that there was no evidence of a new phase (intermetallic compounds). Reinforcement of SiC particles significantly enhanced the wear characteristics, as well (26.3%). Field emission scanning electron microscopy (FESEM) evidenced the uniform distribution of SiC particles in the weld nugget zone. In addition, the fractography of the samples is presented and discussed. Full article

In recent years, there has been extensive research into the development of cheaper and more sustainable carbon fiber (CF) precursors, and air-gap-spun cellulose-lignin precursors have gained considerable attention where ionic liquids have been used for the co-dissolution of cellulose and lignin. However, ionic liquids are expensive and difficult to recycle. In the present work, an aqueous solvent system, cold alkali, was used to prepare cellulose-lignin CF precursors by wet spinning solutions containing co-dissolved dissolving-grade kraft pulp and softwood kraft lignin. Precursors containing up to 30 wt% lignin were successfully spun using two different coagulation bath compositions, where one of them introduced a flame retardant into the precursor to increase the CF conversion yield. The precursors were converted to CFs via batchwise and continuous conversion. The precursor and conversion conditions had a significant effect on the conversion yield (12–44 wt%), the Young’s modulus (33–77 GPa), and the tensile strength (0.48–1.17 GPa), while the precursor morphology was preserved. Structural characterization of the precursors and CFs showed that a more oriented and crystalline precursor gave a more ordered CF structure with higher tensile properties. The continuous conversion trials highlighted the importance of tension control to increase the mechanical properties of the CFs. Full article

This paper examines analytically the design criteria for the composite retrofit of reinforced concrete (RC) columns with a short lap splice length of steel rebars inside the critical region. The advanced potential of pseudo-dynamic three-dimensional (3D) finite element (FE) modelling is utilized to investigate critical design parameters for the required carbon fiber-reinforced polymer (FRP) jacketing of RC columns with a rectangular cross-section based on the experimental lateral force-to-drift envelope behavior of characteristic cases from the international literature. The satisfactory analytical reproduction of the experimental results allows for the systematic numerical investigation of the developed stress along the lap splice length. The maximum lateral force and the horizontal displacement ductility of the column, as well as the maximum developed tensile axial force on the longitudinal bars, their variation along the lap, the bar yielding, and the plastic hinge length variation, are considered to determine the seismic behavior of the columns. For the first time, cases of smooth bar slip together with delayed bar yielding or without bar yielding are identified that may be recorded through a “ductile” P-d seismic response. Such pseudo-ductile response cases are revisited through suitably revised redesign criteria for adequate FRP jacketing. Full article

Interventional therapy is one of the most effective methods for diagnosing and treating vascular-related diseases at present. It relies on achieving precise and safe navigation of intravascular tools within a patient’s vasculature. Vascular Interventional Surgical Robots (VISR) can reduce surgeons’ exposure to operational hazards including radiation. However, the absence of apt position control and force feedback remains a challenge. This study presents an isomorphic master–slave VISR for precise navigation of endovascular tools viz. catheters and guidewires. The master console aids operators in issuing manipulation commands and logs feedback from the force, rotation, and translation data. The slave manipulator uses the commands received from the master platform for actual tool navigation. However, precise master–slave position control and force feedback are precursors for optimal patient outcomes. This study utilized a fuzzy-PID controller for precise tool navigation and a neural network model for resistance force modulation with 50 mN precision. Furthermore, we evaluated the performance of using the learning-based models within our VISR and compared it with the performances from conventional methods. Results show that the models enhanced the proposed robotic system with better navigation precision, faster response speed, and improved force measurement capabilities. Full article

Aircraft structures must be capable of performing their function throughout their design life while meeting safety objectives. Such structures may contain defects and/or damages that can occur for several reasons. Therefore, aircraft structures are inspected regularly and repaired if necessary. The concept of combining an inspection plan with knowledge of damage threats, damage growth rates, and residual strength is referred to as “damage-tolerant design” in the field of aircraft design. In the present study, we fabricated a composite panel with a cutout (which is generally found in the bottom skin of the wing) using a resin infusion process and studied the damage tolerance of a co-cured skin-stringer composite panel. The composite panel was subjected to low-velocity impact damage, and the extent of damage was studied based on non-destructive inspection techniques such as ultrasonic inspection. Fixtures were designed and fabricated to load the composite panel under static and fatigue loads. Finally, the panel was tested under tensile and fatigue loads (mini TWIST). Deformations and strains obtained from FE simulations were compared and verified against test data. Results show that the impact damages considered in this study did not alter the load path in the composite panel. Damage did not occur under the application of one block (10% life) of spectrum fatigue loads. The damage tolerance of the stiffened skin composite panel was demonstrated through test and analysis. Full article

Conventional concrete is a common building material that is often ridden with cracks due to its low tensile strength. Moreover, it has relatively low shear strength and, unless reinforced, undergoes brittle failure under tension and shear. Thus, concrete must be adequately reinforced to prevent brittle tensile and shear failures. Steel fibres are commonly used for this purpose, which can partially or fully replace traditional steel reinforcement. The strength properties and bond characteristics between reinforcing steel fibres and the concrete matrix are crucial in ensuring the effective performance of the composite material. In particular, the quality of the bond has a significant impact on crack development, crack spacing, and crack width, among other parameters. Hence, the proper application of steel fibre-reinforced concrete (SFRC) requires a thorough understanding of the factors influencing its bond behaviour and strength properties. This paper offers a comprehensive review of the main factors controlling the bond behaviour between concrete and steel fibres in SFRC. In particular, we focus on the effects of the physical and mechanical properties of steel fibres (e.g., geometry, inclination angle, embedded length, diameter, and tensile strength) on the bond behaviour. We find that the addition of up to 2% of steel fibres into concrete mixtures can significantly enhance the compressive strength, tensile strength, and flexural strength of concrete components (by about 20%, 143%, and 167%, respectively). Furthermore, a significant enhancement in the pull-out performance of the concrete is observed with the addition of steel fibres at various dosages and geometries. Full article

This paper aims to investigate the effect of using different configurations of near-surface mounted carbon-fiber-reinforced polymer (NSM-CFRP) strips on the shear strength of strengthened and rehabilitated reinforced concrete (RC) T-beams with different internal shear stirrup spacing. The internal shear stirrup spacing was 50 and 150 mm. The NSM-CFRP strips were at an inclination of 45° and spaced at 75 and 150 mm. A total of eight beams were tested in this study: two beams without NSM-CFRP as control beams for the purpose of comparison; three beams were strengthened by NSM-CFRP; and three beams were rehabilitated by NSM-CFRP. The experimental shear capacities were compared with the theoretical values predicted by the ACI 440.2R-17. The results indicated that the use of NSM-CFRP strips enhanced the shear capacity for all beams compared to their corresponding control beams. The enhancements in the shear capacity increased with the decrease in the spacing of the internal shear stirrups and NSM-CFRP strips. The ACI 440.2R-17 was conservative in predicting the theoretical shear capacities. Full article

Due to the ever-growing demand for bast fibres for technical and garment textiles, complementary sources to textile flax, whose cultivation in western Europe cannot really be extended, need to be proposed. In this study, the interest in harvesting and processing linseed flax straw is studied for geotextile applications. The main critical stages of fibre-to-yarn production for geotextiles were investigated. Different dew retting levels as well as different all-fibre extraction processes were investigated to achieve this objective. It was demonstrated that the fibres extracted from linseed flax stems subjected to 12 weeks of dew retting using breaking rollers, thresher and a breaking card exhibited the most suitable morphological and mechanical properties. The optimal fibres were converted into 100% linseed flax yarns using a flyer spinning machine, and the mechanical properties as well as the biodegradability of the linseed yarns were evaluated to understand their potential as geotextiles. These linseed flax yarns were further coated with linseed oil or chitosan to enhance their durability. It was observed that the linseed oil coating better preserved the yarn’s integrity and mechanical properties over time, and it permitted doubling their service life potential. Full article