Majid Safar Johari

1. Industrial hoses are vital components in fluid transmission systems, ensuring reliable performance in various sectors such as automotive, aerospace, chemical processing, hydraulic and pneumatic ...

Accurate prediction of the elastic constants of braided composites has become increasingly critical, yet the complex geometry of these materials remains challenging for evaluating stiffness. To address this challenge, a novel multiscale finite-element representative volume element (RVE) framework was developed to predict the elastic behavior of two-dimensional biaxial and triaxial braided composites. An analytical approach was first derived to calculate the minimal curved unit-cell dimensions regardless of braid diameter for the three main patterns as a function of curvature angle and yarn pitch length of the braid structure. Subsequently, periodic RVEs were generated to capture the mechanical properties of the resulting composites. Periodic boundary conditions were applied under six independent loading modes to extract the complete anisotropic stiffness tensor. The resulting predictions were validated through uniaxial tensile tests and also three-point bending experiments to confirm the model's robustness under combined stress states, showing an error margin of less than 8% compared to numerical results. A qualitative comparison of maximum principal stress contours further validated the RVE's capability to replicate anisotropic load paths and shear coupling. Taken together, the proposed multiscale RVE–FEM methodology is demonstrated to be a reliable, physics-based tool for the design and optimization of braided composite structures.

Braided composites are gaining attention in the most industrial applications. To design rods with optimal tensile properties against combined loads, experimental studies were conducted to investigate the effect of using axial yarn and core in different categories on the tensile properties of braided reinforced composite rods. In this study, six types of braided composite rods with different arrangements of braid components (axial yarn or core type) were produced using glass and polyester fibers with epoxy resin as the matrix. The elastic modulus, ultimate tensile strength, and work of fracture of these rods were tested, and the experimental elastic modulus of samples were compared with previously developed models. Moreover, comparing the stress-strain results of the samples revealed that the produced hybrid samples demonstrate pseudo-ductile tensile behavior, showing varying trends as the type of reinforcement is altered. The results indicate that using a double-layer triaxial braid as reinforcement for the composite can increase the elastic modulus up to 13% compared to the similar single-layer sample. Additionally, employing a double-layer triaxial braid as reinforcement for the composite leads to a greater work of fracture. However, in terms of ultimate tensile strength, biaxial braid reinforcement demonstrates better performance in reinforcing the composite rods.

This paper aims to investigate the effects of fiber hybridization technique on the mechanical behaviors of non-absorbable braided composite sutures. Fifteen types of hybrid braided sutures (HBSs) made of polyester (PET), polypropylene (PP), and polyamide 6 (PA6) are produced and tested to measure ultimate tensile strength (UTS), maximum strain, elastic modulus, and breaking toughness. Based on the results, it is observed that the suture material plays a significant role in the tensile and mechanical performance of HBSs, and they can be tailored through the different combinations of yarns according to the required mechanical properties. Experiments exhibit occurrence positive hybrid effect in both maximum strain and elastic modulus, and negative hybrid effect in UTS. The optimal tensile performance is associated with the hybrid structure comprising 75% PA6-12.5% PET-12.5% PP. This means the ternary structure with higher PA6 content along with PP and PET, demonstrates a synergistic effect. Thus, such a ternary composite structure is very promising for the design of novel non-absorbable sutures. Due to the absence of similar results in the specialized literature, this paper is likely to advance the state-of-the-art composite non-absorbable sutures and contribute to a better understanding of the hybridization concept for optimizing composite material systems.

This paper presents an experimental investigation of the hybridization impacts on the tensile performance of the two-dimensional (2D) braided tubular composites by varying the types of constituent fibers and combination. Fifteen types of tubular braids with different combinations of three types of yarns - polyester (PET), polypropylene (PP) and polyamide 6 (PA) - were produced on a braiding machine. Subsequently, the vacuum infusion process (VIP) was adopted for the fabrication of hybrid braided composites (HBCs). The hybridization of the yarns with different mechanical properties was carried out so that the influence of the fiber type and ratio on the tensile behavior of the HBCs could be recognized. The mechanical properties (i.e. ultimate tensile strength (UTS), strain at failure, modulus of elasticity and fracture toughness) of HBCs were evaluated, and different types of HBCs were compared against one another to understand the benefits of hybridization and the resulting performance enhancements. Afterward, HBCs with the most satisfying mechanical performance were determined based on the scoring each of the evaluated mechanical parameters. The results indicate that the ternary hybrid composite with a combination of 75% PA-12.5% PET-12.5% PP presents the highest values of tensile performance. Besides, this study reveals that the reinforcement materials and their ratio play a significant role in tensile performance, and also the interaction within each pair of constituent fibers could alter the nature of the final behaviors. Finally, our findings exhibit the existence of positive and negative hybrid effects in UTS, strain at failure, modulus of elasticity and fracture toughness.

Behavior of woven fabrics during complex deformations is most influentially affected by their shear behavior. Shear characteristics of woven fabrics can be explained by fabric shear rigidity and shear hysteresis. In this study, the effects of weft density, weft count, and fiber type on shear behavior of woven fabrics in the principal directions of fabric were statistically evaluated. Statistical methods such as multiple linear regression analysis, univariate test, and correlation analysis were also applied. The univariate test results confirmed that the weft density is the most dominant parameter that affects fabric shear properties. Multiple linear regression results point to poor shear behavior in woven fabrics with cotton weft yarns. In addition, correlation between the shear rigidity of the fabrics along principal directions with the Milasius fabric firmness factor and the fabric cover factor as integrated structural parameters was established. High correlation was found to exist among Milasius fabric firmness factor, fabric cover factor, and shear rigidity of fabrics along principal directions.