Harshvardhan Saraswat

Tensile mechanics of braided sutures

Sutures are the materials primarily used for closing wounds, and their performance is significantly dependent on their mechanical characteristics. Thus, their tensile property is a key parameter responsible for the success of a suture. In this paper, a simple analytical tensile model of braided sutures has been developed based on braid geometry, braid kinematics, and constituent monofilament properties. The model has accounted for the changes in the braid geometry, including braid angle, diameter, and Poisson’s ratio. The kinematics of the braided suture is analyzed pertaining to monofilament locking or jamming in the braid. The model of jamming state of monofilaments has been presented, and both braid angle and diameter are found to be critical design parameters. The experimental results have been compared to the theoretical stress–strain curves of braided sutures, and an excellent agreement has been observed between them.

Geometrical modeling of near-net shape braided preforms

Circular braiding has been successfully adapted for producing near-net shape structures for advanced fiber-reinforced composites. Net-shape manufacturing is significantly important for fabricating complex three-dimensional (3D) preforms. Geometrical modeling of braid patterns on 3D preforms plays a key role in determining their mechanical behavior. In this research work, the geometrical models of strand trajectory on the surface of cylindrical and conical mandrels with diamond, regular and triaxial braid patterns have been developed. These geometrical models of strand profiles were then simulated using Virtual Reality Modeling Language. Subsequently, the strands on complex-shaped mandrels, including ‘bottle’ and ‘funnel’, were simulated and accordingly, the braid angles have been predicted and compared with the experimental results. A virtual experiment was also conducted to compare the trajectory of the strands having constant and varying braid angles on the surface of conical mandrels.

Tensile response of braided structures: a review

Braiding is a highly versatile and cost-effective method of producing structures that has been successfully used for numerous applications ranging from ropes, composites, biomedical uses, insulation to sports and recreation activities, and the list of applications of braided structures is ever-increasing. The prediction of tensile property is a pre-requisite for the success of deployment of braided structures in these applications. This paper reviews the key parameters that control the tensile properties of biaxial and triaxial braided structures along with the models developed for these braids by various researchers with different fields of interest. In general, the tensile properties of braided structures are strongly dependent upon their architecture and the kinematics and mechanics involved in the braid formation. Furthermore, various approaches and methodologies have also been presented for the tensile models of braids consisting of an elastic core and multi-layered structures.

Damage analysis and notch sensitivity of hybrid needlepunched nonwoven materials

Needlepunched nonwovens are complex three-dimensional (3D) entangled fibrous materials which are extensively used for a range of technical and industrial applications. The micromechanisms of deformation and fracture behavior of these materials are complicated and least understood. In this study, the tensile behavior of virgin and notched samples is investigated for hybrid needlepunched nonwoven materials consisting of polypropylene and viscose fibers in defined proportions. The notches in nonwovens were induced by two types of mechanical damage (circular hole and vertical cut) in three spatial positions of hybrid nonwovens tested in the machine, 45°, and cross-machine directions. The notch sensitivity of hybrid nonwovens was demonstrated by localized fiber failures occurring around the region of induced damages. It was established that the shape and spatial position of induced damage have significant influence on the tensile behavior of hybrid nonwoven materials. Higher viscose contents (60–80 wt%) in notched hybrid nonwovens yielded minimal tensile strength reduction specifically in the preferential (cross-machine) direction.

Modeling the compression-induced morphological behavior of nonwoven materials

Nonwovens have the most complex morphologies in textile materials and they are often being compressed in a range of applications. The morphology of a typical nonwoven is defined in terms of fiber orientation, fiber volume fraction, number of fiber-to-fiber contacts, distance between the contacts, porosity, and pore size distribution. In this study, an attempt has been made to predict the morphological characteristics of nonwoven materials under the state of compression. A concept of compression ratio has been introduced in predicting the fiber volume fraction at a defined level of compression strain that has significantly influenced the other morphological characteristics of nonwoven materials. A mechanistic model of pore size distribution of nonwoven has been proposed by updating the structural and morphological parameters under predefined compressive stresses. A comparison has been made between theoretical and experimental pore size distributions of compressed nonwoven fibrous materials. In addition, the out-of-plane fiber orientation distribution was experimentally obtained by analyzing the two-dimensional (2D) cross-sections of fibers in the thickness direction.

Geometrically controlled tensile response of braided sutures

Sutures are the materials used for wound closure that are caused by surgery or trauma. The main pre-requisite to the success of the suture is to obtain ultimate level of tensile properties with defined geometrical constraints. In this communication, the model for tensile properties of braided sutures has been proposed by elucidating the most important geometrical and material parameters. The model has accounted for the kinematical changes occurring in the braid and constituent strand geometries under defined level of strain. A comparison has been made between the theoretical and experimental results of stress-strain characteristics of braided sutures.

Tensile behaviour of structurally gradient braided prostheses for anterior cruciate ligaments.

Anterior cruciate ligament (ACL) is a key fibrous connective tissue that maintains the stability of a knee joint and it is the most commonly injured ligament of the knee. A synthetic prosthesis in the form of a braided structure can be an attractive alternative to biological grafts provided that the mechanical properties can be tailored to mimic the natural ACL. In the present work, the polypropylene based structurally gradient braided prostheses have been designed and developed by understanding their tensile properties. Circular braiding process was employed to fabricate structurally gradient braided prostheses by systematically placing different types of braids in defined set of layers. An analytical model for predicting the tensile properties of structurally gradient braided prostheses has been presented by modifying and combining the existing models available in the literature. Specifically, the full set of stress-strain behaviour of structurally gradient braided prostheses has been computed based upon braid structural characteristics, constituent strand properties and braid kinematics. A triaxial braid in the outer layer of braided prostheses was found to withstand higher tensile stresses in comparison to a biaxial braid having same structural characteristics. A comparison has been made between the theoretical and experimental results of tensile properties of structurally gradient braided prostheses. The tensile properties of structurally gradient braided prostheses predicted through analytical route matched reasonably well with the experimental results.

Tensile behaviour of multi-layered braided structures

Multi-layered braided structures are formed as a result of over-braiding the previously formed braids and they are increasingly being used for numerous applications ranging from hoses to energy absorbing composites. In this research work, a series of multi-layered braided structures were prepared on circular braiding machine for obtaining various combinations of braid angles of 30° and 45° in inner and outer layers. Subsequently, the tensile properties of multi-layered braided structures were analysed and it was found that the braid angle in the outer layer has significantly affected the stress–strain behaviour. A simple analytical model for predicting the tensile behaviour of multi-layered braided structures has also been proposed based on the previously developed model of ‘braid-elastic core’ system. A clear distinction has also been made between the helix and braid angles. Furthermore, a comparison has been made between theoretical and experimental values of braid angle, toughness and stress–strain characteristics of multi-layered braided structures.

Topologically controlled tensile behaviour of braided prostheses for anterior cruciate ligaments

Anterior cruciate ligament (ACL) is one of the most susceptible ligaments of the knee that can suffer injury. These ruptured ligaments can be treated through surgical intervention using a braided structure that either acts as a substitute graft in isolation or an augmentation device alongside the biological tissue. Therefore, the main objective of the research work is to present an analytical model for predicting the complete set of tensile properties of braided prosthesis consisting of multifilament strands based upon predefined braid geometry and constituent material properties. The model has also accounted for the kinematical changes under defined loading conditions. The research findings have been confirmed by making a comparison between the theoretical and experimental results. The tensile properties of braided prostheses predicted via analytical route matched reasonably well with the experimental results.

Creating three-dimensional (3D) fiber networks with out-of-plane auxetic behavior over large deformations

Fiber networks with out-of-plane auxetic behavior have been sporadically investigated. One of the major challenges is to design such materials with giant negative Poisson’s ratio over large deformations. Here in, we report a systematic investigation to create three-dimensional (3D) fiber networks in the form of needlepunched nonwoven materials with out-of-plane auxetic behavior over large deformations via theoretical modeling and extensive set of experiments. The experimental matrix has encapsulated the key parameters of the needlepunching nonwoven process. Under uniaxial tensile loading, the anisotropy coupled with local fiber densification in networks has yielded large negative Poisson’s ratio (up to −5.7) specifically in the preferential direction. The in-plane and out-of-plane Poisson’s ratios of fiber networks have been predicted and, subsequently, compared with the experimental results. Fiber orientation was found to be a core parameter that modulated the in-plane Poisson’s ratio of fiber networks. A parametric analysis has revealed the interplay between the anisotropy of the fiber network and the out-of-plane Poisson’s ratio based upon constant volume consideration.