Sunil C. Joshi

Sol-Gel Behavior of Hydroxypropyl Methylcellulose (HPMC) in Ionic Media Including Drug Release

Sol-gel transformations in HPMC (hydroxypropyl methylcellulose) are being increasingly studied because of their role in bio-related applications. The thermo-reversible behavior of HPMC is particularly affected by its properties and concentration in solvent media, nature of additives, and the thermal environment it is exposed to. This article contains investigations on the effects of salt additives in Hofmeister series on the HPMC gelation. Various findings regarding gelation with salt ions as well as with the ionic and non-ionic surfactants are presented. The gel formation in physiological salt fluids such as simulated gastric and intestine fluids is also examined with the interest in oral drug delivery systems. The processes of swelling, dissolution and dispersion of HPMC tablets in simulated bio-fluids are explored and the release of a drug from the tablet affected by such processes is studied. Explanations are provided based on the chemical structure and the molecular binding/association of HPMC in a media. The test results at the body or near-body temperature conditions helped in understanding the progress of the gelation process within the human body environment. The detailed interpretation of various molecule level interactions unfolded the sol-gel mechanisms and the influence of a few other factors. The obtained test data and the established mathematical models are expected to serve as a guide in customizing applications of HPMC hydrogels.

Enhancing interlaminar fracture characteristics of woven CFRP prepreg composites through CNT dispersion

The inter-ply characteristics of polymeric prepreg composites influence their interlaminar fracture toughness and the overall performance. This article embarks on engineering the inter-ply interfaces of carbon fiber reinforced polymer (CFRP) composites. A novel and practical technique for dispersion of multi-walled carbon nanotubes (MWCNTs) onto woven CFRP prepreg is presented. The interlaminar fracture toughness of these CFRP lay-ups was evaluated experimentally and compared with the regular (without any CNTs) specimen. Double cantilever beam and end notch flexure tests were conducted for interlaminar fracture studies. It was observed that the addition of MWCNTs in between the CFRP prepreg plies helps in strengthening the interface. There existed an optimum percentage in which these nanofillers should be added. The presence of nanotubes increased fiber bridging within the ply interfaces, which in turn controlled the inter-ply crack propagation. The findings and the mechanisms are discussed using the test data, SEM pictures, schematics, and scans of the fractured surfaces.

A numerical approach to the modeling of polymer curing in fibre-reinforced composites

Abstract This paper presents a procedure for using a general-purpose finite-element (FE) package for cure modeling. The package is used to carry out transient heat-transfer analysis and two user programs are developed to simulate resin-cure kinetics by using nodal control volumes based on the FE mesh. The theoretical background and numerical implementation of the procedure are described, and stability with respect to the FE mesh density and the length of the time step employed is investigated. Application of the procedure is demonstrated by modeling the cure of a thick prepreg laminate, a honeycomb sandwich panel and an I-beam. Predicted temperature profiles in the thick laminate are in excellent agreement with available experimental data.

Numerical simulation of the mould-filling process in resin-transfer moulding

This paper presents a simulation procedure for the mould-filling processes in which a field-analysis module of a general-purpose finite-element package is employed. The formulations used in this procedure are based on the finite element/nodal control-volume approach. The numerical concepts employed for modelling the effects of convective heat transfer on temperature and resin cure are discussed. Numerical implementation of the procedure is presented. The procedure was applied to simulate different mould-filling examples under isothermal and non-isothermal conditions. The results show that the simulation procedure developed is numerically valid and stable, and provides reasonably accurate predictions.

Three-dimensional finite-element/nodal-control-volume simulation of the pultrusion process with temperature-dependent material properties including resin shrinkage

This paper discusses the development and application of the finite-element/nodal-control-volume (FE/NCV) approach for three-dimensional pultrusion analysis. A numerical procedure is designed which uses a combination of the field analysis module of a general-purpose finite-element package and a few user-written computer codes. Numerical schemes employed for calculating the effects of convective heat-transfer on temperature and degree of cure, for modelling resin cure kinetics and the effects of temperature-dependent material properties, and for determining the dimensional changes due to chemical shrinkage and thermal expansion of resin are discussed in detail. Case studies are presented demonstrating the simulation of the pultrusion process for different components including irregular and hollow sections.

Mass conservation in numerical simulation of resin flow

Abstract The finite element/control volume (FE/CV) approach is commonly used for numerical simulation of resin flow in many composites manufacturing processes. The law of mass conservation is sometimes violated with the use of this approach. Especially, when the Galerkin formulation is used with isoparametric finite elements to obtain the pressure field, the balance of resin mass cannot be achieved. In this paper, reasons leading to such mass imbalance are investigated. A numerical model based on material incompressibility is developed to eliminate the problem. A few isothermal flow simulation examples are presented to demonstrate the application of the model. The results obtained are in excellent agreement with the analytical solutions.

Curing optimization for pultruded composite sections

In this paper, a mathematical relationship between the degree of cure profile across the cross-section of a pultruded part and the die-heater temperatures was established. The relationship was employed to optimize the die-heating profile such that finally a near-uniformly-cured component could be obtained. The algorithm was implemented using the three-dimensional finite element/nodal control volume (FE/NCV) approach for process simulation. The application of the procedure is demonstrated by simulating the pultrusion of composite sections that use a multi-heater die. The effects of the element aspect ratio and different initial heater conditions were studied. The results of the case studies show that the developed algorithm is numerically stable and provides optimal die temperatures for producing a uniformly cured pultrudate under the prescribed process conditions.

Power law fluids and Bingham plastics flow models for ceramic tape casting

Abstract A generalized pressure flow is used as a basis for developing a flow model for ceramic tape casting with different types of fluids such as Newtonian, power law and Bingham plastics. The slurry flow is modeled as part of a pressure flow through an imaginary parallel channel. Analytical equations for the flow field are presented. Equations for obtaining velocity profiles and flow rates are included. These can be used to estimate the thickness of the ceramic tape to be cast. The formulations were validated by means of published data, the results of which are included in the paper. Finally, the effect of various process parameters on the size of the imaginary flow channel is studied.

Microwave–thermal technique for energy and time efficient curing of carbon fiber reinforced polymer prepreg composites

This paper investigates fabrication and mechanical properties of L-930 carbon fiber reinforced polymer woven prepreg composites cured using three different techniques: (1) thermal, (2) microwave, and (3) the combination of microwave and thermal. The third technique was established through parametric studies and proved to be an efficient method in curing the carbon fiber reinforced polymer prepregs without compromising mechanical properties, but with significant energy and time saving. With 20 min in microwave at 510 W followed by 60 min thermal curing in convection oven at 120℃ provided optimum results in terms of time and energy saving. The process was 2.5 times faster than and consumed only 1/4th of energy required for the autoclave curing. The mechanical properties in tension and flexure of carbon fiber reinforced polymer [0/90] and [±45] laminates cured with this technique were 1–5% better than the autoclave cured laminates. The details of the composites fabrication, the curing techniques, the experiments conducted along with the rationale and underlying reasons for the success of the new “microwave–thermal” curing technique are presented in this paper.

3D printing in aerospace and its long-term sustainability

ABSTRACT Astonishingly 3D printing has excited the world of aerospace. This paper takes stock of the popular 3D printing processes in aerospace. Reasons for their popularity over the traditional manufacturing processes are dwelled upon. Materials developed specially for aerospace applications along with their characteristics are discussed. Ongoing activities related to 3D printing at various companies and organisations around the world are looked into. Project works in the area of extra-terrestrial printing are also highlighted. Even though 3D printing processes are operationally simple, they do have limitations in terms of the type, quality, and quantity of the materials they can handle. This paper underlines these points while discussing drawbacks of the printed components. Challenges associated with 3D printing in microgravity are also touched upon. Finally, a glimpse is taken into the future appearance of aerospace industry with 3D printing.