Ajit Kelkar | North Carolina Agricultural and Technical State University (original) (raw)

Papers by Ajit Kelkar

Computers & Structures, 1995

Abstract A displacement-based, three-dimensional finite element scheme is proposed for analyzing ... more Abstract A displacement-based, three-dimensional finite element scheme is proposed for analyzing thick laminated plates. In the present formulation, a thick laminated plate is treated as a three-dimensional inhomogeneous anisotropic elastic body. Particular attention is focused on the prediction of transverse shear stresses. The plane of a laminated plate is first discretized into conventional eight-node elements. Various through-thickness interpolation is then denned for different regions of the plate; layerwise local shape functions are used in the regions where transverse shear stresses are of interest, while an ad hoc global-local interpolation is used in the region where only the general deformation pattern is concerned. For satisfying the displacement compatibility between these two regions, a transition zone is introduced. The model incorporates the advantages of the layerwise plate theory and the single-layer plate theory. Details of formulation will be presented together with several numerical examples for demonstrating the proposed scheme.

Advances in Mechanical Engineering, 2010

Response of fiberglass epoxy composite laminates under low velocity impact loading is investigate... more Response of fiberglass epoxy composite laminates under low velocity impact loading is investigated using LS-DYNA®, and the results are compared with experimental analysis performed using an instrumented impact test setup (Instron dynatup 8250). The composite laminates are manufactured using H-VARTM© process with basket weave E-Glass fabrics. Epon 862 is used as a resin system and Epicure-W as a hardening agent. Composite laminates, with 10 layers of fiberglass fabrics, are modeled using 3D solid elements in a mosaic fashion to represent basket weave pattern. Mechanical properties are calculated by using classical micromechanical theory and assigned to the elements using ORTHOTROPIC ELASTIC material model. The damage occurred since increasing impact energy is incorporated using ADVANCED COMPOSITE DAMAGE material model in LS-DYNA®. Good agreements are obtained with the failure damage results in LS-DYNA® and experimental results. Main considerations for comparison are given to the impa...

2002 Annual Conference Proceedings

Science Progress, 2021

Polymeric hybrid nanocomposites, due to improved mechanical, thermal, and electrical properties, ... more Polymeric hybrid nanocomposites, due to improved mechanical, thermal, and electrical properties, are key factors in recent technologies. Because of anisotropic characteristics of polymeric hybrid nanocomposites, mechanical properties and their behavior are very difficult to predict. If they are fabricated with complicated woven fabric patterns, it becomes more difficult to predict. This review discusses in detail the properties and manufacturing methods of various fibers, focuses on different manufacturing, processing, and characterization techniques used for polymeric hybrid nanocomposites. Theoretical composite models and some recent advances in modeling and simulation techniques for polymer nanoparticle composites are discussed and thus this review can provide significant guidelines for the development of manufacturing, characterization, testing, modeling, and simulation techniques for high performance hybrid polymer nanocomposites as current state of art.

Space Radiation has become one of the major factors in successful long duration space exploration... more Space Radiation has become one of the major factors in successful long duration space exploration. Exposure to space radiation not only can affect the health of astronauts but also can disrupt or damage materials and electronics. Hazards to materials include degradation of properties, such as, modulus, strength, or glass transition temperature. Electronics may experience single event effects, gate rupture, burnout of field effect transistors and noise. Presently aluminum is the major component in most of the space structures due to its lightweight and good structural properties. However, aluminum is ineffective at blocking space radiation. Therefore, most of the past research involved studying at polymers which contain large amounts of hydrogen. Again, these materials are not structural materials and would require large amounts of material to achieve the structural properties needed. One of the materials to alleviate this problem is polymeric composite materials, which has good stru...

2011 ASEE Annual Conference & Exposition Proceedings

MRS Communications, 2017

In the recent years, several investigators are incorporating nanotechnology, one of the most powe... more In the recent years, several investigators are incorporating nanotechnology, one of the most powerful trendsetters in material research, to conventional polymer prepregs to enhance mechanical properties of composite strucutures. The current paper outlines the role of nanotechnology in reinforcing resin and challenges for fabricating nanomaterial reinforced prepregs. As delamination is the most critical problem for composite materials, the current study only focuses the application nanotechnology as a possible solution to alleviate delamination problems in laminated composites. The importance of nanoengineered prepregs is discussed in a viewpoint of improvement in interlaminar properties of the laminated composite materials.

In recent years, nanotechnology has played an important role in the design of an efficient radiat... more In recent years, nanotechnology has played an important role in the design of an efficient radiation shielding polymeric composites. It is well known that, high loading of nanomaterials with radiation absorption properties can enhance the radiation attenuation efficiency of shielding structures. However, due to difficulties in dispersion of nanomaterials into polymer matrices, there has been a limitation in higher loading percentages of nanoparticles in the polymer matrix. Therefore, the objective of the present work is to provide a methodology to fabricate and then to characterize the functionally graded radiation shielding structures, which can provide an efficient radiation absorption property along with good structural integrity. Sandwich structures composed of Ultra High Molecular Weight Polyethylene (UHMWPE) fabric as face sheets and functionally graded epoxy nanocomposite as core material were fabricated. A method to fabricate a functionally graded core panel with controllabl...

The desired characteristics of materials in modern aircraft applications require high specific mo... more The desired characteristics of materials in modern aircraft applications require high specific modulus and high specific strength for low specific weight. Composite structures, fabricated using carbon and glass fabrics in conjunction with epoxy resin manufactured via the heated vacuum assisted resin transfer molding (H-VARTM) process are now being considered as a low cost alternative to conventional materials without compromising the mechanical properties. It is important to study the response of composite structures under out-of-plane impact loading which may cause considerable damage to the different layers even at low impact energy levels. In the present study, response of composite laminates under low velocity impact loading was investigated using LS-DYNA. The composite laminates were manufactured by the H-VARTM process using basket weave E-Glass fabrics and plain weave AS4 carbon fabrics with the Epon 862 resin system and Epicure-W as a hardening agent. A composite laminate, wi...

Recent Advances in Solids and Structures

Woven composites have good properties in mutually orthogonal directions, more balanced properties... more Woven composites have good properties in mutually orthogonal directions, more balanced properties than unidirectional laminates and have better impact resistance. The use of these composites for primary structural applications in place of conventional laminated composites has been increased considerably in the recent years. They are being manufactured by using new processes such as Resin Infusion (VARIM) and Resin Transfer Molding (RTM). These new processes are low cost, affordable and suitable for high volume manufacturing environment. One of the popular plain woven composites is fabricated using S2-Glass and SC-15 resin system components by using Resin Infusion (VARIM) process. These woven composites are being evaluated for Integral Armor applications. These components are expected to be under fatigue loading. To assess the feasibility of this material manufactured through Resin Infusion (VARIM), it is very important to understand the fatigue behavior of these composite materials....

Volume 14: Emerging Technologies; Engineering Management, Safety, Ethics, Society, and Education; Materials: Genetics to Structures

The mechanical properties of three phase nano-modified carbon fiber reinforced polymeric composit... more The mechanical properties of three phase nano-modified carbon fiber reinforced polymeric composites (CFRP) fabricated using Heated Vacuum Assisted Resin Transfer Molding (HVARTM) is investigated. Eight layers of carbon fiber plain weave mats were stacked in quasi isotropic layup and Epoxy 862 resin (non–modified and modified with Boron Nitride Nanoparticles (BNNPs)) was used. For mechanical properties characterization, three ASTM tests were performed. These tests included Tension Test (ASTM D3039), Compression Test (ASTM D6641) and Flexural Bending Test (ASTM D7264). The behavior of control and nano-modified composite laminates were compared. Results indicated that even small percentage of Boron Nitride Nanoparticle can significantly affect mechanical behavior of CFRP as well as progressive failure mechanisms.

2007 Annual Conference & Exposition Proceedings

2006 Annual Conference & Exposition Proceedings

2004 Annual Conference Proceedings

ABSTRACT

2003 Annual Conference Proceedings