Naresh Bhatnagar

On the machining of fiber reinforced plastic (FRP) composite laminates

Abstract With the increasing use of fiber reinforced plastic (FRP) composites outside the defense, space and aerospace industries, namely, civilian industries, machining of these materials is assuming a significant role. Unit cost rather than solely performance at any cost will be the consideration for the implementation of FRP composites to consumer industries. The current knowledge of machining FRP composites, unfortunately, is inadequate for its optimum utilization in many applications. This paper presents some observations made on the orthogonal machining of unidirectional carbon fiber reinforced plastic (UD-CFRP) laminates with different fiber orientations. Iosipescu shear test was adopted to evaluate the inplane shear strength of varied fiber angle test specimens. A model for predicting the cutting forces and the dependence of cutting direction on machinability requirements is presented.

MACHINING STUDIES OF UD-FRP COMPOSITES PART 2: FINITE ELEMENT ANALYSIS

ABSTRACT A number of parameters and an exhaustive material development and experimental procedure to determine the response variables like cutting forces, surface damage restricts the expensive experimental research. In this context, Finite Element Method (FEM) analysis can be used as a tool for the prediction of the various machining responses. A finite element analysis of the orthogonal machining of Uni-directional Glass Fiber Reinforced Plastic (UD-GFRP) laminates is presented in this study to understand the complex relation between fiber orientation, tool geometry, depth of cut on cutting forces and sub-surface damage.

Determination of Machining-Induced Damage Characteristics of Fiber Reinforced Plastic Composite Laminates

Abstract Machining of fiber reinforced plastic (FRP) components is often needed in spite of the fact that most FRP structures can be made to near net shape. The material removal mechanism of FRP is very difficult as compared with metals due to their inherent inhomogeneity and anisotropy. This results in frequent fiber pullout, delamination, matrix burning, and other damages leading to poor cut surface quality. A finite element model is proposed to quantify the material damage, which has been experimentally validated by means of nondestructive dye-penetrant testing. Good agreement is observed for laminates with fiber orientations up to 60°. Divergence is noticed for higher fiber orientations, and the discrepancies increase with increasing fiber orientation. Proper interfacial properties vis-à-vis machining of FRP materials are considered to be the main reasons for the divergence.

MACHINING STUDIES OF UNI-DIRECTIONAL GLASS FIBER REINFORCED PLASTIC (UD-GFRP) COMPOSITES PART 1: EFFECT OF GEOMETRICAL AND PROCESS PARAMETERS

ABSTRACT Secondary manufacturing processes such as machining is often needed to impart dimensional tolerance and assembly requirements to Fiber Reinforced Plastic (FRP) components despite the numerous difficulties encountered. Sub-surface damages in FRP products and reduction of product life due to machining is a new challenge for the industry and academia alike. Research works are underway to design suitable cutting tools in order to minimize these problems. The present study tried to investigate the various effects of geometrical and process parameters on the machining characteristics of UD-GFRP composites. The results of the study are analyzed in terms of chip formation observation, cutting forces and sub-surface damage.

EXPERIMENTAL INVESTIGATIONS OF DRILLING ON CFRP COMPOSITES

ABSTRACT The paper outlines the various problems associated with the drilling of CFRP composites. The technique of dimensional analysis is used to investigate the complex correlation between thrust force, cutting speed, feed, hole diameter, point geometry and material thickness during the drilling of holes in CFRP composites, A new non-dimensional number (t/D), thickness of layered composites to drill diameter, is found to influence the thrust force. Four drill point geometries specifically found effective in drilling of FRP were tried and among them the eight facet drill point geometry was found to give the best results.

Experiments and finite element modelling for the study of prolapse in the pelvic floor system

Pelvic prolapse affects one woman in three of all ages combined and is quite common for more than 60% of patients over 60 years of age. The treatment of this pathological problem is one of the biggest challenges to the gynaecologist today. The rate of surgical intervention failure is quite significant. The recurrence of prolapse could be related to inadequate surgical technique or the pathology or/and biomechanical deficiency of the soft tissues. The modelling and simulation of the behaviour of the pelvic cavity could be a major tool for specific evaluation of pelvic status. A first stage of this model is being developed and reported. The computer-aided design model of the organs of the pelvic floor is created using magnetic resonance image data and the ligament boundary conditions are defined. A multi-organ geometric model is thus created and studied.

Physical Blowing Agent Residence Conditions Stimulated Morphological Transformations in Extrusion Foaming

In this study, influence of blowing agent residence conditions on foam attributes has been investigated in extrusion foaming process. The blowing agent injection location in the extrusion barrel was found to affect the residence time inside the barrel, which in turn significantly transformed the foam microstructure. The injection location providing higher gas residence time resulted in foams with lower cell size, higher expansion ratio, and enhanced cell density. Further studies were performed to analyze the synergistic influence of residence time variation on foam attributes at different screw rotational speeds, die temperatures, and blowing agent contents. GRAPHICAL ABSTRACT

Digital Image Correlation of Low-Velocity Impact on a Glass/Epoxy Composite

Low-velocity-impact experiments were performed on a unidirectional laminate [0°]8 and cross-ply laminate [0°/90°]4 of E-glass/epoxy composite of thickness of 6.4 mm for incident energies 6.9 J, 9.48 J, and 12.7 J. The energy, contact forces, and displacement plots with respect to time are studied for a drop test. The damage observed as a back face signature on the back face of both cross-ply and unidirectional laminate are plotted. The composite was speckled randomly and the impact phenomenon was recorded using a high-speed camera. The DIC data were analyzed to obtain displacement and strains on the surface of the plate.

Effect of Blood Contamination and Decontamination Protocols on Acetone-Based and Ethanol-Based Total Etch Adhesive Systems

STATEMENT OF THE PROBLEMnThe efficacy of various decontamination protocols to reverse the effect of blood contamination after acid-etching may depend on the type of adhesive.nnnOBJECTIVESnTo compare the effect of blood contamination and various decontamination protocols on acetone-based and ethanol-based total-etch adhesive systems.nnnMETHODSnOcclusal dentin of 64 human molars was etched and contaminated with fresh human blood. The samples were assigned to two groups as per adhesive used: Prime & Bond NT (acetone-based) and Adper Single Bond 2 (ethanol-based) and then subdivided into eight groups: (1) control, (2) no decontamination, (3) water rinsing, (4) re-etching, (5) sodium hypochlorite, (6) sodium hypochlorite/sodium ascorbate, (7) hydrogen peroxide, and (8) ethanol. Adhesives were applied and specimens were prepared for μTBS after composite buildup. The data were subjected to analysis of variance followed by post hoc Tukey test.nnnRESULTSnBlood contamination significantly reduced μTBS of both the adhesives. Re-etching and NaOCl/Asc were effective in restoring μTBS to the level of control for both the adhesives whereas NaOCl was effective only for Prime & Bond NT.nnnCONCLUSIONnBoth re-etching and NaOCl can be used for regaining μTBS of blood-contaminated acid-etched dentin. NaOCl/Asc yields better results than NaOCl alone, specifically for ethanol-based adhesive.nnnCLINICAL SIGNIFICANCEnKnowing the adverse effects of prolonged acid-etching, other alternatives for decontamination of etched dentin after blood contamination should be considered. NaOCl alone or NaOCl followed by sodium ascorbate may prove to be good alternatives. These choices also may determine the type of adhesive system.